Silicon-based photonic crystal zipper cavity optical-mechanical accelerometer chip and preparation method and application thereof

Abstract

The invention relates to the technical field of chips, in particular to a silicon-based photonic crystal zipper cavity optical-mechanical accelerometer chip and a preparation method thereof. The chip provided by the invention comprises a silicon substrate, a fixed block, two supporting beams, a mass block and a photonic crystal zipper cavity, the two supporting beams are symmetrically connected to the silicon substrate, a certain interval is formed between the two supporting beams, and the mass blocks are arranged at the tops of the supporting beams and are suspended relative to the silicon substrate; the fixing block is located on the outer side of one supporting beam and fixedly connected to the silicon substrate; the photonic crystal zipper cavity comprises a first zipper cavity and a second zipper cavity, the first zipper cavity and the second zipper cavity are formed by etching a row of air holes in the silicon substrate respectively, the first zipper cavity is fixedly connected to the fixing block, and the second zipper cavity is located above the mass block; after the mass block is driven, the second zipper cavity located above the mass block can synchronously move along with the mass block. The chip structure provided by the invention can enable the chip to have higher resolution.

Description

Technical Field

[0001] The present invention relates to the field of chip technology, and in particular to a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip and a preparation method and application thereof. Background Art

[0002] Accelerometers are widely used in aerospace, industrial automation, robotics, drones, automobiles, consumer electronics, earthquake recording and other military and civilian fields. There are many accelerometers with different working principles, including piezoresistive, capacitive, resonant, tunneling, optical, etc.

[0003] Traditional piezoresistive and capacitive types use the pressure or displacement caused by external acceleration, and convert it into changes in electrical parameters through structural design to achieve the measurement of acceleration. Its structure is simple and its manufacturing process is mature, but its sensitivity is not high. The resonant accelerometer displacement characterizes the acceleration by detecting the change in resonant frequency caused by acceleration. It has high sensitivity, but the circuit design is relatively complex. The tunneling accelerometer detects acceleration by detecting the tunnel current. It can achieve high precision, but the processing technology is complex. The optical accelerometer uses a system that combines optical devices and mechanical oscillators to characterize and detect changes in acceleration with optical parameters. It has the advantages of high precision and anti-electromagnetic interference, but it also has disadvantages such as poor temperature stability and difficult processing.

[0004] The mechanical oscillators in the cavity optomechanical structure are sensitive to weak forces / displacements in the mechanical oscillation mode, so the cavity optomechanical structure has developed rapidly in the field of high-precision sensing. Through the linearized and nonlinear optomechanical interactions in the cavity optomechanical structure, quantum physics is connected with classical physics, and special physical phenomena such as light springs, quantum ground state cooling, quantum entanglement, slow light generation and quantum state transfer have emerged, which have important scientific research significance in both fields. Using these unique characteristics, the accelerometer of the cavity optomechanical structure can achieve an extremely low noise level, which can theoretically reach the standard quantum noise limit. At the same time, the cavity optomechanical structure can also be integrated to realize an accelerometer with a micro-optomechanical structure.

[0005] In view of the deficiencies in the prior art, there is an urgent need for an accelerometer chip with high sensitivity and simple manufacturing process. Summary of the invention

[0006] The purpose of the present invention is to propose a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip and a preparation method thereof. The chip adopts a cavity optomechanical sensing structure and can combine a mechanical resonator and a high-quality factor optical resonant cavity to enable the chip to have a higher resolution.

[0007] To this end, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip in an optional embodiment, characterized in that it includes a silicon substrate, a fixed block, two support beams, a mass block and a photonic crystal zipper cavity;

[0009] The two support beams are symmetrically connected to the silicon substrate with a certain interval between them, and the mass block is arranged on the top of the support beam so that the mass block is suspended relative to the silicon substrate;

[0010] The fixing block is located outside one of the supporting beams and is fixedly connected to the silicon substrate;

[0011] The photonic crystal zipper cavity comprises a first zipper cavity and a second zipper cavity, the first zipper cavity and the second zipper cavity are respectively formed by etching a row of air holes on a silicon substrate, the first zipper cavity is fixedly connected to the fixed block, and the second zipper cavity is located above the mass block, and the two are adjacent to each other and arranged in parallel;

[0012] When the mass block is driven, the second zipper cavity located above the mass block will move synchronously with the mass block.

[0013] Preferably, the fixing block, the two supporting beams, the mass block and the photonic crystal zipper cavity are all made of silicon dioxide.

[0014] Preferably, a plurality of small holes are provided on the mass block.

[0015] Preferably, the height of the fixing block is higher than the height of the supporting beam, and the first zipper cavity and the second zipper cavity of the photonic crystal zipper cavity are flush.

[0016] Preferably, a silicon dioxide layer is disposed below the silicon substrate, and a silicon bottom layer is disposed below the silicon dioxide layer.

[0017] In a second aspect, the present invention provides, in an optional embodiment, a method for preparing a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip, comprising the following steps:

[0018] S1: Spin-coating an electron beam resist on the silicon top surface of the SOI wafer including a silicon top layer, a silicon dioxide layer and a silicon bottom layer, and after drying, writing the designed chip layout onto the electron beam resist through an electron beam exposure system, and exposing the electron beam resist;

[0019] S2: After the exposure is completed, the chip is developed, cleaned, and dry-etched to etch out the chip structure. Then the electron beam glue on the chip is cleaned off, and the chip is cleaned and dried. Finally, part of the silicon dioxide layer under the mass block is corroded to release the mass block to obtain a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip.

[0020] Preferably, in step S1, the thickness of the electron beam resist layer formed by the electron beam resist on the surface of the SOI wafer is 180-220nm, preferably 200nm, the rotation speed of the spin coating is 3800-4200rpm, preferably 4000rpm, the temperature of the drying is 150-200℃, preferably 180℃, and the time is 1-3min, preferably 2min. The method of writing the designed chip layout onto the electron beam resist through the electron beam exposure system includes: designing the layout of the chip through electronic design automation software, then calibrating the write field of the electron beam exposure system, and then completing the focusing operation on the chip, and finally setting the exposure dose and exposure position, writing the pattern, and causing the electron beam resist to have an exposure reaction.

[0021] In the present invention, the electron beam resist is polymethyl methacrylate, for example: can be 950PMMAA4 electron beam resist or 950PMMAA2 electron beam resist. The surface spin-coating electron beam resist of SOI wafer is to place the chip on a vacuum chuck, and the suction of the chuck is used to fix the chip to prevent the chip from moving during the spin coating process, and then a few drops of electron beam resist are dripped on the chip surface, and under the high-speed rotation of 4000rpm, the electron beam resist is evenly spread on the chip surface under the action of centrifugal force to form a resist layer with a relatively uniform thickness. The purpose of drying is to remove the solvent in the resist, make the resist film more compact and stable, and enhance the adhesion between the resist and the wafer.

[0022] In the present invention, the writing field of the electron beam exposure system is calibrated to ensure the accuracy of the exposure position and size. The focusing operation is completed on the chip so that the electron beam can be accurately focused on the surface of the electron beam resist to form a clear exposure pattern. In addition, the exposure dose and exposure position are determined by the above-mentioned chip structure. The writing of the pattern is to make the electron beam scan on the electron beam resist according to the set layout.

[0023] Preferably, in step S2, the developer used in the development is a mixed solution of isopropyl alcohol and methyl isobutyl ketone, and the volume ratio of isopropyl alcohol to methyl isobutyl ketone is 3:1. The system used for dry etching is an ICP etching system, in which the etching gases used are SF6 and C4F8; the corrosive agent used to etch part of the silicon dioxide layer under the mass block is HF gas. The solvent used to clean the electron beam glue on the chip is selected from one or more of acetone and ethanol; the solvent used to clean the chip is selected from one or more of isopropyl alcohol and ethanol.

[0024] In the present invention, the electron beam resist in the exposed area will dissolve under the action of the developer, thereby revealing the pattern produced by the exposure. The cleaning is to rinse with deionized water for 30 seconds to remove the residual developer on the chip surface to prevent the developer from affecting the subsequent processes.

[0025] In the present invention, an ICP etching system is used for dry etching. During the etching process, SF6 gas is used as the main etching gas. When SF6 gas molecules enter the plasma environment, they are ionized and split into SF x and F y Under the action of bias voltage, these ions etch the silicon surface by physical grinding, forming a vertical sidewall etching effect. y Ions will isotropically chemically etch silicon nitride. To avoid this, C4F8 gas is used at the same time. After ionization, C4F8 gas splits into CF2, C2, and C3. CF2 will cross-link to form long polytetrafluoroethylene-like polymer chains. These polymer chains will attach to the etched sidewalls and protect the sidewalls from F y Chemical etching of ions produces smooth vertical sidewall etching to obtain an ideal chip structure.

[0026] In a third aspect, the present invention provides, in an optional embodiment, an application of the above-mentioned silicon-based photonic crystal zipper cavity optomechanical accelerometer chip in detecting acceleration resolution.

[0027] Preferably, the application includes: placing a tapered optical fiber above and parallel to the photonic crystal zipper cavity of the silicon-based photonic crystal zipper cavity optomechanical accelerometer core, coupling test light from one end of the tapered optical fiber into the tapered optical fiber, receiving emitted test light at the other end of the tapered optical fiber, the wavelength of the test light being close to the resonant wavelength of the photonic crystal zipper cavity, and calculating the resolution of acceleration based on the resonant frequency of the emitted test light; and the diameter of the tapered optical fiber at both ends is larger than the diameter of the middle portion.

[0028] Specifically, the method for detecting acceleration resolution of the silicon-based photonic crystal zipper cavity optical mechanical accelerometer chip of the present invention is:

[0029] A tapered optical fiber is placed above the photonic crystal zipper cavity of the silicon-based photonic crystal zipper cavity optomechanical accelerometer core. The diameter of the two ends of the tapered optical fiber is larger than that of the middle part. When the external acceleration changes, the mass block controlled by the support beam generates a corresponding resonant mechanical mode. Light is coupled from one end of the tapered optical fiber into the photonic crystal zipper cavity. The laser output is adjusted to be near the resonant wavelength of the optical resonant mode. The resonance generated by the mass block drives the change of the spacing of the photonic crystal microcavity, thereby generating a change in the optical mode. An optical detector is used to detect the light coupled from the other end of the tapered optical fiber. The generated electrical signal is connected to an oscilloscope and a spectrum analyzer. The optical resonant frequency and the quality factor of the mass block can be calculated by scanning the laser wavelength according to the oscilloscope waveform. The resonant frequency of the mass block can be obtained by spectrum analysis of the optical resonant frequency. A curve of the mechanical frequency change corresponding to the change of the laser wavelength is plotted. The corresponding acceleration resolution can be analyzed and calculated by formula (1).

[0030]

[0031] Among them, k B is the Boltzmann constant, T is the temperature, ω m is the resonant frequency of the mass block, m is the weight of the mass block, Q m is the quality factor of the mass block.

[0032] Compared with the prior art, the present invention has one of the following beneficial effects:

[0033] 1. The chip provided by the present invention adopts a cavity photoforce sensing structure, which can combine a mechanical resonator and a high-quality factor optical resonant cavity, so that the chip has a higher resolution.

[0034] 2. The chip manufacturing method provided by the present invention is compatible with the CMOS process, and the photolithography and etching processes used in the overall chip manufacturing process have been widely used in the micro-nano manufacturing process of industrial chip production.

[0035] 3. The chip provided by the present invention has a simple overall structure, the main material is only composed of silicon, the cost is low, and the manufacturing process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The advantages of the above and / or additional aspects of the present application will become apparent and easily understood in the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 1 is a schematic diagram of the top view of the structure of the silicon-based photonic crystal zipper cavity optomechanical accelerometer chip in Example 1 of the present invention;

[0038] Figure 2 is a schematic diagram of the three-dimensional structure of the photonic crystal zipper cavity in Example 1 of the present invention;

[0039] Figure 3 is a schematic side view of the structure of the overall chip device in Embodiment 2 of the present invention;

[0040] Figure 4 It is a schematic diagram of the process of preparing a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip in Example 2 of the present invention.

[0041] Among them, 1-silicon substrate; 2-fixed block; 3-support beam; 4-mass block; 5-photonic crystal zipper cavity; 6-accelerometer structure; 7-silicon top layer; 8-silicon dioxide layer; 9-silicon bottom layer. DETAILED DESCRIPTION

[0042] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0043] In the following description, many specific details are elaborated to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present application is not limited to the specific embodiments disclosed below.

[0044] The technical solution of the present invention will be described in detail below in conjunction with embodiments and drawings.

[0045] Example 1

[0046] See also Figure 1 , this embodiment provides a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip, including a silicon substrate, a fixed block, a support beam, a mass block and a photonic crystal zipper cavity;

[0047] Two support beams are symmetrically connected to the silicon substrate with a certain distance between them, and a mass block is arranged on the top of the support beam so that the mass block is suspended relative to the silicon substrate;

[0048] The fixed block is located outside a support beam and is fixedly connected to the silicon substrate;

[0049] The photonic crystal zipper cavity comprises a first zipper cavity and a second zipper cavity, the first zipper cavity and the second zipper cavity are respectively formed by etching a row of air holes on a silicon substrate, the first zipper cavity is fixedly connected to the fixed block, and the second zipper cavity is located above the mass block, and the two are adjacent to each other and arranged in parallel;

[0050] When the mass block is driven, the second zipper cavity located above the mass block will move synchronously with the mass block.

[0051] The materials of the fixed block, two supporting beams, the mass block and the photonic crystal zipper cavity are all silicon dioxide.

[0052] As another implementation of this embodiment, a plurality of small holes are provided on the mass block.

[0053] As another implementation of this embodiment, the height of the fixing block is higher than the height of the supporting beam, and the first zipper cavity and the second zipper cavity of the photonic crystal zipper cavity are flush.

[0054] As another implementation of this embodiment, a silicon dioxide layer is disposed below the silicon substrate, and a silicon bottom layer is disposed below the silicon dioxide layer.

[0055] Example 2

[0056] See also Figure 4 This embodiment provides a method for preparing a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip, comprising the following steps:

[0057] S1: Spin-coating electron beam resist step, placing the SOI wafer on a vacuum chuck, dropping PMMA (950PMMAA4) on the silicon top surface of the SOI wafer, and then spin-coating at a speed of about 4000 rpm, and post-baking at a temperature of 180°C for two minutes to form a 200 nm thick electron beam resist layer on the SOI wafer;

[0058] S2: Electron beam exposure step, the chip layout is designed through electronic design automation software, and then the write field of the electron beam exposure system is calibrated, and then the focusing operation is completed on the chip. Finally, the exposure dose and exposure position are set, and the pattern is written to make the electron beam resist react to exposure.

[0059] S3: Development step: After the exposure, the chip was gently shaken in a PMMA developer solution (IPA and MIBK volume ratio of 3:1) for 45 seconds, then rinsed with deionized water for 30 seconds, and the surface moisture was blown dry;

[0060] S4: Dry etching step, using ICP etching system to dry etch the developed chip to etch out the chip structure, wherein SF6 gas molecules are used to etch silicon, and the ionized SF6 molecules are split into SF x and F y , through the bias voltage, they physically grind and etch the surface, and at the same time, C4F8 gas is used. The ionized C4F8 splits into CF2, C2 and C3. CF2 cross-links to form long polytetrafluoroethylene-like polymer chains to protect the etched sidewalls from chemical reactions, thereby producing smooth vertical sidewall etching;

[0061] S5: Cleaning and characterization step. After dry etching, use acetone to clean the remaining electron beam glue, and then use isopropanol and ethanol to clean the chip, see Figure 3 And use step profiler and SEM to characterize the relevant parameters of the chip after etching;

[0062] S6: Etching release step, introducing HF gas to etch away part of the silicon dioxide layer under the mass block, releasing the mass block, and releasing the mass block so that the mass block can vibrate under driving.

[0063] Application examples:

[0064] The chip of the present invention can be applied to detecting acceleration resolution.

[0065] Specifically:

[0066] A tapered optical fiber is placed above the photonic crystal zipper cavity of the silicon-based photonic crystal zipper cavity optomechanical accelerometer core. The diameter of the two ends of the tapered optical fiber is larger than that of the middle part. When the external acceleration changes, the mass block controlled by the support beam generates a corresponding resonant mechanical mode. Light is coupled from one end of the tapered optical fiber into the photonic crystal zipper cavity. The laser output is adjusted to be near the resonant wavelength of the optical resonant mode. The resonance generated by the mass block drives the change of the spacing of the photonic crystal microcavity, thereby generating a change in the optical mode. An optical detector is used to detect the light coupled from the other end of the tapered optical fiber. The generated electrical signal is connected to an oscilloscope and a spectrum analyzer. The optical resonant frequency and the quality factor of the mass block can be calculated by scanning the laser wavelength according to the oscilloscope waveform. The resonant frequency of the mass block can be obtained by spectrum analysis of the optical resonant frequency. A curve of the mechanical frequency change corresponding to the change of the laser wavelength is plotted. The corresponding acceleration resolution can be analyzed and calculated by formula (1).

[0067]

[0068] Among them, k B is the Boltzmann constant, T is the temperature, ω m is the resonant frequency of the mass block, m is the weight of the mass block, Q m is the quality factor of the mass block.

[0069] Although the present application is disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and are not intended to limit the application of the present application. The scope of protection of the present application is defined by the appended claims and may include various modifications, alterations and equivalents made to the invention without departing from the scope and spirit of the present application.

Claims

1. A silicon-based photonic crystal zipper cavity optomechanical accelerometer chip, characterized in that: It includes a silicon substrate, a fixed block, two support beams, a mass block and a photonic crystal zipper cavity; The two support beams are symmetrically connected to the silicon substrate with a certain interval between them, and the mass block is arranged on the top of the support beam so that the mass block is suspended relative to the silicon substrate; The fixing block is located outside one of the supporting beams and is fixedly connected to the silicon substrate; The photonic crystal zipper cavity comprises a first zipper cavity and a second zipper cavity, the first zipper cavity and the second zipper cavity are respectively formed by etching a row of air holes on a silicon substrate, the first zipper cavity is fixedly connected to the fixed block, and the second zipper cavity is located above the mass block, and the two are adjacent to each other and arranged in parallel; When the mass block is driven, the second zipper cavity located above the mass block will move synchronously with the mass block.

2. The silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 1, characterized in that: The fixed block, the two support beams, the mass block and the photonic crystal zipper cavity are all made of silicon dioxide.

3. The silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 1, characterized in that: The mass block is provided with a plurality of small holes.

4. The silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 1, characterized in that: The height of the fixing block is higher than that of the supporting beam, and the first zipper cavity and the second zipper cavity of the photonic crystal zipper cavity are flush.

5. The silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 1, characterized in that: A silicon dioxide layer is disposed below the silicon substrate, and a silicon bottom layer is disposed below the silicon dioxide layer.

6. A method for preparing a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip, characterized in that: The following steps are involved: S1: Spin-coating an electron beam resist on the silicon top surface of the SOI wafer including a silicon top layer, a silicon dioxide layer and a silicon bottom layer, and after drying, writing the designed chip layout onto the electron beam resist through an electron beam exposure system, and exposing the electron beam resist; S2: After the exposure is completed, the chip is developed, cleaned, and dry-etched to etch out the chip structure. Then the electron beam glue on the chip is cleaned off, and the chip is cleaned and dried. Finally, part of the silicon dioxide layer under the mass block is corroded to release the mass block to obtain a silicon-based photonic crystal zipper cavity optomechanical accelerometer chip.

7. The method for preparing the silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 6, characterized in that: In step S1, the thickness of the electron beam resist layer formed on the surface of the SOI wafer is 180-220 nm, the rotation speed of the spin coating is 3800-4200 rpm, the temperature of the drying is 150-200° C., and the time is 1-3 min; The method of writing the designed chip layout onto the electron beam resist through the electron beam exposure system includes: designing the chip layout through electronic design automation software, then calibrating the writing field of the electron beam exposure system, completing the focusing operation on the chip, and finally setting the exposure dose and exposure position, writing the pattern, and causing the electron beam resist to react with exposure.

8. The method for preparing the silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 6, characterized in that: In step S2, the developer used in the development is a mixed solution of isopropyl alcohol and methyl isobutyl ketone, and the volume ratio of the isopropyl alcohol to the methyl isobutyl ketone is 3:1; The system used for dry etching is an ICP etching system, in which the etching gases used are SF6 and C4F8; The etchant used to etch the portion of the silicon dioxide layer below the proof mass is HF gas.

9. An application of the silicon-based photonic crystal zipper cavity optomechanical accelerometer chip according to claim 1 in detecting acceleration resolution.

10. The use according to claim 9, characterized in that: The application includes: placing a tapered optical fiber above and in parallel with the photonic crystal zipper cavity of the silicon-based photonic crystal zipper cavity optical mechanical accelerometer core, coupling test light from one end of the tapered optical fiber into the tapered optical fiber, receiving emitted test light at the other end of the tapered optical fiber, the wavelength of the test light being close to the resonant wavelength of the photonic crystal zipper cavity, and calculating the resolution of acceleration based on the resonant frequency of the emitted test light; The diameters of the two end portions of the tapered optical fiber are greater than the diameter of the middle portion.

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