DESIGN AND OPTIMIZATION OF JUNCTIONLESS ACCUMULATION-MODE GATE-STACK GATE-ALL-AROUND FINFET FOR RF AND BIOSENSOR APPLICATIONS

Abstract

FinFET has emerged as the most desirable alternative to MOSFETs and is the driving force behind the current integrated circuit (IC) industry, which optimizes short-channel effects (SCEs) to achieve exceptional scalability, augment battery longevity, and minimize power consumption. FinFET ensures superior electrostatic control with three gates surrounding the fin and offers a larger packing density due to its three-dimensional construction. In this thesis, Junctionless-Accumulation-Mode Gate-Stack Gate-All-Around (JAM-GS-GAA) FinFET architecture has been rigorously examined and compared with different structures using the SILVACO ATLAS 3D simulator. The analysis exemplified that JAM-GS-GAA FinFET overcomes the challenges faced by conventional FinFET, such as manufacturing complexity, reliability concerns, variability issues, etc. In addition, approaches such as dual k spacer engineering have been used to further improve the device’s performance. In the beginning, a comprehensive study of the analog and RF characteristics of JAM-GS GAA FinFET has been analyzed with the optimization of the fin aspect ratio at the sub nano level to achieve a high-performance transistor. It has been found that the analog and RF performance of the JAM-GS-GAA FinFET device improved significantly compared to conventional FinFET because of the enhanced gate control on the channel and reduced SCEs. When compared to conventional FinFET, parameters like switching (Ion/Ioff) ratio, gain transconductance frequency product (GTFP), and gain frequency product (GFP) increased by 31, 3.37, and 2.73 times, respectively, for the JAM-GS-GAA FinFET device. It has also been analyzed that the proposed device with the highest fin aspect ratio configuration exhibits the most improved analog and RF performance compared to the other lower fin aspect ratio configurations. The device with a high fin aspect ratio exhibits a considerable reduction of 94.72% in leakage current (Ioff) and 14.90% in subthreshold swing (SS), along with notable improvements in other metrics. Bhavya Kumar viii Further, the performance of the proposed JAM-GS-GAA FinFET device has been compared with other existing devices on different technologies at a fixed gate length of 10 nm to evaluate its significance. Then, the reliability issues of the proposed device have been explored by considering the impact of temperature and gate electrode work function in terms of static, analog, RF, linearity, and harmonic distortion characteristics. The study’s findings indicate that the JAM-GS-GAA FinFET demonstrates satisfactory reliability in the face of temperature fluctuations and changes in the gate electrode work function. The static, linearity, and harmonic distortion metrics do not change much as the temperature increases from 300 K to 500 K, while the peak values of parameters like gm, fT, TFP, gm2, gm3, VIP2, VIP3, HD2, and HD3 are approximately the same for all gate electrode work functions. Moreover, the impact of dual-k spacer (SiO2 + HfO2) engineering on the JAM-GS-GAA FinFET has been investigated to further enhance the performance of the proposed device and make it suitable for sub-10 nm RFIC circuits. Different configurations such as conventional tri-gate JAM-GS-FinFET, JAM-GS-GAA-FinFET without a spacer, JAM GS-GAA-FinFET with single-k spacers, and the proposed JAM-GS-GAA-FinFET with dual-k spacer have been examined. The dual-k spacer configuration uses HfO2 as a high-k spacer for the inner layer and SiO2 as a low-k spacer for the outer layer. Due to the fringing field effects, the dual-k spacer configuration improves the electron velocity, electric field, surface potential, and energy band profiles. Thereby increasing the ON-state (Ion) current of the dual-k spacer configuration by 35.34%, Ion/Ioff ratio by approximately 102 times, transconductance (gm) by 24.03%, transconductance generation factor (TGF) by 39.12%, quality factor (QF) by 46.75%, while decreasing the Ioff by over 76 times and SS by 15.47% compared to the conventional FinFET configuration. Further, the parasitic capacitances and small-signal behavior of JAM-GS-GAA FinFET have been inspected to assess the efficacy of GaAs as a fin material. Capacitance-related FOMs like gain bandwidth product (GBP) and transconductance frequency product (TFP) have also been analyzed for switching applications. It has been noticed that SCEs and parasitic capacitances reduced considerably, and the peak value of both GBP and TFP increased by 10 times with the incorporation of GaAs. Further, the effect that parameters like gate length (Lg), channel doping (NCh), fin width (WFin), gate electrode work function (ϕm), and temperature (T) have on the parasitic capacitances and scattering (S) parameters Bhavya Kumar ix of GaAs JAM-GS-GAA FinFET across the terahertz (THz) frequency range have been examined. The results confirm that the parasitic capacitances decreased appreciably for a device with a shorter Lg, smaller NCh, lower WFin and T, and higher ϕm, whereas, at extremely high frequencies, the S-parameters improved considerably for a device with a larger Lg, smaller NCh, lower WFin and T, and higher ϕm. After analyzing the electrical properties of the proposed device, the GaAs JAM-GS-GAA FinFET has been utilized to accomplish the electrical identification of the MDA-MB-231 breast cancer cell by monitoring the device switching ratio. The switching ratio-based device sensitivity has been evaluated by analyzing the drain current characteristics for air (cell free), MCF-10A (healthy), and MDA-MB-231 (cancerous cells), and it comes out to be 47.78% and 99.72% for healthy and cancerous breast cells, respectively. The sensor has also been assessed for its reproducibility, stability, and capability to distinguish between viable and non-viable cells and was found to be repeatable and adequately stable, with settling times of 55.51 ps for the MDA-MB-231 cell, 60.80 ps for the MCF-10A cell, and 71.58 ps for air. Further, the possibility of early detection of cancerous breast cells using Bruggeman’s model and the effect of biomolecule occupancy and frequency fluctuations on the device’s sensitivity has been investigated. The impact of the physical parameters, like fin height, fin width, gate electrode work function, channel doping, temperature, and drain voltage, on the device’s sensitivity has been explored. Finally, the GaAs JAM-GS-GAA FinFET sensor was compared to already existing breast cancer sensors, and it was found that the proposed sensor performed much better. Thus, JAM-GS-GAA FinFET can be considered a promising candidate for use in low power, analog, RF, and biosensor applications due to its high switching ratio, lower leakage current, better reliability in terms of temperature and gate electrode work function, superior static, analog, and RF performance, suppressed SCEs and parasitic capacitances, and high sensitivity electrical detection of MDA-MB-231 breast cancer cells.