Reduction in current collapse of AlGaN/GaN HEMTs using methyl silsesquioxane‐based low‐k insulator films

Abstract

We have investigated the effect of moisture on current collapse of AlGaN/GaN high‐electron mobility transistors (HEMTs) when using low dielectric constant (low‐k) insulator films to reduce the parasitic capacitance of millimeter‐wave amplifier monolithic microwave integrated circuits. We clarified that current collapse is caused by moisture uptake through the surface and the sidewall of low‐k films. Moreover, the moisture resistance of conventional carbon‐based low‐k films, such as benzocyclobutene, are insufficient to suppress current collapse because of hydrophilic surface and highly hydrophilized sidewall by the contact hole etching. We proposed the use of methyl silsesquioxane (MSQ)‐based low‐k films to improve the moisture resistance because of methyl group's hydrophobic property. This is the first time that MSQ has been used in AlGaN/GaN HEMTs. After appling MSQ, the moisture resistance of low‐k films at the surface and the sidewall improved, and current collapse due to humidification was successfully reduced. Our findings suggest that improving the moisture resistance with hydrophobic low‐k films does play a key role in reducing current collapse of AlGaN/GaN HEMTs.