Resonance type sensor using a mems resonator and detection method of resonance type sensor

Abstract

The temperature sensor (400) is a temperature sensor (400) using a MEMS resonator (500), comprising: a MEMS resonator (500); a frequency sweeping unit (401) that sweeps the frequency of the excitation signal of the oscillator (501) of the MEMS resonator (500) along a predetermined frequency sweeping direction and outputs the frequency-sweeped excitation signal to the MEMS resonator (500); a discontinuity detection unit (412) that obtains a characteristic quantity representing the vibration state of the oscillator (501) based on the excitation signal from the MEMS resonator (500), i.e., a vibration state information signal, and detects the frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously as a detection value; and a conversion unit (415) that determines the physical quantity acting on the MEMS resonator (500) based on the detected detection value.

Description

Technical Field

[0001] This disclosure relates to resonant sensors using MEMS (Micro-Electro Mechanical Systems) resonators and the detection signal processing of resonant sensor detection methods. Background Technology

[0002] Previously, it was known that mechanical resonators (micromechanical resonators or MEMS resonators) using micromechanical oscillators were used (Patent Documents 1-3).

[0003] Figure 27A and Figure 27B This is a diagram showing a structural example of a conventional MEMS resonator 100. This MEMS resonator 100 is a so-called electrostatic capacitive type MEMS resonator. Figure 27A This is a 3D diagram of the MEMS resonator 100. Figure 27B It is along Figure 27A A side cross-sectional view of the MEMS resonator 100 along line A-A'. Additionally, in Figure 27B The BOX (Buried Oxide) layer 104 and silicon substrate 105 are omitted, but the voltage Vi input to the MEMS resonator 100, the output current Io, the bias voltage Vp applied to the oscillator 101, and the vibration direction of the oscillator 101 are shown.

[0004] The MEMS resonator 100 can be fabricated using an SOI (Silicon On Insulator) substrate. In this case, a beam-shaped oscillator 101, an input electrode 102, and an output electrode 103 are formed from the uppermost Si layer of the SOI substrate. Furthermore, by etching away the BOX (Buried Oxide) layer 104 located below the oscillator 101, the oscillator 101 is held in oscillation by oscillator supports 101s on the remaining BOX layer 104. The oscillator 101, along with the input electrode 102 and the output electrode 103, is retained on the silicon substrate 105 by the remaining BOX layer 104.

[0005] Reference Figure 27BThe vibration mechanism of the oscillator 101 will be described. The oscillator 101 is configured to face the input electrode 102 and the output electrode 103 across gaps gi and go, respectively. A bias voltage Vp is applied to provide a DC potential difference between the input electrode 102 and the output electrode 103. When an AC input voltage (AC voltage) Vi is applied to the input electrode 102, the potential difference between the oscillator 101 and the input electrode 102 changes with the AC input voltage Vi, and an excitation force generated by electrostatic force acts on the oscillator 101. When the frequency of the AC input voltage Vi coincides with the mechanical resonant frequency of the oscillator 101, the oscillator 101 vibrates (resonates) with a particularly large amplitude along the vibration direction 106. At this time, a displacement current Io flows from the capacitance Co formed by the gap go to the output electrode 103.

[0006] Applications of MEMS resonator 100 include: filter circuits that utilize the electrical pass-through characteristics between input and output electrodes to improve only at a specific frequency, i.e., the resonant frequency of the oscillator; temperature sensors that utilize the change in the resonant frequency of the oscillator due to temperature; pressure sensors that utilize the change in the resonant frequency of the oscillator due to the stress applied to the oscillator; and mass sensors that utilize the change in the resonant frequency of the oscillator due to a small amount of deposits on the oscillator.

[0007] Non-Patent Document 1 suggests the possibility of realizing a pressure sensor using a MEMS resonator. According to this document, the characteristics of the vibrational motion (e.g., resonant motion) of the oscillator in the MEMS resonator (e.g., the magnitude of the amplitude of the vibrational motion and the Q value) vary depending on the pressure of the atmosphere surrounding the oscillator. Specifically, the kinetic energy or amount of motion of the oscillator in the MEMS resonator undergoing resonant motion is lost due to the viscosity of the atmosphere surrounding the oscillator, and the degree of loss varies depending on the pressure of the atmosphere. Therefore, the amplitude of the oscillator resonating at the resonant frequency varies depending on the pressure of the atmosphere. Thus, quantities such as the amplitude of the oscillator of the MEMS resonator vibrating near the resonant frequency and its Q value correspond well to the pressure of the atmosphere. Therefore, by detecting the amplitude or Q value of the oscillator of the MEMS resonator resonating in the atmosphere, the pressure of the atmosphere can be determined. For example, Figure 4 of Non-Patent Document 1 shows the correspondence between the Q value of the MEMS resonator and the atmospheric pressure.

[0008] Furthermore, Non-Patent Document 2 discusses the nonlinear behavior of a MEMS resonator when the oscillator vibrates with a relatively large amplitude. Generally, when the vibration amplitude of the oscillator 101 of the MEMS resonator 100 is sufficiently small, the influence of the nonlinear effect is negligible (linear region), and the resonant characteristics obtained by sweeping the frequency of the input voltage Vi are as follows... Figure 28The resonance characteristics shown in Figure 111 depict a symmetrical distribution centered on the peak at the resonant frequency f0 of the oscillator 101, with no hysteresis observed due to differences in the sweep direction. However, when the Q value of the oscillator increases and its vibration amplitude reaches a certain level (entering the nonlinear region), as... Figure 29 and Figure 30 As shown, significant nonlinearity appears in the resonant characteristics (e.g., resonant characteristics 121 and 131). For example, when the oscillator 101 of the MEMS resonator 100, which is an electrostatic capacitive type, vibrates in a nonlinear region, its resonant characteristics exhibit hysteresis (123 and 125) due to the difference in the frequency sweep direction, and the vibration amplitude does not show a significant peak at the resonant frequency f0.

[0009] According to non-patent literature 2, this nonlinear phenomenon is caused by two nonlinear effects. The first nonlinear effect is that when the vibration amplitude of the oscillator 101 is large, the input electrode 102 and the output electrode 103 excessively attract the oscillator 101 (capacitive bifurcation). The second nonlinear effect is that the stiffness of the oscillator 101 increases with the increase of the vibration amplitude of the oscillator 101 (mechanical bifurcation). Depending on the structure of the MEMS resonator 100, sometimes only one of these two nonlinear effects occurs, and sometimes they occur simultaneously.

[0010] Figure 29 This is an example of the resonance characteristic 121 of a MEMS resonator 100 with significant capacitive bifurcation. In this case, the resonance characteristic bends to the left (low-frequency side), exhibiting hysteresis due to the difference in frequency sweep direction (arrows 123 and 125), with the peak of the vibration amplitude shifting towards the low-frequency side of the resonant frequency f0.

[0011] Figure 30 This is an example of the resonance characteristic 131 of a MEMS resonator 100 with significant mechanical bifurcation. In this case, the resonance characteristic bends to the right (high-frequency side), exhibiting hysteresis due to the difference in frequency sweep direction (arrows 133 and 135), with the peak of the vibration amplitude varying towards the high-frequency side of the resonant frequency f0.

[0012] Prior art literature

[0013] Patent documents

[0014] Patent Document 1: International Publication No. 2006 / 075717

[0015] Patent Document 2: Japanese Patent Application Publication No. 2-269928

[0016] Patent Document 3: Japanese Patent No. 5367925

[0017] Non-patent literature

[0018] Non-patent literature 1: O. Paul, O. Brand, R. Lenggenhager, H. Baltes, Vacuum gauging with complementary metal-oxide-semiconductor microsensors, J. Vac. Sci. Technol. A, American Vacuum Society, May / Jun, 1995, 13(3), pp. 503-508.

[0019] Non-Patent Literature 2: M. Agarwal, K. Park, R. Candler, M. Hopcroft, C. Jha, R. Melamud, B. Kim, B. Murmann, T.W. Kenny, Non-Linearity Cancellation in MEMS Resonators for Improved Power-Handling, Electron DeVices Meeting 2005 IEDM Technical Digest, IEEE International, pp. 286-289. Summary of the Invention

[0020] The problem the invention aims to solve

[0021] For example, in Figure 27A and Figure 27B In the MEMS resonator 100 (capacitive MEMS resonator) shown, where the oscillator 101 is excited by an electrostatic force varying according to the AC input voltage Vi, a significant nonlinearity based on capacitive bifurcation effect appears approximately when the vibration amplitude of the oscillator 101 is greater than one-third of the sizes of the gaps go and gi. In the vibration motion of the oscillator 101 in the so-called capacitive MEMS resonator, the nonlinearity becomes significant when its vibration amplitude exceeds one-third of the sizes of the gaps go and gi, and its resonant characteristics become... Figure 29The resonant characteristic shown is asymmetrical and hysteretic in the frequency sweep direction 121. Because it is possible to obtain a higher... Figure 28 The linear region has a large vibration amplitude, therefore, the S / N of the electrical signal generated by the vibration is optimized.

[0022] However, on the other hand, the vibration amplitude of the oscillator 101 near the resonant frequency f0 does not show a clear peak. In sensors that use the principle of self-excited vibration near the resonant frequency to link the vibration frequency with the sensing measurement, the vibration frequency is easily affected by noise, and phase noise, which is related to the quality of the vibration frequency, becomes a problem. Furthermore, in sensors that use the principle of applying an excitation signal at a fixed frequency close to or equal to the resonant frequency f0, such as... Figure 31 As shown, even as the Q value increases from Q1 to Q2, the resonant waveform only tilts to the left, and the change in vibration amplitude at this fixed frequency is small, making it difficult to detect changes in the Q value. Therefore, in existing pressure sensors that provide a specified frequency (e.g., a frequency near the resonant frequency f0) of AC input voltage to the MEMS resonator 100 and measure atmospheric pressure based on the output from the MEMS resonator 100, pressure measurement of the MEMS resonator 100's oscillator 101 under atmospheric pressure in a nonlinear region is extremely difficult. Thus, in existing pressure sensors, the range of measurable pressure is limited to the range of linear vibration of the oscillator 101, for example, the vibration amplitude of the oscillator 101 in a resonant state does not exceed 1 / 3 of the size of the gaps go and gi. In the linear region, compared to the nonlinear region, the vibration amplitude of the oscillator 101 is small, resulting in a small output signal from the MEMS resonator 100, necessitating a large, power-consuming, high-gain signal amplifier.

[0023] Therefore, a sensor is proposed that enables the oscillator of a MEMS resonator to operate in a nonlinear region when the oscillation amplitude of the oscillator exceeds 1 / 3 of the size of the gaps go and gi.

[0024] Patent Document 2 discloses a vacuum gauge comprising: a self-excited vibration circuit that causes an oscillator to self-excite in a nonlinear vibration region using the oscillator's natural vibration number; a counter that counts the oscillator's natural vibration number; and an arithmetic circuit that calculates and detects the vacuum level based on the offset of the measured natural vibration number relative to the natural vibration number in the linear region. While Patent Document 2 does not address the issue of phase noise, it constitutes a vacuum gauge with improved signal-to-noise ratio (S / N) due to large-amplitude vibration in the nonlinear region. However, Patent Document 2 does not disclose a crucial issue in MEMS resonators: countermeasures against "resonant frequency changes caused by temperature variations." The principle of the vacuum gauge in Patent Document 2 is that the Q value changes according to the vacuum level, and the vibration point (the point satisfying the vibration condition) on the nonlinear resonant waveform moves, detecting the change in vibration frequency caused by this movement. However, in this vacuum gauge, when the temperature of the silicon oscillator changes with the ambient temperature regardless of the vacuum level, the resonant frequency also changes due to the temperature characteristics of silicon's elastic modulus, i.e., the vibration frequency also changes. If the temperature characteristics of the resonant frequency are not considered, incorrect vacuum levels can sometimes be calculated. In the case of silicon, TCf (temperature coefficient of resonant frequency) is approximately -20 to -30 ppm / ℃. That is, the vacuum gauge must have a table beforehand that records the relationship between the temperature shown by the thermometer, the resonant frequency, and the vacuum level.

[0025] Like Patent Document 2, the MEMS resonator sensor in Patent Document 3 uses resonance in a nonlinear region. However, in this MEMS resonator sensor, self-excited vibration is not performed. Instead, the sensor signal is obtained by adding (or integrating) the output signal of the MEMS resonator while sweeping the frequency of the excitation signal in one direction.

[0026] However, in the past, it was sometimes impossible to achieve high-precision sensing with MEMS resonators.

[0027] Therefore, the purpose of this disclosure is to provide a resonant sensor and a method for detecting the resonant sensor that can perform high-precision sensing of MEMS resonators.

[0028] Problem-solving methods

[0029] To achieve the above objectives, one aspect of the resonant sensor disclosed herein is a resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator. This resonant sensor comprises: a MEMS resonator; a frequency sweeping unit that sweeps the frequency of an excitation signal of the oscillator of the MEMS resonator along a predetermined frequency sweeping direction and outputs the frequency-sweeped excitation signal to the MEMS resonator; a detection unit that acquires a characteristic quantity, i.e., a vibration state information signal, representing the vibration state of the oscillator based on the excitation signal from the MEMS resonator, and detects the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously as a detection value; and a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected detection value.

[0030] Furthermore, these general or specific methods can be implemented through systems, methods, integrated circuits, computer programs, or computer-readable CD-ROMs, or through any combination thereof.

[0031] The effects of the invention

[0032] According to this disclosure, high-precision sensing of MEMS resonators is possible. Attached Figure Description

[0033] Figure 1A This is the wiring diagram of a temperature sensor with a MEMS resonator.

[0034] Figure 1B This is a 3D diagram of a MEMS resonator that uses a silicon oscillator with a triangular cross-section supported by two side beams.

[0035] Figure 2 This is a block diagram showing the structure of a temperature sensor that uses a MEMS resonator.

[0036] Figure 3A This is a timing diagram showing the operation of an electrostatic capacitive MEMS resonator that is swept at an upper frequency accompanied by an excitation signal.

[0037] Figure 3B It represents the frequency f at the point of discontinuity and the temperature. H A diagram showing the relationships between them.

[0038] Figure 3C It is a graph showing the relationship between temperature and the intensity of the detector signal at the discontinuity point.

[0039] Figure 4A This is a timing diagram showing the operation of a capacitive MEMS resonator that is subjected to a frequency sweep below the excitation signal.

[0040] Figure 4B It represents the frequency f at the point of discontinuity and the temperature. L A diagram showing the relationships between them.

[0041] Figure 4C This is a graph showing the relationship between temperature and the peak value of the detected signal intensity.

[0042] Figure 5A This is a timing diagram representing the operation of an electrostatic capacitive MEMS resonator with frequency sweep of the excitation signal caused by a triangular wave.

[0043] Figure 5B It represents the frequency difference f between temperature and the frequencies of two discontinuous points. H -f L A diagram showing the relationships between them.

[0044] Figure 6 This is a timing diagram showing the operation of a capacitive MEMS resonator under the condition of frequency sweep direction switching during timed detection at discontinuous points.

[0045] Figure 7 This is a cross-sectional view of a capacitive MEMS resonator.

[0046] Figure 8A This is a cross-sectional view of a capacitive MEMS resonator with a thermometer integrated into the same chip.

[0047] Figure 8B This is a cross-sectional view of a capacitive MEMS resonator with a thermometer mounted on the same mounting substrate.

[0048] Figure 9 It represents the frequency difference f between the temperature of the MEMS resonator and the frequencies of two discontinuous points. H -f L A diagram showing the relationships between them.

[0049] Figure 10A This represents the change in hydrogen concentration and the frequency difference f. H -f L A graph showing the changes over time (when the temperature sensor is set as a thermocouple).

[0050] Figure 10B This represents the change in hydrogen concentration and the frequency difference f. H -f L The time variation (using the frequency f of the discontinuity point) H The graph shows the temperature information.

[0051] Figure 11 This indicates that the frequency f at the discontinuity point is... H f as temperature information H With frequency difference fH -f L A diagram showing the relationships between them.

[0052] Figure 12 This is a block diagram illustrating the structure of a pressure sensor that uses a MEMS resonator with measurement range switching functionality.

[0053] Figure 13 This represents the difference between the excitation signal strength Vi and the frequency difference f. H -f L A diagram showing the relationships between them.

[0054] Figure 14 This is a cross-sectional view of a capacitive MEMS resonator.

[0055] Figure 15 It represents the frequency difference f as the gap changes due to pressure and fluid pressure. H -f L A graph showing the changes.

[0056] Figure 16 This is a cross-sectional view of a capacitive MEMS resonator.

[0057] Figure 17 It represents the frequency difference f between the temperature of the MEMS resonator and the frequencies of two discontinuous points. H -f L A diagram showing the relationships between them.

[0058] Figure 18 This is a block diagram showing the structure of the infrared sensor array in Modification 1 of Embodiment 4, and an explanatory diagram of the marked electrostatic capacitive MEMS resonator.

[0059] Figure 19 This is a block diagram showing another structure of the infrared sensor array in Modification 2 of Embodiment 4.

[0060] Figure 20 This is a diagram illustrating the electrical connection method of a capacitive MEMS resonator.

[0061] Figure 21 This is a diagram showing an example of the output of a vibration state information signal (vibration velocity information signal).

[0062] Figure 22 This is a diagram showing an example of the output of vibration state information signal (deflection angle information signal).

[0063] Figure 23 This is a three-dimensional diagram showing the structure of a non-electrostatic capacitive MEMS resonator.

[0064] Figure 24 This is a diagram illustrating the Coriolis force applied to the oscillator.

[0065] Figure 25 This is a block diagram showing the structure of a MEMS resonator using a synchronous detection electrostatic capacitor type.

[0066] Figure 26 It is a graph representing the amplitude information, phase information, and discontinuities of the oscillator obtained through synchronous detection.

[0067] Figure 27A This is a three-dimensional diagram showing the structure of a capacitive MEMS resonator.

[0068] Figure 27B This is a cross-sectional view of a capacitive MEMS resonator.

[0069] Figure 28 It is a graph representing the resonance characteristics in a linear region.

[0070] Figure 29 It is a diagram showing the resonance characteristics and hysteresis that occur in the nonlinear region.

[0071] Figure 30 It is a diagram showing the resonance characteristics and hysteresis that occur in the nonlinear region.

[0072] Figure 31 This is a graph showing the resonant characteristics in the nonlinear region under different Q values.

[0073] Figure 32 This is a cross-sectional view of a capacitive MEMS resonator.

[0074] Figure 33 This is a diagram showing the temperature distribution in a capacitive MEMS resonator and its oscillator.

[0075] Figure 34 It is a graph showing the relationship between ambient temperature information and frequency difference.

[0076] Figure 35 This diagram illustrates the cases where the oscillator is kept at the same temperature and the cases where infrared light is irradiated onto the oscillator.

[0077] Figure 36 It is a graph showing the relationship between the change in resonant frequency and the average temperature of the oscillator.

[0078] Figure 37 It is a graph showing the relationship between the spring constant and the resonant frequency. Detailed Implementation

[0079] One aspect of the resonant sensor disclosed herein is a resonant sensor using a MEMS resonator, comprising: a MEMS resonator; a frequency sweeping unit that sweeps the frequency of an excitation signal of the oscillator of the MEMS resonator along a predetermined frequency sweeping direction and outputs the frequency-sweeped excitation signal to the MEMS resonator; a detection unit that acquires a characteristic quantity, i.e., a vibration state information signal, representing the vibration state of the oscillator based on the excitation signal from the MEMS resonator, and detects the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously as a detection value; and a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected detection value.

[0080] Resonant sensors can determine physical quantities such as pressure and force acting on a MEMS resonator based on the sweep frequency of the vibration state information signal as it changes discontinuously. Therefore, sensing information such as the time difference between the start of the frequency sweep and the moment of discontinuity, as well as the time differences between the moments of multiple discontinuities, can be projected onto the time axis. The discontinuity of the vibration state information signal can be detected by setting thresholds, allowing for the detection of abrupt changes in signal strength. Therefore, even with noise superimposed on the signal strength, moments representing discontinuities can be reliably detected relative to the superimposed noise. For example, this can be considered similar to the better sound quality of FM radio reception and demodulation compared to AM radio. Furthermore, pulsed signal detection also provides a secondary effect of high affinity for digital signal processing.

[0081] Therefore, this resonant sensor enables high-precision sensing of MEMS resonators.

[0082] In particular, by using resonance in the nonlinear region, it is possible to excite large amplitudes that cannot be obtained in linear resonance and improve the signal-to-noise ratio (S / N) of the sensed value. Furthermore, by sweeping the frequency, the degree of inflection of the nonlinear resonant waveform can be obtained from the time axis. Thus, instead of extracting the intensity of the sensed value, a signal such as a PWM (Pulse Width Modulation) signal projected onto the time axis is extracted, which becomes robust relative to noise superimposed on the signal intensity, enabling the detection of even minute changes in the resonant state. If set as a PWM signal, it is easy to transmit as a digital signal and easy to process as a signal.

[0083] Furthermore, another method for detecting a resonant sensor disclosed herein is a method for detecting a resonant sensor using a MEMS resonator. This method includes: sweeping the frequency of the excitation signal of the oscillator of the MEMS resonator along a predetermined sweep direction, and outputting the swept excitation signal to the MEMS resonator; obtaining a characteristic quantity representing the vibration state of the oscillator based on the excitation signal, i.e., a vibration state information signal, from the MEMS resonator, and detecting the frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously as a detection value; and determining the physical quantity acting on the MEMS resonator based on the detected detection value.

[0084] This method also achieves the same effect as described above.

[0085] Furthermore, in another aspect of the resonant sensor disclosed herein, the detection unit sets the difference between at least two frequencies of the excitation signal as the detection value, wherein the at least two frequencies of the excitation signal include the frequency at which the vibration state information signal changes discontinuously during the frequency sweep and the frequency at which the vibration state information signal changes discontinuously during the frequency sweep in the opposite direction of the frequency sweep direction.

[0086] Therefore, even if at least two frequencies of the excitation signal have errors, the influence of these errors can be suppressed by calculating the difference between the two frequencies. That is, since the difference between the two frequencies, i.e., the frequency difference, is used as the detected value to determine the physical quantity, it is less susceptible to changes in the resonant frequency caused by variations in ambient temperature. Therefore, this resonant sensor enables higher-precision sensing of MEMS resonators.

[0087] In particular, since it is not necessary to create temperature characteristic tables for resonant frequency changes, or to perform calibrations using temperature characteristic tables, the cost of resonant sensors is less likely to increase.

[0088] Furthermore, in another resonant sensor according to this disclosure, the frequency sweeping unit repeatedly switches the frequency sweeping direction to the reverse direction starting from the detection of discontinuous changes in the vibration state information signal during the frequency sweep, and then switches the frequency sweeping direction to the reverse direction again starting from the detection of discontinuous changes in the vibration state information signal to return. The detection unit outputs a pulse signal having two values ​​representing the two states of the positive and negative directions in the frequency sweeping direction as a detection value. The physical quantity determination unit determines the physical quantity acting on the MEMS resonator based on the pulse time width of the output detection value, i.e., the pulse signal.

[0089] Therefore, physical quantities can be determined based on the pulse duration of the pulse signal, which represents the two states of the sweep direction (positive and negative), thus enabling sensing of changes over time. Furthermore, since the sweep time for frequencies below and above the discontinuity point can be omitted, the amount of measurement data per unit time increases, enabling high-speed measurement.

[0090] In another aspect of the resonant sensor disclosed herein, the MEMS resonator is an electrostatic capacitive MEMS resonator, and the two frequencies of the discontinuous change of the vibration state information signal, namely the first frequency and the second frequency, are frequencies lower than the resonant frequency of the oscillator.

[0091] Therefore, by using a general-purpose MEMS resonator, high-precision sensing with a MEMS resonator is possible. Consequently, it offers good ease of use in resonant sensors.

[0092] Furthermore, in another aspect of the resonant sensor disclosed herein, the oscillator is surrounded in the space where the oscillator is disposed by a gas with a pressure gradually equal to the pressure acting on the MEMS resonator, and the physical quantity determination unit determines the pressure of the gas as the physical quantity based on the detected value.

[0093] Therefore, when pressure is applied to the MEMS resonator, the oscillator vibrates with a specified amplitude and velocity depending on the atmospheric pressure. Thus, this resonant sensor enables higher-precision pressure measurement of the MEMS resonator.

[0094] In another aspect of the resonant sensor disclosed herein, the electrostatic capacitive MEMS resonator includes an oscillator, an electrode disposed with a gap separated from the oscillator, and a transmission unit that changes the size of the gap according to the magnitude of the pressure acting on the electrostatic capacitive MEMS resonator. The physical quantity determination unit determines the pressure as the physical quantity based on the size of the gap.

[0095] Therefore, by applying pressure to the MEMS resonator, the transmission section can change the size of the gap according to the change in atmospheric pressure. By changing the size of the gap, the gap between the electrode and the oscillator can be narrowed or widened, thereby changing the degree of nonlinearity of the oscillator's resonant vibration. Therefore, in this resonant sensor, higher-precision pressure measurement of the MEMS resonator can be achieved.

[0096] Furthermore, in another aspect of the resonant sensor disclosed herein, the MEMS resonator is a capacitive MEMS resonator, and a thermometer is also provided on the MEMS resonator. The MEMS resonator obtains its own temperature T based on the thermometer, and the oscillator obtains the temperature T+ΔT when it is irradiated with infrared light. The physical quantity determination unit calculates the temperature change ΔT based on the temperature measured by the thermometer and the detection value, and determines the infrared power as the physical quantity based on the calculated temperature change ΔT.

[0097] Therefore, even if the ambient temperature surrounding the MEMS resonator changes, the temperature change ΔT can be calculated based on the temperature measured by the thermometer and the detected value. Consequently, this resonant sensor enables more precise infrared power measurement of the MEMS resonator. As a result, this infrared sensor is less susceptible to changes in ambient temperature.

[0098] Furthermore, in another aspect of the resonant sensor disclosed herein, the oscillator is subjected to a rotational speed orthogonal to the vibration direction of the vibration mode determined by the frequency sweeping unit. The physical quantity determination unit calculates a Coriolis force orthogonal to both the vibration mode determined by the frequency sweep and the rotational speed based on the detected value, and determines the rotational speed as the physical quantity based on the calculated Coriolis force.

[0099] Therefore, the Coriolis force can be determined using a capacitive resonant sensor. Thus, by calculating the angular velocity applied to the oscillator based on the Coriolis force, the resonant sensor can be configured as an angular velocity sensor.

[0100] In another aspect of the resonant sensor disclosed herein, the oscillator is subjected to a velocity orthogonal to the vibration direction of the torsional vibration mode determined by the frequency sweeping unit. The physical quantity determination unit calculates a Coriolis force orthogonal to both the torsional vibration mode determined by the frequency sweep and the velocity based on the detected value, and determines the velocity as the physical quantity based on the calculated Coriolis force.

[0101] Here, it also plays the same role and effect as mentioned above.

[0102] In another aspect of the resonant sensor disclosed herein, the vibration state information signal is a signal containing information related to the vibration amplitude of the oscillator.

[0103] Therefore, resonant sensors can detect the vibration amplitude of an oscillator.

[0104] In another aspect of the resonant sensor disclosed herein, the vibration state information signal is a signal that includes information related to the vibration velocity of the oscillator.

[0105] Therefore, resonant sensors can detect the vibration velocity of an oscillator. Vibration velocity is a signal whose phase is offset by 90 degrees from the vibration amplitude, and since the resonance curve represents... Figure 29 , Figure 30 With the same characteristics, it is possible to sense physical quantities at discontinuous points in vibration velocity information using frequency sweep.

[0106] In another aspect of the resonant sensor disclosed herein, the MEMS resonator is a non-electrostatic capacitive MEMS resonator, and the two frequencies of the discontinuous change of the vibration state information signal, namely the first frequency and the second frequency, are frequencies higher than the resonant frequency of the oscillator.

[0107] In this way, using a non-electrostatic capacitive MEMS resonator enables higher precision sensing.

[0108] In addition, in another aspect of the resonant sensor disclosed herein, a measurement range switching control unit is provided, which increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that there is no frequency in the sweep frequency range of the excitation signal where the vibration state information signal changes discontinuously.

[0109] Therefore, the measurement range switching control unit can increase the intensity of the excitation signal by a predetermined amount. Thus, in this resonant sensor, higher precision sensing of the MEMS resonator is possible.

[0110] In addition, in another aspect of the resonant sensor disclosed herein, there is a measurement range switching control unit, which increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that the difference between two frequencies in which the vibration state information signal changes discontinuously.

[0111] This allows for an increase in the intensity of the difference between at least two frequencies of the excitation signal by a predetermined amount. These at least two frequencies include the frequencies at which the vibration state information signal changes discontinuously during a frequency sweep and the frequencies at which the vibration state information signal changes discontinuously during a frequency sweep in the opposite direction of the frequency sweep. Therefore, this resonant sensor enables higher-precision sensing using a MEMS resonator.

[0112] (Implementation Method 1)

[0113] <Summary>

[0114] This embodiment of the resonant sensor detects a specified physical quantity based on the vibration state of the oscillator of a MEMS resonator. The physical quantity is, for example, temperature, pressure, or force. In this embodiment, since the resonant sensor uses a temperature sensor with a MEMS resonator, temperature is used as the physical quantity. The temperature sensor determines the physical quantity acting on the MEMS resonator based on the detected frequency of the excitation signal or the detected value at the time corresponding to that frequency. In this embodiment, the temperature sensor determines the physical quantity acting on the MEMS resonator based on the detected value of the frequency of the excitation signal. The excitation signal is an AC voltage input to the input electrode of the MEMS resonator. The frequency of the excitation signal is swept along a specified frequency sweep direction within a specified frequency range near the resonant frequency f0 of the MEMS resonator's oscillator.

[0115] The frequency representation of the MEMS resonator's oscillator based on the excitation signal is as follows: Figures 28 to 30 The resonance curve shown. There are roughly two factors that contribute to changes in the shape of the resonance curve: the first is the Q value, and the second is temperature.

[0116] Since the Q value, which is the first factor contributing to changes in the shape of the resonance curve, is the reciprocal of the energy loss, the less energy is lost, the higher the Q value. In the linear region, Figure 28 The maximum value at the resonant frequency f0 of the resonance curve increases. When the Q value is high, the peak of the resonance curve becomes sharper, and the half-width W (=f0 / Q) (the width of two frequencies that decreases by 3dB from the maximum value) narrows. Conversely, when vibrational energy is dissipated as heat, or when the viscous drag of the gas surrounding the oscillator increases, the Q value decreases. Figure 28 The maximum value decreases, and the half-value width W increases.

[0117] Temperature, as the second factor contributing to the change in the shape of the resonance curve, primarily causes a change in the resonant frequency f0. The elastic modulus, a mechanical property of the oscillator, has temperature characteristics; generally, as temperature increases, the elastic modulus decreases, thus reducing the elasticity of the oscillator and lowering the resonant frequency f0. Conversely, as temperature decreases, the resonant frequency f0 increases. Furthermore, an increase in temperature generally also leads to a decrease in the Q value. This is because, firstly, the elastic waves propagating in the oscillator dissipate due to the increased temperature. Secondly, in the case of the oscillator oscillating within a depressurization chamber, the pressure of the gas surrounding the oscillator increases due to the increased temperature, decreasing the Q value (indirectly inducing the Q value, which is the first factor contributing to the change in the shape of the resonance curve mentioned above). Therefore, temperature changes cause both changes in the resonant frequency and changes in the Q value, thus altering the resonance curve.

[0118] Here, the resonant frequency f0 refers to the frequency at which the amplitude of the oscillator vibrating in the linear region (which is related to the frequency of the excitation signal) reaches its maximum. Furthermore, this resonant frequency f0 is generally as follows: Figure 28 As shown, the frequency through which the axis of symmetry of the left-right symmetry of the resonant characteristics in the linear region passes.

[0119] Furthermore, in the case of electrostatic MEMS resonators, the resonant frequency f0 includes the effect of an electric spring caused by the DC potential provided between the oscillator and the electrodes. That is, the resonant frequency is determined by the mass and elasticity of the oscillator, which is the inherent elasticity of the material superimposed with the electric spring. Since the electric spring acts in a direction that weakens the inherent elasticity of the material, the resonant frequency decreases when a DC potential is provided compared to when no DC potential is provided. Here, the electric spring refers to the force exerted by the applied DC potential on the oscillator towards the electrode side, which manifests as a negative elasticity, the closer the oscillator is to the electrode.

[0120] Thus, temperature sensors can be constructed by utilizing changes in resonant frequency caused by variations in ambient temperature, or by utilizing changes in Q value caused by temperature, or by utilizing both.

[0121] <Structure>

[0122] Figure 1A This is the wiring diagram of a temperature sensor 400 with a MEMS resonator 500. Figure 1B This is a 3D diagram showing the structure of the MEMS resonator 500. Figure 2 This is a block diagram showing the structure of the temperature sensor 400 in Embodiment 1.

[0123] like Figure 1A , Figure 1B and Figure 2 As shown, the temperature sensor 400 includes a frequency sweep unit 401, a MEMS resonator 500, a signal processing unit 411, and a controller 416. The temperature sensor 400 is an example of a resonant sensor.

[0124] like Figure 1A and Figure 2 As shown, the frequency sweeping unit 401 performs frequency sweeping of the excitation signal and outputs the excitation signal (AC voltage) Vi to the resonator 500 while gradually changing the frequency.

[0125] The frequency sweep unit 401 sweeps the frequency of the excitation signal (also known as frequency sweep) along a predetermined sweep direction of the oscillator 501 of the MEMS resonator 500, and outputs the swept excitation signal to the MEMS resonator 500. The frequency sweep unit 401 has a PLL synthesizer 402 controlled by the controller 416. The PLL synthesizer 402 performs frequency sweep according to the frequency sweep control signal from the controller 416. The frequency sweep can be repeated continuously or intermittently.

[0126] like Figure 1A and Figure 1B As shown, the MEMS resonator 500 is a so-called electrostatic capacitive MEMS resonator that significantly exhibits the effect caused by capacitive bifurcation in a nonlinear region. The MEMS resonator 500 has a silicon substrate 504, a pair of oscillator supports 501s, an oscillator 501, and electrodes 502 and 503.

[0127] The silicon substrate 504 stacks a pair of oscillator supports 501s, an oscillator 501, and electrodes 502 and 503. The silicon substrate 504 is a base for arranging a pair of oscillator supports 501s, an oscillator 501, and electrodes 502 and 503.

[0128] A pair of oscillator support portions 501s are stacked on a silicon substrate 504. The pair of oscillator support portions 501s are integrally formed with the oscillator 501 and are arranged at a predetermined interval. The pair of oscillator support portions 501s are connected by the oscillator 501 arranged between them.

[0129] The oscillator 501 is a long strip oscillator disposed between a pair of oscillator supports 501s and extending from one oscillator support 501s to the other oscillator support 501s. In addition, the oscillator 501 is disposed with a gap between the electrodes 502 and 503 and between the electrodes 502 and 503.

[0130] Oscillator 501 is triangular in shape when cut by a plane orthogonal to its length. Oscillator 501 undergoes torsional vibration with the approximate centroid of the triangular cross-section as its center of rotation. The displacement Δx caused by the torsional vibration is determined by… Figure 1A The dashed line represents this. (And...) Figure 27A The difference in the MEMS resonator 100 shown is that the cross-sectional shape of the oscillator 501 supported by the oscillator support 501s is triangular.

[0131] In this embodiment, the length L of the oscillator 501 is 100 (μm), and the resonant frequency f0 of the oscillator 501 is f0 = 19.6 (MHz) under specified temperature, pressure, and other conditions (torsional resonance mode). Such a MEMS resonator 500 structure (the structure of a resonator whose oscillator is excited by electrostatic force and whose output is a current caused by capacitance changes accompanying vibration) is easily fabricated using semiconductor processes, making it suitable for integration into integrated circuits. This is advantageous in enabling high integration of sensors and sensor signal processing systems. Furthermore, in this embodiment, the gap between the oscillator 501 and each of the electrodes 502 and 503 is 190 (nm).

[0132] Furthermore, an excitation signal is applied to the oscillator 501, and the electrical signals output from electrodes 502 and 503 are input to a differential amplifier and then flow to the signal processing unit. This is related to... Figure 27B Another difference in the MEMS resonator 100 shown.

[0133] Electrodes 502 and 503 are configured to sandwich and face oscillator 501. Electrodes 502 and 503 are configured with a gap between them and oscillator 501, thereby forming a gap with a pair of oscillator supports 501s and oscillator 501.

[0134] Electrode 502 provides an excitation force to oscillator 501 by being supplied with a DC potential Vp. By providing a DC potential Vp to the electrode 502 side, the excitation force applied to oscillator 501 is applied to the side facing electrode 502, and a displacement current accompanying the vibration is output from electrode 502. However, since the high-frequency signal without vibration flows through both electrodes 502 and 503, it is removed by a differential amplifier because the high-frequency signal without vibration is in phase. The output of the differential amplifier is the component of the displacement current output with vibration. Furthermore, in this embodiment, the cross-sectional shape of oscillator 501 is set to triangular, but it could also be... Figure 27B As shown, it is a square or polygonal shape. Regardless of... Figure 27B The structure is still Figure 1A Both the electrostatic capacitive type MEMS resonator 500 and the structure of the former can be driven. Sometimes the former is called a 2-port structure and the latter is called a 1-port differential structure.

[0135] like Figure 1A , Figure 1B and Figure 2 As shown, an excitation signal Vi, for example, sweeping from frequency f1 to frequency f2 (f1 < f2), is input from the frequency sweep unit 401 to the MEMS resonator 500. The MEMS resonator 500, through the vibration of the oscillator 501 corresponding to the excitation signal Vi, outputs a voltage corresponding to the current flowing through the output electrode as a characteristic quantity representing the vibrational motion, i.e., a vibrational state information signal (AC voltage Vo), to the signal processing unit 411. This is equivalent to performing a frequency sweep proportional to the sawtooth wave, as described later. Here, the vibrational state information signal is a signal containing information related to the vibration amplitude of the oscillator 501. Furthermore, the vibrational state information signal has two discontinuously varying frequencies, i.e., frequencies f1 and f2. L (First frequency) and frequency f H The (second frequency) is a frequency lower than the resonant frequency f0 of the oscillator 501. Alternatively, the MEMS resonator 500 can perform a frequency sweep from frequency f1 to frequency f2 (f1 < f2), and then a frequency sweep from f2 to f1. This is equivalent to performing the triangular wave-shaped frequency sweep described later.

[0136] The signal processing unit 411 obtains a characteristic quantity, i.e. a vibration state information signal, representing the vibration state of the oscillator 501 from the MEMS resonator 500 during frequency sweep, and outputs temperature information, which determines the temperature based on the obtained vibration state information signal, to the outside.

[0137] The signal processing unit 411 includes a discontinuity detection unit 412 and a conversion unit 415.

[0138] The discontinuity detection unit 412 acquires a characteristic quantity, i.e., a vibration state information signal, representing the vibration state of the oscillator 501 from the MEMS resonator 500 during frequency sweep, and detects the frequency of the excitation signal when the acquired vibration state information signal changes discontinuously. The discontinuity detection unit 412 is an example of a detection unit. The discontinuity detection unit 412 includes a detector 413 and a threshold detection unit 414.

[0139] Detector 413 performs envelope detection of the amplitude of the vibration state information signal obtained from MEMS resonator 500. Detector 413 outputs the detected signal, as a result of the envelope detection, to threshold detection unit 414.

[0140] The threshold detection unit 414 detects that the signal value shown by the detected signal exceeds a preset threshold (or determines whether the signal value has exceeded the preset threshold). The threshold detection unit 414 outputs the time information when the detected signal exceeds the preset threshold to the conversion unit 415. Here, since the time information corresponds one-to-one with the sweep frequency information, the time information and the frequency information are synonymous. In addition, sometimes there are two functions: threshold detection in a sweep from frequency f1 to f2 and threshold detection in a sweep from f2 to f1, so the thresholds can be different values. Alternatively, when crossing a discontinuity point frequency f, which becomes a discontinuity point... H The frequency, i.e., the frequency sweep from f1 to f2, is due to frequency f H The vibration amplitude has a peak value, so peak detection can be used instead of threshold detection. Alternatively, it can be set to peak detection when crossing discontinuity frequency f. L The frequency f is the frequency in the sweep from f2 to f1. L The vibration amplitude is close to the peak value but slightly smaller than the peak value, so peak detection can be used instead, or it can be used to detect f with higher precision. L Threshold detection is used instead.

[0141] The conversion unit 415 determines the physical quantity acting on the MEMS resonator 500 based on the detected value of the frequency of the excitation signal at the discontinuity point. Specifically, the conversion unit 415 has a conversion table 415T, which is used to determine the physical quantity acting on the MEMS resonator 500. The conversion table 415T is a table used to replace the time information of the discontinuous change of the vibration state information signal in the frequency sweep of the excitation signal with the frequency of the excitation signal, and to calculate the temperature of the oscillator based on the replaced frequency information. The conversion unit 415 is an example of a physical quantity determination unit. In addition, since the time information and frequency information correspond one-to-one, it is not always necessary to replace the time information with frequency information. For example, the actual state of the time information counted by counterpulses is the number of counted pulses, and the number of pulses can also be used in the table used to calculate the temperature. Alternatively, the conversion unit 415 can also determine the physical quantity acting on the MEMS resonator 500 by reading the conversion table 415T stored in a different storage device than the conversion unit 415. Therefore, the conversion unit 415 having a conversion table 415T is not a necessary component.

[0142] The controller 416 controls the frequency sweep unit 401 by outputting a frequency sweep control signal to the frequency sweep unit 401. That is, the controller 416 controls the PLL synthesizer 402 of the frequency sweep unit 401 through the frequency sweep control signal, thereby performing a frequency sweep from frequency f1 to f2 at a predetermined period. The controller 416 may be an example of a measurement range switching controller.

[0143] Furthermore, the controller 416 controls the signal processing unit 411 by outputting a counting control signal to the signal processing unit 411. That is, the controller 416 controls the threshold detection unit 414 of the signal processing unit 411 according to the counting control signal, thereby detecting that the signal value shown by the detector signal exceeds a preset threshold, and outputting the time information when the threshold is exceeded to the conversion unit 415.

[0144] Furthermore, if the discontinuity detection unit 412 determines that there are no frequencies within the sweep frequency range of the excitation signal where the vibration state information signal changes discontinuously, the controller 416 may increase the intensity of the excitation signal by a predetermined amount. Furthermore, if the discontinuity detection unit 412 determines that the difference between two frequencies where the vibration state information signal changes discontinuously is less than a predetermined value, the controller 416 may increase the intensity of the excitation signal by a predetermined amount.

[0145] <Temperature sensing unit>

[0146] The following is an example of a temperature sensing unit.

[0147] Figure 3AAn example is temperature sensing using the temperature sensor 400 to perform a sawtooth-shaped frequency sweep and utilize the temperature-induced change in resonant frequency. Figure 3A This is a timing diagram showing the operation of a capacitive MEMS resonator 500 as the frequency of the excitation signal is swept upwards. Figure 3A (1) represents the vibration state information signal after detection. Figure 3A (2) represents the frequency of the excitation signal. Figure 3A (3) indicates the start signal of frequency sweep. Figure 3A (4) represents the gate signal. Figure 3A (5) represents the counter pulse.

[0148] exist Figure 3A In the middle, the signal sent from controller 416 Figure 3A The sweep start signal of (3) is triggered (indicated by the arrow), if Figure 3A The frequency sweep of the excitation signal in (2) starts from frequency f1, then simultaneously Figure 3A The gate signal of (4) becomes open. Figure 3A The counting of the counter pulse of (5) begins. Figure 3A The vibration state information signal (after detection) shown in (1) rises discontinuously at a certain frequency, and is detected by the threshold detection unit 414. The signal processing unit 411 then closes the gate signal. In this embodiment, peak detection is used instead of threshold detection. The frequency of this discontinuity point is equivalent to... Figure 29 The frequency f of the nonlinear resonant curve of the resonant characteristic 121 shown is... H The frequency f at the discontinuity point H It is approximately equal to the resonant frequency f0. Since the resonant frequency f0 changes with temperature, the frequency at the discontinuity point f... H This also changes with temperature. By varying the time width of the gate signal's open state, temperature information can be obtained based on changes in the counter pulse count. Alternatively, the gate signal can be opened starting from the point where a discontinuity is detected, and the counter pulses can be used to count the time until the next sweep start signal (equivalent to...). Figure 3A (4) The off-time counts the counter pulses.

[0149] Since the frequency of the excitation signal is linearly swept at the same time as the frequency sweep begins, the discontinuity frequency f can be easily calculated based on the number of counter pulses being counted. H The actual test example is shown below. Figure 3B The curve graph. Figure 3B It represents the temperature (ambient temperature) and the frequency f at the discontinuity point. H A diagram showing the relationships between them.

[0150] exist Figure 3B The diagram illustrates placing a MEMS resonator 500 in a temperature-controlled thermostat and providing the discontinuity frequency f when the temperature varies from room temperature ± 5°C. H The measured values ​​were obtained. At each temperature, there were N=100 measurement points, yielding the discontinuity frequency f with minimal temperature deviation. H The measured values ​​were obtained, and the temperature and the frequency f at the discontinuity points were also obtained. H The result has a linear relationship. Therefore, if the conversion unit 415 will... Figure 3B If the relationship is stored as a conversion table 415T, then when the MEMS resonator 500 is used as a temperature sensor, only the discontinuity frequency f is measured. H It can be based on Figure 3B The relationship allows for the precise acquisition of temperature information.

[0151] In addition, such as Figure 3C As shown, it is believed that the correlation between the detected signal intensity at discontinuity points and temperature is weak, so it is difficult to use the detected signal intensity at discontinuity points to construct a high-precision temperature sensor. Figure 3C It is a graph showing the relationship between temperature and the intensity of the detector signal at the discontinuity point.

[0152] In addition, due to Figure 3A The time period during which the gate signal (4) is open contains temperature information. Therefore, when the start signal is repeated with a period T, the gate signal becomes a pulse width modulation signal (PWM signal) related to the temperature information. The PWM signal is transmitted as a digital signal before being demodulated, and has high affinity with digital signal processing circuits.

[0153] In addition, in order to demodulate the pulse width modulation signal to obtain temperature information, the number of counter pulses during the gate opening time is counted in this embodiment, but it is not limited to this method. Alternatively, the pulse width modulation signal can be passed through an analog integrator circuit to read the integral value in each period T.

[0154] exist Figure 4A The example illustrates temperature measurement using the temperature sensor 400 by performing a downward-facing frequency sweep in a sawtooth wave pattern, utilizing the change in resonant frequency caused by temperature. Figure 4A This is a timing diagram showing the operation of a capacitive MEMS resonator 500 as the excitation signal sweeps its frequency downwards. Figure 4A (1) represents the vibration state information signal after detection. Figure 4A (2) represents the frequency of the excitation signal. Figure 4A (3) indicates the start signal of frequency sweep. Figure 4A (4) represents the gate signal. Figure 4A (5) represents the counter pulse.

[0155] exist Figure 4A In the middle, the signal sent from controller 416 Figure 4A The sweep start signal of (3) is triggered (indicated by the arrow), if Figure 4A The frequency sweep of the excitation signal in (2) starts from frequency f2, then simultaneously Figure 4A The gate signal of (4) becomes open. Figure 4A The counting of the counter pulse of (5) begins. Figure 4A The vibration state information signal (after detection) shown in (1) decreases discontinuously at a certain frequency, which is detected by the threshold detection unit 414, and the signal processing unit 411 turns the gate signal off. The frequency of this discontinuity is equivalent to Figure 29 The frequency f of the nonlinear resonant curve of the resonant characteristic 121 shown is... L Since the resonant frequency f0 changes with temperature, the frequency at the discontinuity point f... L This also changes with temperature. By varying the time width of the gate signal's open state, temperature information can be obtained based on changes in the counter pulse count. Alternatively, the gate signal can be opened starting from the point where a discontinuity is detected, and the counter pulses can be used to count the time until the next sweep start signal (equivalent to...). Figure 4A (4) The off-time counts the counter pulses.

[0156] Since the frequency of the excitation signal is linearly swept at the start of the frequency sweep, the discontinuity frequency f can be easily calculated based on the number of counter pulses being counted. L The actual test example is shown below. Figure 4B The curve graph. Figure 4B It represents the frequency f at the point of discontinuity and the temperature. L A diagram showing the relationships between them.

[0157] Figure 4B This illustrates placing the MEMS resonator 500 in a temperature-controlled thermostat and providing the discontinuity frequency f when the temperature varies from room temperature ± 5°C. L The measured values ​​were obtained. At each temperature, there were N=100 measurement points, yielding the discontinuity frequency f with minimal temperature deviation. L The measured values ​​were obtained, and the temperature and the frequency f at the discontinuity points were also obtained. L The result has a linear relationship. Therefore, if the conversion unit 415 will... Figure 4B If the relationship is stored as a conversion table 415T, then when the MEMS resonator 500 is used as a temperature sensor, only the discontinuity frequency f is measured. L Therefore, it is possible to base on Figure 4B The relationship allows for the precise acquisition of temperature information.

[0158] in addition, Figure 4C This is a graph showing the relationship between temperature and the peak value of the detected signal intensity. That is, Figure 4C This represents the relationship between temperature and the peak value of the detector signal intensity near the discontinuity; the two are correlated. Therefore, it is assumed that if the peak value of the detector output signal is measured, this value can be used to obtain temperature information. However, if compared... Figure 4C and Figure 4B Then in Figure 4C The deviation of the plotted points is relatively large, therefore, if the peak value of the detected signal intensity is used to construct the temperature sensor 400, the measurement accuracy will be reduced. In other words, observing the change in detected signal intensity accompanying temperature change corresponds to observing the change in Q value accompanying temperature change. In observing this Q value change, the detected signal intensity obtained by using nonlinear resonance is larger than that obtained by linear resonance, which is considered advantageous in terms of S / N. However, it is believed that temperature information can be extracted with high accuracy by not using the detected signal intensity of the sloping nonlinear resonance curve, but by using the time axis (which is equivalent to frequency due to frequency sweep) to grasp the degree of sloping.

[0159] in addition, Figure 4A The gate signal of (4) becomes a pulse width modulation signal related to temperature information, thus having high affinity with digital signal processing circuits. In addition, the demodulation method is not limited to counting the number of counter pulses; it can also be a method of reading the integral value of the pulse width modulation signal in each cycle T by passing it through an analog integrator circuit.

[0160] exist Figure 5A The example illustrates temperature measurement using the change in Q value caused by temperature-induced resonance, achieved by frequency sweeping in a triangular wave pattern via temperature sensor 400. Figure 5A This is a timing diagram showing the operation of a capacitive MEMS resonator 500 during frequency sweeping with a triangular wave-based excitation signal. Figure 5A (1) represents the vibration state information signal after detection. Figure 5A (2) represents the frequency of the excitation signal. Figure 5A (3) indicates the start signal of frequency sweep. Figure 5A (4) represents the gate signal. Figure 5A (5) represents the counter pulse.

[0161] exist Figure 5A In the middle, the signal sent from controller 416 Figure 5A The sweep start signal of (3) is triggered (indicated by the arrow). Figure 5A The frequency sweep of the excitation signal in (2) starts from frequency f1, and at the same time... Figure 5A The gate signal used for frequency sweeping above a in (4) becomes open. Figure 5A The counting of the counter pulse of (5) begins. Figure 5A The vibration state information signal (after detection) shown in (1) is at the discontinuity frequency f H The signal increases discontinuously, and is detected by the threshold detection unit 414. The signal processing unit 411 then closes the gate signal. In this embodiment, peak detection is used instead of threshold detection. The number of pulses, which is the result of counting the counter pulses during the gate's open time, is set to N. H In the case of a triangular wave with period T, the frequency of the excitation signal is swept downwards from f2 to f1 during the second half of period 1. Figure 5A The vibration state information signal (after detection) shown in (1) is at the discontinuity frequency f L The discontinuous decrease is detected by the threshold detection unit 414, and the signal processing unit 411 will... Figure 5A The lower frequency sweep signal of (4)b is turned on. When the lower frequency sweep ends, the signal processing unit 411 turns the gate signal off. The number of pulses, which is the result of counting the counter pulses during the gate's open time, is set to N. L The difference N between the counting results H -N L Equivalent to Figure 29 The frequency difference f of the nonlinear resonance curve of the resonance characteristic 121 shown is... H -f L Since the resonant frequency f0 changes with temperature, the frequency difference f H and f L Both change with temperature, but by making the temperature-induced change in the resonant frequency the frequency difference f... H -f L This change is cancelled. That is, the frequency difference f H -f L This is a quantity representing the degree of tilt of the nonlinear resonant waveform. Generally, the Q value decreases as the temperature rises, but if observed in the linear resonant region, a decrease in the detector signal strength of the resonant curve or a widening of the -3dB bandwidth is observed. By exciting the oscillator 501 in the nonlinear resonant region, it is possible to achieve a Q value through a frequency difference f. H -f L The decrease in temperature leads to a decrease in the Q value that accompanies the increase in temperature.

[0162] Since the frequency of the excitation signal is linearly swept during the upward / downward frequency sweep, the counted counter pulses N can be used. H and N L Easily calculate the frequency difference f H -f L That is, the discontinuity detection unit 412 detects the difference between at least two frequencies of the excitation signal (frequency difference f). H -f LThe excitation signal is set as the detection value, and at least two frequencies of this excitation signal are included in the discontinuity frequency f when the vibration state information signal (after detection) changes discontinuously during the frequency sweep. H The discontinuity frequency f when the vibration state information signal (after detection) changes discontinuously during frequency sweeps in the opposite direction of the sweep direction. L .

[0163] Next, actual test examples will be shown. Figure 5B . Figure 5B It represents the frequency difference f between temperature and the frequencies of two discontinuous points. H -f L A diagram showing the relationships between them.

[0164] exist Figure 5B The diagram illustrates the frequency difference f of a MEMS resonator 500 placed in a temperature-controlled thermostat bath, providing the frequency difference f at discontinuous points when the temperature varies from room temperature to ±5°C. H -f L The measured values. At each temperature, there are N=100 measurement points, yielding frequency differences f with minimal temperature deviation. H -f L The measured values ​​were obtained, and the temperature and frequency difference f was also obtained. H -f L The result has a linear correlation. Therefore, if the conversion unit 415 converts this... Figure 5B If the relationship is stored as a conversion table 415T, then when the MEMS resonator 500 is used as a temperature sensor, only the frequency difference f is measured. H -f L It can be based on Figure 5B The relationship allows for the precise acquisition of temperature information.

[0165] The frequency f of the discontinuity point determined by sawtooth wave sweep frequency measurement H or f L Compared to temperature measurements used to calculate temperature, the method based on the frequency difference f determined by triangular wave sweep frequency measurement... H -f L There are advantages to using this method to calculate temperature. This advantage is that even... Figure 5A When the frequencies f1 and f2 of the excitation signal in (2) sweep frequency sweep contain error δ due to fluctuations and other factors, and change to frequencies f1+δ and f2+δ, the differential frequency f H -f L It will not be affected by the error δ. Even if the counter pulse count value N H The count value N increases due to the influence of error δ. L Also increase by the same amount, therefore N H -N L It can maintain a constant value.

[0166] and, Figure 6 This illustrates the use of differential frequency f based on triangular wave sweep. H -f L Another advantage of temperature measurement is that it provides the necessary conditions for temperature determination. Figure 6 This is a timing diagram showing the operation of the electrostatic capacitive MEMS resonator 500 under the condition of frequency sweep direction switching during timed switching at discontinuous point detection. Figure 6 (1) represents the vibration state information signal after detection. Figure 6 (2) represents the frequency of the excitation signal. Figure 6 (3) indicates the start signal of frequency sweep. Figure 6 (4) represents the sweep direction control signal (also a gate signal). Figure 6 (5) represents the counter pulse.

[0167] exist Figure 6 In the middle, the signal sent from controller 416 Figure 6 The sweep start signal of (3) is triggered (indicated by the arrow). Figure 6 The frequency sweep of the excitation signal in (2) starts from frequency f1 to frequency f2 (f2 > f1), and at the same time... Figure 6 The sweep direction control signal (and gate signal) of (4) a is reset to the upward sweep. Figure 6 The vibration state information signal (after detection) shown in (1) is at the discontinuity frequency f H The frequency increases discontinuously, and the threshold detection unit 414, which is set to threshold A, detects it and changes the frequency sweep direction control signal to a downward frequency sweep. Figure 6 The frequency of the excitation signal of (2) is swept downwards to frequency f1. Figure 6 The vibration state information signal (after detection) shown in (1) is at the discontinuity frequency f L The frequency decreases discontinuously, and is detected by the threshold detection unit 414, which is set to threshold B. The frequency sweep direction control signal is then changed to upward frequency sweep. This detection of threshold A and threshold B is repeated, and the frequency sweep direction continues to switch. Figure 6 (4) The high state of the sweep direction control signal (indicating a downward sweep here) indicates that the sweep direction starts from the discontinuous frequency f. H To the frequency f of the discontinuity point L The sweep frequency time. That is, the sweep frequency unit 401 repeats the following operation: starting from the detection of discontinuous changes in the vibration state information signal (after detection) during the sweep frequency, the sweep frequency is switched to the reverse direction, and again starting from the discontinuous changes in the vibration state information signal (after detection), the sweep frequency is switched to the reverse direction again.

[0168] The count value N is obtained by using the high state as a gate signal to count the counter pulses. HL Equivalent to the frequency f of the discontinuity pointH With the frequency f of the discontinuity point L The difference, that is, Figure 29 The frequency difference f of the inclination of the nonlinear resonance curve H -f L Information using frequency difference f. H -f L The value is based on Figure 5B Based on this relationship, high-precision temperature information can be obtained. The discontinuity detection unit 412 outputs a pulse signal with two values ​​representing the positive and negative states in the frequency sweep direction as the detection value (frequency difference f). H -f L The conversion unit 415 determines the physical quantity acting on the MEMS resonator 500 based on the pulse duration of the output detection value, i.e., the pulse signal. Then, since the frequency below the discontinuity point f is omitted... L The frequency sweep time and the frequency above the discontinuity point f H The frequency sweep time is increased, so the temperature measurement data per unit time increases, which means that high-speed temperature measurement can be achieved.

[0169] also, Figure 6 (4) The sweep direction control signal (also known as the gate signal) becomes a pulse frequency modulation (PFM) signal related to temperature information, so it has high affinity with digital signal processing circuits. The PFM signal also carries temperature information in the pulse width, so it is similar to PWM. The demodulation method can be the method of counting the number of counter pulses, but it is not limited to this. In addition, there is the following method: pass the pulse width modulation signal through an analog integrator circuit, and reset the integral value each time the sweep direction is switched, and read the integral value.

[0170] <Effects>

[0171] Next, the effects of the temperature sensor 400 in this embodiment will be explained.

[0172] As described above, the temperature sensor 400 of this embodiment is a temperature sensor 400 using a MEMS resonator 500, comprising: a MEMS resonator 500; a frequency sweeping unit 401, which sweeps the frequency of the excitation signal of the oscillator 501 of the MEMS resonator 500 along a predetermined frequency sweeping direction and outputs the frequency-sweeped excitation signal to the MEMS resonator 500; a discontinuity detection unit 412, which obtains a characteristic quantity, i.e., a vibration state information signal, representing the vibration state of the oscillator 501 based on the excitation signal from the MEMS resonator 500, and detects the frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously as a detection value; and a conversion unit 415, which determines the physical quantity acting on the MEMS resonator 500 based on the detected detection value.

[0173] The temperature sensor 400 can determine physical quantities such as pressure and force acting on the MEMS resonator 500 based on the sweep frequency when the vibration state information signal changes discontinuously. Therefore, sensing information such as the time difference between the start of the frequency sweep and the moment of discontinuity, as well as the time differences between multiple moments of discontinuity, can be projected onto the time axis. The discontinuity of the vibration state information signal can be detected by setting a threshold, etc., to detect abrupt changes in signal strength. Therefore, even if noise is superimposed on the signal strength, moments indicating discontinuity can be reliably detected relative to the superimposed noise. For example, this can be considered similar to the effect that FM radio broadcasts have better sound quality than AM radio broadcasts. Furthermore, pulsed detection signals can also yield secondary effects of high affinity for digital signal processing.

[0174] Therefore, the temperature sensor 400 enables high-precision sensing of the MEMS resonator 500.

[0175] In particular, by using resonance in the nonlinear region, it is possible to excite large amplitudes that cannot be obtained in linear resonance and improve the signal-to-noise ratio (S / N) of the sensed value. Furthermore, by sweeping the frequency, the degree of inflection of the nonlinear resonant waveform can be obtained from the time axis. Thus, instead of taking the intensity as the sensed value, it is taken as, for example, a PWM signal projected onto the time axis, which becomes robust relative to noise superimposed on the signal intensity and allows for the detection of even minute changes in the resonant state. If it is set as a PWM signal, it is easy to transmit as a digital signal and easy to process as a signal.

[0176] Furthermore, in the detection method of the temperature sensor 400 in this embodiment, the detection method of the temperature sensor 400 using the MEMS resonator 500 includes: sweeping the frequency of the excitation signal of the oscillator 501 of the MEMS resonator 500 along a predetermined sweep direction, and outputting the frequency-sweeped excitation signal to the MEMS resonator 500; obtaining a characteristic quantity, i.e., a vibration state information signal, representing the vibration state of the oscillator 501 based on the excitation signal from the MEMS resonator 500, and detecting the frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously as a detection value; and determining the physical quantity acting on the MEMS resonator 500 based on the detected detection value.

[0177] This method also achieves the same effect as described above.

[0178] Furthermore, in the temperature sensor 400 of this embodiment, the discontinuity detection unit 412 sets the difference between at least two frequencies (frequency difference) of the excitation signal as the detection value. The at least two frequencies of the excitation signal include the frequency when the vibration state information signal changes discontinuously during the frequency sweep and the frequency when the vibration state information signal changes discontinuously during the frequency sweep in the opposite direction of the frequency sweep direction.

[0179] Therefore, even if at least two frequencies of the excitation signal have errors, the influence of these errors can be suppressed by calculating the difference between the two frequencies. That is, since the difference between the two frequencies, i.e., the frequency difference, is used as the detected value to determine the physical quantity, it is less susceptible to changes in the resonant frequency caused by variations in ambient temperature. Therefore, this temperature sensor 400 enables higher-precision sensing of the MEMS resonator 500.

[0180] In particular, since it is not necessary to manufacture temperature characteristic tables for resonant frequency changes or to perform calibration using temperature characteristic tables, the cost of temperature sensor 400 is not likely to increase significantly.

[0181] Furthermore, in the temperature sensor 400 of this embodiment, the frequency sweeping unit 401 repeatedly switches the frequency sweeping direction to the reverse direction starting from the detection of discontinuous changes in the vibration state information signal during the frequency sweep, and then switches the frequency sweeping direction to the reverse direction again starting from the detection of discontinuous changes in the vibration state information signal to return. The discontinuity detection unit 412 outputs a pulse signal having two values ​​representing the two states of the positive and negative directions in the frequency sweeping direction as a detection value. The conversion unit 415 determines the physical quantity acting on the MEMS resonator 500 based on the pulse time width of the output detection value, i.e., the pulse signal.

[0182] Therefore, physical quantities can be determined based on the pulse duration of the pulse signal, which represents the two states of the sweep direction (positive and negative), thus enabling sensing of changes over time. Furthermore, since sweep times at frequencies below and above the discontinuity point can be omitted, the amount of temperature measurement data per unit time increases, enabling high-speed temperature measurement.

[0183] Furthermore, in the temperature sensor 400 of this embodiment, the MEMS resonator 500 is a capacitive MEMS resonator. The vibration state information signal varies discontinuously at two frequencies (i.e., frequency f). L and frequency f H () is a frequency lower than the resonant frequency f0 of oscillator 501.

[0184] Therefore, by using a general-purpose MEMS resonator 500, high-precision sensing by the MEMS resonator 500 is possible. Consequently, the temperature sensor 400 is easy to use.

[0185] Furthermore, in the temperature sensor 400 of this embodiment, the vibration state information signal is a signal that includes information related to the vibration amplitude of the oscillator 501.

[0186] Therefore, the temperature sensor 400 is able to detect the vibration amplitude of the oscillator 501.

[0187] Furthermore, the temperature sensor 400 in this embodiment includes a controller 416, which increases the intensity of the excitation signal by a predetermined amount when the discontinuity detection unit 412 determines that there is no frequency in which the vibration state information signal changes discontinuously within the sweep frequency range of the excitation signal.

[0188] Therefore, the controller 416 can increase the intensity of the excitation signal by a predetermined amount. Thus, in this temperature sensor 400, higher precision sensing by the MEMS resonator 500 is possible.

[0189] Furthermore, the temperature sensor 400 in this embodiment includes a controller 416, which increases the intensity of the excitation signal by a predetermined amount when the discontinuity detection unit 412 determines that the difference between two frequencies in which the vibration state information signal changes discontinuously.

[0190] This allows for an increase in the intensity of the difference between at least two frequencies of the excitation signal by a predetermined amount. These at least two frequencies include the frequencies at which the vibration state information signal changes discontinuously during a frequency sweep and the frequencies at which the vibration state information signal changes discontinuously during a frequency sweep in the opposite direction of the frequency sweep. Therefore, this temperature sensor 400 enables higher-precision sensing by the MEMS resonator 500.

[0191] (Implementation Method 2)

[0192] <Structure>

[0193] The basic structure of the pressure sensor in this embodiment is the same as that of the temperature sensor in Embodiment 1. Therefore, the description of the basic structure of the pressure sensor in this embodiment will be omitted as appropriate. Furthermore, the basic structure of the MEMS resonator 500x in this embodiment is the same as that in Embodiment 1. Figure 2 The basic structure of the MEMS resonator 500x in this embodiment is the same as that of the MEMS resonator 500x in embodiment 1, so the description of the basic structure of the MEMS resonator 500x in this embodiment is appropriately omitted. The MEMS resonator 500x of the pressure sensor in this embodiment is similar to that in embodiment 1 in that it has a partition layer 504x and a diaphragm 505x. Figure 1B The MEMS resonator 500 is different.

[0194] Figure 7 This is a cross-sectional view of the 500x MEMS resonator, which is a type of electrostatic capacitor.

[0195] The resonant sensor in this embodiment uses Figure 7 The MEMS resonator 500x shown is used as a pressure sensor to measure the gas pressure of an atmosphere. This pressure sensor is an example of a resonant sensor. The vibration of the oscillator 501x ​​of the MEMS resonator 500x in the atmosphere is damped by the viscosity of the atmosphere. Therefore, the vibration amplitude and velocity of the oscillator 501x ​​depend on the pressure of the atmosphere. More specifically, the Q value, representing the sharpness of the resonance of the MEMS resonator 500x, is relative to... Figure 7 The gas pressure Pi around the oscillator 501x ​​has a relationship of approximately Q∝(1 / Pi). Furthermore, the amplitude X of the resonance in the linear resonance region has a relationship of X∝Q. Therefore, when X∝(1 / Pi) and the pressure Pi around the oscillator 501X decreases, the sharpness of the resonance increases, and the vibration amplitude X also increases. If the vibration amplitude X increases, the vibration velocity of the oscillator 501X also increases. The pressure sensor of this embodiment extends this principle to the nonlinear region and utilizes it.

[0196] Like the MEMS resonator 500 in Figure 1, the MEMS resonator 500x is a torsional resonator of a beam with a triangular cross-section. In addition to the oscillator 501x, electrodes 502x and 503x, the MEMS resonator 500x also has a partition layer 504x and a diaphragm 505x.

[0197] The MEMS resonator 500x has an oscillator 501x, electrodes 502x and 503x disposed within a closed space 507x formed by a partition layer 504x and a diaphragm 505x. Specifically, the oscillator 501x, electrodes 502x and 503x, partition layer 504x, and diaphragm 505x are disposed on a silicon substrate 510x. The oscillator 501x ​​is surrounded by a gas at a pressure gradually equal to the pressure acting on the MEMS resonator 500x via the partition layer 504x and the diaphragm 505x. The partition layer 504x is stacked on the silicon substrate 510x to cover a portion of the electrodes 502x and 503x and is configured to surround the oscillator 501x. The diaphragm 505x is stacked on the partition layer 504x, thereby forming a closed space 507x around the oscillator 501x.

[0198] The pressure Pi of the enclosed space 507x remains constant. In particular, by making the pressure Pi of the enclosed space 507x a vacuum, the oscillator 501x ​​becomes capable of resonating at a high Q value without the viscous resistance of the gas. The MEMS resonator 500x is electrostatically driven, so the effect of capacitive bifurcation is easily demonstrated. Figure 29The nonlinear resonance characteristics are shown. If the partition layer 504x and the membrane 505x are dense films made of Si-based, Ge-based, or SiGe-based materials, or their oxide and nitride films, then the film functions as a molecular "sieve." Oxygen and nitrogen in the air do not permeate the partition layer 504x and the membrane 505x, but helium and hydrogen with smaller molecular diameters do. For example, if the pressure inside the enclosed space 507x is set to Pi and the external pressure is set to P, and the pressure inside the enclosed space 507x is reduced in the manner of Pi << P, then the partial pressure of hydrogen remaining in the enclosed space 507x can be set to be lower than the partial pressure of hydrogen in the atmosphere. Due to this pressure difference, hydrogen in the atmosphere permeates through the partition layer 504x or the membrane 505x, and the partial pressure of hydrogen in the enclosed space 507x increases. This increase continues until the partial pressure of hydrogen in the enclosed space 507x is equal to that in the atmosphere. On the other hand, due to the increased hydrogen partial pressure within the enclosed space 507x, the Q value of the oscillator 501x's resonance decreases. A hydrogen pressure sensor can be configured such that it performs a frequency sweep of the excitation signal in the nonlinear resonance region to obtain the moment when the vibration state information signal undergoes discontinuous changes, thereby detecting changes in the hydrogen partial pressure. When the hydrogen partial pressure within the enclosed space 507x is balanced with the hydrogen partial pressure in the atmosphere, and hydrogen ceases to permeate into the partition wall layer and the membrane 505x, the hydrogen partial pressure in the atmosphere is detected; when the balance is not achieved, the hydrogen partial pressure within the enclosed space 507x is detected. That is, the conversion unit 415 bases the detection value (the moment when the vibration state information signal undergoes discontinuous changes) on the frequency difference f (described later). H -f L The change in gas pressure over time determines the gas pressure, thereby detecting the partial pressure of hydrogen in the enclosed space 507x.

[0199] <Unit for Pressure Measurement>

[0200] The following describes a pressure measurement unit. The method for extracting hydrogen pressure information as a pulse width modulation signal is also the same as in Embodiment 1. Figure 3A , Figure 4A , Figure 5A , Figure 6 Since they are the same, the explanation is appropriately omitted.

[0201] When measuring minute changes in hydrogen pressure, the Q-value of the oscillator 501x ​​changes only slightly. Therefore, the Q-value variation caused by changes in ambient temperature can sometimes be substantial. In such cases, the temperature characteristics of the discontinuous frequency are obtained beforehand, and temperature correction is applied.

[0202] Another example is the case where a thermometer 508x is configured in the MEMS resonator 500x. Figure 8AThis is a cross-sectional view of a capacitor-type MEMS resonator 500x that incorporates a thermometer 508x within the same chip. Figure 8A Examples are shown in Figure 7 The pressure sensor has a built-in thermometer to measure the ambient temperature in the 508x manner. Figure 8B This is a cross-sectional view of a capacitor-type MEMS resonator 500x with a thermometer 508x mounted on the same mounting substrate. Figure 8B An example is shown where a thermometer 508x is mounted near the MEMS resonator 500x on the mounting substrate of the MEMS resonator 500x. The thermometer 508x can be a PN diode type, thermocouple type, or thermoelectric type, but the method of sensing temperature is not limited to these.

[0203] In the pressure sensor, as a pretreatment to obtain the temperature characteristics of the discontinuity frequency, the atmospheric pressure P is reduced by a vacuum pump to sufficiently decrease the hydrogen partial pressure. Then, the residual hydrogen in the sealed space 507x is fully vented. Next, the pressure sensor is driven in a temperature-controlled thermostat in a nonlinear resonant region to obtain the relationship between the temperature shown by the thermometer 508x and the obtained discontinuity frequency.

[0204] Figure 9 It represents the frequency difference f between the temperature of the MEMS resonator at 500°C and the frequencies at two discontinuous points. H -f L A diagram showing the relationships between them. Figure 9 and Figure 5B same. Figure 9 The curve represents the frequency difference f caused by temperature changes. H -f L The changes in temperature allow us to use this curve as a reference to exclude the temperature-dependent components as described below.

[0205] When using a MEMS resonator 500x as a hydrogen pressure sensor, if the thermometer indicates a certain temperature T1 but the frequency difference f H -f L The value shown in the figure indicates the value marked with ★, meaning the value of the ★ mark is lower than the baseline curve. This situation illustrates that hydrogen gas permeates from the outside of the MEMS resonator 500x into the enclosed space 507x, degrading the Q value of the oscillator 501x. That is, the frequency difference f H -f L The deviation Δ of the measured value from the baseline curve indicates the hydrogen partial pressure within the enclosed space 507x.

[0206] Figure 10A It represents the change in hydrogen concentration and the frequency difference f. H -f L A graph showing the changes over time (when the temperature sensor is set as a thermocouple). Figure 10A The frequency difference f is measured at time t1 when air mixed with 200 ppm of hydrogen begins to flow into the atmosphere, and at time t2 when the hydrogen content increases to 1000 ppm. H -f L The result of the offset Δ.

[0207] like Figure 10A As shown, the deviation Δ from the reference curve begins to decrease in the negative direction from time t1. This is because 200 ppm of hydrogen in the atmosphere gradually permeates into the enclosed space 507x, and the hydrogen begins to hinder the vibration of the oscillator 501x, thus reducing the Q value. This decrease in Q value is taken as the frequency difference f between the two discontinuities in the nonlinear resonant region. H -f L The detection was performed. From time t2, the rate of decrease in the deviation Δ from the baseline curve increased. This is because, due to the increase in the hydrogen content of the atmosphere to 1000 ppm, the amount of hydrogen per unit time passing through the enclosed space 507x increases.

[0208] Furthermore, when the hydrogen concentration in the atmosphere was 200 ppm and 1000 ppm, the deviation Δ from the reference curve did not reach the saturation value within the measurement time. This can be attributed to the fact that the partial pressure of hydrogen in the enclosed space 507x and the partial pressure of hydrogen in the atmosphere did not reach equilibrium within the measurement time. Therefore, Figure 10A The vertical axis does not represent the partial pressure of hydrogen in the atmosphere, but rather the partial pressure of hydrogen within the enclosed space 507x. To obtain a sensor for measuring the partial pressure of hydrogen in the atmosphere, the following design can be made: the measurement time can be sufficiently extended, or the dimensions of the partition layer 504x and the diaphragm 505x can be adjusted to allow hydrogen to easily permeate into the enclosed space 507x, thereby shortening the hydrogen permeation path.

[0209] Alternatively, the thermometer 508x can be omitted from the MEMS resonator 500x, and the MEMS resonator 500x itself can be used as the temperature sensor. In the temperature sensor of Embodiment 1, a discontinuous frequency f is shown that can be obtained by sweeping the frequency above the excitation frequency based on a sawtooth wave. H It is used as temperature information. The frequency f at discontinuity points. H The resonant frequency f0 of the MEMS resonator is close to 500x, and the discontinuity frequency f varies with temperature. H It also changes in the same way as the resonant frequency f0. On the other hand, the frequency f at the discontinuity point... H It is not easily affected by changes in Q value (changes caused by temperature, and other changes caused by ambient gas pressure, etc.). Therefore, the frequency f at the discontinuity point is considered to be... H It only has temperature information. This is achieved by using the frequency f at discontinuities. HUtilizing this as temperature information can reduce the area and manufacturing cost of additional thermometers (508x). This is achieved by reducing the frequency f at discontinuous points. H When used as temperature information, not using Figure 9 The temperature and frequency difference f shown H -f L The baseline curve, and using Figure 11 The frequency f at the discontinuity point is shown. H With frequency difference f H -f L The baseline curve of the relationship is used, and the deviation Δ from the baseline curve is regarded as the change in hydrogen partial pressure.

[0210] Figure 10B It represents the change in hydrogen concentration and the frequency difference f. H -f L The time variation (using the frequency f of the discontinuity point) H The graph shows the temperature information. Figure 11 This indicates that the frequency f at the discontinuity point is... H f as temperature information H With frequency difference f H -f L A diagram showing the relationships between them. Figure 10B It is measured Figure 11 f shown H -f L The result of the offset Δ from the baseline curve.

[0211] Figure 10A This is the result of using a thermocouple with a resolution of 0.1℃ in the temperature sensor. Figure 10B In the middle, f represents temperature information. H The resolution is sufficiently finer than 0.1℃, so it represents... Figure 10A The same deviation Δ from the baseline curve changes, but with... Figure 10A In comparison, a smoother curve with less noise was obtained.

[0212] Additionally, the discontinuity frequency f obtained by sweeping the frequency below the sawtooth wave. L The data contains information about both the change in resonant frequency f0 caused by temperature and the change in Q value (caused by temperature changes, as well as other changes caused by ambient gas pressure). Therefore, in this embodiment, which aims to obtain the change in Q value caused by gas pressure, the discontinuity frequency f0 is considered to be... L It is not appropriate to use it as a replacement for the 508x thermometer.

[0213] Similarly, the frequency difference f obtained by triangular wave frequency sweep H -f LThe temperature-induced change in resonant frequency f0 is eliminated, and information about the change in Q value (changes caused by temperature, and other changes caused by ambient gas pressure, etc.) is obtained. Therefore, in this embodiment, which aims to obtain the change in Q value caused by gas pressure, the frequency difference f0 is considered to be the key factor. H -f L It is not appropriate to use it as a substitute for the 508x thermometer.

[0214] Next, the scenario is presented where the enclosed space 507x is filled with hydrogen gas, and the Q value decreases to the point where discontinuities disappear. In this case, the controller 416 can change the measurement range and detect discontinuities. Figure 12 This is a block diagram showing the structure of a pressure sensor 400a using a MEMS resonator 500x with a measurement range switching function.

[0215] Figure 12 The basic structure of the pressure sensor 400a shown is the same as that of the temperature sensor in Embodiment 1. The difference lies in the fact that the conversion unit 415 uses a conversion table 415T to output pressure information, representing the pressure as a physical quantity acting on the MEMS resonator 500x, to the outside. Furthermore, in... Figure 12 The pressure sensor 400a shown differs from the temperature sensor in Embodiment 1 in that it adds a path for feeding back discontinuity information from the signal processing unit 411 to the controller 416.

[0216] The controller 416 determines whether the Q value has decreased based on discontinuity information. Specifically, the controller 416 determines whether the Q value has decreased at the frequency f, which is a discontinuity that cannot be detected. L It can only detect the frequency f of discontinuities. H In the case of, or the frequency f of the discontinuity point L and f H If neither of these methods can be detected, it is determined that the gas pressure surrounding the oscillator has increased excessively, resulting in a decrease in the Q value. The controller 416, having made this determination, controls the frequency sweep unit 401 to increase the amplitude of the excitation signal Vi according to the measurement range table 416T it maintains, or controls the MEMS resonator 500x to increase the bias DC voltage Vp, thereby increasing the vibration amplitude and restoring the lost discontinuity.

[0217] As an earlier response method, the signal processing unit 411 can also process the frequency difference f between the two discontinuous frequency points. H -f LThe condition that the value is less than a predetermined value is fed back as discontinuity information to the controller 416. Based on the feedback discontinuity information, the controller 416 outputs a sweep frequency control signal to the sweep frequency unit 401 in a manner that increases the amplitude Vi of the excitation signal according to the measurement range table 416T, thereby controlling the MEMS resonator 500x via the sweep frequency unit 401. Alternatively, the controller 416 outputs a bias DC control signal to the MEMS resonator 500x in a manner that increases the bias DC voltage Vp, thereby controlling the MEMS resonator 500x.

[0218] Conversely, at frequency difference f H -f L When the amplitude Vi of the excitation signal exceeds a certain specified value, the oscillator begins to contact the electrode. Therefore, the controller 416 outputs a sweep control signal to the sweep unit 401 in a manner that reduces the amplitude Vi of the excitation signal according to the measurement range table 416T, thereby controlling the MEMS resonator 500x via the sweep unit 401. Alternatively, the controller 416 outputs a bias DC control signal to the MEMS resonator 500x in a manner that reduces the bias DC voltage Vp, thereby controlling the MEMS resonator 500x.

[0219] Figure 13 This represents the difference between the excitation signal strength Vi and the frequency difference f. H -f L A diagram showing the relationships between them. Figure 13 The frequency difference f is shown when the amplitude of the excitation signal Vi is varied under constant temperature and hydrogen pressure conditions. H -f L The change in frequency f. The excitation signal Vi is above 100 (mV). H -f L The region where the signal transitions to a constant value without change. This region represents the contact area between the oscillator and the electrode. The measuring distance meter 416T of the controller 416 stores the excitation signal Vi, which, under the assumed minimum hydrogen pressure, does not enter resonance in this contact area, and the bias DC voltage Vp of the resonator.

[0220] <Effects>

[0221] Next, the effects of the pressure sensor in this embodiment will be explained.

[0222] As described above, in the pressure sensor of this embodiment, the oscillator 501x ​​is surrounded within the enclosed space 507x (the space in which the oscillator 501x ​​is disposed) by a gas whose pressure gradually equals the pressure acting on the MEMS resonator 500x. The conversion unit 415 determines the gas pressure as a physical quantity based on the detected value.

[0223] Therefore, when pressure is applied to the MEMS resonator 500x, the oscillator 501x ​​vibrates with a specified amplitude and velocity depending on the atmospheric pressure. Thus, this pressure sensor enables more precise pressure measurement of the MEMS resonator 500x.

[0224] In this embodiment, it also has the same effect as in embodiment 1.

[0225] (Implementation Method 3)

[0226] <Structure>

[0227] The basic structure of the MEMS resonator 500x3 in this embodiment is described below, and it is similar to that in Embodiment 2. Figure 7 The basic structure of the MEMS resonator 500x3 in this embodiment is the same as that in embodiment 2, so the description of the basic structure of the MEMS resonator 500x3 in this embodiment is appropriately omitted. The MEMS resonator 500x3 in this embodiment is similar to that in embodiment 2 in that it has pillars 506x. Figure 7 The MEMS resonator 500x is different.

[0228] Figure 14 This is a cross-sectional view of a 500x3 electrostatic capacitive MEMS resonator.

[0229] like Figure 14 As shown, the resonant sensor in this embodiment is a pressure sensor that uses a MEMS resonator 500x3. The MEMS resonator 500x3 is a type in which the gap (distance) between the oscillator 501x ​​and the electrodes 502x and 503x varies according to the external pressure (fluid pressure and pressure) of the resonant sensor.

[0230] MEMS resonator 500x3 is a torsional resonator of a beam with a triangular cross-section. In addition to the oscillator 501x, electrodes 502x and 503x, partition layer 504x, and diaphragm 505x, MEMS resonator 500x3 also has multiple pillars 506x.

[0231] The plurality of pillars 506x are columnar members arranged such that they are sandwiched between the electrode 502x and the diaphragm 505x, and between the electrode 503x and the diaphragm 505x. The plurality of pillars 506x can be integrally connected to at least one of the electrodes 502x, 503x, and the diaphragm 505x, or they can be arranged individually. The plurality of pillars 506x transmit stress corresponding to the deflection amount of the diaphragm 505x to the electrodes 502x and 503x through the deflection of the diaphragm 505x. The gap between the diaphragm 505x and the pillars 506x varies according to the magnitude of the pressure acting on the MEMS resonator 500x3. The diaphragm 505x and the pillars 506x constitute the transmission part.

[0232] The MEMS resonator 500x3 comprises an oscillator 501x, a post 506x, and electrodes 502x and 503x disposed within a closed space 507x formed by a partition layer 504x and a diaphragm 505x. The pressure Pi of this closed space 507x remains constant. Specifically, by maintaining a vacuum pressure Pi in the closed space 507x, the oscillator 501x ​​is able to resonate at a high Q value without being subject to the viscous resistance of the gas. The MEMS resonator 500x3 is electrostatically driven, and therefore, the effect of capacitive bifurcation is readily apparent. Figure 29 The nonlinear resonant characteristics are shown. When the pressure P (fluid pressure and pressing) acting on the diaphragm 505x from outside the enclosed space 507x increases, the diaphragm 505x flexes. The flexure of the diaphragm 505x causes the electrodes 502x and 503x to flex via the column 506x. The mechanism by which the gaps between the electrodes 502x and the oscillator 501x, and between the electrodes 503x and the oscillator 501x, change under the external pressure P is the diaphragm 505x and the column 506x. For example, by flexing the electrode 503x, the gap between the electrode 503x and the oscillator 501x ​​narrows or widens, thereby changing the degree of nonlinearity of the resonant vibration of the oscillator 501x. The amount of flexure of the electrodes 502x and 503x shows a constant correspondence with the amount of flexure of the diaphragm 505x.

[0233] Figure 15 It represents the frequency difference f as the gap changes due to pressure and fluid pressure. H -f L A graph showing the changes. For example... Figure 15 As shown, f represents the frequency difference f at the discontinuity points of a nonlinear resonance. H -f L The relationship (calculated value) between the gap (distance between oscillator 501x ​​and electrode 502x or distance between oscillator 501x ​​and electrode 503x). Circuit connection to MEMS resonator 500x3 and implementation method 1. Figure 1A Similarly, specifically, the bias voltage Vp is set to 5 (V), and the voltage Vi (maximum value) of the excitation signal to electrode 503x is set to 100 (mV). From Figure 15 It can be seen that as the gap shrinks to 250nm, 230nm, 210nm, and 190nm, the resonant characteristics exhibit stronger nonlinearity, f H -f L The pressure is increased. The conversion unit 415 determines the pressure as a physical quantity based on the size of the gap. Using this relationship, the pressure outside the pressure sensor (fluid pressure and pressure) can be measured. That is, the conversion unit 415 uses the conversion table 415T to determine the pressure as a physical quantity acting on the MEMS resonator 500x3. The conversion unit 415 outputs pressure information indicating the determined pressure to the outside.

[0234] <Effects>

[0235] Next, the effects of the pressure sensor in this embodiment will be explained.

[0236] As described above, in the pressure sensor of this embodiment, the capacitive MEMS resonator 500x3 includes an oscillator 501x; electrodes 502x and 503x, which are spaced apart from the oscillator 501x; and a transmission unit that varies the size of the gap according to the magnitude of the pressure acting on the capacitive MEMS resonator 500x3. The conversion unit 415 determines the pressure as a physical quantity based on the size of the gap.

[0237] Therefore, by applying pressure to the MEMS resonator 500x3, the transmission section can change the size of the gap according to the change in atmospheric pressure. By changing the size of the gap, the gap between electrodes 502x and 503x and the oscillator 501x ​​narrows or widens, thus changing the degree of nonlinearity of the resonant vibration of the oscillator 501x. Therefore, this pressure sensor enables higher-precision pressure measurement of the MEMS resonator 500x3.

[0238] In this embodiment, it also has the same effect as in embodiment 1.

[0239] (Implementation Method 4)

[0240] The basic structure of the MEMS resonator 500x4 in this embodiment is similar to that in Embodiment 2. Figure 8B The basic structure of the MEMS resonator 500x4 in this embodiment is the same as that in embodiment 2; therefore, the description of the basic structure of the MEMS resonator 500x4 in this embodiment is appropriately omitted. The MEMS resonator 500x4 in this embodiment has a metal film 509x formed on the surface of the oscillator 501x, which is the same as that in embodiment 2. Figure 8B The MEMS resonator 500x is different.

[0241] The resonant sensor in this embodiment is an infrared sensor that uses a MEMS resonator 500x4. The MEMS resonator 500x4 is of the type where the oscillator 501x ​​absorbs infrared light irradiated from the outside of the resonant sensor and the temperature of the oscillator 501x ​​changes.

[0242] Figure 16 This is a cross-sectional view of a 500x4 MEMS resonator of the electrostatic capacitive type. Figure 16 In the middle, it is shown that... Figure 8B Similarly, an example of a thermometer 508x is mounted on the mounting plate.

[0243] like Figure 16As shown, the MEMS resonator 500x4 is a torsional resonator of a beam with a triangular cross-section. The MEMS resonator 500x4 is contained in a closed space 507x formed by an oscillator 501x, electrodes 502x and 503x, a partition layer 504x, and a diaphragm 505x.

[0244] In addition, the MEMS resonator 500x4 obtains the temperature T+ΔT when the oscillator 501x ​​is irradiated with infrared light, and obtains the temperature change ΔT related to the power of the incident infrared light based on the thermometer 508x.

[0245] The pressure Pi of the enclosed space 507x remains constant. In particular, by making the pressure Pi of the enclosed space 507x a vacuum, the oscillator 501x ​​becomes capable of resonating at a high Q value without the viscous resistance of the gas. The MEMS resonator 500x is electrostatically driven, so the effect of capacitive bifurcation is easily demonstrated. Figure 29 The nonlinear resonant characteristics are shown. Infrared light shines from the outside of the enclosed space 507x through the diaphragm 505x onto the oscillator 501x. A metal film 509x is formed on the side surface of the oscillator 501x. If the material of the oscillator 501x ​​is silicon and the material of the metal film 509x is TiN, then since silicon is a dielectric, the optical properties of the TiN metal film and the oscillator 501x ​​are different. In order to satisfy the electromagnetic boundary conditions of infrared light as an electromagnetic wave at the boundary between the two, a small current is generated on the side of the metal film 509x, thereby heating the metal film 509x and causing its temperature to rise. Macroscopically, it can be regarded as the absorption of infrared light through the metal film 509x, and the oscillator 501x ​​shows a temperature change of ΔT. The conversion unit 415 calculates the temperature change ΔT based on the temperature T (ambient temperature, a representative value of the temperature of the MEMS resonator 500x4) measured by the thermometer 508x and the temperature T+ΔT of the oscillator 501x, and determines the incoming infrared power as a physical quantity based on the calculated temperature change ΔT. Furthermore, if the temperature of the object emitting infrared radiation is calculated based on the infrared power, this infrared sensor becomes the imaging element of a thermal imager.

[0246] As described below in the temperature sensor of Embodiment 1, the temperature change (ΔT) of the oscillator 501x ​​can be measured using the discontinuity frequency f of the nonlinear resonance. H f L Or f H -f L Come and get tested.

[0247] Furthermore, the material of the metal film 509x on the side of the oscillator 501x ​​can also be silicide. However, in constructing an infrared sensor, it is important to determine whether the temperature change of the oscillator 501x ​​is caused by temperature changes in the device accompanying changes in ambient temperature, etc., or by infrared radiation absorbed by the metal film 509x. For this purpose, as described in the pressure sensor of Embodiment 2... Figure 8A or Figure 8B In this way, a thermometer 508x can be included within the MEMS resonator 500x4, or the thermometer 508x can be placed on the mounting substrate on which the MEMS resonator 500x4 is mounted. In this case, the temperature indicated by the thermometer 508x is set as a representative value of the temperature of the MEMS resonator 500x4.

[0248] In the infrared sensor, as a preprocessing step to obtain the temperature characteristics of discontinuous point frequencies, the MEMS resonator 500x4 is driven in a nonlinear resonant region within a temperature-controlled thermostat to obtain the relationship between the temperature shown by thermometer 508x and the obtained discontinuous point frequencies. At this time, the infrared wavelength region that the infrared sensor should normally sense is blocked. Furthermore, measurements are taken after a sufficient period, including for the oscillator 501x, to ensure that the overall temperature of the MEMS resonator 500x4 is uniform.

[0249] Figure 17 This represents the frequency difference f between the temperature of the MEMS resonator at 500x4 and the frequencies at two discontinuous points. H -f L A diagram showing the relationships between them. Figure 17 and Figure 9 Same. Figure 17 The figure shows the effect of temperature change caused by temperature variation in MEMS resonator 500x4 indicated by thermometer 508x. H -f L The changes. Therefore, it is possible to use Figure 17 Using the curve as a reference, the temperature-dependent components of the MEMS resonator 500x4 are excluded as described below.

[0250] When using the MEMS resonator 500x4 as an infrared sensor, regardless of whether the thermometer 508x indicates a certain temperature T1 as the temperature of the MEMS resonator 500x4, if f H -f L The values ​​shown in the figure are those marked with ★, indicating that the value of the ★ mark is lower than the baseline curve. In this case, the metal film 509x absorbs infrared radiation from external illumination and the temperature of the oscillator 501x ​​rises, causing the Q value of the oscillator 501x ​​to decrease. This is considered to manifest as f in nonlinear resonance. H -f L The decrease. That is, the deviation from f. H -fL The measured value of the baseline curve, Δ (which is negative in this case), shows the infrared power irradiated onto the 501x ​​oscillator.

[0251] Furthermore, as described in the temperature sensor of Embodiment 1, in order to read the temperature change of the oscillator 501x, Figure 17 The vertical axis of the reference curve is not limited to f obtained by frequency sweeping through the triangular wave of the excitation signal. H -f L Alternatively, the f frequency obtained by sweeping the sawtooth wave upwards can be used. H Or f obtained by sweeping the frequency below the sawtooth wave. L .

[0252] Furthermore, the thermometer 508x can be of the PN diode type, thermocouple type, or thermoelectric type, but the method of temperature sensing is not limited. Alternatively, a temperature sensor using the MEMS resonator described in Embodiment 1 can be used instead of the thermometer 508x. That is, Figure 16 The MEMS resonator 500x4 functions as an infrared sensor, but adjacent MEMS resonators of the same shape can also be used as temperature sensors. However, since the purpose of using the MEMS resonator 500x4 as a temperature sensor is to obtain the temperature of the MEMS resonator 500x4, a structure is adopted in which the metal film 509x for infrared absorption is not placed on the side of the oscillator 501x, or a metal film for reflecting or absorbing infrared light is stacked on the diaphragm 505x to avoid being easily affected by the irradiated infrared light.

[0253] Furthermore, the infrared sensor in this embodiment utilizes a torsional vibration mode. Here, the advantages of using a torsional vibration mode will be explained in comparison to the commonly used flexural vibration mode.

[0254] In flexural vibration mode, during one reciprocating motion of the vibration, one of the upper and lower surfaces of the vibrating element, which is the beam, is compressed while the other is stretched. Therefore, heat repeatedly flows between the upper and lower surfaces, and a portion of this heat dissipates to the oscillator support, which serves as the support for the beam. That is, in addition to the minute heat flow generated in the oscillator through infrared irradiation, the heat flow accompanying flexural vibration is also superimposed on the oscillator, making it unsuitable for detecting minute amounts of infrared radiation. On the other hand, torsional vibration is a special type of vibration that does not involve volume changes at various points within the oscillator, and therefore does not involve the inflow of heat associated with the vibration. Therefore, the heat generated in the oscillator is limited to heat caused by the ambient temperature transmitted through the oscillator support, or heat caused by infrared irradiation. If the former can be eliminated, minute amounts of infrared radiation can be detected based on the heat generated by the oscillator.

[0255] Furthermore, compared to the resonant frequency of flexural vibration, the resonant frequency of torsional vibration is less sensitive to changes in the axial stress of the beam. While there are methods that utilize changes in the axial stress of the oscillator caused by heat generated in the oscillator due to infrared irradiation, using this as a change in the resonant frequency of flexural vibration, it is difficult to mass-produce MEMS resonators with identical axial stresses because the axial stress of the beam oscillator is highly dependent on the manufacturing process. In this respect, as in this embodiment, the MEMS resonator 500x4 using torsional vibration is insensitive to deviations in axial stress during the manufacturing process or to changes in axial stress caused by temperature variations.

[0256] Therefore, as in this embodiment, by taking the temperature change of the oscillator 501x ​​caused by infrared absorption as the Q-value change, this Q-value change can be used as the frequency difference f in the nonlinear resonance region. H -f L Testing is performed. In this embodiment, it is suitable for mass production of 500x4 MEMS resonators with uniform quality.

[0257] The following describes a modified example of an infrared sensor using a MEMS resonator 500x4. In these modifications, since the basic structure of the infrared sensor and its MEMS resonator 500x4 is the same as that of Embodiment 4, the same reference numerals will be used and descriptions will be omitted as appropriate for the infrared sensor and its MEMS resonator 500x4 in these modifications. Furthermore, while the MEMS resonator 500x4 is used in these modifications, any MEMS resonator from this embodiment may also be used.

[0258] <Variation Example 1>

[0259] Figure 18 This is a block diagram showing the structure of the infrared sensor array in Modification 1 of Embodiment 4, and an explanatory diagram of the marked electrostatic capacitive MEMS resonator 500x4. Figure 18 The image shows an infrared sensor array consisting of multiple 500x4 electrostatic capacitive MEMS resonators arranged in an array. Figure 18The electrostatic capacitive MEMS resonators 500x4 have a 2-port electrical connection. A frequency-sweeped excitation signal is applied to the electrodes 502x of all MEMS resonators 500x4. A bias DC voltage Vp is applied to each oscillator 501x ​​of the multiple MEMS resonators 500x4, exciting them in the non-linear resonance region. A multiplexer 601 changes the sequentially selected columns to obtain infrared power information from all the arrayed MEMS resonators 500x4. The displacement current (vibration state information signal) caused by the resonance of each oscillator 501x ​​is used by the multiplexer 601 to output only the output signals (Out1, Out2, etc.) from columns C1, C2, etc., selected via MOS switches connected to each electrode 503x from each electrode 503x. The output signals from each electrode 503x selected by the multiplexer 601 are input to the signal processing unit 411, from which infrared power information is output.

[0260] <Variation Example 2>

[0261] Figure 19 This is a block diagram illustrating another structure of the infrared sensor array in Modification 2 of Embodiment 4. Figure 19 In this context, the 500x4 bias DC voltage applied to the MEMS resonator has a resonant on / off function, therefore, as... Figure 19 As shown, if the multiplexer 601 is connected to the oscillator 501x ​​with the bias DC voltage function enabled, it is not necessary to set electrodes 503x on the output side of each MEMS resonator 500x4. Figure 18 The MOS switch shown simplifies the circuit structure.

[0262] Figure 20 This is a diagram showing the electrical connection method of a 500x4 electrostatic capacitive MEMS resonator.

[0263] in addition, Figure 18 , Figure 19 The connection structure of the 500x4 MEMS resonator is as follows: Figure 20 The diagram shows a 2-port structure, but the connection structure is not limited to a 2-port structure; it can also be... Figure 20 port 1 structure of b Figure 20 c Figure 20 The d-port differential output structure. Figure 20 The bias-T in the equation is a component that superimposes a DC voltage Vp onto an AC signal.

[0264] exist Figure 20In step a, a frequency-sweeped excitation signal is applied to electrode 502x of MEMS resonator 500x4, a bias DC voltage Vp is applied to oscillator 501x, and the output signal is output from electrode 503x. Figure 20 In step b, a frequency-sweeped excitation signal is applied to the oscillator 501x ​​of the MEMS resonator 500x4, and the output signal is output from the electrode 503x. Figure 20 In step c, a frequency-sweeped excitation signal is applied to the oscillator 501x ​​of the MEMS resonator 500x4. The output signal is a differential signal, consisting of a DC voltage Vp superimposed on the output signal from electrode 503x via bias-T, and the output signal from electrode 502x1. Figure 20 In d, the excitation signal after frequency sweep is applied to the oscillator 501x ​​of MEMS resonator 500x4, and the output is a differential signal between the output signal from electrode 503x with DC voltage Vp superimposed via bias-T and the output signal from electrode 502x1 with DC voltage -Vp superimposed via bias-T.

[0265] Furthermore, the device for generating the excitation signal after frequency sweep is not limited to a digital PLL synthesizer; an analog voltage-controlled oscillator (VCO) can also be used. In order to establish a correlation between the discontinuous frequency points and time information during the frequency sweep process, an oscillator that can accurately maintain a constant frequency sweep speed (df / dt) is preferred.

[0266] <Effects>

[0267] Next, the effects of the infrared sensor in this embodiment will be explained.

[0268] As described above, in the infrared sensor of this embodiment, the MEMS resonator 500x4 is a capacitive MEMS resonator. The infrared sensor also includes a thermometer 508x disposed on the MEMS resonator 500x4. The MEMS resonator 500x4 obtains its own temperature T based on the thermometer 508x, and the oscillator 501x ​​obtains the temperature T+ΔT when irradiated by infrared radiation. The conversion unit 415 calculates the temperature change ΔT based on the temperature measured by the thermometer 508x and the detected value, and determines the infrared power as a physical quantity based on the calculated temperature change ΔT.

[0269] Therefore, even if the ambient temperature surrounding the MEMS resonator 500 changes, the temperature change ΔT can be calculated based on the temperature measured by the thermometer 508x and the detected value. Thus, this infrared sensor enables more precise infrared power measurement of the MEMS resonator 500x4. Consequently, this infrared sensor is less susceptible to changes in ambient temperature.

[0270] In this embodiment, it also has the same effect as in embodiment 1.

[0271] (Implementation Method 5)

[0272] Figure 32 This is a cross-sectional view of a 500x5 electrostatic capacitive MEMS resonator.

[0273] The basic structure of the MEMS resonator 500x5 in this embodiment is similar to that in embodiments 2, 4, etc. Figure 16 The basic structure of the MEMS resonator 500x4 is the same, so the description of the basic structure of the MEMS resonator 500x5 in this embodiment is appropriately omitted. The MEMS resonator 500x5 in this embodiment differs from the MEMS resonators in Embodiment 2, etc., in that it uses infrared light. Furthermore, in the MEMS resonator 500x5 of this embodiment, as... Figure 32 As shown, it differs from the MEMS resonator in Embodiment 4, etc., in that the thermometer 508x is not installed.

[0274] The resonant sensor in this embodiment is also an infrared sensor that uses a MEMS resonator 500x4. The MEMS resonator 500x4 is of the type where the oscillator 501x ​​absorbs infrared light irradiated from the outside of the resonant sensor and the temperature change of the oscillator 501x ​​is induced.

[0275] <Summary>

[0276] For example, such as Figure 16 As shown, when the temperature around the MEMS resonator 500x4, i.e., the ambient temperature, changes, the thermometer 508x detects the change in ambient temperature. At the same time, the temperature of the mounting substrate and other components of the MEMS resonator 500x4 also changes. This temperature change of the mounting substrate is transmitted to the oscillator 501x ​​via the silicon substrate 510x between the partition layer 504x and the mounting substrate. In this case, due to the time difference between the point at which the thermometer 508x detects the temperature change and the point at which the temperature changes in the oscillator 501x, Figure 17 The f marked with ★ H -f L The value deviates from the baseline curve. Thus, if the thermometer 508x is far from the oscillator 501x ​​of the MEMS resonator 500x4, it can sometimes be difficult to distinguish whether the temperature change is caused by infrared radiation or by a simple change in ambient temperature.

[0277] <Temperature sensing unit>

[0278] Therefore, in this embodiment, in order to distinguish between temperature changes caused by infrared radiation and changes in ambient temperature, the following temperature sensing unit will be described.

[0279] Figure 33 This is a diagram showing the temperature distribution in the electrostatic capacitive MEMS resonator 500x5 and its oscillator 501x.

[0280] like Figure 33 a and Figure 33 As shown in b, in this embodiment, one end of the oscillator 501x ​​of the MEMS resonator 500x5 along the length direction is supported by one oscillator support portion 501x1, and the other end is supported by another oscillator support portion 501x1.

[0281] In this MEMS resonator 500x5, such as Figure 33 As shown in a, when the oscillator 501x ​​is not exposed to infrared radiation, the temperatures of the silicon substrate 510x, the oscillator 501x, one oscillator support portion 501x1, and the other oscillator support portion 501x1 become the same after the ambient temperature changes and a specified period has elapsed.

[0282] Furthermore, in this MEMS resonator 500x5, such as Figure 33 As shown in Figure b, when the oscillator 501x ​​is irradiated with infrared radiation, a temperature distribution is generated within the oscillator 501x. This can be considered as follows: even when the oscillator 501x ​​is irradiated with infrared radiation in the same manner, the heat generated inside the oscillator 501x ​​will be conducted within the oscillator 501x ​​and dissipated from both ends to the silicon substrate 510x, thus generating a temperature distribution. Figure 33 In b, areas with higher temperatures due to the same infrared radiation are represented by black shading. Starting from the areas with higher temperatures, the lower the temperature, the smaller the size and density of the shading points are used to represent the areas with lower temperatures.

[0283] In this embodiment, in order to distinguish Figure 33 The state of a and Figure 33 In state b, the temperatures at both ends of the oscillator 501x ​​are considered as ambient temperatures. This is because, as described above, when the ambient temperature changes, the temperature changes from both ends of the oscillator 501x ​​via the silicon substrate 510x, so the temperatures at both ends of the oscillator 501x ​​are considered as ambient temperatures. The temperatures at both ends of the oscillator 501x ​​refer to the temperatures of one end of the oscillator 501x ​​and the other end of the oscillator 501x, or the temperatures of one oscillator support portion 501x1 and the other oscillator support portion 501x1.

[0284] like Figure 33As shown in b, when the oscillator 501x ​​is irradiated with infrared light in the same manner, the temperature of the central portion of the oscillator 501x ​​is higher than the temperature of its two ends. That is, when the oscillator 501x ​​is irradiated with infrared light in the same manner, the same heat flow is generated per unit length in the longitudinal direction within the oscillator 501x. However, because heat escapes from the two ends of the oscillator 501x ​​towards the silicon substrate 510x, heat always flows from the central portion of the oscillator 501x ​​to the two ends, creating a temperature gradient. Specifically, a temperature difference is generated from the central portion of the oscillator 501x ​​to the two ends, with the temperature being highest at the center and decreasing towards the two ends. Conversely, when the infrared sensor detects an object with a lower temperature than itself, infrared light is emitted from the oscillator 501x, resulting in the lowest temperature at the center and increasing temperature towards the two ends.

[0285] Therefore, based on the above records, a distinction is made between temperature changes caused by infrared radiation and simple changes in ambient temperature.

[0286] Figure 34 f represents ambient temperature information H With frequency difference f H -f L A graph showing the relationship between δf and f. Figure 34 The horizontal axis represents ambient temperature information, and the vertical axis represents the frequency difference δf. Figure 34 The ★ indicates the frequency f of the discontinuity point. H The value of the frequency difference δf at time, Figure 34 Δ indicates the deviation from the baseline curve when the temperature of the oscillator 501x ​​is the same as the ambient temperature.

[0287] The offset Δ from the reference curve represents the intensity of the irradiated infrared radiation.

[0288] The conditions under which the oscillator 501x ​​is at the same temperature (without infrared irradiation) and under conditions where the oscillator 501x ​​is irradiated with infrared light are compared. Figure 35 The Chinese side indicated that... Figure 35 The figure shows the simulation results of the oscillator 501x ​​being kept at the same temperature and the oscillator 501x ​​being irradiated with infrared light.

[0289] like Figure 35 As shown, one end of the oscillator 501x ​​is connected to one oscillator support 501x1 and does not vibrate. Similarly, the other end of the oscillator 501x ​​is also connected to the other oscillator support 501x1 and does not vibrate. The oscillator 501x ​​vibrates except for the portion connected to the oscillator support 501x1.

[0290] exist Figure 35In diagram 'a', it represents the state where infrared radiation does not reach oscillator 501x, and the temperature distribution of oscillator 501x ​​becomes the same as that of the ambient temperature. At an ambient temperature of 24.79℃, the resonant frequency of oscillator 501x ​​is 20.66467MHz. In this case, compared to the case of oscillator 501x ​​with the same temperature distribution at an ambient temperature of 24.00℃, the spring constant of oscillator 501x ​​changes by -40.6ppm.

[0291] exist Figure 35 In step b, when the oscillator 501x ​​is irradiated with infrared light, heat flow is generated from inside the oscillator 501x, resulting in a temperature distribution. In this case, when the temperature at both ends of the oscillator 501x ​​is set to the ambient temperature of 24.00°C, the temperature rises as it approaches the center from these ends, reaching 25.58°C at the center. The spring constant of the oscillator 501x ​​at this point changes by -53.5 ppm compared to the oscillator 501x ​​with the same temperature distribution at the ambient temperature of 24.00°C.

[0292] This can be interpreted as the temperature of the oscillator 501x ​​rising due to infrared radiation, thereby making the oscillator 501x ​​more flexible. At this point, because... Figure 35 The oscillator of b, 501x ​​and Figure 35 The oscillator 501x ​​of a further decreases compared to the spring constant, thus exhibiting a tendency for larger vibration amplitude.

[0293] Next, use Figure 36 Explain the relationship between the change in resonant frequency and the average temperature of the 501x ​​oscillator. Figure 36 This is a graph showing the relationship between the change in resonant frequency and the average temperature of the oscillator (501x). Figure 36 The vertical axis represents the change in resonant frequency, and the horizontal axis represents the average temperature of the oscillator at 501x. Figure 36 The thick solid line represents the baseline for the case without thermal radiation (e.g., without infrared radiation) (an example of a temperature-related baseline value). The dotted solid line represents the case with thermal radiation at an ambient temperature of 24.0°C. The triangular solid line represents the case with thermal radiation at an ambient temperature of 24.5°C. The square-dotted solid line represents the case with thermal radiation at an ambient temperature of 25.0°C. Here, in the case of the oscillator 501x ​​with a temperature distribution, the average temperature is the average temperature of its entirety. The baseline for the case without thermal radiation is a value obtained through prior measurement.

[0294] Figure 36 Point R1 on the baseline corresponds to Figure 35As shown in Figure a, without infrared radiation, the temperature of oscillator 501x ​​is the same as the ambient temperature of 24.79°C, and the resonant frequency is 20.66467MHz. Even with the same resonant frequency of 20.66467MHz, the average temperature of oscillator 501x ​​differs by ΔT relative to point R1 on the reference line across the solid lines of the dots, triangles, and corners. For example, at a resonant frequency of 20.66467MHz, the average temperature of oscillator 501x ​​differs by ΔT between point R2 on the solid line of the dots and point R1 on the reference line. Point R2 corresponds to... Figure 35 As shown in b, the two ends of the oscillator 501x ​​are at an ambient temperature of 24.00℃, and the temperature at the center of the length of the oscillator 501x ​​rises to 25.58℃ due to infrared irradiation.

[0295] Next, use Figure 37 Explain the relationship between the spring constant and the resonant frequency. Figure 37 It is a graph showing the relationship between the spring constant and the resonant frequency. Figure 37 The vertical axis represents the spring constant, and the horizontal axis represents the change in resonant frequency. Figure 37 The thick dashed line indicates the case without thermal radiation (e.g., without infrared radiation), where the heat outflow per unit volume from the oscillator 501x ​​is 0 nW / µm. 3 The baseline is shown by the dashed line, which represents a difference of -100 nW / µm relative to the baseline. 3 -50nW / um 3 50nW / um 3 100nW / um 3 150nW / um 3 200nW / um 3 Furthermore, the dashed line above the baseline indicates a decrease in the temperature of the oscillator 501x, while the dashed line below the baseline indicates a rise in the temperature of the oscillator 501x. Additionally, the dots indicate thermal radiation at an ambient temperature of 24.0°C (e.g., infrared radiation). The triangles indicate thermal radiation at an ambient temperature of 24.5°C. The four corner dots indicate thermal radiation at an ambient temperature of 25.0°C.

[0296] exist Figure 37 For example, when observing the change in resonant frequency at -20 ppm, even at the same resonant frequency, the spring constant differs at the dot, triangle, and quadrangle points relative to point P1 on the single-dotted baseline. For instance, when the resonant frequency changes by -20 ppm, the spring constant at point P2 differs relative to point P1 on the baseline.

[0297] Therefore, even if the resonant frequencies are the same, if the spring constants of the oscillator 501x ​​differ, the frequency difference δf will become larger. That is, if a temperature distribution (temperature gradient) is known to exist within the oscillator 501x, it can be determined that infrared radiation is irradiating the oscillator 501x. Thus, it is possible to distinguish between temperature changes caused by infrared radiation and those caused by simple changes in ambient temperature. Consequently, even without additional components such as... Figure 16 The thermometer 508x shown can also detect temperature changes caused by infrared radiation. That is, infrared power information can be obtained in the MEMS resonator 500x5.

[0298] Alternatively, the bias voltage Vp between the oscillator 501x ​​and the electrode of the MEMS resonator 500x5 can be applied (the method for applying the bias voltage is described in...). Figure 20 The resonance value is increased to improve the detection sensitivity of infrared light. In this case, Figure 29 The nonlinear resonance curve shown slopes significantly to the left, thus increasing the conversion rate from the minute change in the spring constant caused by irradiation to the frequency difference δf. In this way, it is possible to obtain... Figure 37 The frequency difference f between P1 and P2 H -f L =The difference in δf is 3.7Hz.

[0299] <Effects>

[0300] Next, the effects of the infrared sensor in this embodiment will be explained.

[0301] As described above, in the infrared sensor of this embodiment, the MEMS resonator 500x5 is a capacitive MEMS resonator. Furthermore, the physical quantity determination unit (conversion unit 415) calculates the temperature change ΔT based on a temperature-related reference value (included in the reference line) and the detected value, and determines the infrared power as a physical quantity based on the calculated temperature change ΔT.

[0302] Therefore, even without an attached thermometer, it is possible to determine whether infrared radiation has reached the oscillator 501x ​​based on the temperature distribution generated within the oscillator 501x. Consequently, this infrared sensor can mitigate the increase in manufacturing costs.

[0303] Furthermore, even if the ambient temperature (around temperature) surrounding the 500x5 MEMS resonator changes, the infrared sensor is less susceptible to changes in ambient temperature because the physical quantity being processed is the temperature distribution within a very limited and tiny space like the oscillator.

[0304] (Other variations)

[0305] The present disclosure has been described above based on embodiments 1 to 5, but the present disclosure is not limited to these embodiments 1 to 5.

[0306] In the resonant sensors described in embodiments 1 to 5 above, the oscillator of the resonant sensor is not limited to the two-sided support beams. The oscillator can also be of various shapes, such as cantilever beam, disk, ring, and square. These shapes of oscillators can all be used as oscillators in the MEMS resonator of the resonant sensor. The vibration mode excited in the oscillator of the MEMS resonator by the input of the excitation signal can be any vibration mode such as flexural vibration mode or torsional vibration mode. Furthermore, the manufacturing method of the MEMS resonator is not limited to the method of using an SOI substrate.

[0307] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, the vibration state information signal is not limited to a signal originating from the displacement current flowing with the change in capacitance. Figure 21 This is a diagram showing an example of the output of a vibration state information signal (vibration velocity information signal). Figure 21 In this process, the vibration velocity of the oscillator 501 is optically detected, and the signal of the vibration velocity information of the oscillator 501 is output as vibration state information. Figure 21 In the resonant sensor, a Doppler interferometer 418 (velocity meter) is also provided to detect the vibration velocity of the oscillator 501. Information related to the detected vibration velocity is output from the Doppler interferometer 418 to the signal processing unit 411 as a vibration state information signal (vibration velocity information signal). In the resonant sensors of embodiments 1 to 5 described above, the vibration state information signal is a signal containing information related to the vibration velocity of the oscillator 501. Therefore, the resonant sensor can detect the vibration velocity of the oscillator 501. The vibration velocity is a signal whose phase is offset by 90 degrees from the vibration amplitude, but since the resonance curve represents... Figure 29 , Figure 30 With the same characteristics, it is possible to sense physical quantities at discontinuous points in vibration velocity information using frequency sweep.

[0308] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, the vibration state information signal may also be information related to the deflection of the oscillator 501. Figure 22The resonant sensor includes a laser source 419. In the resonant sensor, the laser source 419 illuminates the oscillator 501 of the MEMS resonator 500 with laser light, and the reflected laser light is received by a four-segment photodiode to detect the deflection angle of the oscillator 501. In the resonant sensor, the degree of deflection (deflection angle) of the oscillator 501 is detected using a four-segment photodiode, and the detected deflection angle information is output to the signal processing unit 411 as a vibration state information signal (deflection angle information signal). Furthermore, the number of segments of the photodiode used to detect the deflection angle of the oscillator is not limited to four; it can be three or less or five or more. In the resonant sensor, any number of photodiodes can be used as photodiodes for detecting the deflection angle of the oscillator.

[0309] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, the vibration state information signal input to the signal processing unit is not limited to the amplitude information signal of the oscillator. The vibration state information signal only needs to contain information that well reflects the characteristics of the oscillator's vibration motion (amplitude and velocity of vibration, etc.).

[0310] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, not only for the representation as... Figure 29 The resonant characteristics of 121 are due to the nonlinear phenomenon of capacitive bifurcation, which is effective for representing, as Figure 30 The resonant characteristics of 131, which are caused by the nonlinear phenomenon of mechanical bifurcation, are also valid. This is because the frequency f at the discontinuity point is... H Read as f L The frequency f at the discontinuity point L Read as f H That's it. Mechanical bifurcation is due to the nonlinearity of the oscillator's elasticity, such as... Figure 30 Similar to the resonance characteristic 131, the resonance curve slopes towards higher frequencies. The nonlinearity of the oscillator's elasticity is a phenomenon that occurs when the vibration amplitude is large. For example... Figure 27A and Figure 1B As shown in the electrostatic capacitive MEMS resonators 100 and 500, in structures where the electrodes and oscillator are arranged opposite each other in a manner that hinders vibration, the nonlinear effect caused by capacitive bifurcation is greater than the nonlinear effect caused by mechanical bifurcation. Figure 30 The nonlinearity shown is usually not easy to occur.

[0311] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, such as Figure 23 As shown, a cantilever beam 801 serving as an oscillator and an oscillator support portion 801s are formed, and the oscillator support portion 801s has a structure fixed to a base plate portion (not shown). Figure 23This is a 3D diagram showing the structure of a non-electrostatic capacitive MEMS resonator 800. Figure 23 In this design, a non-capacitive MEMS resonator 800 is used to generate mechanical bifurcation. A piezoelectric element 802 is mounted on the MEMS resonator 800 near the end of the cantilever beam 801 on the oscillator support 801s side. An excitation signal is applied to the piezoelectric element 802. As a result, the cantilever beam 801 vibrates in response to the excitation signal. Laser light irradiated from the laser source 803 and reflected by the cantilever beam 801 is received by a quad-segment photodiode 804. The quad-segment photodiode 804 detects the deflection angle of the vibrating cantilever beam 801 and outputs it as a deflection angle information signal to the signal processing unit 411. The deflection angle information signal is input to the signal processing unit 411 as a vibration state information signal. Furthermore, the number of segments in the photodiode 804 used to detect the deflection angle of the cantilever beam 801 is not limited to 4; it can be 3 or less or 5 or more. Dividing the photodiodes into any number can be used as photodiodes 804 for detecting the deflection angle of the cantilever beam 801. In a MEMS resonator 800 with such a structure, if the amplitude of the cantilever beam 801 increases, a nonlinear effect caused by mechanical bifurcation occurs. Therefore, as... Figure 30 As shown in resonance characteristic 131, the resonance characteristic bends to the right (towards the high-frequency side). In the resonant sensor of embodiments 1 to 5 described above, the MEMS resonator 800 is a non-electrostatic capacitive MEMS resonator. The two frequencies of the discontinuous change in the vibration state information signal are frequency f. H and frequency f L It is a frequency higher than the resonant frequency f0 of the oscillator. In this way, using a non-electrostatic capacitive MEMS resonator enables higher precision sensing.

[0312] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, in Figure 23 In this design, a piezoelectric element 802 is used as the element that provides strain to the oscillator 801 according to the excitation signal, but the element providing strain is not limited to the piezoelectric element 802. For example, the element providing strain can be a magnetostrictive element. Furthermore, the oscillator 801 is not limited to a cantilever beam 801, but can also be a beam supported on both sides. In this case, by inputting an alternating current to the beams supported on both sides and applying an external static magnetic field in a manner that passes through the beams, the oscillator 801 can be excited using the Lorentz force.

[0313] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, optical excitation caused by the photothermal effect can also be used. By focusing a flashing laser and irradiating the oscillator at a point, the point portion of the oscillator is heated and strained, thus exciting the oscillator.

[0314] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, the method for generating and outputting vibration state information signals is not limited to the method using a four-segment photodiode. For example, if a piezoelectric resistor or piezoelectric element formed on the oscillator is used, the strain accompanying the vibration of the oscillator can be output as a change in electrical signal.

[0315] Furthermore, the fluid pressure and pressure sensor described in Embodiment 3 above, which is a resonant sensor, is configured to detect the force that causes a change in the gap between the oscillator and the electrode. However, it is not limited to this sensor method that detects the force acting on the electrode side; it is also effective in methods that read the force by applying it to the oscillator side. It is also possible to... Figure 1A That connection Figure 1B The 500 is a capacitive MEMS resonator used to detect Coriolis force. Figure 24 This is a diagram illustrating the Coriolis force applied to the oscillator. Figure 24 In diagram 'a', the cross-section of the oscillator and electrodes is schematically shown. The oscillator inputs a frequency-sweeped excitation signal to the resonator to detect nonlinear resonance in the lateral flexural vibration mode. When a rotational angular velocity is applied along the axial direction of the oscillator, a Coriolis force acts upward on the oscillator's cross-section. Although the Coriolis force is orthogonal to the excitation direction, the displacement caused by the Coriolis force slightly reduces the inclined gap distance between the oscillator's side and the electrodes. This changes the extension of the inclination of the nonlinear resonance curve, thus allowing the Coriolis force to be detected based on the frequency of the discontinuities in the vibration state information signal. By converting the angular velocity applied to the oscillator from the Coriolis force, it functions as an angular velocity sensor. Figure 24 In b, it means with Figure 24The structure detects the applied velocity of the oscillator using the same principle as in embodiment a. The excitation signal after frequency sweep is input to the MEMS resonator to induce nonlinear resonance in the oscillator during torsional vibration. When a velocity is applied in a horizontal direction perpendicular to the oscillator's axis, a Coriolis force acts upwards on the oscillator's cross-section. Although the Coriolis force is orthogonal to the excitation direction, the displacement caused by the Coriolis force slightly narrows the inclined gap between the oscillator's side and the electrode (bringing the oscillator's side closer to the electrode). This causes a change in the extension of the inclination of the nonlinear resonance curve, allowing the Coriolis force to be detected based on the frequency of the discontinuity in the vibration state information signal. This resonant sensor functions as a velocity sensor by converting the applied velocity of the oscillator into the Coriolis force. Thus, in the resonant sensor of embodiment 3 described above, the oscillator is subjected to a rotational velocity orthogonal to the vibration direction of the vibration mode determined by the frequency sweep. The conversion unit calculates a Coriolis force orthogonal to both the vibration mode and rotational speed determined by the frequency sweep based on the detected value, and determines the rotational speed as the physical quantity based on the calculated Coriolis force. Therefore, the Coriolis force can be calculated using a capacitive MEMS resonator. Thus, by calculating the angular velocity applied to the oscillator based on the Coriolis force, the resonant sensor can be used as an angular velocity sensor. Furthermore, in the resonant sensor of Embodiment 3 described above, the oscillator is applied a velocity orthogonal to the vibration direction of the torsional vibration mode determined by the frequency sweep unit. The physical quantity determination unit calculates a Coriolis force orthogonal to both the torsional vibration mode and velocity determined by the frequency sweep based on the detected value, and determines the velocity as the physical quantity based on the calculated Coriolis force. Here, the same effect as described above is achieved.

[0316] Furthermore, in the resonant sensors described in embodiments 1 to 5 above, in Figure 2 In the process, the vibration state information signal is detected by the detector 413 in the signal processing unit 411, but synchronous detection can also be performed to extract the amplitude information. Figure 25 In the resonant sensor, a signal with the same frequency and phase as the excitation signal is sent from the frequency sweep unit 401 to the detector 413 as a reference signal for synchronous detection. Figure 25 This is a block diagram showing the structure of a capacitor-type MEMS resonator 500 using synchronous detection. Furthermore, with synchronous detection, not only the amplitude of the vibration state information signal can be extracted, but also the phase information (the phase shift relative to a reference signal) can be extracted. Figure 26 This is a graph representing the amplitude, phase, and discontinuities of the oscillator obtained through synchronous detection. Figure 26 In the middle, it represents the amplitude and phase information obtained through phase detection. Figure 26Point A is the discontinuity obtained by sweeping the frequency above the current frequency, at which frequency f is... H Point B is a discontinuity obtained by sweeping the frequency downwards; the frequency at this point is f. L In phase information, due to the frequency f L and f H The lower phase signal also changes abruptly and discontinuously, therefore a threshold can be set for phase information to detect f. L and f H .

[0317] Industrial applicability

[0318] The resonant sensors using the MEMS resonators disclosed herein can be used in temperature sensors, gas concentration sensors, fluid pressure sensors, pressure sensors, infrared sensors, velocity sensors, and angular acceleration sensors, etc.

[0319] Explanation of reference numerals in the attached figures

[0320] 400, 400a temperature sensors

[0321] 401 Sweep Frequency Section

[0322] 402 PLL Synthesizer

[0323] 411 Signal Processing Department

[0324] 412 Discontinuity Detection Unit

[0325] 413 Detector

[0326] 414 Threshold Detection Unit

[0327] 415 Conversion Section

[0328] 416 Controller (Measurement Range Switching Control Unit)

[0329] 500, 500x, 500x3, 500x4, 500x5 electrostatic capacitive MEMS resonators

[0330] 501, 501x ​​oscillators

[0331] Electrodes 502, 503, 502x, 503x

[0332] 505x Diaphragm (Transfer Section)

[0333] 506x column (transmission section)

[0334] 508x Thermometer

[0335] 800 Non-electrostatic Capacitive MEMS Resonator

[0336] 801 Oscillator (Cantilever Beam)

Claims

1. A resonant sensor using a microelectromechanical system (MEMS) resonator, wherein, have: MEMS resonators; The frequency sweeping section sweeps the frequency of the excitation signal of the oscillator of the MEMS resonator along a predetermined frequency sweeping direction, and outputs the frequency-sweeped excitation signal to the MEMS resonator. The detection unit obtains a characteristic quantity representing the vibration state of the oscillator, i.e., a vibration state information signal, based on the excitation signal from the MEMS resonator, and detects the frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously as a detection value. as well as The physical quantity determination unit determines the physical quantities acting on the MEMS resonator based on the detected values. The detection unit uses the difference between at least two frequencies of the excitation signal as the detection value. The at least two frequencies of the excitation signal include the frequencies at which the vibration state information signal changes discontinuously during the frequency sweep and the frequencies at which the vibration state information signal changes discontinuously during the frequency sweep in the opposite direction of the frequency sweep.

2. The resonant sensor according to claim 1, wherein, The frequency sweeping unit repeatedly switches the frequency sweep in the opposite direction starting from the detection of discontinuous changes in the vibration state information signal during the frequency sweep, and then switches the frequency sweep in the opposite direction again starting from the detection of discontinuous changes in the vibration state information signal to return. The detection unit outputs a pulse signal with two values ​​representing the positive and negative states in the frequency sweep direction as the detection value. The physical quantity determination unit determines the physical quantity acting on the MEMS resonator based on the output detection value, i.e., the pulse time width of the pulse signal.

3. The resonant sensor according to claim 2, wherein, The MEMS resonator is a capacitive MEMS resonator. The two frequencies at which the vibration state information signal changes discontinuously, namely the first frequency and the second frequency, are frequencies lower than the resonant frequency of the oscillator.

4. The resonant sensor according to claim 3, wherein, The electrostatic capacitive type MEMS resonator includes an oscillator, electrodes arranged with a gap separated from the oscillator, and a transmission part that changes the size of the gap according to the magnitude of the pressure acting on the electrostatic capacitive type MEMS resonator. The physical quantity determination unit determines the pressure as the physical quantity based on the size of the gap.

5. The resonant sensor according to any one of claims 1 to 3, wherein, The MEMS resonator is a capacitive MEMS resonator. It also includes a thermometer installed in the MEMS resonator. The MEMS resonator obtains its own temperature T based on the thermometer. The oscillator obtains the temperature T+ΔT when it is irradiated with infrared light. The physical quantity determination unit calculates the temperature change ΔT based on the temperature measured by the thermometer and the detection value, and determines the infrared power as the physical quantity based on the calculated temperature change ΔT.

6. The resonant sensor according to any one of claims 1 to 3, wherein, The MEMS resonator is a capacitive MEMS resonator. The physical quantity determination unit calculates the temperature change ΔT based on a temperature-related reference value and the detected value, and determines the infrared power as the physical quantity based on the calculated temperature change ΔT.

7. The resonant sensor according to any one of claims 1 to 3, wherein, The oscillator is subjected to a rotational speed orthogonal to the vibration direction of the vibration mode determined by the frequency sweep performed by the frequency sweep section. The physical quantity determination unit calculates the Coriolis force, which is orthogonal to the vibration mode and rotational speed determined by the frequency sweep, based on the detected value, and determines the rotational speed as the physical quantity based on the calculated Coriolis force.

8. The resonant sensor according to any one of claims 1 to 3, wherein, The oscillator is subjected to a velocity orthogonal to the vibration direction of the torsional vibration mode determined by the frequency sweep performed by the frequency sweep section. The physical quantity determination unit calculates the Coriolis force, which is orthogonal to the torsional vibration mode and velocity determined by the frequency sweep, based on the detected value, and determines the velocity as the physical quantity based on the calculated Coriolis force.

9. The resonant sensor according to any one of claims 1 to 3, wherein, The vibration state information signal is a signal that contains information related to the vibration amplitude of the oscillator.

10. The resonant sensor according to any one of claims 1 to 3, wherein, The vibration state information signal is a signal that contains information related to the vibration velocity of the oscillator.

11. The resonant sensor according to claim 2, wherein, The MEMS resonator is a non-electrostatic capacitive MEMS resonator. The two frequencies at which the vibration state information signal changes discontinuously, namely the first frequency and the second frequency, are frequencies higher than the resonant frequency of the oscillator.

12. The resonant sensor according to any one of claims 1 to 3, wherein, The device includes a measurement range switching control unit, which increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that there is no frequency in the sweep frequency range of the excitation signal where the vibration state information signal changes discontinuously.

13. The resonant sensor according to any one of claims 1 to 3, wherein, The device has a measurement range switching control unit, which increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that the difference between two frequencies in which the vibration state information signal changes discontinuously is less than a predetermined value.

14. The resonant sensor according to any one of claims 1 to 3, wherein, The oscillator is surrounded by a gas in the space where it is arranged, with the pressure gradually equal to that acting on the MEMS resonator. The physical quantity determination unit determines the pressure of the gas, which is the physical quantity, based on the detected value.

15. A detection method for a resonant sensor, wherein the resonant sensor uses a microelectromechanical system (MEMS) resonator, wherein, The detection method of the resonant sensor includes: The frequency of the excitation signal of the oscillator of the MEMS resonator is swept along a specified sweep direction, and the frequency-sweeped excitation signal is output to the MEMS resonator. The vibration state information signal, representing the vibration state of the oscillator, is obtained from the MEMS resonator based on the excitation signal. The frequency of the excitation signal or the time corresponding to the frequency when the obtained vibration state information signal changes discontinuously is detected as a detection value. The physical quantities acting on the MEMS resonator are determined based on the detected values. In the detection method, the difference between at least two frequencies of the excitation signal is used as the detection value. The at least two frequencies of the excitation signal include the frequencies at which the vibration state information signal changes discontinuously during the frequency sweep and the frequencies at which the vibration state information signal changes discontinuously during the frequency sweep in the opposite direction of the frequency sweep.

16. The detection method of the resonant sensor according to claim 15, wherein, The oscillator is surrounded by a gas in the space in which it is configured, the pressure of which is gradually equal to the pressure acting on the MEMS resonator, and the pressure of the gas, which is the physical quantity, is determined based on the detected value.

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