Hydrogen sensitivity of InP HEMTs with WSiN-based gate stack

We have experimentally investigated the hydrogen sensitivity of InP high-electron mobility transistors (HEMTs) with a WSiN-Ti-Pt-Au gate stack. We have found that exposure to hydrogen produces a shift in the threshold voltage of these devices that is one order of magnitude smaller than published data on conventional Ti-Pt-Au gate HEMTs. We have studied this markedly improved reliability through a set of quasi-two-dimensional mechanical and electrostatic simulations. These showed that there are two main causes for the improvement of the hydrogen sensitivity. First, the separation of the Ti-layer from the semiconductor by a thick WSiN layer significantly reduces the stress in the heterostructure underneath the gate. Additionally, the relatively thinner heterostructure used in this study and the presence of an InP etch-stop layer with a small piezoelectric constant underneath the gate reduces the amount of threshold voltage shift that is caused by the mechanical stress.