A High-Performance Short-Channel Bottom-Contact OTFT and Its Application to AM-TN-LCD

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Abstract
We have demonstrated an organic thin-film-transistor (OTFT)-driven active-matrix twisted-nematic liquid crystal display (AM-TN-LCD) on a glass substrate, with a resolution of 160/spl times/120 pixels, 79 ppi. Substrate temperature was kept below the plastic-compatible temperature of 180/spl deg/C throughout the fabrication process. In order to realize an OTFT-driven display with fine resolution, we employed short-channel bottom-contact (BC) pentacene OTFTs. It has been known that their drivability is limited by contact resistance at source/drain (S/D). We found that the S/D contact resistance was markedly reduced when the thickness of the nonohmic Ti adhesion layer for ohmic Au S/D electrodes was reduced less than /spl sim/3 nm. We elucidate that this 3 nm corresponds to the thickness of the accumulating layer in a pentacene channel. When we use a self-assembled monolayer of mercapto-silane-coupling agent as the adhesion layer, the contact resistance becomes negligibly small and BC OTFTs scalable below 10 /spl mu/m were obtained. In addition to this OTFT-cell technology, we developed a low-damage pentacene patterning technique for integration of OTFTs and introduced low-temperature panel assembly process to suppress thermal-stress degradation of pentacene OTFTs, which are the key technologies to achieve OTFT-driven AM-TN-LCD.