Design and Modeling of InxGa(1−x)As/InP based Nanosheet Field Effect Transistors for High Frequency Applications

Sammanfattning: The advancement of CMOS technology has been fueled by the need to satisfy Moore’s law by shrinking transistors to progressively smaller sizes and increasing the transistor density per unit area [1]. The dimension of the state-of-the-art MOSFET is now down to a few nanometers. However, with continued device scaling, the performance of Integrated Chips (ICs) starts to deteriorate, making it essential to implement novel technology solutions. The novel technologies, such as reshaping the devices’ geometries in [2], achieved better excellent electrostatic performance than planar technologies. For example, 3D finFETs or tri-gate architectures showed improved electrostatic control and necessitated further scaling of the transistor length. Nanosheet FETs showed higher drive currents than FinFET technology at a given fin pitch and can further provide gate length scaling [3]. The geometry of the nanosheets allows all-around gate contact offering excellent electrostatic integrity. Power dissipation in CMOS applications is getting worse due to aggressive scaling [4]. One can overcome this by adding material to the channel with higher transport qualities, such as InGaAs [5]. The higher carrier mobility compared to Si enables high current at low operating voltages. In this thesis, InGaAs nanosheet FETs high-frequency performance is investigated. The wider and thinner nanosheets are considered for analysis and are modeled with quasi 2D ballistic model. The device's extrinsic part, such as extrinsic capacitance, is modeled using electrostatic model in COMSOL. The intrinsic and extrinsic parts are combined, and the high-frequency metrics such as transition frequency, f_{T}, and the oscillation frequency, f_{max}, are evaluated. The device is optimised in terms of nanosheet width, thickness, separation between two stacks, source/drain spacer distance, the number of stacked channels and the composition of the material are optimized to get the best performance.