A resonant temperature sensor based on a two-degree-of-freedom resonator and a preparation method thereof

Abstract

This invention discloses a resonant temperature sensor based on a two-degree-of-freedom resonator and its fabrication method. The disclosed sensor includes anchor points and two resonators, which are weakly coupled together by a coupling structure. The two-degree-of-freedom resonator system is fixed to four anchor points. The two resonators vibrate at their resonant frequencies with equal amplitudes. When the external temperature changes, the difference in thermal expansion coefficients between the sensor and the substrate material causes the anchor points to move, increasing the stress on one of the resonators. This stress causes a change in the stiffness of one of the resonators. The stress-relieving structure of the other resonator eliminates the stress generated by the anchor point movement, thus leaving its stiffness unaffected. The external temperature can then be obtained by detecting the amplitude ratio of the two resonators.

Description

Technical Field

[0001] This invention relates to the field of temperature sensor technology, specifically to a resonant temperature sensor based on a two-degree-of-freedom resonator. Background Technology

[0002] Temperature sensors are widely used, and accurate temperature measurement is a crucial task in production and scientific research. Traditional temperature measurement methods employ platinum resistance thermometers, thermistors, thermocouples, and silicon-based integrated temperature sensors. Platinum resistance thermometers are the most commonly used resistive temperature sensors. While they offer good linearity, repeatability, stability, and a wide temperature range, they are not convenient for integrated manufacturing. Resistors made of semiconductor compound materials such as nickel, manganese sulfides, and selenides exhibit high temperature nonlinearity and are incompatible with integrated circuit (IC) processes. Thermocouple temperature measurement requires a constant reference temperature environment (reference temperature point). Integrated temperature sensors using thermistors or transistors as the sensing core, although manufactured using silicon-based processes and fully compatible with IC processes, have a narrow temperature measurement range (-50 to 120°C), typically used for on-chip temperature monitoring, and cannot measure temperatures below -50°C. These temperature sensors, along with thermocouples, are not suitable for measuring ambient temperatures, especially meteorological temperatures.

[0003] The output signal of a resonant temperature sensor based on a two-degree-of-freedom resonator is a frequency signal. This not only facilitates the digitization of secondary instruments but also improves the sensor's anti-interference capability and enables long-distance transmission. Applying it to high-precision testing systems can save on analog-to-digital converters, simplify the system, and improve its accuracy and reliability. Therefore, resonant temperature sensors based on two-degree-of-freedom resonators have gained attention and application due to their high resolution and frequency signal output.

[0004] However, current resonant temperature sensors based on two-degree-of-freedom resonators are mainly based on quartz materials. Due to the anisotropic nature of quartz and the fact that they only use the temperature effect of quartz vibration frequency as the detection principle, their accuracy depends on the cutting shape of the quartz crystal, i.e., the precision of the cutting. Furthermore, their processing technology is incompatible with micromechanical (MEMS) technology, so this method has not yet been applied to micromechanical devices. Summary of the Invention

[0005] In view of the defects or deficiencies of the prior art, the present invention provides a resonant temperature sensor based on a two-degree-of-freedom resonator.

[0006] To this end, the present invention provides a resonant temperature sensor based on a two-degree-of-freedom resonator, comprising a substrate, wherein two first anchor points, two second anchor points, and a driving electrode are provided on the substrate;

[0007] The first anchor point and the second anchor point have the same structure; the first straight line where the two first anchor points are located is parallel to the second straight line where the two second anchor points are located, and the driving electrode is located between the two straight lines;

[0008] A first resonator is provided between the two first anchor points, and a second resonator is provided between the two second anchor points; a coupling structure is provided between the first resonator and the second resonator.

[0009] The first resonator includes a first detection capacitor, a first mass block, a first resonant beam, and two stress relief structures; the second resonator includes a second detection capacitor, a second mass block, and a second resonant beam.

[0010] The first resonator has two stress relief structures connected to two first anchor points respectively. The first detection capacitor, the first mass block and the first resonant beam are located between the two stress relief structures, and the first resonant beam is connected to the two stress relief structures. The stiffness of the stress relief structure along the direction of the first straight line is less than the stiffness along the direction perpendicular to the first straight line.

[0011] The second resonator's second resonant beam is connected to the second anchor point at both ends;

[0012] Meanwhile, the first detection capacitor, the first mass block, and the first resonant beam of the first resonator and the second detection capacitor, the second mass block, and the second resonant beam of the second resonator are symmetrically arranged with respect to the driving electrode, and the driving electrode is located between the first mass block and the second mass block.

[0013] The coupling structure is connected to the first resonant beam and the second resonant beam. The stiffness of the coupling structure is less than the stiffness of the first resonator and also less than the stiffness of the second resonator.

[0014] An alternative is that both the first anchor point and the second anchor point are square.

[0015] An alternative approach is to connect stress relief structures to both ends of the first resonant beam, and to provide a first mass block in the middle of the first resonant beam, with the first detection capacitor located on one side of the first mass block.

[0016] The second resonant beam is connected to the second anchor point at both ends, and a second mass block is provided in the middle of the second resonant beam. The second detection capacitor is located on one side of the second mass block.

[0017] An alternative approach is that the first mass block is a rectangular structure; the first detection capacitor is a rectangular structure; the second mass block is a rectangular structure; and the second detection capacitor is a rectangular structure.

[0018] Alternatively, the stress relief structure can be a hollow rectangular structure.

[0019] This invention also provides a method for fabricating the above-mentioned resonant temperature sensor based on a two-degree-of-freedom resonator, characterized in that the fabrication method includes the following steps:

[0020] 1) Apply resist and perform photolithography on the front side of the SOI silicon wafer;

[0021] 2) The SOI silicon wafer is etched to form the first resonator, the second resonator, two first anchor points, two second anchor points, the coupling structure and the driving electrode, and the photoresist is removed;

[0022] 3) Remove the silicon dioxide layer that is connected to the bottom of the first resonator, the second resonator, and the coupling structure.

[0023] The resonant temperature sensor based on a two-degree-of-freedom resonator of the present invention greatly improves the sensitivity and detection accuracy of the resonant temperature sensor based on a two-degree-of-freedom resonator through the energy concentration effect of the two-degree-of-freedom resonator.

[0024] The present invention proposes a resonant temperature sensor based on a two-degree-of-freedom resonator, comprising anchor points and two resonators. The two resonators are weakly coupled together by a coupling structure, and the two-degree-of-freedom resonator system is fixed at four anchor points. The two resonators vibrate at their resonant frequencies, and the amplitudes of the two resonators are equal. When the external temperature changes, the difference in the thermal expansion coefficients between the sensor and the substrate material causes the anchor points to move, thereby increasing the stress on one of the resonators. This stress causes a change in the stiffness of one of the resonators. The stress relief structure of the other resonator eliminates the stress generated by the movement of the anchor points, thus the stiffness of that resonator remains unaffected.

[0025] Therefore, the stiffness of the two resonators changes differently. This change in stiffness causes an energy concentration effect in the two-degree-of-freedom resonator system, resulting in unequal amplitudes of the two resonators. The magnitude of the external temperature can be obtained by detecting the amplitude ratio of the two resonators. Furthermore, the output sensitivity based on the amplitude ratio is significantly improved compared to frequency output. Therefore, the temperature sensor proposed in this invention has extremely high sensitivity compared to traditional resonant temperature sensors based on two-degree-of-freedom resonators. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the degree-of-freedom resonator system in Embodiment 2 of the present invention.

[0027] Figure 2 This is the temperature response output by the temperature sensor in this embodiment of the invention, based on the frequency and amplitude ratio.

[0028] Figure 3 The following is a flowchart of the fabrication process of the temperature sensor of the present invention. (a), (b), and (c) are schematic diagrams of each process step in turn. Detailed Implementation

[0029] Unless otherwise stated, the terms or methods in this document are based on the understanding of those skilled in the art or implemented using existing methods.

[0030] like Figure 1 As shown, the resonant temperature sensor based on a two-degree-of-freedom resonator of the present invention includes a substrate, on which two first anchor points 5, two second anchor points 6 and a driving electrode 3 are provided;

[0031] Among them, the first anchor point 5 and the second anchor point 6 have the same structure, such as their cross-section being square or other square structures; the two first anchor points are located on a straight line (also referred to as the first straight line in this article), and the two second anchor points are located on another straight line (also referred to as the second straight line in this article), and the two straight lines are parallel; the driving electrode is located between the two straight lines.

[0032] A first resonator 1 is provided between two first anchor points, with its two ends respectively connected to the first anchor points. A second resonator 2 is provided between two second anchor points, with its two ends respectively connected to the second anchor points. Both resonators include a detection capacitor for amplitude detection, a resonant beam, and a mass block. The first resonator also includes two stress relief structures. The stiffness of both the first and second resonators is greater than the stiffness of the coupling structure.

[0033] The two stress relief structures of the first resonator are respectively connected to the two first anchor points. The first detection capacitor, the first mass block and the first resonant beam are located between the two stress relief structures, and the first resonant beam is connected to the two stress relief structures. The stiffness of the stress relief structure along the direction of the first straight line is less than the stiffness along the direction perpendicular to the first straight line.

[0034] Meanwhile, the first detection capacitor, the first mass block, and the first resonant beam of the first resonator and the second detection capacitor, the second mass block, and the second resonant beam of the second resonator are symmetrically arranged with respect to the driving electrode, and the driving electrode is located between the first mass block and the second mass block.

[0035] In addition, a coupling structure 4 is provided between the first resonator and the second resonator, and the coupling structure is connected to the resonant beam of the first resonator and the second resonator.

[0036] The resonant temperature sensor based on a two-degree-of-freedom resonator of this invention can be equivalently represented as a two-degree-of-freedom spring-damped-mass model, and its working principle is as follows:

[0037] A DC voltage is applied to the two-degree-of-freedom resonator through any anchor point (including all first and second anchor points), and an AC voltage is applied to the driving electrode 3. The first resonator 1 and the second resonator 2 are electrostatically driven through the driving electrode 3.

[0038] When the first resonator 1, the second resonator 2 and the driving electrode 3 form a potential difference, an electrostatic force is generated between the driving electrode 3 and the first resonator 1 and the second resonator 2. When the frequency of the applied AC voltage is the same as the resonant frequency of the two-degree-of-freedom resonator (i.e. the first resonator and the second resonator), the two-degree-of-freedom resonator generates a displacement at the resonant frequency under the action of the electrostatic force. The amplitude of the first resonator 1 and the second resonator 2 can be obtained by detecting the output current of the two detection capacitors.

[0039] When the external temperature remains unchanged, the amplitudes of the first resonator 1 and the second resonator 2 are equal.

[0040] When the external temperature changes, due to the difference in the coefficients of thermal expansion between the sensor device layer (usually silicon) and the substrate material (usually alumina), the two materials shrink differently, causing the first and second anchor points to shift relative to the substrate. This displacement leads to the movement of the first anchor point 5 and the second anchor point 6. The movement of the second anchor point 6 directly affects the second resonant beam 2-1, causing a change in its stiffness. Meanwhile, the movement of the first anchor point 1 directly affects the stress relief structure 1-4. The stress relief structure 1-4 has lower stiffness in the direction perpendicular to the direction of the first resonator's movement (which is left-right vibration as shown in the diagram) (i.e., the direction of the first straight line), thus eliminating the stress generated by the first anchor point 5. Therefore, the stiffness of the first resonant beam 1-1 remains unaffected.

[0041] Therefore, when the external temperature changes, only the stiffness of the second resonator 2 changes. When the stiffness of the coupling structure 4 is much smaller than the stiffness of the first resonator 1 and much smaller than the stiffness of the second resonator 2, the change in the stiffness of the second resonator 2 will cause the two-degree-of-freedom resonator to produce an energy concentration effect, resulting in unequal amplitudes of the first resonator 1 and the second resonator 2. The temperature change can be obtained by detecting the amplitude ratio of the first resonator 1 and the second resonator 2.

[0042] Due to the energy concentration effect of the two-degree-of-freedom resonator, the sensitivity of the resonant sensor can be greatly amplified by using the amplitude ratio of the first resonator 1 and the second resonator 2 as the output dimension.

[0043] In some preferred embodiments, the structures of the first resonator and the second resonator are as follows: Figure 1 As shown, the first resonator includes a first resonant beam 1-1, a first mass block 1-2, a first detection capacitor 1-3, and two stress relief structures 1-4. The first mass block is located between two first anchor points and connected to the first resonant beam (i.e., the first mass block is located in the middle of the first resonant beam), and the first detection capacitor is located on one side of the first mass block.

[0044] The second resonator includes a second resonant beam 2-1, a second mass block 2-2, and a second detection capacitor 2-3. The two ends of the second resonant beam are connected to second anchor points, the second mass block is located between the two second anchor points, and the second detection capacitor is located on one side of the second mass block.

[0045] In a further embodiment, the shapes of the first mass block, the first detection capacitor, the second mass block, and the second detection capacitor can be designed as needed, with the principle being to enable the operation of the sensor of the present invention. In the figure, the first mass block, the first detection capacitor, the second mass block, and the second detection capacitor are all rectangular structures.

[0046] In a specific design, the shape of the stress relief structure can be selected to meet the design and functional requirements of the sensor in this invention, such as the hollow rectangular structure shown in the figure.

[0047] Reference Figure 3 The method for fabricating a resonant temperature sensor based on a two-degree-of-freedom resonator according to the present invention includes the following steps:

[0048] (a) Spin-coating photoresist 7 onto the device layer 8 of the SOI silicon wafer and performing photolithography to form the area to be etched, including the first resonator 1, the second resonator 2, the driving electrode 3, the coupling structure 4, the two first anchor points 5 and the two second anchor points 6.

[0049] (b) The device layer 8 of the SOI silicon wafer is etched to form a first resonator 1, a second resonator 2, a driving electrode 3, a coupling structure 4, two first anchor points 5, two second anchor points 6, and the photoresist 7 is removed.

[0050] (c) Remove the silicon dioxide layer 9 below the two-degree-of-freedom resonator system (first resonator, second resonator and coupling structure); specifically, the silicon dioxide layer connected to the two-degree-of-freedom resonator system can be etched with HF solution.

[0051] A specific example of a resonant temperature sensor based on a two-degree-of-freedom resonator is shown in the accompanying drawings. The sensor in this example is fabricated from an SOI silicon wafer and includes a silicon substrate 10 with a thickness of 400 μm and a silicon dioxide layer 9 with a thickness of 4 μm. A first resonator 1, a second resonator 2, a driving electrode 3, a coupling structure 4, two first anchor points 5, and two second anchor points 6 are located in the device layer 8 of the SOI silicon wafer with a thickness of 30 μm.

[0052] Among them, the two first anchor points 5, the two second anchor points 6 and the driving electrode 3 are respectively fixed to the silicon substrate 10 through the silicon dioxide layer 9;

[0053] The first resonator 1 is fixed to two first anchor points 5, and the second resonator 2 is fixed to two second anchor points 6;

[0054] The structures of the first and second resonators are as follows: Figure 1 As shown, the first resonator includes a first resonant beam 1-1, a first mass block 1-2, a first detection capacitor 1-3, and two stress relief structures 1-4. The stress relief structures are connected to both ends of the first resonant beam, and the stress relief structures are connected to the first anchor points. The first mass block is located between the two first anchor points, and the first detection capacitor is located on one side of the first mass block. The first mass block and the first detection capacitor are both rectangular structures. The stress relief structures are hollow rectangular structures.

[0055] The second resonator includes a second resonant beam 2-1, a second mass block 2-2, and a second detection capacitor 2-3, wherein the second mass block and the second detection capacitor are both rectangular structures; the two ends of the second resonant beam are connected to second anchor points, the second mass block is located between the two second anchor points, and the second detection capacitor is located on one side of the second mass block;

[0056] The first and second resonant beams are connected by two coupling structures.

[0057] When the sensor in this embodiment is working, a DC voltage is applied to the first resonator 1 and the second resonator 2 through one of the anchor points, and an AC voltage is applied to the driving electrode 3. When a potential difference is formed between the first resonator 1, the second resonator 2 and the driving electrode 3, an electrostatic force is generated between the driving electrode 3 and the first resonator 1 and the second resonator 2. When the frequency of the applied AC voltage is the same as the resonant frequency of the two-degree-of-freedom resonator, the first resonator 1 and the second resonator 2 will move at the resonant frequency under the action of the electrostatic force. The amplitude of the first resonator 1 and the second resonator 2 can be obtained by detecting the output current of the first detection capacitor 1-3 and the second detection capacitor 2-3. When the external temperature does not change, the amplitudes of the first resonator 1 and the second resonator 2 are equal.

[0058] When the external temperature changes, the change in external temperature can be obtained by detecting the amplitude ratio of the first resonator 1 and the second resonator 2.

[0059] The sensitivity of the sensor in the above example was simulated using COMSOL software. A temperature load was applied to the sensor, and the amplitude ratio and resonant frequency of the two resonators under different temperatures were obtained by solving for the characteristic frequencies of the two-degree-of-freedom resonator system. The simulation results are as follows: Figure 2 As shown, the specific example temperature sensor described above has a relative sensitivity of 4.59 ppm / ℃ based on frequency output and a relative sensitivity of 4.39 × 10⁻⁶ based on amplitude ratio output. 5 ppm / ℃, which is 95,708 times higher than the frequency output.

Claims

1. A resonant temperature sensor based on a two-degree-of-freedom resonator, comprising a substrate, characterized in that: The substrate is provided with two first anchor points, two second anchor points, and driving electrodes; The first anchor point and the second anchor point have the same structure; the first straight line where the two first anchor points are located is parallel to the second straight line where the two second anchor points are located, and the driving electrode is located between the two straight lines; A first resonator is provided between the two first anchor points, and a second resonator is provided between the two second anchor points; a coupling structure is provided between the first resonator and the second resonator. The first resonator includes a first detection capacitor, a first mass block, a first resonant beam, and two stress relief structures; the second resonator includes a second detection capacitor, a second mass block, and a second resonant beam. The first resonator has two stress relief structures connected to two first anchor points respectively. The first detection capacitor, the first mass block and the first resonant beam are located between the two stress relief structures, and the first resonant beam is connected to the two stress relief structures. The stiffness of the stress relief structure along the direction of the first straight line is less than the stiffness along the direction perpendicular to the first straight line. The second resonator's second resonant beam is connected to the second anchor point at both ends; Meanwhile, the first detection capacitor, the first mass block, and the first resonant beam of the first resonator and the second detection capacitor, the second mass block, and the second resonant beam of the second resonator are symmetrically arranged with respect to the driving electrode, and the driving electrode is located between the first mass block and the second mass block. The coupling structure is connected to the first resonant beam and the second resonant beam. The stiffness of the coupling structure is less than the stiffness of the first resonator and also less than the stiffness of the second resonator.

2. The resonant temperature sensor based on a two-degree-of-freedom resonator as described in claim 1, characterized in that, Both the first anchor point and the second anchor point are square.

3. The resonant temperature sensor based on a two-degree-of-freedom resonator as described in claim 1, characterized in that: The first resonant beam is connected to stress relief structures at both ends, and a first mass block is provided in the middle of the first resonant beam, with the first detection capacitor located on one side of the first mass block; The second resonant beam is connected to the second anchor point at both ends, and a second mass block is provided in the middle of the second resonant beam. The second detection capacitor is located on one side of the second mass block.

4. The resonant temperature sensor based on a two-degree-of-freedom resonator as described in claim 3, characterized in that, The first mass block is a rectangular structure; the first detection capacitor is a rectangular structure; the second mass block is a rectangular structure; the second detection capacitor is a rectangular structure.

5. The resonant temperature sensor based on a two-degree-of-freedom resonator as described in claim 3, characterized in that, The stress relief structure is a hollow rectangular structure.

6. The method for fabricating the resonant temperature sensor based on a two-degree-of-freedom resonator as described in claim 1, characterized in that, The preparation method includes the following steps: 1) Apply adhesive and perform photolithography on the front side of the SOI silicon wafer; 2) The SOI silicon wafer is etched to form the first resonator, the second resonator, two first anchor points, two second anchor points, the coupling structure and the driving electrode, and the photoresist is removed; 3) Remove the silicon dioxide layer that is connected to the bottom of the first resonator, the second resonator, and the coupling structure.

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