Wafer MEMS air pump based on PZT piezoelectric film

Abstract

The invention provides a wafer MEMS air pump based on a PZT piezoelectric film, and relates to the technical field of MEMS and fluid control, the wafer MEMS air pump comprises an upper plate, a middle plate and a lower plate, the top of the middle plate and the bottom of the upper plate are mutually bonded and connected based on an Au-Sn eutectic bonding part, and the middle plate and the lower plate are connected in a covalent bonding mode adopting PDMS pretreatment. The invention is suitable for various small and miniature portable equipment and other application scenes, adopts an MEMS (Micro-Electro-Mechanical System) integrated process, does not need to be assembled, and is good in process consistency and low in batch production cost; the working frequency of the core PZT piezoelectric film resonator is high (usually in an ultrasonic frequency band), ultrasonic waves generated by vibration cannot be heard, and compared with a traditional mechanical miniature air pump in a noise-pollution-free preparation mode, the miniature air pump is simple in structure, good in impact resistance and not prone to damage.

Description

Technical Field

[0001] This invention relates to the fields of microelectromechanical systems (MEMS) and fluid control technology, and in particular to a wafer MEMS air pump based on PZT piezoelectric thin film. Background Technology

[0002] PZT thin-film resonators based on MEMS technology are an important type of piezoelectric MEMS device. A typical MEMS piezoelectric resonator consists of a Si substrate layer, a lower electrode layer, a piezoelectric thin film layer, and an upper electrode layer, which together form the diaphragm of the device. The diaphragm is connected to and constrained by the Si substrate around its perimeter, and the bottom is a closed or open cavity structure.

[0003] The working principle of the device is related to the piezoelectric effect of the piezoelectric thin film layer. When the piezoelectric effect is positive, the diaphragm receives external vibration and continuously generates up-and-down reciprocating deformation, periodically stretching / compressing the piezoelectric layer, causing the piezoelectric layer to generate charge. This charge is then connected to the outside through the upper and lower electrodes, and the external circuit can receive the changing charge signal. When the piezoelectric effect is reversed, a high-frequency alternating voltage (such as a sine wave) is applied to the upper and lower electrodes through the external circuit. The upper and lower electrodes generate an alternating electric field in the piezoelectric layer. The electric field causes the piezoelectric layer to undergo stretching / compression deformation. The deformation amplitude depends on the electric field strength, thereby causing the piezoelectric layer to drive the diaphragm to vibrate, thus compressing / stretching the air and generating airflow.

[0004] Current pumps suffer from problems such as excessive size, low integration, and the need for manual assembly.

[0005] Therefore, it is essential to design a wafer MEMS air pump based on PZT piezoelectric thin film. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a wafer MEMS air pump based on PZT piezoelectric thin film.

[0007] To achieve the above objectives, the present invention provides the following solution: This invention provides a wafer MEMS air pump based on a PZT piezoelectric thin film, comprising: The upper plate has a flow channel etched on its top and a cavity hole etched on its bottom. The diameter of the cavity hole is larger than the diameter of the flow channel, and the cavity hole communicates with the flow channel. The middle plate has its top and bottom connected to the upper plate via Au-Sn eutectic bonding. The middle plate has four through-hole internal flow channels. A Pt bottom electrode and a PZT piezoelectric film are sequentially arranged on the top of the middle plate. A lower electrode PAD is located on the top of the Pt bottom electrode on the left side of the middle plate and is connected to the PZT piezoelectric film via the Pt bottom electrode. A diaphragm upper electrode is located at the top center of the PZT piezoelectric film and is connected to the Au-Sn eutectic bonding via an upper electrode connection line. An upper electrode PAD is located on the top right side of the PZT piezoelectric film and is connected to the Au-Sn eutectic bonding. A diaphragm cavity is etched on the bottom of the middle plate. The lower plate has a pressure balance hole etched at its center, and the pressure balance hole is connected to the diaphragm cavity. The lower plate has an internal flow channel that is symmetrical to the internal flow channel of the middle plate. The internal flow channels of the middle plate and the internal flow channels of the lower plate together form the internal flow channel.

[0008] Preferably, the upper plate is a Si substrate with a thickness of 425 μm.

[0009] Preferably, the flow channel is etched using anisotropic wet etching or RIE dry etching with KOH solution, and the etching depth is 200 μm.

[0010] Preferably, the cavity hole is etched using anisotropic wet etching or RIE dry etching with KOH solution, and the etching depth is 225 μm.

[0011] Preferably, the middle plate is an SOI substrate, and the thickness of its Handle-BOX-Device layer is 300-1-30um.

[0012] Preferably, the thickness of the PZT piezoelectric film is 4 μm.

[0013] Preferably, the lower plate is a Si substrate with a thickness of 425 μm.

[0014] Preferably, a thin layer of PDMS is provided on the top of the lower plate.

[0015] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention provides a wafer MEMS air pump based on a PZT piezoelectric thin film, comprising an upper plate, the top of which is etched with flow channels, and the bottom of which is etched with cavity holes communicating with the flow channels; and a middle plate, the top of which is bonded to the bottom of the upper plate based on Au-Sn eutectic bonding sites. The middle plate has four through-flow channels. A Pt bottom electrode and a PZT piezoelectric thin film are sequentially disposed on the top of the middle plate, and a lower electrode PAD is disposed on the top of the Pt bottom electrode located on the left side of the middle plate. The lower electrode PAD is connected to the PZT piezoelectric thin film through the Pt bottom electrode. A diaphragm upper electrode is disposed at the top center of the PZT piezoelectric film. This upper electrode is connected to the Au-Sn eutectic bonding site via an upper electrode connection line. An upper electrode PAD is disposed on the top right side of the PZT piezoelectric film, and this upper electrode PAD is connected to the Au-Sn eutectic bonding site. A diaphragm cavity is etched at the bottom of the middle plate. A lower plate has a pressure balance hole etched at its center, which communicates with the diaphragm cavity. The lower plate has symmetrical internal flow channels corresponding to the internal flow channels of the middle plate. The internal flow channels of the middle plate and the lower plate together form the internal flow channels. This invention is suitable for various small and micro portable devices and other applications, and has the following beneficial effects: 1. It adopts MEMS integrated technology, which eliminates the need for assembly, ensures good process consistency, and reduces mass production costs; 2. The core PZT piezoelectric thin film resonator operates at a high frequency (usually in the ultrasonic band), and the ultrasonic waves generated by the vibration are inaudible, resulting in no noise pollution compared to traditional mechanical miniature air pumps; 3. The covalent bonding of PDMS pretreatment and the eutectic bonding of Au-Sn used in the preparation method of this invention both adopt a low temperature (≤200℃) process, which is low in cost and high in reliability. It is lower than the Curie temperature of PZT, which ensures that the performance of PZT film is not compromised. It is also lower than the reflow temperature of PDMS, which does not damage PDMS and ensures sealing in subsequent work. 4. It has a simple structure, good impact resistance, and is not easily damaged. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1This is a schematic diagram of a wafer MEMS air pump structure based on a PZT piezoelectric thin film provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the upper plate preparation process; Figure 3 This is a schematic diagram of the process flow for preparing the medium plate. Figure 4 This is a schematic diagram of the process flow for preparing the lower plate.

[0018] Figure reference numerals: 1. Upper plate; 2. Middle plate; 3. Lower plate; 4. Lower electrode PAD; 5. Cavity; 6. Au-Sn eutectic bonding area; 7. Internal flow channel; 8. Flow channel; 9. Pressure balance hole; 10. Diaphragm upper electrode; 11. Diaphragm cavity; 12. Upper electrode connection line; 13. Upper electrode PAD. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide a wafer-based MEMS air pump based on PZT piezoelectric thin film, suitable for various small and micro portable devices and other applications. It adopts MEMS integrated technology, which eliminates the need for assembly, ensures good process consistency, and reduces mass production costs. The core PZT piezoelectric thin film resonator operates at a high frequency (usually in the ultrasonic band), and the ultrasonic waves generated by the vibration are inaudible. Compared with traditional mechanical micro air pumps, it has no noise pollution in its manufacturing process, has a simple structure, good impact resistance, and is not easily damaged.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, this invention provides a wafer MEMS air pump based on a PZT piezoelectric thin film, comprising: The upper plate 1 has a flow channel 8 etched on its top and a cavity hole etched on its bottom. The diameter of the cavity hole is larger than the diameter of the flow channel. The cavity hole communicates with the flow channel and forms a cavity 5 with the middle plate. The middle plate 2 is bonded to the bottom of the upper plate 1 via an Au-Sn eutectic bonding portion 6. The middle plate 2 has four through-hole internal flow channels. A Pt bottom electrode and a PZT piezoelectric film are sequentially arranged on the top of the middle plate 2. A lower electrode PAD4 is located on the top of the Pt bottom electrode on the left side of the middle plate 2 and is connected to the PZT piezoelectric film via the Pt bottom electrode. A diaphragm upper electrode 10 is located at the center of the top of the PZT piezoelectric film and is connected to the Au-Sn eutectic bonding portion 6 via an upper electrode connecting line 12. An upper electrode PAD13 is located on the right side of the top of the PZT piezoelectric film and is connected to the Au-Sn eutectic bonding portion 6. A diaphragm cavity 11 is etched on the bottom of the middle plate 2. The lower plate 3 has an air pressure balance hole 9 etched at its center, and the air pressure balance hole 9 is connected to the diaphragm cavity 11. The lower plate 3 has a lower plate internal flow channel that is symmetrical to the middle plate internal flow channel of the middle plate 2. The middle plate internal flow channel and the lower plate internal flow channel together form the internal flow channel 7.

[0023] The upper plate 1 and the middle plate 2 are bonded to each other by Au-Sn eutectic bonding, and the middle plate 2 and the lower plate 3 are connected by covalent bonding using PDMS pretreatment.

[0024] When the PZT piezoelectric film moves upward, the air accumulated in the cavity is compressed, forming a positive pressure, which is then discharged from the upper channel while gas is replenished from the lower channel hole. Conversely, a negative pressure is formed in the upper cavity, replenishing the cavity with air. The air pressure balance hole 9 allows the internal gas to be discharged in time during the reciprocating motion of the diaphragm, preventing the formation of large positive / negative pressures in the diaphragm cavity 11, thus ensuring the amplitude of the diaphragm movement. When an AC drive signal with a frequency equal to the pump's resonant frequency is applied to the upper and lower electrodes, the diaphragm will vibrate up and down, thereby compressing or stretching the air. Theoretically, the piezoelectric actuator layer can discharge / extract L of air per second. a for: L a =απsfd 2 / 4; Where α is the effective area adjustment coefficient, f is the resonant frequency, s is the displacement sensitivity, and d is the diameter of the diaphragm. The pump needs to work in conjunction with a corresponding unidirectional gas conduction device so that the gas discharged / drawn by the pump can flow in one direction. If the unidirectional rejection rate of the check valve is β, then the total gas flow rate L that the pump can pump out in 1 second is: L=βLa.

[0025] Next, the process flow and parameters of the upper plate 1, middle plate 2, and lower plate 3 will be described in detail: like Figure 2 As shown, the specific process flow for the upper plate 1 is as follows: 1. The upper plate 1 is a Si substrate with a thickness of 425um; 2. Perform anisotropic wet etching or RIE dry etching from the top of the Si substrate using KOH solution, with an etching depth of 200um; 3. Use a lift-off process at the bottom to grow and pattern the Au-Sn-Au layer in preparation for subsequent bonding processes; 4. Perform anisotropic wet etching or RIE dry etching from the back side using KOH solution until the via in step 2 is exposed. The via is formed on the front side, and a cavity with a thickness of (425-200=225um) and a depth of 225um is formed on the back side.

[0026] like Figure 3 As shown, the specific process flow for the middle plate 2 is as follows: 1. The middle plate 2 is an SOI substrate, and the thickness of its Handle-BOX-Device layer is 300-1-30um; 2. Surface treatment and growth of Pt bottom electrode and buffer layer; 3. Grow a PZT film with a thickness of 4µm (a certain designed thickness, which, together with the device layer thickness of SOI, determines the resonant frequency of the device). 4. Pattern the grown PZT film using wet or dry etching methods; 5. Etch the Pt bottom electrode layer using IBE (ion beam etching, a semiconductor etching process); 6. Continue using the mask from step 5, and use KOH to etch the device layer Si below the bottom electrode layer until the SiO2 of the BOX layer automatically stops; 7. Using a lift-off process, grow and pattern the Au layer to form the lower and upper electrode PADs, connecting wires, the top electrode of the central resonator, and the outer ring for bonding. 8. Perform anisotropic wet etching or RIE dry etching from the back side using KOH solution until the SiO2 in the BOX layer is reached and then the etching stops. 9. Use ICP (Inductively Coupled Plasma Etching, a semiconductor etching process) from the back to etch away the SiO2 of the BOX layer.

[0027] like Figure 4 As shown, the specific process flow for the lower plate is as follows: 1. The bottom plate is a Si substrate with a thickness of 425um; 2. Use KOH solution for anisotropic wet etching or RIE dry etching from the front side of the Si substrate to form vias; 3. Spin-coat PDMS onto the surface, remove air bubbles under vacuum, bake at 100°C for 1 hour, and then clean in an organic solvent (such as acetone). After this process, a PDMS thin layer with a thickness of about 5 nm will remain on the Si surface.

[0028] After the upper, middle and lower three layers are prepared, the PDMS surface of each Si substrate is treated with O2-plasma for several seconds, then aligned, and a low-temperature bonding process is performed at 200°C (example temperature). Finally, metal eutectic bonding and covalent bonding are achieved between the three Si wafers, which together form the pump shell.

[0029] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0030] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A wafer MEMS air pump based on PZT piezoelectric thin film, characterized in that, The application relates to a diaphragm loudspeaker, which comprises the following parts: an upper plate, the top of which is etched with a flow channel, and the bottom of which is etched with a cavity hole which is communicated with the flow channel; a middle plate, the top of which is bonded with the bottom of the upper plate at an Au-Sn eutectic bonding site, four through middle plate internal flow channels are arranged on the middle plate, a Pt bottom electrode and a PZT piezoelectric film are sequentially arranged on the top of the middle plate, a lower electrode PAD is arranged on the top of the Pt bottom electrode located at the left side of the middle plate, the lower electrode PAD is connected with the PZT piezoelectric film through the Pt bottom electrode, a diaphragm upper electrode is arranged at the top center of the PZT piezoelectric film, the diaphragm upper electrode is connected with the Au-Sn eutectic bonding site through an upper electrode connecting wire, an upper electrode PAD is arranged at the top right side of the PZT piezoelectric film, and the upper electrode PAD is connected with the Au-Sn eutectic bonding site, and a diaphragm cavity is etched on the bottom of the middle plate; a lower plate, the center of which is etched with an air pressure balance hole which is communicated with the diaphragm cavity, and the lower plate is provided with a lower plate internal flow channel which is symmetrical to the middle plate internal flow channel of the middle plate, and the middle plate internal flow channel and the lower plate internal flow channel jointly form an internal flow channel.

2. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The upper plate is a Si substrate with a thickness of 425 um.

3. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The flow channel is etched by using KOH solution for anisotropic wet etching or RIE dry etching, and the etching depth is 200 um.

4. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The cavity hole is etched by using KOH solution for anisotropic wet etching or RIE dry etching, and the etching depth is 225 um.

5. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The middle plate is an SOI substrate with a Handle-BOX-Device layer thickness of 300-1-30 um.

6. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The PZT piezoelectric film has a thickness of 4 um.

7. The PZT piezoelectric thin film based wafer MEMS gas pump according to claim 1, wherein, The lower plate is a Si substrate with a thickness of 425 um.

8. The PZT piezoelectric thin film based wafer MEMS gas pump of claim 1, wherein, A PDMS thin layer is arranged on the top of the lower plate.

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