Fabrication and Characterization of AlGaN/GaN Enhancement-Mode MOSHEMTs With Fin-Channel Array and Hybrid Gate-Recessed Structure and LiNbO<sub>3</sub> Ferroelectric Charge Trap Gate-Stack Structure
Hsin-Ying Lee, Chia‐Hung Lin, Ching-Ting Lee
Abstract
In this work, a hybrid combination structure of fin-channel array, gate-recessed structure, and LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ferroelectric charge trap gate-stacked oxide layers was utilized in AlGaN/gallium nitride (GaN) enhancement-mode metal–oxide–semiconductor high-electron-mobility transistors (E-MOSHEMTs). The C <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ferroelectric polarization of the LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> blocking layer, deposited by a pulsed laser deposition system, increased the stored amount of electron charges in the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> charge trap layer, leading to a high positive threshold voltage of 2.9 V for the enhancement-mode operation. In studying the initialization features, it was found that the threshold voltage shifted to a more positive voltage with an increase of initialization voltage. The devices changed to enhancement-mode from depletion-mode when the gate voltage larger than 4 V was applied to initialize the devices. Compared with a planar channel structure, the devices with 500-nm-wide fin-channel array structure improved the maximum extrinsic transconductance from 89.5 to 110.9 mS/mm, the subthreshold swing from 224.8 to 120.5 mV/dec, the extrinsic unit gain cutoff frequency from 5.0 to 7.4 GHz, the maximum oscillation frequency from 9.1 to 11.7 GHz, and the normalized noise power from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9\times 10^{-{14}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5\times 10^{-{15}}$ </tex-math></inline-formula> Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> .