Heterogeneous integrated suspended strip line filter

Abstract

The heterogeneous integrated suspended strip line filter comprises a metal cavity and a strip line substrate suspended in the middle of the metal cavity, the metal cavity is divided into an upper part and a lower part, low-resistance silicon is etched into grooves to form an upper silicon cap and a lower silicon cap, and the inner surfaces of the upper silicon cap and the lower silicon cap are metalized; the lower silicon cap is provided with a plurality of grounded metalized through holes, and the bottom surface of the lower silicon cap is a metalized surface. The strip line substrate is an insulating substrate, a strip line circuit is attached to the strip line substrate, and metal layers and metalized through holes are arranged on the edges of the upper surface and the lower surface of the strip line substrate in the length direction and are bonded with the upper silicon cap metalized layer and the lower silicon cap metalized layer to form the whole suspended strip line structure. The strip line circuit is developed by a high-precision thin film process, various flexible or hard substrates and the like can be adopted, the line error is extremely small, the filter performance with higher requirements is easy to realize, and various requirements of devices are met in a wider range; the structure can realize broadband transmission, has good insertion loss and standing wave, and is easy to be interconnected with an external circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to a filter, in particular to a heterogeneous integrated suspended stripline filter. BACKGROUND

[0002] As a kind of electronic equipment, filter is used to select specific frequency or effectively filter out frequency outside passband, filter out unnecessary part, retain the required signal, and is widely used in communication, audio processing, image processing and control system and many other fields.Microstrip filter is based on microstrip line structure, which has the characteristics of small size, light weight, easy integration, etc., and is suitable for planar circuit.However, microstrip filter has large loss, no shielding, and is easily affected by external interference, especially when the working frequency is high, the defect is more obvious.Waveguide filter has small insertion loss, high Q value and good performance compared with microstrip filter, and can meet the requirements of some high performance occasions, but waveguide filter is large in size and heavy in weight, which is not conducive to integration, while air cavity suspended stripline structure is beneficial to realize low insertion loss and high filtering performance, and has small size and weight compared with waveguide filter, and high integration with external circuit.Suspended stripline filter is a filter with low insertion loss and small size, which places the stripline substrate circuit in the metal cavity, reduces external interference and radiation loss through the shielding effect of the metal cavity, and the dielectric substrate is very thin, so the dielectric loss is small.However, the upper and lower metal cover plates of the traditional suspended stripline filter are positioned by pins, fixed by screws or welded, which has large positioning error;Moreover, the substrate of suspended stripline structure is usually a soft plate, and the conventional PCB stripline manufacturing process has large error and complex assembly, which needs constant debugging and process is complicated, so it is difficult to realize mass production of high performance filter. SUMMARY

[0003] The present application aims to realize high performance suspended stripline filter in a highly integrated manner, and provides a high performance heterogeneous integrated suspended stripline filter with high processing precision, batch production, integration and good compatibility.

[0004] Technical scheme: The heterogeneous integrated suspended stripline filter provided by the present application comprises a metal cavity and a stripline substrate suspended in the middle of the metal cavity, the metal cavity is divided into upper and lower parts, the upper and lower silicon caps are formed by etching grooves in low resistance silicon, and the inner surfaces of the upper and lower silicon caps are metalized, the stripline substrate is an insulating substrate, and a stripline circuit is attached to the substrate, metal layers and metalized vias are arranged on the lengthwise edges of the upper and lower surfaces of the stripline substrate, and the metal layers and metalized vias are interconnected and bonded with the metalized layers of the upper and lower silicon caps to form the entire suspended stripline structure.

[0005] Further, the low-resistance silicon has low cost and good conductivity, and a closed metal cavity is formed by a low-resistance silicon wafer process (internal surface gold plating). The metal cavity can be a rectangular cavity or a circular cavity, which shields external signals and avoids interference between lines. Compared with the traditional metal cavity fixed by screws or welded, the metal cavity has high processing precision, can be mass-produced, is conducive to integration, has good compatibility, can be used as a resonant cavity, has better shielding effect on the outside world, has no radiation loss, has good standing wave performance, and ensures stable performance of the filter in various complex environments. The upper and lower silicon caps are etched cavities formed on a silicon substrate, and the length of the lower silicon cap is greater than that of the upper silicon cap, thereby supporting the input and output ports formed by the microstrip line. The microstrip line is directly connected to the input and output ends of the suspended strip line structure filter, and the microstrip line is matched with a 50-ohm characteristic impedance to realize the connection between the internal strip line circuit and the external microstrip circuit, has full-band transmission characteristics, is conducive to planar integration, increases the applicability of the filter, has good standing wave and insertion loss characteristics, and can meet the requirements of various microwave and millimeter wave components.

[0006] Further, the upper and lower silicon caps and the metalized layer of the strip line substrate are processed by vacuum evaporation / sputtering or chemical vapor deposition. For example, vacuum evaporation / sputtering is used, titanium, tungsten titanium or nickel is selected for priming, and then gold is selected for metalization treatment. The thickness of the gold layer is about 3 μm, the surface roughness is controlled to be less than Ra 0.1 μm, and the subsequent gold-gold bonding process is facilitated.

[0007] Further, the lower silicon cap is provided with a plurality of grounded metalized through holes, and the bottom surface of the lower silicon cap is a metalized surface. The strip line substrate is suspended on the lower silicon cap, the upper silicon cap is buckled on the strip line substrate, and then the wafer bonding of the three is completed to package the device. The metalized through holes on the lower silicon cap realize good grounding of the entire device. In addition, the metal cavity made of low-resistance silicon has good conductivity and good adhesion to the metalized layer, which further improves the good grounding performance of the device and enhances the shielding effect on external signals. In addition, the low-resistance silicon has low price, which further reduces the processing cost of the device.

[0008] Further, the strip line substrate is an insulating substrate, which can be made of polytetrafluoroethylene substrate, high-resistance silicon substrate or ceramic substrate, and can be a flexible or hard substrate. The thickness of the strip line substrate is less than 10% of the thickness of the metal cavity.

[0009] Further, the strip line substrate is a flexible substrate or a hard substrate, and in a wider range, various requirements of the device are met according to specific application occasions. The strip line circuit is made by a thin film process, the thickness of the gold layer is about 3 μm, the surface roughness formed by the gold layer is controlled to be less than Ra 0.1 μm, and the subsequent gold-gold bonding process is facilitated. The strip line substrate material has a large loss factor, which increases the loss and reduces the Q value, so it is necessary to select a material with a low loss factor. The strip line circuit is made by a thin film process, which improves the processing precision of the microstrip structure and better realizes the small and compact structure. In addition, the metal cavity cooperates with the strip line circuit to form various resonator designs, and high selectivity of frequency selection can be realized to meet different application scenarios.

[0010] Further, the metal cavity is filled with air medium, which further reduces the transmission loss, increases the Q value, and enhances the selectivity of the filter.

[0011] Further, the specific size of the lower silicon cap and the cuboid metal cavity formed in the lower silicon cap and the strip line circuit is determined by a filter synthesis method and electromagnetic simulation software such as HFSS and ADS. The shape of the metal cavity is mostly cylindrical or rectangular, which is used to limit the propagation of electromagnetic waves and form a closed space. The shape of the metal cavity can be designed according to the requirements, and the frequency response characteristics of the filter can be changed by adjusting the size and shape of the metal cavity in combination with the strip line circuit to meet different application requirements. For example, by using electromagnetic simulation tools such as HFSS and ADS, the size of the strip line circuit and the thickness of the dielectric substrate can be adjusted through parameter optimization.

[0012] Design principle: The Q value of the conventional microstrip filter is relatively low compared with the Q value of the waveguide filter, and the insertion loss is large, which cannot meet the requirements in some cases. However, the waveguide filter has large size and weight, which is not conducive to integration. The air cavity suspended strip line structure is beneficial to realizing low insertion loss and high filtering performance while having relatively small size and weight compared with the waveguide filter, and has high integration with external circuits. Therefore, the method realizes an air cavity suspended strip line filter based on a semiconductor heterogeneous integration process, which has excellent filtering performance and relatively small size and weight.

[0013] Advantages: Compared with the prior art, the present application has the following advantages: 1. The upper and lower silicon cavities are accurately aligned by a semiconductor process, the middle substrate is processed by a high-precision thin film process, the line error is extremely small, and the filter performance with high requirements can be easily realized, and the production is good; 2. The middle substrate can be made of various substrates, including flexible substrates, hard substrates, etc., which meet various requirements of the device in a wider range according to specific application occasions; 3. The filling medium is air, this structure can also realize wideband transmission, has good insertion loss and standing wave, and is easy to interconnect with external circuits. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1This is a schematic diagram of the structure of the present invention;

[0015] Figure 2 This is a schematic diagram of the wire circuit patterns on the front and back sides of the wire substrate of the present invention.

[0016] Figure 3 This is a schematic diagram of the upper and lower silicon caps of the present invention;

[0017] Figure 4 This is a schematic diagram of a specific wired circuit in an embodiment of the present invention;

[0018] Figure 5 This is a schematic diagram of the wire circuit patterns on the front and back sides of the wire substrate in an embodiment of the present invention;

[0019] Figure 6 This is a simulation data diagram of an embodiment of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0021] like Figure 1 The illustrated heterogeneous integrated suspended stripline filter includes an upper silicon cap 1 and a lower silicon cap 2 formed by etching grooves into low-resistivity silicon. The inner surfaces of the upper and lower silicon caps 1 and 2 are then vacuum sputtered with Ti as the base material, approximately 0.2 μm thick (tungsten-titanium or nickel can also be used as the base material), followed by gold plating with a gold layer thickness of 3 μm. The upper and lower silicon caps 1 and 2 clamp a stripline substrate 3 between them and then bond them together. After bonding, the upper and lower silicon caps form a metal cavity filled with air, and the stripline substrate 3 is suspended within the metal cavity. Figure 2 As shown, the stripline substrate 3 is an insulating substrate on which the stripline circuit 5 is attached. Metal layers and metallized vias 4 are disposed along the edges of the upper and lower surfaces of the stripline substrate 3 in the length direction, interconnecting and bonding with the metallized layers of the upper silicon cap 1 and the lower silicon cap 2. The insulating substrate uses a low-loss material, such as a polytetrafluoroethylene (PTFE) substrate (or a high-resistivity silicon substrate or ceramic substrate, which can be flexible or rigid, depending on requirements), with a thickness less than 10% of the metal cavity thickness. The stripline circuit 5 is fabricated using a thin-film process, with a titanium underlayer of 0.2 μm (tungsten-titanium or nickel underlayers can also be used), followed by gold plating, typically with a gold layer thickness of 3 μm. Figure 3As shown, the upper and lower silicon caps 1 and 2 are etched by ICP, the upper cavity height is 0.85 mm, the lower cavity height is 0.35 mm, the cavity width is 5.52 mm, the cavity length is 10.68 mm, the length of the lower silicon cap 2 is greater than the length of the upper silicon cap 1, so that the device forms input port 6 and output port 7 in the form of a microstrip, and is directly connected with the input and output ends of the strip line circuit 5, the microstrip line is matched with the characteristic impedance of 50 ohms, the lower silicon cap 2 is provided with a plurality of grounded lower silicon cap metallized through holes 8, and the bottom surface is metallized; the length, width and depth of the rectangular metal cavity formed in the upper and lower silicon caps 1 and 2 and the size of the strip line circuit 5 are determined by filter synthesis method and electromagnetic simulation software such as HFSS and ADS. As shown in Figure 4 and 5 As shown, an example diagram of the strip line circuit 5 on the strip line substrate 3 is given, the strip line circuit 5 can be designed according to actual needs, and then processed by thin film process. After the upper and lower silicon caps 1 and 2 and the strip line substrate 3 are manufactured, the strip line substrate 3 is suspended on the lower silicon cap 2, the upper silicon cap 1 is buckled on the strip line substrate 3, and then the wafer bonding of the three is completed to package the device, as shown in Figure 6 As shown, a simulation data diagram of the above filter is given, the device has small insertion loss, and has excellent input and output standing wave and out-of-band suppression.

Claims

1. A heterogeneously integrated suspended stripline filter comprising a metal cavity and a stripline substrate suspended in the middle of the metal cavity, characterized in that, The metal cavity is divided into two parts, the upper and lower silicon caps are formed by etching grooves in low-resistance silicon, and the inner surfaces of the upper and lower silicon caps are metallized; the strip-line substrate is an insulating substrate with a strip-line circuit attached thereto, and the edges of the upper and lower surfaces of the strip-line substrate in the length direction are provided with metal layers and metallized through-holes, which are interconnected and bonded with the metallized layers of the upper and lower silicon caps to form the entire suspended strip-line structure.

2. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The length of the lower silicon cap in the length direction is greater than that of the upper silicon cap, thereby supporting the input and output ports formed by microstrip lines, which are directly connected with the input and output ends of the suspended strip-line structure filter.

3. The heterogeneously integrated suspended stripline filter of claim 2, wherein, The input and output ports are matched with the characteristic impedance of 50 ohms.

4. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The roughness of the inner surfaces of the upper and lower silicon caps and the surface of the strip-line substrate after metallization is controlled to be less than Ra 0.1 μm.

5. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The lower silicon cap is provided with a plurality of metallized through-holes connected with ground, and the bottom surface of the lower silicon cap is a metallized surface.

6. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The insulating substrate of the strip-line substrate is made of polytetrafluoroethylene, high-resistance silicon or ceramic, and the thickness is less than 10% of the thickness of the metal cavity.

7. The heterogeneously integrated suspended stripline filter of claim 6, wherein, The strip-line substrate is an insulating substrate, which is a flexible substrate or a hard substrate.

8. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The strip-line circuit is made by thin-film technology.

9. The heterogeneously integrated suspended stripline filter of claim 1, wherein, The metal cavity is filled with air medium.

10. The heterogeneously integrated suspended stripline filter of claim 9, wherein, The length, width and depth of the cuboid metal cavity formed by the lower silicon cap and the lower silicon cap, and the width of the strip-line structure are determined by magnetic simulation software.

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