MEMS Fabry-Perot optical filter chip based on wafer direct bonding
The MEMS FP filter chip addresses FP cavity length instability by employing direct silicon-oxide bonding and integrated capacitors for precise electrostatic control, ensuring stable spectral performance.
Patent Information
- Application Number
- CN202510396416.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-07-15
AI Technical Summary
The existing MEMS Fabripeo filter chips have high bonding stress during wafer bonding, resulting in the long FP cavity being compressed, and the filter spectrum range cannot be accurately controlled.
The SOI wafer is directly bonded with a single crystal silicon wafer, and parallel plate capacitors and detection feedback capacitors are made on the fixed mirror and the movable mirror structure respectively, silicon-silica bonding is used to form an insulating interface, and the cavity length is controlled by capacitance changes to avoid the cavity length deviation caused by bonding stress.
It achieves low bonding stress, uncompressed cavity length, stable spectral performance of the filter, and can accurately control the FP cavity length. It is suitable for spectral analysis, laser technology, optical fiber communication and other fields.
Smart Images
Figure CN120308906A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of micro-optoelectromechanical devices, and relates to a MEMS Fabry-Perot filter chip based on direct wafer bonding. Background Art
[0002] Due to its high resolution and adjustable properties, Fabry-Perot filters are applied in technical fields such as spectral analysis, laser technology, and optical fiber communication. In recent years, MEMS Fabry-Perot (FP) filters based on micro-nano manufacturing technology have attracted the attention of relevant research institutions and enterprises at home and abroad due to their advantages such as miniaturization, low cost, and customization, and have been widely used in industries such as food safety, medical diagnosis, environmental monitoring, anti-counterfeiting identification, and security reconnaissance.
[0003] The construction of the interference chamber of the MEMS FP filter chip is generally achieved through the bonding of two wafers. The gap between the two wafers after bonding is the cavity length of the Fabry-Perot interference cavity (FP cavity), and this cavity length determines the spectral wavelength that can pass through the filter. Therefore, wafer bonding has become a key process in the manufacture of MEMS FP filter chips. The reported MEMS Fabry-Perot (FP) filter chips at home and abroad generally use organic glue bonding and metal thermocompression bonding. Gold-gold bonding, organic glue bonding, etc. require the introduction of a metal or organic glue intermediate layer. Under certain bonding temperatures and pressures, the metal and organic glue materials are compressed and undergo uncontrollable deformation, resulting in an uncontrollable offset between the FP cavity length and the designed value, and the spectral range of the MEMS-FP filter chip cannot be accurately controlled accordingly. Summary of the Invention
[0004] The purpose of the invention is to provide a MEMS Fabry-Perot filter chip based on direct wafer bonding, so as to solve the disadvantages of large wafer bonding stress and compressed FP cavity length after bonding in the prior art.
[0005] The technical solution adopted by the invention is as follows: A MEMS Fabry-Perot filter chip based on direct wafer bonding, which is characterized by comprising the following components: A fixed mirror structure, including a SOI wafer composed of a top silicon layer, a buried oxide layer, and a substrate silicon layer. A first shallow cavity is formed in the middle of the top silicon layer of the wafer, and a second shallow cavity reaching the substrate silicon layer is further formed downward in the middle of the first shallow cavity. A low-resistance silicon electrode is formed between the top silicon layer of the first shallow cavity part and the buried oxide layer. A high-reflection film is formed on the substrate silicon in the middle of the second shallow cavity, an anti-reflection film is formed on the back of the substrate silicon, a first bonding pad is formed on the surface of the top silicon layer, and a second bonding pad is formed on the surface of the substrate silicon; The movable mirror structure includes a deep cavity formed in the middle of a monocrystalline silicon bulk silicon. A cantilever beam is formed in the deep cavity. An antireflection film is formed on the upper surface of the monocrystalline silicon bulk silicon at the central position connected to the cantilever beam. A high-reflection film is formed on the lower surface of the monocrystalline silicon bulk silicon at the central position connected to the cantilever beam. A third pad is formed on the upper surface of the monocrystalline silicon bulk silicon connected to the periphery of the cantilever beam. An annular silicon dioxide layer is formed on the lower surface of the monocrystalline silicon bulk silicon, which surrounds the deep cavity and the cantilever beam. Bond the movable mirror and the fixed mirror through silicon-silicon dioxide bonding of the top silicon and the annular silicon dioxide layer. The bonded annular silicon dioxide layer insulates the monocrystalline silicon bulk silicon from the low-resistance silicon electrode, forming a parallel-plate capacitor. At the same time, the monocrystalline silicon bulk silicon is insulated from the SOI wafer substrate silicon, forming a detection feedback capacitor. In the above technical solution, the SOI wafer and the monocrystalline silicon wafer are respectively used to fabricate the fixed mirror and the movable mirror of the MEMS FP filter chip. Two cavities with different depths are fabricated on the SOI of the fixed mirror. The remaining part of the top silicon of the SOI at the bottom of the shallower first shallow cavity serves as the conductive electrode for applying voltage to the fixed mirror. The bottom of the deeper second shallow cavity is the surface of the SOI substrate silicon. A high-reflection optical film and a metal are deposited on the bottom of this cavity, serving as the light-transmitting area and the pad of the detection feedback capacitor respectively.
[0006] The monocrystalline silicon of the movable mirror and the top silicon of the fixed mirror are firmly bonded through direct silicon-silicon dioxide wafer bonding. The silicon dioxide on the bonding surface ensures complete insulation of the fixed mirror / movable mirror capacitor plates. On the monocrystalline silicon of the movable mirror, a deep cavity, a cantilever beam and a metal are fabricated on the front side. By adjusting the depth of the deep cavity, a cantilever beam with appropriate elastic force can be obtained. The metal serves as the pad connecting the movable mirror capacitor plate. An antireflection film is fabricated on the front side of the movable mirror, and a high-reflection film is fabricated on the back side to ensure that the transmittance and bandwidth of the filter within the working spectral range meet the requirements. When a voltage is applied to the fixed mirror, the movable mirror moves downward under the action of electrostatic force, causing the cavity length to change the FP, thereby realizing the tuning of the filtering spectrum.
[0007] Advantages of the present invention: The MEMS Fabry-Perot filter chip based on direct wafer bonding proposed by the present invention has the advantages of small bonding stress and non-compression of the cavity length. In addition, the present invention uses the SOI wafer to fabricate two electrodes on the fixed mirror structure, forming a parallel-plate electrostatic capacitor and a detection feedback capacitor with the movable mirror structure respectively, having the advantage of closed-loop control. Description of the drawings
[0008] Figure 1 It is a cross-sectional structure diagram of the MEMS FP filter chip based on direct wafer bonding of the present invention.
[0009] Specific implementation manners As Figure 1As shown in the figure, a MEMS Fabry-Perot filter chip based on direct wafer bonding of the present invention comprises two parts: 1. The fixed mirror structure includes an SOI wafer composed of a top silicon layer 101, a buried oxide layer 102, and a substrate silicon layer 103. A first shallow cavity 104 is formed in the middle of the top silicon layer 101 of the wafer. A second shallow cavity 106 reaching the substrate silicon layer 103 is further formed downward in the middle of the first shallow cavity 104. A low-resistance silicon electrode 105 is formed between the top silicon layer 101 of the first shallow cavity 104 part and the buried oxide layer 102. A high-reflection film 107 is formed on the substrate silicon layer 103 in the middle of the second shallow cavity 106. An antireflection film 110 is formed on the back of the substrate silicon layer 103. A first pad 108 is formed on one side of the surface of the top silicon layer 101. A second pad 109 is formed on one side surface of the substrate silicon layer 103. The low-resistance silicon electrode 105 is electrically connected to the first pad 108 as the first electrode on the fixed mirror structure. The second pad 109 is electrically connected to the substrate silicon layer 103 of the SOI wafer as the second electrode on the fixed mirror structure.
[0010] 2. The movable mirror structure includes a single-crystalline bulk silicon 201. A deep cavity 204 is formed in the middle thereof, and a cantilever beam 205 is formed in the deep cavity. An antireflection film 207 is formed on the single-crystalline bulk silicon 201 at the central position connected to the cantilever beam 205. A high-reflection film 203 is formed under the single-crystalline bulk silicon 201 at the central position connected to the cantilever beam 205. A third pad 206 is formed on the single-crystalline bulk silicon 201 above the periphery connected to the cantilever beam 205. The third pad 206 is electrically connected to the single-crystalline bulk silicon 201. An annular silicon dioxide layer 202 is formed under the single-crystalline bulk silicon 201, which surrounds the deep cavity 204 and the cantilever beam 205.
[0011] 3. After the movable mirror and the fixed mirror are silicon-silicon dioxide bonded through the top silicon layer 101 and the annular silicon dioxide layer 202, a MEMS FP filter chip based on direct wafer bonding of the present invention is formed. The bonded annular silicon dioxide layer 202 insulates the single-crystalline bulk silicon 201 from the low-resistance silicon electrode 105, forming a parallel-plate capacitor. At the same time, the single-crystalline bulk silicon 201 is insulated from the substrate silicon layer 103 of the SOI wafer, forming a detection feedback capacitor.
[0012] By applying a voltage between the first pad 108 and the third pad 206, the electrostatic force between the parallel-plate capacitors drives the high-reflection film 203 to move towards the high-reflection film 107, reducing the FP cavity length. At this time, the capacitance value between the second pad 109 and the third pad 206 will also change accordingly. By detecting this capacitance, a feedback signal of the FP cavity length change can be obtained.
[0013] The manufacturing process of the present invention is a conventional technology in the art, and the main process steps are as follows: 1. The first shallow cavity 104, the low-resistance silicon electrode 105, the second shallow cavity 106, and the high-reflection film 107 are fabricated on the SOI wafer of the fixed mirror.
[0014] 2. An annular silicon dioxide layer 202 is fabricated on the lower surface of the monocrystalline silicon bulk silicon 201 of the movable mirror. A high-reflection film 203 is fabricated below the middle of the monocrystalline silicon bulk silicon 201, and a deep cavity 204 is fabricated on the monocrystalline silicon bulk silicon 201.
[0015] 3. After the movable mirror and the fixed mirror are silicon-silicon dioxide bonded through the top silicon 101 and the annular silicon dioxide layer 202, the cantilever beam 205 and the third pad 206 are continuously fabricated on the movable mirror structure. Then, the first pad 108, the second pad 109, and the antireflection film 110 are fabricated on the fixed mirror. Finally, the antireflection film 207 is fabricated on the upper surface of the monocrystalline silicon bulk silicon 201. The SiO2 layer provided on the surface of the low-resistance silicon 105 in the first shallow cavity 104 part is used to protect the 105 low-resistance silicon lead below from being etched and damaged when the cantilever beam 205 structure is formed by deep silicon etching after bonding.
[0016] The advantages of the present invention are as follows: 1. A planar capacitor is formed between the electrode (the second pad) 109 and the electrode (the third pad) 206, with the optical transmission area 208 of the movable mirror and the substrate silicon 103 of the fixed mirror as the electrodes. The capacitance change is inversely proportional to the FP cavity length. This capacitance is used in the closed-loop feedback system to adjust the driving voltage generating the electrostatic force by monitoring the change in the capacitance value, canceling the interference of factors such as environmental temperature and mechanical deformation, thereby precisely controlling the FP cavity length and maintaining the stable spectral performance of the filter.
[0017] The top silicon 101 of the fixed mirror and the movable mirror 201 are firmly bonded through the silicon-silicon dioxide low-temperature direct bonding process. This bonding adheres by hydrogen bond adsorption at room temperature and then forms stable Si-O-Si covalent bonds after annealing at 300°C. The bonding interface is composed of the silicon / silicon dioxide material with very stable mechanical properties, and has extremely small geometric deformation after non-pressure fitting and annealing at 300°C. In contrast, gold-gold bonding, organic glue bonding, etc. need to introduce a metal or organic glue intermediate layer. Under certain bonding temperatures and pressures, the metal and organic glue materials are compressed and undergo uncontrollable deformation, resulting in an uncontrollable offset between the FP cavity length and the designed value, and the filter spectral range of the MEMS-FP filter chip cannot be accurately controlled accordingly.
Claims
1. A MEMS Fabry - Perot filter chip based on direct wafer bonding, characterized in that It includes the following components: Fixed mirror structure: A first shallow cavity (104) is formed in the middle of the top silicon layer (101) of the SOI wafer. A second shallow cavity (106) reaching the substrate silicon (103) is further formed downward in the middle of the first shallow cavity (104). A low-resistance silicon electrode (105) is formed between the top silicon layer (101) in the part of the first shallow cavity (104) and the buried oxide layer (102). A high-reflection film (107) is formed on the substrate silicon (103) in the middle of the second shallow cavity (106). An antireflection film (110) is formed on the back of the substrate silicon (103). A first pad (108) is formed on the surface of the top silicon layer (101). A second pad (109) is formed on the surface of the substrate silicon (103). Movable mirror structure: A deep cavity (204) is formed in the middle of the single-crystalline bulk silicon (201). A cantilever beam (205) is formed in the deep cavity. An antireflection film (207) is formed on the single-crystalline bulk silicon (201) at the central position connected to the cantilever beam (205). A high-reflection film (203) is formed under the single-crystalline bulk silicon (201) at the central position connected to the cantilever beam (205). A third pad (206) is formed on the single-crystalline bulk silicon (201) connected to the periphery of the cantilever beam (205). An annular silicon dioxide layer (202) is formed under the single-crystalline bulk silicon (201), which surrounds the deep cavity (204) and the cantilever beam (205). The movable mirror and the fixed mirror are bonded by silicon-silicon dioxide bonding through the top silicon layer (101) and the annular silicon dioxide layer (202). The bonded annular silicon dioxide layer (202) insulates the single-crystalline bulk silicon (201) from the low-resistance silicon electrode (105) to form a parallel-plate capacitor. At the same time, the single-crystalline bulk silicon (201) is insulated from the SOI wafer substrate silicon (103) to form a detection feedback capacitor.