UV illumination technique for leakage current reduction in a-Si:H thin-film transistors

The high photoconductivity of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) is responsible for the leakage current under illumination-particularly in projectors and displays with high-intensity backlight illumination. This work investigates a leakage current reduction approach, in which the inverted staggered a-Si:H TFTs are exposed to the ultraviolet (UV) laser. An 85% reduction in the leakage current in a-Si:H TFTs is experimentally observed. The general SPICE model (such as the RPI model) lacks the proper term to capture the photo-induced phenomena; therefore, the physical mechanisms that are associated with the illumination of a-Si:H TFTs under UV, including the energy state and the density of traps, are analyzed using device simulation. The I-V characteristics of the inverted staggered a-Si:H TFTs under different magnitudes of UV exposure are calibrated with experimentally measured data. The preliminary results show the change of trap states in amorphous silicon film and a shift of the Fermi level with UV illumination. UV illumination may induce traps in the active layer of the device and thereby reduce the OFF-state leakage current.