A piezoelectric layer etching method for improving electromechanical coupling coefficient of surface acoustic wave device

Abstract

This invention discloses a piezoelectric layer etching method for improving the electromechanical coupling coefficient of surface acoustic wave (SAW) devices, belonging to the semiconductor field. The method uses an Al / ZnO / Si structure SAW device as the etching object. First, fixed parameters for 3D modeling and etching structure parameters are set. Three etching structure simulation models are constructed by changing the length of the bottom surface of the trapezoidal etching. Based on Rayleigh simulations with etching ratio as the variable, the K values ​​of each model are evaluated. 2 With the speed of sound V p The variation characteristics of K were observed, and the coupling state between mechanical energy and electric field within the piezoelectric layer was investigated; the K-value was extracted. 2 With normalized thickness and V p By identifying common patterns, the optimal parameter combination was selected. A dry etching process, supplemented by wet etching, was used to etch the ZnO piezoelectric layer. The etching effect was then verified and parameters fine-tuned using SEM and AFM. This invention significantly improves the sensitivity, bandwidth, and operational reliability of SAW devices, providing a novel technical path for enhancing the electromechanical coupling coefficient of SAW devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductors, and particularly relates to a piezoelectric layer etching method for improving the electromechanical coupling coefficient of surface acoustic wave devices. Background Technology

[0002] Surface acoustic wave (SAW) devices have been widely used, especially in sensing gases, pressures, temperatures, strains, humidity, electric fields, and torques. However, with the increasing complexity of detection environments, the requirements for SAW devices are shifting towards larger bandwidths and higher sensitivity. The electromechanical coupling coefficient at the device level directly determines the sensitivity and bandwidth of SAW devices. 2 The larger the value, the more energy is converted, the faster the response speed, the wider the bandwidth, and the higher the sensitivity.

[0003] Currently, the more common way to improve K 2 The method is doping, which achieves high K by doping the piezoelectric layer of the SAW device with metal ions such as V and Al. 2 For example, Sulei Fu et al. doped V ions into the ZnO piezoelectric substrate of ZnO / SiC devices, thereby increasing the K2 content of the devices. 2 The K2 content increased from 2.8% to 5.12%. Ralib MAA et al. compared the piezoelectric properties of ZnO and AZO (Al-doped ZnO), finding that the K2 content of AZO increased from 0.044% to 0.069% compared to conventional ZnO. However, doping does not significantly improve the piezoelectric properties of piezoelectric materials and can sometimes even lead to a decrease in K2 content. 2 The K-axis decreased. For example, E. Iborra et al. found that doping V ions into AlN piezoelectric films did not increase the K-axis of the AlN piezoelectric films. 2 In fact, it decreased by 1.2% compared to the traditional structure. Furthermore, the stacking method, which involves layering other materials onto a piezoelectric layer to form a multilayer structure, also improves Kp. 2 For example, authors such as Luo J et al. selected ZnO with the 110 crystal orientation and stacked it to form a SAW device with an IDT / (110)ZnO / SiO three-layer structure, achieving a high K-axis yield of 3.37%. 2 Junyao S et al. proposed a method that satisfies K 2 The highest possible content is 7% in a-ZnO / a-GaN / r multilayer SAW structures. Achieving this method requires precise material selection and crystal orientation control, which significantly increases the manufacturing difficulty.

[0004] In recent years, an etching method that significantly improves K2 by etching piezoelectric layers, offering a simple and effective solution, has attracted considerable attention from researchers. However, current etching methods still have limitations in enhancing the electromechanical coupling coefficient, and K2 remains a concern. 2The improvement effect is not significant. This is because the mechanical energy diffusion and electric field spatial mismatch in the traditional Al / ZnO / Si structure lead to K... 2 Improvement is limited. Summary of the Invention

[0005] The purpose of this invention is to provide a piezoelectric layer etching method for improving the electromechanical coupling coefficient of surface acoustic wave (SAW) devices. This addresses the significant shortcomings of existing methods for improving the electromechanical coupling coefficient of SAW devices, and the inherent core problems in the structural design of traditional SAW devices themselves, which lead to K... 2 The improvement is limited, and it cannot meet the application requirements of high sensitivity and large bandwidth of the device.

[0006] To achieve the above objectives, the present invention provides a piezoelectric layer etching method for improving the electromechanical coupling coefficient of surface acoustic wave devices, comprising the following steps: S1. Determine the basic structure of the device and pre-set the fixed parameters and etching structure parameters for 3D modeling; S2. Based on the device basic structure determined in S1 and the pre-set etching structure parameters, construct simulation models for three etching structures. S3. Simulate and evaluate the electrical properties of the true models of the three etched structures; S4. Based on the simulation results of S3, optimize the etching structure parameters and select the optimal combination of etching structure parameters. S5. Perform actual etching of the ZnO piezoelectric layer of the SAW device according to the optimal etching structure parameters determined in S4. S6. Verify the etching effect and optimize and fine-tune the etching structure parameters.

[0007] Preferably, the specific content of S1 is as follows: S101, The Al / ZnO / Si structure SAW device, which consists of a Si substrate layer, a ZnO piezoelectric layer, an Al interdigitated electrode layer, and a SPLM absorber layer, is used as the etching target. S102. Pre-set the fixed parameters for 3D modeling and the etching structure parameters; Set a fixed surface acoustic wave wavelength λ=2μm, set a fixed constraint on the bottom surface of the Si perfectly matched layer, and connect the left side of the Al interdigitated electrode to +1V and the right side to ground; The minimum mesh size is set to 1 / 8λ, and periodic conditions are set for the four sides (front, double sides, and back) excluding the piezoelectric etching layer. Set etching structure parameter H ZnO d represents the thickness of the ZnO piezoelectric layer. ZnO The height of the piezoelectric etched trapezoid; S ZnO Let d be the length of the bottom surface of the trapezoidal etching; and define the etching ratio as d. ZnO / HZnO Normalized thickness is H ZnO / λ.

[0008] Preferably, the specific content of S2 is as follows: Keeping the Al electrode layer dimensions completely fixed, the length S of the bottom surface of the trapezoidal etching is changed. ZnO Based on the numerical values, the etching structure of the ZnO piezoelectric layer was modeled, resulting in three simulation models of etching structures: trapezoidal, rectangular, and inverted trapezoidal. The structural division criteria are as follows: Trapezoidal structure: 0.5μm < S ZnO ≤1μm; Rectangular structure: S ZnO =0.5μm; Inverted trapezoidal structure: 0.1μm≤S ZnO <0.5μm.

[0009] Preferably, the specific content of S3 is as follows: Simulation tests were conducted on three etching structure simulation models based on Rayleigh propagation modes to evaluate the electromechanical coupling coefficient K. 2 With the speed of sound V p The changing characteristics; S301. Using the etching ratio as a variable, set a total of 6 gradients: 0.1, 0.3, 0.5, 0.7, 0.9, and 1, and simulate the device characteristics under different etching ratios in sequence. S302. Detect K at each etching ratio. 2 With V p The law and numerical values ​​of the variation with normalized thickness; S303. Observe the distribution of mechanical energy and electric field within the ZnO piezoelectric layer to verify the concentration effect of mechanical energy and the degree of coupling between mechanical energy and electric field, and preliminarily screen the etching structure parameters with no obvious diffusion of mechanical energy and dense electric field lines.

[0010] Preferably, the specific content of S4 is as follows: S401. Based on the simulation test results of S3, the common patterns of the three etching structures are extracted: Etching ratio and K 2 The correlation pattern: When the etching ratio is <0.5, the etching effect is weak, K 2 The improvement is slow and lower than that of traditional structures. When the etching ratio is ≥0.5, K 2 Significant improvement; an etching ratio of ≥0.5 is taken as the lower limit of the effective parameter; Normalized thickness and K 2 The correlation pattern: When S ZnO When K is fixed, 2 It is positively correlated with the normalized thickness; the maximum value of the normalized thickness is selected. K 2 With the speed of sound V p The correlation pattern: Speed ​​of sound V p With K 2 They show a negative correlation; providing a basis for performance customization and serving as a verification indicator for parameter optimization. S402. Based on the common characteristics of the three etching structures, set the optimal parameters for the three etching structures: Regular trapezoidal structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.522%, V p The minimum value is 995.1 m / s; Rectangular structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.875%, V p The minimum value is 1034.4 m / s; Inverted trapezoidal structure: S ZnO =0.1μm, d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 Reaching the global maximum of 14.34%, V p This corresponds to the minimum value; S403. Based on the optimal parameters of the three etching structures, select the optimal combination of etching structure parameters: Based on the lower limit of mechanical manufacturing process and K 2 To increase the upper limit, select the inverted trapezoidal structure S. ZnO =0.1μm, d ZnO / H ZnO =1 and H ZnO / λ=1 represents the optimal combination of etching parameters.

[0011] Preferably, the specific content of S5 is as follows: Etching is performed only on the ZnO piezoelectric layer without damaging the Al electrode layer, Si substrate layer, and PLM absorber layer; the size and shape of the etching are controlled according to the designed inverted trapezoidal structure.

[0012] Preferably, the specific content of S6 is as follows: Detecting K of SAW devices in Rayleigh propagation mode 2 Actual value, speed of sound V p The coupling state between mechanical energy and electric field within the piezoelectric layer: If K 2If the actual value does not meet the design target, then S should be readjusted. ZnO Or the etching ratio parameter, repeat S2-S5; if K 2 If the actual value reaches the design target, the etching effect verification is complete.

[0013] Preferably, the mechanical manufacturing process in S4 is a ZnO piezoelectric layer precision etching process system.

[0014] Preferably, the actual etching process in S5 adopts dry etching process and wet etching process. Wet etching is only used to remove residual impurities and minor etching defects on the surface of the piezoelectric layer after dry etching.

[0015] Preferably, the etching effect verification in S6 is performed using one or more of scanning electron microscopy (SEM), atomic force microscopy (AFM), and profilometer to verify the consistency between the actual size and structural shape of the etched piezoelectric layer and the optimal parameters in S4.

[0016] Therefore, the piezoelectric layer etching method for improving the electromechanical coupling coefficient of surface acoustic wave devices, as described above, has the following beneficial effects: (1) K is transformed through the optimal inverted trapezoidal structure 2 The efficiency was increased to 14.34%, which is more than 19 times that of the traditional structure and far superior to existing doping, stacking and conventional etching methods, significantly improving device sensitivity, bandwidth and response speed; (2) By blocking the mechanical energy diffusion channel through trapezoidal etching, the mechanical energy is confined to the top of the piezoelectric layer, achieving full coupling with the dense electric field, and fundamentally optimizing the sound-to-electric conversion mechanism; (3) Based on the traditional Al / ZnO / Si structure, SAW devices are optimized by maintaining the original material and stacking relationship of the device substrate, piezoelectric layer, electrode layer and PLM absorption layer. The ZnO piezoelectric layer can be etched with a single structure. The process steps are simple and highly compatible with the existing SAW device fabrication process. No additional fabrication equipment or process system needs to be developed, which greatly reduces the cost of process modification. (4) Through S ZnO Switching between three etching structures to clarify K 2 The variation patterns of sound velocity, etching ratio, and normalized thickness can be used to adjust structural parameters within the feasible range of the process according to actual application requirements (such as focusing on high sensitivity / large bandwidth or taking sound velocity into account), thereby achieving precise control of device performance and solving the problems of single structural design and lack of clear basis for performance control in existing methods. (5) Through etching ratio gradient optimization, it is clear that when the etching ratio is ≥0.5, the K-factor caused by weak etching can be avoided. 2The method achieves slow or even worse performance than traditional structures, and only modifies the piezoelectric layer after etching, without damaging the Al interdigitated electrode layer, Si substrate layer, and PLM absorber layer, thus preserving the original performance of each functional layer of the device. Simultaneously, the acoustic wave vibration intensity decreases from top to bottom along the piezoelectric layer depth after etching, with the displacement mainly concentrated between 0.5λ and 1.5λ. This results in stable surface acoustic wave propagation characteristics, significantly improving the reliability and consistency of SAW device operation and resolving the uncertainties and susceptibility to K-type defects associated with doping methods. 2 The problem of decline; (6) By deeply integrating the etching process with the acoustic-electric coupling characteristics of SAW devices, a unique trapezoidal etching structure system was designed, and a precise matching relationship between "structure shape - parameter value - electromechanical coupling performance" was established, realizing the upgrade of the etching method from "simple processing" to "precise design optimization". At the same time, it provides a new technical path for improving the electromechanical coupling coefficient of SAW devices. Compared with existing methods, it has the advantages of significant improvement effect, simple process and strong controllability.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a flowchart of a piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to the present invention; Figure 2 The diagrams show the Al / ZnO / Si structure and traditional model of the surface acoustic wave device, where (a) is the overall structure diagram, (b) is the traditional structure model diagram, and (c) is the mesh diagram of the traditional structure model. Figure 3 The diagrams show the mechanical energy and electric field distribution of the SAW device, where (a) is the actual electric field distribution and (b) is the simulated electric field and mechanical energy distribution. Figure 4 For S ZnO =1μm trapezoidal etching model diagram, where (a) is the overall diagram of the trapezoidal etching model, (b) is the front view of the trapezoidal etching, and (c) is the top view of the trapezoidal etching; Figure 5 The figure shows the simulation diagram of the mechanical energy electric field of the trapezoidal etching, where (a) is S ZnO Simulation diagram of the mechanical energy electric field of trapezoidal etching with a diameter of 1μm, (b) is S ZnO Simulation diagram of the mechanical energy electric field of trapezoidal etching with a diameter of 0.1 μm; Figure 6 The diagrams show the mode shapes and displacements of the trapezoidal etching, where (a) is the mode shape diagram and (b) is the displacement diagram. Figure 7 For positive trapezoidal etching of Al / ZnO / Si structure K 2 With Vp The graph shows the change curves, where (a) represents S. ZnO =1μm positive trapezoidal etching of Al / ZnO / Si structure K 2 The curve of change, (b) is S ZnO =1μm positive trapezoidal etching of Al / ZnO / Si structure V p The curve of change, (c) is S ZnO =0.8μm positive trapezoidal etching of Al / ZnO / Si structure K 2 The curve of change, (d) is S ZnO =0.8μm positive trapezoidal etching of Al / ZnO / Si structure V p The curve of change, (e) is S ZnO =0.6μm trapezoidal etching of Al / ZnO / Si structure K 2 The curve of change, (f) is S ZnO =0.6μm trapezoidal etching of Al / ZnO / Si structure V p Change curve graph; Figure 8 For S ZnO =0.5μm rectangular etching of Al / ZnO / Si structure K 2 and The graph shows the change curves, where (a) represents S. ZnO =0.5μm rectangular etching of Al / ZnO / Si structure K 2 The curve of change, (b) is S ZnO =0.5μm rectangular etching Al / ZnO / Si structure Change curve graph; Figure 9 For etching the Al / ZnO / Si structure in an inverted trapezoidal shape, K 2 and The graph shows the change curves, where (a) represents S. ZnO Inverted trapezoidal etching of Al / ZnO / Si structure K = 0.4 μm 2 The curve of change, (b) is S ZnO Inverted trapezoidal etching of Al / ZnO / Si structure with a diameter of 0.4 μm The curve of change, (c) is S ZnO Inverted trapezoidal etching of Al / ZnO / Si structure K = 0.2 μm 2 The curve of change, (d) is S ZnO Inverted trapezoidal etching of Al / ZnO / Si structure with a diameter of 0.2 μm The curve of change, (e) is S ZnO Inverted trapezoidal etching of Al / ZnO / Si structure K = 0.1 μm 2 The curve of change, (f) is S ZnOInverted trapezoidal etching of Al / ZnO / Si structure with a diameter of 0.1 μm Change curve graph. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0020] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0021] The following is combined Figures 1-9 The embodiments of the present invention will be described in detail below.

[0022] Example 1 A method for etching a piezoelectric layer to improve the electromechanical coupling coefficient of a surface acoustic wave device includes the following steps: S1. Determine the basic structure of the device and pre-set the fixed parameters and etching structure parameters for 3D modeling; S101, The Al / ZnO / Si structure SAW device, which consists of a Si substrate layer, a ZnO piezoelectric layer, an Al interdigitated electrode layer, and a SPLM absorber layer, is used as the etching target. S102. Pre-set the fixed parameters for 3D modeling and the etching structure parameters; Set a fixed surface acoustic wave wavelength λ=2μm, set a fixed constraint on the bottom surface of the Si perfectly matched layer, and connect the left side of the Al interdigitated electrode to +1V and the right side to ground; The minimum mesh size is set to 1 / 8λ, and periodic conditions are set for the four sides (front, double sides, and back) excluding the piezoelectric etching layer. Set etching structure parameter H ZnO d represents the thickness of the ZnO piezoelectric layer. ZnO The height of the piezoelectric etched trapezoid; S ZnO Let d be the length of the bottom surface of the trapezoidal etching; and define the etching ratio as d. ZnO / H ZnONormalized thickness is H ZnO / λ.

[0023] S2. Based on the device basic structure determined in S1 and the pre-set etching structure parameters, construct simulation models for three etching structures. Keeping the Al electrode layer dimensions completely fixed, the length S of the bottom surface of the trapezoidal etching is changed. ZnO Based on the numerical values, the etching structure of the ZnO piezoelectric layer was modeled, resulting in three simulation models of etching structures: trapezoidal, rectangular, and inverted trapezoidal. The structural division criteria are as follows: Trapezoidal structure: 0.5μm < S ZnO ≤1μm; Rectangular structure: S ZnO =0.5μm; Inverted trapezoidal structure: 0.1μm≤S ZnO <0.5μm.

[0024] S3. Simulate and evaluate the electrical properties of the true models of the three etched structures; Simulation tests were conducted on three etching structure simulation models based on Rayleigh propagation modes to evaluate the electromechanical coupling coefficient K. 2 With the speed of sound V p The changing characteristics; S301. Using the etching ratio as a variable, set a total of 6 gradients: 0.1, 0.3, 0.5, 0.7, 0.9, and 1, and simulate the device characteristics under different etching ratios in sequence. S302. Detect K at each etching ratio. 2 With V p The law and numerical values ​​of the variation with normalized thickness; S303. Observe the distribution of mechanical energy and electric field within the ZnO piezoelectric layer to verify the concentration effect of mechanical energy and the degree of coupling between mechanical energy and electric field, and preliminarily screen the etching structure parameters with no obvious diffusion of mechanical energy and dense electric field lines.

[0025] S4. Based on the simulation results of S3, optimize the etching structure parameters and select the optimal combination of etching structure parameters. S401. Based on the simulation test results of S3, the common patterns of the three etching structures are extracted: Etching ratio and K 2 The correlation pattern: When the etching ratio is <0.5, the etching effect is weak, K 2 The improvement is slow and lower than that of traditional structures. When the etching ratio is ≥0.5, K 2 Significant improvement; an etching ratio of ≥0.5 is taken as the lower limit of the effective parameter; Normalized thickness and K 2 The correlation pattern: When S ZnO When K is fixed, 2 It is positively correlated with the normalized thickness; the maximum value of the normalized thickness is selected. K 2 With the speed of sound V p The correlation pattern: Speed ​​of sound V p With K 2 They show a negative correlation; providing a basis for performance customization and serving as a verification indicator for parameter optimization. S402. Based on the common characteristics of the three etching structures, set the optimal parameters for the three etching structures: Regular trapezoidal structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.522%, V p The minimum value is 995.1 m / s; Rectangular structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.875%, V p The minimum value is 1034.4 m / s; Inverted trapezoidal structure: S ZnO =0.1μm, d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 Reaching the global maximum of 14.34%, V p This corresponds to the minimum value; S403. Based on the optimal parameters of the three etching structures, select the optimal combination of etching structure parameters: Based on the lower limit of mechanical manufacturing process and K 2 To increase the upper limit, select the inverted trapezoidal structure S. ZnO =0.1μm, d ZnO / H ZnO =1 and H ZnO / λ=1 represents the optimal combination of etching parameters.

[0026] S5. Perform actual etching of the ZnO piezoelectric layer of the SAW device according to the optimal etching structure parameters determined in S4. Etching is performed only on the ZnO piezoelectric layer without damaging the Al electrode layer, Si substrate layer, and PLM absorber layer; the size and shape of the etching are controlled according to the designed inverted trapezoidal structure.

[0027] S6. Verify the etching effect and optimize and fine-tune the etching structure parameters.

[0028] Detecting K of SAW devices in Rayleigh propagation mode 2 Actual value, speed of sound V p The coupling state between mechanical energy and electric field within the piezoelectric layer: If K 2 If the actual value does not meet the design target, then S should be readjusted. ZnO Or the etching ratio parameter, repeat S2-S5; if K 2 If the actual value reaches the design target, the etching effect verification is complete.

[0029] The mechanical manufacturing process in S4 is a precision etching process system for ZnO piezoelectric layers.

[0030] The actual etching process in S5 uses both dry etching and wet etching processes. Wet etching is only used to remove residual impurities and minor etching defects on the surface of the piezoelectric layer after dry etching.

[0031] The etching effect in S6 was verified using one or more of scanning electron microscopy (SEM), atomic force microscopy (AFM), and profilometer to verify the consistency between the actual size and structural shape of the etched piezoelectric layer and the optimal parameters of S4.

[0032] Example 2 This invention provides a piezoelectric layer etching method to improve the electromechanical coupling coefficient of surface acoustic wave devices, thereby enhancing the coupling effect between mechanical energy and electric field in the structure. This is achieved by changing the length of the bottom surface (S). ZnO To achieve three etching structures—trapezoidal, rectangular, and inverted trapezoidal—K-axis etching is applied to these three structures in the Rayleigh propagation mode. 2 With the speed of sound (V) p ) with d ZnO / H ZnO and H ZnO Evaluation of the changing characteristics to obtain the optimal K 2 The combination of structural parameters to improve the effect, and the specific process are as follows: Figure 1 As shown.

[0033] This invention proposes a trapezoidal etching structure. While keeping the basic dimensional parameters and material constant, the structure was obtained according to the 3D modeling parameters set in Table 1, as shown below. Figure 4 (a) S ZnO = Simulation model of the trapezoidal Al / ZnO / Si structure. Figure 4 (b) and (c) represent the front view and top view of the trapezoidal etching, respectively.

[0034] Table 1. 3D Model Parameter Settings

[0035] Figure 5(a) is S ZnO = Simulation results of mechanical energy and electric field of the trapezoidal etching model. It is evident that the trapezoidal etching exhibits a significant concentration effect on mechanical energy; that is, the mechanical energy is primarily concentrated in the top region of the piezoelectric layer, without the presence of... Figure 2 (b) shows the large diffusion exhibited by the traditional model.

[0036] However, the concentration effect of mechanical energy is affected by the dimensions of the trapezoidal structure. ZnO = At that time, the electric field after etching is not strong in the rightmost region of the piezoelectric layer where mechanical energy is concentrated, so the mechanical energy on the rightmost side does not couple strongly with the electric field, affecting K. 2 Its effect on improvement is limited. ZnO = At that time, etching removed more mechanical energy diffusion channels, so the mechanical energy hardly diffused and was entirely confined to the top of the piezoelectric layer, where the electric field lines were also most dense, achieving full coupling between mechanical energy and the electric field, such as... Figure 5 As shown in (b).

[0037] Figure 6 The image shows the acoustic wave modes and displacements generated after etching. It is evident that the vibration intensity of the acoustic waves decreases from top to bottom with increasing piezoelectric layer depth, such as... Figure 6 As shown in (a). Settings , and These represent the displacement components of the sound wave along the X, Y, and Z directions, respectively. The displacement diagram is shown below. Figure 6 As shown in (b). In the figure and The component basically does not undergo displacement, u z The components are the main displacements and are concentrated between 0.5λ and 1.5λ. After that, it approaches zero. Therefore, the acoustic waves generated by the etched SAW device conform to the Rayleigh polity.

[0038] At the same time, by Figure 6 It can also be seen that S ZnO = The displacement is greater than S ZnO = The displacement (0.036 > 0.0038) indicates that S ZnO = The electric field coupling effect is better, resulting in larger amplitude and displacement, consistent with the derivation above. That is, the surface acoustic waves generated by the trapezoidal etching of the Al / ZnO / Si structure change the mechanism of traditional structures that directly rely on piezoelectric material excitation to generate surface acoustic waves. It takes into account the coupling effect of electric field and mechanical energy at the structural boundary and adds etching process to optimize the structural dimensions.

[0039] However, the above analysis clearly shows that the length S of the lower base is... ZnO Different values ​​will lead to different optimization results. Therefore, this invention proposes to examine the structural dimensions (H). ZnO d ZnO / H ZnO S ZnO The optimal K is determined by its influence on the electrical characteristics of SAW devices. 2 The method.

[0040] First, by changing S ZnO The numerical value is used to obtain different etching shapes. For example, 0.5 <S ZnO ≤1 At that time, its shape is a regular trapezoid; S ZnO =0.5 At that time, its shape is rectangular; 0.1 ≤S ZnO <0.5 At that time, its shape is an inverted trapezoid.

[0041] Secondly, define d ZnO / H ZnO Let K be the etching ratio, and use it as a variable to evaluate the SAW device K under different etching ratios. 2 With V p With normalized thickness (H) ZnO / The changes that have occurred.

[0042] Finally, based on the evaluation results, the etching ratio that meets the requirements is determined, that is, the optimal trapezoidal etching structure is determined.

[0043] like Figure 7 As shown in (a), (c) and (e), when d ZnO / H ZnO When K = 0.1~0.3, K2 grows more slowly compared to the traditional structure, and K may exhibit [further characteristics]. 2 Smaller than traditional structures, this is due to the negative effects of weaker etching; until d ZnO / H ZnO When K = 0.5, the etched structure is more obvious. 2 Compared to the traditional structure (0.742%), a significant increase began to appear; when it reached d ZnO / H ZnO =1 and H ZnO / =1,K 2 The maximum value was achieved, which was 10.522%. Compared with the traditional structure, the K value of the trapezoidal etching structure was higher. 2 The maximum increase was 9.78% compared to the traditional structure, reaching 14.18 times that of the traditional structure. Conversely, V p In K 2 The maximum value reached a minimum of 995.1 m / s, such as Figure 7 As shown in (b), (d) and (f).

[0044] K-shaped etched rectangle 2 With V p The pattern of change is consistent with that of trapezoidal etching. For example... Figure 8 As shown in (a), when S ZnO Fixed, d ZnO / H ZnO =1 and H ZnO / When =1, the K of the SAW device 2 It reaches its maximum value of 10.875%, which is 10.133% higher than the traditional structure and 14.65 times that of the traditional structure. At this point, V... p It reaches a minimum value of 1034.4 m / s, such as Figure 8 As shown in (b).

[0045] During inverted trapezoidal etching, when S ZnO =0.1 d ZnO / H ZnO =1 and H ZnO / When =1, the K of the SAW device 2 V reaches its maximum value. p Reaching the minimum value, such as Figure 9 As shown in (e) and (f). At this time, K 2 The maximum value is 14.34%, which is 13.598% higher than the traditional structure, reaching the level of the traditional structure K. 2 More than 19 times.

[0046] The above results fully demonstrate that when SZnO is fixed, K 2 The variation pattern shows a positive correlation with the normalized thickness; and as the piezoelectric etching ratio increases, K... 2 It will gradually reach its maximum value, V p Then with K 2 The trend of change is the opposite.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for etching a piezoelectric layer to improve the electromechanical coupling coefficient of a surface acoustic wave (SAW) device, characterized in that, Includes the following steps: S1. Determine the basic structure of the device and pre-set the fixed parameters and etching structure parameters for 3D modeling; S2. Based on the device basic structure determined in S1 and the pre-set etching structure parameters, construct simulation models for three etching structures. S3. Simulate and evaluate the electrical properties of the true models of the three etched structures; S4. Based on the simulation results of S3, optimize the etching structure parameters and select the optimal combination of etching structure parameters. S5. Perform actual etching of the ZnO piezoelectric layer of the SAW device according to the optimal etching structure parameters determined in S4. S6. Verify the etching effect and optimize and fine-tune the etching structure parameters.

2. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 1, characterized in that, The specific content of S1 is as follows: S101, The Al / ZnO / Si structure SAW device, which consists of a Si substrate layer, a ZnO piezoelectric layer, an Al interdigitated electrode layer, and a SPLM absorber layer, is used as the etching target; S102. Pre-set the fixed parameters and etching structure parameters for 3D modeling; Set a fixed surface acoustic wave wavelength λ=2μm, set a fixed constraint on the bottom surface of the Si perfectly matched layer, and connect the left side of the Al interdigitated electrode to +1V and the right side to ground; The minimum mesh size is set to 1 / 8λ, and periodic conditions are set for the four sides (front, double sides, and back) excluding the piezoelectric etching layer. Set etching structure parameter H ZnO d represents the thickness of the ZnO piezoelectric layer. ZnO The height of the piezoelectric etched trapezoid; S ZnO Let d be the length of the bottom surface of the trapezoidal etching; and define the etching ratio as d. ZnO / H ZnO Normalized thickness is H ZnO / λ.

3. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 2, characterized in that, The specific details of S2 are as follows: Keeping the Al electrode layer dimensions completely fixed, the length S of the bottom surface of the trapezoidal etching is changed. ZnO Based on the numerical values, the etching structure of the ZnO piezoelectric layer was modeled, resulting in three simulation models of etching structures: trapezoidal, rectangular, and inverted trapezoidal. The structural division criteria are as follows: Trapezoidal structure: 0.5μm < S ZnO ≤1μm; Rectangular structure: S ZnO =0.5μm; Inverted trapezoidal structure: 0.1μm≤S ZnO <0.5μm.

4. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 3, characterized in that, The specific details of S3 are as follows: Simulation tests were conducted on three etching structure simulation models based on Rayleigh propagation modes to evaluate the electromechanical coupling coefficient K. 2 With the speed of sound V p The changing characteristics; S301. Using the etching ratio as a variable, set a total of 6 gradients: 0.1, 0.3, 0.5, 0.7, 0.9, and 1, and simulate the device characteristics under different etching ratios in sequence. S302. Detect K at each etching ratio. 2 With V p The law and numerical values ​​of the variation with normalized thickness; S303. Observe the distribution of mechanical energy and electric field within the ZnO piezoelectric layer to verify the concentration effect of mechanical energy and the degree of coupling between mechanical energy and electric field, and preliminarily screen the etching structure parameters with no obvious diffusion of mechanical energy and dense electric field lines.

5. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 4, characterized in that, The specific details of S4 are as follows: S401. Based on the simulation test results of S3, the common patterns of the three etching structures are extracted: Etching ratio and K 2 The correlation pattern: When the etching ratio is <0.5, the etching effect is weak, K 2 The improvement is slow and lower than that of traditional structures. When the etching ratio is ≥0.5, K 2 Significant improvement; an etching ratio of ≥0.5 is taken as the lower limit of the effective parameter; Normalized thickness and K 2 The correlation pattern: When S ZnO When K is fixed, 2 It is positively correlated with the normalized thickness; the maximum value of the normalized thickness is selected. K 2 With the speed of sound V p The correlation pattern: Speed ​​of sound V p With K 2 They show a negative correlation; providing a basis for performance customization and serving as a verification indicator for parameter optimization. S402. Based on the common characteristics of the three etching structures, set the optimal parameters for the three etching structures: Regular trapezoidal structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.522%, V p The minimum value is 995.1 m / s; Rectangular structure: d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 The maximum value is 10.875%, V p The minimum value is 1034.4 m / s; Inverted trapezoidal structure: S ZnO =0.1μm, d ZnO / H ZnO =1、H ZnO When / λ=1, K 2 Reaching the global maximum of 14.34%, V p This corresponds to the minimum value; S403. Based on the optimal parameters of the three etching structures, select the optimal combination of etching structure parameters: Based on the lower limit of mechanical manufacturing process and K 2 To increase the upper limit, select the inverted trapezoidal structure S. ZnO =0.1μm, d ZnO / H ZnO =1 and H ZnO / λ=1 represents the optimal combination of etching parameters.

6. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 5, characterized in that, The specific details of S5 are as follows: Etching is performed only on the ZnO piezoelectric layer without damaging the Al electrode layer, Si substrate layer, and PLM absorber layer; the size and shape of the etching are controlled according to the designed inverted trapezoidal structure.

7. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 6, characterized in that, The specific details of S6 are as follows: Detecting K of SAW devices in Rayleigh propagation mode 2 Actual value, speed of sound V p The coupling state between mechanical energy and electric field within the piezoelectric layer: If K 2 If the actual value does not meet the design target, then S should be readjusted. ZnO Or the etching ratio parameter, repeat S2-S5; if K 2 If the actual value reaches the design target, the etching effect verification is complete.

8. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 7, characterized in that: The mechanical manufacturing process in S4 is a precision etching process system for ZnO piezoelectric layers.

9. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 6, characterized in that: The actual etching process in S5 uses both dry etching and wet etching processes. Wet etching is only used to remove residual impurities and minor etching defects on the surface of the piezoelectric layer after dry etching.

10. The piezoelectric layer etching method for improving the electromechanical coupling coefficient of a surface acoustic wave device according to claim 6, characterized in that: The etching effect in S6 was verified using one or more of scanning electron microscopy (SEM), atomic force microscopy (AFM), and profilometer to verify the consistency between the actual size and structural shape of the etched piezoelectric layer and the optimal parameters of S4.

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