• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.126-129
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• 1999

Dielectric and piezoelectric properties of perovskite materials such as La modified $Pb(Zr,Ti)O_3$ ceramics and $Pb(Zn_{1/3}Nb_{2/3})O_3-PbTiO_3$ single crystals were investigated for cryogenic capacitor and actuator applications. Enhanced extrinsic contributions resulted in piezoelectric coefficient (d33) as high as 250 pC/N at 30 K, superior to that of PZT ($d_{33}$ ~ 100 pC/N). This cryogenic property enhancement was associated with retuning the MPB (or cryogenic temperatures. PZN-PT single crystals exhibited dramatic property improvements such as $d_{33}$ > 500 pC/N at 30 K as a result of an engineered domain state.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.382-383
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• 2006

The tungsten bronze type of strontium barium niobate(SBN) thin film was synthesized by metal organic decomposion method for SBN stock solution and the SBN thin film process were deposited by spin-coating process on Pt-deposited si-wafer(100) by magnetron sputtering system. The thickness of SBN thin film was 150~200 nm and were optimized for rpm of spin-coater system. The structural variation of SBN thin film was studied by TG-DTA and XRD. The deposited SBN stock solution on annealing at $400{\sim}800^{\circ}C$ a pure tungsten bronze SBN phase and the corresponding. average grain size about 500~1000 nm influenced by annealing temperature. The piezoelectric properties of prepared SBN thin film, the remanent polarization value(2Pr) and coercive field was $1.2{\mu}C/cm^2$ and 2.15V/cm, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.297.2-297.2
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• 2013

Scavenging electricity from wasteful energy resources is currently an important issue and piezoelectric nanogenerators (NGs) based on zinc oxide (ZnO) are promising energy harvesters that can be adapted to various portable, wearable, self-powered electronic devices. Although ZnO has several advantages for NGs, the piezoelectric semiconductor material ZnO generate an intrinsic piezoelectric potential of a few volts as a result of its mechanical deformation. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. Oxygen vacancies (Vo) that work as donors exist in ZnO thin film and usually screen some parts of the piezoelectric potential. Consequently, the ZnO NGs' piezoelectric power cannot reach to its theoretical value, and thus decreasing the effect from Vo is essential. In the present study, c-axis oriented insulator-like sputtered ZnO thin films were grown in various temperatures to fabricate an optimized nanogenerator (NGs). The purity and crystalinity of ZnO were investigated with photoluminescence (PL). Moreover, by introducing a p-type polymer usually used in organic solar cell, it was discussed how piezoelectric passivation effect works in ZnO thin films having different types of defects. Prepared ZnO thin films have both Zn vacancies (accepter like) and oxygen vacancies (donor like). It generates output voltage 20 time lager than n-type dominant semiconducting ZnO thin film without p-type polymer conjugating. The enhancement is due to the internal accepter like point defects, zinc vacancies (VZn). When the more VZn concentration increases, the more chances to prevent piezoelectric potential screening effects are occurred, consequently, the output voltage is enhanced. Moreover, by passivating remained effective oxygen vacancies by p-type polymers, we demonstrated further power enhancement.

• Korean Journal of Materials Research
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• v.17 no.12
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• pp.660-663
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• 2007

Piezoelectric energy harvesting from our surrounding vibration has been studied for driving the wireless sensor node. To change the vibration energy into the electric-energy efficiently, the natural frequency of cantilever needs to be adjusted to that of a vibration source. When adding 6.80g mass on the end of the fabricated cantilever, a natural frequency shifts from 136 Hz into 49.5 Hz. In addition, electro-mechanical coupling factor increased from 10.20% to 11.90% and resulted in the 1.18 times increase of maximum output power.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.139-141
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• 2008

The piezoelectric properties of tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals are characterized along the <111> direction, which composed the engineering domain configuration in the tetragonal phase. The <111>-oriented crystal possessed smaller $d_{33}$ values compared to the crystal along the <001> spontaneous polarization direction. Based on phenomenological theory, it is shown that the engineering domain configuration does not enhance the piezoelectric constant in tetragonal 0.88Pb$(Zn_{1/3}Nb_{2/3)O_3-0.12PbTiO_3$ single crystals. In addition, the electrostrictive coefficients of $Q_{12}=-0.03706m^4/C^2,\;Q_{11}=0.10765m^4/C^2,\;and\;Q_{44}=0.02020m^4/C^2$ of tetragonal 0.88PZN-0.12PT single crystals were calculated.

• Proceedings of the KIEE Conference
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• 1998.07g
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• pp.2509-2511
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• 1998

In this study, we formed the piezoelectric film and estimated its characteristics for sensor application. The $Pb(Zr,Ti)O_3(PZT)$ was chosen as piezoelectric material and we used Sol-Gel method to form film. To increase film thickness, the multiple coatings were performed, and the good characteristics obtained in thick film compared to thin film. Because PZT film showed fine etching property as well as other good characteristics, it was thought that it was appropriate material for sensor fabrication.

• Ceramist
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• v.22 no.1
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• pp.82-95
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• 2019

Piezoelectric materials can directly convert mechanical energy to electrical one, and vice versa. Research on piezoelectric materials and devices has a long history, and now many relevant products are available in a wide range of applications such as medical, military, industrial, home appliance, and mobile electronics. One of the major research trends now is not only to further improve the physical properties of the piezoelectric materials, but also to reduce the size of the piezoelectric devices. This review focuses on the development of piezoelectric thin films that can enhance the performance of microtransducers.

• Smart Structures and Systems
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• v.12 no.1
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• pp.55-71
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• 2013

Structural health monitoring (SHM) is vital for detecting the onset of damage and for preventing catastrophic failure of civil infrastructure systems. In particular, piezoelectric transducers have the ability to excite and actively interrogate structures (e.g., using surface waves) while measuring their response for sensing and damage detection. In fact, piezoelectric transducers such as lead zirconate titanate (PZT) and poly(vinylidene fluoride) (PVDF) have been used for various laboratory/field tests and possess significant advantages as compared to visual inspection and vibration-based methods, to name a few. However, PZTs are inherently brittle, and PVDF films do not possess high piezoelectricity, thereby limiting each of these devices to certain specific applications. The objective of this study is to design, characterize, and validate piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensing and SHM applications. These films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to pristine PVDF copolymers. This study started with spin coating dispersed ZnO- and PVDF-TrFE-based solutions to fabricate the piezoelectric nanocomposites. The concentration of ZnO nanoparticles was varied from 0 to 20 wt.% (in 5 % increments) to determine their influence on bulk film piezoelectricity. Second, their electric polarization responses were obtained for quantifying thin film remnant polarization, which is directly correlated to piezoelectricity. Based on these results, the films were poled (at 50 $MV-m^{-1}$) to permanently align their electrical domains and to enhance their bulk film piezoelectricity. Then, a series of hammer impact tests were conducted, and the voltage generated by poled ZnO-based thin films was compared to commercially poled PVDF copolymer thin films. The hammer impact tests showed comparable results between the prototype and commercial samples, and increasing ZnO content provided enhanced piezoelectric performance. Lastly, the films were further validated for sensing using different energy levels of hammer impact, different distances between the impact locations and the film electrodes, and cantilever free vibration testing for dynamic strain sensing.

• 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.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.220-225
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• 2008

In this research, the P(VDF-TrFE) copolymer thin films were prepared by the physical vapor deposition and studied to their piezoelectric properties. In the case of a specimen produced by varying the deposition temperature from $260^{\circ}C$ to $300^{\circ}C$, its piezoelectric coefficient($d_{33}$) increased from 32.3pC/N to 36.28pC/N, and piezoelectric voltage coefficient($g_{33}$) from $793{\times}10^{-3}V{\cdot}m/N$ to $910.5{\times}10^{-3}V{\cdot}m/N$. On the basis of these experimental results, we concluded that the P(VDF-TrFE) copolymer thin film prepared at $300^{\circ}C$ showed the optimum piezoelectric properties. At the deposition temperature of $320^{\circ}C$, its piezoelectric coefficient(d33) decreased 25.3 pC/N and piezoelectric voltage coefficient($g_{33}$) $680{\times}10^{-3}V{\cdot}m/N$.