Prevention of tapering in the tube-shaped sputtering target via initial heat treatment under external pressure

The tube-type transparent conducting oxide target is preferred to the planar type owing to a prolonged life. The uniaxial pressing of 2 wt% Al-ZnO powder into a tube shape and subsequent sintering resulted in a tapered product owing to the nonuniform green density. To suppress the taper, an initial heat treatment (IHT) under an external pressure was applied prior to the main final sintering. The degree of the taper was estimated from the difference in the percentage between the longer and shorter diameters of the tube. The application of pressure (1 MPa) during the IHT at 800 °C decreased the taper from 4.3% to 0.9% after pressureless final sintering at 1250 °C. The application of pressure during the IHT activated shrinkage at the bottom part of the tube and consequently reduced the tapering. With the IHT under pressure, micron-sized voids fragmented into the submicron pores, and the sintering potential was improved.