| AVS 57th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Friday Sessions |
| Session EL+AS+EM+MS+TF-FrM |
| Session: | Spectroscopic Ellipsometry - Inorganic Thin Films |
| Presenter: | M.A. Motyka, Penn State University |
| Authors: | M.A. Motyka, Penn State University B.D. Gauntt, Penn State University E.C. Dickey, Penn State University M.W. Horn, Penn State University N.J. Podraza, Penn State University |
| Correspondent: | Click to Email |
Vanadium oxide (VOx) thin films are commonly used as an imaging material in uncooled infrared sensing devices. Material properties that make VOx useful for this application are a high temperature coefficient of resistance (TCR), controllable resistivity (ρ), and low electrical noise. A difficulty in growing VOx thin films arises from the many valence states of vanadium, which may result in formation of a film consisting of an undesirable phase or with the presence of multiple phases. Each phase has varying electrical properties and thus, the reliability and consistency in industrial fabrication is lowered. Furthermore, atmospheric exposure of the VOx films has been shown to alter the electrical and optical properties. In order to prevent changes in the desired material, VOx films are commonly capped with a thin layer of SiO2 before atmospheric exposure. In this study, vanadium oxide thin films were studied using in situ real time spectroscopic ellipsometry (RTSE) over a spectral range of 0.75 to 5.15 eV during deposition via pulsed DC-magnetron sputtering in an argon and oxygen atmosphere, with the set of variables being the total pressure, the oxygen-to-argon ratio, target power and the target material (metallic V, VO2, V2O5). These variables control the material growth and resulting optical and electrical properties. The growth evolution, complex dielectric function spectra (ε = ε1 + iε2), and structure obtained from RTSE have been shown to correlate with the electrical properties of the film. Ex situ Fourier transform infrared spectroscopic ellipsometry (FTIR-SE) measurements were also made to help characterize the materials in the spectral range of 0.05 to 0.75 eV, so that the optical properties in the range of microbolometer operation are obtained. Electrical measurements include temperature dependent I-V curve measurements to determine the VOx film resistivity and TCR as a function of processing conditions. Changes in the optical and electrical properties as a function of processing conditions including film thickness are explored for materials exhibiting amorphous or nanocrystalline (V, V2O, and VO phase) structures. RTSE is also used to monitor the changes in optical properties of the VOx layer and interfacial formation arising from the deposition of the SiO2 capping layer. The environmental stability of VOx with and without capping layers is also monitored via RTSE as the samples are initially exposed to the atmosphere after deposition. In this manner both intentional variations in film microstructure and electrical properties as a function of processing conditions and unintentional variations arising from material instability are studied.