Surface acoustic wave filter and preparation method

Abstract

The invention discloses a surface acoustic wave filter and a preparation method thereof, and belongs to the field of filter devices, the TCF can be effectively regulated and controlled by doping fluorine contents with different proportions into SiO2 of a temperature compensation layer, and accurate signal transmission and receiving, frequency stability improvement, signal bit error rate reduction and communication quality improvement of the filter in the use process are ensured.

Description

Technical Field

[0001] The present invention belongs to the field of filter devices, and in particular relates to a surface acoustic wave filter and a preparation method thereof. Background Art

[0002] Surface acoustic wave filters typically use piezoelectric materials (such as quartz, lithium niobate, or lithium tantalate) as their substrates. Their temperature coefficient (TCF) directly determines the degree of temperature drift. For example, the TCF of lithium niobate (LiNbO3) can be as high as -75 to -94 ppm / °C. Existing technologies generally address temperature drift in surface acoustic wave filters by: 1. Modify the substrate material and use temperature-compensated piezoelectric materials (such as SiO2-coated lithium tantalate substrates) to reduce temperature drift by offsetting the positive and negative temperature coefficients.

[0003] 2. Design the structure of the entire surface acoustic wave filter, such as topologically optimizing the shape of the IDT, designing asymmetric interdigital electrodes, and offsetting the temperature drift effect by adjusting the local stress distribution.

[0004] 3. Active compensation technology: A silicon dioxide temperature compensation layer is deposited between the piezoelectric layer and the electrode, redistributing acoustic energy to reduce temperature drift. Some structures also use multiple layers of temperature compensation layers to further reduce temperature drift, but zero temperature drift is still not achieved.

[0005] Through the above-mentioned process improvements, the TCF of traditional TC-SAW has been greatly improved, but it has not yet reached the ideal optimal solution, that is, 0ppm / ℃. Summary of the Invention

[0006] This invention addresses the temperature drift problem of existing surface acoustic wave filters and proposes a surface acoustic wave filter and its fabrication method. By doping the SiO2 layer with varying proportions of fluorine, the TCF can be effectively controlled, ensuring accurate signal transmission and reception during filter operation. This improves frequency stability, reduces signal bit error rates, and enhances communication quality.

[0007] In order to achieve the above-mentioned purpose, the present invention is implemented through the following technical scheme: a surface acoustic wave filter, including a substrate layer, an interdigitated electrode layer, a temperature compensation layer, an electrode layer and an insulating film layer, the interdigitated electrode layer is located above the substrate, the temperature compensation layer covers the interdigitated electrode layer, the suspended metal layer is located above the temperature compensation layer, the electrode layer is connected to the interdigitated electrode layer and the surface is exposed outside the insulating film layer, and the temperature compensation layer is made of fluorine-doped silicon dioxide material.

[0008] Furthermore, the fluorine content in the temperature compensation layer is 1%-20%.

[0009] Another solution protected by the present invention is: a method for preparing a surface acoustic wave filter, which is carried out according to the following steps: Step S1, prepare lithium niobate LN substrate material and clean it; Step S2, preparation of interdigitated electrode layer: coating, exposing and developing photoresist according to the interdigitated electrode pattern, so that the photoresist presents the corresponding interdigitated morphology, and then vacuum coating the interdigitated metal using a lift-off process to finally form the interdigitated electrode layer; Step S3, preparing a temperature compensation layer: using a fluorine-doping process to prepare a fluorine-containing silicon dioxide temperature compensation layer; Step S4, preparation of suspended metal layer: according to the position and pattern of the suspended metal layer, photoresist coating, exposure, and development are performed to make the photoresist present the corresponding morphology; suspended metal vacuum coating is performed using a lift-off process to finally form a suspended metal layer; Step S5, electrode layer preparation: coating, exposing, and developing the photoresist of the electrode layer, so that the photoresist presents a corresponding morphology; vacuum coating the electrode metal using a lift-off process to finally form the electrode layer; Step S6, preparation of the insulating film layer: photoresist coating, exposure, development, dry etching, stripping of the photoresist, and finally opening holes in the electrode layer area.

[0010] Furthermore, the fluorine doping process in step S3 is specifically as follows: using raw materials containing silicon, oxygen and fluorine, and performing fluorine doping treatment by chemical vapor deposition or physical vapor deposition to prepare a fluorine-containing temperature compensation layer.

[0011] Furthermore, the raw materials containing silicon, oxygen and fluorine are SiF4 and O2, or SiH4, O2 and CF4, or a fluorine-containing target.

[0012] Furthermore, the physical vapor deposition adopts a PECVD process or a LPCVD process.

[0013] Compared with existing technologies, this invention offers the following advantages: Unlike traditional TC-SAW filters, which simply cover SiO2 as a temperature compensation layer, this invention incorporates varying proportions of fluorine into the SiO2 layer to effectively regulate the filter's TCF. This ensures accurate signal transmission and reception during filter operation, improves frequency stability, reduces signal bit error rates, and enhances communication quality. This improved TCF minimizes the effects of temperature on this type of filter, potentially expanding its application areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of the surface acoustic wave filter of the present invention.

[0015] Figure 2 TCF for resonatorf Graph showing the change of r with the fluorine content ratio.

[0016] Figure 3 TCF for resonator fa Graph showing changes with fluorine content.

[0017] Figure 4 The TCF performance of the resonator at different fluorine doping ratios. DETAILED DESCRIPTION

[0018] The following will describe the embodiments of the present invention in detail with reference to the accompanying drawings and examples, so as to fully understand and implement the process of how the present invention applies technical means to solve technical problems and achieve technical effects.

[0019] like Figure 1 The present invention shows a surface acoustic wave filter comprising a substrate layer, an interdigitated electrode layer, a temperature compensation layer, an electrode layer, and an insulating film layer. The interdigitated electrode layer is located above the substrate, the temperature compensation layer covers the interdigitated electrode layer, the suspended metal layer is located above the temperature compensation layer, and the insulating film layer covers the suspended metal layer, the temperature compensation layer, and the electrode layer. However, the electrode layer is connected to the interdigitated electrode layer, and the upper surface of the electrode layer is exposed outside the insulating film layer. The main difference between the present invention and existing structures is that the temperature compensation layer is made of fluorine-doped silicon dioxide.

[0020] Fluorine-doped silicon dioxide (SiO2) is primarily used in surface acoustic wave (SAW) filters to improve device stability by reducing dielectric loss and optimizing acoustic performance. It is typically used in the substrate material or piezoelectric layer. Existing technology does not yet exist to modify TCF performance by adjusting the fluorine doping ratio in the temperature compensation layer. Typically, the fluorine content in the temperature compensation layer ranges from 1% to 20%. The actual fluorine content needs to be determined experimentally based on the device structure.

[0021] Another technical solution protected by the present invention is: a method for preparing a surface acoustic wave filter, which is carried out according to the following steps: Step S1: prepare a lithium niobate (LN) substrate material and clean it. The substrate material may also be other materials according to actual conditions and is not limited to the lithium niobate substrate.

[0022] Step S2, preparation of interdigitated electrode layer: coating, exposing and developing photoresist according to the interdigitated electrode pattern, so that the photoresist presents the corresponding interdigitated morphology, and then vacuum coating the interdigitated metal using a lift-off process to finally form the interdigitated electrode layer.

[0023] Step S3, Temperature Compensation Layer Preparation: A fluorine-containing silicon dioxide temperature compensation layer is prepared using a fluorine-doping process. Raw materials containing silicon, oxygen, and fluorine are doped with fluorine via chemical vapor deposition or physical vapor deposition (PECVD or LPCVD) to form the fluorine-containing temperature compensation layer. The raw materials containing silicon, oxygen, and fluorine can be SiF4 and O2, or SiH4, O2, and CF4, or a fluorine-containing target.

[0024] The fluorine doping ratio can be controlled by controlling the reaction gas flow rate or replacing sputtering targets with different fluorine contents, so that TCF can achieve the optimal solution of "zero temperature drift".

[0025] Step S4, preparation of suspended metal layer: according to the position and pattern of the suspended metal layer, photoresist coating, exposure and development are performed to make the photoresist present the corresponding morphology; suspended metal vacuum coating is performed by lift-off process, and finally the suspended metal layer is formed. Step S5, electrode layer preparation: photoresist coating, exposure, and development of the electrode layer, the photoresist presents the corresponding morphology; electrode metal vacuum coating, using lift-off process, finally forming the electrode layer Step S6, preparation of the insulating film layer: photoresist coating, exposure, development, dry etching, stripping of the photoresist, and finally opening holes in the electrode layer area.

[0026] During the preparation of the temperature compensation layer, this invention incorporates varying proportions of fluorine into a conventional SiO2 layer, effectively regulating the TCF. This ensures accurate signal transmission and reception during filter operation, improves frequency stability, reduces signal bit error rates, and enhances communication quality. This optimized TCF minimizes the effects of temperature on this type of filter, potentially expanding its application areas.

[0027] In order to verify the effect of the present invention, a standard resonator (metallization rate 50%) was used as an example to prepare devices with different fluorine content ratios using the above preparation process. The relationship between TCF and fluorine content is as follows: Figure 2 Figure 3 As shown in the figure, it can be seen that at the same SiO2 thickness, as the fluorine content changes, the corresponding TCF becomes controllable.

[0028] Figure 4 This is a graph showing the TCF performance of the resonator at different fluorine doping ratios. As the fluorine content changes, the temperature drift difference changes accordingly. From left to right, the fluorine content is 8%, 6%, 4%, and 2%. The performance of each fluorine content was tested at four temperatures: -25℃, 25℃, 75℃, and 100℃. Figure 4 .from Figure 4It can be seen that when the fluorine doping ratio of this resonator design is 4%, the four color curves basically coincide with each other. Therefore, the frequency difference is minimal as the temperature changes, that is, the TCF is optimal, close to 0ppm / ℃.

[0029] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A surface acoustic wave filter, characterized in that: It includes a substrate layer, an interdigitated electrode layer, a temperature compensation layer, an electrode layer and an insulating film layer. The interdigitated electrode layer is located above the substrate, the temperature compensation layer covers the interdigitated electrode layer, the suspended metal layer is located above the temperature compensation layer, the electrode layer is connected to the interdigitated electrode layer and the surface is exposed outside the insulating film layer, and the temperature compensation layer is made of fluorine-doped silicon dioxide material.

2. The surface acoustic wave filter according to claim 1, wherein: The fluorine content in the temperature compensation layer is 1%-20%.

3. A method for preparing a surface acoustic wave filter, characterized in that: Follow these steps: Step S1, prepare lithium niobate LN substrate material and clean it; Step S2, preparation of interdigitated electrode layer: coating, exposing and developing photoresist according to the interdigitated electrode pattern, so that the photoresist presents the corresponding interdigitated morphology, and then vacuum coating the interdigitated metal using a lift-off process to finally form the interdigitated electrode layer; Step S3, preparing a temperature compensation layer: using a fluorine-doping process to prepare a fluorine-containing silicon dioxide temperature compensation layer; Step S4, preparation of the suspended metal layer: performing photoresist coating, exposure, and development according to the position and pattern of the suspended metal layer, so that the photoresist presents a corresponding morphology; Suspended metal vacuum coating uses lift-off process to finally suspend the metal layer; Step S5, electrode layer preparation: coating, exposing, and developing the photoresist of the electrode layer, so that the photoresist presents a corresponding morphology; Electrode metal vacuum coating, using lift-off process, ultimately forms the electrode layer; Step S6, preparation of the insulating film layer: photoresist coating, exposure, development, dry etching, stripping of the photoresist, and finally opening holes in the electrode layer area.

4. The method for preparing a surface acoustic wave filter according to claim 3, wherein: The fluorine doping process in step S3 is specifically as follows: using raw materials containing silicon, oxygen and fluorine, and performing fluorine doping treatment by chemical vapor deposition or physical vapor deposition to prepare a fluorine-containing temperature compensation layer.

5. The method for preparing a surface acoustic wave filter according to claim 4, wherein: The raw materials containing silicon, oxygen and fluorine are SiF4 and O2, or SiH4, O2 and CF4, or a fluorine-containing target material.

6. The method for preparing a surface acoustic wave filter according to claim 4, wherein: The physical vapor deposition adopts a PECVD process or a LPCVD process.

Images