Velocity-field characteristics and device performance in nanoscale amorphous oxide Thin-Film-Transistors

TL;DR

This paper investigates electron velocity-field characteristics in nanoscale amorphous oxide FETs, combining experimental data with a physics-based model to understand device operation for advanced memory and AI applications.

Contribution

It introduces a comprehensive physical model that accounts for trapping, transport, and heating effects in amorphous oxide FETs, applicable to various emerging semiconductors.

Findings

Carrier velocity saturates at high electric fields.

Velocity exceeds 2 million cm/s on average, over 4 million cm/s in the band.

Model includes contact resistance, Joule heating, and carrier heating effects.

Abstract

The electron velocity-electric field characteristics in short channel length (50-100 nm) amorphous oxide field-effect transistors (FETs) are described using measured experimental data from indium gallium zinc oxide (IGZO) FETs in conjunction with a physics-based model. Such understanding is crucial for the design of FETs for emerging applications such as in back-end-of-line circuitry for advanced memories and artificial intelligence hardware. In such semiconductor systems, there is an interplay between trapping and extended state (band) transport that has to be considered in detail for a more complete physical understanding of device operation. The approach described in this paper demonstrates such a method and its use for an exemplary semiconductor IGZO. It can be used in many emerging thin-film semiconductors, including several amorphous oxide semiconductors. The carrier mobility is calculated for dominant scattering mechanisms such as trapped carrier scattering and optical phonon scattering. The carrier velocity is computed from the mobility using a modified Caughey-Thomas equation. The physical model considers contact resistance, Joule heating, and electric-field-induced carrier heating, all of which are very important in small geometry FETs. The carrier velocity exhibits a tendency to saturate at high electric fields and reaches values > 2*10^6 cm/s when averaged over all induced carriers (both trapped and in the band) and > 4*10^6 cm/s for carriers in the band.