SAW filters in a structure of ZnO/IDT/glass, have periodic convex and concave roughness on the surface of ZnO thin films which is caused by IDT electrodes. This investigation reports that the convex and concave roughness affects the SAW velocity, and mechanical polishing of the ZnO thin films has great effect on SAW filter frequency characteristics.

In the process of producing ZnO/glass SAW filters, a desired frequency cannot always be obtained after sputtering ZnO thin films on IDT/glass substrates. It is therefore necessary to adjust the center frequency of each SAW filter within 0.05% tolerance after sputtering. We have developed a method to adjust the center frequency in a mass production process by overlaying organic polymer resin on the substrates. The frequency deviation then becomes very small not only in one lot, but also between lots, and the mass production cost of SAW filters can be reduced tremendously.