Research About On-chip GaN Beam Optomechanical Accelerometer

With the increasing demand for high-performance inertial sensors,the performance of Micro Electro-Mechanical System(MEMS)devices is limited.However,Micro-Optical ElectroMechanical System(MOEMS)accelerometers represented by optical microcavities use the optical readout method and are not affected by electromagnetic interference.In terms of resolution,it has been proven to be superior to other types of accelerometers.At present,the light source and the sensing components of MOEMS accelerometer are separated,so it is difficult to realize highdensity optoelectronic integration.As the third generation of semiconductor material,GaN has a wide band gap and good mechanical,piezoelectric and optoelectronic properties.In addition,GaN has the characteristics of acid resistance,alkali resistance and high-temperature resistance,which makes it suitable for various extreme environments.In this dissertation,a GaN beam accelerometer is proposed.Its working mechanism is that when the GaN beam structure is under acceleration load,due to the quantum-confined stark effect(QCSE),the beam’s luminous center wavelength will change,so there is a corresponding relationship between the acceleration and the luminous wavelength shift.Consequently,the acceleration can be sensed through the change of peak wavelength.The research of this dissertation is mainly divided into the following three aspects:1.An optically pumped GaN beam accelerometer is designed and fabricated.GaN beam optomechanical accelerometers with different structures are fabricated by photolithography,dry etching of GaN and wet etching of Si,and the structures are characterized by SEM to optimize the process parameters.2.The optical properties of optically pumped beam accelerometers are investigated.In order to quantitatively study the optical properties of the accelerometer,the laser spectra of four GaN beam accelerometers with the same length and different widths are firstly investigated under the condition of optical pumping.With the increase of beam width,the emission spectrum gradually redshifts,and the simulation results also show the difference in the sensitivity of the four accelerometers.Secondly,the influence of beam length variation on the optical properties of the accelerometer is studied.The research shows that under the action of the gravity field,when the beam structure size increases,the bending strain of the beam increases.Due to the piezoelectric polarization effect,the maximum value of the Fabry-Perot(FP)laser oscillation and the boundary of oscillation produce redshift phenomena.At the same time,it also shows that the length of the beam can improve the sensitivity of the accelerometer.3.Based on the optically pumped GaN beam accelerometer,an electrically pumped GaN beam LED optomechanical accelerometer is designed and fabricated.Under the condition of electrical pumping,the movement of electroluminescence spectrum can directly reflect the magnitude of acceleration.To qualitatively study the optical sensing characteristics of the electrically pumped accelerometer,two different beam structures(with and without sensitive masses)are designed.The study reveals that with the increase of injection current,the screening of the built-in electric field leads to the reduction of the QCSE,showing a blue shift of the EL spectrum.Moreover,the blueshift phenomenon of the accelerometer with an extra mass block in the beam structure is more obvious and the sensitivity is higher.The uniqueness of the beam accelerometer proposed in this dissertation is that the lightemitting and sensing components are combined into one,and the electrically pumped GaN beam LED accelerometer can realize the miniaturization of the device through on-chip integration.Furthermore,due to the good mechanical properties of GaN,high sensitivity and large range testing can be achieved at the same time,so this structure has a good application prospect in the navigation field(such as micro aircraft,and small intelligent missile).