| As an enabler of human-computer interaction interfaces,MEMS microphones are growing more rapidly in demand in the era of artificial intelligence and the internet of everything,which has shown their excellent ability in areas such as hearing aids,mobile electronics and automatic driving,and so on.The foreign layout in the field of MEMS microphone has been made in a long time.Although there are still gaps in domestic research,the "Fourteenth FiveYear Plan" has focused on the layout of the sensor field.Therefore,the research and design of MEMS microphones has practical significance and strategic value for improving intelligent systems.Foreign researches focus on high-performance microphones based on new principles,new materials and new structures.Compared with other structures,capacitive MEMS microphones have the flatter response and the better performance.However,the traditional capacitive MEMS microphone has some technical bottlenecks such as low sensitivity and signal-to-noise ratio in the case of small size and low power consumption,which can not meet the needs of the rapid development in practical applications.In order to solve the above problems of MEMS microphone,the research and design of the low noise capacitive MEMS microphone is carried out.The influence mechanism of different structures on the device characteristics is analyzed,and the characteristic analysis and performance characterization are carried out aiming at the traditional single-backplane capacitive MEMS microphone and the microphone structure with the double-profile backplane and the edge hole diaphragm proposed in this thesis.And the research results and rules with practical value are obtained.The main work and research results are as follows.A single-backplane capacitive microphone model is constructed by using multi-physics simulation software.The effects of diaphragm shape,air gap height,acoustic hole distribution and residual stress on the microphone characteristics are simulated.And the operation mechanism of the microphone is analyzed.The results show that the thinner diaphragm and the larger radius of polysilicon diaphragm lead to the higher mechanical sensitivity of the microphone.The circular diaphragm with the same properties has higher mechanical sensitivity and more uniform stress distribution compared to the square diaphragm.When the pressure film damping in the microphone air gap is released,both the sensitivity and the noise increase with the decrease of the air gap.The sound hole can reduce the device noise and improve the device sensitivity.The backplane sound hole can increase the flat frequency response range.And the device with the diaphragm and the backplane having sound holes can achieve better performance.The greater diaphragm stress will lead to the decrease in the microphone sensitivity and noise.The influence of stress on the reduction of sensitivity will be decreased with the increasing diaphragm radius.On this basis,the model of the double-parallel backplane microphone is constructed.The simulation results show that the performance of the double-parallel backplane microphone model(sensitivity-70.3d BV,bandwidth 200Hz～20k Hz)is close to that of the actual devices(sensitivity-70.99 d BV,bandwidth 300Hz～20k Hz),which is better than that of the singlebackplane microphone with the same structure parameters.The influence of double-parallel backplane with curve profile on the device characteristics is studied.And the microphone structure with a double-profile backplane and the edge hole diaphragm is proposed,whose the correlation between device structure and characteristics is studied.The simulation results show that the backplane profile can effectively improve the performance of the microphone.The proposed microphone with the double-profile backplane and the edge hole diaphragm microphone shows the better performance,such as sensitivity of-37.2d BV at a bias of 6V,the flat frequency response range of 20Hz～25.4k Hz,a maximum sound pressure level of higher than 120 d B SPL and a pull-in voltage of 26 V. |
PDF Full Text Request