The Anomalous Effect of Oxygen Ratio on the Mobility and Photobias Stability of Sputtered Zinc–Tin–Oxide Transistors

The oxygen ratio-dependent device performance and reliability of zinc tin oxide (ZTO) thin-film transistors (TFTs) were examined. ZTO TFTs fabricated under pure Ar conditions exhibited a high saturation mobility of 21.5 cm
²
/Vs, low subthreshold gate swing of 0.34 V/decade, and high I
_ON/OFF
ratio (10
⁹
), whereas modest mobility of 7.3 cm
²
/Vs was obtained for the ZTO TFTs prepared at an oxygen ratio [R = O
₂
/(Ar + O
₂
)] of 0.3. The photobias stability (AV
_th
≈-2.0 V) of the ZTO TFTs under the Ar only condition was much better than that (AV
_th
≈-5.9 V) of the device at R of 0.3, even though their channel layers contained the larger density of oxygen vacancies. This abnormal behavior was attributed to the compressive stress of ZTO films retarding the phototransition of oxygen vacancies.