A high temperature stable film bulk acoustic wave filter

Abstract

The utility model belongs to filter technical field, concretely relates to a kind of high temperature stability film bulk acoustic wave filter;The filter includes the silicon substrate of laminated arrangement, lower electrode layer, first upper electrode layer and second upper electrode layer, and first upper electrode layer and second upper electrode layer right part fold so as to contact silicon substrate;Silicon substrate is provided with recess, lower electrode layer is covered on the recess, forms cavity;Polysilicon layer is formed in silicon substrate using laser microfabrication technology;The utility model reduces the stress influence of piezoelectric film of filter due to temperature dramatic change, improves the performance stability of filter when temperature changes.

Description

Technical Field

[0001] This utility model belongs to the field of filter technology, specifically relating to a high-temperature-stability thin-film bulk acoustic filter. Background Technology

[0002] In the radio frequency (RF) front-end module of a wireless communication system, filters are an indispensable and crucial component. Their main function is to filter signals, thereby enabling signal reception and transmission. Common filters in mobile phones include surface acoustic wave (SAW) filters, solid-state assembled bulk acoustic wave (BAS) filters, and thin-film bulk acoustic wave (FBAS) filters. FBAS filters, as a relatively new technology, are characterized by their small size, low insertion loss, high frequency, and good rectangularity coefficient, and are widely used in mobile phones, tablets, smart wearables, and other electronic products.

[0003] Existing thin-film bulk acoustic wave filters have a very thin piezoelectric film. Since silicon itself has a thermal conductivity of 150 W / (mk) at room temperature, the resonant structure cavity film stress of the thin-film bulk acoustic wave filter is easily affected by temperature. Temperature conduction comes from the silicon substrate material (traditional packaging) and silicon cover plate (wafer-level packaging). Changes in external temperature are quickly transmitted to the working surface of the filter. Repeated temperature changes and rapid temperature changes cause the piezoelectric film structure stress to accumulate rapidly, which can easily lead to piezoelectric film damage and reduced reliability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a high-temperature-stability thin-film bulk acoustic wave filter. The filter includes a silicon substrate, a lower electrode layer, a first upper electrode layer, and a second upper electrode layer stacked together. The right sides of the first and second upper electrode layers are folded to contact the silicon substrate. A groove is provided on the silicon substrate, and the lower electrode layer is disposed on the groove to form a cavity. A polycrystalline silicon layer is formed in the silicon substrate using laser micromachining technology.

[0005] Preferably, the polycrystalline silicon layer is located in other areas of the silicon substrate not covered by the groove.

[0006] Furthermore, the number of polycrystalline silicon layers is at least two.

[0007] Furthermore, the polysilicon layer is arranged horizontally and / or vertically.

[0008] Preferably, if the high-temperature stability thin-film bulk acoustic wave filter adopts wafer-level packaging, the polycrystalline silicon layer is located in both the silicon substrate and the packaging cover.

[0009] Furthermore, the thickness of the polycrystalline silicon layer is 40 μm.

[0010] The beneficial effects of this invention are as follows: By using laser micromachining technology to form a polycrystalline silicon layer in a silicon substrate, this invention reduces the stress impact on the piezoelectric film of the filter caused by drastic temperature changes, thereby improving the performance stability of the filter under temperature variations; at the same time, the cost is not significantly increased, and it has good application prospects. Attached Figure Description

[0011] Figure 1 This is a side view of the structure of the medium-high temperature stability thin-film bulk acoustic filter of this utility model;

[0012] Figure 2 Photograph of the polycrystalline silicon layer in this utility model;

[0013] Figure 3 This is a schematic diagram showing the position of the polycrystalline silicon layer in this invention;

[0014] Figure 4 This is a side view of a preferred embodiment of the present invention;

[0015] Figure 5 This is a side view of another preferred embodiment of the present invention. Detailed Implementation

[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0017] This invention proposes a high-temperature-stability thin-film bulk acoustic wave filter, such as... Figure 1 As shown, the filter includes a silicon substrate, a lower electrode layer, a first upper electrode layer, and a second upper electrode layer stacked together, with the right sides of the first and second upper electrode layers folded to contact the silicon substrate; a groove is provided on the silicon substrate, and the lower electrode layer is covered on the groove to form a cavity; a polycrystalline silicon layer is formed in the silicon substrate using laser micromachining technology.

[0018] Because the resonant structure cavity membrane stress of the thin-film bulk acoustic wave filter is affected by temperature, and the temperature is conducted from the silicon substrate material (traditional packaging) and silicon cover plate (wafer-level packaging), rapid temperature changes cause stress accumulation in the piezoelectric film, reducing reliability.

[0019] To address this problem, this invention utilizes laser micromachining technology to modify the internal structure of the silicon substrate, forming a polycrystalline silicon layer. Preferably, since the polycrystalline silicon layer has a loose structure, to ensure the mechanical strength of the entire chip, the polycrystalline silicon layer of this invention is located in other areas of the silicon substrate not covered by grooves.

[0020] The polycrystalline silicon layer contains polycrystalline silicon and voids, and its low thermal conductivity is utilized to create a temperature buffer layer. Specifically: such as... Figure 2 As shown, a silicon modification layer is formed inside a silicon substrate using a nanosecond or higher laser. This layer includes a void portion and a polycrystalline silicon material portion (the silicon is modified into polycrystalline silicon by the laser). Preferably, the thickness of the single layer of the modification layer is 40 μm.

[0021] Compared to silicon's thermal conductivity of 150 W / (m*K), polycrystalline silicon has a thermal conductivity of only 20~50 W / (m*K). This significantly extends the time it takes for heat to be conducted to the working area (near the piezoelectric layer), greatly reducing the thermal impact of temperature changes on the device under repeated temperature variations.

[0022] This invention utilizes laser micromachining technology to conveniently fabricate polycrystalline silicon layers, allowing for adjustment of the polycrystalline silicon layer's position according to the device's structure. Figure 3 As shown.

[0023] like Figure 4 As shown, in some preferred embodiments of this utility model, the number of polycrystalline silicon layers is at least two; that is, by controlling the depth of laser micromachining, multiple polycrystalline silicon layers can be formed to achieve a better temperature buffering effect.

[0024] like Figure 5 As shown, if a high-temperature-stability thin-film bulk acoustic wave filter is packaged at the wafer level, the polysilicon layer is located in both the silicon substrate and the package cover as a temperature buffer layer for the filter. The wafer-level packaged thin-film bulk acoustic wave filter incorporates temperature isolation layers in both the cover layer and the functional wafer layer, improving the device's reliability against temperature shocks. These temperature isolation layers can be positioned horizontally or vertically to block heat from below and the sides.

[0025] In summary, this invention utilizes laser micromachining technology to form a polycrystalline silicon layer in a silicon substrate as a temperature buffer layer. When the temperature changes drastically, the temperature buffer layer can significantly reduce the rate of temperature conduction, decrease stress accumulation in the piezoelectric film, and improve the reliability of the device, thus demonstrating promising application prospects.

[0026] The above-described embodiments further illustrate the purpose, technical solution, and advantages of this utility model. It should be understood that the above-described embodiments are merely preferred embodiments of this utility model and are not intended to limit this utility model. Any modifications, equivalent substitutions, improvements, etc., made to this utility model within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A high-temperature-stability thin-film bulk acoustic wave filter, characterized in that, The device includes a silicon substrate, a lower electrode layer, a first upper electrode layer, and a second upper electrode layer stacked together, with the right sides of the first and second upper electrode layers folded to contact the silicon substrate; a groove is provided on the silicon substrate, and the lower electrode layer is disposed on the groove to form a cavity; a polycrystalline silicon layer is formed in the silicon substrate using laser micromachining technology.

2. The high-temperature stability thin-film bulk acoustic wave filter according to claim 1, characterized in that, The polycrystalline silicon layer is located in other areas of the silicon substrate that are not covered by the groove.

3. A high-temperature-stability thin-film bulk acoustic wave filter according to claim 2, characterized in that, The number of polycrystalline silicon layers is at least 2.

4. A high-temperature stability thin-film bulk acoustic wave filter according to claim 2, characterized in that, The polysilicon layer is arranged horizontally and / or vertically.

5. A high-temperature-stability thin-film bulk acoustic wave filter according to claim 1, characterized in that, If a high-temperature-stability thin-film bulk acoustic wave filter is packaged at the wafer level, the polysilicon layer is located in both the silicon substrate and the package cover.

6. A high-temperature-stability thin-film bulk acoustic wave filter according to any one of claims 1 to 5, characterized in that, The thickness of the polycrystalline silicon layer is 40 μm.

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