120 RITESH GUPTA : SHORT CHANNEL ANALYTICAL MODEL FOR HIGH ELECTRON MOBILITY TRANSISTOR TO ~ Manuscript received Jan. 21, 2007; revised May 21, 2007. Semiconductor Device Research Laboratory Department of Electronic Science, University of Delhi South Campus New Delhi – 110 021, India E-mail: rsgu@bol.net.in Short Channel Analytical Model for High Electron Mobility Transistor to Obtain Higher Cut-Off Frequency Maintaining the Reliability of the Device Ritesh Gupta, Sandeep Kumar Aggarwal, Mridula Gupta, and R. S. Gupta Abstract—A comprehensive short channel analytical model has been proposed for High Electron Mobility Transistor (HEMT) to obtain higher cut-off frequency maintaining the reliability of the device. The model has been proposed to consider generalized doping variation in the directions perpendicular to and along the channel. The effect of field plates and different gate-insulator geometry (T- gate, etc) have been considered by dividing the area between gate and the high band gap semiconductor into different regions along the channel having different insulator and metal combinations of different thicknesses and work function with the possibility that metal is in direct contact with the high band gap semiconductor. The variation obtained by gate-insulator geometry and field plates in the field and channel potential can be produced by varying doping concentration, metal workfunction and gate-stack structures along the channel. The results so obtained for normal device structure have been compared with previous proposed model and numerical method (finite difference method) to prove the validity of the model. Index Terms—Gate-insulator geometries, field plate, gate-stack, retrograde doping, metal workfunction, cut-off frequency, breakdown voltage, hot-carrier effect, Field engineering, DIBL, threshold voltage. I. INTRODUCTION An InGaAs/InAlAs high electron mobility transistor (HEMT) on InP substrate has shown the excellent high speed characteristics due to the enhanced electron’s mobility and the increased conduction band discontinuity. Ever since its introduction the challenges among the researchers are to increase the reliability of the device without finding the middle ground for the operating speed of the device. Several approaches have been proposed for MOSFET, MESFET, HEMT etc following different criterion for reliability, speed and their applications. Among them the most common approaches are variation of doping concentration, variation of metal workfunction, gate-stack variation and the variation of gate-insulator geometries or field plates engineering [1-33]. The T-gate geometry has generally been used for higher cut-off frequency performance due to the use of upper and lower gate electrode offering lower gate resistance and capacitance to the device [33-45]. The enhancement of these variations includes improved breakdown voltage, current voltage swing, linearity, efficiency, stability, reliability by suppressing phenomenon, namely surface traps effects, hot-carriers effects, current collapse, gate leakage, junction leakage, subthreshold leakage and DC- to-RF dispersion. To study all these devices a generalized short channel model has been proposed in this paper considering doping variation in the directions perpendicular and along the channel, where region between gate and the high band gap semiconductor is divided into different regions along the channel having different insulator and metal combinations of different thicknesses and work