The application of an ordered mesoporous silica film to a GaAs device

Pseudomorphic high electron mobility transistors (PHEMTs) are promising devices for use in millimeter-wave and optical communications systems due to their excellent high frequency and low-noise performances. In order to further improve the performance of these devices, their gate lengths must be reduced to the technological limit and a small gate resistance must be realized. However, shorter gates result in an increase of short channel effects that limit microwave performance. In order to reduce the gate resistance, T-shaped gates with large cross-sectional areas are required. However, the thickness and dielectric constant of the passivation layer have major impacts on the gate capacitance. In this study, an ordered mesoporous silica film was introduced as a passivation layer between T-gates. Si₃N₄ with a dielectric constant of 7.4 and ordered mesoporous silica with a dielectric constant of 2.48 were used as passivation layers. The Si₃N ₄ dielectric layer and the ordered mesoporous silica film were stacked together and the device characteristics were investigated.