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

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 (P-O2) of 0 Pa consisted of 2 % Sn (Sn-0), 42 % Sn2+, and 56 % SnO2 (Sn4+). However, compared with the Sn2+ fraction observed after PDA under N-2 and low-vacuum (similar to 1 Pa) conditions, that after PDA at 300 degrees C under high vacuum (< 5 x 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 degrees C, exhibited p-type properties, including a relatively high on-current/off-current (I-on/I-off) ratio of 5.1 x 10(4) and a hole field-effect mobility (<mu>(FE)) of 1.8 cm(2)/(V<middle dot>s).