Stacked crystal resonator: A highly linear BAW device

Abstract

Besides small size, exceptional insertion loss and outstanding isolation, bulk acoustic wave (BAW) filters and duplexers are often the preferred choice in the transmit path of mobile frontend due to their excellent power handling capabilities. However, they exhibit a nonlinear behavior, causing generation of higher harmonics and a sensitivity of the resonance frequency towards a DC voltage bias. In this paper we present a new BAW device, a stacked crystal resonator (SCR), which intrinsically cancels out the second order nonlinearity and compare it to standard BAW resonators and current solutions for improved linearity. Measurements of first devices demonstrate a 30 dB improvement in worst case second order harmonic generation of a SCR over a standard BAW solid mounted resonator. Furthermore, the frequency sensitivity on a DC voltage bias is reduced by a factor of 20 and the coupling coefficient increased by 10%.