Investigation On Characteristics Of Novel GaN Based FinFETs

AlGaN/GaN high electron mobility transistors(HEMTs)are considered to be the most promising candidate for microwave devices,power electronics devices,and GaN digital circuits due to their superior material properties,such as large bandgap,high critical electric voltage,high thermal conductivity,and high electron saturation velocity.Traditional AlGaN/GaN HEMTs are natural depletion devices,and the material and device physics of GaN HEMTs have been extensively studied over the past decades.But the implementation of high-performance GaN-based enhancement devices still has a series of problems,such as small positive shift of threshold voltage,insufficient saturation current,and low-linearity properties.And with the development of integrated circuits,the device size will continue to decrease in order to meet the increase in integration,and the short channel effect will become an important factor that constrains the reduction of device size,similar to Si-based Fin FET devices,the short channel effect can be suppressed in GaN-based FinFETs and the three-dimensional gate structure can enhance the gate control capability.Moreover,the enhancement-mode device can be realized by optimizing the device structure.Based on the novel AlGaN/GaN Fin FET devices,this paper studies the device characteristics and temperature reliability around the implementation of enhancement-mode devices and high performance.AlGaN/GaN FinFETs with different fin widths have been successfully fabricated,and the recessed-gate FinFETs was fabricated for comparison.The transconductance peak of a 5 nm recessed-gate Fin FET device is about 11% higher than that of a conventional Fin FET device,and the threshold voltage shift is nearly 0.6 V.Moreover,with the fin width increasing of the recessed-gate FinFETs,the variation of both threshold voltage and the transconductance increased.Next,transfer characteristics of the recessed-gate FinFETs with different fin widths and recessed-gate depths are simulated by Silvaco software.The relationship between the threshold voltage and the AlGaN layer thickness has been investigated.The simulation results indicate that the slope of threshold voltage variation reduces with the fin width decrease.Finally,a simplified threshold voltage model for recessed-gate Fin FET is established,which agrees with both the experimental results and simulation results.In this work,GaN-based enhancement-mode fin-shaped field-effect transistor(Fin FET)with double-channel AlGaN/GaN heterostructure is proposed.DC characteristic of AlGaN/GaN Fin FET is simulated by sentaurus TCAD software.The simulation results indicate that double-channel AlGaN/GaN Fin FET with doping AlGaN layers makes the saturation current and the control ability of the gate improved.Moreover,the single and double-channel AlGaN/GaN FinFETs with short gate length,an SS of 60 m V/dec and 63 m V/dec have been achieved.Next,both the first and the second AlGaN layer thickness are set to 20 nm,the enhancement-mode double-channel AlGaN/GaN Fin FET can be obtained with 30 nm Fin width,and the peak transconductance reaches 417 m S/mm.Finally,double-channel AlGaN/GaN Fin FET with narrow Fin width or thin AlGaN layer can achieve enhancement-mode device,and the effect of the side gate could play a dominant role at the same narrow Fin width compared to the single-channel AlGaN/GaN Fin FET,which can provide valuable theoretical reference for the double-channel AlGaN/GaN Fin FET.Finally,three different Fin-width AlGaN/GaN FinFETs and conventional devices have been fabricated,and the temperature characteristics of the Fin FET are studied.The temperature coefficient ? of the conventional HEMT is-1.74,and the temperature coefficient ? of the Fin FET is-1.5,-1.37,-1.25,respectively.The conventional HEMT is more affected by the temperature than the Fin FET,and at the same time,as the Fin width increases,the Fin FET is less affected by temperature.In terms of threshold voltage,the variation of the threshold voltage of the conventional HEMT reaches 0.37 V,and the threshold voltage variation of the Fin FET is 0.12 V,0.23 V,0.25 V,indicating that the Fin FET has better temperature stability.In DIBL,the conventional HEMT's DIBL value is increased by 150% from 20 °C to 300 °C,which is greatly affected by temperature,while the DIBL value of the 100 nm channel width Fin FET is increased by 86% from 20 °C to 300 °C and was minimally affected by temperature.In addition,this paper focuses on two significant phenomena of transconductance with temperature and studies its intrinsic mechanism.As the temperature increases,the transconductance peak of the narrow Fin width Fin FET decreases more obviously.It can be obtained by calculation that the smaller the Fin width,the stronger the phonon scattering and the greater the mobility decrease.For the transconductance curve dispersion phenomenon of the Fin FET,the analysis shows that the more electrons accumulate in the Fin FET under the same gate voltage,the easier the Coulomb scattering dominates.