Fabrication Of Ion Gel Gated Organic Thin Film Transistor And Application

The organic thin film transistor(OTFT) shows great potential for a wide range of innovative applications including flexible displays, low cost smart tags and so on. Attributed to its advantages of excellent mechanical flexibility, capability of being fabricated by low temperature solution processes, and compatibility with arbitrary substrates such as plastic and paper. However, OTFTs generally require high operation voltage and present low driving current, which severely restrict their applications. To address this issue, this thesis investigates OTFTs using ion gel films as the gate dielectric layer. In an ion gel film, moving of cation and anion ions under a voltage bias can form an electric double layer structure, resulting very large specific capacitance in the level of μF/cm2, even with a micrometer-level thick film. Therefore, the required voltages for switching the OTFT can be significantly reduced, and the ON state curreng can also be much improved.To fabricate the ion gel gated OTFTs, a “cut and bond” process was developed in this thesis. Large size ion gel film formed with a simple coating process was cut into small size pieces. The obtained small size ion gel sheets were then placed onto the organic semiconductor layer by a commercial die bonder to fabricate top gate bottom contact OTFTs. The technology addresses the issues of damaging or contaminating the channel layer when depositing the ion gel layer on top in conventional fabrication approach, and enable accurate control of alignment and pressure during the lamination process for circuit integration. The formed isolated dielectric regions can help to eliminate possible lateral electric field coupling through the dielectric layer when several devices are integrated to construct functional circuits. The fabricated OTFTs provide mA-level ON current, and an ON/OFF current ratio higher than 105 with the gate swing voltage of less than 3 V. As an application examples, inorganic light emitting diodes(LEDs) in different colors were integrated with the OTFTs using the same die bonder on plastic substrate, and the light emission of the LED can be modulated in a wide range from dark to high brightness with change of the gate voltage less than 3 V.