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

• Sputtered SnO x films from a SnO x target at P O2 = 0 Pa consisted of 42 % SnO. • The Sn 2+ fraction increased to 62 % after high vacuum post-deposition annealing. • The p-SnO thin-film transistor exhibited I on/ I off = 5.1 × 10 4 and μ = 1.8 cm 2 /V·s. p-Type tin(II) oxide (SnO (Sn 2+ )) formation using radiofrequency (RF) reactive magnetron sputtering and post-deposition annealing (PDA) processes was investigated. The as-grown SnO x film deposited from an SnO x (SnO:Sn = 60:40) target by RF sputtering at an oxygen partial pressure ( P O2 ) of 0 Pa consisted of 2 % Sn (Sn 0 ), 42 % Sn 2+ , and 56 % SnO 2 (Sn 4+ ). However, compared with the Sn 2+ fraction observed after PDA under N 2 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 SnO 2 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 ( I on / I off ) ratio of 5.1 × 10 4 and a hole field-effect mobility (µ FE ) of 1.8 cm 2 /(V·s).