Research On Tuning Characteristics Of MEMS Based On Tunable Vertical Cavity Surface Emitting Laser

The Vertical-cavity surface-emitting laser?VCSEL?is firstly proposed by Professor Kenichi Iga of Tokyo Institute of Technology in Japan in 1977.Its light exiting direction is perpendicular to the substrate.It has the advantages of being able to test in the chip,low threshold current,easy integration,small divergence angle and high modulation rate.The main research directions of VCSEL are:wavelength integration,wavelength extension,wavelength tuning,large-scale two-dimensional array,control mode and so on.Wavelength continuous tunable VCSEL have broad application prospects in optical communication networks,computer optical interconnections,gas detection,atomic clocks,etc.due to their large tuning range and high spectral purity.This thesis focuses on the tuning characteristics of tunable VCSEL microelectromechanical systems?MEMS?,and explores the design ideas for improving device reliability and structural optimization.Based on this,device process preparation and device characterization are performed.The following are the main contents of this paper:1.A low-stress bow-tie MEMS cantilever structure was designed for the problem that the end of the MEMS cantilever structure was easily concentrated and the structure was fatigue-fractured.The structure adopted an isosceles trapezoidal design at the fixed end,which can effectively improve the force distribution of the fixed end of the cantilever structure and reduce the Mises stress at the end.The maximum Mises stress of the fixed end of GaAs-based material was reduced by 37%⁶4%compared with the iso-section structure;the maximum Mises stress of the fixed end of InP-based material was reduced by 33%⁵0%compared with the equal-section structure.A MEMS cantilever structure with a lower stress range and higher reliability with a tunable wavelength range covering the free spectral range was realized.2.The multi-physics coupling analysis software was used to break through the constraints of the original electrostatic actuation method.The methods of thermoelectric actuation and piezoelectric actuation to achieve cantilever deflection were studied,and the feasibility of improving the tuning characteristics of the device was explored.Thermoelectric actuation can achieve both continuous wavelength tuning and small wavelength thermal drift;piezoelectric actuation eliminates catastrophic damage caused by electrostatically actuated pull-in effects,providing a potentially tunable solution.3.Low stress MEMS fabrication and device characterization.The MEMS preparation cantilever with a bow-tie shape,and a double-sided alignment engraving process was performed using the designed mask.The effects of different etching conditions on etching rate,etching morphology and etching selectivity ratio were studied for the GaAs back hole deep etching process.The optimal etching conditions were obtained by optimizing the composition ratio ofgas pressure,power and Cl2/BCl3/Ar gas mixture,and the ideal etching depth and sidewall morphology were obtained.The maximum etching rate was 6.5?m/min.The SiO₂/resist double layer mask was used in the ICP dry etching process to protect the surface integrity.After the device was fabricated,the tuning bias voltage was from 0V to 3V,the wavelength of the device was shifted from 865.5nm to 854.2nm,and the tuning range was11.3nm.