A surface acoustic wave microsensor and its preparation method

Abstract

The present invention discloses a surface acoustic wave microsensor and a preparation method thereof, wherein the microsensor comprises: a lower substrate, a blind groove is provided on the lower substrate; an upper substrate, a first through hole, a second through hole, a first stress release bridge connecting the first through hole and the second through hole, a second stress release bridge, and a stress isolation beam surrounded by the first through hole, the second through hole, the first stress release bridge and the second stress release bridge, wherein the stress isolation beam is suspended near the lower substrate side; the blind groove is sealed with the upper substrate to form a pressure sensitive unit, the stress isolation beam is connected with the lower substrate to form a temperature sensitive unit, the pressure sensitive unit and the temperature sensitive unit have no overlap area and their surface acoustic wave resonant frequency and working frequency band are different; a conductive layer is configured to convert an alternating current signal into a periodic electromagnetic field and load it into the upper substrate to obtain the surface acoustic wave of the pressure sensitive unit and the temperature sensitive unit. The high-temperature rotor pressure and temperature measurement is realized, and the measurement accuracy is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a surface acoustic wave microsensor and a preparation method thereof. Background Art

[0002] Aerospace engines, the power core of aircraft, and gas turbines, the power core of ships, are all high-temperature and high-speed equipment. These equipment are subjected to high-temperature airflow for a long time (especially high-temperature rotors of compressors and turbines), and their operating temperatures are higher than 500°C. Therefore, high-temperature pressure measurement can timely understand the operating status of high-temperature and high-speed equipment, providing data support for intelligent control, structural optimization, and performance improvement.

[0003] With the development of aerospace, when measuring the pressure of high-temperature rotors, the sensing system is required to be passive and wireless, high temperature resistant, and small in size. At present, surface acoustic wave has received extensive attention in the field of high-temperature rotor measurement, but the surface acoustic wave pressure sensor based on lanthanum gallium silicate has problems such as difficulty in manufacturing sensitive structures, complex demodulation of pressure and temperature sensing signals, and poor stability of thin film interdigital electrodes, which hinder the development of surface acoustic wave sensors and make surface acoustic wave sensors less accurate when measuring the pressure and temperature of high-temperature rotors. Summary of the invention

[0004] Based on this, the present invention provides a surface acoustic wave microsensor and a preparation method thereof, which solves the problem of insufficient accuracy in passive wireless measurement of the pressure and temperature of a high-temperature rotor.

[0005] The present invention provides a surface acoustic wave microsensor, the microsensor comprising:

[0006] A lower substrate, wherein a blind groove is provided on the lower substrate;

[0007] An upper substrate is provided on the side of the lower substrate where the blind groove is located, the upper substrate is provided with a first through hole, a second through hole, a first stress release bridge connecting the first through hole and the second through hole, a second stress release bridge, and a stress isolation beam surrounded by the first through hole, the second through hole, the first stress release bridge and the second stress release bridge, and the stress isolation beam is suspended near the lower substrate side;

[0008] The blind groove is sealed with the upper substrate to form a pressure sensitive unit, and the pressure sensitive unit is used to measure pressure; the stress isolation beam is connected with the lower substrate to form a temperature sensitive unit, and the temperature sensitive unit is used to measure temperature; the pressure sensitive unit and the temperature sensitive unit have no overlapping area, and the surface acoustic wave resonance frequency and working frequency band of the pressure sensitive unit and the temperature sensitive unit are different;

[0009] A conductive layer is disposed on the upper substrate, and the conductive layer is configured to convert an alternating current signal into a periodic electromagnetic field, load the periodic electromagnetic field into the upper substrate, and obtain surface acoustic waves of the pressure sensitive unit and the temperature sensitive unit.

[0010] Furthermore, the lower substrate and the upper substrate are single crystal wafers with the same crystal orientation, the pressure sensitive unit is arranged along the main tangent direction of the upper substrate and the lower substrate, and the temperature sensitive unit is arranged along the secondary tangent direction of the upper substrate and the lower substrate.

[0011] Furthermore, the single crystal wafer is lanthanum gallium silicate.

[0012] Furthermore, the surface acoustic wave resonance frequency of the pressure sensitive unit is 193 MHz, and the operating frequency band is 190-200 MHz; the surface acoustic wave resonance frequency of the temperature sensitive unit is 223 MHz, and the operating frequency band is 215-225 MHz.

[0013] Furthermore, the conductive layer comprises:

[0014] A first interdigital electrode, the first interdigital electrode is located in the center of the pressure sensitive unit, and the first interdigital electrode includes a first signal end interdigital electrode and a first ground end interdigital electrode;

[0015] a second interdigital electrode, the second interdigital electrode being located in the center of the temperature sensitive unit, the second interdigital electrode comprising a second signal end interdigital electrode and a second ground end interdigital electrode; one end of the second signal end interdigital electrode is connected to one end of the first signal end interdigital electrode; one end of the first ground end interdigital electrode is connected to one end of the second ground end interdigital electrode;

[0016] A signal end, one end of the signal end is connected to the other end of the first signal end interdigital electrode, and the other end of the signal end is connected to the other end of the second signal end interdigital electrode;

[0017] A grounding end, one end of the grounding end is connected to the other end of the first grounding end interdigital electrode, and the other end of the grounding end is connected to the other end of the second grounding end interdigital electrode.

[0018] Furthermore, the conductive layer further comprises:

[0019] a first Bragg reflector, wherein the first Bragg reflector is disposed on both sides of the first interdigital electrode;

[0020] The second Bragg reflector is arranged on both sides of the second interdigital electrode.

[0021] Furthermore, the microsensor further comprises:

[0022] A barrier layer disposed between the upper substrate and the conductive layer;

[0023] A surface coating, the surface coating comprising a surface protection layer disposed on the conductive layer, a first top pad and a second top pad disposed on the surface protection layer;

[0024] The first top pad is disposed corresponding to the signal terminal, and the second top pad is disposed corresponding to the ground terminal.

[0025] Furthermore, the barrier layer and the surface protection layer are one or more of aluminum oxide, silicon oxide and titanium oxide ceramic films, and the conductive layer is one or more of platinum, platinum-rhodium alloy and platinum-iridium alloy films.

[0026] Further, the thickness of the first stress release bridge and the second stress release bridge is smaller than the thickness of the stress isolation beam.

[0027] The present invention also provides a method for preparing a surface acoustic wave microsensor, the method comprising:

[0028] Etching blind grooves layer by layer on the lower substrate by laser; etching first through holes and second through holes layer by layer on the upper substrate by laser; then reducing the thickness of the stress isolation beam by laser etching layer by layer; after the thickness of the stress isolation beam reaches a predetermined thickness, reducing the thickness of the first stress release bridge and the second stress release bridge by laser etching layer by layer;

[0029] Aligning and contacting the side of the blind groove of the lower substrate with the suspended side of the stress isolation beam of the upper substrate, and pressing the lower substrate and the upper substrate with a preset pressure; after maintaining the pressing for a preset time threshold, keeping the pressed lower substrate and the upper substrate warm for a preset time at a set temperature and then cooling them to form a substrate;

[0030] Preparing a barrier layer on the substrate by alternating current magnetron sputtering aluminum oxide deposition;

[0031] A conductive layer is prepared on the barrier layer by direct current magnetron sputtering, and vacuum heat treatment is performed; a photoresist mask is prepared on the surface obtained by the heat treatment, and the photoresist mask is patterned; a noble metal electrode is etched by an argon ion beam, the pattern is transferred to the noble metal electrode, the photoresist mask is removed, and heating is performed at a preset temperature for a certain period of time;

[0032] An oxide ceramic thin film protection layer, a first top pad and a second top pad are prepared on the noble metal electrode by AC magnetron sputtering.

[0033] The present invention provides a surface acoustic wave microsensor, wherein a blind groove is provided on the lower substrate, and a first through hole, a second through hole, a first stress release bridge, a second stress release bridge, and a stress isolation beam surrounded by the first through hole, the second through hole, the first stress release bridge, and the second stress release bridge are provided on the upper substrate, wherein the stress isolation beam is suspended near the lower substrate side; the lower substrate surface on the side where the blind groove is located contacts the upper substrate surface on the suspended side of the stress isolation beam, the blind groove is sealed with the upper substrate to obtain a pressure sensitive unit, the stress isolation beam is connected with the lower substrate to obtain a temperature sensitive unit, the pressure sensitive unit and the temperature sensitive unit have no overlapping area, the temperature sensitive unit is specifically sensitive to temperature, and the surface acoustic wave resonant frequency and working frequency band of the pressure sensitive unit and the temperature sensitive unit are different. In addition, the conductive layer obtains the ambient temperature through the surface acoustic wave of the temperature sensitive unit in the same measurement cycle by allocating the RF signal band, and obtains the ambient pressure through the obtained ambient temperature and the pressure sensitive unit, thereby measuring the high-temperature rotor pressure and temperature, and improving the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 A schematic structural diagram of a surface acoustic wave microsensor provided in an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the structure of a lower substrate provided by an embodiment of the present invention;

[0037] Figure 3 for Figure 2 The cross-section along the AA direction;

[0038] Figure 4 A schematic diagram of the structure of an upper substrate provided by an embodiment of the present invention;

[0039] Figure 5 for Figure 4 The cross-section along the BB direction;

[0040] Figure 6 for Figure 4 The cross-section along the CC direction,

[0041] Figure 7 It is the reflection coefficient spectrum diagram measured by the vector network analyzer in one measurement cycle;

[0042] Figure 8 A schematic diagram of the structure of a conductive layer provided by an embodiment of the present invention;

[0043] Fig. 9 A schematic flow chart of a method for preparing a surface acoustic wave microsensor provided in an embodiment of the present invention;

[0044] Fig.10 A schematic diagram of a substrate preparation process provided by an embodiment of the present invention.

[0045] In the figure, 1 is a lower substrate, 11 is a blind groove; 2 is an upper substrate, 21 is a first through hole, 211 is a first sub-through hole, 212 is a second sub-through hole, 213 is a third sub-through hole, 22 is a second through hole, 221 is a fourth sub-through hole, 222 is a fifth sub-through hole, 223 is a sixth sub-through hole, 23 is a first stress release bridge, 24 is a second stress release bridge, and 25 is a stress isolation beam; 5 is a conductive layer, 51 is a first interdigitated electrode, 511 is a first signal end interdigitated electrode, 512 is a first ground end interdigitated electrode, 52 is a second interdigitated electrode, 521 is a second signal end interdigitated electrode, 522 is a second ground end interdigitated electrode, 55 is a signal end, 58 is a ground end, 591 is a first Bragg reflector, and 592 is a second Bragg reflector; 6 is a barrier layer; 7 is a surface coating, 71 is a surface protective layer, 72 is a first top pad, and 73 is a second top pad. DETAILED DESCRIPTION

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of the present application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0047] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0048] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0049] In the following description, use of suffixes such as “module,” “part,” or “unit” used to refer to elements is merely for facilitating description of the present application, and has no specific meaning by itself.

[0050] like Figure 1 As shown, it is a schematic structural diagram of a surface acoustic wave microsensor provided by an embodiment of the present invention, the microsensor comprises: a lower substrate 1, the lower substrate 1 is provided with a blind groove 11; an upper substrate 2 is arranged on the side of the blind groove 11 on the lower substrate 1, the upper substrate 2 is provided with a first through hole 21, a second through hole 22, a first stress release bridge 23 and a second stress release bridge 24 connecting the first through hole 21 and the second through hole 22, and a stress isolation beam 25 surrounded by the first through hole 21, the second through hole 22, the first stress release bridge 23 and the second stress release bridge 24, the stress isolation beam 25 is suspended near the side of the lower substrate 1; the blind groove 11 and the upper substrate 2 are sealed to form a pressure sensitive unit (not shown in the figure), the pressure sensitive The pressure sensing unit (not shown in the figure) is used to measure pressure; the stress isolation beam 25 is connected to the lower substrate 1 as a temperature sensitive unit (not shown in the figure), and the temperature sensitive unit (not shown in the figure) is used to measure temperature; the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) have no overlapping area, and the surface acoustic wave resonance frequency and working frequency band of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) are different; a conductive layer 5 is arranged on the upper substrate 2, and the conductive layer 5 is configured to convert an alternating current signal into a periodic electromagnetic field, load the periodic electromagnetic field into the upper substrate 2, and obtain the surface acoustic wave of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure).

[0051] Specifically, in this embodiment, Figure 2-3 As shown, Figure 2 A schematic diagram of the structure of a lower substrate provided by an embodiment of the present invention, Figure 3 for Figure 2 In the cross-sectional view along the AA direction, a blind groove 11 is provided on the lower substrate 1. Optionally, the cavity of the blind groove 11 can be a cylinder or a cuboid. Figure 4-6 As shown, Figure 4A schematic diagram of the structure of an upper substrate provided by an embodiment of the present invention, Figure 5 for Figure 4 The cross-section along the BB direction, Figure 6 for Figure 4 In the cross-sectional view along the CC direction, first, the upper substrate 2 is provided with a first through hole 21 and a second through hole 22. Preferably, the first through hole 21 includes a first sub-through hole 211, a second sub-through hole 212 connected to one end of the first sub-through hole 211, and a third sub-through hole 213 connected to the second sub-through hole 212. The second through hole 22 includes a fourth sub-through hole 221, a fifth sub-through hole 222 connected to one end of the fourth sub-through hole 221, and a sixth sub-through hole 223 connected to the fifth sub-through hole 222. The other end of the first sub-through hole 211 is connected to the fourth sub-through hole 221 through a first stress release bridge 23, and the other end of the third sub-through hole 213 is connected to the other end of the sixth sub-through hole 223 through a second stress release bridge 24. , and the second sub-through hole 212 and the third sub-through hole 213 are located on the side of the first sub-through hole 211 close to the second through hole 22, the fifth sub-through hole 222 and the sixth sub-through hole 223 are located on the side of the second through hole 22 close to the first sub-through hole 211, and the first through hole 21 and the second through hole 22 are arranged in correspondence; the middle area surrounded by the first through hole 21, the second through hole 22, the first stress release bridge 23 and the second stress release bridge 24 is a stress isolation beam 25, that is, the stress isolation beam 25 is connected to the upper substrate 2 through the first stress release bridge 23 and the second stress release bridge 24, and the other parts of the stress isolation beam 25 are isolated from the upper substrate 2 through the first through hole 21 and the second through hole 22. And the stress isolation beam 25 is suspended near the side of the lower substrate 1 to avoid contact with the lower substrate 1. The depth of the first through hole 21 and the second through hole 22 penetrates the upper substrate 2. In this embodiment, the lower substrate 1 and the upper substrate 2 are piezoelectric substrates.

[0052] The lower substrate 1 surface on the side where the blind groove 11 is located and the upper substrate 2 surface on the suspended side of the stress isolation beam 25 are sealed by low pressure and high temperature induction bonding. The blind groove 11 is sealed with the upper substrate 2 to obtain a pressure sensitive unit (not shown in the figure), and the stress isolation beam 25 is connected to the lower substrate 1 to obtain a temperature sensitive unit (not shown in the figure). The pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) have no overlapping area, and the surface acoustic wave resonant frequency and working frequency band of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) are different. The environmental pressure loads stress in the upper substrate 1, changes the wavelength of the surface acoustic wave, and shifts the resonant frequency of the surface acoustic wave. At a certain temperature, the resonant frequency of the surface acoustic wave output by the pressure sensitive unit (not shown in the figure) increases linearly with the increase of pressure. The resonant frequency of the surface acoustic wave output by the temperature sensitive unit (not shown in the figure) decreases monotonically with the increase of temperature, and the corresponding relationship is a quadratic function. Since the ambient temperature changes the stiffness and density of the lower substrate 1 and the upper substrate 2, causing thermal expansion of the structure, temperature drift will be introduced into the pressure sensing signal. However, in the embodiment of the present application, the temperature sensitive unit (not shown in the figure) is specifically sensitive to temperature through the stress isolation beam 25, avoiding the surface acoustic wave interference between the sensitive units, while the output of the pressure sensitive unit (not shown in the figure) is disturbed by temperature changes. At the same time, the stress isolation beam 25 in the present application can also avoid the surface acoustic wave signals of the pressure sensitive unit and the temperature sensitive unit from interfering with each other, but makes the pressure sensitive unit and the temperature sensitive unit close enough, so that the sensor structure is compact.

[0053] When the surface acoustic wave microsensor measures the pressure and temperature of the high-temperature rotor, an alternating current signal is input into the conductive layer 5, and the conductive layer 5 converts the received alternating current signal into a periodic electromagnetic field, and loads the converted periodic electromagnetic field onto the upper substrate 2, generating surface acoustic waves on the surface of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure). In the same measurement cycle, the signals of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) are read, and the offset of the resonance peak of the temperature sensitive unit (not shown in the figure) is obtained according to the frequency and reflection coefficient curve of the surface acoustic wave output by the temperature sensitive unit (not shown in the figure), and the ambient temperature is obtained according to the offset of the resonance peak of the temperature sensitive unit (not shown in the figure). After obtaining the ambient temperature, the corresponding pressure sensitive curve is selected to obtain the offset of the resonance peak of the pressure sensitive unit (not shown in the figure), and the ambient pressure is obtained. The resonance peaks of the surface acoustic waves of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) are allocated in frequency bands, and the working frequency bands of the two do not overlap. Surface acoustic wave (SAW) is very sensitive to disturbances on the waveguide surface. Changes in elastic modulus, density, and strain will cause shifts in acoustic wave frequency, amplitude, and phase. Compared with capacitive and inductive sensors, surface acoustic wave sensors have the advantages of high quality factor, long communication distance, and small size. In an embodiment of the present invention, the pressure response of a pressure sensitive unit (not shown in the figure) at different temperatures can be calibrated first, and then, during measurement, the pressure-temperature coupling signal of the pressure sensitive unit (not shown in the figure) can be demodulated using the specific sensitive signal of the temperature sensitive unit (not shown in the figure).

[0054] In some embodiments, the lower substrate 1 and the upper substrate 2 are single crystal wafers with the same crystal orientation, the pressure sensitive unit (not shown in the figure) is arranged along the main tangent direction of the upper substrate 2 and the lower substrate 1, and the temperature sensitive unit (not shown in the figure) is arranged along the secondary tangent direction of the upper substrate 2 and the lower substrate 1.

[0055] Specifically, in this embodiment, the Euler angles of the upper substrate 2 and the lower substrate 1 are (0°, 138.5°, 0-60°).

[0056] Furthermore, the single crystal wafer is lanthanum gallium silicate.

[0057] Specifically, in this embodiment, the lower substrate 1 and the upper substrate 2 are double-polished lanthanum gallium silicate single crystal wafers with the same crystal orientation, and the Euler angle of the main tangent is preferably (0°, 138.5°, 0°), and the Euler angle of the secondary tangent is (0°, 138.5°, 26.7°).

[0058] In some embodiments, the surface acoustic wave resonance frequency of the pressure sensitive unit (not shown in the figure) is 193 MHz, and the operating frequency band is 190-200 MHz; the surface acoustic wave resonance frequency of the temperature sensitive unit (not shown in the figure) is 223 MHz, and the operating frequency band is 215-225 MHz.

[0059] Specifically, in this embodiment, by setting the surface acoustic wave resonance frequency and the operating frequency band of the pressure sensitive unit (not shown in the figure) and the temperature sensitive unit (not shown in the figure) close to each other and without crossing, the frequency band input to the conductive layer 5 is 190 MHz-230 MHz, and the reflection coefficient spectrum measured by the vector network analyzer in one measurement cycle is as follows: Figure 7 As shown, the pressure-temperature coupling sensing signal and the temperature sensing signal are collected in the same measurement cycle through surface acoustic wave frequency band allocation, and the resonant frequency offset of the pressure sensitive unit (not shown in the figure) and the resonant frequency offset of the temperature sensitive unit (not shown in the figure) are obtained to obtain the temperature and pressure of the environment with high measurement accuracy.

[0060] In some embodiments, Figure 8 , which is a schematic diagram of the structure of a conductive layer provided in an embodiment of the present invention, the conductive layer 5 comprises: a first interdigitated electrode 51, the first interdigitated electrode 51 is located in the center of the pressure sensitive unit (not shown in the figure), and the first interdigitated electrode 51 comprises a first signal end interdigitated electrode 511 and a first ground end interdigitated electrode 512; a second interdigitated electrode 52, the second interdigitated electrode 52 is located in the center of the temperature sensitive unit (not shown in the figure), and the second interdigitated electrode 52 comprises a second signal end interdigitated electrode 521 and a second ground end interdigitated electrode 522; the second signal end interdigitated electrode 52 is located in the center of the temperature sensitive unit (not shown in the figure), and the second signal end interdigitated electrode 52 comprises a second signal end interdigitated electrode 521 and a second ground end interdigitated electrode 522; One end of the finger electrode 521 is connected to one end of the first signal end forked electrode 511; the first ground end forked electrode 512 is connected to one end of the second ground end forked electrode 522; the signal end 55, one end of the signal end 55 is connected to the other end of the first signal end forked electrode 511, and the other end of the signal end 55 is connected to the other end of the second signal end forked electrode 521; the ground end 58, one end of the ground end 85 is connected to the other end of the first ground end forked electrode 512, and the other end of the ground end 58 is connected to the other end of the second ground end forked electrode 522.

[0061] Specifically, in this embodiment, the alternating current signal is converted into an electromagnetic field by the first interdigital electrode 51, and the pressure sensitive unit (not shown in the figure) is excited by the electromagnetic field to generate a surface acoustic wave, and the first interdigital electrode 51 converts the surface acoustic wave into an electrical signal and then transmits it, thereby obtaining the resonant frequency offset of the pressure sensitive unit (not shown in the figure). The alternating current signal is converted into an electromagnetic field by the second interdigital electrode 52, and the temperature sensitive unit (not shown in the figure) is excited by the electromagnetic field to generate a surface acoustic wave, and the second interdigital electrode 52 converts the surface acoustic wave into an electrical signal and then transmits it, thereby obtaining the resonant frequency offset of the temperature sensitive unit (not shown in the figure).

[0062] In some embodiments, Figure 8 As shown, the conductive layer 5 further includes: a first Bragg reflector 591 , which is disposed on both sides of the first interdigital electrode 51 ; and a second Bragg reflector 592 , which is disposed on both sides of the second interdigital electrode 52 .

[0063] Specifically, the first Bragg reflector grating 591 is arranged on both sides of the first interdigital electrode 51 to reduce the surface acoustic wave loss of the pressure sensitive unit (not shown in the figure); the second Bragg reflector grating 592 is arranged on both sides of the second interdigital electrode 52 to reduce the surface acoustic wave loss of the temperature sensitive unit (not shown in the figure). The first interdigital electrode 51 and the first Bragg reflector grating 591 correspond to the same surface acoustic wave wavelength, and the second interdigital electrode 52 and the second Bragg reflector grating 592 correspond to the same surface acoustic wave wavelength.

[0064] In some embodiments, Figure 1 As shown, the microsensor also includes: a barrier layer 6 arranged between the upper substrate 2 and the conductive layer 5; a surface coating 7, the surface coating 7 includes a surface protection layer 71 arranged on the conductive layer 5, and a first top pad 72 and a second top pad 73 arranged on the surface protection layer 71; the first top pad 72 is arranged corresponding to the signal terminal 55, and the second top pad 73 is arranged corresponding to the ground terminal 58.

[0065] Specifically, in this embodiment, the high-stability composite film composed of the barrier layer 6, the conductive layer 7 and the surface protection layer 71 is used as the sensor electrode. The barrier layer 6 is located between the upper substrate 2 and the conductive layer 5 to prevent the penetration of elements between the upper substrate 2 and the conductive layer 5; the surface protection layer 71 covers the upper surface of the conductive layer 5 to isolate the air; the barrier layer 6 and the surface protection layer 71 cover the conductive layer 5 to reduce the molecular thermal motion in the conductive layer 5. The barrier layer 6 and the surface protection layer 71 enclose the conductive layer 5 inside, and the two are combined into one by chemical bonds at the gap of the conductive layer 5. The introduction of the barrier layer 6 and the surface protection layer 71 in the sensor improves the stability of the sensor. The AC signal is transmitted between the first top pad 72 and the signal terminal 55 and between the second top pad 73 and the ground terminal 58 through the capacitive coupling effect through the surface protection layer 71. Taking advantage of the characteristic that the radio frequency signal can be transmitted through capacitive coupling, the first top pad 72 and the second top pad 73 are arranged above the surface protection layer 71. The RF signal is transmitted to the conductive layer 5 through the capacitive coupling effect to load the surface acoustic wave sensor. This signal transmission mode has good stability in high temperature air. The first top pad 72 and the second top pad 73 are connected to the coaxial line or the RF antenna through a platinum-rhodium alloy wire. The connection point is a solder point sintered with platinum slurry. The RF antenna can be an on-chip integrated antenna or an independent antenna.

[0066] In some embodiments, the barrier layer 6 and the surface protection layer 71 are one or more of aluminum oxide, silicon oxide and titanium oxide ceramic films, and the conductive layer 5 is one or more of platinum, platinum-rhodium alloy and platinum-iridium alloy films.

[0067] In some embodiments, the thickness of the first stress relief bridge 23 and the second stress relief bridge 24 is smaller than the thickness of the stress isolation beam 25 .

[0068] Specifically, in this embodiment, the thickness of the stress isolation beam 25 is less than the thickness of the upper substrate 2, the thickness of the first stress release bridge 23 and the second stress release bridge 24 is less than the thickness of the stress isolation beam 25, and the thickness of the first stress release bridge 23 and the second stress release bridge 24 is as small as possible within the allowable range, further reducing the stress transmission path to the temperature sensitive unit (not shown in the figure).

[0069] like Fig. 9 FIG. 1 is a flow chart of a method for preparing a surface acoustic wave microsensor provided by an embodiment of the present invention, wherein the method comprises:

[0070] Step S1: etching blind grooves layer by layer on the lower substrate by laser; etching first through holes and second through holes layer by layer on the upper substrate by laser; then reducing the thickness of the stress isolation beam by laser etching layer by layer; after the thickness of the stress isolation beam reaches a predetermined thickness, reducing the thickness of the first stress release bridge and the second stress release bridge by laser etching layer by layer;

[0071] Specifically, in this embodiment, Fig.10 As shown, a schematic diagram of a substrate preparation process provided by an embodiment of the present invention is provided. The etching layer is etched layer by layer by ultraviolet laser with a wavelength of 150-500nm, and a blind groove 11 corresponding to the pressure sensitive unit is formed on the lower substrate 1, and the first through hole 21, the second through hole 22, the first stress release bridge 23, the second stress release bridge 24, and the stress isolation beam 25 are etched layer by layer in the upper substrate 2. Then, the thickness of the first stress release bridge 23, the second stress release bridge 24, and the stress isolation beam 25 are thinned by etching layer by layer. During the etching process, the main laser scanning paths of adjacent etching layers are perpendicular to each other, and the laser etching paths of the same etching layer have rounded transitions and cover the etching plane. The main etching paths between adjacent etching layers intersect with each other, and the laser etching paths have rounded transitions at the corners. The laser layer-by-layer etching refers to local material removal by laser-induced chemical bond breaking. Compared with wet etching, ion etching and mechanical processing, this method has the characteristics of good anisotropy, precise size control and fast processing speed, and can process complex and fragile sensitive structures on lanthanum gallium silicate substrates. In this method, the main etching paths of adjacent etching layers intersect, and the roughness of the etching surface is small. Among them, laser layer-by-layer etching refers to the layer-by-layer removal of lanthanum gallium silicate by laser-induced chemical bond breaking, and the predetermined structure is superimposed. During the etching process, the main laser etching paths between adjacent etching layers are perpendicular to each other, and the laser etching path has a rounded transition to reduce etching stress. The laser parameters are preferably a wavelength of 355nm, a power of 12W, and a scanning speed of 600mm / s.

[0072] Step S2: aligning and contacting the side of the blind groove of the lower substrate with the suspended side of the stress isolation beam of the upper substrate, and pressing the lower substrate and the upper substrate with a preset pressure; after the pressing reaches a preset time threshold, keeping the pressed lower substrate and the upper substrate warm for a preset time at a set temperature and then cooling them to form a substrate;

[0073] Specifically, the pre-bonding of the lower substrate 1 and the upper substrate 2 is completed according to the low-pressure and high-temperature induced bonding method of the lanthanum gallium silicate wafer. The pre-bonded substrate is heated to complete the high-temperature resistant and high-strength bonding of the lower substrate 1 and the upper substrate 2 to form the pressure-sensitive cavity and the stress isolation beam. First, the surface of the lower substrate 1 on the side where the blind groove 11 is located is aligned and contacted with the surface of the upper substrate 2 on the suspended side of the stress isolation beam 25 at room temperature, and pressed with a pressure of less than 50 kPa to form a pre-bonding surface; then the pre-bonded substrate is pressed with a pressure of less than 50 kPa, and heated at 1176-1323°C for 2-5h to melt the pre-bonding surface to form a high-temperature resistant and high-strength amorphous transition zone to complete the wafer bonding.

[0074] Among them, low-pressure and high-temperature induced bonding refers to aligning and contacting the upper substrate 1 and the lower substrate 2, and pressing them with a pressure of less than 50kPa, heating to produce a molten layer on the surface of the substrate, and combining the molten layers of the upper substrate and the lower substrate into an amorphous transition zone to complete the high-temperature and high-strength bonding of the substrate. The low-pressure and high-temperature induced bonding method of the lanthanum gallium silicate wafer first aligns and contacts the lower substrate 1 and the upper substrate 2 at room temperature, and after the interface is in contact, the two substrates are pressed at a pressure of preferably 40kPa, and the bonding interface is fully contacted after 1h to form a pre-bonded surface attracted by van der Waals force. Then, the pre-bonded substrate is pressed at a pressure of preferably 40kPa, and the substrate is kept at a preferred temperature of 1250℃ for 3h and then cooled, so that the substrate melts at the interface to form an amorphous transition zone, and the high-temperature and high-strength bonding of the substrate is completed. During the heating process, the heating and cooling rate is preferably 8℃ / minute. Since the thermal expansion coefficients of the two substrates are the same, no microcracks are generated in the substrate after bonding. The lower substrate 1 and the upper substrate 2 are combined to form a pressure sensitive cavity and a stress isolation beam.

[0075] Step S3: preparing a barrier layer on the substrate by AC magnetron sputtering aluminum oxide deposition;

[0076] A barrier layer 6 is formed by depositing aluminum oxide with a certain thickness (eg, 20 nm) on the substrate by AC magnetron sputtering.

[0077] Step S4: preparing a conductive layer on the barrier layer by direct current magnetron sputtering, and performing vacuum heat treatment; preparing a photoresist mask on the surface obtained by the heat treatment, and patterning the photoresist mask; etching the noble metal electrode by argon ion beam, transferring the pattern to the noble metal electrode, removing the photoresist mask, and heating at a preset temperature for a certain period of time;

[0078] Specifically, a platinum electrode with a certain thickness (e.g., 150 nm) is prepared on the barrier layer 6 by direct current magnetron sputtering; the prepared film is subjected to vacuum heat treatment at 700° C. for 1 hour, and the vacuum degree is 5×10 -4Pa, the heating and cooling rate is 5°C / min; a photoresist mask is prepared on the surface of the electrode after heat treatment, and the mask is patterned, wherein the photoresist thickness can be 2um; the platinum electrode is etched by an argon ion beam, and the pattern is transferred to the platinum electrode; the photoresist mask is removed, and then the substrate is baked on a hot plate at 80°C for 30 minutes; finally, an aluminum oxide protective layer of a certain thickness (such as 120nm) is deposited on the dried platinum electrode by AC magnetron sputtering to isolate the air.

[0079] Step S5: preparing an oxide ceramic thin film protective layer, a first top pad and a second top pad on the noble metal electrode by AC magnetron sputtering.

[0080] Specifically, first, a tungsten mask of a certain thickness (such as 150um) is fixed on the surface of the alumina protective layer; then, platinum slurry is scraped on the surface of the tungsten mask and heated at 80°C for 1 hour to complete the preliminary sintering of the platinum slurry; finally, the mask is removed, and the preliminary sintered platinum slurry is heated at 800°C for 1 hour to form a first top pad and a second top pad.

[0081] The low-pressure and high-temperature induced bonding method and the laser layer-by-layer etching method proposed in the present invention have the advantages of low processing stress, good anisotropy, and precise size control, and are suitable for the processing of sensitive structures such as pressure-sensitive cavities and stress isolation beams. In addition, the stress during the bonding process is low, which can avoid stress brittle fracture or introduction of microcracks in sensitive structures. In addition, the method does not require surface activation, which avoids the destruction of the interface microstructure.

[0082] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A surface acoustic wave microsensor, characterized in that: The micro sensor comprises: A lower substrate, wherein a blind groove is provided on the lower substrate; An upper substrate is provided on the side of the lower substrate where the blind groove is located, the upper substrate is provided with a first through hole, a second through hole, a first stress release bridge connecting the first through hole and the second through hole, a second stress release bridge, and a stress isolation beam surrounded by the first through hole, the second through hole, the first stress release bridge and the second stress release bridge, and the stress isolation beam is suspended near the lower substrate side; The stress isolation beam is connected to the upper substrate through the first stress release bridge and the second stress release bridge, and the other parts of the stress isolation beam are isolated from the upper substrate through the first through hole and the second through hole; The blind groove is sealed with the upper substrate to form a pressure sensitive unit, and the pressure sensitive unit is used to measure pressure; the stress isolation beam is connected with the lower substrate to form a temperature sensitive unit, and the temperature sensitive unit is used to measure temperature; the pressure sensitive unit and the temperature sensitive unit have no overlapping area, and the surface acoustic wave resonance frequency and working frequency band of the pressure sensitive unit and the temperature sensitive unit are different; A conductive layer is disposed on the upper substrate, and the conductive layer is configured to convert an alternating current signal into a periodic electromagnetic field, load the periodic electromagnetic field into the upper substrate, and obtain surface acoustic waves of the pressure sensitive unit and the temperature sensitive unit.

2. The surface acoustic wave microsensor according to claim 1, characterized in that: The lower substrate and the upper substrate are single crystal wafers with the same crystal orientation, the pressure sensitive unit is arranged along the main tangent direction of the upper substrate and the lower substrate, and the temperature sensitive unit is arranged along the secondary tangent direction of the upper substrate and the lower substrate.

3. The surface acoustic wave microsensor according to claim 2, characterized in that: The single crystal wafer is lanthanum gallium silicate.

4. The surface acoustic wave microsensor according to claim 1, characterized in that: The surface acoustic wave resonance frequency of the pressure sensitive unit is 193 MHz, and the operating frequency range is 190-200 MHz; the surface acoustic wave resonance frequency of the temperature sensitive unit is 223 MHz, and the operating frequency range is 215-225 MHz.

5. The surface acoustic wave microsensor according to claim 1, characterized in that: The conductive layer comprises: A first interdigital electrode, the first interdigital electrode is located in the center of the pressure sensitive unit, and the first interdigital electrode includes a first signal end interdigital electrode and a first ground end interdigital electrode; a second interdigital electrode, the second interdigital electrode being located in the center of the temperature sensitive unit, the second interdigital electrode comprising a second signal end interdigital electrode and a second ground end interdigital electrode; one end of the second signal end interdigital electrode is connected to one end of the first signal end interdigital electrode; one end of the first ground end interdigital electrode is connected to one end of the second ground end interdigital electrode; A signal end, the signal end is connected to the other end of the first signal end interdigital electrode, and the other end of the signal end is connected to the other end of the second signal end interdigital electrode; A grounding end, one end of the grounding end is connected to the other end of the first grounding end interdigital electrode, and the other end of the grounding end is connected to the other end of the second grounding end interdigital electrode.

6. The surface acoustic wave microsensor according to claim 5, characterized in that: The conductive layer further comprises: a first Bragg reflector, wherein the first Bragg reflector is disposed on both sides of the first interdigital electrode; The second Bragg reflector is arranged on both sides of the second interdigital electrode.

7. The surface acoustic wave microsensor according to claim 5, characterized in that: The microsensor also includes: A barrier layer disposed between the upper substrate and the conductive layer; A surface coating, the surface coating comprising a surface protection layer disposed on the conductive layer, a first top pad and a second top pad disposed on the surface protection layer; The first top pad is disposed corresponding to the signal terminal, and the second top pad is disposed corresponding to the ground terminal.

8. The surface acoustic wave microsensor according to claim 7, characterized in that: The barrier layer and the surface protection layer are one or more of aluminum oxide, silicon oxide and titanium oxide ceramic films, and the conductive layer is one or more of platinum, platinum-rhodium alloy and platinum-iridium alloy films.

9. The surface acoustic wave microsensor according to claim 1, characterized in that: The thickness of the first stress release bridge and the second stress release bridge is smaller than the thickness of the stress isolation beam.

10. A method for preparing a surface acoustic wave microsensor, the method being based on the surface acoustic wave microsensor according to claim 1, characterized in that: The method comprises: Etching blind grooves layer by layer on the lower substrate by laser; etching first through holes and second through holes layer by layer on the upper substrate by laser; then reducing the thickness of the stress isolation beam by laser etching layer by layer; after the thickness of the stress isolation beam reaches a predetermined thickness, reducing the thickness of the first stress release bridge and the second stress release bridge by laser etching layer by layer; Aligning and contacting the side of the blind groove of the lower substrate with the suspended side of the stress isolation beam of the upper substrate, and pressing the lower substrate and the upper substrate with a preset pressure; after maintaining the pressing for a preset time threshold, keeping the pressed lower substrate and the upper substrate warm for a preset time at a set temperature and then cooling them to form a substrate; Preparing a barrier layer on the substrate by alternating current magnetron sputtering aluminum oxide deposition; A conductive layer is prepared on the barrier layer by direct current magnetron sputtering, and vacuum heat treatment is performed; a photoresist mask is prepared on the surface obtained by the heat treatment, and the photoresist mask is patterned; a noble metal electrode is etched by an argon ion beam, the pattern is transferred to the noble metal electrode, the photoresist mask is removed, and heating is performed at a preset temperature for a certain period of time; An oxide ceramic thin film protection layer, a first top pad and a second top pad are prepared on the noble metal electrode by AC magnetron sputtering.

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