Amorphous oxide semiconductors (AOS) have been extensively studied for their application in thin-ﬁlm electronics; an area which is currently dominated by hydrogenated amorphous silicon (a Si:H) technology. Indium-gallium-zinc oxide (IGZO) has garnered most of the AOS materials focus due to its high carrier mobility and process simplicity. When modifying an existing process ﬂow for fabrication of TFTs, the eﬀect of each modiﬁcation on the electrical characteristics must be determined. The compatibility of the process with the constraints of a glass substrate must also be considered. A new test chip layout was created that enables the fabrication of TFTs with a variety of electrode conﬁgurations including top-gate, bottom-gate, double-gate, and either staggered or co-planar source/drain regions. TFTs were fabricated on glass and oxidized silicon substrates, consisting of sputter-deposited IGZO surrounded by SiO2 dielectric layers, an oxidizing ambient anneal treatment, and a capping layer deposited by atomic layer deposition (ALD). Electrical characteristics from each process treatment and gate conﬁguration were compared, with some noted diﬀerences in device operation related to process integration. A SPICE level 2 compatible IGZO TFT model was developed, with extracted parameter values providing quantitative measures for comparison.
Library of Congress Subject Headings
Thin film transistors--Materials; Electrodes; Gallium compounds; Zinc compounds; Oxides
Microelectronic Engineering (MS)
Department, Program, or Center
Microelectronic Engineering (KGCOE)
Powell, Eli P., "The Influence of Alternative Electrode Configurations and Process Integration Schemes on IGZO TFT Operation" (2017). Thesis. Rochester Institute of Technology. Accessed from
Thin-film transistors (TFTs) with channel materials made out of hydrogenated amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si) have been extensively investigated. Amorphous silicon continues to dominate the large-format display technology; however newer technologies demand a higher performance TFT which a-Si:H cannot deliver due to its low electron mobility, µn ~ 1 cm2/V*s. Metal-oxide materials such as Indium-Gallium-Zinc Oxide (IGZO) have demonstrated semiconductor properties, and are candidates to replace a Si:H for TFT backplane technologies.
This work involves the fabrication and characterization of TFTs utilizing a-IGZO deposited by RF sputtering. An overview of the process details and results from recently fabricated IGZO TFTs following designed experiments are presented, followed by analysis of electrical results. The investigated process variables were the thickness of the IGZO channel material, passivation layer material, and annealing conditions. The use of electron-beam deposited Aluminum oxide (alumina or Al2O3) as back-channel passivation material resulted in improved device stability; however ID VG transfer characteristics revealed the influence of back-channel interface traps.
Results indicate that an interaction effect between the annealing condition (time/temperature) and the IGZO thickness on the electrical behavior of alumina-passivated devices may be significant. A device model implementing fixed charge and donor-like interface traps that are consistent with oxygen vacancies (OV) resulted in a reasonable match to measured characteristics. Modified annealing conditions have resulted in a reduction of back-channel interface traps, with levels comparable to devices fabricated without the addition of passivation material.
Walsh, Nathaniel, "Passivation of Amorphous Indium-Gallium-Zinc Oxide (IGZO) Thin-Film Transistors" (2014). Thesis. Rochester Institute of Technology. Accessed from