Fabrication and characterization of multifunctional thin multi-layer films for transparent conducting oxides

Dielectric/metal/dielectric (D/M/D) multi-layer thin films have been fabricated on a well-properly clean Mari-Enfield (commercial) glass substrate using an electron beam evaporation technique. In these three-layer nanostructures, different metals, i.e., Silver (Ag), Aluminium (Al), and Copper (Cu) have been selected as inter-layer while Hafnium oxide (HfO₂) used as a dielectric material. The substrate temperature during fabrication was kept at 150 °C, and the overall thickness of these sandwiched structures was 25 nm, i.e., Dielectric =10 nm (top layer), Metal =5 nm (inter-layer), and Dielectric =10 nm (bottom layer). X-ray diffraction (XRD) and atomic force microscopy (AFM) was used for the structural and surface analysis, respectively. XRD patterns indicate that these D/M/D layers were poly-crystalline with monoclinic phase, while the crystallinity of Cu based films were relatively better than Al or Ag. AFM micrographs reveal the smooth surfaces with low values of average and/or root mean surface (RMS) roughness. Optical properties were measured by using UV/VIS/NIR dual-beam lambda-9 spectrophotometer. The better transmission (in the visible region) and reflection (in the near-infrared region) may be a favorable characteristic for energy-efficient applications, heat mirror, and transparent conductive oxide, etc. Using measured transmission and reflection, various optical constants such as refractive index, extinction coefficient, and energy losses, etc. have been calculated. The electrical properties of these multi-layer films were determined through Keithley-2400 source meter using a four-point probe method. Sheet resistance values for Ag, Al and Cu based films are 5.62, 5.75, and 6.23 Ω/square, respectively.