Additive effect of poly(4-vinylphenol) gate dielectric in organic thin film transistor at low temperature process.

We fabricated pentacene-based organic thin film transistors (OTFTs) with formulated poly[4-vinylphenol] (PVP) gate dielectrics. The solution of gate dielectrics is prepared by adding methylated poly[melamine-co-formaldehyde] (MMF) and photo-initiator (PI) [1-phenyl-2-hydroxy-2-methylpropane-1-one, Darocur1173@Ciba] to PVP By using a small amount (2.4 wt%) of PI, the cross-linking temperature is lowered to 90 degrees C, which is lower than general thermal curing reaction temperature for the cross-linked PVP (> 180 degrees C). The hysteresis and the leakage current of the OTFTs are also decreased by adding the MMF and PI in the PVP gate dielectric.

The effect of thermal annealing on pentacene thin film transistor with micro contact printing.

We used micro contact printing (micro-CP) to fabricate inverted coplanar pentacene thin film transistors (TFTs) with 1-microm channels. The patterning of micro-scale source/drain electrodes without etch process was successfully achieved using Polydimethylsiloxane (PDMS) elastomer stamp. We used the Ag nano particle ink as an electrode material, and the sheet resistance and surface roughness of the Ag electrodes were effectively reduced with the 2-step thermal annealing on a hotplate, which improved the mobility, the on-off ratio, and the subthreshold slope (SS) of the pentacene TFTs. In addition, the device annealing on a hotplate in a N2 atmosphere for 30 sec can enhance the off-current and the mobility properties of OTFTs without damaging the pentacene thin films and increase the adhesion between pentacene and dielectric layer (SiO2), which was investigated with the pentacene films phase change of the XRD spectrum after device annealing.

Study of surface-modified PVP gate dielectric in organic thin film transistors with the nano-particle silver ink source/drain electrode.

We have fabricated the flexible pentacene based organic thin film transistors (OTFTs) with formulated poly[4-vinylphenol] (PVP) gate dielectrics treated by CF4/O2 plasma on poly[ethersulfones] (PES) substrate. The solution of gate dielectrics is made by adding methylated poly[melamine-co-formaldehyde] (MMF) to PVP. The PVP gate dielectric layer was cross linked at 90 degrees under UV ozone exposure. Source/drain electrodes are formed by micro contact printing (MCP) method using nano particle silver ink for the purposes of low cost and high throughput. The optimized OTFT shows the device performance with field effect mobility of the 0.88 cm2/V s, subthreshold slope of 2.2 V/decade, and on/off current ratios of 1.8 x 10(-6) at -40 V gate bias. We found that hydrophobic PVP gate dielectric surface can influence on the initial film morphologies of pentacene making dense, which is more important for high performance OTFTs than large grain size. Moreover, hydrophobic gate dielelctric surface reduces voids and -OH groups that interrupt the carrier transport in OTFTs.