Densification of tube-shaped transparent conducting oxide target at reduced temperature via initial heat treatment under pressure

Transparent conducting oxide such as aluminum doped ZnO (Al-ZnO) needs to be prepared in a tube-shaped target for prolonged life time during sputtering. To prevent warping and coarsening during preparation, the densification of tube-shaped target need to be achieved at reduced temperature. In this study, tube-shaped 2 wt% Al-ZnO was prepared via two-step sintering route, consisted with initial heat treatment (IHT) at 700 °C or 800 °C under mild external pressure (1 MPa) and subsequent pressureless sintering at 1300 °C or 1350 °C. By applying pressure during the IHT, the density obtained by sintering at 1300 °C increased by 2.38% and reached the same level of density as material sintered at 1350 °C. The reduced sintering temperature rendered a fine grained tube, suitable for prevention of nodules during sputtering. The IHT under external pressure had limited effects for tall tubes, where loss of pressure was anticipated due to the difficulty in fine filling the pressing medium within the mold.