Miniaturized MEMS cavity filter and preparation method thereof

Abstract

The present invention provides a miniaturized MEMS cavity filter and a preparation method thereof, which belongs to the technical field of radio frequency MEMS devices. The MEMS filter preparation process is adopted. First, an air cavity is etched on the lower surface of a lower silicon wafer by a deep cavity etching method as an embedded cavity for a subsequent high dielectric block; then, metallization patterns are prepared on the upper and lower surfaces of the lower silicon wafer. Metallization patterns are prepared on the upper and lower surfaces of an upper silicon wafer; then, the upper silicon wafer and the lower silicon wafer are bonded by a wafer-level bonding method to form the basic structure of a MEMS cavity filter; finally, a high dielectric block equivalent to the air cavity of the lower silicon wafer is embedded in the air cavity, and then welded together with a Kovar / molybdenum copper carrier by a eutectic process, and finally a miniaturized MEMS cavity filter is formed, which has the characteristics of miniaturization, low loss, high rectangular ratio, high reliability, high consistency, high precision, high integration, full shielding, and anti-interference.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency MEMS devices, and in particular relates to a miniaturized MEMS cavity filter and a preparation method thereof. Background Art

[0002] Filters are used to control the frequency response of microwave systems by providing signal transmission within the filter passband frequency and signal attenuation within the stopband. They are widely used in various civil and military radio systems. Cavity filters have attracted much attention due to their high rectangular ratio, low loss, high shielding, and anti-interference. There are two main types of traditional miniaturized cavity filters. One is a MEMS cavity filter based on high-precision processing, but the dielectric constant of dielectric silicon is only 11.9, and the cavity size is relatively large; the other is a dielectric cavity filter with a high dielectric constant, but the processing accuracy is low, debugging is required after processing, and it is difficult to ensure batch consistency.

[0003] The main problem with traditional miniaturized cavity filters is how to reduce the volume of cavity filters while improving processing accuracy to ensure product performance and batch consistency. Summary of the invention

[0004] The embodiment of the present invention provides a miniaturized MEMS cavity filter and a preparation method thereof, aiming to solve the problems of large cavity size, low processing precision and inconsistent performance of traditional miniaturized cavity filters.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for preparing a miniaturized MEMS cavity filter, the method comprising:

[0006] Preparation of the lower silicon wafer:

[0007] Etching one or more air cavities on the lower surface of the lower silicon wafer;

[0008] Performing metallization on the upper and lower surfaces of the lower silicon wafer;

[0009] Preparation of upper silicon wafer:

[0010] Metallization is performed on the upper and lower surfaces of the upper silicon wafer;

[0011] Preparation of high-k dielectric blocks:

[0012] The high-dielectric block is prepared by laser scribing or machine scribing;

[0013] Grinding and polishing the high-dielectric dielectric block;

[0014] Metallizing the lower surface of the high-dielectric dielectric block;

[0015] Wafer Level Bonding:

[0016] Bonding the lower silicon wafer and the upper silicon wafer to form a double-layer silicon wafer, and performing a dicing process to obtain a miniaturized MEMS cavity filter chip;

[0017] Assembly of miniaturized MEMS cavity filters:

[0018] Putting the high-dielectric dielectric block into the air cavity of the miniaturized MEMS cavity filter chip to obtain a miniaturized MEMS cavity filter chip having the high-dielectric dielectric block;

[0019] The miniaturized MEMS cavity filter chip with the high-dielectric dielectric block is soldered together with a carrier by soldering to finally form a miniaturized MEMS cavity filter; the carrier is a kovar carrier or a molybdenum-copper carrier.

[0020] In combination with the first aspect, in one achievable manner, the preparation of the lower silicon wafer further includes:

[0021] Etching a plurality of lower through holes on the lower silicon wafer and performing metallization treatment to form a lower resonant cavity of the filter;

[0022] A first metallization pattern is prepared on the upper surface of the lower silicon wafer for coupling and signal transmission between the upper and lower resonant cavities;

[0023] A second metallization pattern is prepared on the lower surface of the lower silicon wafer for grounding.

[0024] In combination with the first aspect, in one achievable manner, the air cavity penetrates the lower silicon wafer, and the depth of the air cavity is consistent with the thickness of the lower silicon wafer.

[0025] In combination with the first aspect, in one achievable manner, the shape of the air cavity is circular, elliptical or polygonal.

[0026] In combination with the first aspect, in one achievable manner, the lower through hole has a shape of a cone or a polygonal pyramid.

[0027] In combination with the first aspect, in one achievable manner, photolithography, sputtering, electroplating, and etching are used to prepare coupling holes, circuits, and resonant cavities as the first metallization pattern on the upper surface of the lower silicon wafer.

[0028] In combination with the first aspect, in one achievable manner, the preparation of the upper silicon wafer further includes:

[0029] Etching a plurality of upper through holes on the upper silicon wafer and performing metallization treatment to form an upper resonant cavity;

[0030] Preparing a third metallization pattern on the lower surface of the upper silicon wafer so as to be aligned with the first metallization pattern during wafer-level bonding;

[0031] A fourth metallization pattern is prepared on the upper surface of the upper silicon wafer for grounding.

[0032] In combination with the first aspect, in one practicable manner, the upper through hole is in a cone or polygonal pyramid shape.

[0033] In combination with the first aspect, in one achievable manner, photolithography, sputtering, electroplating, and etching are used to prepare coupling holes, circuits, and resonant cavities as the third metallization pattern on the lower surface of the upper silicon wafer.

[0034] In the second aspect, an embodiment of the present invention further provides a miniaturized MEMS cavity filter, which is prepared by the preparation method of the miniaturized MEMS cavity filter, and includes a carrier, on which a lower silicon wafer and an upper silicon wafer are sequentially arranged, an air cavity is arranged on the lower silicon wafer, and a high dielectric block is arranged in the air cavity; the carrier is a kovar carrier or a molybdenum-copper carrier.

[0035] Compared with the prior art, the miniaturized MEMS cavity filter and the preparation method thereof provided by the present invention have the following beneficial effects:

[0036] (1) Two layers of high-resistance silicon are used as the substrate material of the miniaturized MEMS cavity filter, an air cavity is set on the lower silicon wafer, and a high-dielectric dielectric block is placed in the air cavity to form a resonant cavity, which is conducive to the formation of a miniaturized MEMS cavity filter; in addition, the use of high-resistance silicon material for silicon wafers can be more conveniently applied to silicon-based microsystems, thereby improving the integration of products or microsystems.

[0037] (2) The resonant frequency of the cavity resonator of the miniaturized MEMS cavity filter provided by the present invention will decrease as the dielectric constant of the high-dielectric dielectric block increases. Therefore, at the same resonant frequency, the higher the dielectric constant of the high-dielectric dielectric block, the smaller the cavity size, eventually reaching 1 / 2 or 1 / 4 the size of the original resonant cavity, thereby realizing the miniaturization of the filter.

[0038] (3) The dielectric constant of the high-dielectric block can be flexibly adjusted according to the design to achieve different resonant frequencies at the same size, which provides great flexibility for the design.

[0039] (4) The chip adopts wafer-level packaging technology. The upper ground plane, metallized through-hole and lower ground plane form a fully metal-shielded cavity structure, which increases the Q value of the resonant cavity, reduces the loss of the filter, and achieves a low loss and high rectangular ratio effect.

[0040] (5) The MEMS process is stable and reliable, which is conducive to reducing product costs and improving product reliability and consistency.

[0041] Therefore, the miniaturized MEMS cavity filter provided by the present invention utilizes the MEMS process to manufacture the cavity filter, and uses a high dielectric constant high dielectric block to fill the air cavity in the MEMS cavity filter, which can greatly reduce the overall size of the MEMS cavity filter and has the characteristics of miniaturization; and because the cavity filter is prepared by the MEMS process, it has the characteristics of low loss, high rectangular ratio, high reliability, high consistency, high precision, high integration, full shielding, and anti-interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of the overall structure of a miniaturized MEMS cavity filter provided by an embodiment of the present invention;

[0043] Figure 2 A schematic diagram of a manufacturing process of a miniaturized MEMS cavity filter provided in an embodiment of the present invention;

[0044] Figure 3 A schematic diagram of the assembly structure of a miniaturized MEMS cavity filter provided in an embodiment of the present invention;

[0045] Figure 4 A working principle diagram of a miniaturized MEMS cavity filter provided by an embodiment of the present invention;

[0046] Description of reference numerals:

[0047] 1. Carrier; 2. Lower silicon wafer; 3. Upper silicon wafer; 4. High-k dielectric block; 5. Lower through hole; 6. Upper through hole; 7. Air cavity. DETAILED DESCRIPTION

[0048] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0049] Please also read Figures 1 to 3 , the miniaturized MEMS cavity filter provided by the present invention is now described.

[0050] The main processes adopted by the miniaturized MEMS cavity filter provided by the present invention are as follows: adopting the MEMS filter preparation process, using two layers of high-resistance silicon as the substrate material of the miniaturized MEMS cavity filter, firstly etching an air cavity 7 on the lower surface of the lower silicon wafer 2 by a deep cavity etching method, as an embedded cavity for the subsequent high-dielectric dielectric block 4; then preparing metallization patterns on the upper and lower surfaces of the lower silicon wafer 2 (the metallization pattern on the upper surface is a coupling pattern with the upper silicon wafer 3, the metallization pattern on the lower surface is a grounding layer, and the inner wall of the air cavity 7 hollowed out on the lower surface is not metallized).

[0051] In the same way, metallization patterns are prepared on the upper and lower surfaces of the upper silicon wafer 3 (the metallization pattern on the lower surface is a coupling pattern with the upper surface of the lower silicon wafer 2, and the metallization pattern on the upper surface is a ground layer); the upper silicon wafer 3 and the lower silicon wafer 2 are then bonded by wafer-level bonding to form the basic structure of the MEMS cavity filter; finally, a high-dielectric dielectric block 4 equivalent to the air cavity 7 of the lower silicon wafer 2 is embedded into the air cavity 7, and then welded together with a kovar carrier or a molybdenum-copper carrier using a eutectic process to ultimately form a miniaturized MEMS cavity filter.

[0052] See also Figures 2 to 3 , the specific preparation process is as follows:

[0053] The preparation process includes the preparation of a miniaturized MEMS cavity filter chip and the assembly process of a miniaturized MEMS cavity filter.

[0054] like Figure 2 The figure shows the preparation process of miniaturized MEMS cavity filter chip. The specific steps are as follows:

[0055] 1. Preparation process of lower silicon wafer 2:

[0056] 1) A deep cavity etching method is used to etch one or more air cavities 7 on the lower surface of the lower silicon wafer 2. The depth of the air cavity 7 is the thickness of the lower silicon wafer 2. The shape of the air cavity 7 can be circular, square or polygonal.

[0057] 2) A deep cavity etching method is used to etch a plurality of lower through holes 5 on the lower silicon wafer 2. The lower through holes 5 may be circular holes or square holes, or conical holes or polygonal pyramid holes. Photolithography, sputtering, electroplating, corrosion and other methods are used to metallize the lower through holes 5 on the lower silicon wafer 2. The etched air cavity 7 is not metallized. The lower through holes 5 are used to form the side wall of the lower resonant cavity of the filter to realize the function of the metal electric wall.

[0058] 3) Using photolithography, sputtering, electroplating, etching and other methods, coupling holes, circuits, resonant cavities and the like are prepared on the upper surface of the lower silicon wafer 2 to form a first metallization pattern for coupling between the upper and lower resonant cavities and signal transmission.

[0059] 4) A second metallization pattern is prepared on the lower surface of the lower silicon wafer 2 by photolithography, sputtering, electroplating, etching and the like, as a grounding layer for grounding.

[0060] 2. Preparation process of upper silicon wafer 3:

[0061] 1) A deep cavity etching method is adopted to etch a plurality of upper through holes 6 for the resonant cavity on the upper silicon wafer 3. The upper through holes 6 may be round holes or square holes, or conical holes or polygonal pyramid holes, and their shapes and sizes may be consistent with the lower through holes 5, or may not be consistent with the lower through holes 5; the upper through holes 6 on the upper silicon wafer 3 are metallized by photolithography, sputtering, electroplating, corrosion and other methods. The upper through holes 6 are used to form the side walls of the upper resonant cavity of the filter to realize the function of the metal electric wall.

[0062] 2) Using methods such as photolithography, sputtering, electroplating, and etching, metal circuits, coupling holes, etc. are prepared on the lower surface of the upper silicon wafer 3 to form a third metallization pattern. The third metallization pattern is consistent with the first metallization pattern of the corresponding part of the upper surface of the lower silicon wafer 2, and has the function of aligning the upper and lower silicon wafers.

[0063] 3) A fourth metallization pattern is prepared on the upper surface of the upper silicon wafer 3 by photolithography, sputtering, electroplating, etching and the like to form a grounding layer for grounding.

[0064] 3. Preparation process of high dielectric block 4:

[0065] 1) The high-dielectric block 4 is prepared by laser scribing or machine scribing.

[0066] 2) The high-dielectric block 4 is polished by machine polishing to ensure the dimensional accuracy of the high-dielectric block 4.

[0067] 3) Metallizing the lower surface of the high-dielectric block 4 by sputtering, electroplating or the like.

[0068] 4. Wafer-level bonding process:

[0069] The lower silicon wafer 2 and the upper silicon wafer 3 are wafer-level bonded to form the basic structure of the miniaturized MEMS cavity filter. The basic structure of the miniaturized MEMS cavity filter is diced to obtain a single miniaturized MEMS cavity filter chip.

[0070] like Figure 3 The following is the assembly process of the miniaturized MEMS cavity filter.

[0071] A high dielectric block 4 that matches the size of the air cavity 7 is placed into the previously etched air cavity 7 to obtain a miniaturized MEMS cavity filter chip with a high dielectric block 4; the miniaturized MEMS cavity filter chip with the high dielectric block 4 is soldered together with a kovar carrier or a molybdenum copper carrier through solder to finally form a miniaturized MEMS cavity filter.

[0072] See also Figure 4 When working, the miniaturized MEMS cavity filter is bonded to the RF input and RF output with gold wires respectively.

[0073] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0074] Based on the same inventive concept, an embodiment of the present application also provides a miniaturized MEMS cavity filter, which is prepared by the preparation method of the miniaturized MEMS cavity filter, including a carrier 1, which is a kovar carrier or a molybdenum-copper carrier, on which a lower silicon wafer 2 and an upper silicon wafer 3 are sequentially arranged, an air cavity 7 is arranged on the lower silicon wafer 2, and a high-dielectric dielectric block 4 is arranged in the air cavity 7.

[0075] The miniaturized MEMS cavity filter provided by the present invention uses a high dielectric constant high dielectric block 4 to fill the air cavity 7 in the MEMS cavity filter, which can greatly reduce the overall size of the MEMS cavity filter and has the characteristics of miniaturization; and because the cavity filter is prepared by MEMS technology, it has the characteristics of low loss, high rectangular ratio, high reliability, high consistency, high precision, high integration, full shielding and anti-interference.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a miniaturized MEMS cavity filter, characterized in that: The method comprises: Preparation of the lower silicon wafer (2): Etching one or more air cavities (7) on the lower surface of the lower silicon wafer (2); Preparation of the upper silicon wafer (3): Preparation of high-k dielectric block (4): The high-dielectric block (4) is prepared by laser scribing or machine scribing; Grinding and polishing the high-dielectric dielectric block (4); Metallizing the lower surface of the high-dielectric dielectric block (4); Wafer Level Bonding: The lower silicon wafer (2) and the upper silicon wafer (3) are bonded to form a double-layer silicon wafer, and a miniaturized MEMS cavity filter chip is obtained by scribing. Assembly of miniaturized MEMS cavity filters: Placing the high-dielectric dielectric block (4) into the air cavity (7) of the miniaturized MEMS cavity filter chip to obtain a miniaturized MEMS cavity filter chip having the high-dielectric dielectric block (4); A miniaturized MEMS cavity filter chip having the high-dielectric dielectric block (4) is soldered to a carrier (1) by soldering, thereby finally forming a miniaturized MEMS cavity filter; the carrier is a Kovar carrier or a molybdenum-copper carrier.

2. The method for preparing a miniaturized MEMS cavity filter according to claim 1, characterized in that: The preparation of the lower silicon wafer (2) further includes: Etching a plurality of lower through holes (5) on the lower silicon wafer (2) and performing metallization processing to form a lower resonant cavity of the filter; A first metallization pattern is prepared on the upper surface of the lower silicon wafer (2) for coupling and signal transmission between the upper and lower resonant cavities; A second metallization pattern is prepared on the lower surface of the lower silicon wafer (2) for grounding.

3. The method for preparing a miniaturized MEMS cavity filter according to claim 2, characterized in that: The air cavity (7) penetrates the lower silicon wafer (2), and the depth of the air cavity (7) is consistent with the thickness of the lower silicon wafer (2).

4. The method for preparing a miniaturized MEMS cavity filter according to claim 2, characterized in that: The shape of the air cavity (7) is circular, elliptical or polygonal.

5. The method for preparing a miniaturized MEMS cavity filter according to claim 2, characterized in that: The lower through hole (5) is in the shape of a cone or a polygonal pyramid.

6. The method for preparing a miniaturized MEMS cavity filter according to claim 2, characterized in that: Photolithography, sputtering, electroplating and etching are used to prepare coupling holes, circuits and resonant cavities as the first metallization pattern on the upper surface of the lower silicon wafer (2).

7. The method for preparing a miniaturized MEMS cavity filter according to claim 2, characterized in that: The preparation of the upper silicon wafer (3) further includes: Etching a plurality of upper through holes (6) on the upper silicon wafer (3), and performing metallization treatment to form an upper resonant cavity; Preparing a third metallization pattern on the lower surface of the upper silicon wafer (3) so as to align with the first metallization pattern during wafer-level bonding; A fourth metallization pattern is prepared on the upper surface of the upper silicon wafer (3) for grounding.

8. The method for preparing a miniaturized MEMS cavity filter according to claim 7, characterized in that: The upper through hole (6) is in the shape of a cone or a polygonal pyramid.

9. The method for preparing a miniaturized MEMS cavity filter according to claim 7, characterized in that: Photolithography, sputtering, electroplating and etching are used to prepare coupling holes, circuits and resonant cavities as the third metallization pattern on the lower surface of the upper silicon wafer (3).

10. A miniaturized MEMS cavity filter, prepared by the method for preparing a miniaturized MEMS cavity filter according to any one of claims 1 to 9, characterized in that: The invention comprises a carrier (1), on which a lower silicon wafer (2) and an upper silicon wafer (3) are arranged in sequence, an air cavity (7) is arranged on the lower silicon wafer (2), and a high-dielectric dielectric block (4) is arranged in the air cavity (7); the carrier (1) is a kovar carrier or a molybdenum-copper carrier.

Images