Low-Temperature Materials and Thin Film Transistors for Flexible Electronics

This paper addresses the low-temperature deposition processes and electronic properties of silicon based thin film semiconductors and dielectrics to enable the fabrication of mechanically flexible electronic devices on plastic substrates. Device quality amorphous hydrogenated silicon (a-Si:H), nanocrystalline silicon (nc-Si), and amorphous silicon nitride (a-SiN_x) films and thin film transistors (TFTs) were made using existing industrial plasma deposition equipment at the process temperatures as low as 75°C and 120°C. The a-Si:H TFTs fabricated at 120°C demonstrate performance similar to their high-temperature counterparts, including the field effect mobility (μ_FE) of 0.8 cm²V^-1s^-1, the threshold voltage (V_T) of 4.5 V, and the subthreshold slope of 0.5 V/dec, and can be used in active matrix (AM) displays including organic light emitting diode (OLED) displays. The a-Si:H TFTs fabricated at 75°C exhibit μ_FE of 0.6 cm²V^-1s^-1, and V_T of 4 V. It is shown that further improvement in TFT performance can be achieved by using n⁺ nc-Si contact layers and plasma treatments of the interface between the gate dielectric and the channel layer. The results demonstrate that with appropriate process optimization, the large area thin film Si technology suits well the fabrication of electronic devices on low-cost plastic substrates.