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Screen printed organic thin film transistors (OTFTs) on a flexible substrate

OTFTs have recently received much attention because organic materials are more compatible with low temperature and low cost on flexible substrates than a-Si TFTs1. In addition, printing processes are more compatible with OTFT fabrication than a-Si TFTs2. This paper reports a materials compatibility study of various organic gate dielectrics with screen-printed electrodes for pentacene based TFTs. Standards were prepared using the polymer dielectrics and gold drain/source electrodes on a glass substrate. Poly(vinylphenol) (PVP) and benzocyclobutene (BCB) were spin coated and parylene was vapor deposited as dielectric materials. Pentacene was vapor deposited onto the substrates. Test devices were fabricated by painting drain/source electrodes onto the 3 dielectrics. The pentacene/PVP/gold devices had the best performance with mobilities near 0.3 cm2/V-sec, on/off current ratios between 103-104. When screen printable electrodes were introduced to the PVP system, device performance was significantly degraded. The BCB device performance was nearly the same for each device material; the parylene device performance was superior with the screen printable conductive inks relative to the gold devices. Using these data, a potentially low cost device was fabricated on a Mylar substrate with an ITO gate electrode, parylene dielectric, and screen-printed silver ink for drain/source electrodes. On/off current ratios were between 103 and 104. Mobilities ranged from 0.02 - 0.08 cm2/V-sec.