Development of 4 GHz bulk acoustic wave resonators by sputtered Pb(Mn,Nb)O3-Pb(Zr,Ti)O3 thin films

The 4 GHz bulk acoustic wave (BAW) resonators have been fabricated by thin films of Pb(Zr,Ti)O
₃
based ternary perovskite compounds. The Pb(Mn
_1/3
Nb
_2/3
)O
₃
-Pb(Zr,Ti)O
₃
(PMnN-PZT) thin films were deposited on (100)MgO substrates by RF magnetron sputtering. The PMnN-PZT thin films showed tetragonal crystal structure and highly (001) orientation. The surface roughness of the thin films was about 2 nm. The cross section TEM image of PMnN-PZT thin films showed single c-domain/ single crystal structure. The bulk acoustic wave (BAW) resonators composed by PMnN-PZT thin films were fabricated by MEMS technology. The RF properties of the resonator were evaluated by VNA (Vector Network Analyzer). The BAW resonator by 0.1PMnN-0.9PZT(55/45) thin film exhibited high electro-mechanical coupling constant kt and high Q value at 3.87GHz. Values of k
_t
, Q, and k
_t

²
Q were found to be 0.56, 185 and 58, respectively. These values are highest, in our knowledge, comparing with those of previously reported PZT-BAW resonators.