A high-yield vacuum-evaporation-based R2R-compatible fabrication route for organic electronic circuits

• Published in: Organic electronics Vol. 15; no. 7; pp. 1493 - 1502
• Main Authors: Patchett, Eifion R., Williams, Aled, Ding, Ziqian, Abbas, Gamal, Assender, Hazel E., Morrison, John J., Yeates, Stephen G., Taylor, D. Martin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2014; Elsevier
• Subjects: Applied sciences; Circuit properties; Circuit simulation; Cross-disciplinary physics: materials science; rheology; DNTT; Electric, optical and optoelectronic circuits; Electronic circuits; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Organic TFTs; Oscillators, resonators, synthetizers; Physics; Ring oscillators; Roll-to-roll process; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Transistors; Vacuum deposition; Vacuum-fabrication; Ring oscillators; DNTT; Organic TFTs; Circuit simulation; Vacuum-fabrication; Roll-to-roll process; Electric conductors; Performance evaluation; Spurious capacity; Chemical stability; Inverters; Thiophene; High vacuum; Degradation; Ring oscillator; Low voltage; Manufacturing processes; Drain current; Small molecule; Damage; Vacuum evaporation; Electronic circuits; Organic electronics; Semiconductor materials; Output signal; Buffer system; Thin film transistors; Polystyrene; Arrays; Vacuum deposition; On off effect
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2014.03.043

[Display omitted] •Low-cost vacuum-evaporation route for roll-to-roll production of organic circuits demonstrated.•DNTT transistors with mobility ∼1cm2/Vs produced at high yield: 90% for 90-TFT arrays, 100% for 27-inverter arrays.•Ring oscillator frequency ∼2kHz, severely limited by parasitic gate overlap capacitances.•Stable RO frequency for 8h continuous operation but amplitude decreases.•Environmentally stable – untested ring oscillators operate as new after 1month in storage. Advances are described in a vacuum-evaporation-based approach for the roll-to-roll (R2R) production of organic thin film transistors (TFTs) and circuits. Results from 90-transistor arrays formed directly onto a plasma-polymerised diacrylate gate dielectric are compared with those formed on polystyrene-buffered diacrylate. The latter approach resulted in stable, reproducible transistors with yields in excess of 90%. The resulting TFTs had low turn-on voltage, on–off ratios ∼106 and mobility ∼1cm2/Vs in the linear regime, as expected for dinaphtho[2,3-b:2′,3′-f] thieno[3,2-b]thiophene the air stable small molecule used as the active semiconductor. We show that when device design is constrained by the generally poor registration ability of R2R processes, parasitic source–drain currents can lead to a >50% increase in the mobility extracted from the resulting TFTs, the increases being especially marked in low channel width devices. Batches of 27 saturated-load inverters were fabricated with 100% yield and their behaviour successfully reproduced using TFT parameters extracted with Silvaco’s UOTFT Model. 5- and 7-stage ring oscillator (RO) outputs ranged from ∼120Hz to >2kHz with rail voltages, VDD, increasing from −15V to −90V. From simulations an order of magnitude increase in frequency could be expected by reducing parasitic gate capacitances. During 8h of continuous operation at VDD=−60V, the frequency of a 7-stage RO remained almost constant at ∼1.4kHz albeit that the output signal amplitude decreased from ∼22V to ∼10V. Over the next 30days of intermittent operation further degradation in performance occurred although an unused RO showed no deterioration over the same period.