T-shaped gate based on poly Si/polyimide supported layers

A novel poly Si/polyimide dielectric bilayer system was designed to form a T-shaped gate on GaAs substrate using a two-step direct writing electron-beam lithography in combination with a selective reactive ion etching technique. Excellent breakdown properties and thermal stability of the supported polyimide layer were found also to be used for passivation of GaAs based T-shaped gate HFETs.