Substrate induced 3rd order nonlinear effects in BAW devices

Besides exceptional low insertion loss and high isolation, BAW duplexers are often the preferred choice in the transmit path of mobile frontends due to their excellent power handling capabilities. Thereby, they are subject to high power RF signals, which can cause their nonlinear response to get system relevant. In this paper we will demonstrate that besides reported piezoelectrical nonlinearities the metal-insulator-semiconductor (MIS) interface can be a relevant nonlinearity source in silicon based BAW devices. A comparison of a silicon substrate duplexer vs. an identical one on a glass substrate yields that the nonlinearity induced by the semiconductor surface effect dominates the 3rd order intermodulation distortion (IMD3) of handset duplexers. Silicon surface treatments, which are known to reduce the voltage dependence of the MIS capacitance, are investigated and characterized by the use of capacitance vs. voltage C(V) measurements and IMD3 measurements on wafer level. Application of the amorphous silicon surface passivation to a duplexer showed a substantial improvement in linearity performance: in comparison to an untreated wafer a 20dB better worst case IMD3 product of -123dBm was demonstrated.