Hexagonal a-Si:H TFTs: A New Advanced Technology for Flat-Panel Displays

Inverted stagger hexagonal hydrogenated amorphous silicon thin-film transistors (a-Si:H HEX-TFTs) were fabricated with a five-photomask process used in the processing of the active-matrix liquid crystal displays. We show that the output current of a-Si:H HEX-TFTs connected in parallel increases linearly with their number within a given pixel circuit. Current-voltage measurements indicate that a high ON-OFF current ratio and a low subthreshold slope can be maintained for multiple HEX-TFTs connected in parallel, whereas the field-effect mobility and threshold voltage remain identical to a single a-Si:H HEX-TFT. Due to a unique device geometry, an enhanced electrical stability and a larger pixel aperture ratio can be achieved in the multiple a-Si:H HEX-TFT in comparison to a standard single a-Si:H TFT having the same channel width. These HEX-TFT electrical characteristics are very desirable for active-matrix organic light-emitting displays.