Introduction of charge-trapping Al2O3/Ta2O5/Al2O3 dielectric stack in AlGaN/GaN high electron mobility transistors for programmable threshold voltage

Abstract

The GaN family as an electronic material and AlGaN/GaN high electron mobility transistors (HEMTs) as electronic devices have found their widespread usage in power electronics and radio frequency (RF) applications. The threshold voltage is a crucial parameter, and application-specific threshold voltage is a requirement for this technology. A large positive threshold voltage with enhancement-mode operation is useful for power electronics. A depletion-mode transistor is used for radio frequency (RF) applications where the electron mobility is much larger in the channel region due to low interface roughness. A multi-threshold voltage transistor is a desired feature to reduce nonlinearity through compensation in RF applications. We address the issue with threshold voltage by demonstrating a programmable threshold AlGaN/GaN transistor using a dielectric stack as the charge-trapping layer. We have fabricated and characterized a triple-layer dielectric gate stack for AlGaN/GaN metal–insulator–semiconductor HEMTs. The gate stack comprises a high-k tantalum oxide sandwiched between two aluminum oxide layers. The structure is analogous to the polysilicon–aluminum oxide–nitride–oxide–silicon memory used in silicon technology. In addition to providing a large programmable threshold voltage window, the fabricated diodes reduce the gate leakage current by more than four orders of magnitude. The experimental observations are explained by the band edge alignment of the AlGaN/GaN heterostructure with the dielectric stack and using a charge-trapping process by a high positive program voltage.