Compositional changes between metastable SnO and stable SnO2 in a sputtered film for p-type thin-film transistors

•Sputtered SnOx films from a SnOx target at PO2 = 0 Pa consisted of 42 % SnO.•The Sn2+ fraction increased to 62 % after high vacuum post-deposition annealing.•The p-SnO thin-film transistor exhibited Ion/Ioff = 5.1 × 104 and μ = 1.8 cm2/V·s. p-Type tin(II) oxide (SnO (Sn2+)) formation using radiofrequency (RF) reactive magnetron sputtering and post-deposition annealing (PDA) processes was investigated. The as-grown SnOx film deposited from an SnOx (SnO:Sn = 60:40) target by RF sputtering at an oxygen partial pressure (PO2) of 0 Pa consisted of 2 % Sn (Sn0), 42 % Sn2+, and 56 % SnO2 (Sn4+). However, compared with the Sn2+ fraction observed after PDA under N2 and low-vacuum (∼1 Pa) conditions, that after PDA at 300 °C under high vacuum (< 5 × 10−4 Pa) (HVPDA) increased substantially to greater than 62 %. This result was attributed to the transformation from SnO2 to SnO during HVPDA. A staggered bottom-gate thin-film transistor with an SnO channel (10 nm), which was fabricated by HVPDA at 300 °C, exhibited p-type properties, including a relatively high on-current/off-current (Ion/Ioff) ratio of 5.1 × 104 and a hole field-effect mobility (µFE) of 1.8 cm2/(V·s).