Dependence of the sheet resistance of indium-tin-oxide thin films on grainsize and grain orientation determined from X-ray diffraction techniques

ITO thin films (100-200 nm) are deposited on glass and plastic (PET and pol ycarbonate) substrates by r.f. sputtering. Process parameters such as oxyge n partial pressure, r.f, power, and post deposition annealing parameters ar e varied to determine the dependence of the sheet resistance on process par ameters. The microstructure of these thin films is determined using an X-ra y diffractometer (XRD) and a transmission electron microscope (TEM). The ex perimentally observed dependence of the sheet resistance on the grain size and grain orientation of these films is correlated to the dependence of the electron mobility on grain boundary scattering. Larger grain sizes (approx imate to 25 nm) in ITO films result in lower sheet resistance (250 Ohm/squa re). This type of large grain size microstructure is produced with moderate r.f. power (approximate to 100 W) and low oxygen partial pressure (approxi mate to 10%). There is a unique correspondence between grain size and grain orientation. ITO films with a strong peak intensity ratio of (400) orienta tion to all other orientations (approximate to 0.35) have the largest grain size (approximate to 25 nm) resulting in the lowest sheet resistance (250 Ohm/square) and high transmission( approximate to 86.7%) at lambda = 550 nm . (C) 1999 Published by Elsevier Science Ltd. All rights reserved.