Investigation of a Cryogenic RF-MEMS Filter for Quantum Bit State Controller

This paper presents a commercial cryogenic piezoelectric bulk acoustic wave (BAW) MEMS filter for Superconducting quantum bit (qubit) state controllers. As the core of the MEMS filter, the piezoelectric resonator adopts scandium-doped aluminum nitride (Sc-AlN) as a piezoelectric material to realize a bandwidth of 3.4-3.6 GHz. In this work, the filtering properties of the MEMS filter was characterized at temperatures of 300K, 77K, and 4K, respectively. Surprisingly, the measurement results show that the filter works normally and exhibits superior performance in cryogenic environment. At 77K, the filter has excellent bandpass characteristics with a low insertion loss of 0.79 dB and a low in-band ripple of 0.22 dB. Similarly, it shows good filtering performance with high roll-off and out-of-band suppression at 4K. To the best of our knowledge, it is the first time to demonstrate a piezoelectric RF-MEMS filter which is capable of working at cryogenic environment. This initial exploration lays a foundation for future research.