Protective insulator for HFET devices

A high-voltage field effect transistor (HFET), comprising:

• a first semiconductor material, a second semiconductor material, and a heterojunction, wherein the heterojunction is disposed between the first semiconductor material and the second semiconductor material;
• a plurality of composite passivation layers, wherein a first composite passivation layer in the plurality of composite passivation layers includes a first insulation layer and a first passivation layer, wherein a second composite passivation layer in the plurality of composite passivation layers includes a second insulation layer and a second passivation layer, wherein the first insulation layer is disposed between the first passivation layer and the second passivation layer, and the second passivation layer is disposed between the first insulation layer and the second insulation layer, wherein the first insulation layer and the second insulation layer have wider bandgaps than the first passivation layer and the second passivation layer, and wherein the plurality of composite passivation layers further comprises a third composite passivation layer including a third insulation layer and a third passivation layer, wherein the second insulation layer is disposed between the second passivation layer and the third passivation layer;
• a gate dielectric disposed between the second semiconductor material and the first passivation layer;
• a gate electrode disposed above the gate dielectric;
• a first gate field plate disposed between the first passivation layer and the second passivation layer;
• and
• a source electrode and a drain electrode, wherein the source electrode and drain electrode are coupled to the second semiconductor material.