Ink-jet Printed CdS Thin Film Transistors Fabricated In-situ by Micro-reaction

J.C. Ramos, D. Kabir, J.I. Mejia, C.A. Martinez, M.A. Quevedo-Lopez
University of Texas at Dallas, US

Keywords: ink-jet printing, cadmium sulfide, thin film transistors

Summary:

Printed electronics has become a promising technology due to its lithography and vacuum-free processing. However, several issues remain unsolved: most printable semiconductors nowadays are organic molecules with low mobilities and poor air and moisture stability. Inorganic chalcogenides, such as CdS have reported as active layers in TFTs, by printing nanoparticles. However, these devices have poor performance. Furthermore, this technique requires complicated synthesis of nanoparticles and the use of organic stabilizers that layers degrade the electrical performance. Here, we report the study of a new, simple, reduced material wastage and inexpensive additive method, combining merits of the on-chip synthesis approach (does not require nanoparticle synthesis) and ink-jet printing to grow nanocrystalline CdS thin films as semiconducting layer in TFTs. The TFTs showed n-type modulation with resistivities in the order 1x105 Ω•cm, on/off ratios of 103, VT of 3.4 V and mobility of ~0.1 cm2/V•s in atmospheric conditions. We have also studied the physicochemical and morphological properties of the films as function of deposition parameters, such as solvents, concentration, substrate temperature and post deposition treatments. This approach demonstrates a new and efficient solution-processed route for manufacturing semiconductor CdS thin films, offering performance that can be comparable or better than several organic semiconductors.