Investigation of rheological, structural, surface, optical and thermal properties of low temperature produced silver doped ZnO thick film as thermal interface material in lighting application

Effects of screen-printed Ag_xZn_1−xO thick film deposited on Al substrate with composition 3 wt% ≤ x ≤ 9 wt% on the rheological, surface, vibrational and thermal properties were investigated in this paper. Ag_xZn_1−xO powder with different doping concentration was synthesized through co-precipitation method and further mixed with solvent to form a thixotropic paste. The paste was screen-printed on Al substrate. Rheological behavior of pastes showed shear thinning phenomenon with increment of shear rate. Structural properties of pure and doped thick films were investigated by X-ray diffraction (XRD). It showed that (101) was a strong preferred orientation among other peaks. Field emission scanning electron microscopy (FESEM) results indicated the aggregated flake-like structure that become more prominent with increase of doping from 3 to 7 wt%. Surface roughness of the films exhibited a decreasing trend with the increase of silver content whereas the step analysis facilitated to identify the contact surface point of the film for thermal conduction in application purposes. By increasing the dopant’s concentration, peak position of ZnO had shifted within the range from 503 to 506 cm⁻¹. FTIR spectra of the films showed no vibrational peaks related to AgO or Ag₂O. Thermal characterization revealed a decreasing trend of film’s resistivity when the doping was increased to 7 wt%. The lowest achieved junction temperature with tested LED was measured at 47.32 °C at 7 wt% of silver doping.