Preparation and surface morphology of black lithium tantalate wafers

Black lithium tantalate (BLT) wafers were prepared by annealing and reduction; a mixture of high purity aluminium powder and silicon powder were used as a reducing agent. The congruent lithium tantalate (CLT) wafers and the BLT wafers were prepared by reduction under different conditions and taken as the research objects. The surface of CLT wafers after annealing and reduction showed uniform orange-peel morphology by scanning electron microscope observation; the surface oxygen content was reduced and uniform. However, a local dark orange-peel spot formed in the wafers directly after the reduction process without annealing, and the oxygen content on the surface was reduced and uneven. Atomic force microscope observation revealed that the average surface roughness of the wafers was reduced and more uniform after annealing and reduction. The data showed that high-temperature annealing before reduction is helpful for the stress release of CLT wafers and a blackening effect is more easily achieved. The reduction treatment condition of CLT wafers determines the quality of BLT wafers. Good reduction and early treatment technology make it easy to prepare uniform and consistent blackening wafers, which can reduce the pyroelectric property of wafers and improve the yield in the subsequent process of making surface acoustic wave filter devices.