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Open Access Publications from the University of California

Gravure-printed Highly-scaled Organic Thin-film Transistors for Low-cost and Large-area Electronics

  • Author(s): Kang, Hong Ki
  • Advisor(s): Subramanian, Vivek
  • et al.

Printed electronics using recently developed solution-processed electronic materials and incorporating conventional graphic arts printing presses has been proposed as an emerging technology for low-cost large-area electronic systems on flexible substrates (e.g. disposable RFID tags, flexible displays, and various types of sensors and actuators). For more than a decade, a significant amount of research in printed electronics has been focused on the development of high mobility printable semiconductor materials. Despite the recent achievements of the high mobility semiconductor materials that surpass the performance of amorphous silicon, overall performance of printed transistors on plastic is not adequate for the proposed applications due to the large dimension of the transistors with significant parasitic capacitance, and underperforming semiconductor materials when incorporated with mass-production printing techniques.

In this dissertation, we present a highly-scaled direct-gravure printing technique that allows sub-femtoliter scaling of printed inks, resulting in printed features as small as 4 μm while printed at high speed up to 1 m/s. By using this novel printing technique with the optimization of the high mobility organic semiconductors for the printed device fabrication processes, operation of gravure-printed inverters on plastic at frequencies above 1 MHz is achieved, which satisfies the performance requirements for most of the proposed applications. Along with the demonstration, we discuss how accurate pattern generation in various printing systems can be achieved with the knowledge of using contact angle hysteresis.

In addition, we discuss experimental results on understanding of the origin of 1/f noise in organic thin-film transistors, which particularly affects the performance of the devices in sensor applications. Based on detailed analysis of observed non-idealities in the 1/f noise with respect to various grain sizes, operation regions, and bias conditions, we found that the trapping/de- trapping of carriers within the semiconductor is the dominant mechanism of the low-frequency noise generation in the organic thin-film transistors.

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