Filter and preparation method therefor

Abstract

Provided in the present invention are a filter and a preparation method therefor. The method comprises the steps of: S1, preparing an acoustic layer on one side of a piezoelectric wafer; S2, depositing a dielectric layer on the side of the piezoelectric wafer that is close to the acoustic layer; S3, performing a first instance of planarization on the dielectric layer; S4, using a photoresist to affix and protect a low-frequency functional area portion that corresponds to the dielectric layer; S5, performing frequency trimming on a high-frequency functional area portion that corresponds to the dielectric layer; S6, using the photoresist to affix and protect the high-frequency functional area portion that corresponds to the dielectric layer; S7, performing a second instance of planarization on the dielectric layer that corresponds to the low-frequency functional area portion; and S8, cleaning off all the photoresist to obtain a filter. The filter prepared by means of the method can meet thickness requirements for different dielectric layers, so that each frequency band thereof can achieve optimal performance.

Description

Filter and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, 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 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 between the 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 between a certain degree of trade-off, that is, between the two best thickness of the average approach to compromise, to a certain extent, the best performance of the two frequency bands, equivalent to not every frequency band can achieve good performance. SUMMARY

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

[0008] In a first aspect, the present application provides a preparation method of a filter, the filter comprising a low-frequency functional area and a high-frequency functional area, the preparation method comprising 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, first flattening the dielectric layer;

[0012] Step S4, pasting protection on the low-frequency functional area part of the dielectric layer after the first flattening using photoresist;

[0013] Step S5, frequency correction on the high-frequency functional area part of the dielectric layer after the first flattening;

[0014] Step S6, pasting protection on the high-frequency functional area part of the dielectric layer after the frequency correction using photoresist;

[0015] Step S7, second flattening the dielectric layer corresponding to the low-frequency functional area part;

[0016] Step S8, cleaning all photoresists to obtain the filter.

[0017] 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.

[0018] Preferably, in the step S1, 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.

[0019] 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; the thickness of the medium layer is 5-200 nm.

[0020] Preferably, in the step S3, the first flattening is performed by chemical mechanical polishing; the thickness of the medium layer after the first flattening is 70-100 nm.

[0021] Preferably, in the step S5, the frequency trimming is performed by reactive ion etching or plasma etching; the thickness of the part of the medium layer corresponding to the high-frequency functional area after the frequency trimming is 10-30 nm.

[0022] Preferably, in the step S7, the second flattening is performed by chemical mechanical polishing; the thickness of the part of the medium layer corresponding to the low-frequency functional area after the second flattening is 40-60 nm.

[0023] In a second aspect, the present application provides a filter prepared by the method for preparing a filter.

[0024] Compared with the related art, the method for preparing a filter in the present application can meet the thickness requirement of the medium layer in different frequency bands by flattening all the medium layers on the piezoelectric wafer for the first time, trimming the part of the medium layer corresponding to the high-frequency functional area after the first flattening, and flattening the part of the medium layer corresponding to the low-frequency functional area for the second time, so that the thickness requirement of the medium layer in different frequency bands can be met, and thus the filter prepared can have good performance in each frequency band. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort, wherein:

[0026] Fig. 1 is a step flow diagram of a method for preparing a filter according to an embodiment of the present application;

[0027] 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;

[0028] Fig. 3 is a schematic diagram of a material of a filter in a method for manufacturing the filter according to an embodiment of the present application;

[0029] Fig. 4 is a conductance diagram of the same resonator under different thicknesses of the dielectric layer. DETAILED DESCRIPTION

[0030] 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", "have" and "include" or variations such as "comprises", "comprising", "including" and "includes", are intended to be inclusive or open-ended and do not exclude additional, unrecited elements or method steps; the use of terms such as "first", "second" and the like in the description herein is intended to distinguish between similar objects only and is not intended to be an actual description of the order in which the described objects occur.

[0031] 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 mutually exclusive of one another. It is expressly understood that any of the embodiments described herein can be incorporated into any other embodiment.

[0032] It should be noted that the terms "upper", "lower", "left", "right", and the like in the description of the embodiments of the present application are described with reference to the placement state in the drawings, and should not be interpreted as 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.

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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 skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Embodiment one

[0035] The embodiments of the present application provide a method for manufacturing a filter, as shown in Figs. 1 to 3, the filter comprising a low-frequency functional area and a high-frequency functional area, and the method comprising the following steps:

[0036] S1, preparing an acoustic layer on one side of the piezoelectric wafer.

[0037] The piezoelectric wafer is a lithium tantalate wafer or a lithium niobate wafer, and 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.

[0038] The acoustic layer is prepared by photolithography stripping or photolithography etching, and the acoustic layer is an Al layer or a composite layer formed by Ti, Al and AlCu, and 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.

[0039] 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.

[0040] The dielectric layer is a silicon oxide layer, and the dielectric layer is formed by magnetron sputtering or chemical vapor deposition, and the thickness of the dielectric layer is 5-200 nm, and preferably, the dielectric layer is a silicon dioxide layer with a thickness of 150 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.

[0041] S3, first polishing the dielectric layer.

[0042] The first polishing is performed by chemical mechanical grinding, and the thickness of the dielectric layer after the first polishing is 70-100 nm. Of course, according to actual requirements, the thickness of the dielectric layer after the first polishing can also be designed to be less than 70 nm or more than 100 nm.

[0043] S4, pasting and protecting the part of the low-frequency functional area of the dielectric layer after the first polishing by using photoresist.

[0044] S5, frequency correction is performed on the part of the high-frequency functional area of the dielectric layer after the first polishing.

[0045] The frequency correction is performed by reactive ion etching or plasma etching, and the thickness of the part of the high-frequency functional area of the dielectric layer after the frequency correction is 10-30 nm.

[0046] 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 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, and it is difficult to ensure the overall yield. The low-frequency functional area in the embodiment works at 1805MHz-1880MHz, and the high-frequency functional area works at 2110MHz-2200MHz.

[0047] S6, the part of the high-frequency functional area corresponding to the medium layer after the frequency correction is pasted and protected by photoresist.

[0048] S7, the medium layer corresponding to the low-frequency functional area is ground for the second time.

[0049] The second grinding is performed by chemical mechanical grinding; and the thickness of the part of the medium layer corresponding to the low-frequency functional area after the second grinding is 40-60nm. The thickness and roughness of the medium layer on the low-frequency functional area can reach the required uniformity at the piezoelectric wafer level by this grinding.

[0050] S8, all photoresists are cleaned to obtain the filter.

[0051] After the cleaning is completed, the filter can realize different thicknesses on different frequency bands of a single chip.

[0052] In the embodiment, the low-frequency functional area is B3, and the high-frequency functional area is B66.

[0053] Of course, according to actual needs, the preparation method of the filter in the embodiment can also be applied to the 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 and the like.

[0054] Fig. 4 is an admittance diagram of the same resonator under different medium layer thicknesses. Based on the admittance diagram, it can be known that the different thicknesses of the medium layer on different frequency bands in the filter can make the performance best. Therefore, the preparation method of the filter in the embodiment grinds all the medium layers on the piezoelectric wafer for the first time, corrects the part of the high-frequency functional area corresponding to the medium layer after the first grinding, and grinds the medium layer corresponding to the low-frequency functional area for the second time. In this way, the thickness requirements of different medium layers can be realized on the piezoelectric wafer, that is, the thickness requirements of the medium layers on different frequency bands are met, so that each frequency band of the prepared filter can achieve better performance, and better insertion loss is realized. At the same time, the two grinding processes can also ensure that the thickness uniformity of the frequency band with a larger medium layer thickness is better, so that the selectivity of the prepared filter is better.

[0055] Embodiment two

[0056] The embodiment of the present application provides a filter which is prepared by the preparation method of the filter in embodiment one.

[0057] Since the filter in the embodiment is prepared by the preparation method of the filter in embodiment one, the technical effects achieved by the preparation method of the filter in embodiment one can also be achieved, which will not be repeated here.

[0058] It should be noted that the various embodiments described above with reference to the drawings are merely intended to illustrate the present application rather than limit the scope of the present application, and those of ordinary skill in the art should understand that modifications or equivalent replacements made to the present application without departing from the spirit and scope of the present application should be included 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, the filter comprising 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 closest to the acoustic layer, and make the dielectric layer completely cover the acoustic layer; Step S3: Perform the first grinding of the dielectric layer; Step S4: Use photoresist to adhere and protect the low-frequency functional area corresponding to the dielectric layer after the first smoothing. Step S5: Perform frequency correction on the high-frequency functional area corresponding to the dielectric layer after the first grinding. Step S6: Use photoresist to adhere and protect the high-frequency functional area corresponding to the frequency-corrected dielectric layer; Step S7: The dielectric layer corresponding to the low-frequency functional area is ground flat for the second time; Step S8: Clean all photoresist to obtain the filter.

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 first grinding is performed by chemical mechanical polishing; the thickness of the dielectric layer after the first grinding is 70nm-100nm.

6. The method for fabricating the filter as described in claim 1, characterized in that, In step S5, frequency correction is performed using reactive ion etching or plasma etching; the thickness of the portion of the dielectric layer corresponding to the high-frequency functional region after frequency correction is 10nm-30nm.

7. The method for fabricating the filter as described in claim 1, characterized in that, In step S7, the second grinding is performed by chemical mechanical polishing; the thickness of the dielectric layer corresponding to the low-frequency functional region after the second grinding is 40-60 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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