AbstractsComputer Science

Investigation of ultra-thin In-Ga-Zn-O thin-film transistors

by Tsung-Han Chiang

Institution: Oregon State University
Department: Electrical & Computer Engineering
Degree: MS
Year: 2015
Keywords: ultra-thin; Thin film transistors  – Design and construction
Record ID: 2058222
Full text PDF: http://hdl.handle.net/1957/55642


The objective of the work reported herein is to explore the impact of decreasing channel thickness on radio-frequency (RF) sputtered amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) electrical performance through the evaluation of drain current versus gate voltage (I[subscript D] − V[subscript G]) transfer curves. For a fixed set of process parameters, it is found that the turn-on voltage, V[subscript ON] (off drain current, I[superscript OFF][subscript D]) increases (decreases) with decreasing a-IGZO channel thickness (h) for h < 11 nm. The V[subscript ON] − h trend is attributed to a large density (3.5 × 10¹² cm⁻²) of backside surface acceptor-like traps and an enhanced density (3 × 10¹⁸ cm⁻³) of donor-like trap states within the upper ∼11 nm from the backside surface. The precipitous decrease observed in I[superscript OFF][subscript D] − h when h < 11 nm is ascribed to the backside surface acceptor-like traps and the closer physical proximity of the backside surface when the channel layer is ultra-thin. By altering the process parameters of gas ratio of Ar/O₂ from 9/1 to 10/0 and reducing the anneal temperature from 400 to 150°C, a h ≈ 5 nm a-IGZO TFT is demonstrated with V[subscript ON] ≈ 0 V, field-effect mobility of µFE = 9 cm⁻²V⁻¹s⁻¹, subthreshold slope of S = 90 mV/dec, and drain current on–to-off ratio of I[superscript ON/OFF][subscript D] = 2.0×10⁵.