두께 변화에 따른 (111) 방향으로 성장된 PZT 후막의 미세구조와 전기적 특성

조삼연,양선아,부상돈 한국물리학회 2011 새물리 Vol.61 No.10

Pb(Zr,Ti)O₃ (PZT) thick films have attracted considerable attention because they are widely used in micro-electromechanical systems (MEMS), micro-power harvesting systems and high frequency ultrasonic transducers for higher imaging resolution. Their popularity is based on their high ferroelectric and piezoelectric properties. However, these properties are closely related to the film's thickness. Therefore, we investigated the thickness dependent ferroelectric and dielectric properties of PZT films. The PZT thick films were fabricated on (111) Pt/Ti/SiO2₂/Si (Pt/Si) substrats by using a sol-gel method with a multi-coating process. Their orientation was controlled by using a layer(s) by layer(s) annealing process. The X-ray diffraction (XRD) analysis showed that all the films were highly oriented along the (111) direction. Increases in the remnant polarization and the dielectric constant with increasing film thickness were observed in the thickness range from 0.3㎛to 1.7㎛. However, thicker films greater than (2.3㎛)showed abrupt decreases in the remnant polarization and the dielectric constant. Thickness dependent of the ferroelectric and the dielectric properties can be explained in terms of the domain structure, non-switching interface layer, and grain size. 솔-젤 (sol-gel) 방법으로 Pt(111)/Ti/SiO₂/Si(100) (Pt/Si) 기판위에 (111) 방향으로 Pb(Zr_(0.52)Ti_(0.48)O₃ (PZT) 후막을제작하였다. 박막 증착시 각 층들을 반복 열처리 방법으로 배향성을조절하였으며, X-선 회절 분석으로부터 0.3~2.3㎛의두께에서 PZT 후막은 (111) 방향으로 성장 되었다. 이와 같이 후막증착시 증착된 한 층을 반복 열처리 방법으로 후막의 배향성에 따른전기적 특성 변화를 최소화 한 후, 두께 변화에 따른 PZT 후막의 전기적특성을 조사하였다. PZT 후막은 두께 증가에 따라 강유전 및 유전 특성이향상되었으며, 1.7㎛ 두께에서 PZT 후막의 잔류분극 및 유전상수값은 29.2μC/cm², 1279로 최대값을 나타내었다. 그러나 후막의두께가 2.3㎛ 일 때 25.42μC/cm², 1065로 감소하였다. 이현상은 두께 변화에 따른 PZT 후막의 구역 (domain) 구조 변화, 계면의non-switching 층의 존재와 낟알 크기 (grain size) 변화에 기인한것이다.

Effects of Annealing on Domain-wall Contributions to the Dielectric Properties of PZT Thin Films

조삼연,곽진호,양선아,부상돈,박성균,이민구 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.10

We studied the effects of the annealing process on domain-wall contributions to the dielectricproperties of PZT thin films. Two annealing processes, single annealing and layer-by-layer annealing,were used to fabricate PZT thin films. The film thickness was controlled by repeating thespin-coating process. Field-emission scanning electron microscopy and an X-ray diffraction analysisshowed the morphological and the structural differences, respectively, between the two films. Basedon the analysis of ferroelectric hysteresis loops, we found that PZT thin films fabricated with thesingle annealing process had larger values of the remanent polarization (Pr) and the coercive field(Ec) than PZT thin films fabricated with the layer-by-layer annealing process. The values for the Prand the Ec in the two films differed by, at most, 9 µC/cm2 and 23 kV/cm. This maximum differenceoccurred between films that underwent the same number of spin-coating cycles. Using Rayleigh relations,we could explain the differences in ferroelectric properties in terms of domain-wall motioncontributions to the dielectric properties.

Comparison between the Electrical Properties of Bismuth Layer-Structured and Intergrowth Bismuth Layer-Structured Ferroelectric Ceramics

조삼연,최기품,부상돈 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.10

Bismuth layer-structured ferroelectric (BLSF)-type Bi4Ti3O12 (BiT), Bi3.25La0.75Ti3O12 (BLaT), and Bi3.1Nd0.9Ti3O12 (BNdT) ceramics and intergrowth BLSF-type BiT-CaBi4Ti4O15 (CBTO), BLaT-CBTO, and BNdT-CBTO ceramics were prepared using the solid-state reaction method. The electrical and the high-temperature properties of the intergrowth BLSF ceramics were compared with those of BLSF ceramics to investigate the possibility of using the former for high-temperature applications. The X-ray diffraction (XRD) analysis revealed well-formed stable structures in all BLSF and intergrowth BLSF ceramics without any second-phase formation. When their electrical properties were examined, the intergrowth BLSF ceramics BiT-CBTO, BLaT-CBTO, and BNdTCBTO were found to outperform the BLSF ceramics BiT, BLaT, and BNdT, respectively, in terms of the remanent polarization and piezoelectric coefficient values. Among the intergrowth BLSF ceramics, those doped with rare-earth ions La and Nd, i.e., BLaT-CBTO and BNdT-CBTO ceramics, were found to have improved electrical properties compared to the BiT-CBTO ceramics. In particular, the dielectric constants and the piezoelectric coefficients of the BNdT-CBTO ceramics were observed to be as high as 146 and 15.4 pC/N, respectively, which were 28% and 10% higher than those of BNdT ceramics. In the thermal depoling behavior measured to examine high-temperature stability, the intergrowth BLSF ceramics, compared to the BLSF ceramics, demonstrated improvements in the thermal depoling temperature ranging from 100 to 300 C.

Effects of excess Bi2O3 on grain orientation and electrical properties of CaBi4Ti4O15 ceramics

조삼연,최기쁨,전도현,JOHNSONTRENTALLEN,이민구,이경자,부상돈 한국물리학회 2015 Current Applied Physics Vol.15 No.11

A CaBi4Ti4O15 (CBTO) ceramic in which the Bi2O3 concentration was controlled from 0 to 10 wt% was fabricated using a solid-state reaction method. Structural analysis by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) indicated differences in the preferred grain orientation and size of the plate-like grains according to the Bi2O3 concentration. The orientation of plate-like grains was also found to vary with the Bi2O3 concentration. There was no noticeable change trend of dielectric properties with different Bi2O3 concentrations. Relatively low dielectric constants (about 135) were exhibited by the CBTO ceramic with 1 wt% Bi2O3 and CBTO ceramic with 10 wt% Bi2O3 only, and similar values (about 150) were exhibited by the other ceramics. The dielectric loss exhibited a low value in the range of 0.01e0.09 for all samples (frequency range of 1e100 kHz). Regarding the ratio changes of the piezoelectric coefficient (d33) and the ratio of a-axis orientation of plate-like grains, the trends of these two values were shown to be similar. These results suggest that the addition of Bi2O3 greatly influences the microstructure of CBTO ceramics, including the grain size and orientation of plate-like grains. In particular, the change in the preferred grain orientation is closely related to the change in the piezoelectric properties.

Nd가 치환된 Bi4-xNdxTi3O12 세라믹스의 구조 및 전기적 특성 변화

최기쁨,조삼연,전도현,부상돈,이경자,이민구 한국물리학회 2015 새물리 Vol.65 No.7

Bismuth-layer-structured ferroelectric/piezoelectric Bi4−xNdxTi3O12 (BNdT) ceramics in which the Nd substitution was controlled from x = 0.25 to 1.00 were prepared by using the conventional solid-state-reaction method. Structural analysis by using X-ray diffraction (XRD) showed that all the BNdT ceramics had a polycrystalline structure without second phases, which was consistent with the data for Bi4Ti3O12 (JCPDS No. 35-0795). We found that the BNdT ceramics had grains with elongated shapes. The change in the orientation ratio of a − b plane in the grains with increasing Nd substitution was found to be similar to the changes in their electrical properties. In particular, a notable improvement in the electrical properties was observed in the x = 0.75 - 0.90 composition ratio of the BNdT ceramics. For the Bi3.1Nd0.9Ti3O12 (x = 0.90) ceramics, the values of the dielectric constant and the piezoelectric coefficients exhibited maximum values of about 209 and 15 pC/N, respectively. On the other hand, with increasing Nd concentration, the phase transition temperature (Tc) continuously decreased from 613 ℃ (Bi3.75Nd0.25Ti3O12, x = 0.25) to 218 ℃ (Bi3.00Nd1.00Ti3O12, x = 1.00). These results suggest that controlling the Nd substitution in BNdT ceramics is essential for changing the dielectric constant and piezoelectric coefficients of bismuth-layer-structured piezoelectric materials. Nd 치환량을 조절하여 Bi4-xNdxTi3O12 (BNdT) 세라믹스의 조성을 x = 0.25에서 1.00까지 범위에서 제어한 세라믹스를 고상반응법으로 제작하였다. X-선 회절 분석을 통해 모든 시료에서 다결정의 Bi4Ti3O12 구조가 잘 형성되었음을 확인 하였다. Nd 치환량에 따른 구조 변화를 살펴보기 위해 조사된 a-b 방향면들의 비율 변화는 전기적 특성 변화와 밀접한 관계가 있는 것으로 확인 되었다. BNdT 세라믹스는 Nd 치환량이 증가함에 따라서 x = 0.75 이상의 조성비에서 주목할만한 전기적 특성 향상을 보였으며, x = 0.90의 조성비에서 가장 우수한 특성을 나타내었다. Bi3.1Nd0.9Ti3O12 세라믹스 (x = 0.90)에서 측정된 유전상수 값과 압전계수 값은 각 각 209와 15 pC/N으로 최대값을 나타내었으며, 항전기장 (2Ec) 값은 38 kV/cm 로 최소값을 보였다. 이러한 결과들을 통해서 BNdT 세라믹스에서 Nd 치환에 따른 최적의 조성비를 확인하였다.

Effect of the Number of PZT Coatings on the Crystal Structure and Piezoelectric Properties in PZT-CNT Nanocomposites

강신욱,조삼연,부상돈,한진규,이경자,이민구 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.10

In this study, a nanocomposite was successfully fabricated by mixing Pb(Zr,Ti)O3 (PZT) prepared by using the sol-gel method and functionalized multi-walled carbon nanotubes (MWCNTs). During this process, the effect of the change in the molar concentration of PZT on the crystallinity and the piezoelectric properties of the PZT in the nanocomposite was investigated. As the number of PZT coatings was increased from one to three, PZT was confirmed as having completely covered the MWCNT nanocomposite. Also, the tetragonality of PZT in the crystal structure was confirmed to have increased with increasing number of PZT coatings. Such an increase in crystallinity was followed by an increase in the ferroelectricity of the nanocomposite. A nano-generator was fabricated by using the nanocomposite fabricated as described above, and the characteristics of the nanogenerator were confirmed to have been improved with increasing number of coatings.

Bi 첨가량에 따른 (Bi3.84Nd0.16)Ti3O12 세라믹스의 배향성 및 전기적 특성 변화

전도현,조삼연,김병훈,강신욱,곽진호,양선아,부상돈,이경자,이민구 한국물리학회 2014 새물리 Vol.64 No.6

(Bi3.84Nd0.16)Ti3O12 (BNdT) ceramics with different excess bismuth (Bi) contents from 0 mol% to 20 mol% were prepared by using the solid-state reaction method. No secondary phases were in any of the ceramics. The amount of a-axis orientation changed with increasing excess Bi contents, and the maximum a-axis orientation was observed in the BNdT ceramic with 5 mol% excess Bi content. The value of the remanent polarization of the ceramics also changed with changing excess of Bi content, and the maximum value of the remanent polarization was observed in the ceramic with 5 mol% excess Bi content. The change in the behavior of the remanent polarization was observed to be similar to that of the a-axis orientation, which suggests that the amount of a-axis orientation highly affects ferroelectric properties such as the remanent polarization in BNdT ceramics. The maximum phase-transition temperature (T_c) was observed to be 632℃ in the BNdT ceramic without excess Bi content, and the T_c was observed to decrease continuously to 616℃ with increasing excess Bi content. From these results, we can conclude that a 5 mol% excess Bi content to enhances the electrical properties of BNdT ceramics favor. Bi를 0 mol%에서 20 mol%까지 범위에서 과잉 첨가한 (Bi3.84Nd0.16)Ti3O12 (BNdT) 세라믹을 고상반응법으로 제작하였다. 모든 시료에서 이차상의 형성은 관찰 되지 않았다. Bi 첨가량이 증가함에 따라서 a-축 방향면의 배향성이 변화하는 것을 확인 하였으며, a-축 방향면의 배향성의 최대 값은 Bi가 5 mol% 첨가된 BNdT 세라믹 시료에서 관찰 되었다. 세라믹의 잔류분극 값 역시 Bi 첨가량이 변화함에 따라서 변화하는 것을 관찰 하였으며, 잔류분극 값의 최대 값은 Bi가 5 mol% 첨가된 BNdT 세라믹 시료에서 관찰 되었다. 잔류분극 값의 변화 양상이 a-축 방향면의 배향성 변화양상과 비슷하다는 점을 관찰하였으며, 이는 a-축 방향면의 배향성이 BNdT 세라믹의 잔류분극과 같은 강유전 특성 변화에 큰 영향을 미친다는 것을 시사한다. 상전이 온도의 최대값은 632℃로 Bi가 과잉 첨가되지 않은 BNdT 시료에서 관찰 되었으며, 상전이 온도는 Bi 첨가량이 증가함에 따라서 616℃까지 지속적으로 낮아 졌다. 이러한 결과들로부터 5 mol%의 Bi 과잉 첨가가 BNdT 세라믹 시료의 전기적 특성 향상에 가장 유리하게 작용하는 것으로 판단된다.

Surface-adsorbate-induced fluorescence-type Raman background of Pb(Zr0.4Ti0.6)O3 nanotubes

최용찬,조삼연,박성균,부상돈 한국물리학회 2012 Current Applied Physics Vol.12 No.5

We report the effects of adsorbates on the Raman spectra of Pb(Zr0.4Ti0.6)O3 nanotubes (PZT-NTs). PZTNTs with adsorbates were prepared by exposing PZT-NTs to air for 1 day. We found that the presence of surface adsorbates can cause an intense and broad Raman background that hinders the observation of the Raman vibrational modes of the PZT-NTs. This background can be suppressed by adjusting the Raman excitation wavelength from 514.5 nm to 414.6 nm. It can also be removed by post-annealing the PZT-NTs at 500 ℃, but it returns readily after re-exposure to air. X-ray photoelectron and Fourier transform infrared spectroscopies show that hydroxyl and carbonate groups are adsorbed onto the surfaces of the PZT-NTs during exposure to air. Moreover, dispersive Raman spectra reveal that the background is a tail of a very broad band from 1000 to 4000 cm-1, which corresponds to hydroxyl groups. These results suggest that the main contribution to the Raman background of the PZT-NTs is that of surface hydroxyl groups rather than carbonate groups.

Effect of the Molar Concentration of a Solution on Nanocomposite Crystal Growth in Ferroelectric-Carbon Nanotube Composites Fabricated by using the Sol-gel Method

강신욱,조삼연,부상돈,한진규 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.7

In this study, Pb(Zr,Ti)O3 (PZT) nanoparticles directly were successfully grown on carbon nanotubes by mixing a PZT solution prepared by using the sol-gel method with functionalized carbon nanotubes. During this process, the effects of the concentration of the PZT solution on the size, crystallinity, and composition ratio of the PZT nanoparticles on the carbon nanotubes were investigated. As the molar concentration of the PZT solution was increased from 0.05 M to 0.2 M, the particle size increased from 6.628 nm to 10.877 nm. As the size of the nanoparticles increased, the surface directions became more diverse. In terms of the crystal structure, the tetragonality of PZT increased with increasing molarity of the PZT solution. This improvement in crystallinity can be further linked to an increase in the ferroelectricity of the PZT-carbon nanotubes, so the nanocomposite fabrication method using carbon nanotubes is expected to affect the characteristics of ferroelectric materials and can be used to further improve the properties of those.

양극산화 용액 및 화학적 식각이 다공성 양극산화 알루미나 형태에 미치는 영향

김진우,최기쁨,조삼연,부상돈 한국물리학회 2016 새물리 Vol.66 No.9

We report here the effects of an anodizing solution and chemical etching on the shape of porous anodic alumina (PAA). PAA was synthesized by using a conventional anodization method for aluminum in two mixed solutions: (1) an oxalic acid and phosphoric acid mixture and (2) an oxalic acid and ethanol mixture. We prepared various samples of PAA anodized at various voltages from 40 to 120 V, various mixing ratios, and various etching times; then, we examined their pore morphologies. We found that the inter-pore distance of PAA grown in the oxalic acid and phosphoric acid solution could be controlled over a wide range from 192 nm to 282 nm. The fastest PAA growth rate of about 153.15 nm/min was found for the mixed anodizing solution of 95% oxalic acid and 5% ethanol. Also, the pore arrangement of PAA grown in the mixed solution of 90% oxalic acid and 10% ethanol was the best. The pore size, inter-pore distance, and pore arrangement of PAA can be controlled in various metal-oxide nanostructures. 본 연구에서는 옥살산 그리고 인산 혼합 용액, 옥살산 그리고 에탄올 혼합 용액의 두 가지 혼합 용액에서 2차 양극산화 방법으로 다공성 양극산화 알루미나 (porous anodic alumina, PAA)를 성공적으로 성장시켰다. 이 과정에서 양극산화 전압과 용액 혼합 비율이 PAA에서의 기공 크기, 기공 사이의 거리, 기공 정렬도 그리고 기공 성장 속도에 미치는 영향을 조사하였다. 옥살산 그리고 인산 혼합 용액에서 성장된 PAA의 경우 기공 사이의 거리를 192 nm 에서부터 282 nm까지의 넓은 범위에서 조절하면서 성장시킬 수 있었다. 또한 5%의 에탄올이 들어 있는 옥살산 그리고 에탄올 혼합 용액에서 성장된 PAA가 가장 큰 성장속도, 약 153.15 nm/min을 가지는 것을 알 수 있었다. 그리고 10%의 에탄올이 들어 있는 옥살산 그리고 에탄올 혼합 용액에서 성장된 PAA가 가장 좋은 기공 정렬도를 가지는 것을 알 수 있었다. 아울러 기공 크기 조절의 경우, 화학적 식각을 통해서 기공의 크기를 32 nm에서 64 nm까지 넓힐 수 있었다. 이러한 기공 크기, 기공 사이의 거리, 기공 정렬도 조절은 다양한 기능성 나노 구조물 제작에 있어서 주형틀로 사용되는 PAA 조절 기술로 사용될 수 있다.