Investigation of ultra-thin In-Ga-Zn-O thin-film transistors
Institution: | Oregon State University |
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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.