RF MEMS filter and its manufacturing method

Abstract

The present invention proposes an RF MEMS filter comprising: a silicon substrate or piezoelectric substrate; a piezoelectric film deposited on the silicon substrate; metal electrodes deposited on the piezoelectric substrate or piezoelectric film; an insulating layer interposed between the metal electrodes, and a piezoelectric layer deposited on the metal electrodes and the insulating layer, thereby achieving surface acoustic wave (SAW) filtering; and a temperature compensation layer deposited on the piezoelectric layer. The present invention utilizes a dual piezoelectric layer, which can adjust the device's electromechanical coupling performance by combining piezoelectric layer materials and controlling the film's crystal orientation and thickness. Furthermore, compared to conventional single-piezoelectric-layer SAW filters, the lithographic linewidth requirements for achieving the same frequency can be significantly reduced.

Description

Technical Field

[0001] The present invention relates to a wireless communication radio frequency front-end device, in particular to an RF MEMS filter. Background Art

[0002] With the development of wireless communication applications, people's demand for data transmission speeds is increasing. In the field of mobile communications, the first generation was analog technology, the second generation achieved digital voice communication, the third generation (3G) featured multimedia communication, and the fourth generation (4G) increased communication speeds to 1Gbps and reduced latency to 10ms. The fifth generation (5G) is the next generation of mobile communication technology after 4G. Although the technical specifications and standards of 5G are not yet fully defined, its network transmission speed and network capacity will be significantly improved compared to 3G and 4G. If 1G to 4G mainly solved communication between people, 5G will also solve communication between people and things, and between things and things, that is, the Internet of Everything, realizing the vision of "information at your fingertips, everything at your fingertips."

[0003] The rise in data rates is accompanied by increased spectrum utilization and the increasing complexity of communication protocols. Given the limited spectrum, full utilization is essential to meet data rate demands. Furthermore, carrier aggregation has been employed since 4G, enabling a single device to transmit data simultaneously using different carrier spectrums. Furthermore, to support sufficient data rates within limited bandwidth, communication protocols have become increasingly complex, placing stringent demands on various RF system performance requirements.

[0004] RF filters play a crucial role in RF front-end modules. They filter out out-of-band interference and noise to meet the signal-to-noise ratio requirements of RF systems and communication protocols. As communication protocols become increasingly complex, the requirements for both in-band and out-of-band performance are also becoming increasingly stringent, making filter design increasingly challenging. Furthermore, as the number of frequency bands supported by mobile phones continues to increase, the number of filters required in each phone is also increasing.

[0005] Currently, the most mainstream implementation methods for RF filters are surface acoustic wave filters and filters based on thin film bulk acoustic wave resonator technology. Thin film bulk acoustic wave resonators are mainly used for high frequencies (such as frequencies greater than 2.5 GHz), and the manufacturing process is relatively complex and the cost is relatively high. Surface acoustic wave filters, on the other hand, are mainly used for medium and low frequencies (such as frequencies less than 2.5 GHz), and the manufacturing process is relatively simple. Compared with thin film bulk acoustic wave resonators, the cost is much lower, making them more easily accepted by the market.

[0006] In traditional structures and fabrication methods, metal interdigitated structures are primarily fabricated on piezoelectric substrates, such as quartz, lithium niobate, and barium titanate. However, due to the material properties of these substrates, achieving higher frequencies requires increasingly smaller line widths, significantly increasing the complexity of the photolithography process, reducing the yield of the finished product, and limiting the scope of SAW applications. Summary of the Invention

[0007] In order to reduce the high requirements of the existing process technology on the photolithography process and adjust the electromechanical coupling performance of the SAW device, the present invention designs an RF MEMS filter with a double piezoelectric layer.

[0008] Specifically, the technical solutions of the present invention are as follows:

[0009] An RF MEMS filter, comprising:

[0010] a first piezoelectric layer;

[0011] a metal electrode deposited on the first piezoelectric layer;

[0012] a dielectric layer filled between the metal electrodes; and

[0013] A second piezoelectric layer is deposited on the metal electrode and the dielectric layer.

[0014] Preferably, the device further comprises a temperature compensation layer located on the second piezoelectric layer.

[0015] Preferably, the material of the metal electrode is one or a combination of tungsten, silver, zirconium, molybdenum, platinum platinum, ruthenium, iridium, titanium tungsten, copper, titanium, chromium, hafnium, and aluminum.

[0016] Preferably, the dielectric layer filled between the metal electrodes is made of silicon dioxide, silicon nitride or other insulating materials.

[0017] Preferably, the temperature compensation layer is silicon dioxide or a doped silicon dioxide film.

[0018] The present invention also provides a method for preparing an RF MEMS filter, which is characterized by comprising the following steps:

[0019] Depositing a metal electrode layer on the first piezoelectric layer and patterning it;

[0020] Depositing a dielectric filling layer, wherein the dielectric filling layer is filled between the patterned metal electrodes;

[0021] A second piezoelectric layer is deposited and patterned.

[0022] Preferably, the method further comprises the following steps:

[0023] The dielectric filling layer is polished flat by a chemical mechanical polishing (CMP) process so as to have the same height as the metal electrode.

[0024] Preferably, the method further comprises the following steps:

[0025] A temperature compensation layer is deposited on the second piezoelectric layer and patterned.

[0026] Preferably, the first piezoelectric layer is a piezoelectric substrate or a piezoelectric film deposited on other substrate materials.

[0027] Preferably, the material of the first piezoelectric layer and / or the second piezoelectric layer is one or a combination of lithium niobate, lithium tantalate, aluminum nitride, lead zirconate titanate, and zinc oxide.

[0028] The beneficial technical effects of the present invention are: using a dual piezoelectric layer structure to adjust the electromechanical coupling capability of the SAW device, reducing the process difficulty of photolithography, and increasing the frequency of the device under the same photolithography process capability conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 2 is a schematic structural diagram of a silicon substrate structure RF MEMS filter according to an embodiment of the present invention;

[0030] Figure 2 2 is a schematic structural diagram of an RF MEMS filter having a piezoelectric substrate structure according to an embodiment of the present invention;

[0031] Figure 3 This is a performance comparison chart of a dual-layer piezoelectric SAW resonator and a traditional SAW resonator under the same process parameters and size conditions, where: Figure 3 The curve marked with "□" on the left is the admittance curve of a single-layer SAW resonator with lithium niobate as the piezoelectric substrate, and the curve marked with "△" on the right is the admittance curve of a double-layer SAW resonator with a lithium niobate substrate as the first piezoelectric layer and a lithium niobate film as the second piezoelectric layer. The positive resonant frequency and electromechanical coupling coefficient of the two are 1882MHz, 4.62% and 2270MHz, 5.39%, respectively:

[0032] FIG4 is a schematic diagram of a process flow for preparing a silicon substrate structure RF MEMS filter according to the present invention;

[0033] FIG5 is a schematic diagram of the process flow of manufacturing the RF MEMS filter with a piezoelectric substrate structure according to the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] The present invention proposes a novel RF MEMS filter, the specific structure of which is shown in FIG. Figure 1 、 2 It includes: a first piezoelectric layer; metal electrodes deposited on the first piezoelectric layer; a dielectric layer filled between the metal electrodes; and a second piezoelectric layer deposited on the metal electrodes and the dielectric layer.

[0037] The first piezoelectric layer comprises a piezoelectric film 200 deposited on a silicon substrate 100, or directly using a piezoelectric substrate 101; a metal electrode 300 deposited on the piezoelectric substrate 100 or the piezoelectric film 200; a dielectric layer 400 filling the gap between the metal electrodes 300; a second piezoelectric film 500 deposited on the metal electrodes and the dielectric layer; and a temperature compensation layer 600 deposited on the second piezoelectric film. The RF MEMS in this invention stands for radio frequency micromechanical system, and SAW stands for surface acoustic wave resonator and its derivative devices.

[0038] In the present invention, the electromechanical coupling capability of the SAW device is adjusted by using the combination of two layers of piezoelectric layer materials, thereby increasing the frequency of the device under the same lithography line width conditions and reducing the difficulty of the lithography process. Figure 2 As shown, the present invention uses lithium niobate as the material of the piezoelectric layer as an example to compare the admittance curves of lithium niobate single piezoelectric layer and double piezoelectric layer SAW resonators. From the comparison results, it can be seen that the positive resonant frequency and electromechanical coupling coefficient of the double piezoelectric layer are both higher than those of the single piezoelectric layer, which are 2270MHz, 5.39% and 1882MHz, 4.62%, respectively.

[0039] Furthermore, the present invention does not impose strict restrictions on the materials of the two layers of piezoelectric material, and commonly used piezoelectric materials can be selected and matched, as long as they are conducive to improving the electromechanical coupling capability and device frequency of the SAW device.

[0040] Example 2

[0041] 4 , the silicon substrate structure RF MEMS filter of Example 1 of the present invention can be manufactured by the following process steps:

[0042] A piezoelectric film 200 of a certain thickness, i.e., a first piezoelectric layer, is deposited on the surface of the prepared silicon wafer 100. The first piezoelectric layer is, for example, one of lithium niobate, lithium tantalate, aluminum nitride, lead zirconate titanate, zinc oxide, or a combination thereof, as shown in FIG4(a).

[0043] A metal electrode layer 300 is deposited on the piezoelectric film 200 and patterned. The patterning may be performed by dry etching or a lift-off process, as shown in FIG4( b ).

[0044] A dielectric filling layer 400, such as silicon dioxide, silicon nitride, etc., is deposited until the metal electrode layer 300 is completely covered, as shown in FIG4(c).

[0045] The dielectric layer is polished flat by a chemical mechanical polishing (CMP) process so that the dielectric layer and the metal electrode have the same height, as shown in FIG4( d ).

[0046] Then, a second piezoelectric layer film 500 is deposited on the surface and patterned, wherein the second piezoelectric layer is, for example, lithium niobate, lithium tantalate, aluminum nitride, lead zirconate titanate, zinc oxide, or a combination thereof, as shown in FIG4(e).

[0047] A temperature compensation layer 600 is deposited and formed into a desired pattern by photolithography, wherein the temperature compensation layer is, for example, silicon dioxide or a doped thin film thereof, as shown in FIG4(f).

[0048] Example 3

[0049] Regarding the method of directly selecting a piezoelectric substrate to manufacture the RF MEMS filter of the present invention, the specific preparation process is shown in FIG. Figure 5(a)-5(e) As shown, the difference from Example 2 is that there is no need to select another substrate and then deposit the first piezoelectric layer. Other identical steps are not repeated here.

[0050] Compared with the existing technology, the present invention uses a dual piezoelectric layer structure and utilizes the combination of two layers of piezoelectric layer materials to adjust the electromechanical coupling capability of the SAW device, thereby increasing the frequency of the device under the same lithography line width conditions and reducing the process difficulty of lithography.

[0051] Although the specific embodiments of the present invention have been described in detail with respect to the technical solutions of the invention, the present invention is not limited thereto, and those skilled in the art may make various modifications based on the principles of the present invention. Therefore, any modifications made based on the principles of the present invention should be understood to fall within the scope of protection of the present invention.

Claims

1. An RF MEMS SAW filter, characterized in that: include: a first piezoelectric layer; Metal electrodes are provided on the first piezoelectric layer, wherein the metal electrodes are patterned to be spaced apart; a dielectric layer filled between the metal electrodes, the dielectric layer having the same height as the metal electrodes; and a second piezoelectric layer disposed on the metal electrode and the dielectric layer; A temperature compensation layer is also included on the second piezoelectric layer.

2. The RF MEMS SAW filter according to claim 1, wherein: The material of the metal electrode is one or a combination of tungsten, silver, zirconium, molybdenum, platinum, ruthenium, iridium, titanium tungsten, copper, titanium, chromium, hafnium, and aluminum.

3. The RF MEMS SAW filter according to claim 1, wherein: The dielectric layer filled between the metal electrodes is made of silicon dioxide or silicon nitride.

4. The RF MEMS SAW filter according to claim 1, wherein: The temperature compensation layer is silicon dioxide or a doped silicon dioxide film.

5. A method for preparing the RF MEMS SAW filter according to claim 1, characterized in that: The following steps are involved: Depositing a metal electrode layer on the first piezoelectric layer and patterning it; Depositing a dielectric filling layer, wherein the dielectric filling layer is filled between the patterned metal electrodes; A second piezoelectric layer is deposited and patterned.

6. The method for preparing the RF MEMS SAW filter according to claim 5, wherein: The following steps are also included: The dielectric filling layer is ground flat by a chemical mechanical polishing process so as to have the same height as the metal electrode.

7. The method for preparing the RF MEMS SAW filter according to claim 5, wherein: The following steps are also included: A temperature compensation layer is deposited on the second piezoelectric layer and patterned.

8. The method for preparing the RF MEMS SAW filter according to claim 5, wherein: The first piezoelectric layer is a piezoelectric substrate or a piezoelectric film deposited on a substrate material.

9. The method for preparing the RF MEMS SAW filter according to claim 5, wherein: The material of the first piezoelectric layer and / or the second piezoelectric layer is one of lithium niobate, lithium tantalate, aluminum nitride, lead zirconate titanate, and zinc oxide, or a combination thereof.

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