S -Band Micromechanical Resonant Impedance Transformers Based on Aluminum Nitride FBARs

This work presents an intensive study of passive voltage amplification offered by one-port microelectromechanical systems (MEMS) piezoelectric resonators used as matching network (MN) inS-band RF wake-up receiver (WuRX) front-ends. Through theoretical modeling and numerical analysis, a large electromechanical coupling coefficient (kₜ²), high quality factor (Q), low transducer capacitance (Cₒ), and light capacitive loading (CL) are the keys to obtain high passive voltage gain at gigahertz (GHz) frequencies. To evaluate the performance of GHz MEMS-based MNs, several thin-film bulk acoustic wave resonators (FBARs) with different transducer capacitances at 2.3 GHz were designed and fabricated using a 200-mm commercial aluminum nitride (AlN) piezoelectric MEMS-CMOS process. The fabricated resonators achieve a high figure-of-merit (FoM =kₜ² · Q) from 90 to 175, resulting in a high passive gain of around 21 dB at a reasonable reactive load of 100 fF. Based on a small FBAR device with aCₒof only 67 fF, the highest gain achieved in this study is 23.4 dB based on a complex load (CL =50fF andRL =50\,\,kΩ) while attaining good input matching (S₁₁ < -10dB). In addition, the effect of spurious modes on the passive voltage gain is numerically investigated by the 2-D finite element method (FEM), which is in good agreement with the experimental results.