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

ITO thin films (100‐200 nm) are deposited on glass and plastic (PET and polycarbonate) substrates by r.f. sputtering. Process parameters such as oxygen partial pressure, r.f. power, and post deposition annealing parameters are varied to determine the dependence of the sheet resistance on process parameters. The microstructure of these thin films is determined using an X-ray diffractometer (XRD) and a transmission electron microscope (TEM). The experimentally 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 (<25 nm) in ITO films result in lower sheet resistance (250 V/A). This type of large grain size microstructure is produced with moderate r.f. power (<100 W) and low oxygen partial pressure (<10%). There is a unique correspondence between grain size and grain orientation. ITO films with a strong peak intensity ratio of (400) orientation to all other orientations (<0.35) have the largest grain size (<25 nm) resulting in the lowest sheet resistance (250 V/A) and high transmission ( < 86.7%) at la 550 nm. q 1999 Published by Elsevier Science Ltd. All rights reserved.