Multi-pulse atomic layer deposition of p-type SnO thin films: growth processes and the effect on TFT performance

Abstract

This work demonstrates p-type SnO thin film transistors, where the SnO active layers were deposited with atomic layer deposition (ALD) using the Sn(II) alkoxide precursor, Sn(II) bis(tert-butoxide). The deposition optimisation explores the use of multiple Sn pulses per ALD cycle and the use of an exposure mode (where the pump extraction is paused before the Sn precursor purge) to increase the residence time and allow for more effective saturation of the surface. The fabricated devices required post deposition annealing of the active layer, with device performance further improved by back-channel passivation using ALD Al₂O₃. The performance of devices deposited using the varying precursor delivery modes has also been compared, with the devices utilizing deposition with multiple Sn pulses and a post deposition anneal at 250 °C achieving an on/off ratio of ∼4 × 10⁴ and field effect mobility (μ_FE) of 0.6 cm² (V s)⁻¹. The growth processes present during deposition with the different precursor delivery modes was investigated using fractal geometry and topographical scaling methods, with the poor device performance for the single Sn pulse deposition attributed to 2D lateral island growth.