Ansan, South Korea
Ansan, South Korea

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Cross J.S.,Tokyo Institute of Technology | Kim S.-H.,INOSTEK Inc. | Wada S.,Yamanashi University | Chatterjee A.,Accelrys
Science and Technology of Advanced Materials | Year: 2010

Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100°C. With this goal in mind, co-doping of thin Pb(Zr40, Ti60)O3 (PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO3 (BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 1010 cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method. © 2010 National Institute for Materials Science.


PubMed | Yamanashi University, Tokyo Institute of Technology, Accelrys and INOSTEK Inc.
Type: Journal Article | Journal: Science and technology of advanced materials | Year: 2016

Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 C. With this goal in mind, co-doping of thin Pb(Zr


Jung Y.,Yonsei University | Jung Y.,Samsung | Yang W.,Yonsei University | Koo C.Y.,Yonsei University | And 4 more authors.
Journal of Materials Chemistry | Year: 2012

Highly stable and high performance solution-processed amorphous oxide semiconductor thin film transistors (TFTs) were produced using a Li and Zr co-doped ZnO-based aqueous solution. Li and Zr co-doping at the appropriate amounts enhanced the oxide film quality in terms of enhanced oxygen bonding and reduced defect sites. The 0.5 mol% Li and 1.0 mol% Zr co-doped ZnO TFTs annealed at 320 °C exhibited noticeably lower threshold voltage shifts of 3.54 V under positive bias stress and -2.07 V under negative bias temperature stress than the non-doped ZnO TFTs. The transistors revealed a good device mobility performance of 5.39 cm 2 V -1 s -1 and an on/off current ratio of 10 8 when annealed at 320 °C, compared to a mobility performance of 2.86 cm 2 V -1 s -1 and an on/off current ratio of ∼10 7 when annealed at 270 °C. Our results suggest that Li and Zr co-doping can be a useful technique to produce more reliable and low temperature solution-processed oxide semiconductor TFTs. © The Royal Society of Chemistry 2012.


Kim S.-H.,Brown University | Leung A.,Brown University | Koo C.Y.,INOSTEK Inc. | Kuhn L.,Brown University | And 3 more authors.
Materials Letters | Year: 2012

Sol-gel-derived lead-free piezoelectric (Na 0.5,K 0.5)(Nb 0.95,Ta 0.05)O 3-BiFeO 3 (NKNT-BF) thin films were successfully prepared for microelectromechanical system (MEMS) energy harvesting device applications. Small concentrations of BF (5 mol%) in NKNT films led to dense and uniform microstructures. The maximum dielectric constant and the piezoelectric d 33 value of the NKNT-BF films were around 600 and 57 pm/V, respectively. These results were notably superior to those of pure NKNT films. The first successful lead-free NKNT-BF thin film-based piezoelectric vibration energy harvesting device was fabricated using MEMS process. This device showed the excellent performance with a maximum power of 1.82 μW at low resonance frequency of 130 Hz. © 2011 Elsevier B.V.


Cross J.S.,Tokyo Institute of Technology | Shinozaki K.,Tokyo Institute of Technology | Yoshioka T.,Tokyo Institute of Technology | Tanaka J.,Tokyo Institute of Technology | And 3 more authors.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2010

Co-doping of thin Pb(Zr,Ti)O3 (PZT) films with Bi and Fe to optimize the ferroelectric properties has recently gained attention particularly, for ferroelectric random access memory applications (FeRAM). This study was undertaken to understand how co-doping PZT with one atomic% Bi and Fe impacts the characteristics of capacitor ferroelectric and material properties. XRD patterns of PZT-BiFeO3 (BF) and PZT 150 nm thick showed strong (1 1 1) orientation and changing the sample stage angle Chi to 50° revealed multiple PZT and PZT-BF diffractions peaks. Bi and Fe co-doping of PZT results in a 0.01 decrease in lattice dimensions which indicates that Bi and Fe are substituting into the PZT lattice. Polarization hysteresis loops show similar characteristics but pulse measured polarization values were higher for PZT-BF than PZT which indicates PZT-BF has potential for thin film ferroelectric devices. © 2010 Elsevier B.V.


Kim S.-H.,Brown University | Leung A.,Brown University | Lee E.Y.,INOSTEK Inc. | Kuhn L.,Brown University | And 3 more authors.
Proceedings - 2011 IMAPS/ACerS 7th International Conference and Exhibition on Ceramic Interconnect and Ceramic Microsystems Technologies, CICMT 2011 | Year: 2011

Non-lead based piezoelectric thin films of (K,Na)(Nb,Ta)O 3-BiFeO3 (NKNT-BF) were successfully fabricated by the chemical solution deposition method. Small concentration of BF (5 mol %) added into NKNT films led to a fully dense microstructure and enhanced dielectric and piezoelectric properties compared to pure NKNT films. The measured dielectric constant and piezoelectric da values were around 575 and 50 pC/N, respectively. A thin film NKNT-BF piezoelectric cantilever with a micromachined Si proof mass was fabricated for a low frequency vibration energy harvesting device. The average power and the power density' of NKNT-BF energy harvesting cantilever with the device volume of 0.007 cm were 1.82 μW and 260 μW/cm3 at the resonance frequency of 130 Hz and the acceleration of 0.75 G. Even if these values were somewhat inferior to those of the conventional PZT energy harvesting device, NKNT-BF thin film provided the promising results as an alternative material of PZT for the piezoelectric MEMS applications in the future. © Copyright Honeywell Federal Manufacturing & Technologies LLC, 2011.


Kim S.-H.,Brown University | Koo C.Y.,INOSTEK Inc. | Lee J.,Brown University | Jiang W.,Brown University | Kingon A.I.,Brown University
Materials Letters | Year: 2011

High quality PZT thick films over 10 μm were successfully prepared using a chemical solution infiltration into the porous screen-printed PZT thick films. The hybrid films prepared with solution infiltration process showed very dense and uniform microstructure with large grain size at a low annealing temperature such as 700 °C. The hybrid films showed markedly enhanced electrical properties. The measured dielectric constant, the remanent polarization and the piezoelectric d33 coefficient of the films were 1900, 27 μC/cm2, and 230 pC/N, respectively, which were over two times higher than those of the screen printed films without the solution infiltration process. © 2011 Elsevier B.V. All Rights Reserved.


Maiwa H.,Shonan Institute of Technology | Kim S.-H.,INOSTEK Inc.
Ceramics International | Year: 2013

The electrocaloric effects (EC) of PZT and PMN-PNN-PZT films were evaluated. PZT and PMN-PNN-PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN-PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN-PNN-PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN-PNN-PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated. © 2012 Elsevier Ltd and Techna Group S.r.l.


Jang Y.H.,Pusan National University | Zhang Q.,Pusan National University | Kim C.H.,Pusan National University | Hwang H.J.,Pusan National University | And 2 more authors.
Journal of the Korean Physical Society | Year: 2010

A mechanism for the switching behaviors of ferroelectric thin films has been investigated using piezoresponse force microscopy (PFM), and PFM successfully visualized the magnitude and the phase of the domain. PbZr 1-xTixO3(PZT) thin films with a (111) texture were deposited onto commercial Pt/Ti/SiO2/Si substrates via the sol-gel technique. A combination of in-plane and outof-plane modes for PFM were used to reconstruct the three-dimensional polarization distribution, and the allowed domain configurations for the PZT films for different symmetries and different textures are illustrated schematically. Also, the domain and the domain switching properties were studied for PZT films with different compositions by applying a DC bias voltage to a localized area.

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