Two-step sputtered ZnO piezoelectric films for film bulk acoustic resonators |
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Authors: | Re-Ching Lin Ying-Chung Chen Kuo-Sheng Kao |
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Institution: | (1) Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, R.O.C.;(2) Department of Computer and Communication, Shu-Te University, 59 Hun Shan Rd., Yen Chau, Taiwan, 82445, R.O.C. |
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Abstract: | This study investigates high-performance ZnO piezoelectric films used for thin film bulk acoustic resonators (TFBAR). The
ZnO piezoelectric film was deposited on a Pt/Ti electrode using an RF magnetron sputter by a two-step method at room temperature.
The Pt/Ti electrode was deposited by a DC sputtering system, on which, ZnO piezoelectric films were deposited in one step
and in two steps to minimize roughness in the first step and produce the preferred orientation in the second. Both field-emission
scanning electron microscopy (FESEM) and atom force microscopy (AFM) revealed that ZnO piezoelectric film deposited by two-step
sputtering exhibited favorable characteristics, such as a rigidly precise surface structure with surface roughness of 7.37 nm,
even better than in one-step sputtering. Examining the ZnO thin film by X-ray diffraction (XRD) showed a much higher c-axis-preferring
orientation than in one-step sputtering. The reflection coefficient of the resonator device was measured using an HP8720 network
analyzer. The frequency response of the FBAR device exhibited a return loss of -25 dB at a resonant frequency of 2212 MHz
with a high coupling coefficient of 6.7%.
PACS 68.55.Jk; 43.35.Ns; 81.15.-z |
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Keywords: | |
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