A constant temperature control micromechanical resonator and a constant temperature control method and a preparation method thereof

Abstract

This invention belongs to the field of micromechanical resonator technology, and discloses a temperature-controlled micromechanical resonator and its temperature control method and preparation method. The resonator structure includes a micro-heating cavity and a resonant oscillator, and is symmetrical about the angle bisector of the crystal orientation of the resonant oscillator. This invention utilizes the difference in frequency offset-temperature curves of resonant oscillators with different crystal orientations to perform frequency temperature measurement, thereby achieving a higher precision temperature control function and improving the frequency stability of the resonator.

Description

Technical Field

[0001] This invention belongs to the field of micromechanical resonator technology, specifically relating to a structural design scheme for a temperature-controlled micromechanical resonator and its temperature control and fabrication methods. Background Technology

[0002] Clocks provide a frequency reference and time reference for digital circuits. Resonators are the fundamental components of clocks. A resonator, along with peripheral oscillation circuits, amplifier circuits, and filter circuits, can form an oscillator that outputs a fixed frequency signal. Traditional quartz clocks are made of brittle materials with poor vibration resistance. They are fabricated by mechanical cutting along certain crystal orientations, which cause a sharp deterioration in frequency-temperature characteristics at high temperatures. For the harsh environments of high temperature and high vibration in emerging and important applications such as 5G and future 6G communication base stations and automotive electronics, quartz crystal oscillators struggle to meet the requirements for high stability and low failure rate. In recent years, micro-mechanical resonators fabricated based on Micro-Electro-Mechanical Systems (MEMS) technology have emerged. These resonators are characterized by small size, low power consumption, high reliability and stability, and compatibility with integrated circuit manufacturing processes. Market demand for them is increasing daily, making them a future alternative to traditional quartz clocks.

[0003] Frequency-temperature drift is a key performance indicator of a resonator. The frequency-temperature stability of a resonator is measured by the temperature coefficient of frequency (TCF). The first-order TCF is determined by the thermoelastic coefficient (TCE) and the coefficient of thermal expansion (α) of the resonator material.

[0004]

[0005] Uncompensated micromechanical resonators typically have a large temperature coefficient of frequency (TCF). Within the industrial temperature range of -40°C to 85°C, the output frequency of a micromechanical resonator will experience a frequency drift exceeding 3500 ppm, which cannot meet the requirements of practical industrial applications. Therefore, micromechanical resonators require temperature compensation when used in clock applications. For high-precision clock applications, such as base station clocks, frequency stability at the ppb level is usually required. Micro-heated cavity thermostatic control systems are currently the best choice for improving the frequency stability of micromechanical resonators. The micro-heated cavity thermostatic control method generally places the micromechanical resonator in a thermally isolated micro-heated cavity, and then uses a Joule-heated heater to maintain the resonator's temperature. The temperature of the micro-heated cavity typically needs to be precisely controlled at the temperature value corresponding to the resonator's temperature inflection point ("0" TCF point).

[0006] Typically, temperature measurement for thermostatically controlled micromechanical resonators is achieved through resistance measurement. This can be done by measuring the resonator's own structural resistance. However, due to the small temperature coefficient of resistance in single-crystal silicon, the accuracy of temperature measurement using structural resistance is limited, making it difficult to meet the requirements of high-performance thermostatically controlled micromechanical resonators for precise temperature control and frequency stability. Alternatively, resistance measurement can be achieved by adding a thermistor around the resonator and measuring its resistance. However, because there is a temperature gradient between the resonator and its surroundings, it is difficult to accurately measure the resonator's own temperature, again failing to meet the requirements of high-performance thermostatically controlled micromechanical resonators for precise temperature control and frequency stability. Summary of the Invention

[0007] This invention provides a thermostatically controlled micromechanical resonator, its thermostatic control method, and its fabrication method, thereby solving the problems of low thermostatic control accuracy and poor frequency stability in existing thermostatically controlled micromechanical resonators.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a thermostatically controlled micromechanical resonator, comprising: a micro-heating cavity and a resonant oscillator; the micro-heating cavity includes a thermostatic control module, a drive detection module, and a connection module; the resonant oscillator includes a clock output resonant oscillator and a temperature sensing resonant oscillator;

[0010] The constant temperature control module includes a micro heating beam, a heat insulation frame, support anchor points, an inner support beam, heating electrodes, and resistance temperature measuring electrodes; the drive detection module includes drive / detection electrodes; the connection module includes a substrate silicon wafer and at least four fixed anchor points.

[0011] The clock output resonator and the temperature sensing resonator are both located inside the heat insulation frame and are directly connected to the heat insulation frame via the support anchor point and the inner support beam, respectively. The heat insulation frame and the fixed anchor point are connected via the micro-heating beam. The clock output resonator, the temperature sensing resonator, the heat insulation frame, and the micro-heating beam are all suspended above the substrate silicon wafer and are connected to the substrate silicon wafer via the fixed anchor point. The driving / detection electrode, the heating electrode, and the resistance temperature measuring electrode are all located on the fixed anchor point.

[0012] The clock output resonator and the temperature sensing resonator are arranged along different crystal orientations, and the thermostatically controlled micromechanical resonator is symmetrical about the angle bisector of the crystal orientation formed by the clock output resonator and the temperature sensing resonator.

[0013] Preferably, the clock output resonant oscillator is arranged along a crystal orientation where the temperature inflection point of its frequency offset-temperature curve is higher than the operating temperature range, and the temperature sensing resonant oscillator is arranged along a crystal orientation where its frequency offset-temperature curve is a linear curve within the operating temperature range.

[0014] Preferably, the structure of the heat insulation frame is any one or more combinations of various axisymmetric shapes, including circles, squares, and hexagons; the micro-heating beam adopts any one or more combinations of serpentine folded beams, U-shaped beams, and straight beams; the clock output resonant oscillator and the temperature sensing resonant oscillator have the same structure, and the corresponding structure is any one or more combinations of rectangular plates, fixed beams, disks, rings, and fixed beams; the support anchor point is a straight beam, T-beam, or folded beam structure.

[0015] Preferably, the operating mode of the resonator is any one or more combinations of volume mode and bending mode, wherein the volume mode includes length stretching, width stretching, square plate stretching, circular plate stretching, lame, surface shearing, width shearing, length shearing, and goblet type.

[0016] Preferably, the temperature-controlled micromechanical resonator is a single-crystal silicon structure or a metal-piezoelectric layer-single-crystal silicon composite thin film structure.

[0017] Preferably, the single-crystal silicon is heavily doped with N-type or P-type silicon, and its doping concentration ranges from 4.0 × 10⁻⁶. 19 / cm 3 Up to 2.0×10 20 / cm 3 The doping concentration of the single-crystal silicon is used to adjust the temperature inflection point of the resonant oscillator; the crystal orientation range of the resonant oscillator includes the area along the single-crystal silicon. <100> , <110> and along <100> and <110> The crystal orientation of the resonator is determined by the doping concentration and the arrangement of the crystals between them.

[0018] Secondly, the present invention provides a method for controlling the temperature of the above-mentioned temperature-controlled micromechanical resonator, the temperature control method comprising:

[0019] A heating voltage is applied to the heating electrode of the thermostatically controlled micromechanical resonator to heat the resonator to a preset temperature;

[0020] The frequency offset-temperature curves of the clock output resonant oscillator and the temperature sensor resonant oscillator were obtained respectively.

[0021] Based on the difference between the frequency offset-temperature curve of the clock output resonant oscillator and the temperature sensing resonant oscillator, the actual temperature change of the isothermal control micromechanical resonator is monitored in real time to obtain temperature change information.

[0022] Based on the temperature change information, the operating temperature of the thermostatically controlled micromechanical resonator is adjusted to achieve thermostatic control.

[0023] Preferably, when applying the heating voltage, a positive heating voltage Vh+ is applied between two heating electrodes located on one side of the axis of symmetry of the thermostatically controlled micromechanical resonator, and a negative heating voltage Vh- is applied between two heating electrodes located on the other side of the axis of symmetry of the thermostatically controlled micromechanical resonator.

[0024] Preferably, the resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator is output through the driving / detecting electrode and fed back to the PID controller. The PID controller adjusts the output heating voltage based on the resonant frequency difference, controlling the resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator to a preset frequency difference corresponding to the clock output resonant oscillator at the temperature inflection point, so as to keep the operating temperature of the constant temperature control micromechanical resonator constant.

[0025] Thirdly, the present invention provides a method for fabricating the above-mentioned temperature-controlled micromechanical resonator, the method comprising the following steps:

[0026] Step 1: Provide an SOI wafer with a cavity structure, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer and a device layer silicon wafer;

[0027] Step 2: Sequentially deposit piezoelectric material and upper electrode on the silicon device layer, and pattern the upper electrode;

[0028] Step 3: Deposit a top layer oxide on the upper electrode;

[0029] Step 4: Etch the top oxide layer to obtain the upper electrode via and expose the upper electrode;

[0030] Step 5: Etch the top oxide and the piezoelectric material to obtain the lower electrode via and expose the device layer silicon;

[0031] Step 6: Deposit and pattern metal in both the upper electrode via and the lower electrode via to form metal pads;

[0032] Step 7: Etch to obtain the structure of the temperature-controlled micromechanical resonator.

[0033] The advantages and beneficial effects of this invention are as follows:

[0034] 1. The thermostatically controlled micromechanical resonator proposed in this invention includes a micro-heating cavity and a resonant oscillator. The resonant oscillator includes a clock output resonant oscillator and a temperature sensing resonant oscillator, which are arranged along different crystal orientations. The thermostatically controlled micromechanical resonator is symmetrical about the angle bisector of the crystal orientation angle formed by the clock output resonant oscillator and the temperature sensing resonant oscillator. Based on the above structure, this invention can utilize the difference in frequency offset-temperature curves (i.e., the difference in frequency-temperature sensitivity, where frequency-temperature sensitivity refers to the slope of the frequency offset-temperature curve, and the larger the slope, the higher the temperature sensitivity at that point) of the resonant oscillators arranged along different crystal orientations to perform frequency temperature measurement, thereby achieving a higher precision thermostatic control function and improving the frequency stability of the resonator.

[0035] 2. The isothermal control micromechanical resonator proposed in this invention adopts a heat insulation frame design, which can provide thermal isolation between the resonator and the external environment, and helps to improve the frequency stability of the resonator.

[0036] 3. The constant temperature control micromechanical resonator proposed in this invention can ensure uniform temperature distribution of the resonator and the heat insulation frame through symmetrical heating, which is conducive to further improving the temperature control accuracy and thus improving the temperature stability of the resonator. Attached Figure Description

[0037] Figure 1 Example 1: A three-dimensional structural schematic diagram of the temperature-controlled micromechanical resonator.

[0038] Figure 2 Example 1: A schematic diagram of the planar structure of the temperature-controlled micromechanical resonator.

[0039] Figure 3 The frequency shift-temperature curves of the resonant oscillator arranged along different crystal orientations in the isothermal controlled micromechanical resonator provided in Example 1;

[0040] Figure 4 Example 2: Temperature distribution diagram of the thermostatically controlled micromechanical resonator under symmetrical heating mode in the thermostatic control method of the thermostatically controlled micromechanical resonator.

[0041] Figure 5 Example 2: Temperature control principle diagram based on frequency temperature measurement in the temperature control method of the temperature-controlled micromechanical resonator.

[0042] Figures 6-a to 6-g The process flow corresponding to the fabrication method of the temperature-controlled micromechanical resonator provided in Example 3; wherein: Figure 6-a To provide SOI discs with cavities; Figure 6-b To deposit piezoelectric material and top electrode, and to pattern the top electrode; Figure 6-c For depositing top oxide; Figure 6-d To etch and obtain the upper electrode through hole; Figure 6-e To etch and obtain the lower electrode via; Figure 6-f To form metal pads; Figure 6-g A schematic diagram of the structure of a temperature-controlled micromechanical resonator obtained by etching.

[0043] Figure 1 and Figure 2 In the middle: 1-Clock output resonant oscillator, 2-Temperature sensing resonant oscillator, 3-Support anchor point, 4-Inner support beam, 5-Insulation frame, 6-Upper electrode through hole, 7-Electrode lead, 8-Resistance temperature sensing electrode, 9-Heating electrode, 10-Drive / detection electrode, 11-Micro heating beam, 12-Lower electrode through hole, 13-Fixed anchor point.

[0044] Figures 6-a to 6-g In the middle: 21-substrate silicon wafer, 22-buried oxide layer, 23-device layer silicon, 24-piezoelectric material, 25-upper electrode, 26-top oxide layer, 27-metal pad. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to specific embodiments.

[0046] Example 1:

[0047] The three-dimensional and planar structural schematic diagrams of the temperature-controlled micromechanical resonator provided in Example 1 are shown below. Figure 1 and Figure 2 As shown, the thermostatically controlled micromechanical resonator includes a micro-heating cavity and a resonant oscillator. The micro-heating cavity includes a thermostatic control module, a drive detection module, and a connection module.

[0048] The constant temperature control module includes a support anchor point 3, an inner support beam 4, a heat insulation frame 5, a resistance temperature measuring electrode 8, a heating electrode 9, and a micro heating beam 11; the drive detection module includes a drive / detection electrode 10; and the connection module includes a substrate silicon wafer and at least four fixed anchor points 13.

[0049] The resonant oscillator includes a clock output resonant oscillator 1 and a temperature sensing resonant oscillator 2. The clock output resonant oscillator and the temperature sensing resonant oscillator are arranged along different crystal orientations, that is, the two have different crystal orientations.

[0050] The clock output resonant oscillator 1 and the temperature sensing resonant oscillator 2 are both located inside the heat insulation frame 5 and are directly connected to the heat insulation frame 5 through the support anchor point 3 and the inner support beam 4, respectively. The heat insulation frame 5 and the fixed anchor point 13 are connected through the micro heating beam 11. The clock output resonant oscillator 1, the temperature sensing resonant oscillator 2, the heat insulation frame 5 and the micro heating beam 11 are all suspended above the substrate silicon wafer and are connected to the substrate silicon wafer through the fixed anchor point 13. The driving / detection electrode 10, the heating electrode 9 and the resistance temperature measuring electrode 8 are all located on the fixed anchor point 13.

[0051] The overall structure of the thermostatically controlled micromechanical resonator is symmetrical about the angle bisector of the crystal orientation angle θ between the resonators (i.e., the crystal orientation angle formed by the clock output resonator 1 and the temperature sensing resonator 2), ensuring that the resonator is an axisymmetric structure. Conventional heating methods in the prior art involve diagonal heating. In this invention, due to the presence of multiple resonators with different crystal orientations, diagonal heating would lead to uneven temperature distribution between the two resonators. Based on the specific structure of this invention, symmetrical heating ensures a uniform temperature distribution within the resonator.

[0052] The clock output resonant oscillator 1 is arranged along a crystal orientation where the temperature inflection point of its frequency offset-temperature curve is higher than the operating temperature range, and the temperature sensing resonant oscillator 2 is arranged along a crystal orientation where its frequency offset-temperature curve is a linear curve within the operating temperature range.

[0053] For example, the clock output resonant oscillator 1 has a high temperature inflection point along its frequency offset-temperature curve. <100> Crystal orientation arrangement; a high temperature inflection point refers to a temperature inflection point that is higher than the actual operating temperature range of the device. Generally, the temperature inflection point is required to be higher than the industrial temperature range (-40-85℃), i.e., higher than 85℃; the temperature sensing resonator 2 is along its temperature-sensitive axis. <110> Crystal orientation and high temperature sensitivity refer to the linearity of its frequency-temperature curve within the operating temperature range. For example... Figure 3 The figure shows the frequency shift-temperature curves of the resonant oscillator when arranged along different crystal orientations, obtained from simulation.

[0054] The clock output resonant oscillator 1 and the temperature sensing resonant oscillator 2 have the same structure, which is any one or more combinations of rectangular plate, fixed beam, disk, ring, and fixed beam. For example, both the clock output resonant oscillator 1 and the temperature sensing resonant oscillator 2 are rectangular plates.

[0055] The supporting anchor point 3 is a straight beam, T-beam, or folded beam structure. The structure of the heat insulation frame 5 is any one or more combinations of various axisymmetric shapes, including circles, squares, hexagons, etc. The micro-heating beam 11 can be any one or more combinations of serpentine folded beams, U-shaped beams, and straight beams.

[0056] The operating modes of the resonant oscillator are any one or more combinations of volume modes and bending modes. The volume modes include length stretching, width stretching, square plate stretching, circular plate stretching, lame, surface shearing, width shearing, length shearing, and goblet-shaped.

[0057] The temperature-controlled micromechanical resonator is a single-crystal silicon structure or a metal-piezoelectric layer-single-crystal silicon composite thin film structure. The single-crystal silicon is heavily doped with N-type or P-type silicon, with a doping concentration ranging from 4.0 × 10⁻⁶. 19 / cm 3 Up to 2.0×10 20 / cm 3 The doping concentration of the single-crystal silicon is used to adjust the temperature inflection point of the resonant oscillator; the crystal orientation range of the resonant oscillator includes the area along the single-crystal silicon. <100> , <110> and along <100> and <110> The crystal orientation of the resonator is determined by the doping concentration and the arrangement of the crystals between them.

[0058] The frequency-temperature characteristics of the single-crystal silicon can be adjusted by both the doping concentration and crystal orientation, with the crystal orientation playing a major role. Specifically, changing the crystal orientation can significantly alter the temperature coefficient of the first-order frequency of the resonant oscillator; for example, for the frequency along the crystal orientation... <100> Crystal orientation and <110> The frequency-temperature curves of resonators with different crystal orientations show almost opposite trends. The doping concentration can fine-tune the temperature inflection point; generally, for both n-type and p-type doping, increasing the doping concentration will raise the resonator's temperature inflection point. For example, for an n-type doped width-stretching mode resonator, the higher the doping concentration, the higher the inflection point along the frequency-temperature curve. <100> The higher the temperature inflection point of the resonator with the crystal orientation, the more preferably it is heavily doped to improve the temperature inflection point of the clock output resonator 1.

[0059] Alternatively, it can be understood that the clock output resonant oscillator 1 and the temperature sensing resonant oscillator 2 are arranged along the crystal direction according to the specific doping concentration of the single-crystal silicon. For example, the resonator structure along... <100> Crystal orientation arrangement, that is, the clock output resonator 1 along <100> Crystal orientation arrangement, the temperature sensing resonator 2 along <110> Crystal orientation arrangement; the single crystal silicon is heavily N-type doped, with a doping concentration ranging from 7.5 × 10⁻⁶. 19 / cm 3 .

[0060] When the single-crystal silicon is n-type doped, for most bulk mode resonators along... <100> When the crystal orientation is aligned, the resonator has a higher temperature inflection point, along with <110> When the crystal orientation is aligned, the resonator has a low temperature inflection point and is approximately linear within the operating temperature range. When single-crystal silicon is heavily p-type doped, for Lamé and shear mode resonators, along... <110> When the crystal orientation is aligned, the resonator has a higher temperature inflection point, along with <100> When the crystal orientation is aligned, the resonator has a low temperature inflection point and is approximately linear within the operating temperature range. When the doping concentration is fixed and the resonator is aligned along a conventional crystal orientation, the resonator has a particularly high temperature inflection point. The temperature inflection point can be adjusted to a suitable temperature by changing the single-crystal silicon crystal orientation of the resonator. For unconventional crystal orientations, the frequency shift-temperature curve is... <100> Crystal orientation and <110> The temperature inflection point is between the curves corresponding to the two crystal orientations. Therefore, when the doping concentration of single-crystal silicon is constant, the crystal orientation of single-crystal silicon is determined according to the specific doping concentration.

[0061] When the temperature-controlled micromechanical resonator is a metal-piezoelectric layer-monocrystalline silicon composite thin film structure, the resonator operates in a dual-port excitation mode. When an AC signal is applied to the driving / detecting electrode 10 at one end, a voltage is applied to the piezoelectric layer through the electrode lead 7 and the upper electrode through-hole 6. The piezoelectric material deforms due to the inverse piezoelectric effect, thereby driving the resonant oscillator to vibrate mechanically. The resonant signal is then detected by the driving / detecting electrode 10 at the other end through the upper electrode through-hole 6 and the electrode lead 7, thereby suppressing parasitic signals.

[0062] The heating method of the thermostatically controlled micromechanical resonator involves applying a heating voltage between the symmetrically positioned heating electrodes 9. Current flows through the lower electrode through-hole 12, through the micro-heating beam 11, the heat insulation frame 5, the clock output resonator 1, and the temperature sensing resonator 2, generating Joule heating on the silicon structure. This heats the thermostatically controlled micromechanical resonator to a fixed temperature. The temperature distribution diagram of the thermostatically controlled micromechanical resonator under this heating method is shown below. Figure 4 As shown, the temperature distribution on the clock output resonant oscillator 1, the temperature sensing resonant oscillator 2, and the heat insulation frame 5 is uniform under the symmetrical heating method.

[0063] The temperature measurement method of the thermostatically controlled micromechanical resonator adopts dual-resonator frequency difference temperature measurement, which monitors the actual temperature change of the entire resonator structure in real time by measuring the frequency difference of the resonator elements. The temperature control principle based on frequency measurement is shown in the diagram below. Figure 5As shown, a positive heating voltage Vh+ can be applied between the two heating electrodes 9 located on one side of the symmetry axis of the thermostatic control micromechanical resonator, and a negative heating voltage Vh- can be applied between the two heating electrodes 9 on the other side of the symmetry axis to achieve the heating function. By driving the detection electrode 10, the resonant frequency difference f1-f2=Δf of the two resonators can be output. The detection signal is fed back to the PID control, and the output heating voltage is controlled by the PID algorithm. The resonant frequency difference Δf of the two resonators is controlled to be the frequency difference Δf0 of the two resonators when the clock output resonators are at the temperature inflection point. This controls the overall temperature of the micromechanical resonator to remain constant, and ultimately achieves the thermostatic control function.

[0064] Example 2:

[0065] Example 2 provides a method for isothermal control of a micromechanical resonator as provided in Example 1, the method comprising:

[0066] A heating voltage is applied to the heating electrode of the thermostatically controlled micromechanical resonator to heat the resonator to a preset temperature;

[0067] The frequency offset-temperature curves of the clock output resonant oscillator and the temperature sensor resonant oscillator were obtained respectively.

[0068] Based on the difference between the frequency offset-temperature curve of the clock output resonant oscillator and the temperature sensing resonant oscillator, the actual temperature change of the isothermal control micromechanical resonator is monitored in real time to obtain temperature change information.

[0069] Based on the temperature change information, the operating temperature of the thermostatically controlled micromechanical resonator is adjusted to achieve thermostatic control.

[0070] Specifically, when applying the heating voltage, a positive heating voltage Vh+ is applied between two heating electrodes located on one side of the axis of symmetry of the thermostatically controlled micromechanical resonator, and a negative heating voltage Vh- is applied between two heating electrodes located on the other side of the axis of symmetry of the thermostatically controlled micromechanical resonator.

[0071] The resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator is output through the driving / detection electrode and fed back to the PID controller. The PID controller adjusts the output heating voltage based on the resonant frequency difference, controlling the resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator to a preset frequency difference corresponding to the clock output resonant oscillator at the temperature inflection point, so as to keep the operating temperature of the constant temperature control micromechanical resonator constant.

[0072] Example 3:

[0073] Based on the structure of the temperature-controlled micromechanical resonator in Example 1, Example 3 provides a method for fabricating the above-mentioned temperature-controlled micromechanical resonator, the specific steps of which are as follows:

[0074] (1) Provide an SOI wafer with a cavity structure, wherein the silicon wafer thickness of the device layer is 20–60 μm; see Figure 6-a The SOI wafer, from bottom to top, comprises: a substrate silicon wafer 21, a buried oxide layer 22, and a device layer silicon 23;

[0075] (2) Sequentially deposit a 0.5–1 μm thick piezoelectric aluminum nitride film and a 0.15–0.2 μm thick top electrode molybdenum on the SOI wafer, and pattern the top electrode; see [link to relevant documentation]. Figure 6-b The structure obtained in this step includes, from bottom to top, the following: substrate silicon wafer 21, buried oxide layer 22, device layer silicon 23, piezoelectric material 24 and upper electrode 25;

[0076] (3) Deposit a layer of oxide at least 0.2 μm thick; see Figure 6-c The structure obtained in this step includes, from bottom to top, the following: substrate silicon wafer 21, buried oxide layer 22, device layer silicon 23, piezoelectric material 24, upper electrode 25 and top oxide layer 26.

[0077] (4) Etch the top oxide layer 26 to obtain an upper electrode via, exposing the upper electrode 25. See [link to documentation]. Figure 6-d ;

[0078] (5) Etch the top oxide 26 and the piezoelectric material 24 to obtain a lower electrode via, exposing the device layer silicon 23. See [link to documentation]. Figure 6-e ;

[0079] (6) Aluminum of 1-2 μm thickness is deposited in both the upper electrode via and the lower electrode via, and patterned to form metal pads 27, see [reference]. Figure 6-f ;

[0080] (7) Etching is performed on the above structure to obtain the structure of the temperature-controlled micromechanical resonator as described in Example 1. See [link to example]. Figure 6-g .

[0081] The above embodiments are used to specifically illustrate the present invention. Although specific terms are used in the description, they should not be used to limit the scope of protection of the present invention. Those skilled in the art can make changes or modifications to achieve equivalent purposes after understanding the spirit and principles of the present invention. Such equivalent changes and modifications should all be covered within the scope defined by the claims.

Claims

1. A temperature-controlled micromechanical resonator, characterized in that: include: Micro-heating cavity and resonant oscillator: The micro-heating cavity includes a constant temperature control module, a drive detection module, and a connection module; the resonant oscillator includes a clock output resonant oscillator and a temperature sensing resonant oscillator; The constant temperature control module includes a micro heating beam, a heat insulation frame, support anchor points, an inner support beam, heating electrodes, and resistance temperature measuring electrodes; the drive detection module includes drive / detection electrodes; the connection module includes a substrate silicon wafer and at least four fixed anchor points. The clock output resonator and the temperature sensing resonator are both located inside the heat insulation frame and are directly connected to the heat insulation frame via the support anchor point and the inner support beam, respectively. The heat insulation frame and the fixed anchor point are connected via the micro-heating beam. The clock output resonator, the temperature sensing resonator, the heat insulation frame, and the micro-heating beam are all suspended above the substrate silicon wafer and are connected to the substrate silicon wafer via the fixed anchor point. The driving / detection electrode, the heating electrode, and the resistance temperature measuring electrode are all located on the fixed anchor point. The clock output resonator and the temperature sensing resonator are arranged along different crystal orientations, and the thermostatically controlled micromechanical resonator is symmetrical about the angle bisector of the crystal orientation formed by the clock output resonator and the temperature sensing resonator.

2. The isothermal-controlled micromechanical resonator according to claim 1, characterized in that: The clock output resonant oscillator is arranged along a crystal orientation where the temperature inflection point of its frequency offset-temperature curve is higher than the operating temperature range, and the temperature sensing resonant oscillator is arranged along a crystal orientation where its frequency offset-temperature curve is a linear curve within the operating temperature range.

3. The isothermal-controlled micromechanical resonator according to claim 1, characterized in that: The structure of the heat insulation frame is any one or more combinations of various axisymmetric shapes, including circles, squares, and hexagons; the micro-heating beam adopts any one or more combinations of serpentine folded beams, U-shaped beams, and straight beams; the clock output resonant oscillator and the temperature sensing resonant oscillator have the same structure, and the corresponding structure is any one or more combinations of rectangular plates, fixed beams, disks, rings, and fixed beams; the support anchor point is a straight beam, T-beam, or folded beam structure.

4. The isothermal-controlled micromechanical resonator according to claim 1, characterized in that: The operating modes of the resonant oscillator are any one or more combinations of volume modes and bending modes. The volume modes include length stretching, width stretching, square plate stretching, circular plate stretching, lame, surface shearing, width shearing, length shearing, and goblet-shaped.

5. The isothermal-controlled micromechanical resonator according to claim 1, characterized in that: The temperature-controlled micromechanical resonator is a single-crystal silicon structure or a metal-piezoelectric layer-single-crystal silicon composite thin film structure.

6. The isothermal-controlled micromechanical resonator according to claim 5, characterized in that: The single-crystal silicon is heavily doped with N-type or P-type silicon, and its doping concentration ranges from 4.0 × 10⁻⁶. 19 / cm 3 Up to 2.0×10 20 / cm 3 The doping concentration of the single-crystal silicon is used to adjust the temperature inflection point of the resonant oscillator; the crystal orientation range of the resonant oscillator includes the area along the single-crystal silicon. <100> , <110> and along <100> and <110> The crystal orientation of the resonator is determined by the doping concentration and the arrangement of the crystals between them.

7. A method for isothermal control of a micromechanical resonator as described in any one of claims 1-6, characterized in that: The constant temperature control method includes: A heating voltage is applied to the heating electrode of the thermostatically controlled micromechanical resonator to heat the resonator to a preset temperature; The frequency offset-temperature curves of the clock output resonant oscillator and the temperature sensor resonant oscillator were obtained respectively. Based on the difference between the frequency offset-temperature curve of the clock output resonant oscillator and the temperature sensing resonant oscillator, the actual temperature change of the isothermal control micromechanical resonator is monitored in real time to obtain temperature change information. Based on the temperature change information, the operating temperature of the thermostatically controlled micromechanical resonator is adjusted to achieve thermostatic control.

8. The method for isothermal control of a micromechanical resonator according to claim 7, characterized in that: When a heating voltage is applied, a positive heating voltage Vh+ is applied between two heating electrodes located on one side of the axis of symmetry of the thermostatically controlled micromechanical resonator, and a negative heating voltage Vh- is applied between two heating electrodes located on the other side of the axis of symmetry of the thermostatically controlled micromechanical resonator.

9. The method for controlling the temperature of a thermostatically controlled micromechanical resonator according to claim 7, characterized in that: The resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator is output through the driving / detection electrode and fed back to the PID controller. The PID controller adjusts the output heating voltage based on the resonant frequency difference, controlling the resonant frequency difference between the clock output resonant oscillator and the temperature sensing resonant oscillator to a preset frequency difference corresponding to the clock output resonant oscillator at the temperature inflection point, so as to keep the operating temperature of the constant temperature control micromechanical resonator constant.

10. A method for fabricating a temperature-controlled micromechanical resonator as described in any one of claims 1-6, characterized in that: The preparation method includes the following steps: Step 1: Provide an SOI wafer with a cavity structure, wherein the SOI wafer comprises, from bottom to top, a substrate silicon wafer, a buried oxide layer and a device layer silicon wafer; Step 2: Sequentially deposit piezoelectric material and upper electrode on the silicon device layer, and pattern the upper electrode; Step 3: Deposit a top layer oxide on the upper electrode; Step 4: Etch the top oxide layer to obtain the upper electrode via and expose the upper electrode; Step 5: Etch the top oxide and the piezoelectric material to obtain the lower electrode via and expose the device layer silicon; Step 6: Deposit and pattern metal in both the upper electrode via and the lower electrode via to form metal pads; Step 7: Etch to obtain the structure of the temperature-controlled micromechanical resonator.

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