Sun Hee Kang

Enhanced ferroelectric properties of LiNbO3 substituted Na0.5K0.5NbO3 lead-free thin films grown by chemical solution deposition

We have fabricated environmental friendly lead-free ferroelectric Na0.5K0.5NbO3 (NKN) and 0.95Na0.5K0.5NbO3–0.05LiNbO3 (0.95NKN-0.05LN) thin films by chemical solution deposition using metal-organic compounds, and studied the effects of LN substitution through the dielectric and ferroelectric properties. The small amount of LN substitution for NKN thin film led to a marked improvement in leakage current properties at the high electric field region. Furthermore, the 0.95NKN-0.05LN thin film (350nm) displayed clear ferroelectricity with well saturated P-E hysteresis loop with 2Pr and 2Ec values of 19.5μC∕cm2 and 91kV∕cm, respectively. The 0.95NKN-0.05LN films will be interesting for applications in lead-free ferroelectric and piezoelectric devices.

Antiferroelectric characteristics and low frequency dielectric dispersion of Pb1.075La0.025(Zr0.95Ti0.05)O3 thin films

Abstract La-modified lead zirconate titanate Pb 1.075 La 0.025 (Zr 0.95 Ti 0.05 )O 3 , antiferroelectric thin films are fabricated by excimer laser ablation technique on Pt/Ti/SiO 2 /Si substrates. The measured dielectric constant and dissipation factor are 642 and 0.021 at room temperature, respectively, and Curie temperature is 196 °C. The antiferroelectric double hysteresis loops of Pb 1.075 La 0.025 (Zr 0.95 Ti 0.05 )O 3 film are confirmed by measuring the polarization vs. the electric field. With increasing temperature, the double hysteresis loop behavior is reduced and gradually becomes a loose single ferroelectric hysteresis loop. The complex dielectric constants and a.c. conductivities are measured as a function of frequency (10 −2 –10 6 Hz) and temperature (25–250 °C) in order to investigate the influence of microstructure on the charge transport mechanism. We observe the strong low-frequency dielectric dispersion due to migration of thermally activated oxygen vacancies at higher temperature above 175 °C. The activation energy calculated from the a.c. conductivity is 0.63 eV.

Polarization Characteristics of High Valence Ion Doped Bismuth Lanthanum Titanate Ceramics

Bi3.25La0.75Ti3−3x Nb3x O12 (BLTN) and Bi3.25La0.75Ti3−3x V3x O12 (BLTV) ceramics (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1) were prepared by a solid state reaction method. For all BLTN and BLTV compositions, bismuth-layered perovskite structures were confirmed using X-ray diffraction. The remanent polarization increases and reaches to the maximum value at x = 0.05 for BLTN and at x = 0.01–0.03 for BLTV ceramics. With increasing doping concentrations, the Curie temperature of BLTV ceramics increased while that of BLTN ceramics decreased. For the substitutions of high-valence Nb5 + and V5 + ion for Ti4 + ion, effects of ion doping on dielectric and ferroelectric properties were investigated.

The Ferroelectric Properties of (Na0.5K0.5)NbO3 Thin Films Fabricated by rf-Magnetron Sputtering

Fatigue-free Na 0.5 K 0.5 NbO 3 (NKN) thin films were grown on Pt/Ti/SiO 2 /Si substrates by the radio frequency magnetron sputtering method. The addition of enriched Na 2 CO 3 and K 2 CO 3 into the NKN ceramic target was necessary in order to compensate for a deficiency in the Na and K concentrations in the film. The remnant polarization (2P r) and the coercive field (2E c) of the NKN films annealed at 600°C were 32.2 μ C/cm 2 and 90 kV/cm at an applied field of 200 kV/cm, respectively. A leakage current density was obtained around 7.3×10−8 A/cm 2 at 150 kV/cm. The film showed fatigue-free characteristics under a ± 5 V bipolar square pulse of 1 MHz for up to 1.0×10 10 cycles. The NKN film prepared by radio frequency magnetron sputtering is an attractive alternative for applications involving nonvolatile ferroelectric random access memory (FRAM) devices.

Pyroelectric and Transient Current Properties of Multilayer Pb1.1(Zr0.3Ti0.7)O3/PbTiO3 and Pb1.1 (Zr0.3Ti0.7)O3 Thin Films

Pb 1.1 (Zr 0.30 Ti 0.70 )O 3 (PZT) and Pb 1.1 (Zr 0.30 Ti 0.70 )O 3 /PbTiO 3 (PZT/PT) multi-layered thin films are grown on Pt/Ti/SiO 2 /Si substrate by sol-gel method. The kinetics of current change of pyroelectric and transient response between PZT and PZT/PT ferroelectric thin films is investigated. The shape of peak in the PZT film is sharp, but that of PZT/PT is broadened. An increase in the peak value of switching current and switching time in the PZT/PT film is observed. The change of pyroelectric and transient current between PZT/PT and PZT films is discussed in terms of internal field.

Ferroelectric Properties of Ta- and Mn-Doped Bi 3.3 La 1.0 Ti 3 O 12 Thin Films

Bi 3.3 LaTi 3 O 12 (BLT), Bi 3.3 LaTi 3 O 12 :Ta (BLT:Ta), and Bi 3.3 LaTi 3 O 12 :Mn (BLT:Mn) thin films are synthesized on Pt/Ti/SiO 2 /Si substrates using a pulsed laser deposition technique. The BLT:Ta and BLT:Mn films enhanced the ferroelectric properties, compared to BLT film. The remnant polarization (2P r ) and the coercive field (2E c ) of BLT:Ta film are 17 w C/cm 2 , and 78 kV/cm, respectively. All of the films show little polarization fatigue up to 5 2 10 10 switching cycles. I-V characteristics of the BLT films exhibit the mechanism of a space charge limited conduction (SCLC). However, BLT:Ta and BLT:Mn films show the Ohmic like behavior with no space-charge region up to the 170 kV:cm. This new BLT:Ta thin film seems to be very attractive for nonvolatile ferroelectric random access memory devices.

High Strain and Piezoelectric Characteristics of Textured Bi 0.5 (Na 0.85 K 0.15 ) 0.5 TiO 3 Ceramics

The anisotropy of polarization and strain behavior in textured Bi_0.5(Na_0.85K_0.15)_0.5TiO₃ ceramics are investigated for lead-free piezoelectric ceramics actuators. The textured Bi_0.5(Na_0.85K_0.15)_0.5TiO₃ ceramics are fabricated by reactive templated grain growth (RTGG) using plate-like Bi₄Ti₃O₁₂ particles. RTGG[//] (sliced parallel to the casting direction) and RTGG[square] (sliced perpendicularly to the casting direction) specimens show preferred orientation to <001>_pc and <110>_pc, respectively. RTGG[//] specimen has relatively high piezoelectric coefficient of (d₃₃) ~335 pm/V and electric field induced strain levels of 0.067% at 20 kV/cm. This values were 86% higher than those of RTGG[ square] specimen. <001>_pc textured polycrystalline BNKT ceramics, prepared by RTGG, are a strong candidate for lead-free piezoelectric materials of actuators.