Gallium nitride (GaN) possesses remarkable characteristics such as a wide bandgap, high critical electric field, robust antiradiation properties, and a high saturation velocity for high-power devices. These attributes position GaN as a pivotal material for the development of power devices. Among the various GaN-based devices, vertical GaN MOSFETs stand out for their numerous advantages over their silicon MOSFET counterparts. These advantages encompass high-power device applications. This review provides a concise overview of their significance and explores their distinctive architectures. Additionally, it delves into the advantages of vertical GaN MOSFETs and highlights their recent advancements. In conclusion, the review addresses methods to enhance the breakdown voltage of vertical GaN devices. This comprehensive perspective underscores the pivotal role of vertical GaN MOSFETs in the realm of power electronics and their continual progress.

In this work, we investigated the ferroelectric properties of Hf _0.5 Zr _0.5 O ₂ (HZO) Metal-Ferroelectric-Metal (MFM) capacitors on various refractory electrodes, including TiN, TaN, W, and Mo. By comparing different electrodes and annealing temperature, we found that the MFM capacitors with TiN and W electrodes showed both higher remanent polarization (2P _r ) and lower leakage current for post-metal annealing (PMA) temperatures ranging from 400 °C to 600 °C. Moreover, the MFM capacitor with W electrode showed better saturated polarization-voltage (P-V) curve and less “wake up effect” during the polarization switching cycles, while the MFM capacitor with TiN electrode showed the lowest leakage current. The correlation of crystallization quality studied by X-ray diffraction and the ferroelectric characteristics for each type of MFM capacitors were also presented and compared in this study.

This study presents the ferroelectric polarization stability characteristics of ultrathin (6 nm) superlattice (SL) ferroelectric layer metal-ferroelectric-metal (MFM) capacitors fabricated with varying ferroelectric layer stacks. Notably, ZrO ₂ -HfO ₂ SL MFM capacitors with 1 nm ZrO ₂ as the starting layer exhibited enhanced polarization stability characterized by nearly wake-up free and fatigue -free behavior. The research demonstrates the deposition of ZrO ₂ -HfO ₂ superlattice by atomic layer deposition (ALD), resulting in highly stable remanent polarization (2P _r @ 3.3 MV/cm) of approximately 30 μC/cm ² . The variation remained small (Δ2P _r ≤ 2.5 μC/cm ² ; Δ2P _r /2P _{r, pristine} ≤ 8%) over an impressive 10 ¹⁰ cycles of field cycling. This result is a crucial technique to address the polarization instability commonly reported in ultrathin (≤ 6 nm) Hf _0.5 Zr _0.5 O by utilizing the SL structure to achieve nearly wake-up free and fatigue -free polarization performance up to 10 ¹⁰ cycles.

This study investigates the impact of varying compositions of Al_xIn_yGa_zN barrier layers on the performance of Al_xIn_yGa_zN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MISHEMTs) using Sentaurus TCAD simulation. By systematically increasing the compositions of Al and In and decreasing the Ga composition of the Al_xIn_yGa_zN layer, we maintained the lattice-matched conditions with GaN and explored the effects of compositions on channel charge, drain current, and threshold voltages. Under the lattice-matching conditions, it was shown that the Al_xIn_yGa_zN barrier with higher Al/In and lower Ga exhibited significantly enhanced channel charges and drain current while making threshold voltages more negative. Additionally, the influence of Al_xIn_yGa_zN layer thickness was studied. Subsequently, we analyzed the electrical characteristics of Al_xIn_yGa_zN/GaN MISHEMT based on systematically changing the compositions of each group III element. The lattice mismatch-related piezoelectric polarization was also taken into consideration. Our results indicate that total polarization increases as Al composition increases; however, the total polarization decreases as In composition increases. Notably, the change in total polarization looked slightly stronger by varying In composition compared to Al. Furthermore, we compared the charge density and band structures of MISHEMT heterostructures with and without the AlN spacer layer. The inclusion of an AlN spacer layer was found to enhance carrier confinement and reduce the dependence of charge density on composition due to the presence of large polarization between the barrier layer and channel layer. These findings highlight the importance of precise material composition control in optimizing MISHEMT performance.

In this work, we demonstrated the thermal analysis of different flip-chip bonding designs for high power GaN HEMT developed for power electronics applications, such as power converters or photonic driver applications, with large gate periphery and chip size, as well as an Au metal heat-spreading layer deposited on top of a planarized dielectric/passivation layer above the active region. The Au bump patterns can be designed with high flexibility to provide more efficient heat dissipation from the large GaN HEMT chips to an AlN package substrate heat sink with no constraint in the alignment between the HEMT cells and the thermal conduction bumps. Steady-state thermal simulations were conducted to study the channel temperatures of GaN HEMTs with various Au bump patterns at different levels of current and voltage loadings, and the results were compared with the conventional face-up GaN die bonding on an AlN package substrate. The simulations were started from a single finger isolated HEMT cell and then extended to multiple fingers HEMT cells (total gate width > 40 mm) to investigate the “thermal cross-talk” effect from neighboring devices. Thermal analysis of the GaN HEMT under pulse operation was also performed to better reflect the actual conditions in power conversion or pulsed laser driver applications. Our analysis provides a combinational assessment of power GaN HEMT dies under a working condition (e.g., 1MHz, 25% duty cycle) with different flip chip packaging schemes. The analysis indicated that the channel temperature rise (∆T) of a HEMT cell in operation can be reduced by 44~46% by changing from face-up die bonding to a flip-chip bonding scheme with an optimized bump pattern design.

This article attempts to disclose a high-efficiency laser driver that controls laser sources for high-frequency light detection and ranging (LiDAR) applications. The specific LiDAR requisites encompass a 20-MHz laser repetition rate, a 10-ns pulse duration, and an instantaneous power of 50 W. The power efficiency of a LiDAR used in autonomous vehicles is critical, which shall yield a total input power within 15 W. To enhance power efficiency, a half-bridge pulse laser drive is proposed, featuring a depletion mode gallium nitride (D-mode GaN) transistor on the high-side and an enhancement mode (E-mode) GaN transistor on the low-side. A high-side gate drive is also introduced and analyzed for the D-mode GaN transistor, which can greatly minimize oscillation during laser-pulse capacitor charging due to no body diode effect. Key efficiency factors include the equivalent series resistance of multilayer ceramic capacitor, high-side transistor switching loss, and transistor resistive loss. A peak efficiency of 75% is found at the compromise of all losses, which is verified in both theoretical and experimental methods. The pulse laser drive operation is proven to be stable in the experiments over a wide range of laser repetition rates from 10 kHz to 20 MHz.