Novel Three State Quantum Dot Gate Field Effect Transistor: Fabrication, Modeling and Applications

Date of Completion

January 2011


Engineering, Electronics and Electrical




This dissertation presents the fabrication and circuit modeling of quantum dot gate field effect transistor (QDGFET) and quantum dot gate NMOS inverter (QDNMOS inverter). A conventional metal-oxide-semiconductor field effect transistor (MOSFET) conducts when the applied gate voltage is more than the threshold voltage of the device. Therefore, a MOSFET acts as a switch which cannot conduct below its threshold voltage and conducts beyond its threshold voltage. A quantum dot gate FET (QDGFET) produces three states in its transfer characteristic: OFF, ON and a low current saturation state known as intermediate state ("i") because of the presence of quantum dots in the gate region. Self consistent solution of Schrodinger and Possion equations can explain the manifestation of the intermediate state between OFF and ON states of the QDGFET. ^ The long channel QDGFETs were fabricated on (100) p-type silicon wafer as well as on silicon-on-insulator wafer. Two different types of quantum dots (SiOx cladded - Si and GeOx cladded - Ge) are site-specifically self assembled on top of the gate 20 Å silicon dioxide gate insulator grown by thermal oxidation and II-VI ZnS-ZnMgS gate insulator by metal organic chemical vapor deposition (MOCVD) technique. In QDNMOS inverter, SiO x cladded -Si dots are self assembled on top of thermally grown silicon dioxide in the gate region of the QDGFETs in the inverter circuit. ^ This thesis also introduces the development of a circuit model of QDGFET based on Berkley Short Channel IGFET model (BSIM). Different ternary logic circuits based on QDGFET are also investigated in this thesis. Advanced circuit such as three-bit and six bit analog-to-digital converter (ADC) and digital-to-analog converter (DAC) were also simulated. ^