Browsing by Author "Teferi, Demisew"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Modeling Carbon Nanotube Field Effect Transistor for Analog and Digital Circuit Design with VHDL-AMS
    (Addis Ababa University, 2011-07) Teferi, Demisew; Adeyabeba, Abera (PhD)
    The objective of this thesis is to study the basic electronic properties of carbon nanotubes (CNTs here after) and to model the I-V characteristics of metal-oxide-semiconductor field-effect transistor like carbon nanotube field effect transistor (MOSFET-like CNTFET). And finally validate the model by constructing circuits. Electronic properties such as energy band structure, density of state, carrier density, carrier velocity and effective mass are investigated. A complete analytical model of MOSFET-like CNTFET is developed and it was validated by construction of circuits. MOSFET-like CNTFET is chosen because of their relative unipolar property. The model developed is based on analytical calculation of channel potential using electrostatic capacitance and quantum capacitance. Electron phonon scattering effect, band to band tunneling effect (BTBT), source/drain doped region resistance and contact resistance effects are considered in this model. The model requires neither iteration nor numeric integration, hence suitable for hardware description language (HDL) implementation. The model was implemented in VHDL-AMS. Parameters such as gate insulator thickness, gate insulator dielectric constant, CNT diameter, channel length and temperature are examined to observe the performance dependency. Results showed that reducing insulator thickness and increasing dielectric constant improve performance with no compromise other than cost. Channel length scaling increases on-current and also increases off-current, for high bias voltage due to BTBT effect. In addition, the effect of temperature on performance of MOSFET-like CNTFET and the dependency of threshold voltage on diameter of CNT was observed. Finally, using the VHDL-AMS model, circuits were constructed. Resistive-Load inverter, CMOS inverter, and phase shift oscillator circuits are constructed, simulated, and analyzed.