HETERO-DIELECTRIC NANOWIRE FET FOR RADIATION SENSING DOSIMETER APPLICATIONS

Abstract

Due to the downsizing of semiconductor devices to nanometers scale regime, there are numerous reliability concerns arising from the modern electronics. The conventional MOSFET based electronic devices face a variety of challenges, which include short-channel effects, increased leakage current, threshold voltage instabilities and lack of electrostatic control. All these issues become even more significant when the electronic devices are subjected to environments prone to radiation such as nuclear plants, medical equipment using radiotherapy treatment, aircraft, military equipment and satellites. This is due to ionizing radiation leading to the formation of charge traps in the oxide. Radiation sensor based dosimeters find extensive applications for measuring and recording the radiation dose level. However, conventional MOSFET-based dosimeters suffer from poor sensitivity, large gate leakage currents and instability in their electrical characteristics owing to the long term radiation effect. For solving such problems, more sophisticated high performing devices in terms of electrostatic control and minimizing short-channel effect including nanoscale transistors, NW FETs and GAA devices can be used. This research paper presents a new design approach to the HD-NW FET dosimeter. The basic principle of the proposed approach involves the application of the double layered gate structure that consists of two materials with different dielectric constants in the channel region. As a result of that design, it is possible to create asymmetry in the electric field distribution, which provides effective Gate-Induced Drain Leakage control, reduces band-to-band tunneling, and increases sensitivity to radiation-induced trapped charge generation. The selected design approach for the dosimeter includes the utilization of the Gate-All-Around structure of a transistor, providing effective gate controllability, carrier mobility, and analog characteristics of operation. Design and simulation of the HD-NW dosimeter have been performed using Silvaco ATLAS 3D TCAD. Several physical models, including Shockley-Read- xii Hall (SRH) recombination, field-dependent mobility (FLDMOB), concentration dependent mobility (CONMOB), drift-diffusion transport, and band-to-band tunneling (BTBT) have been implemented for the purpose of modeling the electrical behavior of the dosimeter. Radiation effects are modeled via trap charges at the oxide and interface between semiconductor and dielectric. From the results obtained, it can be seen that the device performs better than the conventional single-dielectric nanowire FETs when it comes to reduced leakage current and increased sensitivity to radiation. The analysis was performed on some important device parameters which include threshold voltage shift, drain current variations, transconductance, sub-threshold slope, and sensitivity to radiation. The device shows good linearity, low OFF-state leakage, and sensitivity, making it appropriate for use in real time radiation detection systems.