• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.4
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• pp.41-54
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• 2002

In this study, we have analyzed the effects of the membrane layer and the bragg reflector layers on the resonance characteristics through comparing the characteristics of the membrane type FBAR (Film Bulk Acoustic Wave Resonator) and the one type bragg reflector layers with those of the ideal FBAR with top and bottom electrode contacting air by using equivalent circuit technique. It is assumed that ZnO is used for piezoelectric film, $SiO_2$ are used for membrane layer and low acoustic impedance layer, W are used for the high acoustic reflector layer and Al is used for the electrode. Each layer is considered to have a acoustic propagation loss. ABCD parameters are picked out and input impedance is calculated by converting 1-port equivalent circuit to simplified equivalent circuit that ABCD parameters are picked out possible. From the variation of resonance frequency due to the change of thickness of electrode layers, reflector layers and membrane layer it is confirmed that membrane layer and the reflector layer just under the electrode have the greatest effect on the variation of resonance frequency. From the variation of resonance properties, K and electrical Q with the number of layers, K is not much affected by the number of layers but electrical Q increases with the number of layers when the number of layers is less than seven. The electrical Q is saturated when the number of layers is large than six. The electrical Q is dependent of mechanical Q of reflector layers and membrane layer. Both ladder filter and SCF (Stacked Crystal Filters) show higher insertion loss and out-of-band rejection with the increase of the number of resonators. The insertion loss decreases with the increase of the number of reflector layers but the bandwidth is not much affected by the number of reflector layers. Ladder Filter and SCF with membrane layer show the spurious response due to spurious resonance properties. Ladder filter shows better skirt-selectivity characteristics in bandwidth but SCF shows better characteristics in insertion loss.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2003.12a
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• pp.54-58
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• 2003

본 연구에서는 $SiO_2/Si$ 기판 위에 $1.1\mu\textrm{m}$ 두께의 ZRO 압전층을 다양한 조건 하에서 증착하고, 그 특성을 분석하고, film bulk acoustic wave resonator 소자에 적용하였다. 증착조건으로 $Ar/O_2$ 유량비를 25-75 %로 변화시켰으며, working pressure는 3~15 mtorr, RF power는 213~300 W로 변화시켜가며 실험을 하였다. 증착된 ZnO 박막은 XRD (X-ray diffractomter)와 SEM (scanning electron microscopy)을 통해 특성이 분석되었다. LFE모드의 BAW 공진기는 $50\times50\mu\textrm{m}^2$ 공진면적을 가지며, $W/SiO_2$의 5층 Bragg reflector와 상하부 전극으로 $1800{\AA}$의 Al-3% Cu, 그리고 $1.4\mu\textrm{m}$ 두께의 ZnO 압전박막으로 구성되었다. 2.128-2.151 GHz 주파수 사이에서 공진이 일어났으며, Q factor는 400으로 측정되었다.

• Journal of the Korean Ceramic Society
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• v.40 no.3
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• pp.268-272
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• 2003

The microstructures of tungsten films were controlled by changing the sputtering pressure and substrate temperatures during D.C. sputter deposition. As the sputtering pressures were decreased, the sputtered models of the tungsten films were changed from the zone I model to zone T model. The tungsten film having zone T model microstructure shows a resistivity of 10${\times}$10$\^$-6/ $\Omega$-cm and (110) preferred orientation. FBAR with Bragg reflector composed of $SiO_2$and tungsten films having zone T model microstructure shows quality factor, Q$\_$s/, of 494 and K$\_$eff/$\^$2/ of 5.5% due to the high acoustic impedance and the smooth surface.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.11
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• pp.9-18
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• 2003

Two configurations of Film Bulk Acoustic Wave Resonators with acoustic quater-wave bragg reflector layers are theoretically analyzed using equivalent circuits and the difference of their characteristics are discussed. We compare the characteristics of λ/2 mode to those of ideal FBAR with top and bottom electrode contacting air and the characteristics of λ/4 mode to those of ideal FBAR with top electrode contacting air and bottom electrode clamped. We assume that the piezoelectric film is ZnO, the electrode is A1 and the substrate is Si, ABCD parameters are extracted and input impedance is calculated by converting the equivalent circuit from Mason equivalent circuits to the simplified equivalent circuits that ABCD parameters are extracted possible, From the variation of resonance frequency due to the change of thickness of reflector layers and the variation of electrical Q due to the change of mechanical Q of reflector layers, it is confirmed that the reflector layer just under the bottom electrode have the greatest effect on the varation of resonance frequency and electrical Q. It is shown that the number of reflector layers required for the saturation of electrical Q decreases with the increase of the impedance ratio of reflector layers and electrical Q of λ/2 mode is larger than that of λ/4 mode, Electromechanical coupling factor is independent of the number of layers, The impedance ratio of reflector layers becomes larger as the electromechanical coupling factor becomes larger, The electromechanical coupling factor of the two mode are smaller than those of ideal FBARs because of the trapping of acoustic energy in the reflector layers, The insertion loss of the ladder filter decreases with the increase of the number of reflector layers but the bandwidth is not affected much by the number of reflector layers, As the impedance ratio of reflector layers becomes larger the insertion loss becomes smaller and the bandwidth becomes wider, In our analysis of the two mode, characteristics of λ/2 mode appear to be slightly more favorable than that of λ/4 mode