WO2019056350A1

WO2019056350A1 - Mems coaxial filter, and manufacturing method

Info

Publication number: WO2019056350A1
Application number: PCT/CN2017/103120
Authority: WO
Inventors: 梅迪; 朱其玉
Original assignee: 上海诺基亚贝尔股份有限公司
Priority date: 2017-09-25
Filing date: 2017-09-25
Publication date: 2019-03-28
Also published as: CN111133628A; CN111133628B

Abstract

The present invention provides a MEMS coaxial filter and manufacturing method. According to one aspect of the present invention, a MEMS coaxial filter is provided, and characterized in that: the MEMS coaxial filter comprises a structural layer wafer having both faces polished, a silicon dielectric cavity using a metal wall or metalized through holes to realize an electric wall, and an internal coaxial structure comprising metalized blind holes. The present invention has the following advantage: MEMS technology, a coaxial resonator structure, and SIW technology are combined by using the MEMS technology to fabricate the coaxial filter on a silicon wafer. Compared with existing metal waveguide filters or SIW filters, the MEMS coaxial filter in embodiments of the present invention significantly reduces the size and cost of millimeter-wave filters, and enables high machining precision, thus improving production time and costs of millimeter-wave filters.

Description

MEMS coaxial filter and manufacturing method

Technical field

The present invention relates to the field of communications technologies, and in particular, to a MEMS coaxial filter and a manufacturing method thereof.

Background technique

Micro Electro Mechanical System (MEMS) is based on semiconductor manufacturing technology and has high processing accuracy, which can fully meet the processing accuracy requirements of millimeter wave filters. However, due to the high cost of MEMS filters, it has hindered its promotion. Since the cost of a wafer is constant, the smaller the filter, the more filters can be produced in one wafer and the lower the cost of the filter. This means that miniaturization is very important for the commercial and practical application of millimeter wave MEMS filters.

The Substrate Integrated Waveguide (SIW) is the most promising millimeter wave filter for many years. But one of its fatal flaws is that the first harmonic is very close to the operating frequency, which is about 1.58 times the operating frequency. And this harmonic can hardly be suppressed. At the same time, the size of the SIW filter is still too large for a wafer, which is contrary to the miniaturization of the MEMS filter.

The existing millimeter wave filters are mainly the following three types:

1) a metal waveguide filter;

Most of the existing millimeter wave filters are metal waveguide filters, which are bulky and heavy. It is estimated that the volume of the metal waveguide filter at 28 Ghz is approximately 280 times larger than that of the SIW filter. In addition, its processing accuracy does not meet the requirements of millimeter wave filters. Therefore, it can basically be said that the metal waveguide filter is far from being the best choice for millimeter wave and MIMO RF systems.

2) SIW filter;

SIW is the most promising millimeter wave filter for many years. It has the advantages of strong power handling capability, easy manufacture, and small size. SIW filters can be fabricated on most mainstream RF planar substrates, such as PCBs and silicon, even on paper. But a fatal disadvantage of the SIW filter is that its first harmonic is very close to the operating frequency, about 1.58 times the operating frequency, and the harmonic It is difficult to be suppressed. Therefore, when the operating frequency can reach millimeter waves, strict processing accuracy becomes a major obstacle to the millimeter wave filter including the SIW filter.

3) Ceramic Filter / Low Temperature Co-Fired Ceramic (LTCC);

Ceramics and LTCC are based on ceramics. It can greatly reduce the size of the filter. However, its volume changes greatly during the sintering process. Ceramic filters can solve this problem by adjusting the size after sintering. Of course, this is a time consuming process and performance is also affected. The Q value and processing accuracy of the LTCC cannot meet the requirements of the millimeter wave filter.

Summary of the invention

It is an object of the present invention to provide a MEMS coaxial filter and a method of fabricating the same.

According to an aspect of the invention, a MEMS coaxial filter is provided, characterized in that the MEMS coaxial filter comprises:

a structural layer wafer polished on both sides;

a silicon dielectric cavity of the electrical wall realized by a metal wall or a metallized through hole;

Internal coaxial structure realized by metallized blind holes.

According to an embodiment of the invention, the MEMS coaxial filter adopts a SIW resonator structure, and a blind hole is etched in the center of the SIW resonator structure, and the structural layer wafer is an SOI sheet.

According to an embodiment of the invention, the structural layer wafer is a high resistance silicon wafer, and the MEMS coaxial filter further includes a carrier sheet, and the high resistance silicon wafer and the carrier sheet are bonded in a wafer level manner. combine together.

According to an embodiment of the invention, the structural layer wafer is an SOI sheet, and the MEMS coaxial filter further comprises a carrier sheet, and the SOI sheet and the carrier sheet are bonded together in a wafer level bonding manner.

According to an embodiment of the present invention, a metal pattern of a dumbbell shape is formed on a front surface of the structural layer wafer, the metal pattern being located between two resonant cavities for generating electrical coupling;

Wherein, under the electrically coupled metal pattern, the back side of the structural layer wafer simultaneously etches holes or trenches in the metallization blind via etching step to suppress magnetic coupling between the two resonant cavities.

Preferably, the resonant frequency of the MEMS coaxial filter according to the present invention is adjusted based on any of the following:

- changing the size of the silicon dielectric cavity;

- Change the diameter of the metallized blind hole.

According to an aspect of the present invention, a method for fabricating a MEMS coaxial filter using a SIW structure is provided, wherein a structural layer wafer of the MEMS coaxial filter is an SOI wafer, the method comprising the following steps :

- performing ICP etching on the back side of the SOI sheet to stop etching on the silicon dioxide layer;

- removing the exposed silicon dioxide layer;

- ICP etching the front side of the SOI sheet;

- Metallization of the SOI sheet on both sides and fabrication of the port structure and the electrical coupling structure.

According to an aspect of the invention, a method for fabricating a MEMS coaxial filter is provided, wherein the structural layer wafer of the MEMS coaxial filter is a high resistance silicon wafer, the method comprising the steps of:

- performing ICP etching on the back side of the high resistance silicon wafer;

- metallizing the back side of the ICP-etched high resistance silicon wafer;

- bonding the metallized high resistance silicon wafer and the carrier sheet in a wafer level bonding manner;

- ICP etching the front side of the high resistance silicon wafer;

- Metallization of the ICP-etched high resistance silicon wafer and fabrication of the port structure and the electrical coupling structure.

According to an aspect of the invention, a method for fabricating a MEMS coaxial filter is provided, wherein a structural layer wafer of the MEMS coaxial filter is an SOI chip, the method comprising the steps of:

- performing ICP etching on the back side of the SOI sheet and stopping etching on the silicon dioxide layer;

- removing the exposed silicon dioxide layer;

- metallizing the back side of the ICP-etched SOI sheet;

- bonding the metallized SOI sheet and the carrier sheet in a wafer-level bonding manner;

- performing ICP etching on the front side of the SOI sheet and stopping etching on the metal layer;

- Metallization of the front side of the ICP-etched SOI wafer and fabrication of the port structure and the electrical coupling structure.

Compared with the prior art, the present invention has the following advantages: by using MEMS technology to fabricate a coaxial filter on a silicon wafer, combining the advantages of MEMS technology, coaxial resonator structure and SIW technology, compared with existing metals A waveguide filter or a SIW filter, the MEMS coaxial filter according to an embodiment of the present invention greatly reduces the size and cost of the millimeter wave filter, and has high processing precision, simplifying the millimeter wave filter Production time and cost.

DRAWINGS

Other features, objects, and advantages of the present invention will become more apparent from the Detailed Description of Description

1a shows a top view of a resonator structure of an exemplary MEMS coaxial filter in accordance with the present invention;

Figure 1b shows a top view of a resonator structure of an exemplary MEMS coaxial filter in accordance with the present invention;

2 is a block diagram showing the structure of a MEMS coaxial filter employing a SIW resonator structure in accordance with one embodiment of the present invention;

3 shows a flow chart of a method for fabricating a MEMS coaxial filter employing a SIW structure in accordance with one embodiment of the present invention;

4 shows a process flow diagram for fabricating a MEMS coaxial filter employing a SIW structure in accordance with one example of the present invention;

Figure 5 illustrates a flow chart of a method for fabricating a MEMS coaxial filter in accordance with one embodiment of the present invention;

6 shows a process flow diagram for fabricating a MEMS coaxial filter using a high resistance silicon wafer in accordance with one example of the present invention;

FIG. 7 shows a flow chart of a method for fabricating the MEMS coaxial filter of the present embodiment;

FIG. 8 illustrates a fabrication of a MEMS using an SOI wafer in accordance with one example of the present invention. Process flow diagram of the coaxial filter;

Figure 9 is a block diagram showing the structure of a MEMS coaxial filter having an electrical coupling structure in accordance with one embodiment of the present invention.

Figure 10 illustrates a process flow diagram for fabricating a MEMS coaxial filter having an electrically coupled structure in accordance with one example of the present invention.

The same or similar reference numerals in the drawings denote the same or similar components.

Detailed ways

The invention is further described in detail below with reference to the accompanying drawings.

A MEMS coaxial filter according to an embodiment of the present invention includes: a double-sided polished structural layer wafer; a silicon dielectric cavity in which an electric wall is realized by a metal wall or a metallized through hole; and an internal coaxial by a metallized blind hole structure.

Wherein, the structural layer wafer comprises various wafers which can be used for fabricating MEMS filters, including silicon wafers, high resistance silicon wafers, SOI wafers, glass wafers or quartz wafers.

Preferably, the structural layer wafer is an SOI sheet.

For example, reference is made to the two resonator structures shown in Figures 1a and 1b. Wherein, the resonator structure shown in FIG. 1a has a blind hole in the center, and a plurality of metallized through holes are formed around the blind hole, and the plurality of metalized through holes are used to realize an electric wall, and the metallized blind hole is used for realizing MEMS The internal coaxial structure of the coaxial filter. The resonator structure shown in Fig. 1b has a blind hole in the center, and the metallized blind hole is used to realize the internal coaxial structure of the MEMS coaxial filter.

Among them, the key process for preparing MEMS coaxial filters on SOI structural layer wafers is inductively coupled plasma (ICP) etching. The ICP etch depth determines the length of the coaxial filter cavity. It should be noted that those skilled in the art should be familiar with the structure layer wafers that are not silicon materials, and other etching processes may be used to etch them. Those skilled in the art may select a suitable etching process based on actual needs. Prepare a MEMS coaxial filter.

Preferably, the resonant frequency of the MEMS coaxial filter is adjusted based on any of the following:

- changing the size of the silicon dielectric cavity;

- Change the diameter of the metallized blind hole.

According to a preferred embodiment of the invention, the MEMS coaxial filter employs a SIW resonator structure. The MEMS coaxial filter comprises a double-sided polished structural layer wafer, a silicon dielectric cavity of the electric wall by the metallized through hole, an internal coaxial structure and a carrier sheet. Preferably, the structural layer wafer is an SOI sheet.

Wherein, the SIW is a periodic structure based on integration of a waveguide structure, and the electromagnetic wave is radiated outward through the array metal through hole, thereby constructing a waveguide structure similar to the waveguide to replace the traditional metal waveguide.

Referring to FIG. 2, the MEMS coaxial filter etches a blind via at the center of the SIW resonator structure for forming an internal coaxial structure based on the SIW structure.

Wherein, the structural layer wafer is provided with a plurality of metallized through holes, and the spacing and arrangement of the plurality of metalized through holes satisfy the requirements of the SIW structure.

FIG. 3 shows a flow chart of a method for fabricating a MEMS coaxial filter using the SIW structure of the present embodiment. Wherein, the structural layer wafer of the MEMS coaxial filter is an SOI slice, and the method includes steps S301, S302, S303, and S304.

Referring to Fig. 3, in step S301, ICP etching is performed on the back surface of the SOI wafer, and etching is stopped in the silicon dioxide layer.

In step S302, the exposed silicon dioxide layer is removed.

In step S303, ICP etching is performed on the front surface of the SOI wafer.

In step S304, the SOI sheet is double-sided metallized, and a port structure and an electrical coupling structure are fabricated.

For example, referring to the process flow diagram of fabricating a MEMS coaxial filter using a SIW structure as shown in FIG. 4, the process flow includes processes (a) through (e). A two-side polished SOI sheet was selected as the structural layer wafer as shown in (a). The back side of the SOI sheet is subjected to ICP etching, and etching is stopped in the silicon dioxide layer as shown in (b). Next, the exposed silicon dioxide layer is removed as shown in (c). Next, the front side of the SOI sheet is subjected to ICP etching as shown in (d). Next, the SOI sheet is double-sided metallized, and a port structure and an electrical coupling structure are produced as shown in (e).

According to an embodiment of the invention, the MEMS coaxial filter comprises a double-sided polished high-resistance silicon wafer, a silicon dielectric chamber of an electrical wall realized by a metal wall, an internal coaxial structure and a carrier sheet.

Wherein, the carrier sheet can adopt any material capable of carrying a load. Preferably, the carrier sheet is a low resistance silicon, glass or other organic material.

Wherein, the high resistance silicon wafer and the carrier sheet are bonded together in a wafer level bonding manner.

Preferably, the wafer level bonding is performed by a low temperature bonding process such as BCB bonding, gold tin solder bonding, or the like. Those skilled in the art can also select other bonding methods based on actual needs, such as, for example, gold-gold thermocompression bonding, glassfrit bonding, and the like.

5 illustrates a method for fabricating a MEMS coaxial filter, wherein the structural layer wafer of the MEMS coaxial filter is a high resistance silicon wafer, and the method includes steps S501, S502, S503, and S504. And S505.

Referring to FIG. 5, in step S501, ICP etching is performed on the back surface of the high resistance silicon wafer;

Next, in step S502, the back surface of the ICP-etched high resistance silicon wafer is metallized;

Next, in step S503, the metallized high resistance silicon wafer and the carrier sheet are bonded together in a wafer level bonding manner;

Next, in step S504, ICP etching is performed on the front surface of the high resistance silicon wafer;

Next, in step S505, the ICP-etched high resistance silicon wafer is metallized on the front side, and a port structure and an electrical coupling structure are fabricated.

For example, referring to the process flow diagram of the MEMS coaxial filter of the present embodiment shown in FIG. 6, the process flow includes the processes (a) to (f). A high-resistance silicon wafer polished on both sides is selected as the structural layer wafer as shown in (a). The back side of the high resistance silicon wafer is subjected to ICP etching as shown in (b). Next, the back side of the ICP-etched high resistance silicon wafer is metallized as shown in (c). Next, the metallized high resistance silicon wafer and the carrier sheet are bonded together in a wafer level bonding as shown in (d). Next, the front side of the high resistance silicon wafer is subjected to ICP etching (e). Next, the ICP-etched high-resistance silicon wafer is metallized on the front side, and a port structure and an electrical coupling structure are fabricated as shown in (f).

According to a preferred embodiment of the invention, the MEMS coaxial filter comprises a double-sided throw The SOI sheet of light, the silicon dielectric cavity of the electric wall by the metal wall, the internal coaxial structure and the carrier sheet.

Wherein, the silicon dioxide layer of the SOI sheet is used to ensure the precision of the ICP etching depth.

FIG. 7 shows a flow chart of a method for fabricating the MEMS coaxial filter of the present embodiment. Wherein, the structural layer wafer of the MEMS coaxial filter is an SOI slice, and the method includes steps S701, S702, S703, S704, S705 and S706.

Referring to FIG. 7, in step S701, ICP etching is performed on the back surface of the SOI sheet, and etching is stopped in the silicon dioxide layer;

Next, in step S702, the exposed silicon dioxide layer is removed.

Next, in step S703, the back surface of the ICP-etched SOI sheet is metallized.

Next, in step S704, the metallized SOI sheet and the carrier sheet are bonded together in a wafer level bonding manner.

The manner of bonding the wafer level is the same as that described in the embodiment using the high resistance silicon wafer described above, and details are not described herein again.

Next, in step S705, the front side of the SOI wafer is subjected to ICP etching, and etching is stopped in the metal layer.

Next, in step S706, the front surface of the ICP-etched SOI wafer is metallized, and a port structure and an electrical coupling structure are fabricated.

For example, referring to the process flow diagram of the MEMS coaxial filter of the present embodiment shown in FIG. 8, the process flow includes the processes (a) to (g). A two-side polished SOI sheet was selected as the structural layer wafer as shown in (a). The back side of the SOI sheet is subjected to ICP etching, and etching is stopped in the silicon dioxide layer as shown in (b). Next, the exposed silicon dioxide layer is removed as shown in (c). Next, the back side of the ICP-etched SOI sheet is metallized as shown in (d). Next, the metallized SOI sheet and the carrier sheet are bonded together in a wafer-level bonding as shown in (e). Next, the front side of the SOI wafer is subjected to ICP etching, and etching is stopped in the metal layer as shown in (f). Next, the front side of the ICP-etched SOI wafer is metallized, and a port structure and an electrical coupling structure are fabricated as shown in (g).

According to a preferred embodiment of the present invention, the MEMS coaxial filter has a dumbbell-shaped metal pattern on the front surface of the structural layer wafer, the metal pattern being located in two resonant cavities Between, used to generate electrical coupling.

For example, referring to the MEMS coaxial filter with an electric coupling structure shown in FIG. 9, the MEMS coaxial filter has six resonant cavities, and has a dumbbell-shaped metal pattern on the front surface of the structural layer wafer, and two in the lower row. Between the resonators to create an electrical coupling.

A process flow diagram for fabricating the MEMS coaxial filter having an electrically coupled structure is shown in FIG. The process flow includes process (a) to process (c). The metallized blind via etching is etched on the back side of the structural layer wafer, and the holes or trenches are simultaneously etched to suppress magnetic coupling between the two resonant cavities, and the corresponding etching pattern is as shown in (a). Next, the front side of the structural layer wafer is subjected to ICP etching as shown in (b). Next, a metal pattern having a dumbbell shape is formed on the front surface of the structural layer wafer so as to be located between the two resonant cavities in the lower row, and metallizing the region other than the dumbbell-shaped metal pattern, and corresponding metallization The pattern is as shown in (c).

Preferably, the electrical coupling is adjusted by changing the gap of the shape metal of the dumbbell-shaped metal pattern.

According to the solution of the present invention, by using MEMS technology to fabricate a coaxial filter on a silicon wafer, the advantages of MEMS technology, coaxial resonator structure and SIW technology are combined, compared to existing metal waveguide filters or SIW filters. The MEMS coaxial filter according to the embodiment of the present invention greatly reduces the size and cost of the millimeter wave filter, and has high processing precision, which simplifies the production time and cost of the millimeter wave filter.

It is apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the present embodiments are to be considered as illustrative and not restrictive, and the scope of the invention is defined by the appended claims instead All changes in the meaning and scope of equivalent elements are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim. In addition, it is to be understood that the word "comprising" does not exclude other elements or steps. A plurality of units or devices recited in the system claims can also be implemented by a unit or device by software or hardware. The first, second, etc. words are used to denote names and do not denote any particular order.

Claims

A MEMS coaxial filter, characterized in that the MEMS coaxial filter comprises:

a structural layer wafer polished on both sides;

a silicon dielectric cavity of the electrical wall realized by a metal wall or a metallized through hole;

Internal coaxial structure realized by metallized blind holes.
The MEMS coaxial filter according to claim 1, wherein the MEMS coaxial filter adopts a SIW resonator structure, and a blind hole is etched in a center of the SIW resonator structure, and the structural layer wafer is an SOI film. .
The MEMS coaxial filter according to claim 1, wherein the structural layer wafer is a high resistance silicon wafer, and the MEMS coaxial filter further comprises a carrier sheet, the high resistance silicon wafer and the carrier sheet. Bonded together in a wafer-level bond.
The MEMS coaxial filter according to claim 1, wherein the structural layer wafer is an SOI sheet, and the MEMS coaxial filter further comprises a carrier sheet, and the SOI sheet and the carrier sheet are in a wafer level. The bonding methods are bonded together.
The MEMS coaxial filter according to any one of claims 1 to 4, wherein a metal pattern of a dumbbell shape is provided on a front surface of the structural layer wafer, the metal pattern being located between two resonant cavities For generating electrical coupling;

Wherein, under the electrically coupled metal pattern, the back side of the structural layer wafer simultaneously etches holes or trenches in the metallization blind via etching step to suppress magnetic coupling between the two resonant cavities.
The MEMS coaxial filter according to any one of claims 1 to 5, wherein the resonant frequency of the MEMS coaxial filter is adjusted based on any of the following methods:

- changing the size of the silicon dielectric cavity;

- Change the diameter of the metallized blind hole.
A method for fabricating a MEMS coaxial filter using a SIW structure, wherein a structural layer wafer of the MEMS coaxial filter is an SOI chip, the method comprising the steps of:

- performing ICP etching on the back side of the SOI sheet to stop etching on the silicon dioxide layer;

- removing the exposed silicon dioxide layer;

- ICP etching the front side of the SOI sheet;

- Metallization of the SOI sheet on both sides and fabrication of the port structure and the electrical coupling structure.
A method for fabricating a MEMS coaxial filter, wherein a structural layer wafer of the MEMS coaxial filter is a high resistance silicon wafer, the method comprising the steps of:

- performing ICP etching on the back side of the high resistance silicon wafer;

- metallizing the back side of the ICP-etched high resistance silicon wafer;

- bonding the metallized high resistance silicon wafer and the carrier sheet in a wafer level bonding manner;

- ICP etching the front side of the high resistance silicon wafer;

- Metallization of the ICP-etched high resistance silicon wafer and fabrication of the port structure and the electrical coupling structure.
A method for fabricating a MEMS coaxial filter, wherein a structural layer wafer of the MEMS coaxial filter is an SOI chip, the method comprising the steps of:

- performing ICP etching on the back side of the SOI sheet and stopping etching on the silicon dioxide layer;

- removing the exposed silicon dioxide layer;

- metallizing the back side of the ICP-etched SOI sheet;

- bonding the metallized SOI sheet and the carrier sheet in a wafer-level bonding manner;

- performing ICP etching on the front side of the SOI sheet and stopping etching on the metal layer;

- Metallization of the front side of the ICP-etched SOI wafer and fabrication of the port structure and the electrical coupling structure.