Some Studies on Si-nanotube Based FETs

Abstract

Silicon-nano-tube (SiNT) MOSFETs have been analyzed recently in order to investigate their suitability for future ultra-large scale integration (ULSI) applications. Based on the study so for, it could be safely stated that the SiNT MOSFETs are very promising for future ULSI asthey could be scaled down to 22nm gate length and below effectively.
The SiNT MOSFET provides ultimate electrostatic controllability to the gates in order to counter the short-channel effects because of its hollow cylindrical shape. In SiNT MOSFETs, two gates, an outer gate and an inner gate, can act independently or together in order to realize the multi-threshold voltage transistors characteristics or high drain current, respectively. The SiNT MOSFET is particularly considered to be unique in the sense that, unlike other MG MOS structures, it provides excellent SCE immunity even when the diameter of the tube is increased as long as the channel thickness is kept same. Subthreshold electrical characteristics of SiNT FET have been studied through device simulation and it has been confirmed that the device outperforms GAA and other MG devices completely. However, in the best of our knowledge, neither analog nor RF performance of the device has been studied till date in order to access its potential in system-on-chip applications. Therefore, we have analyzed the analog as well as the RF characteristics of SiNT FETs using the ATLAS, a 3D device simulator from SILVACO. Besides, the characteristics of SiNT MOSFETs have also been compared with the same of a nanowire based GAA FET to quantify the improvement in the performance. In this work, Si-nanotube MOSFETs (SiNT FET) with catalytic metal gates are proposed for gas sensing applications. P-channel SiNT FET with palladium (Pd) metal gate is proposed for hydrogen sensing , whereas N-channel SiNT FET with silver (Ag) metal gate can be used foroxygen gas sensing. A simulation based study has been carried out using ATLAS-3D numerical simulator, and it is found that SiNT FETs have more efficiency towards the iii hydrogen and oxygen detection than the recently proposed cylindrical gate-all-around (GAA) MOSFETs. Further, effect of variation of the channel length (Lg) and channel thickness (tSi) on the gas sensing sensitivity of the sensors are also studied. In the presented work, an analysis into the performance of a Dual Material Gate Single Dielectric Si-nanotube Tunnel FET has been done. Numerous simulations were done to determine the influence of work functions of both the gate materials on the electrical characteristics of the device. Comparative study was done between Dual Material Gate device and Single Material Gate device. Parameters like intrinsic capacitances as well as transconducatnce were also determined.
The same analytic approach was extended to Dual Material Gate Hetero Dielectric Sinanotube Tunnel FET to analyze the improved performance of the device compared to itsSingle Dielectric Dua Material Gate counterpart .Thus the work presented had all together analyzed attributes of ncorporating Dual Material Gate as well as Hetero Dielectric in Sinanotube Tunnel FET structures. Extensive simulations for the presented work were performed by using two dimensional device simulator (ATLASTM SILVACO Int.)