• Electrical & Electronic Materials
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• v.10 no.3
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• pp.295-301
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• 1997

다양하고 방대한 양의 정보를 효과적으로 처리, 분배하는 멀티미디어 정보통신 시스템이 광신호에 의한 처리를 통해 구현되어갈 전망이다. 이를 위해 빛을 발생시키는 발광소자, 빛을 검출하는 소광소자, 광신호를 처리하는 광신호 처리소자 그리고 광신호를 전달해주는 광섬유 및 화상정보의 표시를 위한 표시소자 등이 중요한 요소기술이다. 이같은 소자의 제작에 있어 기존 물질로는 요구에 대한 대응이 어려워 보다 우수한 성능의 소재개발이 요구된다. 이에 대한 대체물질로 최근 유기물 또는 고분자가 각광을 받고 있으며, 이를 사용한 소자개발이 활발히 진행되고 있다. 이제까지 무기물로 달성하기 힘들었던 많은 기술들이 유기물로 쉽게 구현이 가능하게 되면 고성능의 소재 및 소자기술은 다가오느 정보화 시대를 더축 풍요롭게 하는데 크게 기여할 것이다.

• Transactions on Electrical and Electronic Materials
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• v.6 no.1
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• pp.6-9
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• 2005

Aging characteristics of 0.2PMN-0.8PZT multilayer ceramic actuators (MCA) has been investigated by applying both triangular wave function for unpoled and unipolar wave for poling. P-E hysteresis loops of the MCA had been distorted after about 90 million cycles running in triangular wave function. Effective electromechanical coupling coefficient was calculated in resonant and anti resonant frequencies. And pseudo-piezoelectric constant $d_{33}$ was also estimated from the strain versus electric field characteristics. The crack growth of MCA was clearly observed along to the boundary between electrode and inactive area. That results were thought due to the internal tensile stress came from both actuation of $d_{33}$ mode and motion of Poisson ratio.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.232.2-232.2
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• 2015

Piezoelectric force microscopy (PFM) is a powerful method to characterize inversed piezoelectric effects directly using conductive atomic force microscopy (AFM) tips. Piezoelectric domains respond to an applied AC voltage with a characteristic strain via a contact between the tip and the surface of piezoelectric material. Electroactive piezoelectric polymers are widely investigated due to their advantages such as flexibility, light weight, and microactuation enabling various device features. Although piezoelectric polymers are promising materials for wide applications, they have the primary issue that the piezoelectric coefficient is much lower than that of piezoelectric ceramics. Researchers are studying widely to enhance the piezoelectric coefficient of the materials including nanoscale fabrication and copolymerization with some materials. In this report, nanoscale electroactive polymers are prepared by the electrospinning method that provides advantages of direct poling, scalability, and easy control. The main parameters of the electrospinning process such as distance, bias voltage, viscosity of the solution, and elasticity affects the piezoelectric coefficient and the nanoscale structures which are related to the phase of piezoelectric polymers. The characterization of such electroactive polymers are conducted using piezoelectric force microscopy (PFM). Their morphologies are characterized by field emission-scanning electron microscope (FE-SEM) and the crystallinity of the polymer is determined by X-ray diffractometer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.966-970
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• 2006

We reported on characteristics of the piezoelectric ceramic-polymer composite for the application of the thick-film speaker. The PVDF-PZT composites were fabricated to incorporate the advantages of both ceramic and polymer with various mixing ratios by 3-roll mill mixer. The composite solutions were coated by the conventional screen-printing method on ITO electrode coated PET (Polyethylene terephthalate) polymer film. After depositing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at $120^{\circ}C$ for 30 min to poling the composite films. The value of $d_{33}$ (piezoelectric charge constant) was increased when the PZT weight percent was increased. The maximum value of the $d_{33}$ was 24 pC/N at 70 wt% PZT. But the $g{33}$ (piezoelectric voltage constant) showed the maximum value of $32mV{\cdot}m/N$ at 65 wt% of PZT powder. The SPL (sound pressure level) of the speaker fabricated with the 65:35 composite film was about 68 dB at 1 kHz.

• Proceedings of the KIEE Conference
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• 2000.11c
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• pp.413-415
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• 2000

Piezoelectric ceramics of PZT have been developed to apply for transformers in notebook. Use of piezoelectric ceramics in applications like piezoelectric transformers was made possible by the development of new materials with high electromechanical coupling coefficients and high mechanical quality factor. "Hard" ferroelectiric ceramics of complex composition based on lead zirconate titanate with Mn additive have been prepared. The perovskitic phase reaction of the oxides. The crucial role played by the intermediate mixing and grinding procedures in the assessment of the final properties of the material was investigated. Densification up to approximately the theoretical density value was achieved. The polarization was obtained by subjecting the samples at $30kVcm^{-1}$ poling electric field, in a silicon oil bath heated at $110^{\circ}C$. Their microstructural and morphological properties were checked by X-ray diffraction analysis and scanning electron microscopy. The optimized samples presented very high qualify and electromechanical coupling factors, together with small dielectric loss.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.40-41
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• 2006

In this work, we developed the 0-3 type piezoelectric composite to incorporate the advantages of both ceramic and polymer. The PVDF-PZT composites were fabricated with various mixing ratio by 3-roll mi11 mixer. The composite solutions were coated on ITO bottom-electrode deposited on PET (polyethylene terephthalate) polymer film by the conventional screen-printing method. After depositing the top-electrode of silver-paste, 4kV/mm of DC field was applied at $120^{\circ}C$ for 30min to poling the 0-3 composite film. The value of $d_{33}$ was increased as the PZT weight percent was increases. But the $g_{33}$ value showed the maximum at 65 wt% of PZT powder.

• Journal of Sensor Science and Technology
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• v.4 no.2
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• pp.7-13
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• 1995

A new FET type semiconductor pressure sensor (PSFET : pressure sensitive field effect transistor) was fabricated and its operational characteristics were investigated. A ZnO thin film as a piezoelectric layer, $5000{\AA}$ thick, was deposited on a gate oxide of FET by RF magnetron sputtering. The deposition conditions to obtain a c-axis poling structure were substrate temperature of $300^{\circ}C$, RF power of 140watt, and working pressure of 5mtorr in Ar ambience. The fabricated PSFET device showed good linearity and stability in the applied pressure range($1{\times}10^{5}\;Pa{\sim}4{\times}10^{5}\;Pa$).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.342-347
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• 2016

We investigated the effect of $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3$ (BNKT) modification on the ferroelectric and electric-field-induced strain (EFIS) properties of lead-free $0.97Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-0.03LaFeO_3$ (BNKTLF) ceramics as a function of BNKT content (x= 0, 0.1, 0.2, 0.3, 0.5, and 1). BNKT-modified BNKTLF powders were synthesized using a conventional solid-state reaction method. As the BNKT content x increased from 0 to 1 the normalized electric-field-induced strain ($S_{max}/E_{max}$) was observed to increase at relatively low fields, i.e., below the poling field. Moreover, BNKTLF-30BNKT showed about 460 pm/V as low as at 3 kV/mm, which is a considerably high value among the lead-free systems reported so far. Consequently, it was confirmed that ceramic-ceramic composite, a mixture of an ergodic relaxor matrix and embedded ferroelectric seeds, is a salient way to make lead-free piezoelectrics practical with enhanced EFIS at low field as well as less hysterical.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.744-746
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• 1992

In this study, we investigated structural, electrical characteristics and studied the conditions which improved hydrostatic constants in hydrophones as we changed x = 0.1, 0.25, 0.35, 0.4 and y = 0.04, 0.08, 0.12, 0.16 in $(Pb_{1-x}Ca_x)[(Mg_{1/3}Nb_{2/3})_yTi_{1-0.01}Mn_{0.01}]O_3$ ceramics in which Ca was substituted with Pb and $Pb(Mg_{1/3}Nb_{2/3})O_3$ was added to decrease sintering temperature in $PbTiO_3$. When Ca was substituted 0.25[mol], the largest electro-mechanical anisotropy ($k_t/k_p$) was found ($k_t{\fallingdotseq}50,k_p{\fallingdotseq}4$), and the less $Pb(Mg_{1/3}Nb_{2/3})O_3$ and the stronger poling field, the larger this anisotropy was. When Ca=0.25[mol], $Pb(Mg_{1/3}Nb_{2/3})O_3=0.08[mol]$ were substituted, ($k_t/k_p$)(=12, 3) was large, permittivity was low and hydrostatic constants were high. Therefore, this composition is promising as wide band ultrasonic devices in water.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.355-361
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• 1999

We have synthesized the soluble polymide based side chain system with covalently attached NLO chromophore Disperse Red 1. The developed polymer is optically transparent in the range of optical communication wave-lengths. Its glass transition temperature$(T_g)$ and thermal decomposition temperature$(T_d)$ are $225^{\circ}C, 310^{\circ}C$ respectively. The poled film with the poling field of $100 V/\mu\textrm{m}$ shows that the dielectric constant is 3.37 at the 10-kHz frequency, the refractive indices of TM and TE modes are both 1.631 at $\lambda = 1300 nm$, and the Electro-optic coefficients are 4.6~9.2 pm/V at $\lambda = 1300 nm$. There are no decays of the EO coefficient in the poled polymer at $180^{\circ}C$ in one hour, and $90^{\circ}C$ in 500 hours.