High-performance inorganic-organic hybrid thin-film transistors (TFTs) are fabricated using semiconducting In2O3 thin-film deposited at room-temperature by ion-assisted deposition and thin organic dielectrics grown at near-room temperature. These hybrid TFTs combine the advantages of a high-mobility inorganic semiconductor with high-capacitance organic gate dielectrics. In2O3 thin-films exhibit high optical transparency in the visible region, a wide band gap, and smooth morphologies. Furthermore, the present In2O3 films are compatible with both inorganic dielectrics and nanoscopic high-capacitance/low-leakage organic dielectrics. The resulting transparent flexible TFTs exhibit near-1.0V operating characteristics with a very large field-effect mobility of > 100 cm2/V•s, and a near-zero threshold voltage. The high performance exhibits a significant improvement over previous organic and metal-oxide-based TFTs, and even rivals that of poly-Si TFTs. In addition, these TFTs exhibit great light- and air-stability when exposed to ambient.
In this paper, we present a novel device structure for organic electro-optic modulators using transparent conducting oxides (TCOs) as electrodes to substantially reduce the switching voltage, and describe their fabrication. We report two different types of device geometry, a top conducting and a side conducting geometry, and discuss their strengths and weaknesses. We discuss how the voltage and speed performance of such modulators are dependant on the conductivity/optical loss ratio of the TCO electrodes. Our device simulation shows that by appropriately engineering the high TCO conductivity/optical loss ratio, 4-6x lower switching voltage can be achieved while still maintaining high modulation frequencies and low optical loss. We show that certain new TCO materials are capable of achieving the high conductivity/optical loss required for efficient modulation in the 1300-1550 nm wavelength range. We summarize the optical loss characteristics at 1300 nm of different types of thin-film TCO materials grown using different deposition techniques. TCO electrodes based on different types of materials, such as In2O3, ZnO, and ITO have been investigated for our device structures. Fabrication issues associated with the deposition of TCO electrodes directly on organic EO materials and our approach to addressing them are discussed. Initial results for organic EO modulators fabricated with TCOs as electrodes are presented, and the performance of these modulators are compared with theoretical modeling results. The new device structures presented here will enable next generation low-voltage organic EO modulators targeting RF photonics applications.