Date of Award

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Committee Chair

Fat Duen Ho

Committee Member

James K. Baird

Committee Member

Sivaguru S Ravindran

Committee Member

Mark Tillman

Committee Member

Buren Earl Wells

Subject(s)

Ferroelectric devices., Field-effect transistors., Analog integrated circuits., Digital integrated circuits.

Abstract

In this dissertation, a novel device, the ferroelectric transistor, is studied, modeled, and applied to various circuit designs. Empirical data of several devices are presented alongside the theory behind the device operation. This theoretical understanding of the device is then used as the basis for a physically derived model, which is shown to agree with the experimental collected data. Lastly, these new devices are applied to several circuit designs ranging from digital to radio frequency and new operation of these circuits developed to highlight the unique and interesting features afforded by the addition of a ferroelectric layer. The primary focus of this work is the physically derived model, which computes the polarization of the ferroelectric material and resulting current in the semiconductor channel as a function of the applied electric field and polarization state. Limited use of empirically defined constants is employed, resulting in strong agreement with the current hysteresis with varying gate voltage with very little reliance on fabricated devices. The basis for a polarization retention model is also presented. Since ferroelectric devices are rarely available, experimental data collected to characterize the devices are presented and highlight the unique features of these novel transistors. Additionally, experimental data of the devices applied to radio frequency and digital circuits are presented. With the use of these ferroelectric transistors, new operation of the circuits is defined. In the ring oscillator, the ferroelectric material polarization is used as an additional tuning mechanism, resulting in increased operation frequency range. In digital circuits, the nonvolatile retention of the ferroelectric material is used as an additional storage device, and the variable conductivity of the channel gives rise to new operational modes. Most notable is the capability to store an additional data bit in the 1T1C memory cell.

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