Short Channel Effect Research And Noval High Breakdown Strcutrure Of AlGaN/GaN HEMT

Due to Ga N’s extraordinary properties of high bandgap, high saturated electron drift velocity, high critical electric field, Al Ga N/Ga N HEMT has been research hotspots of high frequency and high power field. In the field of micro-wave application, scaling gate length is the main method to improve device’s cut-off frequency(?T) and maximum oscillation frequnecy(?max). But aggressive scaling of gate length will cause severe short channel effects(SCEs), leading to decrease of maximum transconductance, frequency gate length product, unsaturation of output characteristic and threshold voltage roll-off. Therefore, SCEs has been an urgent issue to be solved for it can be harmful to the stability of device.Firstly, Al Ga N/Ga N HEMT with composite metal gate is creatively proposed to solve SCEs. Due to the difference of workfunction of gate metal, the horrizontal potential distribution of channel has been reshaped. So, DIBL effect can be supressed as well as SCEs. Furhermore, the additonal electric field at the interface between different gate metal accelerate the drifting velocity of electrons in channel source side, which can increase the maximum output current and maximum transconductance by 17% and 10% relatively, and f T is improved by 14.6%. Then, Al Ga N/Ga N MIS-HEMT with composite gate dieletric layer is proposed to improve RF performance of Al Ga N/Ga N MIS-HEMT. Due to the interface of high-K and low-K gate dielectric, additional electric filed is fromed to improve electron transport effiency. And with the lower gate capacitance, f T of the device is improved by 17%.Secondly, in order to solve the electric field crowding at the drain side of gate Al Ga N/Ga N HEMT with composite Al mole fraction barrier is proposed to improve breakdown performance. Due to the two different Al mole fraction Al Ga N barriers, a low-density drain(LDD) region is created, effectively modifying channel electric field distribution between the gate and the drain. Breakdwon voltege(BV) and figure of merit of Al Ga N/Ga N HEMT with composite Al mole fraction barrier is improved by 160% and 382% relatively. And Al Ga N/Ga N HEMT with negative ion injected passivation layer is proposed, which uses negative ions to deplete part of 2DEG in the channel of drain side to modify the channel electric field distribution, thus 91% increasement of BV can be achieved.Finally, Al Ga N/Ga N MIS-HEMT with composite channel layer and Al Ga N/Ga N enhancement mode MIS-HEMT based GOI technology are proposed to achive Ga N based enhancement mode device for the application of intergrated circuits. Both of two devices utilize the polarization engineering to deplete the 2DEG under the gate and thershold voltge of both devices is 1.2 V and 1.8 V relatively, which means enhancement mode is achieved.