GHz BAW piezoelectric transformers for passive voltage amplification using the epitaxial ZnO thin films

Energy harvesting using ambient electromagnetic waves is one of the promising battery-less power supply methods for sensors. Electromagnetic waves can be converted to the DC energy by a rectifying antenna (called a rectenna). However, it is difficult to activate the rectifier when the electromagnetic wave is weak. In this study, we report BAW transformers based on the epitaxial ZnO thin films for passive voltage amplification. The theoretical voltage gain was simulated by Mason's equivalent circuit model. S parameters of the BAW piezoelectric transformers are measured by a network analyzer. As a result, the RF voltage increased approximately 4 ×in 600 MHz range. This BAW transformer enables high voltage operation of the diode in the rectenna.