Filter and fabrication method therefor

Abstract

The present invention provides a filter and a fabrication method therefor, the method comprising the steps of: S1, fabricating an acoustic layer on one side of a piezoelectric wafer; S2, depositing and forming a dielectric layer on the side of the piezoelectric wafer close to the acoustic layer; S3, planarizing the dielectric layer; S4, using photoresist to perform first protective bonding on the planarized dielectric layer corresponding to a low-frequency functional area or a high-frequency functional area; S5, performing first frequency trimming on the dielectric layer corresponding to the functional area in which first protective bonding is not performed; S6, using photoresist to perform second protective bonding on the dielectric layer corresponding to the functional area in which first frequency trimming was performed; and S7, performing second frequency trimming on the dielectric layer corresponding to the functional area in which second protective bonding is not performed. The resulting filter fabricated by means of the described method can meet the thickness requirements of different dielectric layers, thereby allowing each frequency band thereof to achieve better performance.

Description

A filter and a preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of communication, and in particular to a filter and a preparation method thereof. BACKGROUND

[0002] With the development of the fifth generation of wireless communication technology, intelligent devices (mobile phones, tablets, etc.) need to increase filters to support the increasing number of frequency bands, and the dense frequency bands will make the interference problem between uplinks in the system prominent. In order to ensure high-quality data communication between frequency spectrums, high-end intelligent devices need to be equipped with at least 50 radio frequency front-end filters.

[0003] With the continuous upgrading of communication technology (5G devices) and the deployment of new technologies such as carrier aggregation (CA), multiple-input multiple-output (MIMO), etc., the communication frequency bands are increasing, and this number will show a continuous and fierce growth trend. At the same time, the deployment of various new technologies also puts forward new challenges to the performance of the filter. This requires the performance of the filter to meet the requirements of low insertion loss, large bandwidth, high rectangularity, high isolation, etc.

[0004] The common surface acoustic wave filter has lithium niobate and lithium tantalate, wherein the piezoelectric coupling coefficient of lithium tantalate is relatively small compared with that of lithium niobate, and it is difficult to meet the bandwidth requirement when making a large bandwidth device, and the piezoelectric coupling coefficient of lithium niobate is high, but its temperature drift coefficient is too large, which cannot guarantee good insertion loss and suppression degree performance in the whole working temperature range. The appearance of temperature compensation filter (TCSAW) can well make up for the performance deterioration caused by the too large temperature drift coefficient. A layer of copper electrode is plated on the wafer surface as an interdigital material, and a silicon oxide layer is covered on the surface of the electrode as a temperature compensation layer, so that the temperature drift coefficient of the surface acoustic wave filter based on lithium niobate substrate is reduced from 70ppm / K to 15ppm / K, which greatly improves the electrical performance and selectivity of the filter.

[0005] In the related art, the production and processing of the temperature compensation filter usually adopts the method of magnetic control sputtering (sputtering), that is, the whole wafer is covered, and after the whole grinding process, etching is performed to correct the frequency. The advantage of this method is that the process repeatability is good, the cost is low, and for the traditional diplexer, because the transmission frequency band and the reception frequency band are close, the bandwidth and temperature coefficient requirements can be met.

[0006] But with the development of technology, there has been a need to integrate different frequency bands into a single chip, for the frequency difference of multiplexer, due to the different frequency bands required by the relative bandwidth is inconsistent, the same thickness of silicon oxide, theoretically only to meet a single frequency band of the best performance, or in a certain extent between the frequency bands of the trade-off, that is, between the two best thickness of the average approach to compromise, to a certain extent, the best performance of two frequency bands, equivalent to unable to achieve each frequency band can achieve better performance. SUMMARY

[0007] In view of the above problems of the prior art, the present application provides a filter preparation method to solve the problem that the filter preparation method in the prior art cannot achieve better performance for each frequency band.

[0008] In a first aspect, the present application provides a filter preparation method, the functional area of the filter includes a low-frequency functional area and a high-frequency functional area, and the preparation method comprises the following steps:

[0009] Step S1, preparing an acoustic layer on one side of a piezoelectric wafer;

[0010] Step S2, depositing a dielectric layer on the side of the piezoelectric wafer close to the acoustic layer, and making the dielectric layer completely cover the acoustic layer;

[0011] Step S3, polishing the dielectric layer;

[0012] Step S4, using photoresist to perform first paste protection on the polished dielectric layer corresponding to the low-frequency functional area or the high-frequency functional area;

[0013] Step S5, performing first frequency correction on the dielectric layer corresponding to the functional area which has not been subjected to first paste protection;

[0014] Step S6, using photoresist to perform second paste protection on the dielectric layer corresponding to the functional area after the first frequency correction;

[0015] Step S7, performing second frequency correction on the dielectric layer corresponding to the functional area which has not been subjected to second paste protection.

[0016] Preferably, in step S1, the piezoelectric wafer is a lithium tantalate wafer or a lithium niobate wafer; the thickness of the piezoelectric wafer is 200-500 μm.

[0017] Preferably, in step S1, the acoustic layer is prepared by photolithography stripping or photolithography etching; the acoustic layer is an Al layer or a composite layer composed of Ti, Al and AlCu; the thickness of the acoustic layer is 0.1-2 μm.

[0018] Preferably, in the step S2, the medium layer is a silicon oxide layer; the medium layer is formed by magnetron sputtering or chemical vapor deposition; and the thickness of the medium layer is 5-200 nm.

[0019] Preferably, in the step S3, the flattening is performed by chemical mechanical polishing; and the thickness of the medium layer after the flattening is 60-100 nm.

[0020] Preferably, in the step S5, the first frequency trimming is performed by reactive ion etching or plasma etching; and the thickness of the medium layer corresponding to the functional area after the first frequency trimming is 10-50 nm.

[0021] Preferably, in the step S7, the second frequency trimming is performed by reactive ion etching or plasma etching; and the thickness of the medium layer corresponding to the functional area after the second frequency trimming is 20-60 nm.

[0022] In a second aspect, the present application provides a filter prepared by the method for preparing a filter.

[0023] Compared with the related art, the method for preparing a filter in the present application can achieve the thickness requirement of different medium layers on the piezoelectric wafer by flattening all the medium layers on the piezoelectric wafer and trimming the medium layers on the low-frequency functional area and the high-frequency functional area once respectively, so as to meet the thickness requirement of the medium layers on different frequency bands, thereby making each frequency band of the prepared filter achieve better performance. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on these drawings.

[0025] Fig. 1 is a step flow diagram of a method for preparing a filter according to an embodiment of the present application;

[0026] Fig. 2 is a process flow diagram of steps S2-S7 in a method for preparing a filter according to an embodiment of the present application;

[0027] Fig. 3 is a schematic diagram of the material of a filter in a method for preparing a filter according to an embodiment of the present application;

[0028] Fig. 4 is an admittance diagram of the same resonator under different medium layer thicknesses. DETAILED DESCRIPTION

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application; the use herein of terms such as "comprise", "comprising", "comprises", "including", "includes" or "contain" or "containing" is to be construed in a non-exclusive sense as meaning "comprise, when used in the description herein, the terms "first", "second", and the like, are used to distinguish one element from another, and are not necessarily used in a descriptive sense.

[0030] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a common set of embodiments.

[0031] It should be noted that the terms "upper", "lower", "left", "right", etc. mentioned in the embodiments of the present application are described with reference to the placement state in the drawings, and should not be interpreted as the limiting embodiments of the present application. In addition, it should also be understood that in the text, when referring to an element "above" or "below" another element, it is possible that the element is directly "above" or "below" the other element, or it is possible that the element is "above" or "below" the other element through an intermediate element.

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0033] Embodiment one

[0034] The embodiment of the present application provides a preparation method of a filter, in combination with FIG. 1 to FIG. 3, a functional area of the filter includes a low-frequency functional area and a high-frequency functional area, and the preparation method includes the following steps:

[0035] S1, an acoustic layer is prepared on one side of a piezoelectric wafer.

[0036] The piezoelectric wafer is a lithium tantalate wafer or a lithium niobate wafer; the thickness of the piezoelectric wafer is 200-500 μm. Of course, according to actual requirements, other types of wafers can also be selected, and the thickness of the piezoelectric wafer can also be designed to be less than 200 μm or more than 500 μm.

[0037] The acoustic layer is prepared by photolithography stripping or photolithography etching; the acoustic layer is an Al layer or a composite layer formed by Ti, Al and AlCu; the thickness of the acoustic layer is 0.1-2 μm. Of course, according to actual requirements, the acoustic layer can also be prepared by other methods, and the acoustic layer can also be formed by using other metal materials or a plurality of material composites, and the thickness of the acoustic layer can also be designed to be less than 0.1 μm or more than 2 μm.

[0038] S2, a dielectric layer is deposited on the side of the piezoelectric wafer close to the acoustic layer, and the dielectric layer completely covers the acoustic layer.

[0039] The dielectric layer is a silicon oxide layer; the dielectric layer is formed by magnetron sputtering or chemical vapor deposition; the thickness of the dielectric layer is 5-200 nm, preferably, the dielectric layer is a silicon dioxide layer, and the thickness is 100 nm. Of course, according to actual requirements, the dielectric layer can also be deposited by other methods, and the thickness thereof can also be designed to be less than 5 nm or more than 200 nm.

[0040] S3, the dielectric layer is ground flat.

[0041] The grinding flat is performed by chemical mechanical grinding; the thickness of the dielectric layer after grinding flat is 60-100 nm. Of course, according to actual requirements, the thickness of the dielectric layer after grinding flat can also be designed to be less than 60 nm or more than 100 nm.

[0042] S4, the dielectric layer corresponding to the low-frequency functional area or the high-frequency functional area after grinding flat is protected by first pasting with a photoresist.

[0043] S5, the dielectric layer corresponding to the functional area which is not protected by first pasting is first frequency-modified.

[0044] The first frequency modification is performed by reactive ion etching or plasma etching; the thickness of the dielectric layer corresponding to the functional area after the first frequency modification is 10-50 nm.

[0045] The frequency correction refers to adjusting the thickness of the medium layer above the filter to control the quality load of the filter, so as to correct the center frequency of the filter. The steps of the related technology can only realize the frequency correction of the low-frequency functional area and the high-frequency functional area at the same time, so that in most cases, only the frequency of one frequency band of the low-frequency functional area and the high-frequency functional area can be centered or the bandwidth is optimal, and it is difficult to ensure the overall yield. The low-frequency functional area in the embodiment is working at 1805MHz-1880MHz, and the high-frequency functional area is working at 2110MHz-2200MHz.

[0046] S6, the medium layer corresponding to the functional area after the first frequency correction is secondarily pasted and protected by photoresist.

[0047] S7, the medium layer corresponding to the functional area which has not been secondarily pasted and protected is secondarily frequency corrected.

[0048] The second frequency correction is performed by reactive ion etching or plasma etching, and the thickness of the medium layer corresponding to the functional area after the second frequency correction is 20-60nm.

[0049] In addition, after the second frequency correction, the photoresist can be cleaned by the cleaning step.

[0050] In step S4 of the embodiment, if the ground medium layer corresponding to the low-frequency functional area is first pasted and protected, then in step S5, the medium layer corresponding to the high-frequency functional area is first frequency corrected, and in step S6, the medium layer corresponding to the high-frequency functional area is secondarily pasted and protected by photoresist, and in step S7, the medium layer corresponding to the low-frequency functional area is secondarily frequency corrected. In step S4, if the ground medium layer corresponding to the high-frequency functional area is first pasted and protected, then in step S5, the medium layer corresponding to the low-frequency functional area is first frequency corrected, and in step S6, the medium layer corresponding to the low-frequency functional area is secondarily pasted and protected by photoresist, and in step S7, the medium layer corresponding to the high-frequency functional area is secondarily frequency corrected.

[0051] In the embodiment, the low-frequency functional area is B3, and the high-frequency functional area is B66.

[0052] Of course, according to actual needs, the preparation method of the filter in the embodiment can also be applied to the frequency band combination of B8 low-frequency functional area and B26 high-frequency functional area or B40 low-frequency functional area and B41 high-frequency functional area.

[0053] Fig. 4 is a conductance graph of the same resonator under different medium layer thicknesses, based on which it can be known that the medium layer thicknesses in different frequency bands of the filter can be different to make the performance of the filter optimal, and thus the preparation method of the filter in the embodiment is to grind all the medium layers on the piezoelectric wafer, and to tune the medium layers in the low-frequency functional area and the high-frequency functional area respectively once, so that the thickness requirements of different medium layers on the piezoelectric wafer can be realized, i.e. the thickness requirements of the medium layers in different frequency bands are met, so that each frequency band of the prepared filter can achieve better performance, and the insertion loss is more optimal.

[0054] Embodiment two

[0055] The embodiment of the present application provides a filter prepared by the preparation method of the filter in the embodiment one.

[0056] Since the filter in the embodiment is prepared by the preparation method of the filter in the embodiment one, the technical effects achieved by the preparation method of the filter in the embodiment one can also be achieved, and thus no further description is made here.

[0057] It should be noted that the above-described various embodiments with reference to the accompanying drawings are only used to illustrate the present application and not to limit the scope of the present application, and those skilled in the art should understand that the modifications or equivalent replacements of the present application without departing from the spirit and scope of the present application should be covered in the scope of the present application. In addition, unless otherwise indicated by the context, the word in singular form includes the word in plural form, and vice versa. In addition, unless otherwise specified, all or part of any embodiment can be used in combination with all or part of any other embodiment.

Claims

1. A method for fabricating a filter, wherein the filter's functional regions include a low-frequency functional region and a high-frequency functional region, characterized in that, The method for preparing the filter includes the following steps: Step S1: Prepare an acoustic layer on one side of the piezoelectric wafer; Step S2: Deposit a dielectric layer on the side of the piezoelectric wafer near the acoustic layer, and make the dielectric layer completely cover the acoustic layer; Step S3: Grind the dielectric layer flat; Step S4: Apply photoresist to the smoothed dielectric layer corresponding to the low-frequency or high-frequency functional area for the first time for protection; Step S5: Perform the first frequency correction on the dielectric layer corresponding to the functional area that was not initially protected by adhesive. Step S6: Use photoresist to perform a second bonding protection on the dielectric layer corresponding to the functional area after the first frequency correction; Step S7: Perform a second frequency correction on the dielectric layer corresponding to the functional area that has not been protected by the second pasting.

2. The method for fabricating the filter as described in claim 1, characterized in that, In step S1, the piezoelectric wafer is a lithium tantalate wafer or a lithium niobate wafer; the thickness of the piezoelectric wafer is 200μm-500μm.

3. The method for fabricating the filter as described in claim 1, characterized in that, In step S1, the acoustic layer is prepared by photolithographic lift-off or photolithographic etching; the acoustic layer is an Al layer or a composite layer formed by Ti, Al and AlCu; the thickness of the acoustic layer is 0.1μm-2μm.

4. The method for fabricating the filter as described in claim 1, characterized in that, In step S2, the dielectric layer is a silicon oxide layer; the dielectric layer is formed by magnetron sputtering or chemical vapor deposition; the thickness of the dielectric layer is 5nm-200nm.

5. The method for fabricating the filter as described in claim 1, characterized in that, In step S3, the smoothing is performed by chemical mechanical polishing; the thickness of the smoothed dielectric layer is 60nm-100nm.

6. The method for fabricating the filter as described in claim 1, characterized in that, In step S5, the first frequency correction is performed using reactive ion etching or plasma etching; the thickness of the dielectric layer corresponding to the functional area after the first frequency correction is 10nm-50nm.

7. The method for fabricating the filter as described in claim 1, characterized in that, In step S7, the second frequency correction is performed using reactive ion etching or plasma etching; the thickness of the dielectric layer corresponding to the functional area after the second frequency correction is 20-60 nm.

8. A filter, characterized in that, The filter is prepared using the filter preparation method described in any one of claims 1 to 7.

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