Surface acoustic wave filter based on h-AlN / h-BN composite film structure

Abstract

The invention belongs to the technical field of microelectronic devices and radio frequency communication, and discloses a surface acoustic wave filter based on an h-AlN / h-BN composite film structure. The surface acoustic wave filter sequentially comprises an interdigital transducer, a composite film piezoelectric layer and a substrate layer from top to bottom, wherein the width of the composite film piezoelectric layer is the same as that of the substrate layer. Wherein the composite film piezoelectric layer is located between the substrate layer and the interdigital transducer layer and comprises an upper layer and a lower layer, the upper layer is made of an AlN material of a hexagonal structure, the lower layer is made of a BN material of a hexagonal structure, and the composite film piezoelectric layer is used for converting acoustic signals and electric signals. Compared with a traditional structure, on the premise of not depending on a finer photoetching process, the working frequency of the surface acoustic wave filter is remarkably improved, the insertion loss is reduced, impedance matching is optimized, and the surface acoustic wave filter is particularly suitable for high-frequency requirements of 5G and future communication systems.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic devices and radio frequency communication technology, and relates to a surface acoustic wave filter based on an h-AlN / h-BN composite film structure. Background Technology

[0002] Surface acoustic wave (SAW) filters are electronic components that utilize the piezoelectric effect and the propagation characteristics of sound waves to filter signals. SAW devices offer advantages such as light weight, small size, high reliability, good consistency, flexible design, and suitability for mass production using microelectronic fabrication techniques. They have been widely applied in numerous fields including mobile communications, broadcasting, non-destructive testing, identification and positioning, navigation, and telemetry. However, with the rapid development of wireless communication technology, spectrum resources are becoming increasingly scarce, and low-frequency bands are no longer sufficient to meet communication demands. Against this backdrop, developing SAW devices suitable for higher frequency bands has become a crucial way to alleviate spectrum resource pressure. Therefore, achieving SAW filters with higher operating frequencies has significant research value and application prospects.

[0003] In surface acoustic wave (SAW) propagation modes, Rayleigh waves are the most common, but their phase velocities are typically low, limiting further increases in device operating frequencies. In contrast, the Sezawa mode, a higher-order Rayleigh wave mode, can be excited in SAW devices with a "slow / fast" multilayer composite structure, exhibiting higher phase velocities and electromechanical coupling coefficients, thus contributing to better device performance. Hexagonal aluminum nitride (h-AlN) possesses advantages such as good thermal conductivity and high SAW propagation velocities (5560-6200 m / s), making h-AlN-based SAW devices promising for applications. Hexagonal boron nitride (h-BN), as an emerging two-dimensional piezoelectric material, has extremely high in-plane sound velocities (19600 m / s), far exceeding those of traditional piezoelectric materials. Therefore, the "slow-fast system" formed by combining h-AlN and h-BN is conducive to Sezawa wave excitation. Thus, SAW devices fabricated using h-AlN / h-BN composite film materials provide a feasible solution for improving the performance of SAW filters. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and propose a surface acoustic wave filter based on an h-AlN / h-BN composite diaphragm structure through software simulation. This structure can excite and utilize Sezawa waves with high sound speed and high energy propagation efficiency, thereby significantly improving the performance of the device without significantly reducing the interdigitation width.

[0005] The software used in this invention is Comsol version 6.2, which can perform piezoelectric coupling calculations and analyze the response of two-dimensional or three-dimensional structural devices to voltage and mechanical changes, and is therefore suitable for the simulation of SAW devices.

[0006] The technical solution of this invention: A surface acoustic wave filter based on an h-AlN / h-BN composite film structure includes, from top to bottom, an interdigital transducer (IDT), a composite film piezoelectric layer, and a substrate layer, wherein the composite film piezoelectric layer and the substrate layer have the same width.

[0007] Furthermore, the interdigital transducer is a thin metal electrode film located on the top layer, made of Al metal material, and includes an input terminal, an output terminal, a ground terminal, and a corresponding reflective grating.

[0008] Furthermore, the composite film piezoelectric layer, located between the substrate layer and the interdigital transducer layer, comprises two layers: an upper layer of hexagonal AlN material and a lower layer of hexagonal BN material, used for the conversion of acoustic signals to electrical signals.

[0009] Furthermore, the substrate layer is sapphire, located at the bottom layer, and is used to provide support and propagate surface acoustic waves.

[0010] Furthermore, the input, output, and two ground terminals of the interdigital transducer layer are all finger-shaped electrodes. The input terminal and one ground terminal are alternately arranged to form one set of interdigitated electrodes, and the output terminal and the other ground terminal are alternately arranged to form another set of interdigitated electrodes. The electrode width 'a' is 2 μm, the spacing between the alternately arranged electrodes 'b' is 2 μm, the spacing between the two sets of interdigitated electrodes 'd' is 4 μm, and the length 2(a+b) is one period λ. The structure within this range is a periodic structure, with a total of 50 periodic structures. The electrode thickness is h. Al It is 30 nm.

[0011] Furthermore, the reflective grating consists of parallel strip electrodes arranged on both sides of two sets of interdigital electrodes, with the same electrode width, spacing, and number of cycles as the interdigital electrodes.

[0012] Furthermore, the input terminal of the interdigital transducer layer is connected to a positive voltage, the ground terminal is grounded, and the reflective grid is at a floating potential.

[0013] Furthermore, the thickness of AlN in the composite film piezoelectric layer is 200-500 nm, and the thickness of BN is 50-250 nm.

[0014] The beneficial effects of this invention are as follows: In this invention, the surface acoustic wave propagation speed of hexagonal AlN is higher than that of other traditional piezoelectric materials, while hexagonal BN, as a novel two-dimensional piezoelectric material, has an even higher in-plane sound velocity. Therefore, the two form a "low-velocity layer / high-velocity layer," which can effectively excite Sezawa waves with high sound velocity and high electromechanical coupling coefficient, thereby achieving a higher center frequency. Furthermore, the influence of film thickness on the Sezawa mode filtering performance was analyzed. With a fixed AlN thickness, increasing the BN ratio makes it easier to excite Sezawa waves, but an excessively high BN ratio will reduce the device's operating frequency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the device structure of a traditional IDT / AlN / sapphire SAW filter.

[0016] Figure 2 This is a schematic diagram of the device structure of the SAW filter with the IDT / AlN / BN / sapphire structure proposed in this invention.

[0017] Figure 3 This invention proposes an IDT / AlN / BN / sapphire structure with different AlN and BN thicknesses for S 21 Curves, where (a) represents the S values ​​when the AlN thickness is 200 nm and the BN thickness is 50 nm to 250 nm. 21 Characteristic curves; (b) shows the S values ​​when the AlN thickness is 350 nm and the BN thickness is between 50 nm and 250 nm. 21 Characteristic curves; (c) shows the S values ​​when the AlN thickness is 500 nm and the BN thickness is between 50 nm and 250 nm. 21 Characteristic curves.

[0018] Figure 4 The S based on IDT / AlN / sapphire structure and IDT / AlN / BN / sapphire structure provided in Embodiment 1 and Comparative Example 1 of this invention 11 Characteristic curves.

[0019] Figure 5 The S based on IDT / AlN / sapphire structure and IDT / AlN / BN / sapphire structure provided in Embodiment 1 and Comparative Example 1 of this invention 21 Characteristic curves.

[0020] Figure 6 These are the admittance curves based on IDT / AlN / sapphire structure and IDT / AlN / BN / sapphire structure provided in Embodiment 1 and Comparative Example 1 of the present invention.

[0021] Figure 7 These are Smith impedance circle diagrams based on IDT / AlN / sapphire structures and IDT / AlN / BN / sapphire structures provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0023] Traditional AlN device structures, such as Figure 1 As shown, the structure includes an interdigital transducer layer, a piezoelectric layer, and a substrate layer, wherein the interdigital transducer layer includes an input terminal, an output terminal, a ground terminal, and a reflective grid.

[0024] The input, output, and two ground terminals of the interdigital transducer layer are all finger-shaped electrodes. The input and ground terminals are interleaved to form one set of interdigitated electrodes, and the output and another ground terminal are interleaved to form another set of interdigitated electrodes. The width of the electrodes is a, the electrode spacing is b, the spacing between the two sets of interdigitated electrodes is d, and the length of 2(a+b) is one period λ. The structure within this range is a periodic structure with a total of 50 periods.

[0025] The reflective grid consists of parallel strip electrodes arranged on both sides of two sets of interdigital electrodes. The electrode width, spacing, and number of cycles are the same as those of the interdigital electrodes.

[0026] The input terminal of the interdigital transducer layer is connected to a positive voltage, the ground terminal is grounded, and the reflective grid is at a floating potential.

[0027] The interdigitated electrode at the top is made of Al metal and has a thickness of h. Al .

[0028] The piezoelectric layer is made of AlN material and has a thickness of h. AlN .

[0029] The substrate layer is made of sapphire material with a thickness of h. S .

[0030] The piezoelectric layer has the same width as the substrate layer.

[0031] This invention proposes a surface acoustic wave filter based on an h-AlN / h-BN composite diaphragm structure, such as... Figure 2 As shown, from top to bottom, it includes: an interdigital transducer layer, a composite film piezoelectric layer, and a substrate layer. The interdigital transducer layer includes an input terminal, an output terminal, a ground terminal, and a reflective grid.

[0032] The input, output, and two ground terminals of the interdigital transducer layer are all finger-shaped electrodes. The input and ground terminals are interleaved to form one set of interdigitated electrodes, and the output and another ground terminal are interleaved to form another set of interdigitated electrodes. The width of the electrodes is a, the electrode spacing is b, the spacing between the two sets of interdigitated electrodes is d, and the length of 2(a+b) is one period λ. The structure within this range is a periodic structure with a total of 50 periods.

[0033] The reflective grid consists of parallel strip electrodes arranged on both sides of two sets of interdigital electrodes. The electrode width, spacing, and number of cycles are the same as those of the interdigital electrodes.

[0034] The input terminal of the interdigital transducer layer is connected to a positive voltage, the ground terminal is grounded, and the reflective grid is at a floating potential.

[0035] The interdigitated electrode at the top is made of Al metal and has a thickness of h. Al .

[0036] The composite film piezoelectric layer comprises two layers: an upper layer of hexagonal AlN material and a lower layer of hexagonal BN material, with thicknesses h and h, respectively. AlN and h BN .

[0037] The substrate layer is made of sapphire material with a thickness of h. S .

[0038] The AlN layer, BN layer, and substrate layer in the composite film piezoelectric layer have the same width.

[0039] A simulation method for a surface acoustic wave filter based on an h-AlN / h-BN composite diaphragm structure includes the following steps: A surface acoustic wave (SAW) filter model was established using Comsol software with the following parameters: electrode width a = 2 μm, electrode spacing b = 2 μm, interdigital transducer spacing d = 4 μm, period λ = 8 μm, and electrode thickness h = 2 μm. Al The thickness is 30 nm, and the substrate thickness is h. S The diameter is 24 μm, and the number of cycles for the input, output, and two side reflective gratings is 50.

[0040] The input terminal of the interdigital transducer layer is connected to a positive voltage, and the ground terminal is grounded. The conversion of electrical signals into acoustic signals is completed through the positive and inverse piezoelectric effects. When an electrical signal is input to the input terminal, the electrical signal is converted into mechanical energy through the inverse piezoelectric effect of the piezoelectric substrate and propagates on the surface of the piezoelectric substrate in the form of surface acoustic waves. When the surface acoustic wave signal reaches the output terminal, it is converted back into an electrical signal for output through the piezoelectric effect of the piezoelectric substrate.

[0041] The center frequency and insertion loss of the surface acoustic wave filter can be adjusted by varying the film thicknesses of the low-velocity AlN layer and the high-velocity BN layer, which have the same width as the substrate layer. The filtering performance of the surface acoustic wave (SAW) filter was analyzed by varying the thickness of the high-velocity BN layer at low-velocity AlN layer thicknesses of 200, 350, and 500 nm. The results are as follows: Figure 3 As shown, composite film piezoelectric layers with different low-velocity AlN layer thicknesses can all excite obvious Sezawa waves, and the thickness of both the low-velocity AlN layer and the high-velocity BN layer can affect the device performance.

[0042] When the thickness of the AlN layer is constant at low speeds, the center frequency decreases significantly and the insertion loss tends to decrease as the thickness of the BN layer increases at high speeds, for example, h AlNAt a thickness of 350 nm, as the thickness of the hypersonic BN layer increases from 50 nm to 250 nm, the insertion loss decreases from 21.86 dB to 4.98 dB, and the center frequency decreases from 1.392 GHz to 1.112 GHz. This indicates that increasing the thickness of the hypersonic BN layer makes it easier to excite higher-order modes, but increasing the thickness is not conducive to increasing the frequency.

[0043] Comparative Example 1 Using COMSOL software, Figure 1 The front view of the device structure is used as a reference to establish a two-dimensional model of the IDT / AlN / sapphire structure.

[0044] The filter's proportional scheme model parameters are as follows: electrode width a = 2 μm, electrode spacing b = 2 μm, interdigital transducer spacing d = 4 μm, period λ = 8 μm, and electrode thickness h = 2 μm. Al The thickness of the low-velocity AlN layer is 30 nm, the thickness h is 500 nm, and the thickness h of the substrate layer is 30 nm. S The diameter is 24 μm, and the number of cycles for the input, output, and two side reflective gratings is 50.

[0045] Example 1 Using COMSOL software, Figure 2 The front view of the device structure is used as a reference to establish a two-dimensional model of the IDT / AlN / BN / sapphire structure.

[0046] The model parameters for the surface acoustic wave filter are as follows: electrode width a = 2 μm, electrode spacing b = 2 μm, interdigital transducer spacing d = 4 μm, period λ = 8 μm, and electrode thickness h = 2 μm. Al The thickness h of the low-velocity AlN layer is 30 nm. AlN The thickness h of the high-velocity BN layer is 350 nm. BN The thickness of the substrate is 150 nm, and the thickness of the substrate layer is h. S The diameter is 24 μm, and the number of cycles for the input, output, and two side reflective gratings is 50.

[0047] Example 1 and Comparative Example 1 S 11 Parameter curves as follows Figure 4 As shown in the curve, Example 1 outperforms Comparative Example 1 in both frequency and return loss. Example 1 at center frequency S... 11 The parameter value is -1.56 dB, and the S value at the center frequency of Comparative Example 1 is... 11 The parameter value is -17.10 dB, indicating that Example 1 has superior performance in suppressing signal reflection.

[0048] Example 1 and Comparative Example 1 S 21 Parameter curves as follows Figure 5As shown, Example 1 exhibits a better frequency advantage; the center frequency of Comparative Example 1 is 0.776 GHz, while that of Example 1 is 1.270 GHz. Besides the frequency advantage, the curve visually reflects the lower insertion loss of the composite film structure. The insertion loss of Comparative Example 1 is 16.34 dB, while that of Example 1 is 8.32 dB, indicating that the composite film structure has less energy attenuation during signal transmission, which helps improve transmission efficiency within the passband.

[0049] Figure 6 A comparison of the admittance curves for both examples is further provided. Comparative Example 1 has a resonant frequency of 0.767 GHz and an anti-resonant frequency of 0.781 GHz, while Example 1 has a resonant frequency of 1.247 GHz and an anti-resonant frequency of 1.274 GHz. Calculations show that the speed of sound in Comparative Example 1 is 6192 m / s, and in Example 1 it is 10036 m / s. Compared to the traditional structure, the composite film structure used in Example 1 exhibits a sharper admittance curve, a higher peak admittance, and a higher speed of sound. This characteristic reflects a significantly enhanced frequency selectivity, which is beneficial for signal filtering at higher frequencies within a specific frequency band.

[0050] Figure 7 The analysis of the Smith chart more intuitively reveals the advantages of composite membrane structures in impedance matching: the impedance curve of the composite membrane structure is closer to the center of the chart than that of a single-layer structure. This clearly indicates that its input impedance is closer to the system's standard impedance (50 Ω). This good impedance matching characteristic helps to reduce signal reflection and return loss, thereby further improving the overall efficiency of energy transmission. This, in another respect, confirms the superiority of composite membrane structures in energy transmission efficiency.

Claims

1. A surface acoustic wave filter based on an h-AlN / h-BN composite diaphragm structure, characterized in that, The surface acoustic wave filter based on the h-AlN / h-BN composite film structure includes, from top to bottom, an interdigital transducer, a composite film piezoelectric layer, and a substrate layer, wherein the composite film piezoelectric layer and the substrate layer have the same width.

2. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The interdigital transducer is a thin metal electrode film located on the top layer. It is made of Al metal material and includes an input terminal, an output terminal, a ground terminal, and a corresponding reflective grating.

3. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The composite film piezoelectric layer, located between the substrate layer and the interdigital transducer layer, comprises two layers: an upper layer of hexagonal AlN material and a lower layer of hexagonal BN material, used for the conversion of acoustic signals to electrical signals.

4. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The substrate is sapphire, located at the bottom layer, and is used to provide support and propagate surface acoustic waves.

5. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The input, output, and two ground terminals of the interdigitated transducer layer are all finger-shaped electrodes. The input terminal and one ground terminal are alternately arranged to form one set of interdigitated electrodes, and the output terminal and the other ground terminal are alternately arranged to form another set of interdigitated electrodes. The electrode width 'a' is 2 μm, the spacing between the alternately arranged electrodes 'b' is 2 μm, and the spacing between the two sets of interdigitated electrodes 'd' is 4 μm. The length 2(a+b) is one period λ, and the structure within this range is a periodic structure, with a total of 50 periods. The electrode thickness h is... Al It is 30 nm.

6. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The reflective grating consists of parallel strip electrodes arranged on both sides of two sets of interdigital electrodes. The width, spacing, and number of cycles of the electrodes are the same as those of the interdigital electrodes.

7. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The input terminal of the interdigital transducer is connected to a positive voltage, the ground terminal is grounded, and the reflector grid is at a floating potential.

8. The surface acoustic wave filter based on the h-AlN / h-BN composite diaphragm structure according to claim 1, characterized in that, The thickness of the upper layer in the composite film piezoelectric layer is 200-500 nm, and the thickness of the lower layer is 50-250 nm.

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