Electrochemical Processing Technology Of Terahertz Rectangular Waveguide Micro-cavity

Terahertz wave which can be well applied in many fields such as medicine,life sciences,astronomy,mobile communication,military and security detection has the characteristics of high penetration,low energy,high signal-to-noise ratio,coherence and broadband.Terahertz waveguides are very important components for transmitting terahertz waves.Conventionally rectangular waveguide cavities can be processed by micro-milling,multi-layer metal stacking and photolithography.However,it is hard to process those cavities with finer size and higher precision requirements through these processing methods.The core mold with high dimensional accuracy and surface roughness can be manufactured by Micro-electrochemical machining technology which can remove materials in the form of ions.Microelectroplating and micro-electroforming technologies possess high replication precision and can completely replicate the shape of the core mold and its surface topography.In view of the characteristics of fine dimension and the very high surface roughness of terahertz rectangular waveguide micro-cavity,the waveguide cavity is fabricated by micro-electrochemical machining technology.The main research contents are listed as follows:(1)The process of electroplating gold on the surface of nickel core mold was studied.The effects of machining parameters,including current density,anode-cathode spacing,plating temperature and the speed of cathode,on the surface morphology,surface roughness,uniformity and micro-hardness of the gold plating layer were researched.(2)The process of electroforming copper on the surface of gold plating layer was explored.The effects of electrolyte formula and current density on the surface morphology,surface roughness and micro hardness of the copper plating layer were studied.(3)The selective dissolution of the waveguide cavity was studied by using optimized process conditions after investigating the dissolution effects of nickel and copper in the etchant TFG.It is found that in an open environment,the etchant TFG has a large selectivity ratio to nickel and copper,and copper is hardly corroded.However,the waveguide cavity has a fine size and the ratio of depth to width is very large,so it is difficult to exchange etchants inside the cavity.After the nickel in the cavity is completely etched away,the outer copper layer has also been substantially completely dissolved.What is left is a pure gold cavity.(4)The cavity after selective dissolution is further processed and a copper layer is electroformed on the outside of the pure gold terahertz waveguide micro-cavity to complete the preparation of the cavity.