Xinzhou Wu

Performance improvement for printed indium gallium zinc oxide thin-film transistors with a preheating process

High performance indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) were fabricated by printing and spin-coating IGZO inks as a semiconductor layer at low temperature annealing. A preheating strategy was developed, which significantly enhanced the performance of IGZO TFTs while the post-annealing temperature was kept constant at 300 °C. It was found that when the temperature of preheating on a hotplate increased from 40 °C to 275 °C, the field effect mobility improved from 0.31 cm2 V−1 s−1 to 4.93 cm2 V−1 s−1 for printed IGZO TFTs and from 1.44 cm2 V−1 s−1 to 7.9 cm2 V−1 s−1 for spin-coated IGZO TFTs. The surface roughness of the IGZO films significantly decreased by increasing the preheating temperature from 40 °C to 95 °C. In addition, the analysis of IGZO film composition revealed that an additional nitrate bidentate configuration appeared in the films with preheating at 275 °C, though the substitution of a N atom for O sub-lattice (N)O was found in the film regardless of the preheating temperature. It was suggested that the performance enhancement was primarily attributed to the improvement in film texture brought about by the preheating strategy. Furthermore, the mobility enhancement at high preheating temperature was also related to the appearance of a bidentate configuration (M–O2–N).

Ethanolamine-assisted synthesis of size-controlled indium tin oxide nanoinks for low temperature solution deposited transparent conductive films

Highly conductive indium tin oxide (ITO) nanocrystals and inks have been synthesized by solvothermal dehydration condensation of metal hydroxide in combination with in situ ethanolamine capping. It is found that the addition of ethanolamine can effectively reduce the size of nanocrystals and chemically modify their surfaces. The synthesized ITO nanocrystals can be well dispersed in ethanol with high solid content and the suspension is stable for days. Such a small-molecule capped ITO suspension has been used as a conductive ink to make transparent conductive films by spin coating. Furthermore, a water washing step has been introduced in the ITO film preparation process to improve their conductivity, resulting in a low resistivity of 8.9 × 10−3 Ω cm after 2 hour annealing at 300 °C in a mixed Ar and H2 atmosphere.

Printable poly(methylsilsesquioxane) dielectric ink and its application in solution processed metal oxide thin-film transistors

Thermally cross-linkable poly(methylsilsesquioxane) (PMSQ) has been investigated as a printable dielectric ink to make the gate insulator for solution processed metal oxide (IGZO) thin-film transistors by aerosol jet printing. It was found that by increasing the curing temperature from 150 to 200 °C, the dielectric constant and loss tangent of the printed PMSQ layer reduces dramatically. The mobility, leakage current and gate current of the PMSQ enabled thin-film transistor reduces accordingly, while the on/off ratio increases with the increase of curing temperature. An interfacial layer was introduced to further improve the on/off ratio to 3 × 105 and reduce the leakage current to 2.6 × 10−10 A, which is the best result for the solution processed IGZO thin-film transistors using the PMSQ as the gate insulator at a curing temperature of only 150 °C. The study has demonstrated the feasibility of fabricating IGZO thin-film transistors by an all solution-based process.

Hybrid Printing Metal-mesh Transparent Conductive Films with Lower Energy Photonically Sintered Copper/tin Ink

With the help of photonic sintering using intensive pulse light (IPL), copper has started to replace silver as a printable conductive material for printing electrodes in electronic circuits. However, to sinter copper ink, high energy IPL has to be used, which often causes electrode destruction, due to unreleased stress concentration and massive heat generated. In this study, a Cu/Sn hybrid ink has been developed by mixing Cu and Sn particles. The hybrid ink requires lower sintering energy than normal copper ink and has been successfully employed in a hybrid printing process to make metal-mesh transparent conductive films (TCFs). The sintering energy of Cu/Sn hybrid films with the mass ratio of 2:1 and 1:1 (Cu:Sn) were decreased by 21% compared to sintering pure Cu film, which is attributed to the lower melting point of Sn for hybrid ink. Detailed study showed that the Sn particles were effectively fused among Cu particles and formed conducting path between them. The hybrid printed Cu/Sn metal-mesh TCF with line width of 3.5 μm, high transmittance of 84% and low sheet resistance of 14 Ω/□ have been achieved with less defects and better quality than printed pure copper metal-mesh TCFs.

Printed low temperature metal oxide thin film transistors

Thin film transistors (TFT) were constructed by inkjet printing of indium oxide semiconductor, which were annealed at the temperature of 200-300°C. Good morphology of printed indium oxide films was achieved and the printed thin film transistors exhibited acceptable performances above 250°C of annealing temperature. Furthermore, electron mobility in excess of 0.5cm2/Vs was obtained at processed temperature of 200°C through additional vacuum annealing.

Low temperature synthesis of cubic BaTiO 3 nanoparticles

A new process has been developed to prepare nanocrystalline BaTiO₃ at room temperature and atmospheric pressure. The experimental results show that cubic BaTiO₃ nanoparticles can be prepared even at room temperature (25 °C). These cubic BaTiO₃ nanoparticles are irregular quasi-spheres with the size ranging from hundreds of nanometers to tens of nanometers as the temperature is increased from 25 to 80 °C. Raman spectra of the products obtained at different temperature confirmed that the BaTiO₃ were cubic phase. The influence of reactants concentration on the formation of BaTiO₃ nanoparticles was also investigated.