In this study, we demonstrate ferroelectric GaN high-electron mobility transistors (HEMTs) with a sputtered AlScN gate dielectric, exhibiting a large memory window of ~ 14.6 V and a high on/off ratio of ~ 10 ⁸ . The strong polarization of AlScN layer contributes to the remarkably large threshold voltage (V _th ) tuning range with counterclockwise hysteresis depending on voltage sweep ranges and pulsed parameters. Moreover, a recessed-gate structure enables the pulsed enhancement and depletion mode switching. The reconfigurable V _th via pulse modulation further allows feasibility of NOR logic gate with the single ferroelectric GaN HEMT.

A neuromuscular junction (NMJ) is a particularized synapse that activates muscle fibers for macro-motions, requiring more energy than computation. Emulating the NMJ is thus challenging owing to the need for both synaptic plasticity and high driving power to trigger motions. Here, we present an artificial NMJ using CuInP ₂ S ₆ (CIPS) as a gate dielectric integrated with an AlGaN/GaN-based high-electron mobility transistor (HEMT). The ferroelectricity of the CIPS is coupled with the two-dimensional electron gas channel in the HEMT, providing a wide programmable current range of 6 picoampere per millimeter to 5 milliampere per millimeter. The large output current window of the CIPS/GaN ferroelectric HEMT (FeHEMT) allows for amplifier-less actuation, emulating the biological NMJ functions of actuation and synaptic plasticity. We also demonstrate the emulation of biological oculomotor dynamics, including in situ object tracking and enhanced stimulus responses, using the fabricated artificial NMJ. We believe that the CIPS/GaN FeHEMT offers a promising pathway for bioinspired robotics and neuromorphic vision.

We report the comparison of the atomic layer deposited polycrystalline (p-)/amorphous (a-) HfO ₂ bilayer gate dielectric with p-HfO ₂ /a-Al ₂ O ₃ for enhanced β-Ga ₂ O ₃ metal oxide semiconductor capacitors (MOSCAPs). A discrepancy in the temperature-dependent hysteretic behaviors is observed, and thus, pulse capacitance- voltage (C-V) measurements are employed to investigate interface properties at the border between the amorphous (Al ₂ O ₃ or HfO ₂ ) and polycrystalline (HfO ₂ ) oxide layers. The proposed p-HfO ₂ /a-HfO ₂ exhibits similar interface trap densities (Dit) at the interface between the bilayer dielectric and β-Ga ₂ O ₃ , and shows lower border trap density (Nbt). An effective barrier height of 1.62 eV for the p-HfO ₂ /a-HfO ₂ with a breakdown field of 9.1 MV/cm, which is higher than 1.01 eV of p-HfO ₂ /a-Al ₂ O ₃ , is obtained from the current density-voltage (J-V) characteristics using the Folwer-Nordheim model. Moreover, as compared with a p-HfO ₂ single layer, the additional a-HfO ₂ layer on top of p-HfO ₂ is beneficial to improve hysteretic and leakage characteristics, while maintaining its high-quality interface. The p-HfO ₂ /a-HfO ₂ bilayer with improved interface properties as well as a large positive flat-band voltage of 4.7 V is a promising candidate for the metal/high-k-stack of β-Ga ₂ O ₃ MOSCAPs.

Excessive human exposure to toxic gases can lead to chronic lung and cardiovascular diseases. Thus, precise in situ monitoring of toxic gases in the atmosphere is crucial. Here, we present an artificial olfactory system for spatiotemporal recognition of NO ₂ gas flow by integrating a network of chemical receptors with a near-sensor computing. The artificial olfactory receptor features nano-islands of metal-based catalysts that cover the graphene surface on the heterostructure of an AlGaN/GaN two-dimensional electron gas (2DEG) channel. Catalytically dissociated NO ₂ molecules bind to graphene, thereby modulating the conductivity of the 2DEG channel. For the energy/resource-efficient gas flow monitoring, trust-region Bayesian optimization algorithm allocates many sensors optimally in a complex space. Integrated artificial neural networks on a compact microprocessor with a network of sensors provide in situ gas flow predictions. This system enhances protective measures against toxic environments through spatiotemporal monitoring of toxic gases.

AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOS-HEMTs) with undoped ferroelectric HfO₂ have been investigated. Annealing is often a critical step for improving the quality of as-deposited amorphous gate oxides. Thermal treatment of HfO₂ gate dielectric, however, is known to degrade the oxide/nitride interface due to the formation of Ga-containing oxide. In this work, the undoped HfO₂ gate dielectric was spike-annealed at 600 °C after the film was deposited by atomic layer deposition to improve the ferroelectricity without degrading the interface. As a result, the subthreshold slope of AlGaN/GaN MOS-HEMTs close to 60 mV/dec and on/off ratio>10⁹ were achieved. These results suggest optimizing the HfO₂/nitride interface can be a critical step towards a low-loss high-power switching device.

Germanium (Ge) has gained great attention not only for future nanoelectronics but for back-end of line (BEOL) compatible monolithic three-dimensional (M3D) integration recently. For high performance and low power devices, various high-k oxide/Ge gate stacks including ferroelectric oxides have been investigated. Here, we demonstrate atomic layer deposited (ALD) polycrystalline (p-) HfO ₂ /GeO _x /Ge stack with an amorphous (a-) HfO ₂ capping layer. The consecutively deposited a-HfO ₂ capping layer improves hysteretic behaviors (ΔV) and interface state density (D _it ) of the p-HfO ₂ /GeO _x /Ge stack. Furthermore, leakage current density (J) is significantly reduced (×100) by passivating leakage paths through grain boundaries of p-HfO ₂ . The proposed HfO ₂ layer with the graded crystallinity suggests possible high-k/Ge stacks for further optimized Ge MOS structures.