AVS 60th International Symposium and Exhibition
    Transparent Conductors and Printable Electronics Focus Topic Wednesday Sessions
       Session TC+EM+TF-WeM

Paper TC+EM+TF-WeM1
Characterization of Thermal Plasma....

Wednesday, October 30, 2013, 8:00 am, Room 102 B

Session: Oxide and Flexible Electronics
Presenter: M. Kinsler, San Francisco State University
Authors: M. Kinsler, San Francisco State University
K. Teh, San Francisco State University
R. Harrison, San Francisco State University
Correspondent: Click to Email
A low-vacuum thermal plasma system is designed and developed to enable plasma-enhanced chemical vapor deposition and rapid plasma annealing of metal oxide thin films within the same system. Using this system, we have successfully synthesized optically transparent and electrically conductive, nanocrystalline zinc oxide (ZnO) thin films, with average grain sizes of between 75 nm and 150 nm at substrate temperatures ranging from 550C to 600C. Prior to synthesis, argon and oxygen are first introduced into the synthesis vessel, consisting of a quartz tube positioned in the center of an inductive copper coil, at 42 sccm and 0.07 sccm, respectively, with a background vacuum level of 1.15 PSIA. During synthesis, pure solid zinc precursor is melted and ionized by thermal plasma, and reacted with oxygen to form ZnO which is deposited on the substrate. Keeping the vessel pressure and substrate temperature constant, the growth rate of the ZnO films is approximately 15 nm/min. Using the same system, the ZnO-coated substrate can next be mounted on a different fixture and be annealed by thermal plasma at temperatures from 300C to 800C (0.25 to 0.38 T m of ZnO) in a pure argon environment at 1.15 PSIA background pressure. Comparing the as-synthesized and annealed samples using techniques such as scanning electron microscopy (SEM), x-ray diffraction (XRD), UV-Vis spectroscopy, and four-point probe sheet resistance measurements, we observed improvements in the properties of the post-annealed ZnO films in the following ways: 1) ZnO grain size increased from approximately 50 nm to 100 nm, 2) the number of grains decreased and hence the number of grain boundaries decreased, 3) grain morphology became smoother possibly indicating less internal strain, and 4) sheet resistance of the film decreased. We hypothesize the improved electrical properties are attributed to the reduction in both grain boundaries and internal stress--both of which are known to reduce electron mobility. Synthesizing and annealing metal oxides, such as ZnO, in the same system would reduce overall turnaround time as moving samples between systems is avoided. Ultimately, this method could pave the way for the production of high-quality, optically transparent, and electrically conductive metal oxide semiconductor thin films in a single, rapid operation within a low-cost, small-footprint benchtop system.