【International Papers】Electrothermal enhancement of β-(AlₓGa₁₋ₓ)₂O₃/Ga₂O₃ heterostructure field-effect transistors via back-end-of-line sputter-deposited AlN layer

      Researchers from the U.S. Naval Research Laboratory have published a dissertation titled "Electrothermal enhancement of β-(Al_xGa_1−x)₂O₃/Ga₂O₃ heterostructure field-effect transistors via back-end-of-line sputter-deposited AlN layer" in Journal of Applied Physics.

Abstract

      The electrothermal device performance of β-(Al_0.21Ga_0.79)₂O₃/Ga₂O₃ heterostructure field-effect transistors (HFETs) was enhanced by incorporating a 400 nm thick AlN capping layer via back-end-of-line room-temperature reactive sputter deposition. The AlN-capped HFETs demonstrated DC power densities >5 W/mm, higher than any previous report on lateral β-Ga₂O₃ transistors on native substrates. The breakdown voltage (V_B) of the uncapped HFETs was 569 ± 250 V with a maximum V_B of 947 V. For the AlN-capped HFETs, V_B increased to 1210 ± 351 V with a maximum V_B of 1868 V. The AlN-capped HFETs demonstrated a 27% reduction in device-level thermal resistance (R_TH) as measured from the gate electrode. The combined use of electrical and thermal simulation helped elucidate the coupled electrothermal contributions to the measured reduction in the temperature rise for the AlN-capped HFETs. Although the measured AlN film thermal conductivity (13.3 ± 1.3 W/mK) was comparable to that of bulk β-Ga₂O₃, the capping layer still reduced the simulated peak channel temperature rise by ∼4% due to heat spreading only. Electrical simulation revealed that electric field spreading was an additional mechanism that contributed to the majority of the simulated 18% reduction in the peak channel temperature rise through delocalization and redistribution of the heat generation in the channel. Thermal modeling was used to evaluate further improvements in thermal performance that can be realized by optimizing the sputter deposition process to achieve thicker and higher thermal conductivity AlN.