The Applicability of Ferroelectrics for Analog and Digital Transistor Applications

  • Author / Creator
    Yuan, Zhi Cheng J
  • As transistors scale to ever smaller dimensions, power density becomes an increasingly important issue in integrated circuit (IC) design. Recently, negative-capacitance field-effect transistors (NCFETs), realized by stacking ferroelectric material on top of conventional gate oxides, have been proposed to reduce power consumption in modern aggressively scaled devices. The negative capacitance of these ferroelectric materials provide voltage amplification to the transistor in order to reduce the subthreshold-swing (SS), which would reduce the active power consumption of the device via a reduction of the supply voltage. Beyond reduction of power consumption for individual transistors, the unique negative capacitance behavior in these ferroelectric materials also offers a vast array of options in modern IC design. As a result, ferroelectric materials are an exciting area of research.

    The current state-of-the-art modeling approach for the dynamics of ferroelectric materials is via the Landau-Khalatnikov (LK) equation. In this work, we implement a multi-domain improvement upon the LK equation and combine it with Cadence circuit simulations to model and predict the characteristics of NCFETs and other ferroelectric devices.
    In the first stage of this work, we calibrate our multi-domain LK model to experimental results to show a very strong match. Using this calibrated model, we examine the potential speed limitations of NCFETs and identify the requirement on the viscosity parameter of the ferroelectric materials to provide sub-picosecond rise time required for modern transistors.
    In the second stage, we propose a new measurement technique for extracting the LK parameters of a ferroelectric material. We demonstrate via Cadence circuit simulation that this new measurement technique is able to accurately extract all LK parameters, including the viscosity parameter, which is difficult to extract using standard techniques.
    In the third stage, we propose a new application for ferroelectric materials to increase the unity-current-gain frequency f_T of a transistor. By placing the ferroelectric in parallel with the FET gate, the negative capacitance of the ferroelectric cancels the positive gate capacitance of the FET, which in turn increases the f_T. This new application of ferroelectrics opens new possibilities for IC design.
    Overall, this work improves the understanding of ferroelectric materials pertaining to their applications in IC design, providing critical information for the electron device community as it continues to explore methods to advance the performance of nanoscale electronics into the 2030s and beyond, the current horizon of the International Roadmap for Devices and Systems.

  • Subjects / Keywords
  • Graduation date
    Spring 2022
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.