Abstract

Amorphous oxide semiconductors (AOS) have emerged as compelling candidates for thin film transistors due to their remarkable attributes, including high mobility(>20cm2/Vs), low-temperature deposition, optical transparency, and electrical uniformity. However, current solutions, such as amorphous indium gallium zinc oxide (a-IGZO), exhibit sensitivity to moisture and wet etch processes, leading to suboptimal device performance and stability issues. To address these challenges, this study explores Indium Tungsten Oxide (IWO), an AOS devoid of Ga or Zn, as a potential material for fabricating high-performance and stable flexible enhancement mode thin-film transistors (TFTs). The experiment investigates the impact of oxygen partial pressure during the film deposition, anneal temperature, time, and ambient conditions on TFT performance. Bottom-gate unpassivated TFTs were fabricated with a 30 nm IWO film on a 6” silicon wafer with 650 nm isolation and 100 nm gate dielectric. Oxygen partial pressures (PO2) ranging from 2.5% to 10% were sputtered and deposited. The working metal was molybdenum for the gate electrode and Mo/Al bilayer for source/drain contacts. The unpassivated anneals were conducted across temperatures from 100°C to 300°C with varying durations and ambient conditions. Devices were tested using an HP4145 Semiconductor Parameter Analyzer connected to a probe station, with transfer characteristic measurements used to extract transconductance. The results identified an interaction effect between oxygen partial pressure (PO2), and the passivation anneal conditions on the transfer characteristics and associated parameters (i.e., VT, gm, SS). A 100 °C hotplate anneal for 1 hour established semiconducting behavior, with distinct differences based on PO2 values. All material samples experienced a transformation during a successive anneal for another hour at 200 °C, with significantly higher conductivity (depletion-mode). Semiconducting behavior was restored during additional hotplate annealing at 250 275 °C, with diminished residual oxygen partial pressure dependence. A furnace anneal in O2 at 300 °C for 30 minutes resulted in a convergence of characteristics over all oxygen partial pressure conditions, without obtaining enhancement mode operation.

Library of Congress Subject Headings

Thin film transistors--Materials; Thin film transistors--Testing; Indium alloys; Tungsten alloys

Publication Date

12-2023

Document Type

Thesis

Student Type

Graduate

Degree Name

Microelectronic Engineering (MS)

Department, Program, or Center

Electrical and Microelectronic Engineering, Department of

College

Kate Gleason College of Engineering

Advisor

Karl D Hirschman

Advisor/Committee Member

Michael Jackson

Advisor/Committee Member

Robert Pearson

Campus

RIT – Main Campus

Plan Codes

MCEE-MS

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