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In this work, β-Ga2O3 fin field-effect transistors (FinFETs) with metalorganic chemical vapor deposition grown epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are demonstrated. β-Ga2O3 fin channels with smooth sidewalls are produced by the plasma-free metal-assisted chemical etching (MacEtch) method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages is also characterized. The FinFET with channel perpendicular to the [102] direction is found to exhibit the lowest subthreshold swing and hysteresis.

Gallium oxide (Ga 2 O 3 ), a wide-bandgap (WBG) semiconductor, has emerged as a highly promising material for high-power electronics, high-temperature gas sensors, and solar-blind UV photodetectors. Compared with conventional semiconductors, Ga 2 O 3 has a much larger Baliga's figure of merit (BFOM) of %3400, which makes it beneficial for developing efficient highvoltage power-switching devices. [1] It has five polymorph crystal phases: α-corundum rhombohedral, β-monoclinic, γ-defective spiral, δ-cubic, and ε-orthorhombic or hexagonal. [2,3] Among all these phases, monoclinic β-Ga 2 O 3 is the thermally and chemically most stable crystal structure. β-Ga 2 O 3 is optically transparent to %250 nm because of its wide bandgap (%4.9 eV) and its n-type conductivity can be tuned over 5 orders of magnitude by adding n-type dopants like Ge, Sn, or Si; these characteristics also make it suitable for deep-UV optoelectronic applications. [4,5] In addition, its polycrystalline films with oxygen vacancies have been widely investigated as sensors for several gasses, including O 2 . CO, CH 4 , and H 2 , which adsorb on the film surface changing its electrical conductivity. [6][7][8][9] For power electronics, conventional Si-based transistors with a narrow bandgap of 1.12 eV cannot achieve high voltage and hightemperature operation due to its intrinsic material properties. With continued advances in semiconductor technologies, it has become possible to construct next-generation power devices using WBG compound semiconductors such as GaN, SiC, Ga 2 O 3 , and diamond with excellent electrical characteristics. The GaN devices improved the overall bandwidth and power consumption performance of radio frequency electronics compared with previous generation electronics and enabled the monolithic circuit demonstration. [10,11] The enhanced device performance such as a high electrical breakdown field is attributed to the relatively larger bandgap. Accordingly, WBG semiconductors have been extensively investigated and explored. For instance, GaN has a well-developed growth process and its n-and p-type doping can readily be controlled, and it has been extensively investigated for electronic and optoelectronic applications. [12][13][14][15] Fast chargers

Aluminum nitride (AlN) continues to kindle considerable interest in various microelectromechanical system (MEMS)related fields because of its superior optical, mechanical, thermal, and piezoelectric properties. In this study, we use magnetron sputtering to tailor intrinsic stress in AlN thin films from highly compressive (−1200 MPa) to highly tensile (+700 MPa), with a differential stress of 1900 MPa. By monolithically combining the compressive and tensile ultrathin AlN bilayer membranes (20−60 nm) during deposition, perfectly curved three-dimensional (3D) architectures are spontaneously formed upon dry-releasing from the substrate via a 3D MEMS approach: the complementary metal-oxide-semiconductor (CMOS)-compatible strain-induced self-rolled-up membrane (S-RuM) method. The thermal stability of the AlN 3D architectures is examined, and the curvature of S-RuM microtubes and helical structures as a function of the cumulative membrane thickness and stress are characterized experimentally and simulated using a finite-element physiomechanic method. By combining AlN with various materials such as metal (Cu) and silicon nitride (SiN x ), AlN-based hybrid S-RuM microtubes with diameters as small as ∼6 μm are demonstrated with a near-unity yield (∼99%). Compared with other stressed thin films for S-RuMs, including PECVD SiN x , magnetron-sputtered AlN-based S-RuMs show better structural controllability and versatility, probably due to the high Young's modulus and stress uniformity. This work establishes the sputtered AlN thin film as a superior stress-configurable S-RuM shell material for high-performance applications in miniaturizing and integrating electronic components beyond those based on other materials such as SiN x . In addition, for the first time, a single-crystal Al 1−x Sc x N/AlN bilayer grown by molecular beam epitaxy is successfully rolled-up with the diameter varying from ∼9 to 14 μm, paving the way for 3D tubular Al 1−x Sc x N piezoelectric devices.

Understanding the thermal stability and degradation mechanism of β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2O3 FinFET grown on a native β-Ga2O3 substrate, fabricated by metal-assisted chemical etching with Al2O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion/Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into the stability and promise of β-Ga2O3 FinFETs compared to their planar counterparts.