Ziqian Ding

Organic Digital Logic and Analog Circuits Fabricated in a Roll-to-Roll Compatible Vacuum-Evaporation Process

We report the fabrication of a range of organic circuits produced by a high-yielding, vacuum-based process compatible with roll-to-roll production. The circuits include inverters, NAND and NOR logic gates, a simple memory element (set-reset latch), and a modified Wilson current mirror circuit. The measured circuit responses are presented together with simulated responses based on a previously reported transistor model of organic transistors produced using our fabrication process. Circuit simulations replicated all the key features of the experimentally observed circuit performance. The logic gates were capable of operating at frequencies in excess of 1 kHz while the current mirror circuit produced currents up to 18 μA.

Hysteresis-Free Vacuum-Processed Acrylate–Pentacene Thin-Film Transistors

The electrical characteristics of all-vacuum-processed pentacene thin-film transistors, with stable and reproducible performance, using high-throughput roll-to-roll processing have been demonstrated. The method allows a polymerized tripropyleneglycol diacrylate (TPGDA) insulator layer of thickness up to 1 μm to be obtained in a single pass by ultrahigh flash evaporation of a monomer onto a web travelling at 10 m·min-1and subsequent irradiation with an argon plasma emitted from a dc-sputtering cathode. The resulting organic thin-film transistors (OTFTs) exhibited field-effect mobility of 0.12 cm2 V-1·s-1, a threshold voltage of -21 V, a turn-on voltage of -2 V, and an on/off current ratio of 1 × 105. The effect of ambient air moisture on the device characteristics was investigated, showing that moisture has a reversible effect on the performance of the OTFTs exhibiting a shift in the turn-on voltage and deterioration in the on-off ratio. However, the effect was eliminated using a simple conventional encapsulation method. Our vacuum-based process thus demonstrates excellent potential for providing an alternative route to low-cost large-area organic electronics manufacturing.

Improving the performance of organic thin film transistors formed on a vacuum flash-evaporated acrylate insulator

A systematic investigation has been undertaken, in which thin polymer buffer layers with different ester content have been spin-coated onto a flash-evaporated, cross-linked diacrylate gate-insulator to form bottom-gate, top-contact organic thin-film transistors. The highest device mobilities, ∼0.65 cm2/V s and ∼1.00 cm2/V s for pentacene and dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b]thiophene (DNTT), respectively, were only observed for a combination of large-grain (∼1–2 μm) semiconductor morphology coupled with a non-polar dielectric surface. No correlation was found between semiconductor grain size and dielectric surface chemistry. The threshold voltage of pentacene devices shifted from −10 V to −25 V with decreasing surface ester content, but remained close to 0 V for DNTT.