【International Papers】High-mobility wide bandgap amorphous gallium oxide thin-film transistors for NMOS inverters

      Researchers from the University of California San Diego have published a dissertation titled "High-mobility wide bandgap amorphous gallium oxide thin-film transistors for NMOS inverters " in Applied Physics Reviews.

Abstract

      Wide bandgap gallium oxide thin-film transistor (TFT) is promising for next-generation sustainable energy-efficient power electronics. In particular, amorphous oxide channel exhibits inherent advantages on mass productions based on a low-temperature processability compatible with cost-effective large-sized glass. Here, we developed hydrogen defect termination to produce amorphous-GaO_x (a-GaO_x) channel for n-channel oxide-TFT and demonstrated high-mobility a-GaO_x-TFT exhibiting a high saturation mobility (μ_sat) of ∼31 cm² V⁻¹ s⁻¹, threshold voltage (V_th) of ∼3.3 V, a current on/off ratio of ∼10⁸, and subthreshold swing value (s-value) of ∼1.17 V·dec⁻¹. The study found that oxygen conditions during the channel fabrication process, i.e., oxygen partial pressure during the film deposition and post-thermal annealing atmospheres, were critical for the TFT performances of gallium oxide-TFTs, and subgap defects originated from low-valence Ga⁺ state and excess oxygen rather than oxygen vacancy had a large responsibility for the device performances. The finding explains why the development of gallium oxide-TFTs is largely behind the other oxide-TFTs. We also fabricated depletion and enhancement-mode a-GaO_x-TFTs and developed a full-swing zero-V_GS-load inverter with high voltage gain ∼200 and sufficient noise margins. The present study demonstrates a high potential of gallium oxide channel for low-temperature processed n-channel oxide-TFT for next-generation electronic applications.

FIG. 1. (a) Schematic of the device structure of a-GaO_x-TFT and the optical microscope image of the channel region (scale bar: 200 μm). (b) Variation of transfer characteristics at V_DS = 20 V for the a-GaO_x-TFTs using the unannealed film deposited by different deposition PO₂ at 5, 10, and 20 mTorr at RT. The extracted fundamental TFT parameters (c) μ_sat and V_th, (d) on/off-current ratio and s-value were plotted as a function of the deposition PO₂. (e) The variation of as-deposited film conductivity as the function of PO₂ during a-GaO_x channel deposition.

FIG. 2.The measured (symbols) and simulated (solid) transfer curves at V_DS = 20 V for the as-deposited a-GaO_x-TFT fabricated by PO₂ deposition at (a) 5 and (b) 20 mTorr. (c) and (d) The corresponding subgap defect DOS profiles. The proposed (e) charge trapping and (f) self-compensation mechanisms of carrier compensation for the 5 mTorr-a-GaO_x channel device.

原文链接：https://doi.org/10.1063/5.0159529