Exploration of Ferroelectric Devices for Use in Radio-Frequency Nanoelectronics
Creators: Wang, Ji Kai
Publisher: name: University of Alberta Library
Year: 2023

<p>Since the 1970s, the rapid advancement of semiconductor electronic devices has facilitated an explosive growth of computation power in chips, which is exemplified by the rapid advancement of electronics such as high-tech consumer electronics including personal computers, smartphones, and other smart devices in the past few decades. Historically, this incredible advancement was driven by the geometrical downscaling of transistor dimensions, which allowed more transistors to be packed into the same chip area, thereby improving performance. However, numerous challenges have arisen in recent years, resulting in a gradual slowdown of downscaling. For example, the transistor gate length, a critical dimension affecting device performance, is predicted to stop scaling at 12 nm in 2028. To meet the increasing computational demand of current and emerging applications such as Artificial Intelligence and Internet-of-Things, further innovation at the device level is required.</p>

<p>One important direction to improve device performance that has recently emerged is the proposed use of ferroelectric materials in nanoelectronic devices. Ferroelectric materials are predicted by the Landau-Khalatnikov (LK) model to exhibit negative capacitance. Recently, the integration of ferroelectrics into field-effect-transistors (MOSFETs), creating so-called “negative-capacitance FETs (NCFETs),” has been proposed. Due to negative capacitance, NCFETs are expected to exhibit a higher on-current and a lower subthreshold slope compared to standard FETs, both of which are extremely desirable characteristics for increasing the performance of chips.</p>

<p>Since the inception of NCFETs in 2008, numerous studies have examined the performance of these novel devices for use in digital applications, However, one facet that has not yet been thoroughly explored is their radio-frequency (RF) performance. As such, this work will explore the potential for ferroelectric devices to be used in future RF systems.<br>
In the first stage of this work, an initial assessment of RF performance of NCFETs is conducted using calibrated numerical simulations. Through the comparison of the important figures of merit fT, fmax, and gmfT/ID, where fT is the unity-current-gain frequency, fmax is the unity-power-gain frequency, gm is the transconductance, and ID is the dc bias current, NCFETs were found to be able to exhibit similar fT and fmax, but a higher gmfT/ID compared to a standard MOSFET, demonstrating their potential as strong candidates for future RF electronics.</p>

<p>In the second stage of this work, a further in-depth assessment of RF performance for NCFETs is conducted in terms of fT and gmfT/ID, with an emphasis on the potential for NCFETs to mitigate the effects of parasitic capacitances. Through a comparison of fT and gmfT/ID between an NCFET and a standard MOSFET, it is predicted that NCFETs can indeed mitigate the effects of parasitic capacitances and improve fT and gmfT/ID over a standard MOSFET. This second study further emphasizes the importance of NCFETs for future RF applications, as parasitic capacitance continues to increase as dimensions are scaled down.</p>

<p>In the third stage of this work, the applications of ferroelectrics beyond their use in the gate stack of a FET is explored by examining the potential to use negative capacitance in constructing a tunable oscillator. It was found that tunable oscillations with an extremely wide tuning range can be achieved by replacing the inductor in a standard oscillator with a ferroelectric capacitor, which is much smaller than the inductor. The proposed design is an important step both towards exploring the RF applications of ferroelectrics outside of NCFETs and towards a new oscillator circuit that can address the challenges of existing inductor-based designs.</p>

<p>Overall, this work explores the potential for ferroelectric devices to be used in future RF applications by examining the RF performance of NCFETs and by exploring the use of ferroelectrics for the construction of a tunable oscillator. The results provide important insights and predictions that motivate the continued exploration and optimization of novel ferroelectric devices in the on-going effort to improve the performance of nanoscale electronics to meet the demand of current and future applications.</p>