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Ansan, South Korea

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.

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.

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.

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 | 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.

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