We discuss the role of aluminum oxide (i.e. Al2O3 when stoichiometric) for transistors and sensors based on oxide semiconductors such as InGaZnO (IGZO) and two-dimensional (2D) semiconductors, such as monolayer MoS2. Aluminum oxide is a well-known capping and dielectric layer in semiconductor technology typically deposited by atomic-layer deposition (ALD), which offers a dense and high-quality film with low gas permeability even when deposited on flexible substrates. However, when deposited at low temperature (< 200°C), aluminum oxide can include a significant amount of fixed charges and defects, which lead to unusual charge trapping and doping effects in semiconductor devices. For example, such charge trapping can cause (apparent) sub-60 mV/decade subthreshold swing at room temperature in IGZO transistors, but can also lead to potential applications in neuromorphic computing. We also discuss effective doping (~1013 cm-2) of 2D semiconductors by thin ALD-grown non-stoichiometric AlOx capping layers. This is achieved with an aluminum seed layer, which enables uniform growth of the subsequently deposited ALD film. This approach leads to a negative shift in threshold voltage, record on-state current (~700 μA/μm) in a monolayer semiconductor, and drastic reduction in contact resistance. Finally, we investigate the passivation effects of Al2O3 capping, which limits the interaction of the underlying semiconductors with ambient air and moisture. We demonstrate improved response in MoS2 temperature sensors and long-term stability in flexible MoS2 transistors (8 months). Further, we evaluate the effects of Al2O3 passivation on IGZO transistors after aging for 80 months.
Here we propose a new wide band gap logic circuitry providing emerging power electronics with reliable logic control capabilities with 500 MHz+ switching speeds and withstanding 300V+. Particularly, a three-stage ring oscillator composed of NMOS (μe = 1000 cm2/V-s) and PMOS (μh = 250 cm2/V-s) cubic phase GaN devices (with VT of 0.77 V and –0.84 V, respectively) is simulated. The propagation delay is minimized by optimizing the width-to-length ratio (W/L) between the NMOS and PMOS devices. Transient response of the simulation illustrates the ability of the CMOS inverter to operate at a maximum frequency of 1.22 GHz with a full voltage swing between VDD of 2.5 V and 0 V. The proposed cutting-edge p-channel GaN high hole mobility transistor (HHMT) solves one of the most longstanding problems in power electronics and constitutes the basis of an innovative reduced total life cycle cost that will serve as the cornerstone of the next generation of integrated, scalable, and reliable power systems.
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