High Q value aluminum nitride lamb wave resonator and processing method

Abstract

The present invention provides an aluminum nitride lamb wave resonator with an extremely high Q value and a processing method, comprising: an electrode, a film (2); the electrode comprises: a forked electrode (1) and a bottom electrode (3); one end of the forked electrode (1) is connected to an RF signal; the other end of the forked electrode (1) is connected to the ground; the bottom electrode (3) is electrically floating; the film (2) is arranged between the forked electrode (1) and the bottom electrode (3). By adopting a piezoelectric film, the present invention solves the problems that other conventional piezoelectric films are difficult to be compatible with semiconductor processes, have too high a dielectric constant, and have a low mechanical quality factor. This enables the resonator proposed in this patent to exert more superior performance in the application of high-sensitivity smart sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of resonators, and in particular to an aluminum nitride lamb wave resonator with an extremely high Q value and a processing method thereof. Background Art

[0002] With the rapid development of sensor technology, the Q value of existing resonators is difficult to meet the design requirements of high-precision sensors.

[0003] Patent document CN111404509A discloses a high-Q resonant device, which ensures the high Q value of the resonator and the consistency of the electrical parameters of the device by inserting an additional etching stop layer.

[0004] The shortcomings of the prior art are: conventional piezoelectric films may have problems such as low mechanical quality factor and poor compatibility with semiconductor processes, while the aluminum nitride film or scandium-doped aluminum nitride film used in this patent can be perfectly compatible with semiconductor processes and has strong mechanical stability, which makes the aluminum nitride resonator proposed in this patent have a wide range of applicability; most aluminum nitride acoustic wave resonators increase the Q value of the resonator to a limited extent by reducing mechanical wave leakage, and the method proposed in this patent to introduce "half-finger" electrodes to reduce the electromechanical coupling coefficient K2 will break the bottleneck of conventional methods, greatly improve the Q value, and reach the highest Q value in the field of aluminum nitride resonators. Summary of the invention

[0005] In view of the defects in the prior art, an object of the present invention is to provide an aluminum nitride lamb wave resonator with extremely high Q value and a processing method thereof.

[0006] According to the present invention, an aluminum nitride lamb wave resonator with an extremely high Q value is provided, characterized in that it includes: an electrode, a film 2; the electrode includes: a forked electrode 1 and a bottom electrode 3; one end of the forked electrode 1 is connected to an RF signal; the other end of the forked electrode 1 is connected to the ground; the bottom electrode 3 is electrically floating; and the film 2 is arranged between the forked electrode 1 and the bottom electrode 3.

[0007] Preferably, the material of the electrode may be any one of the following: - platinum; - aluminum; - molybdenum; - gold; - silver; - ruthenium.

[0008] Preferably, the material of the film 2 may be any one of the following: -aluminum nitride; -scandium-doped aluminum nitride.

[0009] Preferably, when an electric field is applied between the interdigital electrodes 1 and the bottom electrode 3 , mechanical vibration can be generated in the aluminum nitride film 2 , thereby forming a lamb wave resonance along the horizontal direction, ie, an S0 resonance mode.

[0010] Preferably, six interdigital electrodes 1 are used; the aluminum nitride lamb wave resonator with an extremely high Q value can excite a sixth-order S0 resonance mode.

[0011] Preferably, the resonant frequency of the S0 resonance mode can be adjusted by the width of the interdigitated electrodes 1 and the electrode spacing;

[0012] The Q value of the aluminum nitride lamb wave resonator having an extremely high Q value can be improved by reducing the electromechanical coupling coefficient K2 of the aluminum nitride lamb wave resonator having an extremely high Q value.

[0013] When the structure of the resonator is determined, its figure of merit is also determined, that is, the product of the electromechanical coupling coefficient K2 and the Q value of the aluminum nitride lamb wave resonator with an extremely high Q value. Therefore, the electromechanical coupling coefficient K2 and the Q value are negatively correlated, which means that the Q value of the resonator can be increased by reducing the electromechanical coupling coefficient K2.

[0014] Preferably, it also includes: a half-finger electrode 4;

[0015] A half-finger electrode 4 having the same length as the original electrode but only half the width is introduced on both sides of the six interdigitated electrodes 1;

[0016] Preferably, one end of the half-finger electrode 4 is connected to the RF signal; the other end of the half-finger electrode 4 is connected to the ground; the aluminum nitride lamb wave resonator with an extremely high Q value can excite the overtone resonance of the S0 resonance mode; that is, the 6th, 8th, 10th and 12th order S0 resonance modes.

[0017] Preferably, the aluminum nitride lamb wave resonator with extremely high Q value can excite any of the following S0 resonance modes: -6th order S0 resonance mode; -8th order S0 resonance mode; -10th order S0 resonance mode; -12th order S0 resonance mode; the 8th order S0 resonance mode is the main mode in the overtone resonance of the S0 resonance mode; and plays a leading role in all resonance modes. The several "overtone" resonances excited by the above method will effectively reduce the electromechanical coupling coefficient K2 of the resonator, and the electromechanical coupling coefficient K2 corresponding to all "overtone" resonance modes is lower than that of the original mode. Figure 1 The S0 resonance mode in the resonator is smaller, so the Q value of the original resonator is greatly improved at each resonance frequency. Figure 1The electromechanical coupling coefficient K2 of the conventional aluminum nitride resonator shown is about 1.4%, and the Q value is 1750, while the electromechanical coupling coefficient K2 of the resonator proposed in this patent can be reduced to 0.86%, and the corresponding Q value has exceeded 5500, which is the highest Q value that can be achieved in the field of aluminum nitride resonators to date as far as the author knows. It is worth mentioning that the number of forked-finger electrodes of the resonator proposed in this patent can also be two or four. When the number of forked-finger electrodes is smaller, the influence of the later introduced "half-finger" electrodes on the performance of the resonator is greater, and the Q value of the resonator is higher. In addition, the width of the "half-finger" electrode can also be adjusted to a certain extent to optimize the resonant mode of the resonator and enhance the performance of the resonator.

[0018] According to the present invention, a processing method of an aluminum nitride lamb wave resonator with an extremely high Q value is provided. The aluminum nitride lamb wave resonator with an extremely high Q value is used, and the method includes: step S1: preparing a single crystal silicon wafer for cleaning; step S2: evaporating a bottom electrode onto a silicon substrate; step S3: sputtering an aluminum nitride film layer; step S4: coating, exposing, and etching the shape of the interdigitated electrodes with a photoresist; step S5: sputtering a metal layer and peeling off the interdigitated electrodes; step S6: preparing a silicon dioxide mask by using plasma enhanced chemical vapor deposition technology PECVD; step S7: etching the aluminum nitride film layer by using reactive ion etching ICP-RIE technology; step S8: removing the silicon dioxide mask; and step S9: releasing the oscillating pile by using xenon difluoride XeF2.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention solves the problems of other conventional piezoelectric films being difficult to be compatible with semiconductor processes, having too high a dielectric constant, and having a low mechanical quality factor by using piezoelectric films. This enables the resonator proposed in this patent to perform more superiorly in the application of high-sensitivity smart sensors.

[0021] 2. The present invention solves the problem that it is difficult to increase the Q value of conventional aluminum nitride resonators by adopting a "half-finger" electrode.

[0022] 3. The "overtone" resonance introduced by the "half-finger" electrode of the present invention will effectively reduce the electromechanical coupling coefficient K2 of the resonator, thereby greatly improving the Q value of the resonator, breaking the bottleneck of the Q value of conventional aluminum nitride resonators, and achieving the highest Q value in the field of aluminum nitride resonators. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0024] Figure 1Schematic diagram of the structure of a first conventional resonator based on aluminum nitride piezoelectric film in an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the structure of a second conventional resonator based on aluminum nitride piezoelectric film in an embodiment of the present invention.

[0026] Figure 3 Schematic diagram of the structure of the first high-Q lamb wave resonator in an embodiment of the present invention.

[0027] Figure 4 Schematic diagram of the structure of the second high Q lamb wave resonator in an embodiment of the present invention.

[0028] Figure 5 FIG. 1 is a flow chart of a method for preparing a high-Q lamb wave resonator according to an embodiment of the present invention by using a standard photolithography technique.

[0029] In the figure:

[0030] 1-Interdigital electrodes 5-Silicon

[0031] 2-Film 6-Photoresist

[0032] 3- Bottom electrode 7- Silicon dioxide

[0033] 4-half finger electrode DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0035] Figure 1 , Figure 2 The figure shows a conventional resonator based on aluminum nitride (AlN) piezoelectric film, which is mainly composed of interdigital electrodes 1, film 2, and bottom electrode 3. The interdigital electrodes in the figure are connected to the RF signal and the ground respectively, and the bottom electrode is electrically floating. The material of the electrode can be platinum (Pt), aluminum (Al), molybdenum (Mo), gold (Au), silver (Ag), ruthenium (Ru), etc. The material of the film can be aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN). When an electric field is applied between the interdigital electrodes and the bottom electrode, mechanical vibration is generated in the aluminum nitride film to form a lamb wave resonance along the horizontal direction, that is, the S0 resonance mode. Figure 1The resonator with 6 interdigitated electrodes shown in the figure can excite a 6th order S0 resonance mode, and the resonance frequency of the resonance mode can be adjusted by the width of the interdigitated electrodes and the electrode spacing. When the structure of the resonator is determined, its figure of merit is also determined, that is, the product of the electromechanical coupling coefficient K2 and the Q value. Therefore, the electromechanical coupling coefficient K2 and the Q value are negatively correlated, which means that the Q value of the resonator can be increased by reducing the electromechanical coupling coefficient K2.

[0036] Based on this, this patent proposes Figure 3 , Figure 4 The high Q lamb wave resonator shown in Figure 1 A "half-finger" electrode 4 with the same length as the original electrode but only half the width is introduced on both sides of the six interdigitated electrodes 1 shown in the figure, and the two electrodes are connected to the RF signal and the ground respectively. By introducing these two "half-finger" electrodes, Figure 1 The original acoustic wave boundary and electric field of the resonator will be changed to a certain extent to stimulate the "overtone" resonance of the S0 resonance mode, namely the 6th, 8th, 10th and 12th order S0 resonance modes. The 8th order resonance mode is the main mode of the "overtone" resonance stimulated, and plays a leading role in all resonance modes. The several "overtone" resonances stimulated by the above method will effectively reduce the electromechanical coupling coefficient K2 of the resonator, and the electromechanical coupling coefficient K2 corresponding to all "overtone" resonance modes is lower than that of the original mode. Figure 1 The S0 resonance mode in the resonator is smaller, so the Q value of the original resonator is greatly improved at each resonance frequency. Figure 1 The electromechanical coupling coefficient K2 of the conventional aluminum nitride resonator shown is about 1.4%, and the Q value is 1750, while the electromechanical coupling coefficient K2 of the resonator proposed in this patent can be reduced to 0.86%, and the corresponding Q value has exceeded 5500, which is the highest Q value that can be achieved in the field of aluminum nitride resonators to date as far as the author knows. It is worth mentioning that the number of forked-finger electrodes of the resonator proposed in this patent can also be two or four. When the number of forked-finger electrodes is smaller, the influence of the later introduced "half-finger" electrodes on the performance of the resonator is greater, and the Q value of the resonator is higher. In addition, the width of the "half-finger" electrode can also be adjusted to a certain extent to optimize the resonant mode of the resonator and enhance the performance of the resonator.

[0037] The high-Q lamb wave resonator proposed in this patent can be prepared by standard photolithography technology. Figure 5As shown, the processing flow of the resonator is: 1. Cleaning and preparing the single crystal silicon wafer; 2. Evaporating the bottom electrode onto the silicon substrate; 3. Sputtering the aluminum nitride film layer; 4. Photoresist coating, exposure, and etching the shape of the interdigitated electrodes; 5. Sputtering the metal layer and peeling off the interdigitated electrodes; 6. Using plasma enhanced chemical vapor deposition technology (PECVD) to prepare a silicon dioxide mask; 7. Using reactive ion etching (ICP-RIE) technology to etch the aluminum nitride film layer; 8. Removing the silicon dioxide mask; 9. Using xenon difluoride (XeF2) to release the oscillating stack.

[0038] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0039] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A high Q value aluminum nitride lamb wave resonator, characterized in that: include: Electrodes, films (2); The electrodes comprise: interdigital electrodes (1) and a bottom electrode (3); One end of the interdigital electrode (1) is connected to an RF signal; The other end of the interdigital electrode (1) is connected to the ground; The bottom electrode (3) is electrically floating; The film (2) is arranged between the interdigitated electrodes (1) and the bottom electrode (3); The invention also comprises: a half-finger electrode (4); the half-finger electrode (4) is arranged on both sides of the interdigital electrode (1); the length of the half-finger electrode (4) is the same as the length of the interdigital electrode (1), and the width of the half-finger electrode (4) is half the width of the interdigital electrode (1); the half-finger electrode (4) is used to reduce the electromechanical coupling coefficient K2 of the aluminum nitride lamb wave resonator and improve the Q value of the aluminum nitride lamb wave resonator.

2. The high-Q aluminum nitride lamb wave resonator according to claim 1, characterized in that: The material of the electrode is any one of the following: -platinum; -aluminum; -molybdenum; -gold; -silver; -ruthenium; The film (2) can be made of any of the following materials: -aluminum nitride; - Scandium-doped aluminum nitride.

3. The high Q value aluminum nitride lamb wave resonator according to claim 1, characterized in that: When an electric field is applied between the interdigital electrodes (1) and the bottom electrode (3), mechanical vibration can be generated in the film (2), thereby forming lamb wave resonance along the horizontal direction.

4. The high-Q aluminum nitride lamb wave resonator according to claim 1, characterized in that: Using 6 interdigitated electrodes (1); The high-Q aluminum nitride lamb wave resonator can excite a sixth-order S0 resonance mode.

5. The high-Q aluminum nitride lamb wave resonator according to claim 4, characterized in that: The resonance frequency of the S0 resonance mode can be adjusted by the width of the interdigitated electrodes (1) and the electrode spacing.

6. The high-Q aluminum nitride lamb wave resonator according to claim 1, characterized in that: One end of the half-finger electrode (4) is connected to an RF signal; The other end of the half-finger electrode (4) is connected to the ground; The high-Q aluminum nitride lamb wave resonator can excite the overtone resonance of the S0 resonance mode.

7. The high-Q aluminum nitride lamb wave resonator according to claim 1, characterized in that: The high-Q aluminum nitride lamb wave resonator can excite any of the following S0 resonance modes: -6th order S0 resonance mode; -8th order S0 resonance mode; -10th order S0 resonance mode; -12th order S0 resonance mode; The 8th-order S0 resonance mode is a main mode in the overtone resonance of the S0 resonance mode.

8. A method for processing an aluminum nitride lamb wave resonator with a high Q value, characterized in that: The high-Q aluminum nitride lamb wave resonator according to any one of claims 1 to 7 comprises: Step S1: preparing single crystal silicon wafer for cleaning; Step S2: evaporating the bottom electrode (3) onto the silicon substrate; Step S3: sputtering thin film (2); Step S4: coating, exposing, and etching the shape of the interdigital electrodes using photoresist; Step S5: sputtering a metal layer and peeling off the interdigital electrodes (1); Step S6: preparing a silicon dioxide mask by using plasma enhanced chemical vapor deposition technology; Step S7: etching the aluminum nitride film layer using reactive ion etching technology; Step S8: removing the silicon dioxide mask; Step S9: Using xenon difluoride to release the shock stack.

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