Non vacuum processing of electronic devices drives new opportunities to develop unconventional products. Among many advantages, inkjet-printers are easy to handle, maintain, and fabricate electronic devices. Furthermore, inkjet-printing eliminates the need for photolithography, resulting in massive cost reductions in fabrication time and cost. Inkjet-printing can be applied to both organic and inorganic materials on any size and material substrate.
At ADRC, we have developed various inorganic materials based on metal oxides semiconductors. Amorphous oxides such as zinc tin oxide (ZTO), polycrystalline indium oxide (InOX), and tin oxide (SnOX) have been investigated. With a maximum process temperature of 300 oC, the TFTs have high mobility’s exceeding 40cm2/Vs, thus competing with vacuum processed devices for flexible applications. Active-matrix displays and electronic circuits based on high performance organic TFT (OTFTs), arrays for E-paper, TFT-LCDs and AMOLEDs were fabricated on plastic substrates by inkjet printing. Soluble p-type and n-type TFTs were also ink-jet printed. We have obtained TFT devices with outstanding performance characteristics. In order to further enhance the performance, more optimization strategies are to be developed.
1) Inkjet Printed TFT Process
Before the oxide material is inkjet printed, a solution of that material is prepared. The solution is prepared by mixing a precursor solution of the oxide material with a solvent. In the case of the InOX TFT, the gate insulator is solution processed AlOX (solvent: Acetonitrile/ Ethylene-glycol; precursor: AlCl3) that is deposited by spin coating, whereas the active layer is solution processed InOX (solvent: Acetonitrile/ Ethylene-glycol; precursor: InCl3) that is deposited by inkjet printing.
2) Operation of Inkjet Printed TFT
Figure 1 shows transfer characteristics of the InOX TFT with a spin coated AlOX gate-insulator and inkjet-printed InOX active layer. The TFT exhibits high mobility, low threshold voltage and very good on/off ratio.
Figure 1.Transfer characteristics of a spin-coated InOX TFT.
[1] C. Avis and J. Jang, Electroch. Solid-State Lett., 14, J9(2011)
[2] C. Avis and J. Jang, J. Mater. Chem., 21, 10649(2011)
