Performance analysis of single and dual channel vertical strained SiGe impact ionization MOSFET (VESIMOS)

Abstract

In this work, single and dual channel SiGe layer for Vertical Strained Silicon Germanium (SiGe) Impact Ionization MOSFET (VESIMOS) has been successfully analyzed. Presence of the SiGe channel, it improved the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio, subthreshold slope for the Dual Channel VESIMOS. Germanium has high impact ionization rates to ensure that the transition from OFF state to ON state is abrupt. It is found that Single Channel (SC) VESIMOS for 10% to 30% Ge mole fraction operate in Conventional MOSFET mode at VDS=1.75V. However, Dual Channel (DC) VESIMOS with the same content was operated in Impact Ionization (II) mode. For DC VESIMOS Ge=30%, it has a fastest switching speed of sub-threshold value, S=10.98 mV/dec compare to others simulated devices. It observed that drain current for SC and DC VESIMOS increase sharply initially due to presence of Germanium. However, breakdown voltage of the SC device was decrease from B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> =2.9V to 2.5V by increasing the composition of Ge from 10% to 30%. The same characteristics were found for DC VESIMOS with B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> = 2V to 1.6V by varying the Ge composition. Ge content justified the appearance of second SiGe channel and affecting the breakdown voltage. A better performance in threshold voltage, V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> , S value and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio were found for DC as compared to SC VESIMOS. The V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> =0.6V and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> = 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> were measured for DC VESIMOS with Ge=30% that justified the advantage of SiGe channel on VESIMOS device. These improvements were mainly affected the enhancement of electron mobility in SiGe layer from 600 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s (first channel) to 1400 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s (second channel). The electron mobility was increased due to splitting of conduction band valley into six fold in which the electron mass are reduced in out of plane direction and thus enhanced the mobility of electron. This was evidence that DC VESIMOS operate with low power and better performance compare to other devices.