Stress control of piezoelectric ZnO films on silicon substrates

Piezoelectric zinc oxide (ZnO) films are widely used for the generation and detection of acoustic waves in non-piezoelectric substrates. The application of these films on silicon offers the possibility of realizing acoustic wave devices integrated with electronic circuits, e.g. sensors. It has been demonstrated that ZnO firms can be combined with standard bipolar or CMOS Ic processes. However, the stress in ZnO is still an important drawback and hinders the further development of silicon integrated acoustic wave devices, particularly if the ZnO layer is deposited an thin membranes, e.g. Lamb wave devices. In this; paper we discuss aspects of stress in ZnO, methods to prevent or reduce the stress and we describe an le-compatible method for the determination of the stress in ZnO films deposited on 100 mm diameter silicon wafers.