• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.441-444
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• 2007

In this paper, the resonance characteristics of ZnO-based film bulk acoustic resonator (FBAR) devices with high-quality multi-layer reflectors are proposed. The ultrathin Cr film $(300\;\AA-thick)$ between $SiO_2$ film and W film is formed by a sputtering-deposition in order to enhance the adherence at their interfaces. The resonance frequency was observed to vary with the number of the reflectors. This seems to be attributed to the change in the effective thickness of the ZnO film. Also, increasing the number of layers has led to a significant improvement of the series/parallel quality factor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.880-883
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• 2003

ZnO thin films for Film Bulk Acoustic Resonator(FBAR) were prepared by FTS (Facing Target Sputtering) system. The FTS methode enable to generate high density plasma, and it has a high deposition rate at 1mTorr pressure. Therefore, the ZnO thin films were deposited on $AZO/SiO_2/Si$ substrates with oxygen gas flow rate, and the other sputtering conditions were fixed such as a sputtering current of 0.8A, a substrate temperature at room temperature. AZO bottom electrode were deposited on $SiO_2/Si$ substrate and by Zn:Al(Al:2wt%) metal target. ZnO thin film thickness and the c-axis preferred orientation of ZnO thin film were evaluated by ${\alpha}-step$ and XRD.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.16-19
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• 2004

In this paper, we present the film bulk acoustic resonator (FBAR) devices fabricated by considering the effects of annealing temperature on zinc oxide (ZnO) film growth characteristics. In order to determine the annealing temperature and annealing time at which the ZnO film can have good material properties, the several resonators containing ZnO layers were fabricated and annealed at various temperatures from 27$^{\circ}C$ to 30$0^{\circ}C$ in Ar gas ambient. The effects of the annealing temperature and annealing time on the ZnO film properties were comprehensively studied in order to further improve the resonance characteristics of FBAR resonators.

• Journal of information and communication convergence engineering
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• v.3 no.3
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• pp.131-136
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• 2005

The effects of the deposition temperature on the growth characteristics of the ZnO films were studied for film bulk acoustic wave resonator (FBAR) device applications. All films were deposited using a radio frequency (RF) magnetron sputtering technique. It was found that the growth characteristics of the ZnO films have a strong dependence on the deposition temperature from 25 to $350^{\circ}C$. The ZnO films deposited below $200^{\circ}C$ exhibited reasonably good columnar grain structures with a highly preferred c-axis orientation while those above 200°C showed very poor columnar grain structures with a mixed-axis orientation. This study seems very useful for the future FBAR device applications.

• Journal of the Korean Ceramic Society
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• v.43 no.1 s.284
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• pp.42-47
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• 2006

In this paper, we prepared high-quality ZnO thin films for application of FBAR (Film Bulk Acoustic Resonator) by using pulse DC magnetron sputtering. To prevent the formation of low dielectric layers between metal and piezoelectric layer, Ru film of 30 nm thickness was used as a buffer layer. In addition we investigated the influence of annealing condition with various temperatures. As the annealing temperature increased, the crystalline orientation with the preference of (002) c-axis and resistance properties improved. The single resonator which was fabricated at $500^{\circ}C$ exhibited the resonance frequency and the return loss 0.99 GHz and 15 dB, respectively. This work demonstrates potential feasibility for the use of thin film Ru buffer layers and the optimization of annealing condition.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.17-20
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• 2001

In this paper, film bulk acoustic resonator(FBAR) with an air-gap is fabricated by removing ZnO sacrificial layer and its characteristics as a various dimension of ZnO sacrificial and piezoelectric layer is evaluated. The center frequency of the FBAR device with the ZnO film is about 1.9 GHz. Because of mass-loading effect, a dimension of sacrificial layer and piezoelectrc layer affect frequency response such as center frequency, insertion loss, band separation, attenuation and so on.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.11
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• pp.2090-2094
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• 2007

Film bulk acoustic wave resonator(FBAR) technology has attracted a great attention as a promising technology to fabricate the next-generation RF filters mainly because the FBAR technology can be integrated with current Si processing. The RF filters are basically composed of several FBAR devices connected in parallel and in series, and their characteristics depend highly on the FBAR device characteristics. Thus, it is important to design high quality FBAR devices by device or process optimization. This kind of effort may enhance the FBAR device characteristics, eventually leading to FBAR filters of high performance. In this paper, we describe the methods to more effectively improve the resonance characteristics of the FBAR devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.140-143
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• 2002

In this study, we prepared ZnO/glass and $ZnO/SiO_{2}/Si$ thin film by Facing Targets Sputtering (FTS) system for Film Bulk Acoustic Resonator (FBAR). When the ZnO thin film applied to piezoelectric thin film, it requires good c-axis preferred orientation. And c-axis orientation has a remarkable difference with preparation conditions. Therefore, c-axis orientation must be significantly evaluated according to changing deposition conditions. Moreover, in order to prepare ZnO thin film with good crystallographic properties and progressive of efficiency of product process, the ZnO thin film should have to prepared as low temperature as possible. In this work, we prepared ZnO thin films on slide glass and $SiO_{2}/Si$ substrate. And the crystallographic characteristics of ZnO thin films on sputtering conditions were investigated by alpha-step and X-ray diffraction.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.630-632
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• 2003

In this paper, we present the fabrication and performance of FBAR filters with ladder and stacked crystal filter (SCF) types. The structure of the unit resonator in our work is the solidly mounted resonator (SMR) with W/SiO$_2$ multi-layer reflectors, the return loss of of which show -24dB at resonant frequency of -2.0GHz. The $K^2$eff, Q$_{s}$, and Q$_{p}$, indicating the performance of resonator were 3.24%, 6,363 and 6,749 and were calculated for the resonator with the resonance area of 21200${\mu}{\textrm}{m}$$^2$. Based on this unit resonator, FBAR filters with ladder and SCF types were fabricated and compared. The sizes of filters were 800$\times$2000(${\mu}{\textrm}{m}$$^2$) for the ladder type and 600$\times$500(${\mu}{\textrm}{m}$$^2$) for the SCF type.e..

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1263-1269
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• 1999

An FBAR(Solidly Mounted Resonator) was fabricated using reflector layers which prohibit the penetration of bulk acoustic wave into substrate. The SMR consisted of top and bottom electrodes(Al films), a piezoelectric layer (ZnO film), reflector layers(W/$Si_2$ films) and Si substrate. The electrodes were deposited by dc sputtering. The piezoelectric layer and the reflector layers were deposited by rf magnetron sputtering. The control of crystallinity, microstructures and electric properties of each layer was essential for attaining the optimum FBAR characteristics. Under the best deposition conditions for FBAR devices, the ZnO films had highly c-axis preferred orientation(${\sigma}=2.17^{\circ}$), resistivity of $10^4\;{\omega}cm$, and surface roughness of 10.6 ${\AA}$. On the other hand, the surface roughness of W and $Si_2$ films was 16 ${\AA}$ and 33 ${\AA}$, respectively, and the resistivity of Al film was $5.1{\times}10^{-6}\;{\Omega}cm$. The SMR devices were fabricated by the conventional semiconductor processes. In the resonance conditions of the SMR, the series resonance frequency (fs) and the parallel resonance frequency(fp) were 1.244 GHz and 1.251 GHz, respectively and the quality factor(Q) was 1200.