Focused Review on Print-Patterned Contact Electrodes for Metal-Oxide Thin-Film Transistors

Metal-oxide-semiconductor-based thin-film transistors (TFTs) are exploited in display backplanes and X-ray detectors fabricated by vacuum deposition and lithographic patterning. However, there is growing interest to use scalable printing technologies to lower the environmental impact and cost of processing. There have been substantial research efforts on oxide dielectric and semiconductor materials and their interfaces. Materials for the source/drain (S/D) contact electrodes and their interface to the semiconductor have received less attention, particularly concerning the usage of printing processes. Specific contact resistivity of oxide TFTs with print-patterned S/D contacts can be 10(-2) to 10(1) omega cm(2), significantly higher than vacuum-deposited contacts around 10(-5) to 10(-3) omega cm(2). Problems at the semiconductor/S/D interface, such as large contact resistance, poor adhesion, or cross-interface contact material migration, affect device characteristics causing hysteresis loops, kink or step-like distortion, and threshold voltage shift. This work reviews advances in materials and fabrication methods of print-patterned S/D electrodes for oxide TFTs. Differences in characterization methods among existing literature hamper comparing the performance of print-patterned S/D contacts. Therefore, systematic and standardized measurements are proposed to assist identification of possible problems, which to some degree can then be mitigated by device fabrication strategies, facilitating well-performing printed contact electrodes for metal-oxide TFTs.