Using Chemical-Mechanical Polishing for Planarizing a High-κ Nanocomposite Polyimide Insulator for Organic Thin Film Transistors Application

To solve the large leakage current of the heavily blended nanocomposite (Polyimide and nano-TiO₂ particles) gate dielectric film exhibiting a high-κ, the chemical-mechanical polishing (CMP) was adopted to flatten the surface of the PI–TiO₂ nanocomposite film. An extremely high dielectric constant (≅13) of the nanocomposite with CMP treatment is obtained and its leakage current is comparable to that of the neat polyimide in our studies. An OTFT based on the nanocomposite gate dielectric exhibiting high capacitance and a smooth surface after CMP treatment shows very promising performance. Compared with the OTFT based on the neat polyimide gate dielectric, the threshold voltage is improved from −22 to −5 (V), the sub-threshold voltage is decreased from 3.44 to 0.50 (V/dec), the current on/off ratio is increased from 1.6 × 10⁶ to 3.53 × 10⁸, and the mobility is increased from 0.416 to 0.624 (cm²V⁻¹s⁻¹). Moreover, it is worth noting that the hysteresis effect of OTFT based the nanocomposite can be significantly reduced due to the few charge trapped in the interface when the nanocomposite dielectric surface was further polished by CMP treatment.