Electrostatic tuning infrared filter based on double-cantilever beam structure

Abstract

An electrostatic tuning infrared filter based on a double-cantilever beam structure comprises an etched silicon substrate layer, a gold electrode layer matched with a cantilever beam, an air suspension layer, a top gold electrode layer and a top etched silicon substrate layer from bottom to top. The top view of the electrostatic tuned filter is square, and a silicon cantilever beam is formed by etching a silicon wafer and is connected with a central reflection domain into a whole. And the gold electrode layer is stripped and deposited by a lift process, and the gold electrode layer is consistent with the cantilever beam of the etched silicon wafer. The lower-layer cantilever beam structure and the upper-layer cantilever beam structure are manufactured in the same mode, and the top electrode and the bottom electrode are opposite in a mirror image mode during assembly so that the electrostatic force can achieve the maximum effect. The problem that bridge floor displacement is too small when driving voltage is insufficient can be effectively solved, the tuning range of the filter can be expanded, and resonant frequency can be effectively selected. The method can be used for integrating a filter on the surface of an infrared detector to obtain a detection function of dynamic filtering tuning integrated on a compact chip.

Description

Technical Field

[0001] The utility model relates to the field of infrared detection, and specifically to an electrostatically driven tuned infrared filter based on a double cantilever beam structure. Aiming at the limited displacement of the elastic deformation area of ​​the existing single cantilever structure, and the risks of lead burning, bridge deck collapse, cantilever fracture, device breakdown, etc. under high voltage bias, the double cantilever beam structure is adopted to greatly increase the displacement of the cantilever bridge deck under the same voltage bias, improve the service life and stability of the device, and introduces the device design in detail. Background Art

[0002] Due to the rich two-dimensional (2D) morphology and one-dimensional (1D) thermal radiation spectral information, infrared spectral imaging (IR-SI) has potential in many important fields, such as spectral imaging, modern astronomy, remote sensing and telemetry, material detection and analysis, etc. However, traditional long-wave infrared spectral imaging based on traditional dispersive elements often has the problems of high cost, large size and complex system structure. Micro-electromechanical system Fabry-Perot filter chip (MEMS-FPFC) provides a feasible way to realize miniaturized, low-cost and customizable long-wave infrared spectral imaging system.

[0003] In a complex background environment, the movement and radiation characteristics of matter will change rapidly over time. Traditional detection methods cannot adjust the reconnaissance spectrum for timely and effective identification. With the development of micro-electromechanical systems (MEMS) technology, various MEMS optical functional chips made using micro-nano processing technology not only overcome the shortcomings of traditional optical components such as large size, poor customization and high cost, but also achieve a qualitative leap from static to dynamic optical components, thereby overcoming the interference of the target background and atmospheric environment, and improving the ability to discover and identify targets in complex environments in the future.

[0004] For electrostatically tuned filters, their structure has a great influence on the tuning performance of the filter. The current technology uses the upper movable bridge deck-the middle suspended layer-the lower fixed bridge deck as the main filtering structure. Under the bias of the upper and lower electrode voltages, the electrostatic force attracts each other to change the suspension height and adjust the filter cavity length, thereby realizing active selection of filtering. Since the lower bridge deck of the traditional structure is fixed, the stress of the lower bridge deck cannot be effectively utilized. In the existing design, the required displacement is relatively high, and there is a risk of cantilever beam breakage and sample breakdown. If the traditional bridge deck structure is replaced by a double cantilever beam structure, the bridge deck displacement brought about by the same driving voltage can be effectively increased, making the tuning range larger. Under the same tuning range, the local stress and load voltage of the cantilever structure can be effectively reduced, reducing the risk of cantilever breakage and breakdown.

[0005] For example, the document "Microelectromechanical systems-based visible-near infraredFabry-Perot tunable filters using quartz substrate" (Optical Engineering, 2012, 51(7): 074007-074007.) systematically introduces the displacement and resonance of a reflective mirror with an annular cantilever beam structure under electrostatic drive as the driving voltage increases. Compared with the document, the present invention has better displacement performance. Utility Model Content

[0006] Aiming at the problem that the existing cantilever beam structure requires a higher voltage, the utility model establishes an electric, optical, and mechanical multi-physical field coupling model and conducts a systematic study on the structure. First, the bridge deck is modeled, then the electrode is modeled and combined with the bridge deck, and then the air domain is divided and the model material properties are given, and the electric, optical, and mechanical physical field coupling is performed. The performance difference between the single cantilever beam and the double cantilever beam under the same driving voltage is tested, and finally it is realized that under the relative driving voltage, the double cantilever beam structure can achieve a higher bridge deck displacement and has good bridge deck displacement consistency.

[0007] The purpose of the utility model is to provide a structural solution of an electrostatically tuned infrared filter for a double cantilever beam bridge deck to solve the following existing technical problems;

[0008] 1. The traditional single cantilever filter structure cannot produce sufficient bridge displacement under a small driving voltage, which limits the tuning range. Figure 6 As shown in (a), only 1.44 μm displacement can be achieved under a voltage of 100 V. If the voltage is further increased, the risk of cantilever beam breakage or device breakdown will increase.

[0009] 2. The cantilever beam length of traditional bridge decks is localized on a smaller scale, making it difficult to efficiently amplify the displacement. This experiment uses a circular cantilever to enlarge the cantilever beam size by 2 to 3 times, which can efficiently and stably amplify the displacement.

[0010] The technical solutions of the utility model are as follows:

[0011] The utility model is an electrostatic tuning filter based on a double cantilever beam structure, which is characterized in that the electrostatic tuning filter is composed of an etched silicon substrate layer, a gold electrode layer matching the cantilever beam, an air suspension layer, a top gold electrode layer, and a top etched silicon substrate layer from bottom to top. The top view of the electrostatic tuning filter is a square, wherein the silicon cantilever beam is integrated with the central reflection domain by etching the silicon wafer. The gold electrode layer is stripped and deposited by the liftoff process and attached to the cantilever beam. The lower cantilever beam structure is manufactured in the same way as the upper layer, and the top and bottom electrodes should be mirror-imaged when assembled so that the electrostatic force can exert the maximum effect.

[0012] The electrostatically tuned filter based on the dual cantilever beam structure mainly includes the following steps:

[0013] 1. First, make the photogenic production:

[0014] 1. Spread the glue on the silicon substrate, use the liftoff process to grow a gold layer, and make a gold electrode. The pattern of the gold electrode layer is roughly similar to that of the cantilever beam.

[0015] 2. Make a cantilever beam structure. Use dry etching to perform deep silicon etching to form a silicon substrate with a cantilever beam, and the central area is used for reflection resonance.

[0016] 2. Make the next mirror:

[0017] 1. Make an electrode layer, apply glue on a silicon substrate, use a liftoff process to grow a gold layer, and make a gold electrode. The pattern of the gold electrode layer is roughly similar to that of the cantilever beam.

[0018] 2. Make a cantilever beam structure. Use dry etching to perform deep silicon etching to form a silicon substrate with a cantilever beam structure, and the central area is used for reflection resonance.

[0019] 3. Make the support layer structure. Spin-pattern SU-8 photoresist, and then cure it after photolithography and development to form a support structure.

[0020] 3. Finally, bond the upper and lower mirrors

[0021] The upper and lower mirrors are bonded together using the reverse solder bonding process to form a dual cantilever beam filter structure.

[0022] The technical effects of the utility model are as follows:

[0023] 1. The annular integrated cantilever beam of the utility model can effectively solve the problem that the traditional straight cantilever beam cannot amplify the displacement by a large proportion. The scale of the traditional straight cantilever beam is roughly equivalent to the scale of the device. The annular cantilever beam can enlarge the cantilever beam by 2 to 3 times compared with the traditional cantilever beam. The three annular cantilever beams can effectively, stably and amplify the displacement on a large scale, and the displacement consistency of the reflector is good.

[0024] 2. The utility model innovatively sets the upper and lower bridge decks as cantilever beam structures. Compared with the single cantilever beam model, the bridge deck displacement of the double cantilever beam structure model is increased by nearly 1.7 times, which greatly reduces the demand for driving voltage

[0025] The utility model can be used for integrating a filter on the surface of an infrared detector to obtain a compact on-chip integrated dynamic filter tuning detection function. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the utility model.

[0027] Figure 2 It is a cross-sectional view of the utility model.

[0028] Figure 3 It is a structural schematic diagram of the upper mirror electrode group of the utility model.

[0029] Figure 4 This is a schematic diagram of the cantilever beam structure of the upper silicon plate of the utility model.

[0030] Figure 5 This is the process flow chart of the utility model.

[0031] Figure 6 This is a comparison chart of the effects of Example 2 of the utility model compared with traditional filter devices.

[0032] (a) Displacement analysis of traditional filter device (b) Displacement analysis of double cantilever beam structure DETAILED DESCRIPTION

[0033] 1. Spread the silicon substrate 9 and grow the gold layer 10 using the liftoff process to make the gold electrodes 6, 7, and 8.

[0034] 2. Fabricate the upper cantilever beam structure. Use dry etching to perform deep silicon etching to form a silicon substrate with cantilever beams 1, 2, and 3, and the central area 4 is used for reflection resonance.

[0035] 3. Use the same method to coat the lower silicon substrate 12, use the liftoff process to grow the gold layer 11, and make gold electrodes 17, 18, 19. The central area 5 is used for reflection resonance.

[0036] 4. Fabricate the lower cantilever beam structure. Use dry etching to perform deep silicon etching to form a silicon substrate with cantilever beams 14, 15, and 16.

[0037] 5. Fabricate the support layer structure: Spin pattern SU-8 photoresist 13, and cure it after photolithography and development to form a support structure.

[0038] 6. Bonding the upper and lower mirrors: Use the reverse welding bonding process to bond the upper and lower mirrors together to form a dual cantilever beam filter structure.

[0039] Embodiment 1:

[0040] The thickness of the silicon substrates 9 and 12 is 200 μm;

[0041] The gold electrode layers 10 and 11 are 10 μm;

[0042] The air layer and SU-8 layer after bonding are 50 μm;

[0043] The distance between the bonded gold electrode layers 10 and 11 is 30 μm;

[0044] When the distance between the gold electrode layers is 30 μm, the displacement under 100 V voltage drive is compared with Example 2. We can find that since the magnitude of the electrostatic force is related to the distance between the two electrode layers, the displacement performance obtained in Example 1 is significantly reduced compared with that in Example 2.

[0045] Embodiment 2:

[0046] The thickness of the silicon substrates 9 and 12 is 200 μm;

[0047] The gold electrode layers 10 and 11 are 15 μm;

[0048] The air layer after bonding is 50 μm;

[0049] The distance between the bonded gold electrode layers 10 and 11 is 20 μm;

[0050] See below Figure 6 , Figure 6 This is a comparison of the bridge deck displacement performance of the new double cantilever beam filter and the traditional single cantilever beam filter. Figure (b) shows the filter using double cantilever beams. Assuming the driving voltage is 100V, the cavity length is 50μm, and the edges of the upper and lower reflectors are fixed constraints, after the driving voltage is applied, the two reflectors approach each other due to the traction of the electrostatic force to shorten the cavity length. By comparison, we can find that the upper and lower mirrors of the double cantilever beam filter both produce a maximum displacement of 1.88μm, while the single cantilever beam filter only produces a maximum displacement of 1.4μm on the upper cantilever beam. The double cantilever beam structure improves the bridge deck displacement performance by nearly 1.7 times.

[0051] Experiments show that the filter based on the dual cantilever beam structure of the utility model can effectively solve the problem of too small bridge displacement when the driving voltage is insufficient, can expand the tuning range of the filter, and can effectively select the resonant frequency. The utility model can be used for integrating filters on the surface of infrared detectors to obtain compact on-chip integrated dynamic filter tuning detection functions.

Claims

1. An electrostatically tuned infrared filter based on a dual cantilever beam structure, characterized in that: The structure of the electrostatically tuned infrared filter from bottom to top is: an etched silicon substrate layer, a gold electrode layer matching the cantilever beam, an air suspended layer, a top gold electrode layer, and a top etched silicon substrate layer, wherein the top view of the electrostatically tuned infrared filter is a square, wherein the silicon cantilever beam is integrated with the central reflection domain by etching the silicon wafer, the gold electrode layer is stripped and deposited by a liftoff process, the gold electrode layer is consistent with the cantilever beam of the etched silicon wafer, the lower cantilever beam structure is manufactured in the same way as the upper layer, and the top and bottom electrodes are mirror-imaged during assembly.

Images