• 한국정보통신학회논문지
• /
• 제11권3호
• /
• pp.570-576
• /
• 2007

본 연구에서는 field-dependent polarization 모델과 square-law FET 모델을 이용하여 Metal- ferroelectic-semiconductor FET (MFSFET) 소자의 특성을 연구하였다. 게이트 전압에 따른 드레인 전류특성에서 강유전체 박막의 항전압이 0.5 와 1 V 일 때, 각각 1와 2 V의 메모리 창 (memory window) 을 나타내었다. 드레인 전류-드레인 전압곡선에서 두 부분의 문턱전압에 의해 나타난 포화 드레인 전류차이는 게이트 전압이 0, 0.1, 0.2, 0.3 V 일 때, 각각 1.5, 2.7, 4.0, 5.7 mA로 명확한 차이를 나타내었다. PLZT(10/30/70), PLT(10), PZT(30/70) 박막의 이력곡선 시뮬레이션과 리텐션 특성의 fitting 결과를 바탕으로 시간경과 후의 드레인 전류를 분석한 결과, PLZT(10/30/70) 박막이 10년 후에도 약 18%의 포화 전류가 감소하는 가장 우수한 신뢰성을 나타내었다.

• 한국표면공학회지
• /
• 제56권6호
• /
• pp.380-385
• /
• 2023

In this study, an MPB PMNT system containing 0.05 to 0.10 wt.% BaTiO₃ was synthesized using a traditional chemical method and its pyroelectricity was investigated. Pyroelectricity, dielectricity, and ferroelectricity of the synthesized BaTiO₃-PMNT system were analyzed by heat treatment at 1240~1280 ℃ for 4 hours to evaluate its applicability as a pyroelectric sensor. Unlike the simple ABO₃ ferroelectric, the BaTiO₃-doped PMNT system exhibited phase transition characteristics over a wide temperature range typical of complex perovskite structures. Although no dramatic change could be confirmed depending on the amount of BaTiO₃ added, stable pyroelectricity was maintained near room temperature and over a wide temperature range. When the amount of BaTiO₃ added increased from 0.05BaTiO₃-PMNT to 0.10BaTiO₃-PMNT, the electric field slightly increased from 5.00×10³ kV/m to 6.75×10³ kV/m, and the maximum value of remanent polarization slightly increased from 0.223 C/m² to 0.234 C/m². The pyroelectric coefficients of 0.05BaTiO₃-PMNT and 0.10BaTiO₃- PMNT at room temperature were measured to be ~0.0084 C/m²K and ~0.0043 C/m²K, respectively. The relaxor ferroelectric properties of the BaTiO₃-PMNT system were confirmed by analyzing the plot of K_max/K versus (T-T_max)^γ. The BaTiO₃-doped MPB PMNT system showed a distinct pyroelectric performance index at room temperature, and the values were F_v ~ 0.0362 m²/C, F_d ~ 0.575×10^-4 Pa^-1/2.

• 한국결정성장학회지
• /
• 제25권4호
• /
• pp.160-165
• /
• 2015

Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, $Pb(Zr_xTi_{1-x}O_3)$, which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, $Na_{0.5}Bi_{0.5}TiO_3$ (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, $(Na_{0.5}Bi_{0.5})_{0.93}Ba_{0.7}TiO_3$ (abbreviated as NBT-7BT), at the region of MPB using 7 % $BaTiO_3$ as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 센서 박막재료 반도체 세라믹
• /
• pp.178-181
• /
• 2003

In this work, we etched PZT films with various additive gases ($O_2$ and Ar) in $Cl_2/CF_4$ plasmas, while mixing ratio was fixed at 8/2. After the etching, the plasma induced damages are characterized in terms of hysteresis curves, leakage current, retention properties, and switching polarization. When the electrical properties of PZT etched in $O_2$ or Ar added $Cl_2/CF_4$ were compared, the value of remanent polarization in $O_2$ added $Cl_2/CF_4$ plasma is higher than that in Ar. added plasma. The maximum etch rate of the PZT thin films was 145 nm/min for 30% Ar added $Cl_2/CF_4$ gas having mixing ratio of 8/2 and 110 nm/min for 10% $O_2$ added to that same gas mixture. In order to recover the ferroelectic properties of the PZT thin films after etching, we annealed the etched PZT thin films at $550^{\circ}C$ in an $O_2$ atmosphere for 10 min. From the hysteresis curves, leakage current, retention property and switching polarization, the reduction of the etching damage and the recovery via the annealing was turned out to be more effective when $O_2$ was added to $Cl_2/CF_4$ than Ar. X-ray diffraction (XRD) showed that the structural damage was lower when $O_2$ was added to $Cl_2/CF_4$. And the improvement in the ferroelectric properties of the annealed samples was consistent with the increased intensities of the (100) and the (200) PZT peaks.

• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2012년도 임시총회 및 하계학술연구발표회
• /
• pp.121-122
• /
• 2012

Iron-excess gallium ferrite, $Ga_{0.6}Fe_{1.4}O_3$ (GFO), is known to have room-temperature ferromagnetic phases and potentially exhibit ferroelectricity as well [1]. But, leaky polarization-electric field (PE) hysteresis curves of the GFO thin film are hurdle to prove its spontaneous polarization, in other words, ferroelecticity. One of the reasons that the GFO films have leaky PE hysteresis loop is carrier hopping between $Fe^{2+}$ and $Fe^{3+}$ sites due to oxygen deficiency. We focus on reducing conducting current by substituting divalent cations at $Fe^{2+}$ sites. GFO thin films were grown epitaxially along b-axis normal to $SrRuO_3/SrTiO_3$ (111) substrates by pulsed laser deposition. Current density of the ion-substituted GFO thin films was reduced by $10^3$ or more. Ferroelectric properties of the ion-substituted GFO thin films were measured using macroscopic and microscopic schemes. In particular, local ferroelectric properties of the GFO thin films were exhibited and their remnant polarization and piezoelectric d33 coefficient were obtained.

• 한국재료학회지
• /
• 제10권5호
• /
• pp.360-363
• /
• 2000

다양한 Zr/Ti 비율을 갖고 있는 강유전체 PZT박막을 졸-겔 법으로 증착하였고 상부 백금전극의 제조방법과 열처리온도의 변화에 따라 강유전체 특성을 측정하여 이력곡선의 변형 원인을 조사하였다. Pt/PZT/Pt 캐패시터는 상부 백금전극을 반응성 이온 식각(RIE) 하는 과정에서 생성된 dc plasma 전압에 의하여 양의 방향으로 분극되었고 도메인 계면에 포획된 전하에 의해 내부전장이 발생되었다. PZT 박막은 sputtering으로 상부전극을 증착하는 과정에서 이력곡선의 중간에 잘룩하게 되는 시효현상이 관찰되었다. 상부전극을 제작한 후 열처리는 포획된 전하흫 제거시켜 양호한 이력곡선 특성을 되찾게 하였다. Zr/Ti 비율이 감소함에 따라 내부전장이 증가하였으며 내부전장이 없어지는 열처리온도가 증가하였다.

• 한국전기전자재료학회논문지
• /
• 제28권6호
• /
• pp.375-378
• /
• 2015

In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, $(Pb_{0.88}La_{0.08})(Zr_{0.65}Ti_{0.35})O_3$ ceramics were fabricated by the conventional solid-state method. Electrocaloric effects of $(Pb_{0.88}La_{0.08})(Zr_{0.65}Ti_{0.35})O_3$ ferroelectric ceramics were investigated and discussed using the characteristics of P-E hysteresis loops at wide temperature range from room temperature to $220^{\circ}C$. The temperature change ${\Delta}T$ due to the electrocaloric effect was calculated by Maxwell's relations, and reached the maximum of ~0.19 at $190^{\circ}C$ under applied electric field of 30 kV/cm.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
• /
• pp.325-328
• /
• 1991

In this study, $0.085Ba(La_{1/2}Nb_{1/2})O_3-0.915Pb(Zr_yTi_{1-y})O_3$(y=0.45, 0.50, 0.55, 0.60, 0.65[mol]) transparent electrooptic ceramics were fabricated by two-stage sintering method. Increasing the $PbZrO_3$ contents, dielectric constant was increased and Curie temperature was decreased. In the composition of 0.55[mol] $PbZrO_3$, electromechanical coupling factor was 0.43. From the results of ferroelectric hysteresis loop and transmitted light intensity with electric field, the compositions of 0.65, 0.60, 0.55[mol] $PbZrO_3$ was applicable to electroopticmemory device and the compositions of 0.50, 0.45[mol] $PbZrO_3$ was applicable to linear electrooptic device.

• 한국세라믹학회지
• /
• 제40권4호
• /
• pp.398-400
• /
• 2003

The YMnO$_3$ thin films were prepared on platinized-silicon substrates by chemical solution deposition and annealed at 750 to 85$0^{\circ}C$ for 1 h under various oxygen pressures, from 2 mTorr to 760 Torr. Effects of annealing oxygen pressures on the crystallization behavior and electrical properties of YMnO$_3$ thin films were investigated. Crystallinity and c-axis preferred orientation of YMnO$_3$ thin film were improved by decreasing the oxygen pressure but were deteriorated at extremely low oxygen pressure, 2 mTorr. Leakage current density of the YMn03 thin film decreased as the oxygen pressure decreased. The film annealed at 80$0^{\circ}C$ under 2 Torr, which had the best crystallinity and the highest c-axis preferred orientation. showed the best-developed ferroelectric C-V hysteresis.

• Journal of Korean Vacuum Science & Technology
• /
• 제4권1호
• /
• pp.6-10
• /
• 2000

Ferroelectric YMnO$_3$ thin films were deposited on $Y_2$O$_3$/si(100) substrates by metalorganic chemical vapor deposition. The YMnO$_3$ thin films annealed in vacuum ambient (100 mTorr) above 75$0^{\circ}C$ show hexagonal structured YMnO$_3$. However, the film annealed in oxygen ambient shows poor crystallinity, and the second phase as $Y_2$O$_3$ and orthorhombic-YMnO$_3$ were shown. The annealing ambient and pressure on the crystallinity of YMnO$_3$ thin films is very important. The C-V characteristics have a hysteresis curve with a clockwise rotation, which indicates ferroelectric polarization switching behavior. When the gate voltage sweeps from +5 to 5 V, the memory window of the Pt/YMnO$_3$/Y$_2$O$_3$/Si gate capacitor annealed at 85$0^{\circ}C$ is 1.8 V. The typical leakage current densities of the films annealed in oxygen and vacuum ambient are about 10$^{-3}$ and 10$^{-7}$ A/cm$^2$ at applied voltage of 5 V.