A piezoelectric MEMS cooler with rectangular symmetric slotted structure and manufacturing method

Abstract

A piezoelectric MEMS cooler with a rectangular symmetrical slit structure, relating to the field of semiconductor cooling, includes: an orifice plate with a plurality of nozzles arranged on the orifice plate; an actuator disposed above the orifice plate, the actuator forming a cavity with the orifice plate, the top of the actuator having a transverse slit and a longitudinal slit, one transverse slit penetrating the actuator along the thickness direction, at least one longitudinal slit penetrating the actuator along the thickness direction, the transverse slit being perpendicular to each longitudinal slit, and each longitudinal slit being located at the equidistant points of the transverse slit; and a sealing membrane bonded to the top surface of the actuator and covering the transverse and longitudinal slits. This application employs a one-horizontal-multiple-vertical layout to divide the actuator into rectangular areas of uniform size and stiffness, ensuring that the vibration direction of each rectangular area is perpendicular to the actuator surface, improving the synchronization of the vibration height of each rectangular area, and ensuring that the superposition of the vibrations of each rectangular area can form a neat and concentrated airflow for uniform heat dissipation from the heat source.

Description

Technical Field

[0001] This invention relates to the field of semiconductor cooling, and in particular to a piezoelectric MEMS cooler with a rectangular symmetrical slit structure and its fabrication method. Background Technology

[0002] With the development of technologies such as 5G and artificial intelligence, the transistor density of compact electronic devices such as smartphones and smartwatches continues to increase, and the heat flux density has exceeded 100W / cm². Overheating of these devices leads to performance degradation and shortened lifespan, becoming a bottleneck in the industry. Existing thermal management technologies have significant shortcomings: passive cooling relies on heat sinks and heat pipes, which can only handle heat flux densities of ≤0.05W / cm², and the heat transfer coefficient in confined spaces of less than 5mm is less than 25W / (m²·K), making it difficult to meet the needs of high-end chips; in active cooling, traditional micro fans consume 500-1800mW, rotating parts are prone to wear and noise, and it is difficult to achieve a lifespan of 100,000 hours. Piezoelectric cooling devices such as the Frore Airjet Mini, although reduced in size to 27.5×41.5×2.8mm, have an airflow leakage rate >15%, poor jet uniformity (velocity deviation >20%), and a COP of only 5-8, resulting in low efficiency.

[0003] Moreover, most cooling devices adopt a circular or square layout, which is not well matched with the long strip heat sources in electronic devices (such as 5G modules and processor arrays). The heat dissipation efficiency in the edge area is reduced by more than 30%, forming local hot spots.

[0004] Therefore, there is an urgent need for miniaturized, low-power, and highly uniform active cooling solutions to adapt to the high-density heat dissipation of compact devices. Summary of the Invention

[0005] This invention provides a piezoelectric MEMS cooler with a rectangular symmetrical slit structure and a method for fabricating it. The purpose is to solve the shortcomings of existing active cooling devices that are difficult to achieve uniform and efficient heat dissipation for long strip-shaped heat sources.

[0006] To achieve the above objectives, embodiments of the present invention provide a piezoelectric MEMS cooler with a rectangular symmetrical slit structure, comprising: An orifice plate, wherein a plurality of spray holes are arranged on the orifice plate; An actuator is disposed above the orifice plate, and the bottom of the actuator is recessed upward and forms a cavity with the orifice plate. The top of the actuator has a transverse slit and a longitudinal slit. One of the transverse slits penetrates the actuator along the thickness direction, and at least one of the longitudinal slits penetrates the actuator along the thickness direction. The transverse slit is perpendicular to each of the longitudinal slits, and each of the longitudinal slits is located at the equidistant points of the transverse slit. A sealing membrane, which is bonded to the top face of the actuator, covers the transverse slit and the longitudinal slit.

[0007] Preferably, the actuator comprises, from bottom to top, a silicon substrate and a piezoelectric functional layer. The piezoelectric functional layer comprises, from bottom to top, a Mo bottom electrode, an AlN piezoelectric film, and a Mo top electrode. The Mo bottom electrode is deposited on the silicon substrate, and the Mo bottom electrode and the Mo top electrode are used for electrical connection with external leads.

[0008] Preferably, the pad areas of the Mo bottom electrode and the Mo top electrode are coated with anisotropic conductive adhesive for electrical connection with external leads; The bottom edge of the silicon substrate is bonded to the perforated plate with non-conductive adhesive.

[0009] Preferably, the transverse slit is arranged along the width direction of the actuator, and the distances between the two ends of the transverse slit and the corresponding edges of the actuator are not zero; Each of the longitudinal slits is arranged along the length of the actuator, and the distance between each end of the longitudinal slit and the corresponding edge of the actuator is not zero.

[0010] Preferably, the axial direction of the nozzle is perpendicular to the length direction of the actuator, and the nozzle is in the shape of an inverted frustum.

[0011] This application also provides a fabrication method for fabricating the aforementioned piezoelectric MEMS cooler with a rectangular symmetrical slit structure, comprising: S100. Fabricate the actuator and etch the actuator to form a transverse slit and a longitudinal slit; S200. Creating the cavity: Etching the bottom surface of the actuator to form a cavity; S300. Fabrication of sealing film: Mix PDMS prepolymer and curing agent at a mass ratio of 10:1 and spin coat them onto the upper surface of the actuator and cure them to form a sealing film. Use oxygen plasma treatment to bond the sealing film to the actuator. S400. Fabrication of an orifice plate: Forming spray holes on the orifice plate; S500. Electrically connect the actuator and fix the actuator to the orifice plate.

[0012] Preferably, step S100 includes: S110. An SOI wafer is selected as the silicon substrate, wherein the SOI wafer comprises, from top to bottom, a silicon device layer, a buried oxide layer, and a silicon substrate layer; S120. An AlN seed layer and a Mo bottom electrode are sequentially deposited on the surface of the silicon device layer using a magnetron sputtering process. A pattern mask is then prepared on the Mo bottom electrode and the AlN seed layer by photolithography. The unmasked material is removed by RIE etching, and a pattern of the Mo bottom electrode is formed. S130. Deposit an AlN piezoelectric film on the Mo substrate electrode, ensuring that the c-axis orientation of the AlN piezoelectric film is not less than 95%; S140. Deposit a Mo top electrode on an AlN piezoelectric thin film and form a pattern of the Mo top electrode.

[0013] Preferably, in step S100, when etching the transverse and longitudinal slits, the Bosch process is used for etching, with etching time and passivation time of 10 seconds and 5 seconds, respectively, and the perpendicularity of the transverse and longitudinal slits is not less than 89°.

[0014] Preferably, in step S300, the surface of the AlN piezoelectric film is activated before spin coating the mixture, and the sealing film is bonded to the AlN piezoelectric film.

[0015] The above-described solution of the present invention has the following beneficial effects: The horizontal and vertical layout can divide the actuator into multiple rectangular areas of the same size, while ensuring that the stiffness distribution of each area is uniform. This ensures that the vibration direction of each rectangular area is perpendicular to the surface of the actuator, improves the synchronization of the vibration height of each rectangular area, and ensures that the superposition of the vibrations of each rectangular area can form a neat and concentrated airflow for uniform heat dissipation from the heat source.

[0016] Furthermore, by adjusting the number of longitudinal slits, the equivalent stiffness of the actuator can be effectively reduced, allowing the overall resonant frequency of the actuator to be adjusted, thus achieving flexible frequency control.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] Figure 1 This is a half-sectional view of the present invention; Figure 2 This is a longitudinal sectional view of the present invention; Figure 3 It is a schematic diagram of a narrow slit arrangement with one horizontal and one vertical axis; Figure 4 It is a schematic diagram of a narrow slit arrangement with one horizontal and two vertical lines.

[0019] [Explanation of Labels in the Attached Image] 10-Orifice plate, 11-Spray nozzle, 12-Anisotropic conductive adhesive, 13-Non-conductive adhesive 20 - Actuator, 21 - Lateral slit, 22 - Longitudinal slit 30 - Sealing film. Detailed Implementation

[0020] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0021] like Figure 1-4 As shown, an embodiment of the present invention provides a piezoelectric MEMS cooler with a rectangular symmetrical slit structure, including an orifice plate 10, an actuator 20, and a sealing membrane 30. The orifice plate 10 is located below the other two components, and a plurality of nozzles 11 are evenly distributed on the orifice plate 10. The elongated actuator 20 is disposed above the orifice plate 10, and the bottom of the actuator 20 is close to the orifice plate 10. The bottom of the actuator 20 is concave upward, forming a cavity when connected to the orifice plate 10. A transverse slit 21 and a longitudinal slit 22 are provided at the top of the actuator 20, and the two types of slits penetrate the actuator 20 along the thickness direction. There is only one transverse slit 21 and at least one longitudinal slit 22. The transverse slit 21 and each longitudinal slit 22 are perpendicular to each other on the upper end face of the actuator 20. Each longitudinal slit 22 is located at the equidistant points of the transverse slit 21. A sealing membrane 30 is disposed on the top surface of the actuator 20 (i.e., the end away from the orifice plate 10), and the sealing membrane 30 is bonded to the top surface of the actuator 20 to cover the transverse slit 21 and the longitudinal slit 22. The sealing membrane 30 is made of an elastic material.

[0022] In this application, a layout with one slit perpendicular to multiple slits (hereinafter referred to as a one-horizontal-multiple-vertical layout) is adopted. The horizontal slit 21 and the vertical slit 22 are parallel to the width and length directions of the actuator 20, respectively. This divides the actuator 20 into multiple rectangular areas of identical size, ensuring uniform stiffness distribution in each area. It also ensures that the vibration direction of each rectangular area is perpendicular to the surface of the actuator 20, and that the phase difference between the rectangular areas during vibration is no greater than 3°. This improves the synchronization of the vibration height of each rectangular area, ensuring that the superimposed vibrations of each rectangular area form a neat and concentrated airflow for uniform heat dissipation. This airflow is ejected at high speed through the nozzles 11 on the perforated plate 10, forming a continuous high-speed airflow band with a jet velocity standard deviation ≤0.3m / s. It covers ≥90% of the effective area of ​​the elongated heat source, and the heat dissipation efficiency at the edge area decreases from 30% to below 8%, significantly improving compatibility with elongated heat sources such as 5G modules and processor arrays.

[0023] In addition, by adjusting the number of longitudinal slits 22, the equivalent stiffness of the actuator 20 can be effectively reduced, so that the overall resonant frequency of the actuator 20 can be adjusted, and the frequency can be flexibly controlled.

[0024] Finally, in the multi-vertical layout, the longitudinal slits 22 do not intersect, and the rectangular areas formed by the division are all connected to the edge of the actuator 20, so that the stress generated by vibration is distributed to the ends of each slit. Compared with the radial slit arrangement (where the stress is concentrated at the central intersection point), the stress concentration peak of this design is less than the fatigue strength threshold of silicon material, which can effectively extend the service life of the actuator 20.

[0025] Specifically, in this application, the actuator 20 comprises, from bottom to top, a silicon substrate and a piezoelectric functional layer. The piezoelectric functional layer includes, from bottom to top, a Mo bottom electrode, an AlN piezoelectric film (aluminum nitride piezoelectric film), and a Mo top electrode. The Mo bottom electrode is deposited on the silicon substrate, and the Mo bottom electrode and Mo top electrode are used for electrical connection to external leads. In this application, the Mo bottom electrode and Mo top electrode are driven by an H-bridge circuit, which allows the voltage to switch or reverse between the Mo top electrode and the Mo bottom electrode.

[0026] Anisotropic conductive adhesive 12 is applied to the pad regions of the Mo bottom electrode and the Mo top electrode, respectively. External leads are electrically connected to the pad regions of the Mo bottom electrode and the Mo top electrode through the anisotropic conductive adhesive 12. Non-conductive adhesive 13 is used to bond the bottom edge of the silicon substrate to the via plate 10 for mechanical fixation.

[0027] In this application, the length of the transverse slit 21 is arranged along the width direction of the actuator 20, and the distances between the two ends of the transverse slit 21 and the corresponding edges of the actuator 20 are not zero. Preferably, the distances between the two ends of the transverse slit 21 and the corresponding edges of the actuator 20 are equal. The length of the longitudinal slits 22 is arranged along the length direction of the actuator 20, and the distances between the two ends of each longitudinal slit 22 and the corresponding edges of the actuator 20 are not zero. Preferably, the distances between the two ends of each longitudinal slit 22 and the corresponding edges of the actuator 20 are equal.

[0028] Preferably, the axial direction of the nozzle 11 is perpendicular to the length direction of the actuator 20, and the nozzle 11 is in the shape of an inverted frustum.

[0029] The inverted frustum shape described in this application refers to the bottom diameter of the nozzle 11 being smaller than the top diameter, and the inclination angle α of the nozzle 11 being an acute angle. Preferably, the inclination angle α of the nozzle is 53°.

[0030] In this application, heat dissipation of a long strip heat source is achieved through a complete working chain of piezoelectric conversion, mechanical vibration, airflow pulsation, and thermal boundary layer disturbance. Specifically, the working process includes an injection stage and an intake stage. During the injection stage: A sinusoidal driving signal is applied to the Mo bottom electrode and the Mo top electrode. The AlN piezoelectric film undergoes in-plane expansion and contraction due to the piezoelectric effect. After mechanical decoupling through the transverse slit 21 and the longitudinal slit 22, it is transformed into multiple rectangular areas that simultaneously bend towards the inside of the cavity, compressing the gas inside the cavity. The airflow is accelerated and ejected through the nozzle 11, forming a symmetrical vortex ring in the nozzle 11. Due to the one-to-one correspondence between the nozzle 11 and the rectangular areas, the vortex ring converges into a high-speed airflow band of a certain thickness along the length of the actuator 20, which vertically impacts the heat source surface and destroys the thermal boundary layer.

[0031] During the intake phase: A driving signal opposite to that applied during the injection phase is applied to the Mo bottom electrode and Mo top electrode. The rectangular area synchronously bends away from the cavity, causing the cavity volume to expand and create negative pressure, drawing in ambient air through the nozzle 11. The vortex ring moves away from the nozzle 11 due to its self-induced velocity, preventing airflow re-absorption.

[0032] The ratio of the injection phase to the intake phase is 1:1.2, ensuring that the net airflow continuously acts on the heat source surface in each cycle.

[0033] This application also provides a method for fabricating a piezoelectric MEMS cooler with a rectangular symmetrical slit structure, comprising the following steps: S100. Fabricate actuator 20 and etch actuator 20 to form transverse slit 21 and longitudinal slit 22; S110. Select an SOI wafer, which includes a silicon device layer, a buried oxide layer and a silicon substrate layer from top to bottom. After ultrasonic cleaning with acetone and isopropanol and drying with nitrogen, the SOI wafer is dried at 120°C to remove residual moisture.

[0034] S120. An AlN seed layer (aluminum nitride seed layer) is deposited on the surface of a silicon device layer using magnetron sputtering, with a sputtering power of 300W and an argon flow rate of 20 sccm. A Mo bottom electrode is deposited on the AlN seed layer with a sputtering power of 250W and an argon flow rate of 15 sccm. A pattern mask is fabricated, and reactive ion etching (RIE) is used to remove the unmasked AlN seed layer and Mo bottom electrode, forming a pattern for the Mo bottom electrode. S130. An AlN piezoelectric thin film was deposited on a Mo substrate electrode using pulsed laser deposition at a deposition temperature of 800℃, an oxygen pressure of 5 Pa, and a laser energy density of 2 J / cm². 2 To ensure that the c-axis orientation of the AlN piezoelectric film is not less than 95%, the film is annealed in a nitrogen atmosphere at 500°C after deposition to eliminate internal stress.

[0035] S140. A Mo top electrode is deposited on an AlN piezoelectric thin film using magnetron sputtering, and the Mo top electrode is patterned by photolithography.

[0036] S150. The silicon device layer is etched using deep reactive ion etching (DRIE) as required to form a lateral slit 21 and a vertical slit 22. The distances of the lateral slit 21 and the vertical slit 22 from their corresponding edges are equal, preferably 0.5 μm. After etching the lateral slit 21 and the vertical slit 22, the buried oxide layer is etched away using a 5% hydrofluoric acid solution to release the actuation area. During the etching of the transverse slit 21 and the longitudinal slit 22, the Bosch process was used for etching, with etching time and passivation time of 10 seconds and 5 seconds, respectively. The perpendicularity of the transverse slit 21 and the longitudinal slit 22 was not less than 89°. It should be noted that, due to processing precision requirements, if the angle error between the transverse slit 21 and the longitudinal slit 22 is within 1°, it can be considered that the transverse slit 21 and the longitudinal slit 22 are perpendicular.

[0037] S200. Create a cavity.

[0038] A cavity is formed by etching the bottom surface of the actuator 20. Specifically, a deep reactive ion etching (DRIE) process is used to etch the side of the silicon substrate away from the silicon device layer, with the etching location directly opposite the actuator 20 and the etching depth equal to the thickness of the silicon substrate layer, so that the etched cavity is connected to the lateral slit 21 and the vertical slit 22. TiW and Au are deposited at the edges of the cavity and patterned by an etching process to form electrode pads for electrical connection.

[0039] S300. Make a sealing film 30. The PDMS prepolymer and curing agent are mixed at a mass ratio of 10:1, and after degassing, the mixture is spin-coated onto the top surface of the actuator 20 (i.e., the side away from the orifice plate 10) to form a film. After curing, a sealing film 30 is obtained. Preferably, the AlN piezoelectric film is activated by oxygen plasma before spin-coating to improve the adhesion between the sealing film 30 and the AlN piezoelectric film and ensure bonding strength.

[0040] The sealing film 30 is bonded to the actuator 20 using oxygen plasma treatment. Specifically, oxygen plasma treatment is used to bond the AlN piezoelectric film to the sealing film 30.

[0041] S400. Fabricate perforated plate 10.

[0042] The orifice plate 10 is made of resin material and has the same size as the actuator 20, both being elongated. Based on the number and position of the longitudinal slits 22, nozzles 11 are made on the orifice plate 10 and are evenly distributed on the orifice plate 10 corresponding to the cavity.

[0043] S500. Electrically connect the actuator 20 and fix the actuator 20 to the orifice plate 10.

[0044] Anisotropic conductive adhesive 12 is applied to the pad regions of the Mo bottom electrode and the Mo top electrode, respectively. External leads are electrically connected to the pad regions of the Mo bottom electrode and the Mo top electrode through the anisotropic conductive adhesive 12. Non-conductive adhesive 13 is used to bond the bottom edge of the silicon substrate to the via plate 10 for mechanical fixation.

[0045] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A piezoelectric MEMS cooler with a rectangular symmetrical slit structure, characterized in that, include: Orifice plate (10), on which a plurality of spray holes (11) are arranged; An actuator (20) is disposed above the orifice plate (10), and the bottom of the actuator (20) is recessed upward and forms a cavity with the orifice plate (10). The top of the actuator (20) is provided with a transverse slit (21) and a longitudinal slit (22). One of the transverse slits (21) penetrates the actuator (20) along the thickness direction, and at least one of the longitudinal slits (22) penetrates the actuator (20) along the thickness direction. The transverse slit (21) is perpendicular to each of the longitudinal slits (22), and each of the longitudinal slits (22) is located at the equidistant points of the transverse slit (21). The sealing membrane (30) is bonded to the top face of the actuator (20) and covers the transverse slit (21) and the longitudinal slit (22).

2. The piezoelectric MEMS cooler with a rectangular symmetrical slit structure according to claim 1, characterized in that: The actuator (20) includes a silicon substrate and a piezoelectric functional layer from bottom to top. The piezoelectric functional layer includes a Mo bottom electrode, an AlN piezoelectric film and a Mo top electrode from bottom to top. The Mo bottom electrode is deposited on the silicon substrate. The Mo bottom electrode and the Mo top electrode are used for electrical connection with external leads.

3. The piezoelectric MEMS cooler with a rectangular symmetrical slit structure according to claim 2, characterized in that: The pad areas of the Mo bottom electrode and the Mo top electrode are coated with anisotropic conductive adhesive (12) for electrical connection with external leads. The bottom edge of the silicon substrate is bonded to the perforated plate (10) with non-conductive adhesive (13).

4. The piezoelectric MEMS cooler with a rectangular symmetrical slit structure according to claim 1, characterized in that: The transverse slit (21) is arranged along the width direction of the actuator (20), and the distances between the two ends of the transverse slit (21) and the corresponding edges of the actuator (20) are not zero. Each of the longitudinal slits (22) is arranged along the length of the actuator (20), and the distance between the two ends of each longitudinal slit (22) and the corresponding edge of the actuator (20) is not zero.

5. The piezoelectric MEMS cooler with a rectangular symmetrical slit structure according to claim 1, characterized in that: The axial direction of the nozzle (11) is perpendicular to the length direction of the actuator (20), and the nozzle (11) is in the shape of an inverted frustum.

6. A method for fabricating a piezoelectric MEMS cooler with a rectangular symmetrical slit structure as described in any one of claims 1-5, characterized in that, include: S100. Fabricate actuator (20) and etch actuator (20) to form transverse slit (21) and longitudinal slit (22). S200. Create a cavity: Etch the bottom surface of the actuator (20) to form a cavity; S300. Fabrication of sealing film (30): PDMS prepolymer and curing agent are mixed at a mass ratio of 10:1 and spin-coated onto the upper surface of actuator (20) and cured to form sealing film (30). Oxygen plasma treatment is used to bond sealing film (30) to actuator (20). S400. Fabricate orifice plate (10): Form nozzles (11) on orifice plate (10). S500. Electrically connect the actuator (20) and fix the actuator (20) onto the orifice plate (10).

7. The manufacturing method according to claim 6, characterized in that, Step S100 includes: S110. An SOI wafer is selected as the silicon substrate, wherein the SOI wafer comprises, from top to bottom, a silicon device layer, a buried oxide layer, and a silicon substrate layer; S120. An AlN seed layer and a Mo bottom electrode are sequentially deposited on the surface of the silicon device layer using a magnetron sputtering process. A pattern mask is then prepared on the Mo bottom electrode and the AlN seed layer by photolithography. The unmasked material is removed by RIE etching, and a pattern of the Mo bottom electrode is formed. S130. Deposit an AlN piezoelectric film on the Mo substrate electrode, ensuring that the c-axis orientation of the AlN piezoelectric film is not less than 95%; S140. Deposit a Mo top electrode on an AlN piezoelectric thin film and form a pattern of the Mo top electrode.

8. The manufacturing method according to claim 6, characterized in that: In step S100, when etching the transverse slit (21) and the longitudinal slit (22), the Bosch process is used for etching, with etching time and passivation time of 10 seconds and 5 seconds respectively, and the perpendicularity of the transverse slit (21) and the longitudinal slit (22) is not less than 89°.

9. The manufacturing method according to claim 7, characterized in that: In step S300, the surface of the AlN piezoelectric film is activated before spin coating the mixture, and the sealing film (30) is bonded to the AlN piezoelectric film.

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