Study On THz Grating Device Micromachining Based On Finite Element Analysis

THz vacuum electronic circuits require submillimeter features of a few microns to a few hundred microns, which pose significant challenges for conventional microstructuring techniques due to tool size and fabrication tolerance requirements. In addition, conventional thermal and mechanical machining approaches has difficulty in achieving nanoscale smoothness on the circuit surface, which is critical for terahertz device operation. UV-LIGA, as a new kind of microstructuring techniques meeting the THz processing requirements, is quickly gaining interest for advancement of THz vacuum electronic devices. However, the stress in SU-8 photoresist layer and dimensional precision of electroforming are the primary obstacles confronted by UV-LIGA technique. To solve the problems during UV-LIGA, works in this paper carried out research on process of the THz grating structure based on finite element analysis.Firstly, an improved spinning chuck was fabricated to improve flatness of SU-8 photoresist layer. The process of THz grating structure was studied using finite element analysis (FEA), and the influence of cooling rate on the stress is much more than that of film thickness and PEB temperature, and the stress drops slightly when the cooling rate is lower than 6°C/h. The optimization experiment has been carried out according to the simulation results and the phenomenon concerning the stress disappears, which proves the validity of the simulation method and results.Secondly, the theory of electrodeposition and the electric field of electroforming process were reviewed. The distribution of fluid velocity and current density around the grating were simulated based on finite element analysis. It was shown that a certain flow will improve the uniform distribution of the flow velocity, and the non-conducting shied can improve the uniform distribution of current density. Experimental results were consistent with the theoretical prediction. Finally, the parameters of the grating such as width, groove depth, surface roughness and sidewall profile were examined. The influence of microfabrication process errors including the depth, sidewall profile and surface roughness on the high frequency characteristics of wave guide are analyzed.