Investigation of Novel Enhancement-Mode Tri-Gate Nanowire GaN-based Power High Electron Mobility Transistors

  • 黃 一平

Student thesis: Doctoral Thesis

Abstract

This dissertation demonstrates a series of novel enhancement-mode (E-mode) tri-gate nanowire GaN-based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) for high power device applications which include a novel E-mode tri-gate nanowire InAlN/GaN power metal-oxide-semiconductor (MOS) HEMT an E-mode tri-gate nanowire InAlN/GaN MOSHEMT with Schottky tri-drain extension (STDE) and a high performance E-mode AlGaN/GaN MISHEMT with nanowire-based low work function metal-source contact ledge (LWFM-SCL) First the novel E-mode tri-gate nanowire InAlN/GaN power MOSHEMT is investigated It exploits a nanowire recess design in the tri-gate nanowire structure to solve the over dependence of conventional E-mode tri-gate nanowire GaN-based HEMTs on the nanowire widths (Wnw) This can significantly improve the severe degradation issues of the maximum drain current (ID max) and on-resistance (Ron) induced by the over narrow Wnw The proposed novel tri-gate device also includes an integrated field plate (FP) design to effectively distribute the electric field (E-field) between the gate and drain increasing the device breakdown voltage (VBD) Therefore the proposed novel E-mode tri-gate device exhibits excellent characteristics including a positive VTH of 2 3 V ID max of 705 mA/mm subthreshold swing (SS) of 65 mV/decade on-state current/off-state current (Ion/Ioff) ratio of 10^9–10^10 VBD of 800 V and Baliga’s figure of merit (BFOM) of 615 MW/cm^2 Then the second investigated novel GaN-based HEMT is a E-mode tri-gate nanowire InAlN/GaN MOSHEMT with STDE The STDE functions as a drain-connected FP to effectively distribute the peak E-field around the ohmic drain edge which suppresses the effects of the ohmic alloy spikes and improves the VBD Compared with the device with conventional ohmic drain the VBD of the device with STDE can be improved about 30% Moreover the tri-drain structure of the STDE can reduce the turn-on voltage (Von) of the Schottky extension portion through the Schottky metal directly contacting the2-DEG from the nanowire sidewalls improving the device overall Ron Through the novel STDE structure the BFOM can be improved to 1019 MW/cm^2 Finally the third investigated novel GaN-based HEMT is a high performance E-mode AlGaN/GaN MISHEMT with nanowire-based LWFM-SCL The nanowire-based LWF-SCL is used to lower the gate-to-source access resistance (Ra) reducing the overall Ron Compared with directly shortening the gate-to-ohmic source distance (LGS) to lower the Ra the nanowire-based LWFM-SCL design reveals an obviously large VBD owing to the alleviation of the source carrier injection (SCI) from the buffer layer Moreover dual dielectric layers of Al2O3/SiNx combined with the tri-gate recessed nanowire structure in this device are used to suppress the E-field assisted electron trapping between the gate and drain This can improve the current collapse phenomenon and dynamic Ron degradation issues The proposed high performance E-mode AlGaN/GaN MISHEMT with nanowire-based LWF-SCL exhibits very excellent performances including a positive VTH of 1 2 V high Ion/Ioff ratio of 10^10 large ID max of 825 mA/mm and steep SS of 76 mV/decade while also possessing excellent temperature stability VTH hysteresis and dynamic Ron characteristics With LGD of 14 ?m a BFOM of up to 1175 MW/cm^2 can be achieved These results indicate that the proposed novel E-mode tri-gate nanowire GaN-based MISHEMTs reveal great potential for future power device applications
Date of Award2021
Original languageEnglish
SupervisorWei-Chou Hsu (Supervisor)

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