Additively Manufactured Zinc Oxide Thin-Film Transistors Using Directed Assembly

Zinc oxide (ZnO) has been extensively investigated for application in thin-film transistors (TFTs) due to its excellent electrical and optical properties. Although some ZnO-based TFTs have been successfully commercialized, the commercially available ZnO TFTs are mainly fabricated by physical vapor deposition methods, such as sputtering, which are costly and require state-of-the-art fabrication facilities. Here, we report the fabrication of ZnO TFTs using additive-directed assembly of ZnO particles into micropatterned films. By controlling the concentration of the ZnO nanoparticle suspension, void-free ZnO micropatterns can be assembled on silicon/silicon dioxide (Si/SiO2) substrates over a 4 in. wafer. The assembled ZnO micropatterns are thermally sintered prior to the deposition of the source/drain electrodes. The results demonstrate that the TFTs fabricated using ZnO micropatterns sintered at or below 800 ? possess high on-currents because of the removal of the stabilizers. However, the TFTs are normally on with I-on/I-off current ratios below 10 due to the intrinsic high carrier concentration of ZnO. Whereas when the patterns are sintered at 1000 ?, a gate-voltage-modulated field effect appears. The TFTs work in an accumulation mode with I-on/I-off ratios above 10(6). The emergent field effect is attributed to high-temperature sintering -induced interdiffusion of Si and Zn elements at the ZnO/SiO2 interface, which causes the formation of the zinc silicate (Zn2SiO4) phase and suppresses the carrier concentration.