Quantum limited stark effect based heterodyne optical microelectromechanical accelerometer and preparation method thereof

Abstract

The application discloses a kind of based on quantum limit stark effect heterodyne optical mechanical-electrical microcavity accelerometer, and the accelerometer takes silicon-based nitride epitaxial sheet as carrier, including from bottom to top sequentially arranged silicon substrate layer, aluminum nitride layer, u-shaped gallium nitride layer, n-type gallium nitride layer, quantum well layer, p-type gallium nitride layer, SiO2Layer, p-type electrode being arranged on the p-type gallium nitride layer, n-type electrode being arranged in the edge of the n-type gallium nitride layer.The nitride material on the silicon substrate utilizes photoetching and ICP etching process to prepare two LDs in two regions of a beam.Due to the difference of stress, the peak center of two LDs will have frequency difference.Under the condition of energization, acceleration load frequency difference will change, and due to the change of frequency difference, the size of acceleration can be more stably and accurately perceived.

Description

Technical Field

[0001] This invention belongs to the fields of quantum electronics and opto-mechatronics, and particularly relates to a quantum-confined Stark effect heterodyne opto-mechatronics microcavity accelerometer and its fabrication method. Background Technology

[0002] Traditional optical accelerometers are mostly obtained by integrating silicon materials with external light sources, which makes it difficult to achieve high-density optoelectronic integration, and the sensitivity, stability, and measurement range of the devices need to be improved. To address these issues, this project proposes to design a dual-laser system on an electrically pumped InGaN quantum well beam to construct an opto-mechatronic microcavity accelerometer. Under acceleration load, the piezoelectric polarization field induced by the mechanical strain of the beam induces the quantum confinement Stark effect in the quantum well, causing a shift in the laser beat frequency of the electrically pumped beam laser. The magnitude of acceleration is sensed through this beat frequency change. This project will investigate the mechanism of the laser mode shift of the beam laser under the above multi-physics field mechanism, establish a quantitative relationship model between acceleration and spectral beat frequency shift, explore the dynamics of the bandgap change in the InGaN quantum well under a piezoelectric polarization field, and investigate the coupling sensing mechanism between the mechanical strain of the beam opto-mechatronic microcavity and the optical and electric fields. The following technical problems currently exist:

[0003] 1. The design of a beam in the overall accelerometer must take into account the influence of beam length on light emission, the realization of the quantum-confined Stark effect, and the feasibility of implementation in actual manufacturing.

[0004] 2. When wiring components, ensure that the wiring location does not affect the normal operation of the components.

[0005] 3. Integrating a light source and a sensor into the same microcavity structure is a complex task, especially when it comes to the photoelectric and mechanical properties of materials. It is necessary to consider that the performance of the light source and the sensor may affect each other.

[0006] 4. Although opto-mechatronics design may improve the integration of accelerometers, miniaturization may encounter problems such as mutual interference between devices and excessive power consumption. Summary of the Invention

[0007] To address the aforementioned issues, this invention discloses a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer. It utilizes the optical, electrical, and mechanical properties of InGaN quantum well material to overlap the optical microcavity region, stress-sensitive region, and electroluminescent region of the beam, integrating the light source and sensing component into one unit. This breaks the limitation of traditional optical accelerometers where the light source and sensing component are separate, and is expected to achieve high sensitivity, high resolution, high stability, and a large acceleration detection range.

[0008] A quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer uses a silicon-based nitride epitaxial wafer as a carrier. The wafer comprises, from bottom to top, a silicon substrate layer, an aluminum nitride layer, a u-type gallium nitride layer, an n-type gallium nitride layer, a quantum well layer, a p-type gallium nitride layer, a SiO2 layer, a p-type electrode disposed on the p-type gallium nitride layer, and an n-type electrode disposed at the edge of the n-type gallium nitride layer. The entire silicon substrate layer is etched away, leaving only the portion below the square disk and beam, exposing the shape of the beam and square disk. The n-type electrode is disposed on the exposed n-type gallium nitride layer.

[0009] This accelerometer is a rectangular cavity connected by a beam in the middle. Two square blocks on both sides of the beam are hollowed out. The beam in the middle and a square electrode form a p-type electrode. At the same time, a SiO2 layer is deposited on the two square blocks except for the middle half and about one-quarter of the beam. The p-type electrode is deposited on the upper surface of the SiO2 layer on the middle beam. The n-type electrode is deposited on the n-type gallium nitride layer on the other side as a square electrode.

[0010] Furthermore, in the accelerometer of this invention, the beam undergoes deformation under static gravity. The piezoelectric polarization field caused by this deformation induces the quantum confinement Stark effect in the indium gallium nitride quantum well material. Due to the different stresses, there will be a frequency difference between the peak centers of the two LDs. When energized, the acceleration load frequency difference will change. Due to the change in frequency difference, the magnitude of acceleration can be sensed more stably and accurately.

[0011] This invention utilizes optical lithography and ICP etching processes, along with a wet etching process using a mixture of hydrofluoric acid and dilute nitric acid, to fabricate a beam. The invention incorporates a well-designed process, including the shape of the etching template, to obtain a single beam with smooth edges and columnar support.

[0012] The present invention provides a method for fabricating a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer, comprising the following steps:

[0013] Step 1: Spin-coat photoresist onto the p-type gallium nitride surface of the silicon-based gallium nitride epitaxial wafer, and then use optical lithography to define a pattern of two square disks connected by a beam on the spin-coated photoresist layer;

[0014] Step 2: Electron beam evaporation is used to deposit 300-500nm thick nickel on the surface of the defined pattern. Then, the wafer is placed in an acetone solution for ultrasonic treatment, followed by cleaning in ultrapure water, and then cleaning in anhydrous ethanol and ultrapure water in sequence. Finally, residual photoresist is removed to obtain a nickel mask pattern.

[0015] Step 3: ICP etching technology is used to etch down 2μm-2.5μm to the n-type gallium nitride layer, thereby transferring the pattern defined in the first step to the n-type gallium nitride layer of the silicon-based nitride wafer, to obtain the structure of a beam of the accelerometer;

[0016] Step 4: Remove metallic nickel with dilute nitric acid, then immediately rinse thoroughly with ultrapure water;

[0017] Step 5: Deposit a SiO2 layer on one beam of the accelerometer, but do not deposit a SiO2 layer on the two small squares in the middle and quarter of the beam.

[0018] Step 6: Spin-coat photoresist onto one beam and the surrounding square surface of the accelerometer to ensure that the beam structure and the surrounding area will not be etched away during the etching process, thus providing protection.

[0019] Step 7: Electron beam evaporation is used to deposit a 300-500nm thick layer of metallic nickel on the defined pattern surface. Then, the epitaxial wafer is placed in an acetone solution for ultrasonic cleaning, followed by cleaning in anhydrous ethanol and ultrapure water. Finally, the residual photoresist is removed to obtain a mask pattern of nickel.

[0020] Step 8: Using ICP etching technology, the pattern is etched downwards until the center is hollowed out;

[0021] Step 9: Electron beam evaporation is used to deposit a positive electrode on the surface of the p-type electrode pattern and a negative electrode on the surface of the n-type electrode pattern, so that positive and negative electrodes are deposited on the p-type gallium nitride layer and the n-type gallium nitride layer respectively. Finally, the residual photoresist is removed to obtain the p-type electrode and the n-type electrode.

[0022] Step 10: Wet etching of silicon is performed using a mixture of hydrofluoric acid and dilute nitric acid until the bottom of the silicon substrate is reached, forming silicon pillars and a bottom surface that support this structure in the silicon substrate, thus creating a suspended beam structure.

[0023] Furthermore, in the method of the present invention, both the positive electrode and the negative electrode are Au / Ni vapor-deposited.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] 1. This invention uses a single epitaxial wafer, eliminating the need to grow different materials, resulting in a simple structure, small size, and easy integration. Compared to current optical accelerometers made with passive materials such as Si and SiN, it offers advantages such as miniaturization, low cost, high sensitivity, resistance to electromagnetic interference, and shock resistance. 2. This project plans to design dual lasers on an electrically pumped InGaN quantum well beam to construct an opto-mechatronic microcavity accelerometer. Under acceleration load, the piezoelectric polarization field caused by the mechanical strain of the beam induces the quantum confinement Stark effect in the quantum well, causing a shift in the laser beat frequency of the electrically pumped beam laser. The magnitude of acceleration is sensed through this beat frequency change. Attached Figure Description

[0026] Figure 1 Side view of an indium gallium nitride quantum well opto-electro-mechanical microcavity accelerometer based on the quantum-confined Stark effect.

[0027] Figure 2 Top view of an indium gallium nitride quantum well opto-electro-mechanical microcavity accelerometer based on the quantum confinement Stark effect.

[0028] Figure 3 Flowchart of the fabrication process for an indium gallium nitride quantum well opto-electro-mechanical microcavity accelerometer based on the quantum confinement Stark effect.

[0029] Figure 4 Stress distribution on the surface of the accelerometer under net gravitational field.

[0030] Figure 5 Displacement and deformation of the intermediate beam of the accelerometer under net gravitational field.

[0031] The figure shows: 1-silicon substrate, 2-aluminum nitride layer, 3-u-type gallium nitride, 4-n-type gallium nitride layer, 5-quantum well layer, 6-p-type gallium nitride layer, 7-SiO2 layer, 8-p-type electrode, 9-n-type electrode, 10-stress-sensitive region; 11-beam. Detailed Implementation

[0032] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, and the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively. Example

[0033] like Figure 1-2As shown, this embodiment uses a silicon-based nitride epitaxial wafer as a carrier. From bottom to top, the layers are: a silicon substrate layer 1, an aluminum nitride layer 2, a u-type gallium nitride layer 3, an n-type gallium nitride layer 4, a quantum hydrazine layer 5, a p-type gallium nitride layer 6, a SiO2 layer 7, a p-type electrode 8 disposed on the p-type gallium nitride layer 6, and a square n-type electrode 9 disposed at the edge of the n-type gallium nitride layer 4. The entire silicon substrate layer is etched away, leaving only the central beam and the area below the perimeter of the accelerometer. The n-type electrodes are disposed on the exposed sides of the n-type gallium nitride layer. The accelerometer features a beam with a mass block located between two square disks. The beam width is 20 μm. The p-type electrode, covering the p-type gallium nitride layer, consists of a beam and a square electrode. The beam is 300 μm long, and the square electrode is 30 μm long and 20 μm wide. The electrode thickness is 120 nm.

[0034] like Figure 3 As shown in the figure, the method for fabricating a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer based on this embodiment, taking the fabrication of a square disk with a side length of 30 μm, a width of 20 μm, and a beam length of 300 μm as an example, is as follows:

[0035] Step 1: Clean the purchased commercial silicon substrate gallium nitride epitaxial wafer with acetone, anhydrous ethanol and ultrapure water by ultrasonication (5 min) in sequence, and then dry it with nitrogen gas; use a spin coater to spin coat the photoresist AZ-5214 on the front side of the epitaxial wafer (the upper surface of the p-type nitride layer 5) at a speed of 4000 rpm for 40 seconds (photoresist thickness is 1.5 micrometers).

[0036] Optical lithography was used to define a pattern of two squares connected to a beam with a mass block on a spin-coated photoresist layer. The lithography machine model was MA6.

[0037] Step 2: Electron beam evaporation is used to deposit 350nm of metallic nickel on the surface of the P-type gallium nitride layer 6, and then the residual photoresist is removed.

[0038] Step 3: ICP etching technology is used to etch the nitride layer down to the n-type gallium nitride layer 4, thereby transferring the pattern defined in the first step to the n-type gallium nitride layer 3 of the silicon-based nitride epitaxial wafer, to obtain the accelerometer beam structure.

[0039] Then, the epitaxial wafer was placed in a dilute nitric acid solution to remove residual metallic nickel, and then rinsed in anhydrous ethanol and ultrapure water in sequence.

[0040] Step 4: Deposit a SiO2 layer on one of the beams in the middle of the accelerometer, but do not deposit a SiO2 layer on a small square at the end of the beam.

[0041] Step 5: Use a spin coater to spin coat the photoresist AZ-5214 on the front side of the epitaxial wafer (the surface of the beam structure and the square surfaces around it) at a speed of 4000 rpm for 40 seconds (the photoresist thickness is 1.5 micrometers).

[0042] Step 6: Electron beam evaporation is used to deposit 420nm metallic nickel on the surface of the n-type gallium nitride layer 4, and then the residual photoresist is removed.

[0043] Step 7: Using ICP etching technology, the pattern is etched downwards until the center is hollowed out;

[0044] Then, the epitaxial wafer was placed in a dilute nitric acid solution to remove residual metallic nickel, and then rinsed in anhydrous ethanol and ultrapure water in sequence.

[0045] Step 8: Wet etching of silicon using a mixture of hydrofluoric acid and dilute nitric acid is performed until the bottom of the silicon substrate, forming silicon pillars and a bottom surface to support the structure, thus suspending one beam structure of the LD. The etching gas is a mixture of HF and HNO3, and the etching time is 1 minute. Finally, residual photoresist is removed.

[0046] COMSOL Multiphysics is a multiphysics simulation platform encompassing multiple modules including fluid dynamics, electromagnetics, heat transfer, structural dynamics, chemical engineering, acoustics, and equations. By simply providing the coupling relationships between various scenarios and physical fields, the software can express these relationships. This software was used to simulate this invention.

[0047] Steady-state studies of the device under net gravity were conducted, and the stress distribution on the device surface is shown in Figures 4 and 5. The following figure illustrates the surface stress distribution of the device under steady-state studies under net gravity. It can be observed that the stress at one-quarter of the beam and in the middle of the beam is significantly greater than the stress around it.

Claims

1. A method for fabricating a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer, characterized in that, The quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer uses a silicon-based nitride epitaxial wafer as a carrier. It includes, from bottom to top, a silicon substrate layer (1), an aluminum nitride layer (2), a u-type gallium nitride layer (3), an n-type gallium nitride layer (4), a quantum well layer (5), a p-type gallium nitride layer (6), and a SiO2 layer (7). A p-type electrode (8) is disposed on the p-type gallium nitride layer (6), and an n-type electrode (9) is disposed at the edge of the n-type gallium nitride layer (4). The silicon substrate layer (1) is completely etched away around its perimeter, leaving a beam (11) in the middle and the part below the beam (11). After being powered on, the two stress-sensitive areas (10) of the beam (11) will emit laser LD; this accelerometer is a rectangular cavity connected by a beam (11) in the middle, and the two square blocks on both sides of the beam (11) will be hollowed out; the middle beam and a square electrode constitute a p-type electrode (8), and at the same time, a SiO2 layer (7) is deposited on the two square blocks except for the half-section and about one-quarter section of the beam. The p-type electrode (8) is deposited on the upper surface of the SiO2 layer (7) on the middle beam; the n-type electrode (9) is deposited on the n-type gallium nitride layer (4) on the other side as a square electrode; the specific method includes the following steps: Step 1: Spin-coat photoresist onto the p-type gallium nitride surface of the silicon-based gallium nitride epitaxial wafer, and then use optical lithography to define a pattern of two square disks connected by a beam on the spin-coated photoresist layer; Step 2: Electron beam evaporation is used to deposit 300-500nm thick nickel on the surface of the defined pattern. Then, the wafer is placed in an acetone solution for ultrasonic treatment, followed by cleaning in ultrapure water, and then cleaning in anhydrous ethanol and ultrapure water in sequence. Finally, the residual photoresist is removed to obtain a mask pattern of nickel. Step 3: ICP etching technology is used to etch down 2μm-2.5μm to the n-type gallium nitride layer (4), thereby transferring the pattern defined in the first step to the n-type gallium nitride layer (4) of the silicon-based nitride wafer, to obtain the structure of a beam of the accelerometer; Step 4: Remove metallic nickel with dilute nitric acid, then immediately rinse thoroughly with ultrapure water; Step 5: Deposit a SiO2 layer on the middle beam of the accelerometer, but do not deposit a SiO2 layer on the two small squares in the middle and quarter of the beam. Step 6: Spin-coat photoresist onto one beam and the surrounding square surface of the accelerometer to ensure that the beam structure and the surrounding area will not be etched away during the etching process, thus providing protection. Step 7: Electron beam evaporation is used to deposit a 300-500nm thick layer of metallic nickel on the defined pattern surface. Then, the epitaxial wafer is placed in an acetone solution for ultrasonic cleaning, followed by cleaning in anhydrous ethanol and ultrapure water. Finally, the residual photoresist is removed to obtain a mask pattern of nickel. Step 8: Using ICP etching technology, the pattern is etched downwards until the center is hollowed out, and finally the residual photoresist is cleaned. Step 9: Electron beam evaporation is used to deposit a positive electrode on the surface of the p-type electrode pattern and a negative electrode on the surface of the n-type electrode pattern, so that positive and negative electrodes are deposited on the p-type gallium nitride layer (6) and the n-type gallium nitride layer (4) respectively. Finally, the residual photoresist is removed to obtain the p-type electrode (8) and the n-type electrode (9). Step 10: Wet etching of silicon is performed using a mixture of hydrofluoric acid and dilute nitric acid until the bottom of the silicon substrate (1) is reached, so that silicon pillars and bottom surfaces supporting this structure are formed in the silicon substrate (1), forming a suspended beam structure.

2. The method for fabricating a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer according to claim 1, characterized in that, Both the positive and negative electrodes are vapor-deposited Au / Ni.

3. The method for fabricating a quantum-confined Stark effect heterodyne opto-electro-mechanical microcavity accelerometer according to claim 1, characterized in that: Because the stresses in the two stress-sensitive areas (10) of the beam are different, there will be a frequency difference between the peak centers of the two LDs; when energized, the frequency difference of the acceleration load will change.

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