p-Type ${\hbox{Cu}}_{x}{\hbox{O}}$ Films Deposited at Room Temperature for Thin-Film Transistors

Thin-films of copper oxide (Cu
x
O) were sputtered from a metallic copper (Cu) target and studied as a function of oxygen partial pressure (O
_PP
). A metallic Cu film with cubic structure obtained from 0% O
_PP
has been transformed to cubic Cu
₂
O phase for the increase in O
_PP
to 9% but then changed to monoclinic CuO phase (for O
_PP
≥ 25%). The variation in crystallite size (calculated from x-ray diffraction data) was further substantiated by the variation in grain size (surface microstructures). The Cu
x
O films produced with O
_PP
ranging between 9% and 75% showed p-type behavior, which were successfully applied to produce thin-film transistors.