• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.61-65
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• 2008

In this paper, we studied a ZnO-based film bulk acoustic resonator (FBAR) device fabricated on a specially designed multi-layerd Bragg reflector part. Very thin chromium adhesion layers (0,03um thick) were additionally deposited to improve the quality of the Bragg reflector and some thermal treatments were performed to improve the resonant characteristics of the device. At the operating frequency of ${\sim}2.7GHz$, excellent resonant characteristics were observed in terms of return loss and quality factor, and effective electromechanical coupling coefficient. These findings are expected to be highly promising and effective for improving the performance of the FBAR devices at high frequency.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.211-214
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• 2007

In this paper, the resonance characteristics of ZnO-based film bulk acoustic resonator (FBAR) devices with thick bottom electrode are investigated. The ultra-thin 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 of three different resonator devices was observed to be ${\sim}2.7$ GHz, and the resonance characteristics $(S_{11})$ of the FBAR devices were found to have a strong dependence on the thickness of bottom electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.358-361
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• 2002

체적파 박막형 공진기 (FBAR: Film Bulk Acoustic wave Resonator)소자를 제조하여, 박막의 c축 우선 배향성을 조절하는 것이 FBAR 소자 특성을 확인하였다. 본 연구에서는 MEMS 공정에 의해 Membrane 구조의 FBAR(Film Bulk Acoustic wave Resonator) 소자를 구현하고자 하였다. 이를 위해 Si 기판을 Back-etching 하여 membrane 구조를 제작하였고 압전층으로 ZnO을 Sputtering 공정에 의해 증착 후, 공정 조건에 따른 우선 배향성을 관찰하였다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.5 no.1
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• pp.38-44
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• 2005

Pyrolyzed polyimide is explored in terms of MEMS material. This paper describes chemical, electrical, mechanical properties of pyrolyzed polyimide (PIX-1400) thin film as MEMS material. When polyimide thin film was pyrolyzed at $800^{\circ}C$ for 60 minutes in $N_{2}$ ambient, the residual ratio of pyrolyzed film thickness measured with a surface profiler is about 49 %, and the resistivity is about $2.17{\times}10^{-2}\;{Omega}cm$. From the result of the load-deflection test, the estimated Young's modulus and initial average stress of pyrolyzed polyimide are 67 GPa and 30 MPa, respectively. As one demonstration of MEMS structures of pyrolyzed polyimide, the fabrication method of the microbridge structure is proposed for a micro heater and a resonator.

• Journal of the Korean Ceramic Society
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• v.40 no.4
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• pp.393-397
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• 2003

To investigate the effect of AIN c-axis orientation on the resonance performance of film bulk acoustic wave resonators, solidly mounted resonators with crybtallographically different AIN piezoelectric films were prepared by changing only the bottom electrode surface conditions. As increasing the degree of c-axis texturing, the effective electromechanical coupling coefficient ($\kappa$$\_$eff/)$^2$ in resonators increased gradually. The least 4 degree of full width at half maximum in an AIN(002) rocking curve, which corresponds to $\kappa$$^2$$\_$eff/ of above 5%, was measured to be necessary for band pass filter applications in wireless communication system. The longitudinal acoustic wave velocity of AIN films varied with the degree of c-axis texturing. The velocity of highly c-axis textured AIN film was extracted to be about 10200 n/s by mathematical analysis using Matlab.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.377-382
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• 2000

Film bulk acoustic resonator (FBAR) using AIN reactively sputtered at room temperature was fabricated. The FBAR is composed of a piezoelectric aluminium nitride thin film, top electrode of Al and bottom electrode of Au connected by a short (200${\mu}{\textrm}{m}$) transmission line on both sides and reflector layers of SiO$_2$- W Pair. The active areas of Al and Au were patterned using 150${\mu}{\textrm}{m}$ diameter shadow mask. The series resonance frequency (fs) and the parallel resonance frequency (fp) were measured at 1.976 GHz and 2.005 GHz, respectively. The minimum insertion loss and return loss were 6.1 dB and 37.19 dB, and the quality factor (Q) was 4261.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.435-443
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• 2001

As power durable RF SAW filters, AL-(0∼2wt%)Cu alloy multi-layered thin electrodes were deposited on 42° LiTaO$_3$ piezoelectric substrates by magnetron sputtering process, and then ladder-type RF SAW filters, satisfying the electrical specification of CDMA transmission band, were fabricated through optimizing SAW resonator structures. The temperature of film electrodes in SAW filter was increased with RF power, and reached the maxima to cause a failure of SAW filters at the cut-off frequencies of the RF filter band. As RF power increases, the electrodes of Al-Cu alloy showed higher power durability than that of pure Al. The multi-layer laminated film of Al-1wt.% Cu/Cu/Al-1wt%Cu resulted in the best power durability up to 4W of RF power. Every film electrode, however, was destroyed within seconds whenever applying a critical RF power to SAW filters, regardless of the composition and structure of film electrodes. The breakdown of film electrodes under FR power seems to believe due to the fatigue of electrodes caused by repetitive cyclic stress of surface acoustic wave, which is amplified as RF power increases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.41-44
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• 1998

Dual mode resonators were fabricated using high temperature superconductor. The deposited material was $Y_1Ba_2Cu_3O_{7-x}$(YBCO) on MgO(100) substrate using pulsed laser deposition. Dual mode resonators were patterned by standard photolithography process and wet etching. At the back-side of the substrate, the ground plane with the metal layer of Ti and Ag was fabricated. The transition temperatures of YBCO films were 85-88 K, and network analyzer was used for testing the performance of the resonators. The input/output feedline angles of each resonator were $60^{\circ}$and $100^{\circ}$. The resonant frequency of resonators was 10 GHz. In this paper, dual mode resonator was fabricated for the application of satellite communication.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.7
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• pp.282-287
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• 2003

″H″ type resonator has the advantage for the miniaturization of high-T7 superconducting (HTS) microstrip antenna in comparison with the conventional microstrip antenna such as rectangular type or circular type. In this paper we designed miniaturized HTS antennas using this "H"-type resonator and reported the characteristics of our antennas including return loss, bandwidth, radiation patterns, efficiency and so on. To fabricate the "H" type antenna, HTS YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) thin films were deposited on MgO substrates using rf-magnetron sputtering. For comparison between normal conducting antennas and superconducting antennas, the gold antennas with the same dimension were also fabricated. An aperture coupling was used for impedance matching between 50 $\Omega$ feed line and HTS radiating patch. The ″H" type superconducting antenna showed the performance of 1.38 in SWR, 26 % in efficiency, and 13.8 dB in the return loss superior to the normal conducting counterpart.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.151-154
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• 2003

AlN/Al/SiO$_2$/Si thin films for application to FBAR(Film Bulk Acoustic Resonator) devices were prepared by FTS(Facing Targets sputtering system) apparatus which provides a stable discharge at low gas pressures and can deposit high quality thin films because of the substrate located apart from the plasma. The AlN thin films were deposited on a $SiO_2(1{\mu}m)/Si(100)$ substrate using an Al bottom electrode. The process parameters were fixed such as sputering power of 200W, working pressures of 1mTorr and AlN thin film thickness of 800nm, respectively and crytallographic characteristics of AlN thin films were investigated as a function of $N_2$ gas flow rate$[N_2/(N_2+Ar)]$. Thickness of AlN thin films were measured by $\alpha$-step, the crystallographic characteristics and c-axis preferred orientation were evaluated by XRD.