Effect of Mg and Zr co-doping on piezoelectric AlN thin films for bulk acoustic wave resonators

This paper reports the crystal structures and piezoelectric properties of Mg and Zr co-doped AlN (MgZr-doped AlN) thin films. MgZr-doped AlN thin films on Si (100) substrates were fabricated by using a radio-frequency magnetron reactive cosputtering system. The relations between dopant concentration...

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Bibliographic Details
Published in:IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2014-08, Vol.61 (8), p.1322-1328
Main Authors: Yokoyama, Tsuyoshi, Iwazaki, Yoshiki, Onda, Yosuke, Nishihara, Tokihiro, Sasajima, Yuichi, Ueda, Masanori
Format: Article
Language:English
Subjects:
Aluminum nitride
Atomic measurements
Crystal structure
Crystals
Doping
Film bulk acoustic resonators
III-V semiconductor materials
Lattices
Magnesium
Piezoelectricity
Resonators
Silicon substrates
Thin films
Zirconium
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Summary:This paper reports the crystal structures and piezoelectric properties of Mg and Zr co-doped AlN (MgZr-doped AlN) thin films. MgZr-doped AlN thin films on Si (100) substrates were fabricated by using a radio-frequency magnetron reactive cosputtering system. The relations between dopant concentration and the crystal structures measured by X-ray diffraction, transmission electron microscopy, and the piezoelectric constant d 33 measured with a piezometer were investigated. Up to total Mg and Zr concentrations of 34.8 at%, the MgZr-doped AlN films maintained the c-axis-oriented wurtzite structure and were likely formed by substituting Mg and Zr atoms into Al atom sites. The d 33 of the MgZr-doped AlN with a total Mg and Zr concentration (Mg + Zr) of 34.8 at% was about three times that of pure AlN. The experimental results on the relation between total Mg and Zr concentration and the crystal structure and the d 33 were in close agreement with the results of first-principles calculations. Finally, thin film bulk acoustic wave resonators (FBARs) that used MgZr-doped AlN as a piezoelectric thin film were fabricated and compared with the AlN-based FBAR. A total Mg and Zr concentration of 13 at% was found to improve the electromechanical coupling coefficient of AlN from 7.1% (for pure AlN) to 8.5%. The results from this study suggest that the MgZr-doped AlN films have potential as piezoelectric thin films for wideband and high-frequency RF applications.
ISSN:0885-3010
1525-8955
DOI:10.1109/TUFFC.2014.3039