Low Subthreshold Swing and High Performance of Ultrathin PEALD InGaZnO Thin-Film Transistors

Amorphous indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) were fabricated by plasma-enhanced atomic layer deposition (PEALD). The thicknesses of the IGZO thin films varied between 3 and 7.5 nm. The device parameters were optimized at 5 nm, at threshold voltage of −0.07 V, effective mob...

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Bibliographic Details
Published in:IEEE transactions on electron devices 2021-04, Vol.68 (4), p.1670-1675
Main Authors: Jeong, Seok-Goo, Jeong, Hyun-Jun, Park, Jin-Seong
Format: Article
Language:English
Subjects:
Accumulation thickness
amorphous oxide thin-film transistor (TFTs)
Atomic layer epitaxy
Carrier density
Electron mobility
Gallium
Hall effect
Indium gallium zinc oxide
indium gallium zinc oxide (IGZO)
Indium tin oxide
interface scattering
Performance evaluation
plasma-enhanced atomic layer deposition (PEALD)
Reliability analysis
Semiconductor device measurement
Semiconductor devices
Stress
Thermal stress
Thickness
Thickness measurement
Thin film transistors
Threshold voltage
Transistors
Transmission line measurements
Zinc oxide
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Summary:Amorphous indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) were fabricated by plasma-enhanced atomic layer deposition (PEALD). The thicknesses of the IGZO thin films varied between 3 and 7.5 nm. The device parameters were optimized at 5 nm, at threshold voltage of −0.07 V, effective mobility of 34.16 cm 2 /Vs, and subthreshold slope of 75 mV/decade and did not further improve with increasing thickness. To understand the origin of the saturated device properties, the accumulation thickness of TFTs was measured and calculated to be 6.4 nm. In addition, to investigate the origin of degraded properties of 3 nm IGZO TFTs, the Hall effect, interface trap density ( {D}_{it} ), and series resistance were measured. The carrier concentrations were nearly constant regardless of the channel thickness, but the resistivity and Hall mobility were degraded considerably in the 3 nm IGZO. In addition, the {D}_{it} and series resistance in the 3 nm TFT were 1.49 \,\times \, 10^{12} /eVcm 2 and 143.9~\Omega cm, respectively, which are relatively higher than those of the other TFTs. Finally, the device reliability of IGZO TFTs under bias thermal stress was assessed. The threshold voltage shift was less than 1 V under 125 °C and 1.5 MV/cm stress conditions.
ISSN:0018-9383
1557-9646
DOI:10.1109/TED.2021.3062321