Research On Enhanced GaN FinFET Device And Tri-gate Regulation Mechanism

In consideration of the problems of the traditional E-Mode AlGaN/GaN FinFET,such as low threshold voltage,small Fin wide(Wfin)process window and low current density,a AlGaN/GaN metal-oxide-semiconductor Fin structure field effect transistor(AlGaN/GaN MOS-FinFET)based on thin barrier technology was proposed.The new structure was realized through introducing a thin barrier layer AlGaN(4 nm)/GaN heterojunction into the traditional GaN MOS-FinFET to reduce the 2DEG under the gate region and inducing the out-of-gate 2DEG enhancement by growing the SiN charge modulation layer.Combined with theoretical simulation and experimental analysis,the characteristics of GaN FinFET devices,and its working principle were studied.The main research results of this paper include:(1)A thin barrier GaN FinFET device physical model was established.First,considering the influence of the thickness of the barrier layer on the polarization charge concentration,fitting a variation function of the polarization effect(Polar.scale)of the AlGaN/GaN heterojunction with the thickness of the barrier layer(HAlGaN),which establishing a model of thin barrier AlGaN/GaN heterojunction polarization.Then,based on the working principle of the planar GaN HEMT,a GaN FinFET mobility model was preliminarily established.Finally,combined with the C-V test and energy band analysis,the SiN induced 2DEG enhancement mechanism was studied.It was determined that the SiN/AlGaN interface positive charge was the main reason for inducing 2DEG enhancement outside the gate,and a thin barrier GaN FinFET device model was established.(2)The preparation process of GaN FinFET devices was improved.First,by comparing the test values with the designed size,the optimal exposure dose and developing time of the nanoscale array were 400 mC/cm2 and 80 s,respectively.Then,two kinds of nanobelt array fabrication processes were developed,and the SiO2 hard mask and AlGaN/GaN heterojunction etching menu were optimized.Then,a nanoband array of Tetramethyl Ammonium Hydroxide(TMAH)wet etching was developed.The nanoband array structure with steep side wall,low damage and smooth surface was obtained.Finally,the ohmic contact and Schottky contact conditions were optimized to achieve ohmic contact with lower contact resistivity,as well as the Schottky contact of low off-state leakage current(60 mA)and higher open voltage(1.75 V).(3)Thin-barrier GaN MES-FinFET metal-semiconductor Schottky contact features were investigated.First,by comparing the gate metal Schottky contact characteristics of the top and sidewalls of the GaN MES-FinFET device,the influence of the direct contact between the sidewall gate and the 2DEG on the forward leakage of the gate was clarified.Then,the working principle of GaN MES-FinFET was analyzed and the improvement scheme was proposed.Finally,a novel GaN Fin structure Schottky diode(GaN Fin-SBD)was proposed based on the high side wall forward leakage and the strong reverse three gate depletion.The device has a lower opening voltage Von=0.548 V,a higher current density IF=459 mA/mm(V=5 V)and a lower reverse leakage current 10-3?10-4 mA/mm.(4)The performance of the thin barrier GaN MOS-FinFET device and the three-gate modulation mechanism were studied.First,the threshold voltage characteristics of thin barrier GaN MOS-FinFET devices were studied,and the mechanism of threshold voltage regulation by tri-gate structure was studied by establishing the electron concentration distribution model under the gate.It was important to point out that the thin barrier device can be enhanced at Wfin=500 nm,and the key size of Fin broadened by nearly 5 times,greatly reducing the process complexity and cost.Then,combined with the dual transconductance characteristics,the concentration distribution of the electrons under the gate and the variation of the on-resistance with the gate voltage,the dual channel conduction mechanism of the GaN MOS-FinFET device was clearly defined:the top 2DEG channel and the sidewall MOS channel.Then,the on-state and sub-threshold properties of thin barrier GaN MOS-FinFET devices were investigated.For the same threshold voltage,thin barrier devices can improve current density and peak transconductance reduction by increasing the Fin width.At the same time,the thin barrier GaN MOS-FinFET device has a lower off-state leakage current of 10-8 mA/mm and a higher switching ratio of Ion/Ioff=1010 than thick barrier device.Finally,the short channel suppression and breakdown characteristics of thin-barrier GaN MOSFinFET devices were studied.The enhancement mechanism of breakdown voltage was analyzed based on field plate theory.