A novel surface acoustic wave filter structure and its manufacturing method

Abstract

An embodiment of the present invention discloses a surface acoustic wave filter structure and a preparation method thereof, including: a stepped interdigital finger and reflection grating structure of the surface acoustic wave filter; a process method for preparing the structure by using a two-photon polymerization process: both the first mask plate and the second mask plate include a plurality of interdigital electrodes and reflection gratings in a hollowed-out type; placing the first mask plate on the surface of the piezoelectric crystal for alignment and coating to obtain initial interdigital electrodes and reflection gratings; aligning the second mask plate with the first mask plate according to a preset stepped electrode deviation size and then performing secondary coating to obtain a plurality of stepped interdigital electrodes and reflection gratings with a preset period. The process flow and cost of designing the surface acoustic wave filter are saved.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technical field of surface acoustic wave filters, and in particular to a structure and a preparation method of a surface acoustic wave filter. Background Art

[0002] Filters have important application values in the field of signal filtering such as radio frequency communication and satellite communication. Traditional LC or ceramic notch filters have disadvantages such as large volume, heavy weight, and being easily affected by external interference, which limit their application scope. Therefore, integrated and small on-chip notch filters have important application values in miniaturized radio frequency devices and aerospace equipment, especially their advantages of small volume and light weight. The current process still focuses on traditional semiconductor processes such as lithography, etching, and coating. When manufacturing filters at multiple adjacent frequency points, multiple filters need to be manufactured separately. After manufacturing, if you want to adjust the operating frequency of such devices, you need to re-design and repeat the original manufacturing process. Therefore, it is very difficult to change the operating frequency points of existing devices using the process to obtain the target frequency devices required. Summary of the Invention

[0003] To solve the above technical problems, one technical solution adopted in the embodiments of the present invention is:

[0004] A surface acoustic wave filter structure, on the chip of the surface acoustic wave filter, there are a plurality of interdigital electrodes and reflection gratings arranged periodically. Among them, each interdigital electrode and reflection grating includes stepped multiple layers in the thickness direction, and there is a deviation between each layer according to a preset size.

[0005] Further, each interdigital electrode and reflection grating includes stepped two layers in the thickness direction.

[0006] A preparation method of a surface acoustic wave filter includes the following steps:

[0007] Using two-photon polymerization technology to prepare a substrate interdigital structure and an overlaid interdigital structure on a substrate respectively to obtain a first mask plate and a second mask plate. Among them, both the first mask plate and the second mask plate include a plurality of interdigital electrodes and reflection gratings in a hollowed-out shape;

[0008] Align the first mask plate with the chip of the surface acoustic wave filter to be processed, and place the first mask plate on the piezoelectric substrate on the surface of the chip to coat a film to obtain interdigital electrodes and reflection gratings;

[0009] Align the second mask with the chip of the surface acoustic wave filter to be processed according to a preset deviation dimension, and place the second mask on the surface of the coated chip to perform secondary coating on the interdigital electrodes and reflection gratings obtained by coating, so as to obtain interdigital electrodes and reflection gratings with a plurality of stepped layers in the thickness direction and arranged periodically.

[0010] Further, it includes:

[0011] Paste photoresist on the surface of the substrate according to a preset arrangement period;

[0012] Use laser to irradiate the photoresist so that the laser and the photoresist produce two-photon polymerization effect to generate a microspot to cure the photoresist, and the obtained microcavity structure is the interdigital electrode;

[0013] Strip the cured hollow substrate with acetone to obtain a first mask and a second mask, wherein the thicknesses of the first mask and the second mask are 10 - 200 um.

[0014] Further, paste multiple pieces of photoresist with preset sizes on the surface of the substrate according to a preset arrangement period, fix the substrate on the carrier wafer through a substrate fixing frame, and use the laser to irradiate the photoresist through the carrier wafer to generate a light spot, so that the light spot cures the photoresist to obtain a plurality of hollow periodic interdigital electrode and reflection grating structures.

[0015] Further, the coating thickness of the first mask is 100 - 200 nm, and the thickness of the second mask for overlay coating is 10 - 200 nm.

[0016] Further, it includes: the widths and slit widths of the plurality of periodically arranged hollow interdigital electrodes in the first mask and the second mask are 0.1 - 10 um.

[0017] Further, the reflection gratings are at least 50 pairs.

[0018] Further, the coated substrate is one of lithium niobate, lithium carbonate, aluminum nitride, zinc oxide, etc.

[0019] Further, the thickness of the piezoelectric substrate is 30 - 500 um, and the thickness of the carrier wafer is 100 - 170 um.

[0020] An embodiment of the present invention provides a novel surface acoustic wave filter structure. There are steps in the thickness direction of the stepped interdigital electrode and the stepped reflection grating. With such a structure, it is convenient to change the arrangement period of the interdigital electrode and the reflection grating, thereby changing the operating frequency of the surface acoustic wave filter device. Through this preparation method, on the basis of the existing chip structure, the interdigital electrode and the reflection grating can be prepared by coating after slight misalignment of the first mask plate and the second mask plate including multiple interdigital electrodes and reflection gratings. This method changes the operating frequency of the surface acoustic wave filter device by changing the arrangement period of the interdigital electrode and the reflection grating, saving the process flow and cost of designing the surface acoustic wave filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 , FIGS. 2 and 3 are the structural diagrams of the surface acoustic wave filter with a stepped structure provided by the embodiments of the present invention, and the enlarged structural diagrams of the interdigital electrode and the reflection grating.

[0023] Figure 4 and Figure 5 FIGS. are the schematic structural diagrams of the first mask plate and the second mask plate provided by the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention.

[0025] As Figure 1 , 2 and FIG. 3 show the structural diagram of a surface acoustic wave filter, and the enlarged structural diagrams of the interdigital electrode and the reflection grating. On the chip of the surface acoustic wave filter, there are multiple periodically arranged interdigital electrodes and reflection gratings. Among them, each interdigital electrode and reflection grating includes stepped multiple layers in the thickness direction, and there is a deviation between each layer according to a preset size.

[0026] Specifically, each interdigital electrode and reflection grating includes two stepped layers in the thickness direction.

[0027] Specifically, the number of pairs of interdigital electrodes N1 and N2 is at least 50 pairs, and the number of reflection gratings is at least 50 pairs. Preferably, the width and slit width of the interdigital electrode are 0.5 - 1.5 μm, the number of reflection gratings is at least 75 pairs, the aperture length is 150 - 200 μm, and preferably 167.6 μm.

[0028] In one embodiment of the present invention, for a 1.2 GHz SAW filter on a 42-degree cut lithium tantalate substrate, the finger electrodes and slit widths of the first mask and the second mask, as well as the widths of the reflection gratings and the slit widths, are taken as 0.838 μm, N1 and N2 are taken as 50 pairs, the number of pairs of the left and right reflection gratings are each taken as 75 pairs, and the aperture length is 167.6 μm. The finger electrodes and the slit widths can be misaligned to 0.848 μm, and the frequency of the filter on the 42-degree cut lithium tantalate substrate is 1.186 GHz, and the minimum frequency shift that can be changed by misalignment is 0.014 GHz. Since the operating frequency of the SAW filter is related to the finger electrode period and the reflection grating period, the operating frequency of the SAW filter can be effectively changed by changing the finger electrode period and the reflection grating period.

[0029] An embodiment of the present invention proposes a novel surface acoustic wave filter structure, in which there are steps in the thickness direction of the stepped interdigitated electrodes and the stepped reflection gratings. With such a structure, it is convenient to change the arrangement period of the finger electrodes and the reflection gratings, thereby changing the operating frequency of the surface acoustic wave filter device.

[0030] A method for manufacturing a surface acoustic wave filter provided by an embodiment of the present invention includes the following steps:

[0031] Step 1: Use two-photon polymerization technology to prepare a substrate interdigitated structure and an overlaid interdigitated structure on a substrate respectively to obtain a first mask and a second mask. Among them, both the first mask and the second mask include a plurality of finger electrodes and reflection gratings in a hollowed-out shape;

[0032] In the embodiment of the present invention, when preparing the first mask and the second mask, the following steps can be followed:

[0033] Paste a photoresist on the surface of the substrate according to a preset arrangement period;

[0034] Use a laser to irradiate the photoresist so that the laser and the photoresist produce a two-photon polymerization effect to generate a small spot to cure the photoresist, and the obtained microcavity structure is the finger electrode;

[0035] Strip the cured hollowed-out substrate with acetone to obtain the first mask and the second mask.

[0036] Among them, when preparing the first mask and the second mask, a plurality of photoresists with a preset size are pasted on the surface of the substrate according to a preset arrangement period, the substrate is fixed on a carrier wafer through a substrate fixing frame, and the laser is used to irradiate the photoresist through the carrier wafer to generate a spot, so that the spot cures the photoresist to obtain a plurality of the finger electrodes.

[0037] Such as Figure 4 and 5The figure shows the schematic diagrams of the prepared first mask and second mask. During the preparation process, the widths and slit widths of the multiple interdigital electrodes in the hollow type of the first mask and the second mask are 0.4 - 2 μm, the number of pairs of interdigital electrodes N1 and N2 is at least 50 pairs, and the number of reflection gratings is at least 50 pairs. Preferably, the widths and slit widths of the interdigital electrodes are 0.5 - 1.5 μm, the number of reflection gratings is at least 75 pairs, the aperture length is 150 - 200 μm, and preferably it is 167.6 μm. The thicknesses of the first mask and the second mask are 10 μm - 200 μm. Among them, the sizes of the interdigital electrodes and reflection gratings in the first mask and the second mask can be equal or have slight differences.

[0038] Step 2: Align the first mask with the chip of the surface acoustic wave filter to be processed, and place the first mask on the piezoelectric substrate on the surface of the chip to deposit a film to obtain interdigital electrodes and reflection gratings;

[0039] Step 3: Align the second mask with the chip of the surface acoustic wave filter to be processed according to a preset deviation size, and place the second mask on the surface of the chip that has been coated with a film to perform secondary coating on the interdigital electrodes and reflection gratings that have been coated with a film, so as to obtain interdigital electrodes and reflection gratings with a plurality of stepped layers arranged periodically in the thickness direction.

[0040] Specifically, the piezoelectric substrate is at least one of lithium niobate, lithium carbonate, or aluminum nitride. As Figure 2 and 3 shown, it is a schematic three-dimensional structure diagram of the stepped interdigital electrodes and reflection gratings. Since the first mask and the second mask are slightly misaligned and then secondary coating is performed on the coated chip to form interdigital electrodes and reflection gratings with a stepped thickness. By misaligning the positions of the first mask and the second mask, the arrangement period of the interdigital electrodes and reflection gratings can be changed, thereby adjusting the frequency of the filter. In an embodiment of the present invention, for a 1.2 GHz SAW filter with a 42-degree cut tantalum lithium substrate, the widths and slit widths of the interdigital electrodes and reflection gratings of the first mask and the second mask are taken as 0.838 μm, N1 and N2 are taken as 50 pairs, and the number of pairs of left and right reflection gratings is taken as 75 pairs each, and the aperture length is 167.6 μm. During the alignment process, a three-dimensional micro-nano platform is used to misalign the two masks, and the alignment accuracy can be controlled within an accuracy of 10 nm. Therefore, the widths and slit widths of the interdigital electrodes can be misaligned to 0.848 μm, and the frequency of the filter with a 42-degree cut tantalum lithium substrate achieved is 1.186 GHz, and the minimum frequency shift that can be misaligned and changed is 0.014 GHz. Since the operating frequency of the SAW filter is related to the period of the interdigital electrodes and the period of the reflection gratings, the operating frequency of the SAW filter can be effectively changed by changing the period of the interdigital electrodes and the period of the reflection gratings.

[0041] In the embodiment of the present invention, a hollow interdigital electrode and a reflective grating mask are fabricated by using two-photon polymerization on the structure of an existing surface acoustic wave filter or on the chip structure after the coating is completed. The existing chip structure is aligned with the hollow reflective grating mask, and then the aligned mask is slightly misaligned along the direction perpendicular to the vertical bars of the interdigital electrode and the reflective grating. Then, the existing chip structure is coated through the hollow mask by using magnetron sputtering coating process. This method changes the operating frequency of the surface acoustic wave filter device by changing the arrangement period of the interdigital electrode and the reflective grating, saving the process flow and cost of designing the surface acoustic wave filter.

[0042] The above are only some embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a surface acoustic wave filter, characterized in that, The steps include: Using a two-photon polymerization process, a first hollow mask and a second hollow mask are respectively prepared, wherein the first mask and the second mask each include a plurality of hollow interdigitated electrodes and a reflective grid; Placing the first mask on the surface of the piezoelectric crystal for alignment and coating to obtain initial interdigitated electrodes and reflective gratings; The second mask is aligned with the first mask according to a preset step electrode deviation size and then subjected to secondary coating to obtain periodically arranged interdigitated electrodes and reflective gratings having multiple step layers in the thickness direction; The method further includes: adhering the photoresist to the surface of the stage according to a preset arrangement period; Utilizing laser light incident on a photoresist to cause the laser light and the photoresist to generate a two-photon polymerization effect to produce a tiny light spot to photo-cure the photoresist to obtain a first mask and a second mask having hollow periodic interdigitated electrodes and a reflective grating; The solidified hollow substrate is peeled off with acetone to obtain a first mask and a second mask.

2. The preparation method according to claim 1, characterized in that, include: The thickness of the first mask and the second mask is 10-200 μm.

3. The preparation method according to claim 1, characterized in that Multiple pieces of photoresist of preset size are placed on the surface of the stage according to a preset arrangement period, and laser is incident on the photoresist through the stage to generate a light spot, so that the light spot cures the photoresist to obtain multiple hollow periodic interdigitated electrodes and reflective grating structures.

4. The preparation method according to claim 1, characterized in that, The coating thickness of the first mask is 100-200 nm, and the thickness of the second mask with overlay coating is 10-200 nm.

5. The preparation method according to claim 1, wherein include: The width and slit width of the plurality of periodically arranged hollow interdigitated electrodes of the first mask and the second mask are 0.1-10 μm.

6. The preparation method according to claim 1 or 4, characterized in that, The number of reflectors is at least 50 pairs.

7. The preparation method according to claim 1, characterized in that The substrate of the coating is one of lithium niobate, lithium carbonate, aluminum nitride, zinc oxide and the like.

8. The preparation method according to claim 7, characterized in that, The thickness of the piezoelectric substrate is 30 to 500 μm, and the thickness of the slide is 100 to 170 μm.

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