Resonant sensor using MEMS resonator and detection method thereof

Abstract

A temperature sensor (400) uses a Micro-Electro Mechanical Systems (MEMS) resonator (500). The temperature sensor (400) comprises: a MEMS resonator (500); a sweep unit (401) for sweeping the frequency of an excitation signal of an oscillator (501) of the MEMS resonator (500) along a predetermined sweep direction, and outputting the swept excitation signal to the MEMS resonator (500); a discontinuous point detection unit (412) for acquiring, from the MEMS resonator (500), a vibrational state information signal that is a feature quantity representing a vibrational state of the oscillator (501) based on the excitation signal, and detecting the frequency of the excitation signal when the acquired vibrational state information signal changes discontinuously, or a time corresponding to the frequency; and a conversion unit (415) for determining, on the basis of the detected detection value, a physical quantity acting on the MEMS resonator (500).

Description

[Technical field]

[0001] The present disclosure relates to a resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator and detection signal processing of a detection method for the resonant sensor. [Background technology]

[0002] Conventionally, mechanical resonators using a micromechanical vibrator (micromechanical resonators or MEMS resonators) have been known (Patent Documents 1 to 3).

[0003] 27A and 27B are diagrams showing a configuration example of a conventional MEMS resonator 100. This MEMS resonator 100 is a so-called capacitive MEMS resonator. FIG. 27A is a perspective view of the MEMS resonator 100, and FIG. 27B is a side cross-sectional view of the MEMS resonator 100 taken along line segment A-A' in FIG. 27A. Note that in FIG. 27B, a BOX (Buried Oxide) layer 104 and a silicon substrate 105 are omitted, and a voltage Vi input to the MEMS resonator 100, a current Io output therefrom, a bias voltage Vp applied to the oscillator 101, a direction of oscillation of the oscillator 101, and the like are also shown.

[0004] The MEMS resonator 100 can be fabricated using an SOI (Silicon On Insulator) substrate. In this case, a beam-type vibrator 101, an input electrode 102, and an output electrode 103 are formed from the topmost Si layer of the SOI substrate. A BOX (Buried Oxide) layer 104 below the vibrator 101 is removed by etching, and the vibrator 101 is held in a vibratory manner by a vibrator support portion 101s on the remaining BOX layer 104. The vibrator 101, together with the input electrode 102 and the output electrode 103, is tethered to a silicon substrate 105 by the remaining BOX layer 104.

[0005] The vibration mechanism of the vibrator 101 will be described with reference to FIG. 27B. The vibrator 101 is disposed so as to face the input electrode 102 and the output electrode 103 with gaps gi and go therebetween, respectively, and a bias voltage Vp is applied so that a DC potential difference is given to 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 vibrator 101 and the input electrode 102 fluctuates according to the AC input voltage Vi, and an excitation force derived from electrostatic force acts on the vibrator 101. When the frequency of the AC input voltage Vi coincides with the mechanical resonance frequency of the vibrator 101, the vibrator 101 vibrates (resonates) particularly largely along the vibration direction 106. At that time, a displacement current Io flows from a capacitance Co formed by the gap go to the output electrode 103.

[0006] Applications of the MEMS resonator 100 include a filter circuit utilizing the fact that the electrical transmission characteristics between the input and output electrodes are improved only at a specific frequency, i.e., near the resonant frequency of the resonator; a temperature sensor utilizing the fact that the resonant frequency of the resonator shifts with temperature; a pressure sensor utilizing the fact that the resonant frequency of the resonator shifts with stress applied to the resonator; and a mass sensor utilizing the fact that the resonant frequency of the resonator shifts with a trace amount of adhesion to the resonator.

[0007] Non-Patent Document 1 suggests the feasibility of a pressure sensor using a MEMS resonator. According to the document, the vibration motion (e.g., resonant motion) of the oscillator of the MEMS resonator changes its characteristics (e.g., the magnitude of the amplitude and Q value of the vibration motion) depending on the pressure of the atmosphere around the oscillator. Specifically, the kinetic energy or momentum of the oscillator of the MEMS resonator that resonates is dissipated due to the viscosity of the atmosphere surrounding the oscillator, and the degree of dissipation differs depending on the pressure of the atmosphere. Therefore, the amplitude of the oscillator resonating at the resonant frequency changes depending on the pressure of the atmosphere. Therefore, the amplitude of the oscillator of the MEMS resonator that vibrates near the resonant frequency and the Q value thereof correspond well to the pressure of the atmosphere. Therefore, it is possible to measure the pressure of the atmosphere by detecting the amplitude or Q value of the oscillator of the MEMS resonator that resonates in the atmosphere. For example, FIG. 4 of Non-Patent Document 1 shows the correspondence between the Q value of the MEMS resonator and the pressure of the atmosphere.

[0008] Also, Non-Patent Document 2 discusses the nonlinear behavior of the MEMS resonator that appears when the vibrator of the MEMS resonator vibrates with a relatively large amplitude. In general, when the vibration amplitude of the vibrator 101 of the MEMS resonator 100 is sufficiently small, the influence of the nonlinear effect is small enough to be ignored (linear region), and the resonance characteristic obtained by sweeping the frequency of the input voltage Vi draws a symmetrical profile centered on the peak at the resonance frequency f0 of the vibrator 101, as shown in resonance characteristic 111 in FIG. 28, and no hysteresis due to differences in the sweep direction is observed. However, when the Q value of the vibrator increases and the vibration amplitude becomes larger than a certain level (enters the nonlinear region), nonlinearity appears prominently in the resonance characteristics (for example, resonance characteristics 121 and 131) as shown in FIG. 29 and FIG. 30. For example, when the oscillator 101 of the capacitive MEMS resonator 100 vibrates in the nonlinear region, the resonance characteristics have hysteresis (123 and 125) depending on the difference in the frequency sweep direction, and the vibration amplitude no longer shows a clear peak at the resonance frequency f0.

[0009] According to Non-Patent Document 2, such a non-linear phenomenon occurs due to two types of non-linear effects. The first non-linear effect is an effect (capacitive bifurcation) in which the input electrode 102 and the output electrode 103 excessively attract the vibrator 101 when the vibration amplitude of the vibrator 101 is large, and the second non-linear effect is an effect (mechanical bifurcation) caused by an increase in the stiffness of the vibrator 101 as the vibration amplitude of the vibrator 101 increases. These two types of non-linear effects may occur either alone or simultaneously depending on the structure of the MEMS resonator 100.

[0010] 29 shows an example of the resonance characteristic 121 of the MEMS resonator 100 when capacitive bifurcation is prominent. In this case, the resonance characteristic curves to the left (toward the low frequency side), and exhibits hysteresis (arrows 123 and 125) due to the difference in the frequency sweep direction, and the peak of the vibration amplitude shifts to the low frequency side from the resonance frequency f0.

[0011] 30 shows an example of the resonance characteristic 131 of the MEMS resonator 100 when mechanical bifurcation is evident. In this case, the resonance characteristic curves to the right (toward higher frequencies), and exhibits hysteresis (arrows 133 and 135) due to differences in the frequency sweep direction, with the peak of the vibration amplitude shifting to the higher frequency side than the resonance frequency f0. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2006 / 075717 [Patent Document 2] Japanese Patent Application Publication No. 2-269928 [Patent Document 3] Patent No. 5367925 [Non-patent literature]

[0013] [Non-Patent Document 1] O. Paul, O. Brand, R. Lenggenhager, and H. Baltes, Vacuum gauging with complementary metal-oxide-semiconductor microsensors, J.Vac.Sci.Technol.A, American Vacuum Society, May / June 1995, 13(3), p.503-508. [Non-Patent Document 2] N. Agarwal, K.Park, R. Candler, M. Hopcroft, C. Jha, R. Melamud, B. Kim, B. Murmann, and T.W. Kenny, Non-Linearity Cancellation in MEMS Resonators for Improved Power-Handling, Electron DeVices Meeting 2005 IEDM Technical Digest, IEEE International, p.286-289 Summary of the Invention [Problem to be solved by the invention]

[0014] For example, in a MEMS resonator 100 (capacitive MEMS resonator) as shown in Fig. 27A and Fig. 27B, in which an electrostatic force that changes according to an AC input voltage Vi acts on the vibrator 101 to excite the vibrator 101, generally, when the vibration amplitude of the vibrator 101 becomes 1 / 3 or more of the gaps go and gi, nonlinearity due to the effect of capacitive bifurcation becomes prominent. In the vibration motion of the vibrator 101 of the so-called capacitive MEMS resonator, nonlinearity becomes prominent when the vibration amplitude exceeds about 1 / 3 of the gaps go and gi, and the resonance characteristic becomes a resonant characteristic 121 that is asymmetrical in the left-right direction and has hysteresis in the sweep direction as shown in Fig. 29. Since a larger vibration amplitude can be obtained compared to the vibration amplitude in the linear region of Fig. 28, the S / N ratio of the electrical signal generated by the vibration is improved.

[0015] However, on the other hand, the vibration amplitude of the oscillator 101 in the vicinity of the resonance frequency f0 does not show a clear peak, and in a sensor that uses the principle of linking the oscillation frequency with the sensing amount by self-oscillating in the vicinity of the resonance frequency, the oscillation frequency is easily influenced by noise, and phase noise related to the quality of the oscillation frequency becomes a problem. In addition, in a sensor that uses the principle of applying an excitation signal of a fixed frequency close to or equal to the resonance frequency f0, as shown in FIG. 31, even if the Q value increases from Q1 to Q2, the resonance waveform only extends its leftward slope, and the change in the vibration amplitude at the fixed frequency is small, making it difficult to detect the change in the Q value. Therefore, in a conventional pressure sensor that applies an AC input voltage of a predetermined frequency (for example, a frequency in the vicinity of the resonance frequency f0) to the MEMS resonator 100 and measures the pressure of the atmosphere based on the output from the MEMS resonator 100, it is extremely difficult to measure pressure under an atmospheric pressure where the oscillator 101 of the MEMS resonator 100 vibrates in a nonlinear region. Therefore, in conventional pressure sensors, the range of measurable pressures is limited to the range in which the oscillator 101 oscillates in the linear region, for example, the range in which the oscillation 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, the oscillation amplitude of the oscillator 101 is smaller than in the nonlinear region, and the associated output signal of the MEMS resonator 100 is small, requiring a high-gain signal amplifier that consumes a large amount of power.

[0016] Therefore, when the vibration amplitude of the vibrator exceeds 1 / 3 of the size of the gaps go and gi, a sensor has been proposed in which the vibrator of the MEMS resonator operates in a nonlinear region.

[0017] Patent Document 2 discloses a vacuum gauge comprising a self-oscillating circuit that causes an oscillator to self-oscillate at the oscillator's natural frequency in a nonlinear oscillation region, a counter that counts the oscillator's natural frequency, and a calculation circuit that calculates and detects the degree of vacuum from the deviation of the measured natural frequency from the natural frequency in the linear region. Patent Document 2 does not mention the problem of phase noise, but since it oscillates with a large amplitude in the nonlinear region, it configures a vacuum gauge with improved S / N. However, Patent Document 2 does not disclose a measure against the "resonant frequency shift due to temperature change," which is an important problem in MEMS resonators. The vacuum gauge of Patent Document 2 is based on the principle that the Q value changes according to the degree of vacuum, the oscillation point (the point that satisfies the oscillation condition) on the nonlinear resonance waveform moves, and the shift in the oscillation frequency that occurs accordingly is detected. However, in this vacuum gauge, when the temperature of the silicon oscillator changes with the environmental temperature regardless of the degree of vacuum, the resonant frequency also changes, i.e., the oscillation frequency also changes according to the temperature characteristics of the elastic modulus of silicon. If the temperature characteristics of this resonant frequency are not taken into consideration, an erroneous degree of vacuum may be calculated. In the case of silicon, TCf (temperature coefficient of resonant frequency) is approximately -20 to -30 ppm / ℃. In other words, this vacuum gauge must have a table that describes the relationship between the temperature indicated by the thermometer, the oscillation frequency, and the degree of vacuum.

[0018] The MEMS resonator sensor of Patent Document 3 uses resonance in the nonlinear region, similar to Patent Document 2. However, in this MEMS resonator sensor, self-oscillation is not allowed, and 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.

[0019] However, conventionally, there are cases where highly accurate sensing cannot be achieved using MEMS resonators.

[0020] Therefore, an object of the present disclosure is to provide a resonant sensor capable of performing highly accurate sensing using a MEMS resonator and a detection method for the resonant sensor. [Means for solving the problem]

[0021] In order to achieve the above object, a resonant sensor according to one embodiment of the present disclosure is a resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator, and includes: a MEMS resonator; a sweep unit that sweeps a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction and outputs the swept excitation signal to the MEMS resonator; a detection unit that acquires a vibration state information signal from the MEMS resonator, the vibration state information signal being a feature quantity representing a vibration state of the oscillator based on the excitation signal, and detects the frequency of the excitation signal or a time corresponding to the frequency when the acquired vibration state information signal discontinuously changes; and a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected detection value. The detection unit detects as a detection value the difference between at least two frequencies of the excitation signal including a frequency at which the vibration state information signal changes discontinuously in the sweep and a frequency at which the vibration state information signal changes discontinuously in a sweep in the opposite direction to the sweep direction. In order to achieve the above-mentioned object, a resonant sensor according to one embodiment of the present disclosure is a resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator, and includes: a MEMS resonator; a sweeping unit that sweeps the frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweeping direction and outputs the swept excitation signal to the MEMS resonator; a detection unit that acquires a vibration state information signal from the MEMS resonator, which is a feature representing the vibration state of the oscillator based on the excitation signal, and detects the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously; and a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected detection value, wherein the oscillator is surrounded by a gas in a space in which the oscillator is disposed, the pressure of the gas as the physical quantity being determined based on the detection value.

[0022] In addition, these comprehensive or specific aspects may be realized in an unmanned aerial vehicle, a storage device, one or more thruster devices, a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or in any combination thereof. Effect of the Invention

[0023] According to the present disclosure, highly accurate sensing can be performed using a MEMS resonator. [Brief description of the drawings]

[0024] [Figure 1A] FIG. 1A is a schematic diagram of a temperature sensor having a MEMS resonator. [Figure 1B] FIG. 1B is a perspective view of a MEMS resonator using a doubly supported beam silicon vibrator with triangular cross section. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a temperature sensor using a MEMS resonator. [Figure 3A] FIG. 3A is a timing diagram illustrating the operation of a capacitive MEMS resonator as the excitation signal is sweeping upward in frequency. [Figure 3B]FIG. 3B is a diagram showing the relationship between temperature and discontinuous point frequency fH. [Figure 3C] FIG. 3C is a diagram showing the relationship between temperature and detected signal strength at a discontinuous point. [Figure 4A] FIG. 4A is a timing diagram illustrating the operation of a capacitive MEMS resonator as an excitation signal is sweeping downward in frequency. [Figure 4B] FIG. 4B is a diagram showing the relationship between temperature and discontinuous point frequency fL. [Figure 4C] FIG. 4C is a diagram showing the relationship between temperature and peak value of detected signal strength. [Figure 5A] FIG. 5A is a timing diagram showing the operation of a capacitive MEMS resonator in response to a frequency sweep of a triangular wave excitation signal. [Figure 5B] FIG. 5B is a diagram showing the relationship between temperature and the difference frequency fH-fL between the two discontinuous frequencies. [Figure 6] FIG. 6 is a timing diagram showing the operation of the capacitive MEMS resonator when the frequency sweep direction is switched at the timing of detecting a discontinuity. [Figure 7] FIG. 7 is a cross-sectional view of a capacitive MEMS resonator. [Figure 8A] FIG. 8A is a cross-sectional view of a capacitive MEMS resonator with a thermometer disposed on the same chip. [Figure 8B] FIG. 8B is a cross-sectional view of a capacitive MEMS resonator in which a thermometer is mounted on the same mounting substrate. [Figure 9] FIG. 9 is a diagram showing the relationship between the temperature of the MEMS resonator and the difference frequency fH-fL between the two discontinuous point frequencies. [Figure 10A] FIG. 10A is a diagram showing a change in hydrogen gas concentration and a change over time in the difference frequency fH-fL (when the temperature sensor is a thermocouple). [Figure 10B] FIG. 10B is a diagram showing the change in hydrogen gas concentration and the change over time in the difference frequency fH-fL (when the discontinuous point frequency fH is used as temperature information). [Figure 11]FIG. 11 is a diagram showing the relationship between the discontinuous frequency fH and the difference frequency fH-fL when the discontinuous frequency fH is used as temperature information. [Figure 12] FIG. 12 is a block diagram showing the configuration of a pressure sensor using a MEMS resonator having a measurement range switching function. [Figure 13] FIG. 13 is a diagram showing the relationship between the excitation signal intensity Vi and the difference frequency fH-fL. [Figure 14] FIG. 14 is a cross-sectional view of a capacitive MEMS resonator. [Figure 15] FIG. 15 is a diagram showing the change in the differential frequency fH-fL when the gap is changed by the pressing force and the fluid pressure. [Figure 16] FIG. 16 is a cross-sectional view of a capacitive MEMS resonator. [Figure 17] FIG. 17 is a diagram showing the relationship between the temperature of the MEMS resonator and the difference frequency fH-fL between the two discontinuous frequencies. [Figure 18] FIG. 18 is a block diagram showing a configuration of an infrared sensor array in a first modification of the fourth embodiment, and an explanatory diagram of a symbolized capacitive MEMS resonator. [Figure 19] FIG. 19 is a block diagram showing another configuration of the infrared sensor array in the second modification of the fourth embodiment. In FIG. [Figure 20] FIG. 20 is a diagram showing an electrical connection method for a capacitive MEMS resonator. [Figure 21] FIG. 21 is a diagram showing an output example of a vibration state information signal (vibration velocity information signal). [Figure 22] FIG. 22 is a diagram showing an example of an output of a vibration state information signal (deflection angle information signal). [Diagram 23] FIG. 23 is a perspective view showing the configuration of a non-capacitive MEMS resonator. [Figure 24] FIG. 24 is an explanatory diagram of the Coriolis force acting on the oscillator. [Diagram 25] FIG. 25 is a block diagram showing a configuration of a capacitive MEMS resonator using synchronous detection. [Figure 26]FIG. 26 is a diagram showing amplitude information, phase information, and discontinuous points of a transducer obtained by synchronous detection. [Figure 27A] FIG. 27A is a perspective view showing the configuration of a capacitive MEMS resonator. [Figure 27B] FIG. 27B is a cross-sectional view of a capacitive MEMS resonator. [Figure 28] FIG. 28 is a graph showing resonance characteristics in the linear region. [Figure 29] FIG. 29 is a diagram showing resonance characteristics and hysteresis that appear in the nonlinear region. [Diagram 30] FIG. 30 is a diagram showing resonance characteristics and hysteresis that appear in the nonlinear region. [Diagram 31] FIG. 31 is a diagram showing resonance characteristics in a nonlinear region when the Q value is different. [Diagram 32] FIG. 32 is a cross-sectional view of a capacitive MEMS resonator. [Diagram 33] FIG. 33 is a diagram showing a capacitive MEMS resonator and a temperature distribution in the vibrator. [Diagram 34] FIG. 34 is a diagram showing the relationship between the environmental temperature information and the differential frequency. [Diagram 35] FIG. 35 is a diagram showing a case where the temperature of the vibrator is made uniform and a case where the vibrator is irradiated with infrared rays. [Diagram 36] FIG. 36 is a diagram showing the relationship between the change in resonance frequency and the average temperature of the vibrator. [Figure 37] FIG. 37 is a diagram showing the relationship between the spring constant and the change in resonance frequency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] A resonant sensor according to one embodiment of the present disclosure is a resonant sensor using a MEMS resonator, and includes: a MEMS resonator; a sweeping unit that sweeps the frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweeping direction and outputs the swept excitation signal to the MEMS resonator; a detection unit that acquires a vibration state information signal from the MEMS resonator, the vibration state information signal being a feature representing a vibration state of the oscillator based on the excitation signal, and detects the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously; and a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected detection value.

[0026] The resonant sensor can determine physical quantities such as pressure and force acting on the MEMS resonator based on the sweep frequency when the vibration state information signal changes discontinuously. Therefore, it is possible to project sensing information on the time axis, such as the time difference between the start time of the frequency sweep and the time when a discontinuity occurs, and the time difference between each time when multiple discontinuities occur. The discontinuity of the vibration state information signal can be detected by setting a threshold value or the like, as a sudden change in signal strength. Therefore, even if noise is superimposed on the signal strength, the time showing the discontinuity can be reliably detected against the superimposed noise. For example, this is considered to be the same effect as that of the sound quality of FM radio broadcasts received and demodulated being superior to that of AM radio broadcasts. In addition, the pulse-shaped detection signal also has the secondary effect of being highly compatible with digital signal processing.

[0027] Therefore, in this resonant sensor, highly accurate sensing can be performed using the MEMS resonator.

[0028] In particular, by using resonance in the nonlinear region, it is possible to excite a large amplitude that cannot be obtained by linear resonance, improving the S / N ratio of the detection value of the sensing amount. Furthermore, by sweeping the frequency, the degree of collapse of the nonlinear resonance waveform can be obtained from the time axis. This makes it robust against noise superimposed on the signal intensity, and makes it possible to detect even more minute changes in the resonance state by extracting it as a PWM (Pulse Width Modulation) signal, for example, projecting the detection value onto the time axis, rather than the intensity of the detection value. If it is a PWM signal, it becomes easier to handle it as a digital signal for transmission and signal processing.

[0029] In addition, in a detection method of a resonant sensor according to another aspect of the present disclosure, the detection method of a resonant sensor using a MEMS resonator includes sweeping a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction, outputting the swept excitation signal to the MEMS resonator, acquiring from the MEMS resonator a vibration state information signal which is a feature representing a vibration state of the oscillator based on the excitation signal, detecting the frequency of the excitation signal when the acquired vibration state information signal changes discontinuously, and determining a physical quantity acting on the MEMS resonator based on the detected detection value.

[0030] This method also provides the same effects as those described above.

[0031] In addition, in a resonant sensor according to another aspect of the present disclosure, the detection unit detects as a detection value the difference between at least two frequencies of the excitation signal, including a frequency at which the vibration state information signal changes discontinuously in the sweep and a frequency at which the vibration state information signal changes discontinuously in a sweep in a direction opposite to the sweep direction.

[0032] According to this, even if there is an error in each of at least two frequencies of the excitation signal, the effect of the error can be suppressed by calculating the difference between the two frequencies. In other words, since the physical quantity is determined as the detection value of the differential frequency, which is the difference between the two frequencies, the effect of the resonance frequency shift caused by the fluctuation of the environmental temperature is reduced. Therefore, this resonance type sensor can perform more accurate sensing with the MEMS resonator.

[0033] In particular, since it is no longer necessary to create a temperature characteristic table of the resonance frequency shift or to perform correction using the temperature characteristic table, the cost of the resonance type sensor is prevented from rising sharply.

[0034] In addition, in a resonant sensor according to another aspect of the present disclosure, the sweep unit switches the sweep in the reverse direction upon detection of a discontinuous change in the vibration state information signal in the sweep, and then repeats the operation of switching the sweep in the reverse direction again upon detection of a discontinuous change in the vibration state information signal, and the detection unit outputs a pulse signal having two values ​​representing two states, forward and reverse, in the sweep direction as a detection value, and the physical quantity determination unit determines the physical quantity acting on the MEMS resonator based on the pulse time width of the pulse signal, which is the output detection value.

[0035] This makes it possible to determine the physical quantity based on the pulse time width of the binary pulse signal that represents the forward and reverse sweep directions, and therefore to sense changes over time.In addition, it is possible to eliminate the sweep time for frequencies lower than the discontinuity frequency and higher than the discontinuity frequency, which increases the amount of measurement data per unit time, i.e., enables faster measurement.

[0036] In addition, in a resonant sensor according to another aspect of the present disclosure, the MEMS resonator is a capacitive MEMS resonator, and the first frequency and the second frequency, which are the two discontinuously changing frequencies of the vibration state information signal, are lower than the resonant frequency of the vibrator.

[0037] According to this, by using a general-purpose MEMS resonator, highly accurate sensing can be performed with the MEMS resonator, making the resonant sensor easy to use.

[0038] In addition, in a resonant sensor according to another aspect of the present disclosure, the oscillator is surrounded by a gas in a space in which the oscillator is disposed, the gas having a pressure that gradually becomes equal to the pressure acting on the MEMS resonator, and the physical quantity determination unit determines the gas pressure as the physical quantity based on the detection value.

[0039] According to this, when pressure is applied to the MEMS resonator, the oscillator vibrates at a predetermined vibration amplitude and speed depending on the atmospheric pressure. Therefore, this resonance type sensor can perform more accurate pressure measurement with the MEMS resonator.

[0040] In addition, in a resonant sensor according to another aspect of the present disclosure, the capacitive MEMS resonator includes an oscillator, an electrode arranged across a gap from the oscillator, and a transmission unit that changes the size of the gap in accordance with the magnitude of pressure acting on the capacitive MEMS resonator, and the physical quantity determination unit determines the physical quantity, that is, pressure, based on the size of the gap.

[0041] According to this, when pressure is applied to the MEMS resonator, the transmission unit can change the size of the gap in response to changes in atmospheric pressure. By changing the size of the gap, the gap between the electrode and the vibrator becomes narrower or wider, so the degree of nonlinearity of the vibrator's resonant vibration can be changed. Therefore, this resonant sensor can perform more accurate pressure measurement with the MEMS resonator.

[0042] In addition, in a resonant sensor according to another aspect of the present disclosure, the MEMS resonator is a capacitive MEMS resonator, and further includes a thermometer provided on the MEMS resonator, the MEMS resonator acquires its own temperature T based on the thermometer, the oscillator acquires a temperature T+ΔT when irradiated with infrared light, and the physical quantity determination unit calculates a temperature change ΔT based on the temperature measured by the thermometer and the detection value, and determines infrared power as the physical quantity based on the calculated temperature change ΔT.

[0043] According to this, even if the environmental temperature (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. Therefore, with this resonant sensor, the MEMS resonator can perform more accurate infrared power measurement. As a result, this infrared sensor is less susceptible to the effects of fluctuations in the environmental temperature.

[0044] In addition, in a resonant sensor according to another aspect of the present disclosure, a rotational speed perpendicular to the vibration direction of the vibration mode swept by the sweeping unit is applied to the oscillator, and the physical quantity determination unit determines a Coriolis force perpendicular to both the vibration mode swept by the sweeping unit and the rotational speed based on the detection value, and determines the rotational speed as the physical quantity based on the determined Coriolis force.

[0045] According to this, the Coriolis force can be obtained using a capacitance type resonance sensor, and the resonance sensor can be used as an angular velocity sensor by converting the Coriolis force into the angular velocity applied to the oscillator.

[0046] In a resonant sensor according to another aspect of the present disclosure, a velocity perpendicular to the vibration direction of the torsional vibration mode caused by the sweep by the sweep unit is applied to the vibrator, and a physical quantity determination unit calculates a Coriolis force perpendicular to both the torsional vibration mode caused by the sweep and the velocity based on the detection value, and determines the velocity as the physical quantity based on the calculated Coriolis force.

[0047] This also provides the same effects as those described above.

[0048] In a resonant sensor according to another aspect of the present disclosure, the vibration state information signal is a signal including information related to the vibration amplitude of the vibrator.

[0049] This allows the resonance sensor to detect the vibration amplitude of the vibrator.

[0050] In a resonant sensor according to another aspect of the present disclosure, the vibration state information signal is a signal including information related to the vibration velocity of the vibrator.

[0051] According to this, the resonance sensor can detect the vibration velocity of the vibrator. The vibration velocity is a signal that is 90 degrees out of phase with the vibration amplitude, but the resonance curve shows the same characteristics as in Figures 29 and 30, so it is possible to sense the physical quantity using the discontinuous points of the vibration velocity information in the frequency sweep.

[0052] In addition, in a resonant sensor according to another aspect of the present disclosure, the MEMS resonator is a non-capacitive MEMS resonator, and the first frequency and the second frequency, which are the two discontinuously changing frequencies of the vibration state information signal, are higher than the resonant frequency of the vibrator.

[0053] In this way, using a non-capacitive MEMS resonator, it is possible to perform sensing with higher accuracy.

[0054] In addition, in a resonant sensor according to another aspect of the present disclosure, a measurement range switching control unit is provided that increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that there is no frequency at which the vibration state information signal changes discontinuously within the sweep frequency range of the excitation signal.

[0055] According to this, the measurement range switching control unit can increase the intensity of the excitation signal by a predetermined amount, which allows the resonant sensor to perform sensing with higher accuracy using the MEMS resonator.

[0056] In addition, in a resonant sensor according to another aspect of the present disclosure, the sensor has a measurement range switching control unit that increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that the difference between the two frequencies at which the vibration state information signal changes discontinuously is smaller than a predetermined value.

[0057] According to this, it is possible to increase the intensity of the difference between at least two frequencies of the excitation signal, including the frequency at which the vibration state information signal changes discontinuously in the sweep and the frequency at which the vibration state information signal changes discontinuously in the sweep in the opposite direction to the sweep direction, by a predetermined amount, so that this resonant sensor can perform more accurate sensing with the MEMS resonator.

[0058] (Embodiment 1) <Summary> The resonant sensor according to the present embodiment is a sensor that detects a predetermined physical quantity based on the vibration state of the oscillator of the MEMS resonator. The physical quantity is, for example, temperature, pressure, force, etc. In the present embodiment, the resonant sensor is a temperature sensor using a MEMS resonator, so the physical quantity is temperature. The temperature sensor determines the physical quantity acting on the MEMS resonator based on a detection value obtained by detecting the frequency of the excitation signal or a time corresponding to the frequency. In the present embodiment, the temperature sensor determines the physical quantity acting on the MEMS resonator based on a detection value obtained by detecting 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 predetermined sweep direction over a predetermined frequency range in the vicinity of the resonance frequency f0 of the oscillator of the MEMS resonator.

[0059] The vibrator of the MEMS resonator shows a resonance curve as shown in Figures 28 to 30 based on the frequency of the excitation signal. There are two main factors that contribute to the change in the shape of the resonance curve: the first is the Q value, and the second is the temperature.

[0060] The Q value, which is the first factor that contributes to changes in the shape of the resonance curve, is the inverse of the dissipation of vibration energy, so the lower the dissipation of vibration energy, the higher the Q value becomes, and in the linear region, the maximum value at the resonance frequency f0 of the resonance curve in Figure 28 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 is -3 dB below the maximum value) becomes narrower. Conversely, if the vibration energy is dissipated as heat or the viscous resistance of the gas surrounding the vibrator increases, the Q value decreases, the maximum value in Figure 28 decreases, and the half-width W increases.

[0061] The second factor that contributes to the change in the shape of the resonance curve is temperature, which mainly changes the resonance frequency f0. The elastic modulus, which is a mechanical characteristic value of the vibrator, has a temperature characteristic, and generally, as the temperature rises, the elastic modulus decreases, so the springiness of the vibrator decreases and the resonance frequency f0 decreases. Conversely, as the temperature decreases, the resonance frequency f0 increases. Also, an increase in temperature generally reduces the Q value. This is because, first, the elastic waves propagating through the vibrator dissipate due to the increase in temperature. Second, in the case where the vibrator vibrates in a reduced pressure cavity, the pressure of the gas surrounding the vibrator increases due to the increase in temperature, which reduces the Q value (indirectly inducing the Q value, which is the first factor that contributes to the change in the shape of the resonance curve mentioned above). Therefore, a change in temperature brings about both a change in the resonance frequency and a change in the Q value, and changes the resonance curve.

[0062] Here, the resonant frequency f0 is the frequency at which the vibration amplitude of the vibrator vibrating in the linear region is maximum (with respect to the change in the frequency of the excitation signal). In addition, the resonant frequency f0 is generally the frequency through which the axis of symmetry of the left-right symmetry of the resonant characteristics in the linear region passes, as shown in FIG.

[0063] In the case of an electrostatic MEMS resonator, the resonant frequency f0 includes the effect of the electric spring caused by the DC potential applied between the vibrator and the electrode. In other words, the resonant frequency is determined by the mass and springiness of the vibrator, but this springiness is a superposition of the electric spring on the springiness inherent to the material. Since the electric spring acts in a direction that weakens the springiness inherent to the material, the resonant frequency decreases when a DC potential is applied compared to when no DC potential is applied. Here, the electric spring refers to the force that pulls the vibrator toward the electrode due to the applied DC potential as the vibrator approaches the electrode, which appears as a negative springiness.

[0064] In this way, the temperature sensor can be configured by utilizing the resonant frequency shift caused by the change in environmental temperature, by utilizing the change in Q value caused by temperature, or by utilizing both of them.

[0065] <Configuration> Fig. 1A is a wiring diagram of a temperature sensor 400 having a MEMS resonator 500. Fig. 1B is a perspective view showing the configuration of the MEMS resonator 500. Fig. 2 is a block diagram showing the configuration of the temperature sensor 400 according to the first embodiment.

[0066] 1A, 1B and 2, the temperature sensor 400 includes a sweep section 401, a MEMS resonator 500, a signal processing section 411, and a controller 416. The temperature sensor 400 is an example of a resonant sensor.

[0067] As shown in FIGS. 1A and 2, the sweep section 401 sweeps the frequency of the excitation signal, and outputs an excitation signal (AC voltage) Vi to the resonator 500 while gradually changing the frequency.

[0068] The sweep unit 401 sweeps the frequency of an excitation signal (also called 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 sweep unit 401 has a PLL synthesizer 402 controlled by a controller 416. The PLL synthesizer 402 performs frequency sweeping in accordance with a sweep control signal from the controller 416. The sweeping may be repeated continuously or may be performed intermittently.

[0069] 1A and 1B, the MEMS resonator 500 is a so-called capacitive MEMS resonator in which the effect of capacitive bifurcation is prominent in the nonlinear region. The MEMS resonator 500 has a silicon substrate 504, a pair of vibrator supports 501s, a vibrator 501, and electrodes 502 and 503.

[0070] The silicon substrate 504 laminates the pair of transducer support portions 501s, the transducer 501, and the electrodes 502 and 503. The silicon substrate 504 is a base for placing the pair of transducer support portions 501s, the transducer 501, and the electrodes 502 and 503.

[0071] The pair of transducer support parts 501s are laminated on a silicon substrate 504. The pair of transducer support parts 501s are formed integrally with the transducer 501 and are disposed at a predetermined interval. The pair of transducer support parts 501s are connected by the transducer 501 disposed therebetween.

[0072] The vibrator 501 is disposed between a pair of vibrator support parts 501s, and is a long vibrator extending from one vibrator support part 501s to the other vibrator support part 501s. The vibrator 501 is disposed between the electrode 502 and the electrode 503 with a gap provided between the electrode 502 and the electrode 503.

[0073] The oscillator 501 has a triangular shape when cut along a plane perpendicular to the longitudinal direction. The oscillator 501 performs torsional vibration with the center of rotation being approximately the center of gravity of the triangular cross section. The displacement Δx due to the torsional vibration is indicated by the dashed line in Fig. 1A. The oscillator 501 supported by the oscillator support portion 501s has a triangular cross section, which is different from the MEMS resonator 100 shown in Fig. 27A.

[0074] In this embodiment, the length L of the oscillator 501 is 100 (μm), and the resonance frequency f0 of the oscillator 501 is f0=19.6 (MHz) (torsional resonance mode) under a predetermined environment of temperature, pressure, etc. Such a configuration of the MEMS resonator 500 (the configuration of the resonator in which the oscillator is excited by electrostatic force and a current is output due to a change in capacitance caused by the vibration) is easy to configure by a semiconductor process, suitable for integration into an integrated circuit, and advantageous in that a high degree of integration of the sensor and the sensor signal processing system can be realized. Also, in this embodiment, the gap between the oscillator 501 and each of the electrodes 502 and 503 is 190 (nm).

[0075] Also, an excitation signal is applied to the vibrator 501, and the electrical signals output from the electrodes 502 and 503 are input to a differential amplifier and sent to a signal processing unit. This is another difference from the MEMS resonator 100 shown in Fig. 27B.

[0076] The electrodes 502 and 503 are arranged to sandwich the vibrator 501 and to face the vibrator 501. The electrodes 502 and 503 are arranged across a gap from the vibrator 501 so that a gap is formed between the electrodes 502 and 503 and the pair of vibrator support parts 501s and the vibrator 501.

[0077] The electrode 502 applies an excitation force to the vibrator 501 by applying a DC potential Vp. When the DC potential Vp is applied to the electrode 502 side, the excitation force applied to the vibrator 501 is applied to the side surface facing the electrode 502, and the displacement current associated with the vibration is output from the electrode 502. However, since the high-frequency signal through the existing capacitance not associated with the vibration flows through both the electrodes 502 and 503, it is removed by the differential amplifier by utilizing the fact that the high-frequency signals not associated with this vibration are in phase. The output of the differential amplifier is the component of the displacement current output along with the vibration. In the present embodiment, the cross-sectional shape of the vibrator 501 is triangular, but it may be a polygonal shape such as a rectangular shape as shown in FIG. 27B. Whether it is the configuration of FIG. 27B or the configuration of FIG. 1A, the electrostatic MEMS resonator 500 can be driven. The former may be called a two-port configuration, and the latter may be called a one-port differential configuration.

[0078] As shown in FIGS. 1A, 1B, and 2, an excitation signal Vi that is frequency-swept from a frequency f1 to a frequency f2 (f1 < f2) is input from the sweep unit 401 to the MEMS resonator 500. The MEMS resonator 500 outputs, as a vibration state information signal (alternating voltage Vo), which is a characteristic quantity representing the vibration motion, a voltage corresponding to the current flowing through the output electrode due to the vibration of the vibrator 501 in response to the excitation signal Vi, to the signal processing unit 411. This corresponds to performing a frequency sweep proportional to the sawtooth wave, which will be described later. Here, the vibration state information signal is a signal including information regarding the vibration amplitude of the vibrator 501. Also, the two frequencies f L (the first frequency) and f H (the second frequency) are frequencies lower than the resonance frequency f0 of the vibrator 501. Note that the MEMS resonator 500 may perform a frequency sweep from the frequency f2 to f1 after performing a frequency sweep from the frequency f1 to the frequency f2 (f1 < f2). This corresponds to performing a triangular-wave-shaped frequency sweep, which will be described later.

[0079] The signal processing unit 411 acquires a vibration state information signal, which is a feature quantity representing the vibration state of the oscillator 501, from the MEMS resonator 500 during the sweep, and outputs the temperature to the outside as temperature information determined based on the acquired vibration state information signal.

[0080] The signal processing unit 411 includes a discontinuity detection unit 412 and a conversion unit 415 .

[0081] The discontinuous point detection unit 412 acquires a vibration state information signal, which is a feature representing the vibration state of the oscillator 501, from the MEMS resonator 500 during the sweep, and detects the frequency of the excitation signal when the acquired vibration state information signal changes discontinuously. The discontinuous point detection unit 412 is an example of a detection unit. The discontinuous point detection unit 412 has a detector 413 and a threshold detection unit 414.

[0082] The detector 413 performs envelope detection of the amplitude of the vibration state information signal acquired from the MEMS resonator 500. The detector 413 outputs to the threshold detection unit 414 a detection signal that is a result of the envelope detection.

[0083] The threshold detection unit 414 detects that the signal value indicated by the detection signal has exceeded a preset threshold (or determines whether the signal value has exceeded). The threshold detection unit 414 outputs time information at the time when it detects that the detection signal has exceeded the set threshold to the conversion unit 415. Here, the time information and the sweep frequency information are in one-to-one correspondence, so the time information and the frequency information are synonymous. Note that since there are cases where the unit has two functions, that is, threshold detection during a sweep from frequency f1 to f2 and threshold detection during a sweep from f2 to f1, the respective thresholds may be different values. Alternatively, the discontinuity frequency f H In the sweep from f1 to f2, which is a frequency that spans f H Since the vibration amplitude of has a peak value, it is possible to use peak detection without using threshold detection. Alternatively, the discontinuous point frequency f L In the sweep from f2 to f1, which is a frequency that spans f LThe vibration amplitude of is close to the peak value but slightly smaller than the peak value, so peak detection can be used instead, and f L Threshold detection may be used to detect.

[0084] The conversion unit 415 determines a physical quantity acting on the MEMS resonator 500 based on a detection value obtained by detecting the frequency of the excitation signal at a discontinuous point. Specifically, the conversion unit 415 has a conversion table 415T, and determines a physical quantity acting on the MEMS resonator 500 using the conversion table 415T. The conversion table 415T is a table for replacing time information at which the vibration state information signal causes a discontinuous change during the frequency sweep of the excitation signal with the excitation signal frequency, and for determining the temperature of the vibrator from the replaced frequency information. The conversion unit 415 is an example of a physical quantity determination unit. Note that the time information is in one-to-one correspondence with the frequency information, so that the task of replacing the time information with the frequency information is not necessarily required. For example, the actual substance of the time information counted by the counter pulse is the number of counted pulses, and the number of pulses may be used in the table for determining the temperature. The conversion unit 415 may determine the physical quantity acting on the MEMS resonator 500 by reading out the conversion table 415T stored in a storage device separate from the conversion unit 415. For this reason, it is not an essential component of the conversion unit 415 to have the conversion table 415T.

[0085] The controller 416 controls the sweep unit 401 by outputting a sweep control signal to the sweep unit 401. That is, the controller 416 controls the PLL synthesizer 402 of the sweep unit 401 by the sweep control signal, thereby performing a frequency sweep from frequency f1 to frequency f2 over a predetermined period. The controller 416 may be an example of a measurement range switching control unit.

[0086] Moreover, the controller 416 controls the signal processing unit 411 by outputting a count 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 by the count control signal to detect that the signal value indicated by the detection signal has exceeded a preset threshold value, and outputs to the conversion unit 415 time information indicating when the threshold value has been exceeded.

[0087] If the discontinuous point detection unit 412 determines that there is no frequency at which the vibration state information signal changes discontinuously within the sweep frequency range of the excitation signal, the controller 416 may increase the intensity of the excitation signal by a predetermined amount. If the discontinuous point detection unit 412 determines that the difference between two frequencies at which the vibration state information signal changes discontinuously is smaller than a predetermined value, the controller 416 may increase the intensity of the excitation signal by a predetermined amount.

[0088] <Temperature sensing method> The temperature sensing means will be exemplified below.

[0089] 3A illustrates temperature sensing where the temperature sensor 400 performs a sawtooth frequency sweep to exploit the resonant frequency shift due to temperature. FIG 3A is a timing diagram showing the operation of the capacitive MEMS resonator 500 with an upward frequency sweep of the excitation signal. In FIG 3A, (1) shows the vibration state information signal after detection, (2) shows the frequency of the excitation signal, (3) shows the sweep start signal, (4) shows the gate signal, and (5) shows the counter pulse.

[0090] In FIG. 3A, the sweep start signal (3) of FIG. 3A issued by the controller 416 is used as a trigger (indicated by an arrow) to start the frequency sweep of the excitation signal (2) of FIG. 3A from frequency f1, and at the same time, the gate signal (4) of FIG. 3A opens and counting of counter pulses (5) of FIG. 3A starts. The vibration state information signal (after detection) shown in FIG. 3A (1) rises discontinuously at a certain frequency, which is detected by the threshold detection unit 414 and the signal processing unit 411 closes the gate signal. In this embodiment, this threshold detection is substituted by peak detection. This discontinuous point frequency is the frequency f of the nonlinear resonance curve of the resonance characteristic 121 shown in FIG. 29. H This discontinuity frequency f H is approximately equal to the resonant frequency f0. Since the resonant frequency f0 changes with temperature, the discontinuity frequency f H changes with temperature, and temperature information can be obtained based on the change in the counter pulse count value by changing the duration of the open state of the gate signal. Note that the open state of the gate signal may be started from the point at which a discontinuity is detected, and the time until the next sweep start signal may be counted using counter pulses (corresponding to counting counter pulses during the close time of (4) in FIG. 3A).

[0091] Since the frequency of the excitation signal is swept linearly from the start of the sweep, the discontinuity frequency f can be easily calculated based on the number of counted counter pulses. H An example of actual measurement is shown in the graph in Figure 3B. Figure 3B shows the relationship between temperature (ambient temperature) and discontinuous frequency f H FIG.

[0092] In FIG. 3B, the discontinuous frequency f H The measured values ​​of the discontinuity frequency f H are measured, and the temperature and discontinuity frequency f H3B as conversion table 415T, when MEMS resonator 500 is used as a temperature sensor, discontinuous point frequency f H By simply measuring the temperature, accurate temperature information can be obtained based on the relationship in FIG. 3B.

[0093] As shown in Fig. 3C, the correlation between the detection signal strength at the discontinuous point and the temperature is weak, so it is considered difficult to configure a highly accurate temperature sensor using the detection signal strength at the discontinuous point. Fig. 3C is a diagram showing the relationship between temperature and the detection signal strength at the discontinuous point.

[0094] In addition, since the open time period (period) of the gate signal in Fig. 3A (4) contains temperature information, when the sweep 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 until it is demodulated, and has high compatibility with digital signal processing circuits.

[0095] In this embodiment, the number of counter pulses within the gate open time is counted to demodulate the pulse width modulated signal and obtain temperature information. However, the present invention is not limited to this method. Alternatively, the pulse width modulated signal may be passed through an analog integration circuit and an integrated value may be read every period T.

[0096] 4A illustrates temperature measurement using a resonant frequency shift with temperature by a temperature sensor 400 performing a sawtooth downward frequency sweep. FIG 4A is a timing diagram showing the operation of a capacitive MEMS resonator 500 with a downward frequency sweep of an excitation signal. In FIG 4A, (1) shows the vibration state information signal after detection, (2) shows the frequency of the excitation signal, (3) shows the sweep start signal, (4) shows the gate signal, and (5) shows the counter pulse.

[0097] In Fig. 4A, the sweep start signal (3) of Fig. 4A issued by the controller 416 is used as a trigger (indicated by an arrow) to start the frequency sweep of the excitation signal (2) of Fig. 4A from frequency f2, and at the same time, the gate signal (4) of Fig. 4A opens and counting of counter pulses (5) of Fig. 4A starts. The vibration state information signal (after detection) shown in Fig. 4A (1) discontinuously decreases at a certain frequency, which is detected by the threshold detection unit 414 and the signal processing unit 411 closes the gate signal. This discontinuous frequency is the frequency f of the nonlinear resonance curve of the resonance characteristic 121 shown in Fig. 29. L Since the resonant frequency f0 changes with temperature, the discontinuity frequency f L changes with temperature, and temperature information can be obtained based on the change in the counter pulse count value by changing the duration of the open state of the gate signal. Note that the open gate signal may be started from the point at which a discontinuity is detected, and the time until the next sweep start signal may be counted using counter pulses (corresponding to counting counter pulses during the close time of (4) in FIG. 4A).

[0098] Since the frequency of the excitation signal is swept linearly from the start of the sweep, the discontinuity frequency f can be easily calculated based on the number of counted counter pulses. L An example of actual measurement is shown in the graph in Figure 4B. Figure 4B shows the relationship between temperature and discontinuous frequency f L FIG.

[0099] In FIG. 4B, the discontinuous frequency f L The measured values ​​of the discontinuous frequency f L are measured, and the temperature and discontinuity frequency f L 4B is stored as a conversion table 415T in the conversion unit 415, the discontinuous frequency f LBy simply measuring the temperature, accurate temperature information can be obtained based on the relationship in FIG. 4B.

[0100] FIG. 4C is a diagram showing the relationship between temperature and the peak value of the detection signal strength. That is, FIG. 4C shows the relationship between temperature and the peak value of the detection signal strength near the discontinuous point, and there is a correlation between the two. For this reason, it is considered that if the peak value of the detector output signal is measured, the temperature information can be obtained using that value. However, when FIG. 4C is compared with FIG. 4B, the plots in FIG. 4C vary widely, so if the temperature sensor 400 is configured using the peak value of the detection signal strength, the measurement accuracy will decrease. In other words, observing the change in the detection signal strength associated with the temperature change corresponds to observing the change in the Q value associated with the temperature change. For observing this Q value change, the detection signal strength obtained using nonlinear resonance is larger than that obtained using linear resonance, and it is considered to be advantageous in terms of S / N. However, it is considered that temperature information can be extracted more accurately by capturing the degree of inclination on the time axis (corresponding to frequency since frequency is swept) rather than the detection signal strength of the inclined nonlinear resonance curve.

[0101] The gate signal (4) in Fig. 4A is a pulse-width modulated signal related to temperature information, and therefore has a high affinity with a digital signal processing circuit. The demodulation method is not limited to counting the number of counter pulses, and may be a method of passing the pulse-width modulated signal through an analog integration circuit and reading the integral value every period T.

[0102] Fig. 5A illustrates an example of temperature measurement using a change in the Q value of resonance due to temperature, in which the temperature sensor 400 sweeps the frequency with a triangular wave. Fig. 5A is a timing diagram showing the operation of the capacitive MEMS resonator 500 in response to the frequency sweep of the excitation signal with a triangular wave. In Fig. 5A, (1) shows the vibration state information signal after detection, (2) shows the frequency of the excitation signal, (3) shows the sweep start signal, (4) shows the gate signal, and (5) shows the counter pulse.

[0103] In Fig. 5A, the sweep start signal (3) of Fig. 5A issued by the controller 416 is used as a trigger (indicated by an arrow) to start the frequency sweep of the excitation signal (2) of Fig. 5A from frequency f1, and at the same time, the gate signal for the upward sweep at a of Fig. 5A (4) opens, and counting of counter pulses (5) of Fig. 5A begins. The vibration state information signal (after detection) shown in Fig. 5A (1) is a signal indicating the discontinuity frequency f H This increases discontinuously at , which is detected by the threshold detector 414 and the signal processor 411 closes the gate signal. In this embodiment, this threshold detection is substituted by peak detection. The number of pulses, which is the result of counting the counter pulses during this gate open time, is set to N. H In the case of a triangular wave with a period T, the frequency of the excitation signal is swept downward from f2 to f1 in the latter half of one period. The vibration state information signal (after detection) shown in FIG. 5A(1) has a discontinuous point frequency f L This is detected by the threshold detector 414, and the signal processor 411 opens the gate signal for the downward sweep at b in (4) of FIG. 5A. When the downward sweep ends, the signal processor 411 closes the gate signal. The number of pulses, which is the result of counting the counter pulses during this gate open time, is set to N. L The difference in counting results is N H -N L is the difference frequency f of the nonlinear resonance curve of the resonance characteristic 121 shown in FIG. H -f L Since the resonant frequency f0 changes with temperature, the difference frequency f H Also L changes with temperature, but the change in the resonant frequency due to temperature is the difference frequency f H -f L That is, the difference frequency f H -f L is a quantity that represents the degree of inclination of the nonlinear resonance waveform. Generally, the Q value decreases as the temperature rises, but if this state is observed in the linear resonance region, the change observed is that the detection signal strength of the resonance curve decreases, or the -3 dB bandwidth widens. By exciting the vibrator 501 in the nonlinear resonance region, the decrease in the Q value that accompanies the increase in temperature can be observed as a function of the difference frequency f H-f L This can be seen as a decrease in

[0104] Since the frequency of the excitation signal is swept linearly both upward and downward, the number of counted counter pulses N H and N L and the difference frequency f H -f L That is, the discontinuous point detection unit 412 can calculate the discontinuous point frequency f when the vibration state information signal (after detection) discontinuously changes during the sweep. H and the discontinuous frequency f when the vibration state information signal (after detection) changes discontinuously in the sweep in the opposite direction to the sweep direction. L and the difference between at least two frequencies of the excitation signal (the difference frequency f H -f L ) is the detection value.

[0105] Next, an example of actual measurement is shown in Figure 5B. Figure 5B shows the temperature and the difference frequency f H -f L FIG.

[0106] In FIG. 5B, the MEMS resonator 500 is placed in a temperature-controllable thermostatic chamber, and a temperature change of room temperature ±5° C. is applied to the MEMS resonator 500. The difference frequency f H -f L The measured values ​​of the difference frequency f H -f L is measured, and the temperature and difference frequency f H -f L 5B is stored in the conversion table 415T, when the MEMS resonator 500 is used as a temperature sensor, the difference frequency f H -f L By simply measuring the temperature, accurate temperature information can be obtained based on the relationship in FIG. 5B.

[0107] Discontinuity frequency f measured by sawtooth sweep Hor f L Compared to the temperature measurement, which calculates the temperature from H -f L This advantage is that even when the frequencies f1 and f2 at the start of the sweep of the excitation signal in FIG. 5A(2) contain an error δ due to the influence of fluctuations and the like and change to frequencies f1+δ and f2+δ, the discontinuous point frequency f H -f L is not affected by the error δ. H increases, the count value N L Since N H -N L can be kept constant.

[0108] Furthermore, the discontinuity frequency f H -f L Another temperature measurement in which the advantage of using is apparent is shown in Fig. 6. Fig. 6 is a timing diagram showing the operation of the capacitive MEMS resonator 500 when the frequency sweep direction is switched at the timing of discontinuity detection. In Fig. 6, (1) shows the vibration state information signal after detection, (2) shows the frequency of the excitation signal, (3) shows the sweep start signal, (4) shows the sweep direction control signal (also gate signal), and (5) shows the counter pulse.

[0109] In Fig. 6, the frequency sweep of the excitation signal in Fig. 6(2) starts from frequency f1 to frequency f2 (f2>f1) with the sweep start signal in Fig. 6(3) issued from the controller 416 as a trigger (indicated by an arrow), and at the same time, the sweep direction control signal (also a gate signal) in Fig. 6(4) a is reset to an upward sweep. The vibration state information signal (after detection) shown in Fig. 6(1) is a signal indicating the discontinuity frequency f H This is detected by the threshold detector 414, which is set to the threshold A, and the sweep direction control signal is changed to a downward sweep. The frequency of the excitation signal in FIG. 6(2) is swept downward toward the frequency f1. The vibration state information signal (after detection) shown in FIG. 6(1) increases at the discontinuous point frequency f LThis is detected by the threshold detector 414 set to threshold B, and the sweep direction control signal is changed to an upward sweep. By repeatedly detecting thresholds A and B and continuing to switch the sweep direction, the high state (here indicating a downward sweep) of the sweep direction control signal in FIG. 6(4) is reached at the discontinuous frequency f H to discontinuity frequency f L That is, the sweep unit 401 switches the sweep in the reverse direction starting from the detection of a discontinuous change in the vibration state information signal (after detection) in the sweep, and then switches the sweep in the reverse direction again starting from the detection of a discontinuous change in the vibration state information signal (after detection), and repeats the operation of switching the sweep back to the original direction.

[0110] This high state is used as a gate signal to count the counter pulses, resulting in a count value of N. HL is the discontinuity frequency f H and discontinuity frequency f L The difference between the two, i.e., the difference frequency f H -f L This corresponds to the information of the difference frequency f H -f L Using the value of f, it is possible to obtain temperature information with high accuracy based on the relationship in FIG. 5B. The discontinuous point detection unit 412 converts a pulse signal having two values ​​representing the two states of the forward and reverse directions in the sweep direction into a detection value (differential frequency f H -f L The conversion unit 415 determines a physical quantity acting on the MEMS resonator 500 based on the pulse time width of the pulse signal, which is the output detection value. Then, the discontinuous point frequency f L Lower frequency sweep time and discontinuity f H Since the sweep time of higher frequencies is eliminated, more temperature measurement data per unit time is obtained, i.e., faster temperature measurement is possible.

[0111] In addition, the sweep direction control signal (and gate signal) (4) in Figure 6 is a pulse frequency modulation (PFM) signal related to temperature information, so it has a high affinity with digital signal processing circuits. This PFM signal is similar to PWM because the pulse width also carries temperature information, and the demodulation method can be a method of counting the number of counter pulses, but it is not limited to this. Another method is to pass the pulse width modulated signal through an analog integration circuit, reset the integration value every time the sweep direction changes, and read the integration value.

[0112] <Action and effect> Next, the effects of the temperature sensor 400 according to this embodiment will be described.

[0113] As described above, the temperature sensor 400 according to this embodiment is a temperature sensor 400 that uses a MEMS resonator 500, and includes the MEMS resonator 500, a sweep unit 401 that sweeps the frequency of an excitation signal of the oscillator 501 of the MEMS resonator 500 along a predetermined sweep direction and outputs the swept excitation signal to the MEMS resonator 500, a discontinuous point detection unit 412 that acquires a vibration state information signal from the MEMS resonator 500, which is a feature representing the vibration state of the oscillator 501 based on the excitation signal, and detects the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously, and a conversion unit 415 that determines a physical quantity acting on the MEMS resonator 500 based on the detected value.

[0114] 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 can be projected on the time axis, such as the time difference between the start time of the frequency sweep and the time when a discontinuity occurs, and the time difference between each time when multiple discontinuities occur. The discontinuity of the vibration state information signal can be detected by setting a threshold value or the like, as a sudden change in signal strength. Therefore, even if noise is superimposed on the signal strength, the time showing the discontinuity can be reliably detected against the superimposed noise. For example, this is considered to be the same as the effect that the sound quality of the received and demodulated FM radio broadcast is superior to that of the AM radio broadcast. In addition, the pulse-shaped detection signal also has the secondary effect of being highly compatible with digital signal processing.

[0115] Therefore, in this temperature sensor 400, highly accurate sensing can be performed in the MEMS resonator 500.

[0116] In particular, by using resonance in the nonlinear region, it is possible to excite a large amplitude that cannot be obtained by linear resonance, improving the S / N ratio of the detection value of the sensing amount. Furthermore, by sweeping the frequency, the degree of collapse of the nonlinear resonance waveform can be obtained from the time axis. In this way, by extracting the detection value not as its intensity but as a PWM signal projected onto the time axis, it becomes robust against noise superimposed on the signal intensity, making it possible to detect even more minute changes in the resonance state. If it is a PWM signal, it becomes easier to handle it as a digital signal for transmission and signal processing.

[0117] Furthermore, the detection method of the temperature sensor 400 according to this embodiment is a detection method of the temperature sensor 400 using the MEMS resonator 500, and includes sweeping the frequency of an excitation signal of the oscillator 501 of the MEMS resonator 500 along a predetermined sweep direction, outputting the swept excitation signal to the MEMS resonator 500, acquiring a vibration state information signal from the MEMS resonator 500, which is a feature representing the vibration state of the oscillator 501 based on the excitation signal, detecting the frequency of the excitation signal or the time corresponding to the frequency when the acquired vibration state information signal changes discontinuously, and determining a physical quantity acting on the MEMS resonator 500 based on the detected detection value.

[0118] This method also provides the same effects as those described above.

[0119] In addition, in the temperature sensor 400 of this embodiment, the discontinuous point detection unit 412 detects the difference (differential frequency) between at least two frequencies of the excitation signal, including the frequency at which the vibration state information signal changes discontinuously in a sweep and the frequency at which the vibration state information signal changes discontinuously in a sweep in the opposite direction to the sweep direction.

[0120] According to this, even if there is an error in each of at least two frequencies of the excitation signal, the effect of the error can be suppressed by calculating the difference between the two frequencies. In other words, since the physical quantity is determined as the detection value of the difference frequency, which is the difference between the two frequencies, the effect of the resonant frequency shift caused by the fluctuation of the environmental temperature is reduced. Therefore, the temperature sensor 400 can perform more accurate sensing with the MEMS resonator 500.

[0121] In particular, since it is no longer necessary to create a temperature characteristic table of the resonant frequency shift or to perform correction using the temperature characteristic table, the cost of the temperature sensor 400 is prevented from rising sharply.

[0122] Furthermore, in the temperature sensor 400 according to this embodiment, the sweep unit 401 switches the sweep in the reverse direction upon detection of a discontinuous change in the vibration state information signal during the sweep, and then repeats the operation of switching the sweep in the reverse direction again upon detection of a discontinuous change in the vibration state information signal, and the discontinuous point detection unit 412 outputs a pulse signal having two values ​​representing the two states of the forward and reverse directions in the sweep direction as a detection value, and the conversion unit 415 determines a physical quantity acting on the MEMS resonator 500 based on the pulse time width of the pulse signal, which is the output detection value.

[0123] This makes it possible to determine the physical quantity based on the pulse time width of the binary pulse signal that represents the forward and reverse sweep directions, and therefore to sense changes over time.In addition, it is possible to eliminate the sweep time for frequencies lower than the discontinuous point frequency and the sweep time for frequencies higher than the discontinuous point, which increases the amount of temperature measurement data per unit time, i.e., makes it possible to measure temperature at a higher speed.

[0124] In the temperature sensor 400 according to the present embodiment, the MEMS resonator 500 is a capacitive MEMS resonator. L and frequency f H is a frequency lower than the resonant frequency f0 of the vibrator 501.

[0125] According to this, by using the widely used MEMS resonator 500, it is possible to perform highly accurate sensing with the MEMS resonator 500. Therefore, the temperature sensor 400 is easy to use.

[0126] In temperature sensor 400 according to this embodiment, the vibration state information signal is a signal including information related to the vibration amplitude of vibrator 501.

[0127] This allows the temperature sensor 400 to detect the vibration amplitude of the vibrator 501.

[0128] In addition, the temperature sensor 400 according to this embodiment is provided with a controller 416 that increases the intensity of the excitation signal by a predetermined amount when the discontinuity detection unit 412 determines that there is no frequency at which the vibration state information signal changes discontinuously within the sweep frequency range of the excitation signal.

[0129] This allows the controller 416 to increase the intensity of the excitation signal by a predetermined amount, thereby enabling the temperature sensor 400 to perform sensing of the MEMS resonator 500 with higher accuracy.

[0130] Furthermore, the temperature sensor 400 according to this embodiment has a controller 416 that increases the intensity of the excitation signal by a predetermined amount when the discontinuity detection unit 412 determines that the difference between the two frequencies at which the vibration state information signal discontinuously changes is smaller than a predetermined value.

[0131] According to this, it is possible to increase by a predetermined amount the intensity of the difference between at least two frequencies of the excitation signal, including the frequency at which the vibration state information signal changes discontinuously in the sweep and the frequency at which the vibration state information signal changes discontinuously in the sweep in the opposite direction to the sweep direction. Therefore, in this temperature sensor 400, it is possible to perform more accurate sensing with the MEMS resonator 500.

[0132] (Embodiment 2) <Configuration> In the following, since the basic configuration of the pressure sensor of this embodiment is similar to the basic configuration of the temperature sensor according to embodiment 1, the description of the basic configuration of the pressure sensor of this embodiment will be omitted as appropriate. Also, since the basic configuration of the MEMS resonator 500x of this embodiment is similar to the basic configuration of the MEMS resonator 500 of FIG. 2 according to embodiment 1, the description of the basic configuration of the MEMS resonator 500x of this embodiment will be omitted as appropriate. The MEMS resonator 500x of the pressure sensor of this embodiment differs from the MEMS resonator 500x of FIG. 1B according to embodiment 1 in that it has a partition layer 504x and a diaphragm 505x.

[0133] FIG. 7 is a cross-sectional view of a capacitive MEMS resonator 500x.

[0134] The resonant sensor according to the present embodiment is a pressure sensor that uses a MEMS resonator 500x as shown in FIG. 7 to measure the gas pressure of the atmosphere. The 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 vibration 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 has a relationship of approximately Q∝(1 / Pi) with respect to the gas pressure Pi around the oscillator 501x ​​in FIG. 7. Also, the amplitude X of the resonance in the linear resonance region has a relationship of X∝Q. Therefore, X∝(1 / Pi), and when 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 according to the present embodiment utilizes this principle by extending it to the nonlinear region.

[0135] MEMS resonator 500x is a torsion resonator of a beam having a triangular cross section, similar to MEMS resonator 500 in Fig. 1. MEMS resonator 500x has a partition layer 504x and a diaphragm 505x in addition to an oscillator 501x ​​and electrodes 502x and 503x.

[0136] The oscillator 501x, electrodes 502x and 503x of the MEMS resonator 500x are disposed in a closed space 507x formed by a partition layer 504x and a diaphragm 505x. Specifically, the oscillator 501x, electrodes 502x and 503x, a partition layer 504x and a diaphragm 505x are disposed on a silicon substrate 510x. The oscillator 501x ​​is surrounded by gas with a pressure that gradually becomes equal to the pressure acting on the MEMS resonator 500x by the partition layer 504x and the diaphragm 505x. The partition layer 504x is laminated on the silicon substrate 510x so as to cover a part of the electrodes 502x and 503x, and is disposed so as to surround the periphery of the oscillator 501x. The diaphragm 505x is laminated on the partition layer 504x to form a space surrounding the periphery of the vibrator 501x ​​as a closed space 507x.

[0137] The pressure Pi in this closed space 507x is kept constant. In particular, by setting the pressure Pi in the closed space 507x to a vacuum state, the vibrator 501x can resonate with a high Q value without being affected by the viscous resistance of the gas. Since the MEMS resonator 500x is electrostatically driven, it is likely to exhibit the non-linear resonance characteristics shown in FIG. 29 due to the effect of capacitive biasing. If the partition layer 504x and the diaphragm 505x are made of a dense film using Si-based, Ge-based, or SiGe-based materials, or their oxide and nitride films, the thin film functions as a molecular "sieve". Oxygen gas and nitrogen gas in the air do not permeate through the partition layer 504x or the diaphragm 505x, but helium gas and hydrogen gas with a small molecular diameter permeate through the partition layer 504x and the diaphragm 505x. For example, when the pressure in the closed space 507x is Pi and the external pressure is P, and the closed space 507x is depressurized so that Pi << P, the partial pressure of hydrogen gas remaining in the closed space 507x can be set to be smaller than the partial pressure of hydrogen gas in the atmosphere. Due to this partial pressure difference, hydrogen gas in the atmosphere permeates through the partition layer 504x or the diaphragm 505x, and the partial pressure of hydrogen gas in the closed space 507x increases. This increase continues until the partial pressures of hydrogen gas in the closed space 507x and the atmosphere become equal. On the other hand, due to the increased partial pressure of hydrogen gas in the closed space 507x, the Q value of the resonance of the vibrator 501x decreases. In the pressure sensor, by performing frequency sweeping of the excitation signal in the non-linear resonance region and obtaining the time when the discontinuous change of the vibration state information signal occurs, a hydrogen pressure sensor that detects the change in the partial pressure of hydrogen gas can be configured. When the partial pressure of hydrogen gas in the closed space 507x and the partial pressure of hydrogen gas in the atmosphere are in equilibrium and the permeation of hydrogen gas through the partition layer and the diaphragm 505x stops, it means that the partial pressure of hydrogen gas in the atmosphere is being detected. When they are not in equilibrium, it means that the partial pressure of hydrogen gas in the closed space 507x is being detected. That is, the conversion unit 415 detects the partial pressure of hydrogen gas in the closed space 507x by determining the gas pressure based on the detection value (the time when the discontinuous change of the vibration state information signal occurs, which is the differential frequency f H -f L of the change over time of the gas pressure).

[0138] <Means for measuring pressure> The pressure measurement means will be exemplified below. The method of extracting hydrogen pressure information as a pulse width modulated signal is also similar to that shown in Figures 3A, 4A, 5A, and 6 of the first embodiment, so the explanation will be omitted as appropriate.

[0139] When measuring minute changes in hydrogen gas pressure, the change in the Q value of the oscillator 501x ​​is also minute, so the Q value fluctuation component due to the fluctuation in the ambient temperature may be larger. In such a case, the temperature characteristics of the discontinuous point frequency are obtained in advance and temperature correction is applied.

[0140] Here, the case where a thermometer 508x is arranged in the MEMS resonator 500x is illustrated. FIG. 8A is a cross-sectional view of a capacitive MEMS resonator 500x in which a thermometer 508x is arranged in the same chip. FIG. 8A illustrates a form in which a thermometer 508x for measuring an ambient temperature is included inside the pressure sensor of FIG. 7. FIG. 8B is a cross-sectional view of a capacitive MEMS resonator 500x in which a thermometer 508x is arranged on the same mounting substrate. FIG. 8B illustrates a form in which a thermometer 508x is mounted in the vicinity of the MEMS resonator 500x on the mounting substrate of the MEMS resonator 500x. The thermometer 508x may be a PN diode type, a thermocouple type, a pyroelectric type, or the like, but the method of sensing the temperature is not limited.

[0141] In the pressure sensor, as a pre-processing step for obtaining the temperature characteristic of the discontinuous point frequency, the atmospheric pressure P is reduced by a vacuum pump to sufficiently reduce the hydrogen partial pressure, and then the remaining hydrogen gas in the closed space 507x is sufficiently exhausted. Next, the pressure sensor is driven in the nonlinear resonance region in a temperature-controllable thermostatic chamber, and the relationship between the temperature indicated by the thermometer 508x and the obtained discontinuous point frequency is obtained.

[0142] FIG. 9 shows the temperature of the MEMS resonator 500x versus the difference frequency f H -f L FIG. 9 is similar to FIG. 5B. The graph in FIG. 9 shows the relationship between the difference frequency f H -f L Since this graph shows the change in temperature, the temperature-dependent components can be eliminated as follows, using this graph as a reference.

[0143] When using MEMS resonator 500x as a hydrogen gas pressure sensor, even though the thermometer indicates a certain temperature T1, the difference frequency f H -f L If the value of f is the value indicated by the star in the figure, it indicates that the value indicated by the star is lower than the reference graph. In this case, it indicates that hydrogen gas has permeated from the outside of the MEMS resonator 500x into the closed space 507x, causing the Q value of the oscillator 501x ​​to deteriorate. In other words, the difference frequency f H -f L The deviation Δ of the actual measured value from the reference curve indicates the partial pressure of hydrogen gas in the closed space 507x.

[0144] FIG. 10A shows the relationship between the change in hydrogen gas concentration and the difference frequency f H -f L FIG. 10A is a graph showing the change over time of the difference frequency f when air mixed with 200 ppm of hydrogen is started to flow into the atmosphere at time t1 and the hydrogen content is increased to 1000 ppm at time t2. H -f L 4 shows the results of actually measuring the amount of deviation Δ.

[0145] As shown in FIG. 10A, the deviation Δ from the reference curve starts to decrease in the negative direction from time t1. This is because 200 ppm hydrogen in the atmosphere gradually permeates into the closed space 507x, and the hydrogen gas starts to interfere with the vibration of the oscillator 501x, causing a decrease in the Q value. This decrease in the Q value is calculated by dividing the difference frequency f between the two discontinuous frequencies in the nonlinear resonance region. H -f L The rate of decrease in the deviation Δ from the reference curve increases from time t2. This is because the amount of hydrogen gas in the atmosphere increases to 1000 ppm, and the amount of hydrogen permeating into the closed space 507x per unit time increases.

[0146] In addition, when the hydrogen in the atmosphere was set to 200 ppm or 1000 ppm, the deviation amount Δ from the reference curve did not reach a saturation value within the measurement time. This is considered to be because the hydrogen gas partial pressure in the closed space 507x and the hydrogen gas partial pressure in the atmosphere did not reach equilibrium within the measurement time. Therefore, the vertical axis of FIG. 10A does not indicate the hydrogen gas partial pressure in the atmosphere, but indicates the hydrogen gas partial pressure in the closed space 507x. In order to make the sensor measure the hydrogen gas partial pressure in the atmosphere, it is necessary to design it so that the permeation path of the hydrogen gas is shortened by making the measurement time sufficiently long or adjusting the dimensions of the partition layer 504x and the diaphragm 505x so that the hydrogen gas can easily permeate the closed space 507x.

[0147] In addition, the MEMS resonator 500x itself may be used as a temperature sensor instead of adding the thermometer 508x to the MEMS resonator 500x. In the temperature sensor of the first embodiment, the discontinuous frequency f obtained by sweeping the excitation frequency upward by the sawtooth wave is H It was shown that the discontinuous frequency f H is close to the resonant frequency f0 of the MEMS resonator 500x, and shifts with temperature change in the same way that the resonant frequency f0 shifts. H On the other hand, the discontinuity frequency f H is not easily affected by changes in the Q value (changes due to temperature and other changes due to the surrounding gas pressure, etc.). Therefore, the discontinuity frequency f H can be considered to have only temperature information. H By using the temperature information, the area and manufacturing cost of the thermometer 508x can be reduced. H When using the temperature information, the temperature and difference frequency f H -f L Instead of using the reference curve with the discontinuity frequency f H and the difference frequency f H -f L A standard curve showing the relationship between the above is used, and the deviation Δ from the standard curve is regarded as a change in hydrogen gas partial pressure.

[0148] FIG. 10B shows the relationship between the change in hydrogen gas concentration and the difference frequency f H -f L Change over time (temperature information is the discontinuous frequency f H FIG. 11 shows the case where the discontinuous point frequency f H When temperature information is f H and the difference frequency f H -f L FIG. 10B is a diagram showing the relationship between f H -f L 4 is a result of measuring the deviation Δ from the reference curve.

[0149] FIG. 10A shows the results when a thermocouple with a resolution of 0.1°C is used as the temperature sensor, and FIG. 10B shows the results when f H Since the resolution of is much finer than 0.1° C., the change in the deviation amount Δ from the reference curve similar to that of FIG. 10A is shown, but a smoother curve with less noise components than that of FIG. 10A is obtained.

[0150] The discontinuous frequency f obtained by sweeping the sawtooth wave downward is L contains both information on the shift of the resonant frequency f0 due to temperature and the change in the Q value (change due to temperature and other changes due to the surrounding gas pressure, etc.). Therefore, in this embodiment, which aims to capture the change in the Q value due to the gas pressure, L It is considered inappropriate to use this as a substitute for the thermometer 508x.

[0151] Similarly, the difference frequency f obtained by sweeping a triangular wave H -f L The shift of the resonant frequency f0 due to temperature is cancelled, and the information on the change in the Q value (change due to temperature and other changes due to the surrounding gas pressure, etc.) is included. Therefore, in this embodiment, which aims to capture the change in the Q value due to the gas pressure, the difference frequency f H -f L It is considered inappropriate to use this as a substitute for the thermometer 508x.

[0152] Next, a case will be shown in which hydrogen gas fills the closed space 507x, causing the Q value to decrease to the point where the discontinuity disappears. In this case, the controller 416 can change the measurement range to cause the discontinuity to appear. Fig. 12 is a block diagram showing the configuration of a pressure sensor 400a using a MEMS resonator 500x having a measurement range switching function.

[0153] The basic configuration of pressure sensor 400a shown in Fig. 12 is similar to that of the temperature sensor of embodiment 1. Conversion unit 415 differs from the temperature sensor of embodiment 1 in that conversion unit 415 uses conversion table 415T to output pressure information indicating pressure as a physical quantity acting on MEMS resonator 500x to the outside. Pressure sensor 400a shown in Fig. 12 also differs from the temperature sensor of embodiment 1 in that a path for feeding back discontinuity information from signal processing unit 411 to controller 416 is added.

[0154] The controller 416 determines whether the Q value has decreased based on the discontinuity information. Specifically, the controller 416 determines the discontinuity frequency f L The discontinuity frequency f H If only the discontinuity frequency f L Also H If no discontinuity is detected, it is determined that the gas pressure surrounding the resonator has increased excessively, causing a decrease in the Q value. After making this determination, controller 416 controls sweep unit 401 to increase the amplitude of excitation signal Vi, or controls MEMS resonator 500x to increase bias DC voltage Vp, according to measurement range table 416T held by controller 416, thereby electrically increasing the vibration amplitude and restoring the disappeared discontinuity.

[0155] As a method for dealing with this issue earlier, the signal processor 411 calculates the difference frequency f H -f Lis smaller than a specified value as discontinuous point information to the controller 416. The controller 416 outputs a sweep control signal to the sweep unit 401 based on the fed back discontinuous point information so as to increase the amplitude Vi of the excitation signal in accordance with 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 so as to increase the bias DC voltage Vp, thereby controlling the MEMS resonator 500x.

[0156] Conversely, the difference frequency f H -f L is equal to or greater than a certain specified value, the transducer is beginning to contact the electrode. Therefore, the controller 416 outputs a sweep control signal to the sweep unit 401 to reduce the amplitude Vi of the excitation signal in accordance with 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 to reduce the bias DC voltage Vp, thereby controlling the MEMS resonator 500x.

[0157] Figure 13 shows the relationship between the excitation signal strength Vi and the difference frequency f H -f L 13 is a graph showing the relationship between the difference frequency f and the amplitude of the excitation signal Vi when the amplitude of the excitation signal Vi is changed under conditions of a certain temperature and hydrogen gas pressure. H -f L The change in the difference frequency f H -f L stops changing and transitions to a region where it is constant. This region represents the contact region between the transducer and the electrode. The measurement range table 416T of the controller 416 stores the excitation signal Vi and the resonator bias DC voltage Vp that do not cause resonance in this contact region at the minimum expected hydrogen gas pressure.

[0158] <Action and effect> Next, the function and effect of the pressure sensor according to this embodiment will be described.

[0159] As described above, in the pressure sensor according to the present embodiment, the oscillator 501x ​​is surrounded by gas in the closed space 507x (the space in which the oscillator 501x ​​is disposed) at a pressure that gradually becomes equal to the pressure acting on the MEMS resonator 500x. The conversion unit 415 determines the pressure of the gas as a physical quantity based on the detection value.

[0160] According to this, when pressure is applied to the MEMS resonator 500x, the oscillator 501x ​​vibrates at a predetermined vibration amplitude and vibration speed depending on the atmospheric pressure. Therefore, this pressure sensor can perform more accurate pressure measurement with the MEMS resonator 500x.

[0161] In this embodiment and the like, the same effects as those in the first embodiment are achieved.

[0162] (Embodiment 3) <Configuration> In the following, since the basic configuration of the MEMS resonator 500x3 of the present embodiment is similar to the basic configuration of the MEMS resonator 500x of the second embodiment in Fig. 7, the description of the basic configuration of the MEMS resonator 500x3 of the present embodiment will be omitted as appropriate. The MEMS resonator 500x3 of the present embodiment differs from the MEMS resonator 500x of the second embodiment in that it has a pillar 506x.

[0163] FIG. 14 is a cross-sectional view of a capacitive MEMS resonator 500x3.

[0164] The resonant sensor of this embodiment is a pressure sensor that uses a MEMS resonator 500x3 in which the gap (distance) between the oscillator 501x ​​and the electrodes 502x and 503x changes depending on the pressure (fluid pressure and pressing force) outside the resonant sensor, as shown in FIG. 14.

[0165] The MEMS resonator 500x3 is a torsion resonator of a beam having a triangular cross section. The MEMS resonator 500x3 includes an oscillator 501x, electrodes 502x and 503x, a partition layer 504x, a diaphragm 505x, and a plurality of pillars 506x.

[0166] Each of the pillars 506x is a columnar member sandwiched between the electrode 502x and the diaphragm 505x and between the electrode 502x and the diaphragm 505x. Each of the pillars 506x may be integrally connected to at least one of the electrodes 502x, 503x, and the diaphragm 505x, or may simply be disposed. Each of the pillars 506x transmits a stress corresponding to the amount of deflection of the diaphragm 505x to the electrodes 502x and 503x when the diaphragm 505x deflects. The diaphragm 505x and the pillars 506x change the size of the gap according to the magnitude of the pressure acting on the MEMS resonator 500x3. The diaphragm 505x and the pillars 506x correspond to a transmission unit.

[0167] The vibrator 501x, pillar 506x, and electrodes 502x and 503x of the MEMS resonator 500x3 are disposed in a closed space 507x formed by a partition layer 504x and a diaphragm 505x. The pressure Pi in the closed space 507x is kept constant. In particular, by making the pressure Pi in the closed space 507x a vacuum state, the vibrator 501x ​​is able to resonate at a high Q value without being subjected to viscous resistance of gas. Since the MEMS resonator 500x3 is an electrostatic drive type, it is easy to exhibit nonlinear resonance characteristics as shown in FIG. 29 due to the effect of capacitive bifurcation. When the pressure P (fluid pressure and pressing force) indicated by the arrow acting on the diaphragm 505x from outside the closed space 507x increases, the diaphragm 505x bends. The bending of the diaphragm 505x causes the electrodes 502x and 503x to bend via the pillar 506x. The mechanisms for changing the gap between the electrode 502x and the vibrator 501x ​​and between the electrode 503x and the vibrator 501x ​​upon receiving the pressure P are the diaphragm 505x and the pillar 506x which receive the external pressure P. For example, the electrode 503x bends, narrowing or widening the gap between the electrode 503x and the vibrator 501x, thereby changing the degree of nonlinearity of the resonant vibration of the vibrator 501x. The amount of bending of the electrodes 502x and 503x shows a certain correspondence relationship with the amount of bending of the diaphragm 505x.

[0168] Figure 15 shows the difference frequency f when the gap is changed by pressure and fluid pressure. H -f L As shown in FIG. 15, the difference frequency f H -f L 15 shows the relationship (calculated value) between the gap (the distance between the vibrator 501x ​​and the electrode 502x or the distance between the vibrator 501x ​​and the electrode 503x). The circuit connection to the MEMS resonator 500x3 is the same as that in FIG. 1A of the first embodiment, and specifically, the bias voltage Vp is set to 5 (V), and the voltage Vi (maximum value) of the excitation signal to the electrode 503x is set to 100 (mV). As is clear from FIG. 15, as the gap is reduced to 250 nm, 230 nm, 210 nm, and 190 nm, the resonance characteristics show stronger nonlinearity,H -f L increases. The conversion unit 415 determines the pressure as a physical quantity based on the size of the gap. Using such a relationship, the pressure (fluid pressure and pressing force) outside the pressure sensor can be measured. That is, the conversion unit 415 determines the pressure as a physical quantity acting on the MEMS resonator 500 using the conversion table 415T. The conversion unit 415 outputs pressure information indicating the determined pressure to the outside.

[0169] <Action and effect> Next, the function and effect of the pressure sensor according to this embodiment will be described.

[0170] As described above, in the pressure sensor according to the present embodiment, the capacitive MEMS resonator 500x3 includes the oscillator 501x, the electrodes 502x and 503x arranged across a gap from the oscillator 501x, and a transmission unit that changes the size of the gap depending on the magnitude of 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.

[0171] According to this, by applying pressure to the MEMS resonator 500x3, the transmission unit can change the size of the gap in response to changes in atmospheric pressure. By changing the size of the gap, the gap between the electrodes 502x and 503x and the oscillator 501x ​​narrows or widens, so that the degree of nonlinearity of the resonant vibration of the oscillator 501x ​​can be changed. Therefore, this pressure sensor can perform more accurate pressure measurement in the MEMS resonator 500x3.

[0172] In this embodiment and the like, the same effects as those in the first embodiment and the like are achieved.

[0173] (Embodiment 4) In the following, since the basic configuration of MEMS resonator 500x4 of the present embodiment is similar to the basic configuration of MEMS resonator 500x of Embodiment 2 in Fig. 8B, a description of the basic configuration of MEMS resonator 500x4 of the present embodiment will be omitted as appropriate. MEMS resonator 500x4 of the present embodiment differs from MEMS resonator 500x of Embodiment 2 in Fig. 8B in that metal film 509x is formed on the surface of oscillator 501x.

[0174] The resonant sensor of this embodiment is an infrared sensor using a MEMS resonator 500x4 in which an oscillator 501x ​​absorbs infrared rays irradiated from outside the resonance sensor, causing a change in temperature of the oscillator 501x.

[0175] Fig. 16 is a cross-sectional view of a capacitive MEMS resonator 500x4. Fig. 16 shows an example in which a thermometer 508x is provided on a mounting substrate, similar to Fig. 8B.

[0176] 16, MEMS resonator 500x4 is a torsion resonator of a beam having a triangular cross section. 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.

[0177] Furthermore, MEMS resonator 500x4 obtains temperature change ΔT correlated with the incident infrared power based on thermometer 508x by obtaining temperature T+ΔT when oscillator 501x ​​is irradiated with infrared rays.

[0178] The pressure Pi in the closed space 507x is kept constant. In particular, by making the pressure Pi in the closed space 507x a vacuum state, the oscillator 501x ​​is not subjected to the viscous resistance of the gas and can resonate with a high Q value. Since the MEMS resonator 500x is an electrostatic drive type, it is easy to exhibit the nonlinear resonance characteristics shown in FIG. 29 due to the effect of capacitive bifurcation. Infrared rays are irradiated onto the oscillator 501x ​​from outside the closed space 507x through the diaphragm 505x. A metal film 509x is formed on the surface, which is 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, the optical characteristics of the TiN metal film and the oscillator 501x ​​are different because silicon is a dielectric. In order to satisfy the electromagnetic boundary conditions of the infrared rays as electromagnetic waves at the boundary between the two, a small amount of current is generated on the metal film 509x side, and the metal film 509x is heated and the temperature rises. Macroscopically, it can be considered that the metal film 509x absorbs the infrared rays, causing the oscillator 501x ​​to show 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 incident infrared power as a physical quantity based on the calculated temperature change ΔT. If the temperature of the object emitting the infrared rays is further calculated from the infrared power, this infrared sensor becomes an imaging element for thermography.

[0179] Hereinafter, the temperature change (ΔT) of the oscillator 501x ​​is expressed as the discontinuous frequency f H , f L , or f H -f L It can be detected using

[0180] The material of the metal film 509x on the side of the resonator 501x ​​may be silicide. However, what is important in configuring an infrared sensor is that it is necessary to determine whether the temperature change of the resonator 501x ​​is due to a temperature change of the device accompanying a change in the environmental temperature or due to infrared rays absorbed by the metal film 509x. For this purpose, as shown in FIG. 8A or FIG. 8B described in the pressure sensor of the second embodiment, the thermometer 508x may be included in the MEMS resonator 500x4, or the thermometer 508x may be provided on the mounting board on which the MEMS resonator 500x4 is mounted. In this case, the temperature indicated by the thermometer 508x is set as the representative value of the temperature of the MEMS resonator 500x4.

[0181] In the infrared sensor, as a pre-processing step to obtain the temperature characteristic of the discontinuous point frequency, the MEMS resonator 500x4 is driven in a nonlinear resonance region in a temperature-controlled thermostatic chamber, and the relationship between the temperature indicated by the thermometer 508x and the obtained discontinuous point frequency is obtained. At this time, the infrared wavelength region that the infrared sensor should originally sense is shielded from light. In addition, the measurement is performed after a sufficient time has elapsed so that the temperature of the entire MEMS resonator 500x4, including the oscillator 501x, becomes uniform.

[0182] FIG. 17 shows the temperature of the MEMS resonator 500x4 and the difference frequency f H -f L FIG. 17 is similar to FIG. 9. In FIG. 17, f due to a temperature change of MEMS resonator 500x4 indicated by thermometer 508x is shown. H -f L 17 is used as a reference, the temperature dependent component of the MEMS resonator 500x4 can be eliminated as follows:

[0183] When the MEMS resonator 500x4 is used as an infrared sensor, even though the thermometer 508x indicates a certain temperature T1 as the temperature of the MEMS resonator 500x4, H -f LIf the value of indicates the value marked with a star in the figure, it indicates that the value marked with a star is lower than the reference graph. In this case, the metal film 509x absorbs the infrared rays irradiated from the outside, the temperature of the oscillator 501x ​​rises, the Q value of the resonance of the oscillator 501x ​​decreases, and this is the nonlinear resonance f H -f L This is thought to be reflected in the decrease in f H -f L The deviation Δ (in this case, a negative value) of the actual measured value from the reference graph indicates the infrared power irradiated to the transducer 501x.

[0184] As described in the temperature sensor of the first embodiment, in order to read the temperature change of the oscillator 501x, the vertical axis of the reference curve in FIG. 17 is f H -f L is not limited to f obtained by sweeping the sawtooth upwards. H , or f obtained by sweeping the sawtooth downwards L may be used.

[0185] The thermometer 508x may be a PN diode type, a thermocouple type, a pyroelectric type, or the like, but the method of sensing the temperature is not limited. Furthermore, instead of the thermometer 508x, a temperature sensor using the MEMS resonator described in the first embodiment may be used. That is, the MEMS resonator 500x4 in FIG. 16 is made to function as an infrared sensor, but a MEMS resonator of the same shape may be provided next to it and used as a temperature sensor. However, since the MEMS resonator 500x4 used as a temperature sensor is intended to acquire the temperature of the MEMS resonator 500x4, the resonator 500x4 may be configured not to have a metal film 509x for absorbing infrared rays on the side of the oscillator 501x, or a metal film that reflects or absorbs infrared rays may be laminated on the diaphragm 505x.

[0186] The vibration mode of the infrared sensor of this embodiment is a torsional vibration mode. Here, the advantages of using the torsional vibration mode will be explained in comparison with the commonly used flexural vibration.

[0187] In the flexural vibration mode, one of the upper and lower surfaces of the vibrator as a beam is compressed during one round trip of vibration, and the other is expanded. Therefore, heat constantly flows in and out between the upper and lower surfaces, and some of the heat is dissipated to the vibrator support part, which supports the beam. In other words, in addition to the heat flow generated in a small amount in the vibrator by infrared irradiation, the heat flow caused by the flexural vibration is superimposed on the vibrator, making it unsuitable for detecting small amounts of infrared rays. On the other hand, torsional vibration is a special vibration that does not involve volumetric changes at each point in the vibrator, so there is no inflow of heat associated with the vibration. Therefore, the heat generated in the vibrator is limited to either the ambient temperature transferred through the vibrator support part or the heat caused by infrared irradiation. If the former can be canceled, it is possible to detect small amounts of infrared rays based on the heat generated in the vibrator.

[0188] Furthermore, compared to the resonant frequency of bending vibration, the resonant frequency of torsional vibration is insensitive to changes in the axial stress of the beam. There is a method in which the axial stress of the resonator changes due to heat generated in the resonator by infrared irradiation, and this is captured as a change in the resonant frequency of bending vibration. However, since the axial stress of the resonator as a beam is highly dependent on the manufacturing process, it is difficult to mass-produce MEMS resonators with the same axial stress. In this respect, the MEMS resonator 500x4 using torsional vibration as in this embodiment is insensitive to both variations in axial stress during the manufacturing process and changes in axial stress due to temperature changes.

[0189] For this reason, as in the present embodiment, the temperature change of the oscillator 501x ​​due to infrared absorption is taken as a change in the Q value, and the change in the Q value is expressed as a difference frequency f H -f L This embodiment is suitable for mass-producing MEMS resonators 500x4 with uniform quality.

[0190] In the following, modified examples of an infrared sensor using the MEMS resonator 500x4 will be described. In the following modified examples, the basic configurations of the infrared sensor and the MEMS resonator 500x4 of the infrared sensor in the fourth embodiment are similar, so the same reference numerals will be used for the basic configurations of the infrared sensor and the MEMS resonator 500x4 of the infrared sensor in the following modified examples, and the description will be omitted as appropriate. Note that, although the following modified examples use the MEMS resonator 500x4, any MEMS resonator in the present embodiment may be used.

[0191] <Variation 1> FIG. 18 is a block diagram showing the configuration of an infrared sensor array in a first modification of the fourth embodiment, and an explanatory diagram of a symbolized capacitive MEMS resonator 500x4. FIG. 18 shows an infrared sensor array in which a plurality of capacitive MEMS resonators 500x4 are arranged in an array. The electrical connection to the capacitive MEMS resonators 500x4 in FIG. 18 has a two-port configuration, and a frequency-swept excitation signal is applied to the electrodes 502x of all the MEMS resonators 500x4. A bias DC voltage Vp is applied to each of the oscillators 501x ​​of the plurality of MEMS resonators 500x4, and the oscillators are excited in a nonlinear resonance region. The multiplexer 601 sequentially changes the columns to be selected to obtain infrared power information incident from all the arrayed MEMS resonators 500x4. Of the displacement currents (vibration state information signals) caused by the resonance of each vibrator 501x, only output signals (Out1, Out2, etc.) from columns C1, C2, etc. selected via MOS switches connected to each electrode 503x by the multiplexer 601 are output from each electrode 503x. The output signals from each electrode 503x selected by the multiplexer 601 are input to the signal processing unit 411, and infrared power information is output from the signal processing unit 411.

[0192] <Variation 2> Fig. 19 is a block diagram showing another configuration of the infrared sensor array in the second modification of the fourth embodiment. In Fig. 19, the bias DC voltage applied to the MEMS resonator 500x4 has a function of turning resonance on and off, so if multiplexer 601 is provided with a bias DC voltage function as shown in Fig. 19 and connected to oscillator 501x, the MOS switch as shown in Fig. 18 provided on the electrode 503x side on the output side of each MEMS resonator 500x4 becomes unnecessary, and the circuit configuration can be simplified.

[0193] FIG. 20 is a diagram showing a method of electrically connecting the capacitive MEMS resonator 500x4.

[0194] Note that the connection configuration of the MEMS resonator 500x4 in Figures 18 and 19 is a two-port configuration as shown in Figure 20a, but the connection configuration is not limited to the two-port configuration and may be a one-port configuration as shown in Figure 20b or a one-port differential output configuration as shown in Figure 20c or 20d. Bias-T in Figure 20 is an element that superimposes a DC voltage Vp on an AC signal.

[0195] In Fig. 20a, a frequency-swept excitation signal is applied to electrode 502x of MEMS resonator 500x4, a bias DC voltage Vp is applied to oscillator 501x, and an output signal is output from electrode 503x. In Fig. 20b, a frequency-swept excitation signal is applied to oscillator 501x ​​of MEMS resonator 500x4, and an output signal is output from electrode 503x. In Fig. 20c, a frequency-swept excitation signal is applied to oscillator 501x ​​of MEMS resonator 500x4, and a differential signal between a signal in which a DC voltage Vp is superimposed via bias-T on the output signal output from electrode 503x and the output signal from electrode 502x1 is output. In FIG. 20d, a frequency-swept excitation signal is applied to oscillator 501x ​​of MEMS resonator 500x4, and a differential signal is output between a signal in which a DC voltage Vp is superimposed via bias-T on the output signal output from electrode 503x, and a signal in which a DC voltage -Vp is superimposed via bias-T on the output signal output from electrode 502x1.

[0196] In addition, the source of the frequency-swept excitation signal is not limited to a digital PLL synthesizer, but may be an analog voltage-controlled oscillator (VCO). In order to associate the discontinuous frequency in the sweep process with time information, it is desirable to use an oscillator that can keep the frequency sweep speed (df / dt) constant with high precision.

[0197] <Action and effect> Next, the function and effect of the infrared sensor according to this embodiment will be described.

[0198] As described above, in the infrared sensor according to the present embodiment, the MEMS resonator 500x4 is a capacitive MEMS resonator. The infrared sensor further includes a thermometer 508x provided on the MEMS resonator 500x4. The MEMS resonator 500x4 acquires its own temperature T based on the thermometer 508x, and the oscillator 501x ​​acquires the temperature T+ΔT when irradiated with infrared rays. The conversion unit 415 calculates a temperature change ΔT based on the temperature measured by the thermometer 508x and the detection value, and determines the infrared power as a physical quantity based on the calculated temperature change ΔT.

[0199] According to this, even if the environmental temperature (ambient temperature) surrounding the MEMS resonator 500 changes, the temperature change ΔT can be obtained based on the temperature measured by the thermometer 508x and the detection value. Therefore, this infrared sensor can perform more accurate infrared power measurement in the MEMS resonator 500x4. As a result, this infrared sensor is less susceptible to the effects of fluctuations in the environmental temperature.

[0200] In this embodiment and the like, the same effects as those in the first embodiment and the like are achieved.

[0201] (Embodiment 5) FIG. 32 is a cross-sectional view of a capacitive MEMS resonator 500x5.

[0202] In the following, since the basic configuration of the MEMS resonator 500x5 of this embodiment is similar to the basic configuration of the MEMS resonator 500x4 of FIG. 16 according to the second, fourth, etc., a description of the basic configuration of the MEMS resonator 500x5 of this embodiment will be omitted as appropriate. The MEMS resonator 500x5 of this embodiment differs from the MEMS resonators of the second embodiment, etc. in that infrared rays are used. Also, the MEMS resonator 500x5 of this embodiment differs from the MEMS resonator of the fourth embodiment, etc. in that a thermometer 508x is not provided, as shown in FIG.

[0203] The resonant sensor of this embodiment is also an infrared sensor using a MEMS resonator 500x4 in which an oscillator 501x ​​absorbs infrared rays irradiated from outside the resonant sensor, causing a change in temperature of the oscillator 501x.

[0204] <Summary> For example, as shown in FIG. 16, when the temperature around the MEMS resonator 500x4, that is, the environmental temperature, changes, the thermometer 508x detects the change in the environmental temperature. At this time, the temperature of the mounting substrate of the MEMS resonator 500x4 also changes. The 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, the f indicated by the star in FIG. 17 is generated depending on the time difference between when the thermometer 508x detects the temperature change and when the temperature change of the oscillator 501x ​​occurs. H -f L In this way, if the distance between thermometer 508x and oscillator 501x ​​of MEMS resonator 500x4 is large, it may be difficult to distinguish whether the temperature change is due to infrared rays or simply a change in the environmental temperature.

[0205] <Temperature sensing method> Therefore, in this embodiment, in order to distinguish between temperature changes caused by infrared rays and changes in the environmental temperature, the following temperature sensing means will be described.

[0206] FIG. 33 is a diagram showing a capacitive MEMS resonator 500x5 and a temperature distribution in its oscillator 501x.

[0207] As shown in Figures 33a and 33b, one longitudinal end of an oscillator 501x ​​of a MEMS resonator 500x5 of this embodiment is supported by one oscillator support part 501x1, and the other longitudinal end is supported by the other oscillator support part 501x1.

[0208] In this MEMS resonator 500x5, as shown in FIG. 33a, when the oscillator 501x ​​is not irradiated with infrared rays, after the environmental temperature changes and a predetermined period of time has elapsed, the temperatures of the silicon substrate 510x, the oscillator 501x, one oscillator support part 501x1, and the other oscillator support part 501x1 become uniform.

[0209] In addition, in this MEMS resonator 500x5, when the oscillator 501x ​​is irradiated with infrared rays, a temperature distribution occurs in the oscillator 501x, as shown in Fig. 33b. This is thought to be because even if the oscillator 501x ​​is irradiated with infrared rays uniformly, the heat generated inside the oscillator 501x ​​is conducted through the oscillator 501x ​​and dissipated from both ends toward the silicon substrate 510x, resulting in a temperature distribution. In Fig. 33b, when the infrared rays are irradiated uniformly, the areas with high temperatures are shown with black hatching, and the size and density of the dots decrease as the temperature decreases from the high temperature area.

[0210] In this embodiment, in order to distinguish between the state of a in Fig. 33 and the state of b in Fig. 33, the temperatures at both ends of the vibrator 501x ​​are regarded as the environmental temperature. This is because, when the environmental temperature changes, as described above, the temperature changes from both ends of the vibrator 501x ​​via the silicon substrate 510x, so the temperatures at both ends of the vibrator 501x ​​are regarded as the environmental temperature. The temperatures at both ends of the vibrator 501x ​​refer to the temperatures at one end of the vibrator 501x ​​and the other end of the vibrator 501x, or the temperatures at one vibrator support part 501x1 and the other vibrator support part 501x1.

[0211] As shown in FIG. 33b, when the vibrator 501x ​​is uniformly irradiated with infrared rays, the temperature is higher in the center of the vibrator 501x ​​than at both ends of the vibrator 501x. In other words, when the vibrator 501x ​​is uniformly irradiated with infrared rays, the same heat flow occurs in the vibrator 501x ​​per unit length in the longitudinal direction, but heat escapes from both ends of the vibrator 501x ​​toward the silicon substrate 510x, so heat always flows from the center of the vibrator 501x ​​to both ends, causing a temperature gradient. In other words, a temperature difference occurs from the center of the vibrator 501x ​​to both ends, with the center being the hottest and the temperature decreasing toward the both ends. Conversely, when the infrared sensor detects an object with a lower temperature than itself, infrared rays are emitted from the vibrator 501x, and the temperature is lowest in the center and increases toward the both ends.

[0212] Based on the above description, a distinction is made between temperature changes caused by infrared rays and simple changes in the environmental temperature.

[0213] FIG. 34 shows the environmental temperature information f H and the difference frequency f H -f L 34 is a graph showing the relationship between the frequency f and the difference frequency Δf. The horizontal axis of FIG. 34 represents the environmental temperature information, and the vertical axis represents the difference frequency Δf. The stars in FIG. 34 represent the discontinuous point frequency f H 34 indicates the value of the differential frequency Δf when the temperature of the transducer 501x ​​becomes uniformly the environmental temperature, and Δ in FIG. 34 indicates the amount of deviation from the reference graph when the temperature of the transducer 501x ​​becomes uniformly the environmental temperature.

[0214] The deviation Δ from the reference graph represents the intensity of the irradiated infrared rays.

[0215] Fig. 35 shows a case where the temperature of the oscillator 501x ​​is uniform (when infrared rays are not irradiated) and a case where the oscillator 501x ​​is irradiated with infrared rays. Fig. 35 shows the simulation results when the temperature of the oscillator 501x ​​is uniform and when the oscillator 501x ​​is irradiated with infrared rays.

[0216] 35, one end of the vibrator 501x ​​is connected to one vibrator support section 501x1 and does not vibrate. The other end of the vibrator 501x ​​is connected to the other vibrator support section 501x1 and does not vibrate. The vibrator 501x ​​vibrates at a portion other than the portion connected to the vibrator support section 501x1.

[0217] 35a shows a state where the oscillator 501x ​​is not irradiated with infrared rays, and the temperature distribution of the oscillator 501x ​​is uniform and the same value as the environmental temperature. When the environmental temperature is 24.79°C, the resonance frequency of the oscillator 501x ​​is 20.66467MHz. In this case, the spring constant of the oscillator 501x ​​has changed by -40.6ppm compared to the case of the oscillator 501x ​​having a uniform temperature distribution at an environmental temperature of 24.00°C.

[0218] In Fig. 35b, the oscillator 501x ​​is irradiated with infrared rays, and a heat flow is generated from inside the oscillator 501x ​​to generate a temperature distribution. In this case, if the temperatures at both ends of the oscillator 501x ​​are the environmental temperature of 24.00°C, the temperature increases from the both ends toward the center, and the center is 25.58°C. The spring constant of the oscillator 501x ​​at this time has changed by -53.5 ppm compared to the oscillator 501x ​​with a uniform temperature distribution at an environmental temperature of 24.00°C.

[0219] This is believed to be because the temperature of oscillator 501x ​​increases due to infrared irradiation, softening oscillator 501x. At this time, oscillator 501x ​​in Fig. 35b has a lower spring constant than oscillator 501x ​​in Fig. 35a, so the vibration amplitude tends to be larger.

[0220] Next, the relationship between the change in resonance frequency and the average temperature of the oscillator 501x ​​will be described with reference to FIG. 36. FIG. 36 is a diagram showing the relationship between the change in resonance frequency and the average temperature of the oscillator 501x. The vertical axis of FIG. 36 is the change in resonance frequency, and the horizontal axis is the average temperature of the oscillator 501x. The thick solid line in FIG. 36 shows a reference line (an example of a reference value related to temperature) in the absence of heat radiation (for example, in the absence of infrared radiation). The solid line with circular dots shows a case in which heat radiation occurs when the environmental temperature is 24.0°. The solid line with triangular dots shows a case in which heat radiation occurs when the environmental temperature is 24.5°. The solid line with square dots shows a case in which heat radiation occurs when the environmental temperature is 25.0°. Here, the average temperature is the overall average temperature in the case of the oscillator 501x ​​with a temperature distribution. The reference line in the absence of heat radiation is a value obtained by measuring in advance.

[0221] Point R1 on the reference line in FIG. 36 corresponds to the state shown in FIG. 35a where there is no infrared irradiation, the temperature of the vibrator 501x ​​is uniform at the same value as the environmental temperature of 24.79°C, and the resonant frequency is 20.66467MHz. Even when the resonant frequency of the above-mentioned vibrator 501x ​​is the same 20.66467MHz, a difference ΔT occurs in the average temperature of the vibrator 501x ​​with respect to point R1 on the reference line at the solid line with circle dots, the solid line with triangular dots, and the solid line with square dots. For example, when the resonant frequency is 20.66467MHz, a difference ΔT occurs in the average temperature of the vibrator 501x ​​with respect to point R1 on the reference line at point R2 on the solid line with circle dots. Point R2 corresponds to the state shown in FIG. 35b where both ends of the vibrator 501x ​​are at the environmental temperature of 24.00°C, and the temperature at the center of the length of the vibrator 501x ​​rises to 25.58°C due to infrared irradiation.

[0222] Next, the relationship between the spring constant and the resonant frequency will be described with reference to FIG. 37. FIG. 37 is a diagram showing the relationship between the spring constant and the change in the resonant frequency. The vertical axis of FIG. 37 is the spring constant, and the horizontal axis is the change in the resonant frequency. The thick dashed dotted line in FIG. 37 indicates the case where there is no heat radiation (for example, when there is no infrared radiation, the heat generated per unit volume inside the resonator 501x ​​is 0 nW / um. 3) is the baseline. The dashed line shows the difference from the baseline of -100nW / um 3 , -50nW / um 3 , 50nW / um 3 , 100nW / um 3 , 150nW / um 3 , 200nW / um 3 The dashed line above the reference line indicates a case where the temperature of the vibrator 501x ​​has decreased, and the dashed line below the reference line indicates a case where the temperature of the vibrator 501x ​​has increased. The circular points indicate a case where there is heat radiation when the environmental temperature is 24.0° (for example, when there is infrared radiation). The triangular points indicate a case where there is heat radiation when the environmental temperature is 24.5°. The square points indicate a case where there is heat radiation when the environmental temperature is 25.0°.

[0223] In Fig. 37, for example, when looking at the change in resonance frequency at -20 ppm, even with the same resonance frequency, there are differences in the spring constant at the circle points, triangle points, and square points compared to point P1 on the dashed-dotted reference line. For example, when the change in resonance frequency is -20 ppm, there is a difference in the spring constant at circle point P2 compared to point P1 on the reference line.

[0224] From this, it can be seen that even if the resonant frequencies are the same, if there is a difference in the spring constant of the oscillator 501x, the differential frequency Δf also becomes larger. In other words, if it is found that a temperature distribution occurs in the oscillator 501x ​​(there is a temperature gradient), it can be determined that infrared rays are irradiating the oscillator 501x. Therefore, it becomes possible to distinguish whether the temperature change is due to infrared rays or simply due to a change in the environmental temperature. As a result, it is possible to detect a temperature change due to infrared rays without adding a thermometer 508x on the mounting board as shown in FIG. 16. In other words, the MEMS resonator 500x5 can obtain infrared power information.

[0225] The infrared detection sensitivity may be improved by resonating the bias voltage Vp between the oscillator 501x ​​and the electrode of the MEMS resonator 500x5 at a larger value (the method of applying the bias voltage is shown in FIG. 20). In this case, the nonlinear resonance curve shown in FIG. 29 leans more to the left, improving the conversion ratio from the minute change in the spring constant due to irradiation to the differential frequency Δf. In this way, the differential frequency f between P1 and P2 in FIG. H -f L = A difference in δf of 3.7 Hz was obtained.

[0226] <Action and effect> Next, the function and effect of the infrared sensor according to this embodiment will be described.

[0227] As described above, in the infrared sensor according to the present embodiment, the MEMS resonator 500x5 is a capacitive MEMS resonator. The physical quantity determination unit (conversion unit 415) calculates the temperature change ΔT based on the reference value (included in the reference line) related to temperature and the detected value, and determines the infrared power as a physical quantity based on the calculated temperature change ΔT.

[0228] According to this, it is possible to determine that the oscillator 501x ​​is irradiated with infrared rays based on the temperature distribution generated in the oscillator 501x ​​without adding a thermometer. Therefore, with this infrared sensor, it is possible to suppress an increase in manufacturing costs.

[0229] Furthermore, even if the environmental temperature (ambient temperature) surrounding the MEMS resonator 500x5 changes, the physical quantity being handled is the temperature distribution in an extremely limited, minute space called the resonator, and therefore this infrared sensor is less susceptible to the effects of fluctuations in the environmental temperature.

[0230] (Other variations) Although the present disclosure has been described above based on the first to fifth embodiments, the present disclosure is not limited to these first to fifth embodiments.

[0231] In the resonance sensors according to the first to fifth embodiments described above, the vibrator of the resonance sensor is not limited to a doubly supported beam. The vibrator may have various shapes such as a cantilever type, a disk type, a ring type, and a square type. Any of these types of vibrators may be used as the vibrator of the MEMS resonator of the resonance sensor. The vibration mode excited in the vibrator of the MEMS resonator by inputting an excitation signal may be any vibration mode such as a flexural vibration mode or a torsional vibration mode. In addition, the manufacturing method of the MEMS resonator is not limited to a method using an SOI substrate.

[0232] In the resonant sensors according to the first to fifth embodiments described above, the vibration state information signal is not limited to a signal derived from a displacement current flowing with a change in capacitance. FIG. 21 is a diagram showing an output example of a vibration state information signal (vibration velocity information signal). In FIG. 21, the vibration velocity of the vibrator 501 is optically detected, and a signal of the vibration velocity information of the vibrator 501 is output as vibration state information. In the resonant sensor of FIG. 21, a Doppler interferometer 418 (velocity meter) is further provided to detect the vibration velocity of the vibrator 501. Information on 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 according to the first to fifth embodiments described above, the vibration state information signal is a signal including information on the vibration velocity of the vibrator 501. According to this, the resonant sensor can detect the vibration velocity of the vibrator 501. Although the vibration velocity is a signal that is 90 degrees out of phase with the vibration amplitude, the resonance curve shows similar characteristics to those in Figures 29 and 30, so it is possible to sense physical quantities using discontinuities in the vibration velocity information in the frequency sweep.

[0233] In the resonance type sensor according to the first to fifth embodiments described above, the vibration state information signal may be information regarding the deflection of the vibrator 501. The resonance type sensor in FIG. 22 includes a laser light source 419. In the resonance type sensor, the laser light source 419 irradiates the vibrator 501 of the MEMS resonator 500 with a laser beam, and the reflected laser beam is received by a four-segment photodiode to detect the deflection angle of the vibrator 501. In the resonance type sensor, the degree of deflection (deflection angle) of the vibrator 501 is detected by the four-segment photodiode, and information on the detected deflection angle is output to the signal processing unit 411 as a vibration state information signal (deflection angle information signal). Note that the number of divisions of the photodiode for detecting the deflection angle of the vibrator is not limited to four, and may be three or less, or five or more. In the resonance type sensor, a photodiode divided into an arbitrary number of parts can be used as a photodiode for detecting the deflection angle of the vibrator.

[0234] In the resonant sensors according to the first to fifth embodiments described above, the vibration state information signal to be input to the signal processing unit is not limited to the amplitude information signal of the vibrator. The vibration state information signal may include information that adequately reflects the characteristics of the vibration motion of the vibrator (such as the amplitude and speed of vibration).

[0235] In addition, the resonant sensors according to the first to fifth embodiments described above are effective not only for nonlinear phenomena caused by capacitive bifurcation, which exhibits a resonant characteristic such as the resonant characteristic 121 in Fig. 29, but also for nonlinear phenomena caused by mechanical bifurcation, which exhibits a resonant characteristic such as the resonant characteristic 131 in Fig. 30. The discontinuous point frequency f H f L , the discontinuity frequency f L f HMechanical bifurcation is a phenomenon in which the resonance curve inclines toward higher frequencies as shown in resonance characteristic 131 in FIG. 30 due to the nonlinear springiness of the vibrator. The nonlinear springiness of the vibrator is a phenomenon that occurs when the vibration amplitude is relatively large. In a configuration in which electrodes are arranged opposite the vibrator so as to inhibit vibration, such as capacitive MEMS resonators 100 and 500 shown in FIG. 27A and FIG. 1B, the nonlinear effect of capacitive bifurcation exceeds the nonlinear effect of mechanical bifurcation, so the nonlinearity shown in FIG. 30 is generally unlikely to occur.

[0236] In addition, in the resonant sensor according to the first to fifth embodiments described above, as shown in FIG. 23, a cantilever 801 as a vibrator and a vibrator support section 801s are formed, and the vibrator support section 801s is fixed to a substrate section (not shown). FIG. 23 is a perspective view showing a configuration of a non-capacitive MEMS resonator 800. In FIG. 23, a non-capacitive MEMS resonator 800 (a non-capacitive MEMS resonator) is used to generate mechanical bifurcation. A piezoelectric element 802 is mounted on the MEMS resonator 800 near the end of the cantilever 801 on the vibrator support section 801s side. An excitation signal is applied to the piezoelectric element 802. As a result, the cantilever 801 performs a vibration motion according to the excitation signal. The laser light irradiated from the laser light source 803 and reflected by the cantilever 801 is received by a four-division photodiode 804. The four-part photodiode 804 detects the deflection angle of the cantilever 801 caused by vibration and outputs it to the signal processing unit 411 as a deflection angle information signal. The deflection angle information signal is input to the signal processing unit 411 as a vibration state information signal. The number of divisions of the photodiode 804 for detecting the deflection angle of the cantilever 801 is not limited to four, and may be three or less, or five or more. A photodiode divided into an arbitrary number of parts can be used as the photodiode 804 for detecting the deflection angle of the cantilever 801. In the MEMS resonator 800 having such a configuration, when the amplitude of the cantilever 801 increases, a nonlinear effect due to mechanical bifurcation appears. Therefore, the resonance characteristic curves to the right (towards the high frequency side) as shown by the resonance characteristic 131 in FIG. 30. In the resonant sensor according to the first to fifth embodiments described above, the MEMS resonator 800 is a non-capacitive MEMS resonator. The frequency f is the two discontinuously changing frequencies of the vibration state information signal. H and frequency f L is a frequency higher than the resonant frequency f0 of the resonator. In this way, using a non-capacitive MEMS resonator, it is possible to perform sensing with higher accuracy.

[0237] In addition, in the resonant sensors according to the above-described first to fifth embodiments, in FIG. 23, a piezoelectric element 802 is used as an element that applies strain to the oscillator 801 in accordance with an excitation signal, but the element that applies strain is not limited to the piezoelectric element 802. For example, the element that applies strain may be a magnetostrictive element. Furthermore, the oscillator 801 is not limited to the cantilever beam 801, but may be a doubly supported beam. In that case, the oscillator 801 can be excited by the Lorentz force by inputting an AC current to the doubly supported beam and applying an external static magnetic field so as to penetrate the beam.

[0238] In addition, in the resonant sensors according to the above-described first to fifth embodiments, optical excitation by the photothermal effect can be used. By concentrating a flickering laser beam and irradiating a spot on the oscillator, the spot on the oscillator is heated, causing distortion, and exciting the oscillator.

[0239] In the resonant sensors according to the first to fifth embodiments described above, the method of generating and outputting the vibration state information signal is not limited to the method using a four-segment photodiode. For example, if a piezoresistance element or a piezoelectric element formed on the vibrator is used, the strain caused by the vibration of the vibrator can be output as a change in an electrical signal.

[0240] In addition, the pressure sensor for fluid pressure and pressing pressure as the resonant sensor according to the third embodiment described above is configured to detect a force that changes the gap between the vibrator and the electrode, but is not limited to such a sensor type that detects a force acting on the electrode side, and is also effective for a type that applies a force to the vibrator side and reads the force. The capacitive MEMS resonator 500 of FIG. 1B can also be connected as in FIG. 1A to detect the Coriolis force. FIG. 24 is an explanatory diagram of the Coriolis force acting on the vibrator. In FIG. 24a, a cross section of the vibrator and the electrode is shown in schematic form, and an excitation signal that has been frequency swept so that nonlinear resonance occurs in the lateral bending vibration mode of the vibrator is input to the resonator. When a rotational angular velocity is applied in the axial direction of the vibrator, a Coriolis force acts upward on the cross section of the vibrator. The Coriolis force is perpendicular to the excitation direction, but the displacement due to the Coriolis force brings the inclined gap distance between the side of the vibrator and the electrode very close to a small amount. This changes the extension of the slope of the nonlinear resonance curve, so that the Coriolis force can be detected from the frequency of the discontinuity of the vibration state information signal. It functions as an angular velocity sensor by converting the Coriolis force into the angular velocity applied to the vibrator. Fig. 24b shows a configuration for detecting the velocity applied to the vibrator using the same principle as Fig. 24a. A frequency-swept excitation signal is input to the MEMS resonator so that the vibrator exhibits nonlinear resonance in torsional vibration mode. When velocity is applied in the horizontal direction perpendicular to the axial direction of the vibrator, a Coriolis force acts upward on the cross section of the vibrator. The Coriolis force is perpendicular to the excitation direction, but the displacement due to the Coriolis force slightly narrows the inclined gap between the side of the vibrator and the electrode (bringing the side of the vibrator and the electrode closer together). This changes the extension of the slope of the nonlinear resonance curve, so that the Coriolis force can be detected from the frequency of the discontinuity of the vibration state information signal. This resonance sensor functions as a velocity sensor by converting the Coriolis force into the velocity applied to the vibrator. In the resonant sensor according to the third embodiment described above, a rotation speed perpendicular to the vibration direction of the vibration mode swept by the sweep unit is applied to the vibrator. The conversion unit obtains a Coriolis force perpendicular to both the vibration mode swept by the sweep and the rotation speed based on the detection value, and determines the rotation speed as the physical quantity based on the obtained Coriolis force.According to this, the Coriolis force can be obtained using a capacitive MEMS resonator. Therefore, by converting the Coriolis force into the angular velocity applied to the vibrator, the resonant sensor can be used as an angular velocity sensor. In the resonant sensor according to the above-described third embodiment, a velocity perpendicular to the vibration direction of the torsional vibration mode caused by the sweep by the sweep unit is applied to the vibrator. The physical quantity determination unit obtains the Coriolis force perpendicular to both the torsional vibration mode caused by the sweep and the velocity based on the detection value, and determines the velocity as the physical quantity based on the obtained Coriolis force. This also provides the same effects as those described above.

[0241] In the resonant sensor according to the first to fifth embodiments described above, the amplitude of the vibration state information signal is detected by the detector 413 in the signal processing unit 411 in FIG. 2, but the amplitude information may be extracted by synchronous detection. In the resonant sensor in FIG. 25, a signal having the same frequency and phase as the excitation signal is sent from the sweep unit 401 to the detector 413 as a reference signal, and synchronous detection is performed. FIG. 25 is a block diagram showing the configuration of a capacitive MEMS resonator 500 using synchronous detection. Note that, when synchronous detection is performed, not only the amplitude of the vibration state information signal but also phase information (amount of phase shift from the reference signal) can be extracted. FIG. 26 is a diagram showing the amplitude information, phase information, and discontinuity of the vibrator obtained by synchronous detection. In FIG. 26, the amplitude information and phase information obtained by phase detection are shown. Point A in FIG. 26 is a discontinuity obtained by sweeping the frequency upward, and the frequency at that time is f H Point B is the discontinuous point obtained by sweeping the frequency downward, and the frequency at that point is f L The phase information is also L and f H Since the phase signal changes sharply and discontinuously at f L and f H may be detected. [Industrial Applicability]

[0242] A resonant sensor using the MEMS resonator of the present disclosure can be used as a temperature sensor, a gas concentration sensor, a fluid pressure sensor, a pressure sensor, an infrared sensor, a speed sensor, an angular acceleration sensor, and the like. [Explanation of symbols]

[0243] 400, 400a Temperature Sensor 401 Sweeping section 402 PLL Synthesizer 411 Signal Processing Unit 412 Discontinuity detection unit 413 Detector 414 Threshold detection unit 415 Conversion Unit 416 Controller (measurement range switching control unit) 500, 500x, 500x3, 500x4, 500x5 Capacitive MEMS resonators 501, 501x ​​Transducers 502, 503, 502x, 503x electrode 505x Diaphragm (transmission part) 506x Pillar (transmission part) 508x thermometer 800 Non-capacitive MEMS resonators 801 Transducer (cantilever beam)

Claims

1. A resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator, A MEMS resonator; a sweep unit that sweeps a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction and outputs the swept excitation signal to the MEMS resonator; a detection unit that acquires a vibration state information signal, which is a feature representing a vibration state of the vibrator based on the excitation signal, from the MEMS resonator, and detects a frequency of the excitation signal or a time corresponding to the frequency when the acquired vibration state information signal discontinuously changes; a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected value, the detection unit determines, as a detection value, a difference between at least two frequencies of the excitation signal including a frequency at which the vibration state information signal changes discontinuously in the sweep and a frequency at which the vibration state information signal changes discontinuously in a sweep in a direction opposite to the sweep direction; Resonant type sensor.

2. A resonant sensor using a MEMS (Micro-Electro Mechanical Systems) resonator, A MEMS resonator; a sweep unit that sweeps a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction and outputs the swept excitation signal to the MEMS resonator; a detection unit that acquires a vibration state information signal, which is a feature representing a vibration state of the vibrator based on the excitation signal, from the MEMS resonator, and detects a frequency of the excitation signal or a time corresponding to the frequency when the acquired vibration state information signal discontinuously changes; a physical quantity determination unit that determines a physical quantity acting on the MEMS resonator based on the detected value, The vibrator is surrounded by a gas in a space in which the vibrator is disposed, the gas gradually becoming equal to a pressure acting on the MEMS resonator; the physical quantity determination unit determines the pressure of the gas as the physical quantity based on the detection value. Resonant type sensor.

3. the sweep unit repeats an operation of switching the sweep in a reverse direction using a detection of a discontinuous change in the vibration state information signal in the sweep as a starting point, and switching the sweep in a reverse direction again using a detection of a discontinuous change in the vibration state information signal as a starting point again, the detection unit outputs a pulse signal having two values ​​representing two states of a forward direction and a reverse direction in the sweep direction as a detection value; the physical quantity determination unit determines a physical quantity acting on the MEMS resonator based on a pulse time width of the pulse signal that is the output detection value. The resonant sensor according to claim 1 .

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

5. the capacitive MEMS resonator includes a vibrator, an electrode disposed across a gap from the vibrator, and a transmission unit that changes the size of the gap in response to a pressure acting on the capacitive MEMS resonator; the physical quantity determination unit determines pressure as the physical quantity based on the size of the gap.

5. The resonant sensor according to claim 4.

6. the MEMS resonator is a capacitive MEMS resonator, Further, a thermometer is provided in the MEMS resonator, The MEMS resonator acquires its own temperature T based on the thermometer; The transducer acquires a temperature T+ΔT when irradiated with infrared light, the physical quantity determination unit determines a temperature change ΔT based on the temperature measured by the thermometer and the detection value, and determines infrared power as the physical quantity based on the determined temperature change ΔT.

5. The resonance type sensor according to claim 1, 3 or 4.

7. the MEMS resonator is a capacitive MEMS resonator, the physical quantity determination unit determines a temperature change ΔT based on a reference value related to temperature and the detected value, and determines infrared power as the physical quantity based on the determined temperature change ΔT.

5. The resonance type sensor according to claim 1, 3 or 4.

8. A rotation speed perpendicular to a vibration direction of a vibration mode caused by the sweeping by the sweeping unit is applied to the vibrator, the physical quantity determination unit determines a Coriolis force perpendicular to both the vibration mode by the sweep and the rotation speed based on the detected value, and determines the rotation speed as the physical quantity based on the determined Coriolis force.

5. The resonance type sensor according to claim 1, 3 or 4.

9. The vibrator is applied with a velocity perpendicular to a vibration direction of a torsional vibration mode caused by the sweeping of the sweeping unit, the physical quantity determination unit determines a Coriolis force perpendicular to both the torsional vibration mode and the velocity due to the sweep based on the detected value, and determines the velocity as the physical quantity based on the determined Coriolis force.

5. The resonance type sensor according to claim 1, 3 or 4.

10. The vibration state information signal is a signal including information regarding the vibration amplitude of the vibrator. The resonance type sensor according to claim 1 .

11. The vibration state information signal is a signal including information regarding the vibration velocity of the vibrator. The resonance type sensor according to claim 1 .

12. the MEMS resonator is a non-capacitive MEMS resonator, and the first and second frequencies, which are the two frequencies at which the vibration state information signal changes discontinuously, are higher than a resonant frequency of the vibrator; The resonance type sensor according to claim 3 .

13. a measurement range switching control unit that increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that there is no frequency at which the vibration state information signal changes discontinuously within the sweep frequency range of the excitation signal; The resonant sensor according to claim 1 .

14. a measurement range switching control unit that increases the intensity of the excitation signal by a predetermined amount when the detection unit determines that the difference between the two frequencies at which the vibration state information signal discontinuously changes is smaller than a predetermined value; The resonant sensor according to claim 1 .

15. A detection method for a resonant sensor using a MEMS resonator, comprising: Sweeping a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction, and outputting the swept excitation signal to the MEMS resonator; acquiring a vibration state information signal, which is a feature representing a vibration state of the vibrator based on the excitation signal, from the MEMS resonator, and detecting a frequency of the excitation signal or a time corresponding to the frequency when the acquired vibration state information signal discontinuously changes; determining a physical quantity acting on the MEMS resonator based on the detected value; and determining as a detection value a difference between at least two frequencies of the excitation signal including a frequency at which the vibration state information signal discontinuously changes in the sweep and a frequency at which the vibration state information signal discontinuously changes in a sweep in a direction opposite to the sweep direction. A detection method for a resonance type sensor.

16. A detection method for a resonant sensor using a MEMS resonator, comprising: Sweeping a frequency of an excitation signal of an oscillator of the MEMS resonator along a predetermined sweep direction, and outputting the swept excitation signal to the MEMS resonator; acquiring a vibration state information signal, which is a feature representing a vibration state of the vibrator based on the excitation signal, from the MEMS resonator, and detecting a frequency of the excitation signal or a time corresponding to the frequency when the acquired vibration state information signal discontinuously changes; determining a physical quantity acting on the MEMS resonator based on the detected value; The vibrator is surrounded by a gas in a space in which the vibrator is disposed, the gas gradually becoming equal to a pressure acting on the MEMS resonator; determining a pressure of the gas as the physical quantity based on the detected value; A detection method for a resonance type sensor.

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