Channel scaling and field-effect mobility extraction in amorphous InZnO thin film transistors

- We obtained high field-effect mobility μFE = 45.4 cm2/V·s in long channel L = 50 μm IZO TFTs.
- The apparent extracted μFE collapses as L is scaled down.
- A method for recovering the correct μFE is illustrated based on our TFT characteristics.

Amorphous oxide semiconductors (AOSs) based on indium oxides are of great interest for next generation ultra-high definition displays that require much smaller pixel driving elements. We describe the scaling behavior in amorphous InZnO thin film transistors (TFTs) with a significant decrease in the extracted field-effect mobility μFE with channel length L (from 39.3 to 9.9 cm2/V·s as L is reduced from 50 to 5 μm). Transmission line model measurements reveal that channel scaling leads to a significant μFE underestimation due to contact resistance (RC) at the metallization/channel interface. Therefore, we suggest a method of extracting correct μFE when the TFT performance is significantly affected by RC. The corrected μFE values are higher (45.4 cm2/V·s) and nearly independent of L. The results show the critical effect of contact resistance on μFE measurements and suggest strategies to determine accurate μFE when a TFT channel is scaled.