Germanium aluminum nitride thin films for piezo-MEMS devices

This paper reports on piezoelectric polarity inversion of AlN thin films by doping. The germanium doped aluminum nitride (GeAlN) thin films are grown by RF magnetron sputtering. Doping amount is varied from 0 to 23%. The maximum piezoelectric polarity inversion from Al polarity to N polarity is observed at 3% of Ge where the piezoelectric d
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value changes from + 7.8 to −7.7 pC/N. The bulk acoustic wave (BAW) resonator with the stack of both N polarity and Al polarity layers is demonstrated. The B AW resonator is excited at 2
^nd
overtone mode at 2.58 GHz. Finally, the mechanism of polarity inversion of GeAlN is discussed and first-principal calculations of GeAlN system are presented.