Piezoelectric cantilever acoustic resonant cavity structure and preparation method thereof

Abstract

The invention discloses a piezoelectric cantilever beam acoustic resonant cavity structure and a preparation method thereof, the structure comprises a resonant cavity silicon layer, an SOI bottom silicon layer, an SOI oxide layer, an SOI top silicon layer, a seed layer, an electrode and a cantilever beam piezoelectric layer, the electrode is deposited on the cantilever beam piezoelectric layer, a top electrode, the piezoelectric layer and a bottom electrode form a sandwich structure, the area a of the top electrode is 0.4 time of the area b of a cantilever beam, and the area b of the piezoelectric layer is 0.4 time of the area b of the cantilever beam. A groove is etched in the resonant cavity silicon layer, openings are formed in the two ends of the groove in a penetrating mode, a second through hole is formed in the middle of the SOI bottom silicon layer in a digging mode and located over the groove, a first through hole is formed in the middle of the SOI oxide layer in a digging mode and located over the second through hole, and the SOI top silicon layer is attached to the SOI oxide layer. And the SOI top silicon layer covers the first through hole and the second through hole, so that the SOI top silicon layer, the first through hole, the second through hole and the groove form a resonant cavity. According to the invention, miniaturization and high integration are improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor integrated circuit technology, specifically to a piezoelectric cantilever beam acoustic resonator structure and its fabrication method. Background Technology

[0002] Photoacoustic spectroscopy systems (such as photoacoustic sensors) can be used for gas detection, and are commonly used to measure trace gases in fields such as environmental monitoring, medical diagnostics, aerospace, and petrochemicals. The main principle of a photoacoustic spectroscopy system is to project a laser beam of a specific wavelength, which falls within the wavelength range that the gas can absorb. By detecting the acoustic signal released after the gas absorbs the specific wavelength of the laser beam, the spectrum of the gas within its characteristic absorption wavelength range can be obtained, thus enabling the detection of the gas's composition and concentration. One of the core structures of a photoacoustic spectroscopy system is the acoustic resonant cavity, the performance of which often determines the final performance of the system.

[0003] Existing acoustic resonators are often structurally complex, resulting in large volumes, and miniaturization and integration require further improvement. Furthermore, due to their large size, existing acoustic resonators suffer from low piezoelectric conversion efficiency (i.e., low energy conversion in the photoacoustic effect), necessitating further improvement in their detection performance for weak sound pressure levels. Additionally, the structural design of existing acoustic resonators needs to further enhance the photoacoustic effect to reduce energy leakage in the photoacoustic sound pressure, thereby improving the signal-to-noise ratio of the photoacoustic sensing system and achieving a lower detection limit. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a piezoelectric cantilever beam acoustic resonator structure and its fabrication method, which can solve the problems described in the background art.

[0005] The technical solution to achieve the objective of this invention is as follows: a piezoelectric cantilever beam acoustic resonator structure, comprising, from bottom to top, a resonator silicon layer, an SOI bottom silicon layer, an SOI oxide layer, an SOI top silicon layer, a seed layer, and a cantilever beam piezoelectric layer, and further comprising electrodes, including a cantilever beam bottom electrode and a cantilever beam top electrode, wherein the SOI top silicon layer, the seed layer, the cantilever beam bottom electrode, the cantilever beam piezoelectric layer, and the cantilever beam top electrode constitute the cantilever beam. Electrodes are deposited on the piezoelectric layer of the cantilever beam, and the resonant frequency of the cantilever beam is <20 kHz. The area of ​​the top electrode of the cantilever beam is denoted as electrode area a, and the area of ​​the cantilever beam is denoted as cantilever beam area b. The electrode area a is 0.4 times the cantilever beam area b. A groove is cut into the silicon layer of the resonant cavity, with openings at both ends of the groove. A second through-hole is drilled in the middle of the SOI bottom silicon layer, and the second through-hole is located directly above the groove. A first through-hole is drilled in the middle of the SOI oxide layer, and the first through-hole is located directly above the second through-hole. The SOI top silicon layer is attached to the SOI oxide layer, and the SOI top silicon layer covers the first and second through holes, so that the SOI top silicon layer, the first through hole, the second through hole and the groove form a resonant cavity.

[0006] Furthermore, a first cantilever beam etching pattern is formed on the seed layer through etching, and a second cantilever beam etching pattern is formed on the SOI top silicon layer through etching. The first and second cantilever beam etching patterns have the same structure, with the first cantilever beam etching pattern located directly above the second cantilever beam etching pattern. When the seed layer is lazily superimposed on the SOI top silicon layer, the first and second cantilever beam etching patterns perfectly overlap. Patterns are etched onto the cantilever beam piezoelectric layer, and the patterns on the cantilever beam piezoelectric layer are identical to the front end structures of the first and second cantilever beam etched patterns. Bottom electrode patterns and top electrode patterns are etched on the bottom electrode and top electrode of the cantilever beam, respectively. The bottom electrode pattern is consistent with the first cantilever beam etching pattern. When the SOI top silicon layer, seed layer, bottom electrode layer, cantilever beam piezoelectric layer and top electrode layer are sequentially bonded together, a multilayer stacked structure is formed.

[0007] Furthermore, the thickness of the resonant cavity silicon layer is greater than the thickness of the SOI bottom silicon layer, the thickness of the SOI top silicon layer, and the thickness of the cantilever piezoelectric layer. The thickness of the cantilever piezoelectric layer is greater than the thickness of the seed layer and the thickness of the SOI oxide layer, respectively.

[0008] Furthermore, the thickness of the silicon layer in the resonant cavity is approximately 1 mm to 2 mm, and the depth of the groove is 0.5 mm to 1.5 mm.

[0009] Furthermore, the length of the second perforation is 1 / 4 of the length of the groove, the width of the second perforation is the same as the width of the groove, and the width of the second perforation is greater than the length or width of the cantilever beam.

[0010] Furthermore, the resonant frequency of the resonant cavity is consistent with the resonant frequency of the cantilever beam.

[0011] Furthermore, the length direction of the cantilever beam is perpendicular to the length direction of the groove.

[0012] Furthermore, the length direction of the cantilever beam is parallel to the length direction of the groove.

[0013] Furthermore, the bottom electrode layer, the cantilever piezoelectric layer, and the top electrode layer form a sandwich structure. By designing two cantilever beams of the same size, the same resonant frequency is achieved. The electrodes are connected in parallel, that is, the two top electrodes are connected and the two bottom electrodes are connected, so that the piezoelectric signal is output in parallel at the resonant point. This increases the device capacitance and reduces the interference of parasitic capacitance, thereby increasing the signal-to-noise ratio of the photoacoustic spectroscopy system.

[0014] A method for fabricating a piezoelectric cantilever beam acoustic resonator structure includes the following steps: a) Clean the SOI device, SOI oxide layer, SOI bottom silicon layer, and SOI top silicon layer; b) A seed layer of aluminum nitride is sequentially deposited on the top silicon layer of SOI. A bottom electrode of cantilever beam is constructed using molybdenum, a piezoelectric layer of cantilever beam is constructed using aluminum nitride, and a top electrode of cantilever beam is constructed using molybdenum. The bottom electrode and the top electrode of cantilever beam are patterned using a dry etching process to obtain electrode patterns, thereby obtaining the bottom electrode pattern of the bottom electrode of cantilever beam and the top electrode pattern of the top electrode of cantilever beam. c) The cantilever beam pattern is etched into the piezoelectric layer of the cantilever beam using a dry etching process, thereby obtaining the cantilever beam pattern, exposing the bottom electrode of the cantilever beam, and etching out the gaps in the cantilever beam pattern. d) Gold deposition is used as wire bonding points for electrical connections using sputtering technology, and the cantilever beam pattern gaps are etched into the top silicon layer of SOI using deep silicon etching technology. e) A silicon dioxide layer is deposited on the front side of the SOI device as a protective layer to obtain a silicon dioxide protective layer, and an aluminum nitride layer is deposited on the back side of the SOI device to obtain a cavity oxide layer, which is used as a hard mask patterning for cavity etching. f) Use deep silicon etching process to etch the SOI bottom silicon layer into the cavity, and use wet process to remove the front silicon dioxide protective layer and the back cavity oxide layer to release the SOI device. g) Use the DSI process to etch a resonant cavity pattern onto a 1-2 mm thick silicon wafer; h) The resonant cavity silicon layer and the cantilever beam device layer are bonded together using an adhesive.

[0015] The beneficial effects of this invention are as follows: This invention is based on SOI to construct a piezoelectric cantilever beam acoustic resonator structure, and by limiting the electrode area a to 0.4 times the cantilever beam area b, the piezoelectric conversion efficiency of the cantilever beam is maximized; by designing the length and width dimensions of the cantilever beam, the resonant frequency is located in the low-frequency band (below 20kHz) of photoacoustic detection, and the photoacoustic spectroscopy system composed of the piezoelectric cantilever beam acoustic resonator structure can operate at the resonant point, thereby improving the signal-to-noise ratio.

[0016] By designing the length of the back cavity to be 1 / 4 of the length of the resonant cavity, and limiting the resonant frequencies of the resonant cavity and the cantilever beam to be consistent, miniaturization and high integration are improved. The resulting piezoelectric cantilever beam acoustic resonant cavity structure has a thickness on the order of millimeters, making it extremely small in size. Furthermore, since the photoacoustic signal is inversely proportional to the volume, it is possible to maximize the photoacoustic signal.

[0017] By using multiple cantilever beams connected in parallel, the capacitance of the device can be increased and the influence of parasitic capacitance can be reduced.

[0018] The above structural design enables a lower detection limit and improved signal-to-noise ratio. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the orthogonal three-dimensional structure of the present invention; Figure 2 This is an orthogonal exploded view of the present invention; Figure 3 This is a schematic diagram of the three-dimensional structure after the orthogonal electrodes and protective coating are assembled. Figure 4 This is a schematic diagram of the parallel three-dimensional structure of the present invention; Figure 5 This is a schematic diagram of the three-dimensional structure of two parallel units of the present invention; Figure 6 This is a parallel explosion diagram of the present invention; Figure 7 This is an exploded schematic diagram of two parallel lines of the present invention; Figure 8 A schematic diagram showing the simulation results of the first-order longitudinal resonant frequency under different ratios of back cavity length to resonant cavity length; Figure 9 A schematic diagram of the simulation results of the normalized output voltage under different electrode areas and piezoelectric cantilever beam area ratios; Figure 10 A schematic diagram showing the simulation results of normalized output power under different electrode areas and piezoelectric cantilever beam area ratios and under different loads; Figure 11 A schematic diagram illustrating the fabrication process of a piezoelectric cantilever beam acoustic resonator structure. In the figure, 1-protective coating, 2-cantilever beam top electrode, 3-cantilever beam piezoelectric layer, 31-cantilever beam piezoelectric layer pattern, 4-cantilever beam bottom electrode, 5-first cantilever beam etched pattern, 6-seed layer, 7-second cantilever beam etched pattern, 8-SOI top silicon layer, 9-first via, 10-SOI oxide layer, 11-second via, 12-SOI bottom silicon layer, 13-groove, 14-resonant cavity silicon layer, 15-electrode pattern, 16-cantilever beam pattern, 17-protective layer, 18-resonant cavity pattern, 19-silicon wafer, 20-wire bonding point, 21-cavity, 22-adhesive, 23-pattern gap, 24-hard mask patterning. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: like Figures 1-10 As shown, a piezoelectric cantilever beam acoustic resonator structure includes, from bottom to top, a resonator silicon layer 14, an SOI bottom silicon layer 12, an SOI oxide layer 10, an SOI top silicon layer 8, a seed layer 6, and a cantilever beam piezoelectric layer 3, and also includes electrodes, including a cantilever beam bottom electrode 2 and a cantilever beam top electrode 4. A first cantilever beam etching pattern 5 is formed on the seed layer 6, and a second cantilever beam etching pattern 7 is formed on the SOI top silicon layer 8. The first cantilever beam etching pattern 5 and the second cantilever beam etching pattern 7 have the same structure, with the first cantilever beam etching pattern 5 located directly above the second cantilever beam etching pattern 7. When the seed layer 6 is tightly superimposed on the SOI top silicon layer 8, the first cantilever beam etching pattern 5 and the second cantilever beam etching pattern 7 overlap perfectly. A cantilever beam pattern 31 is formed on the cantilever beam piezoelectric layer 3, with the front end of the cantilever beam pattern 31 (i.e.,...)... Figure 2 The four structures of the cantilever beam pattern 31 are the same: the end of the cantilever beam pattern 31 near the origin along the X-axis, the front end of the first cantilever beam etched pattern 5, the front end of the second cantilever beam etched pattern 7, and the front end of the bottom electrode pattern. The bottom electrode pattern is a pattern etched on the bottom electrode 4 of the cantilever beam. The bottom electrode 4 of the cantilever beam is described below. When the cantilever beam piezoelectric layer 3, seed layer 6, and SOI top silicon layer 8 are stacked together in sequence, the bottom electrode 4 of the cantilever beam is attached to the lower surface of the cantilever beam pattern 31, the top electrode 2 of the cantilever beam is deposited on the upper surface of the cantilever beam pattern 31, the front end of the cantilever beam pattern 31 is attached to the front end of the first cantilever beam etched pattern 5, and the front end of the first cantilever beam etched pattern 5 is attached to the front end of the second cantilever beam etched pattern 7.

[0021] like Figure 3 As shown, electrode patterns 15 are formed on the top electrode 2 and the bottom electrode 4 of the cantilever beam, respectively serving as the top electrode pattern of the top electrode 2 and the bottom electrode pattern of the bottom electrode 4 of the cantilever beam.

[0022] The resonant cavity silicon layer 14, SOI bottom silicon layer 12, SOI oxide layer 10, SOI top silicon layer 8, seed layer 6 and cantilever piezoelectric layer 3 can be stacked together by bonding.

[0023] The electrodes include a deposited cantilever beam top electrode 2 and a cantilever beam bottom electrode 4, which are located at the upper and lower ends of the cantilever beam piezoelectric layer 3, respectively, so that the cantilever beam top electrode 2 and the cantilever beam bottom electrode 4 are stacked at intervals.

[0024] The length of the top electrode 2 of the cantilever beam (i.e. Figure 2 The length of the cantilever beam (along the X-axis, representing the length of the top electrode 2) is less than the length of the bottom electrode 4, ensuring that the resonant frequency of the cantilever beam is less than 20 kHz. The cantilever beam, from bottom to top, consists of an SOI top silicon layer 8, a seed layer 6, a bottom electrode 4, a piezoelectric layer 3, and the top electrode 2. This design allows the resonant frequency to be lower than the relaxation time of most gas molecules, facilitating energy conversion in the photoacoustic effect. Achieving a resonant frequency below 20 kHz can be achieved by altering the length, width, and electrode thickness of the cantilever beam.

[0025] In this design, the area of ​​the top electrode 2 of the cantilever beam is denoted as electrode area a, and the area of ​​the cantilever beam is denoted as cantilever beam area b. The electrode area a is 0.4 times the cantilever beam area b. By limiting the size of these areas, the piezoelectric conversion efficiency is maximized, thereby improving the detection performance of weak sound pressure.

[0026] refer to Figure 9 and Figure 10 When the electrode area a is 0.4 times the cantilever beam area b, the highest efficiency piezoelectric conversion can be achieved, improving the detection performance of weak sound pressure.

[0027] For example, a protective coating 1 is provided on the electrode to protect the electrode and the wire bonding. The protective coating 1 can be an Au layer (gold layer).

[0028] In the thickness direction, that is Figure 2 In the Z-axis direction, the thickness of the resonant cavity silicon layer 14 is greater than the thickness of the SOI bottom silicon layer 12, the thickness of the SOI top silicon layer 8, and the thickness of the cantilever piezoelectric layer 3. The thickness of the cantilever piezoelectric layer 3 is greater than the thickness of the seed layer 6 and the thickness of the SOI oxide layer 10, respectively. That is, the thickness of the seed layer 6 and the thickness of the SOI oxide layer 10 are both less than the thickness of the cantilever piezoelectric layer 3.

[0029] A groove 13 is formed in the silicon layer 14 of the resonant cavity. The groove 13 has openings at both ends for laser beam insertion. The groove 13 is rectangular and extends along the entire length of the silicon layer 14 of the resonant cavity. Figure 2In the Y-axis direction, the groove 13 extends along the entire length of the silicon layer 14 of the resonant cavity.

[0030] The thickness of the silicon layer 14 in the resonant cavity is approximately 1 mm to 2 mm (including the endpoints), and the depth of the groove 13 is... Figure 2 The depth of the groove 13 (in the Z-axis direction) is 0.5 mm to 1.5 mm.

[0031] A second through hole 11 is provided in the middle of the SOI bottom silicon layer 12. The second through hole 11 is rectangular, and its length is 1 / 4 of the length of the groove 13. The width of the second through hole 11 (i.e., Figure 2 The width of the second through hole 11 is the same as the width of the groove 13 (the X-axis direction is the width direction). The width of the second through hole 11 is slightly greater than the length (corresponding to the orthogonal type) or width (corresponding to the parallel type) of the cantilever beam. That is, the width of the cantilever beam on the top electrode 2 and the width of the cantilever beam on the bottom electrode 4 are both less than the length of the second through hole 11. The second through hole 11 is located directly above the groove 13. When the SOI bottom silicon layer 12 is attached to the resonant cavity silicon layer 14, the second through hole 11 is exactly attached to the groove 13 and communicates with the groove 13.

[0032] A first through hole 9 is provided in the middle of the SOI oxide layer 10. The first through hole 9 is rectangular, and its length is the same as that of the second through hole 11. The width of the first through hole 9 is the same as that of the second through hole 11. The first through hole 9 is located directly above the second through hole 11. When the SOI oxide layer 10 is attached to the SOI bottom silicon layer 12, the first through hole 9 is exactly attached to the second through hole 11, and the second through hole 11 is exactly attached to and connected to the groove 13.

[0033] When the SOI top silicon layer 8 is attached to the SOI oxide layer 10, the second cantilever beam etching pattern 7 on the SOI oxide layer 10 is along the width direction (i.e. Figure 2 The X-axis direction of the second cantilever beam is located directly above the first perforation 9, and the projection of the second cantilever beam etching pattern 7 along the thickness direction (i.e., the Z-axis direction) is located exactly at the center of the first perforation 9, so that the projection of the cantilever beam along the thickness direction is located exactly at the center of the first perforation 9, and naturally it is also located at the center of the second perforation 11 and the groove 13.

[0034] In this structure, the SOI top silicon layer 8 is bonded to the SOI oxide layer 10, and the SOI top silicon layer 8 covers the first through-hole 9 and the second through-hole 11, so that the SOI top silicon layer 8, the first through-hole 9, the second through-hole 11 and the groove 13 form a resonant cavity. A laser is input from an opening on one side of the groove 13 and irradiates along the groove 13, causing the laser and the gas to be measured to generate a photoacoustic effect within the resonant cavity, thereby causing a change in sound pressure, which in turn causes the cantilever beam directly above the resonant cavity to vibrate. Therefore, this piezoelectric cantilever beam acoustic resonant cavity structure can be applied to photoacoustic spectroscopy systems.

[0035] By designing the length of the second perforation 11 to be 1 / 4 of the length of the groove 13, and utilizing the first perforation 9 and the second perforation 11, which simultaneously function as a back cavity, the length of the back cavity is made to be 1 / 4 of the length of the resonant cavity (the length of the resonant cavity is the length of the groove 13). This allows for a smaller resonant cavity length and a lower resonant frequency, which is beneficial for the photoacoustic effect. When the acoustic detector and the resonant cavity are integrated using MEMS adhesive bonding technology, the leakage of photoacoustic sound pressure energy can be reduced, which helps to improve the signal-to-noise ratio of the photoacoustic sensing system and achieve a lower detection limit.

[0036] refer to Figure 8 The first perforation 9 and the second perforation 11, which function as the back cavity, constitute part of the resonant cavity. The first perforation 9 and the second perforation 11 are respectively etched through the cantilever beam on the back side of the SOI oxide layer 10 and the SOI bottom silicon layer 12, and their widths are greater than those of the cantilever beam. According to the transmission theory of acoustic resonant cavities, when the length of the back cavity is 1 / 4 times the wavelength of the sound wave (equal to the length of the resonant cavity), the transmission of the sound wave is the worst and the reflection is the strongest. For the resonant cavity of this application, it adopts the first-order longitudinal resonance mode, and the length of the resonant cavity is one wavelength of the sound wave. Therefore, when the back cavity is 1 / 4 times the length of the resonant cavity, the reflection is the strongest, and the sound wave standing wave effect formed in the cavity is the best, that is, the first-order longitudinal resonance frequency is the lowest at this time.

[0037] For example, the resonant frequency of the resonant cavity is consistent with the resonant frequency of the cantilever beam, so as to amplify the sound pressure at a fixed frequency and achieve the most efficient piezoelectric conversion.

[0038] The resonant frequency of the resonant cavity is the frequency formed by the resonant cavity composed of the groove 13, the first through hole 9, and the second through hole 11.

[0039] It is understandable that the resonant frequency of the resonant cavity is also the longitudinal resonant frequency of the acoustic resonant cavity, and the resonant frequency of the cantilever beam is also the resonator of the cantilever beam detector. The acoustic resonant cavity amplifies the acoustic signal corresponding to the resonant frequency to the maximum extent. Then, the cantilever beam detector converts the amplified acoustic signal into a piezoelectric signal to the maximum extent, realizing two-stage amplification of the signal. This is beneficial to improving the signal-to-noise ratio of the photoacoustic sensing system and achieving a lower detection limit.

[0040] For example, the length direction of the cantilever beam is perpendicular to the length direction of the groove 13, that is, the length direction of the cantilever beam is perpendicular to the incident direction of the laser entering the resonant cavity, thus forming an orthogonal piezoelectric cantilever beam acoustic resonant cavity structure. Figure 1 and Figure 2 The diagram illustrates an orthogonal piezoelectric cantilever beam acoustic resonator structure. Alternatively, the length direction of the cantilever beam is parallel to the length direction of the groove 13, meaning the length direction of the cantilever beam is parallel to the incident direction of the laser entering the resonator, thus forming a parallel piezoelectric cantilever beam acoustic resonator structure. Figures 4-7 The diagram illustrates a parallel piezoelectric cantilever beam acoustic resonator structure.

[0041] The orthogonal piezoelectric cantilever beam acoustic resonator structure and the linear piezoelectric cantilever beam acoustic resonator structure are generally the same or similar in structure. The difference between the two lies in the orientation of the cantilever beam, which in turn requires the electrode shapes to be different.

[0042] refer to Figure 5 and Figure 7 For example, it includes two cantilever beams of exactly the same size, so the resonant frequencies of the two cantilever beams are the same and both are parallel to the direction of the groove 13. The top electrodes 2 of the two cantilever beams are connected and the bottom electrodes 4 of the two cantilever beams are connected. The piezoelectric signal is output in parallel at the resonant point, which can increase the device capacitance and reduce the interference of parasitic capacitance, thereby increasing the signal-to-noise ratio of the photoacoustic spectroscopy system. That is, it can improve the signal-to-noise ratio of the photoacoustic spectroscopy system composed of the piezoelectric cantilever beam acoustic resonant cavity structure.

[0043] This invention is based on SOI to construct a piezoelectric cantilever beam acoustic resonator structure. By limiting the electrode area 'a' to 0.4 times the cantilever beam area 'b', the piezoelectric conversion efficiency is maximized. Furthermore, by designing cantilever beams with different length and width dimensions, the resonant frequency is located in the low-frequency band (below 20kHz) of photoacoustic detection. This allows the photoacoustic spectroscopy system composed of the piezoelectric cantilever beam acoustic resonator structure to operate at the resonant point, thereby improving the signal-to-noise ratio.

[0044] By making the length of the back cavity one-quarter of the length of the resonant cavity, and by defining the resonant frequencies of the resonant cavity and the cantilever beam as known, miniaturization and high integration are achieved. The resulting piezoelectric cantilever beam acoustic resonant cavity structure has a thickness on the millimeter scale, making it extremely small in volume. Furthermore, since the photoacoustic signal is inversely proportional to the volume, it is possible to maximize the photoacoustic signal.

[0045] By using multiple cantilever beams connected in parallel, the capacitance of the device can be increased and the influence of parasitic capacitance can be reduced.

[0046] The above structural design enables a lower detection limit and improved signal-to-noise ratio.

[0047] refer to Figure 11 The present invention also provides a method for fabricating the piezoelectric cantilever beam acoustic resonator structure, comprising the following steps: a) Clean the SOI device, SOI oxide layer 10, SOI bottom silicon layer 12, and SOI top silicon layer 8; b) A seed layer 6 of aluminum nitride (AlN) is sequentially deposited on the top silicon layer 8 of SOI, a bottom electrode 4 of cantilever beam made of molybdenum (Mo), a piezoelectric layer 3 of cantilever beam made of aluminum nitride (AlN), and a top electrode 2 of cantilever beam made of molybdenum (Mo) are obtained. The bottom electrode 4 and the top electrode of cantilever beam are patterned by dry etching process to obtain electrode pattern 15, thereby obtaining the bottom electrode pattern of cantilever beam bottom electrode 4 and the top electrode pattern of cantilever beam top electrode 2. c) The cantilever beam pattern 16 is etched into the cantilever beam piezoelectric layer 3 using a dry etching process to obtain the cantilever beam pattern 16, and the bottom electrode 4 of the cantilever beam is exposed, and the gap 20 of the cantilever beam pattern is etched out. d) Gold (Au) is deposited using a sputtering process as wire bonding points 20 for electrical connections, and the cantilever beam pattern gaps 23 are etched into the SOI top silicon layer 8 using a deep silicon etching process. e) A silicon dioxide layer is deposited on the front side of the SOI device as a protective layer 17 to obtain a silicon dioxide protective layer, and an aluminum nitride layer is deposited on the back side of the SOI device to obtain a back cavity oxide layer, which serves as a hard mask patterning 24 for back cavity etching. f) Use deep silicon etching process to etch the SOI bottom silicon layer 12 into the cavity 21, and use wet process to remove the front silicon dioxide protective layer and the back cavity oxide layer to release the SOI device. g) Using the DSI process, a resonant cavity pattern 18 is etched onto a silicon wafer 19 with a thickness of 1-2 mm; h) The resonant cavity silicon layer and the cantilever beam device layer are bonded using adhesive 22.

[0048] The embodiments disclosed in this specification are merely illustrative of one aspect of the invention, and the scope of protection of the invention is not limited to these embodiments. Any other functionally equivalent embodiments fall within the scope of protection of the invention. Those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts described above, and all such changes and modifications should fall within the scope of protection of the claims of this invention.

Claims

1. A piezoelectric cantilever beam acoustic resonator structure, characterized in that, It includes, from bottom to top, a resonant cavity silicon layer, an SOI bottom silicon layer, an SOI oxide layer, an SOI top silicon layer, a seed layer, and a cantilever piezoelectric layer, and also includes electrodes, including a cantilever bottom electrode and a cantilever top electrode. The SOI top silicon layer, seed layer, cantilever bottom electrode, cantilever piezoelectric layer, and cantilever top electrode together form the cantilever beam. Electrodes are deposited on the piezoelectric layer of the cantilever beam, and the resonant frequency of the cantilever beam is <20 kHz. The area of ​​the top electrode of the cantilever beam is denoted as electrode area a, and the area of ​​the cantilever beam is denoted as cantilever beam area b. The electrode area a is 0.4 times the cantilever beam area b. A groove is cut into the silicon layer of the resonant cavity, with openings at both ends of the groove. A second through-hole is drilled in the middle of the SOI bottom silicon layer, and the second through-hole is located directly above the groove. A first through-hole is drilled in the middle of the SOI oxide layer, and the first through-hole is located directly above the second through-hole. The SOI top silicon layer is attached to the SOI oxide layer, and the SOI top silicon layer covers the first and second through holes, so that the SOI top silicon layer, the first through hole, the second through hole and the groove form a resonant cavity.

2. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, A first cantilever beam etching pattern is formed on the seed layer through etching, and a second cantilever beam etching pattern is formed on the SOI top silicon layer through etching. The first and second cantilever beam etching patterns have the same structure, with the first cantilever beam etching pattern located directly above the second cantilever beam etching pattern. When the seed layer is laminarly superimposed on the SOI top silicon layer, the first and second cantilever beam etching patterns overlap perfectly. Patterns are etched onto the cantilever beam piezoelectric layer, and the patterns on the cantilever beam piezoelectric layer are identical to the front end structures of the first and second cantilever beam etched patterns. Bottom electrode patterns and top electrode patterns are etched on the bottom electrode and top electrode of the cantilever beam, respectively. The bottom electrode pattern is consistent with the first cantilever beam etching pattern. When the SOI top silicon layer, seed layer, bottom electrode layer, cantilever beam piezoelectric layer and top electrode layer are sequentially bonded together, a multilayer stacked structure is formed.

3. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The thickness of the resonant cavity silicon layer is greater than the thickness of the SOI bottom silicon layer, the thickness of the SOI top silicon layer, and the thickness of the cantilever piezoelectric layer. The thickness of the cantilever piezoelectric layer is greater than the thickness of the seed layer and the thickness of the SOI oxide layer, respectively.

4. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The thickness of the silicon layer in the resonant cavity is approximately 1 mm to 2 mm, and the depth of the groove is 0.5 mm to 1.5 mm.

5. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The length of the second perforation is 1 / 4 of the length of the groove, the width of the second perforation is the same as the width of the groove, and the width of the second perforation is greater than the length or width of the cantilever beam.

6. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The resonant frequency of the resonant cavity is the same as that of the cantilever beam.

7. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The length direction of the cantilever beam is perpendicular to the length direction of the groove.

8. The piezoelectric cantilever beam acoustic resonator structure according to claim 1, characterized in that, The length direction of the cantilever beam is parallel to the length direction of the groove.

9. The piezoelectric cantilever beam acoustic resonator structure according to claim 2, characterized in that, The bottom electrode layer, the cantilever piezoelectric layer, and the top electrode layer form a sandwich structure. By designing two cantilever beams of the same size, the same resonant frequency can be achieved. The electrodes are connected in parallel, that is, the two top electrodes are connected and the two bottom electrodes are connected, so that the piezoelectric signal is output in parallel at the resonant point. This increases the device capacitance and reduces the interference of parasitic capacitance, thereby increasing the signal-to-noise ratio of the photoacoustic spectroscopy system.

10. A method for fabricating a piezoelectric cantilever beam acoustic resonator structure, characterized in that, Includes the following steps: a) Clean the SOI device, SOI oxide layer, SOI bottom silicon layer, and SOI top silicon layer; b) A seed layer of aluminum nitride is sequentially deposited on the top silicon layer of SOI. A bottom electrode of cantilever beam is constructed using molybdenum, a piezoelectric layer of cantilever beam is constructed using aluminum nitride, and a top electrode of cantilever beam is constructed using molybdenum. The bottom electrode and the top electrode of cantilever beam are patterned using a dry etching process to obtain electrode patterns, thereby obtaining the bottom electrode pattern of the bottom electrode of cantilever beam and the top electrode pattern of the top electrode of cantilever beam. c) The cantilever beam pattern is etched into the piezoelectric layer of the cantilever beam using a dry etching process, thereby obtaining the cantilever beam pattern, exposing the bottom electrode of the cantilever beam, and etching out the gaps in the cantilever beam pattern. d) Gold deposition is used as wire bonding points for electrical connections using sputtering technology, and the cantilever beam pattern gaps are etched into the top silicon layer of SOI using deep silicon etching technology. e) A silicon dioxide layer is deposited on the front side of the SOI device as a protective layer to obtain a silicon dioxide protective layer, and an aluminum nitride layer is deposited on the back side of the SOI device to obtain a cavity oxide layer, which is used as a hard mask patterning for cavity etching. f) Use deep silicon etching process to etch the SOI bottom silicon layer into the cavity, and use wet process to remove the front silicon dioxide protective layer and the back cavity oxide layer to release the SOI device. g) Use the DSI process to etch a resonant cavity pattern onto a 1-2 mm thick silicon wafer; h) The resonant cavity silicon layer and the cantilever beam device layer are bonded together using an adhesive.

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