Fabrication and Characterization of AlGaN/GaN Enhancement-Mode MOSHEMTs With Fin-Channel Array and Hybrid Gate-Recessed Structure and LiNbO3 Ferroelectric Charge Trap Gate-Stack Structure

In this work, a hybrid combination structure of fin-channel array, gate-recessed structure, and LiNbO
₃
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
⁺
ferroelectric polarization of the LiNbO
₃
blocking layer, deposited by a pulsed laser deposition system, increased the stored amount of electron charges in the HfO
₂
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
$1.9\times 10^{-{14}}$
to
$2.5\times 10^{-{15}}$
Hz
⁻¹
.