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The influence of a SiO2 passivation layer on the electrical properties and reliability of an In–W–Zn–O thin-film transistor (IWZO TFT) was investigated under various post-annealing temperatures (Ta). Although the TFT without passivation showed good transfer characteristics when the Ta is 150 °C, it has huge hysteresis and poor reliability. Furthermore, the TFTs without passivation changed from transistor to conductor when the Ta is 200 °C or higher. In contrast, the TFTs with passivation exhibited switching property even at Ta of 350 °C. Positive bias temperature stress reliability of the TFTs significantly improved by applying the Ta with passivation. Thus, a passivation layer is essential to increase the Ta, resulting in the improvement of electrical properties and reliability of the IWZO TFTs.

It has been progressed to study the effect of the metal composition on the mechanical properties of the hard coating synthesized by the PVD method. In traditional method the film with one metal composition is generally deposited by the alloy cathode with the corresponding metal composition in one running, and thereafter investigated on the mechanical properties. On the other hand, a new efficient method, said as the combinatorial method, was suggested for studying the effect of the metal composition on the film characteristics. In this method, the film with various compositions can be obtained at once in one running. In the present report, the effect of the metal composition on the film hardness and the change of the crystal structure were studied in the Ti-Al-N film prepared by the combinatorial method. In combinatorial method, it was found that the film hardness was rapidly decreased with the deposition of the B4 type crystal. This showed the excellent agreement with the result obtained in the traditional method and the propriety of this combinatorial method was proved in the range of the study about the mechanical property of Ti-Al-N film synthesized by the unbalanced magnetron sputtering.

Using practical high-density sputtering targets, we investigated the effect of Zn and W codoping on the thermal stability of the amorphous film and the electrical characteristics in thin film transistors. zinc oxide is a potentially conductive component while W oxide is an oxygen vacancy suppressor in oxide films. The oxygen vacancy from In-O and Zn-O was suppressed by the W additive because of the high oxygen bond dissociation energy. With controlled codoping of W and Zn, we demonstrated a high mobility with a maximum mobility of 40 cm2/V s with good stability under a negative bias stress in InWZnO thin film transistors.