Materials and Processes in the Fabrication of Particulate-Free and Particulate-Based Screen-Printed Metal and Metal Oxide Films for Electronic Applications

Abstract

In the present study, approaches towards the processing of screen-printed metal and metal oxide films for the optoelectronic and gas sensing applications are elaborated. Phase pure, highly reactive, nanocrystalline functional materials namely conducting (Ag and Ag-Cu) and semiconducting (CaVO3, pristine and doped ZnO) particles of nano to sub-micro size, which are decent for the formulation screen printing inks are obtained using polyol and facile solution combustion synthesis route respectively. A novel aqueous based combustible particle-free silver and ZnO screen printing inks possess the desirable thixotropic and shear thinning properties for the screen printing, are formulated by using eco-friendly binder Na-CMC and solvent water. The conventional particle based pristine and Sr-doped ZnO screen printing inks are comprised of 60 wt % of functional materials (ZnO/Sr-doped ZnO) and remaining organic vehicle made of Na-CMC and water. Crystalline silver films are processed by depositing particle free silver screen printing inks followed by annealing at 200 ºC, displays electrical conductivities in the range of 2-8 ×106 Sm-1. High conductive films with minimal thickness (3 μm) and high dimensional accuracy used as electrode for TFTs exhibit a μsat, Ion/Ioff, and Vth of 0.88 cm2 V−1s−1, 102, and ~0.3 V, respectively. High crystalline screen printed ZnO sensor processed at 500 °C from aqueous particle free-ZnO inks showed significantly high gas response (S = 336) and selectivity towards 5 ppm of NH3 under ambient conditions. Porous, well-adhered particle-based screen printed ZnO sensors processed from glycine fuel system exhibited good gas sensitivity towards NH3, C2H5OH, Cl2. Sr-doped ZnO sensor with smaller crystallite size and lesser lattice distortion exhibited highest gas response 70 towards the 50 ppm of NH3 gas at room temperature and also high selectivity to ammonia against various gases such as xylene, acetone and toluene. Upon RuO2 activation, NH3 response of RuO2/Sr-doped ZnO heterostructure sensor was diminished to ~2. La-doped BaSnO3 sensor exhibited superior gas response upon exposure of both the NH3 and HCHO gases than the BaSnO3, ceria and ruthenate sensitized La-doped BaSnO3 sensors.