W. B. Luo

University of Electronic Science and Technology of China, Hua-yang, Sichuan, China

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Publications (28)51.33 Total impact

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    ABSTRACT: Lead hafnate-titanate (PHT) thin films have been prepared via pulsed laser deposition (PLD) on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates by inserting a low temperature (200–400 °C) self-buffered layer. It is found that the self-buffered layers deposited at different temperatures have a great influence on the microstructure and electric properties. XRD spectra, including θ–2θ and ω scans, show that the PHT films with (1 1 1) preferred orientation were successfully deposited on substrates by inserting a low temperature self-buffered layer. Compared with the PHT films directly deposited at a high temperature, the PHT films with an inserted low temperature (300 °C) self-buffered layer have significantly enhanced electrical properties of four orders of magnitude lower leakage current density (3.2 × 10−8 A/cm2 at 150 kV/cm), 1.5 times larger remnant polarization (2Pr = 63 μC/cm2), 0.4 times smaller coercive field (2Ec = 190 kV/cm), and more excellent fatigue endurance (almost no degradation after 2 × 1010 switching cycles). The use of self-buffered layer is an effective approach to fabricate PHT ferroelectric materials with large ferroelectric polarization and long fatigue endurance.
    Journal of Alloys and Compounds 04/2015; 627. DOI:10.1016/j.jallcom.2014.12.122 · 2.73 Impact Factor
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    ABSTRACT: The effects of SiO2 aerogel film thickness on the properties of pyroelectric device were studied by ANSYS thermal simulation and infrared radiation test. At first, the temperature distributions of the pyroelectric devices with different thicknesses of SiO2 aerogel film were simulated by ANSYS. After that, aerogel films with thicknesses from 300 nm to 1000 nm were deposited on Si substrates by spin coating. Thermal conductivity of SiO2 aerogel film was 2.78 × 10−2 W/mK by 3ω method test. Films were utilized in our pyroelectric infrared detectors as thermal insulators. The detectivity (D*) of these detectors were measured by mechanically chopped blackbody radiation. The D* values was enhanced as the SiO2 aerogel film thickness increased from 300 nm to 800 nm, indicating the thermal isolation effects was improved. Detector with thermal insulation layer thickness of 780 nm possessed the greatest D* over the the whole frequency range from 5.3 Hz to 133.3 Hz. The D* was above 7 × 107 cmHz1/2W−1 and reached the highest value of 9.7 × 107 cmHz1/2W−1, which represented a wide bandwidth of over 128 Hz. This result indicated that SiO2 aerogel film of 780 nm in thickness was a promising thermal isolation material for Monolithic pyroelectric infrared detectors.
    Sensors and Actuators A Physical 03/2015; 228. DOI:10.1016/j.sna.2015.03.006 · 1.94 Impact Factor
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    ABSTRACT: BiFeO3 thin films were irradiated by Ar+ ions with different fluences. The rectifying and resistive switching behaviour were retained on the Au/BiFeO3/Pt stack, and the ON/OFF ratio clearly depends on the Ar+ fluence. It was observed that the transport in high resistance state changes from Poole-Frenkel conduction to space-charge-limited conduction after irradiation. While the conduction of the low resistance state is dominated by both the interface and the bulk thin film in the pristine devices, however, it is only dominated by the interface in the irradiated devices. The observed change of conduction mechanism was explained by additionally created oxygen vacancies (OVs) during irradiation, which also improves the stability of resistive switching.
    Applied Surface Science 12/2014; 336. DOI:10.1016/j.apsusc.2014.12.136 · 2.54 Impact Factor
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    ABSTRACT: Resistive switching (RS) has been investigated in unstructured, polycrystalline BiFeO3 thin films with an emphasis on the possibility to downscale the top electrode size. Reproducible RS can be shown for large-scale top and bottom electrodes. However, distinguishable RS is observed when the top electrode is downscaled to the grain size. The microscopic conduction is found to take place within grains. We demonstrate the recovery of homogeneous RS in unstructured, polycrystalline BiFeO3 with downscaled electrodes and reduced conductive unit size by decreasing the BiFeO3 film thickness.
    Physica Status Solidi (A) Applications and Materials 11/2014; 211(11). DOI:10.1002/pssa.201431298 · 1.53 Impact Factor
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    ABSTRACT: The fabrication method and the pyroelectric response of a single element infrared sensor based lead zirconate titanate (PZT) particles and polyvinylidene fluoride P(VDF-TrFE) copolymer composite thick film is reported in this paper. A special thermal insulation structure, including polyimide (PI) thermal insulation layer and thermal insulation tanks, was used in this device. The thermal insulation tanks were fabricated by laser micro-etching technique. Voltage responsivity (RV), noise voltage (Vnoise), noise equivalent power (NEP), and detectivity (D∗) of the PZT/P(VDF-TrFE) based infrared sensor are 1.2×103V/W, 1.25×10-6VHz1/2, 1.1×10-9W and 1.9×108cmHz1/2W-1 at 137.3 Hz modulation frequency, respectively. The thermal time constant of the infrared sensor τT was about 15ms. The results demonstrate that the composite infrared sensor show a high detectivity at high chopper frequency, which is an essential advantage in infrared detectors and some other devices.
    Infrared Physics & Technology 09/2014; 66. DOI:10.1016/j.infrared.2014.05.010 · 1.46 Impact Factor
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    ABSTRACT: In this paper, a flexible pyroelectric sensor using PbZr0.3Ti0.7O3 PZT/P(VDF-TrFE) materials on the polyimide (PI) flexible printed circuit substrate was reported. The fabrication processes, material electric properties and infrared photoelectric response property of the designed sensor were studied. First, the PZT ceramic powder was annealed at temperatures ranging from 300 to 900 degrees C, and then 0-3 PZT/PVDF-TrFE composites films were produced by casting PZT/PVDF-TrFE suspension onto the flexible PI substrates. The highest pyroelectric coefficient obtained using 700 degrees C annealed PZT particulates was 96 mu C m(-2) K-1, which was 20% higher than that of unannealed powders. The PI thermal insulation layer and thermal insulation tanks fabricated by laser microetching have been used to improve the photoelectric response ability of the infrared sensor. The specific detectivity of the sensors was calculated from the voltage responsivity and noise. Detectivity D* of the PZT/P(VDF-TrFE) infrared sensor was 1.17 x 10(8) cm Hz(1/2) W-1 at 138.3 Hz modulation frequency. These results demonstrate that the pyroelectric infrared sensor possesses potential applications in flexible electronics.
    Material Research Innovations 05/2014; 18(S2):S2-229-S2-232. DOI:10.1179/1432891714Z.000000000409 · 0.47 Impact Factor
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    ABSTRACT: In this study, ultraviolet curing ink is used as absorber of uncooled infrared detector in the near and far wavelength infrared spectrum. The ultraviolet curing ink is patterned by lithography to meet the requirement of industrial production. The absorbance of the radiation wavelength of 320 mm is higher than 80%. Fabricated with the absorber, the infrared sensor shows voltage responsivity of 1186 V W-1 and specific detectivity of 2.6 x 10(8) cm Hz(1/2) W-1 at 5.3 Hz respectively. The detectivity of single crystal LiTaO3 substrate with absorber is around 23.6 times higher than that without it at 138.3 Hz.
    Material Research Innovations 05/2014; 18(S2):S2-433-S2-435. DOI:10.1179/1432891714Z.000000000454 · 0.47 Impact Factor
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    ABSTRACT: In this paper, the effect of surfactant polyvinylalcohol (PVA) and polyacrylate acid (PAA) on shape evolution of Pb(Zr0.3Ti0.7)O3 (PZT) nano materials synthesized by hydrothermal method was studied. PZT nanorod array was grown on the conduction substrate surface of (100) Nb–SrTiO3 with optimized PVA and PAA concentrations. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to characterize the PZT nanomaterials. The results demonstrated that the optimization concentration of PVA and PAA were 0.8 and 3.2 g L−1, respectively. The pyroelectric coefficient of the PZT nanorod array was 1.75 × 10−9 C cm−2 K−1 before poling and 2.56 × 10−9 C cm−2 K−1 after poling. This low temperature synthesized PZT nanorod array shows great potential application in pyroelectric nanodevices.
    Journal of Materials Science Materials in Electronics 04/2014; 25(4). DOI:10.1007/s10854-014-1775-8 · 1.97 Impact Factor
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    ABSTRACT: In this paper, we presented a new pyroelectric detector with back to back silicon cups and micro-bridge structure. The PZT thick film shaped in the front cup was directly deposited with designed pattern by electrophoresis deposition (EPD). Pt/Ti Metal film, which was fabricated by standard photolithography and lift-off technology, was sputtered to connect the top electrode and the bonding pad. The cold isostatic press (CIP) treatment could be applied to improve the pyroelectric properties of PZT thick film. The infrared (IR) properties the CIP-optimized detector were measured. The voltage responsivity (RV) was 4.5 × 102 V/W at 5.3 Hz, the specific detectivity (D*) was greater than 6.34 × 108 cm Hz1/2 W-1 (frequency > 110 Hz), and the thermal time constant was 51 ms, respectively.
    Infrared Physics & Technology 11/2013; 61:313-318. DOI:10.1016/j.infrared.2013.09.002 · 1.46 Impact Factor
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    ABSTRACT: The effects of TiOx diffusion barrier layer thickness on the microstructure and pyroelectric characteristics of PZT thick films were studied in this paper. The TiOx layer was prepared by thermal oxidation of Ti thin film in air and the PZT thick films were fabricated by electrophoresis deposition method (EPD). To demonstrate the barrier effect of TiOx layer, the electrode/substrate interface and Si content in PZT thick films were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The TiOx barrier thickness shows significant influence on the bottom electrode and the pyroelectric performance of the PZT thick films. The average pyroelectric coefficient of PZT films deposited on 400 nm TiOx layer was about 8.94 × 10−9 C/(cm2 K), which was improved by 70% than those without diffusion barrier layer. The results showed in this study indicate that TiOx barrier layer has great potential in fabrication of PZT pyroelectric device.
    Infrared Physics & Technology 05/2013; 58:51–55. DOI:10.1016/j.infrared.2013.01.003 · 1.46 Impact Factor
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    ABSTRACT: SrTiO3 (STO) films have been grown on TiO2-buffered GaN(0002) substrates. The deposition process was in situ monitored by reflective high energy electron diffraction (RHEED). The deposition rate and in-plane lattice parameter of TiO2 were calculated from the oscillation curve and RHEED patterns, respectively. It was found that the TiO2 lattice parameter changed as the thickness increased, which indicated a strain relaxation process of TiO2 buffer layers during the deposition. We show that the thickness of TiO2 can significantly influence the STO growth mode, surface morphology, and crystalline quality. As the TiO2 thickness increased, the STO growth mode is changed from 3D island to 2D growth mode and finally to SK mode as revealed by RHEED. The growth mode evolution shows close relation with the surface morphology and crystalline quality of STO. STO films deposited on 2 nm thick TiO2 film show 2D growth mode and have smoothest surface and smallest full width at half maximum of the STO rocking curve. Our investigation hints towards to a general approach to optimize the crystalline quality of STO, which can be optimized by adjusting the strain state of TiO2 buffer layer.
    Journal of Applied Physics 04/2013; 113(15). DOI:10.1063/1.4801804 · 2.19 Impact Factor
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    ABSTRACT: SrTiO3 films were grown on CeO2/YSZ/TiO2 multilayer buffered GaN/Al2O3 (0 0 0 1) substrates with and without the YBa2Cu3 O7−x (YBCO) bridge layer by pulsed laser deposition (PLD). The deposition process of the buffer layers was in situ monitored by reflection high-energy electron diffraction. The crystallographical orientation of the heterostructure was studied by x-ray diffraction (XRD). With the introduction of the YBCO (0 0 1) layer, the STO (0 0 1) film was epitaxially grown on the GaN substrate. There were three sets of inplane domains separated from each other by 30° in both STO and YBCO buffer layers. The epitaxial relationship was STO (0 0 2)[1 1 0]∥YBCO(0 0 1)[1 1 0]∥CeO2(0 0 2)[0 1 0]∥YSZ (0 0 2)[0 1 0]∥GaN(0 0 0 1)[1 1 -2 0] according to XRD results. By comparing the orientation of STO grown on GaN with and without the YBCO top buffer layer, the surface chemical bonding was found to be a very important factor in determining the orientation relationship of STO.
    Journal of Physics D Applied Physics 01/2013; 46(6):065307. DOI:10.1088/0022-3727/46/6/065307 · 2.52 Impact Factor
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    ABSTRACT: Porous lead zirconate titanate (PbZr0.3Ti0.7O3, PZT30/70) thick films and detectors for pyroelectric applications have been fabricated on alumina substrates by screen-printing technology. Low temperature sintering of PZT thick films have been achieved at 850°C by using Li2CO3 and Bi2O3 sintering aids. The microstructure of PZT thick film has been investigated by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric properties were measured using HP 4284 at 1 kHz under 25°C. The permittivity and loss tangent of the thick films were 94 and 0.017, respectively. Curie temperature of PZT thick film was 425°C as revealed by dielectric constant temperature measurement. The pyroelectric coefficient was determined to be 0.9×10-8 Ccm-2K-1 by dynamic current measurement. Infrared detector sensitive element of dual capacitance was fabricated by laser directly write technology. Detectivity of the detectors were measured using mechanically chopped blackbody radiation. Detectivity ranging from 1.23×108 to 1.75×108 (cmHz1/2W-1) was derived at frequency range from 175.5Hz to 1367Hz, and D∗’s -3dB cut-off frequency bandwidth was 1.2 kHz. The results indicate that the infrared detectors based on porous thick films have great potential applications in fast and wide-band frequency response conditions.
    Infrared Physics & Technology 01/2013; 63. DOI:10.1016/j.infrared.2013.11.013 · 1.46 Impact Factor
  • J. Zhu, X.P. Wang, W.B. Luo, Y.R. Li
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    ABSTRACT: Epitaxial thin films of (00l)- and (104)-oriented Bi4Ti3-xHfxO12(BTH) have been fabricated on (100)- and (111)-oriented SrTiO3 substrates with SrRuO3 bottom electrodes by pulsed laser deposition, respectively. X-ray diffraction scans revealed that a unique epitaxial relationship between film and substrate: BTH (001)//SrTiO3 (001); BTH [1], [2], [3], [4], [5], [6], [7], [8], [9] and [10]////SrTiO3 [100] is valid for both orientations, irrespective of their orientation. The strong dependences of ferroelectric properties on the film orientation were observed. The remanent polarization 2Pr is 45.6 μC/cm2 for (104)-oriented BTH film, while 2Pr is 4.5 μC/cm2 for (00l)-oriented BTH film. The anisotropic properties of BTH are similar to that of pure Bi4Ti3O12(BIT): the polarization vector of BTH films is close to the a axis, indicating that Hf substitution does not change the orientation dependence of electric properties in BIT.
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    ABSTRACT: BiFeO3(BFO) films were deposited by pulsed laser deposition on GaN(0002)/c-sapphire. X-ray diffraction data show that BFO(111) epitaxial films was deposited on SrTiO3/TiO2 double-layer buffered GaN, compared to the polycrystalline film grown directly on GaN. The epitaxial relationships of BFO film with SrTiO3/TiO2 buffer layers were BFO [11-2](111)//GaN [1-100](0002) as revealed by XRD phi scans. Furthermore, BFO films on SrTiO3/TiO2 buffer exhibited enhanced electric properties compared to these deposited directly on GaN. The remnant polarization was improved about 30% while the leakage current was reduced by nearly three orders of magnitude. The epitaxial growth promoted by the SrTiO3/TiO2 buffer layer is a pivotal parameter in the improved electric properties of BFO films on GaN (0002).
    Journal of Applied Physics 05/2011; 109(10):104108-104108-5. DOI:10.1063/1.3585836 · 2.19 Impact Factor
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    ABSTRACT: Epitaxial growth of (111)-oriented BaTiO3 thin films on GaN/Al2O3 (0001) substrates has been realized by intervening epitaxial (111) SrRuO3/(100)TiO2 buffer layers. Rutile TiO2 was deposited by Laser molecular beam epitaxial firstly and the deposition process of TiO2 layer was in-situ monitored by reflective high energy electron diffractions. After that SrRuO3 conductive films and BaTiO3 ferroelectric films were fabricated via pulsed laser deposition. The perovskite BaTiO3 films were epitaxially grown on wurtzite GaN as revealed by X-ray diffraction. Electrical measurements demonstrate that the BaTiO3 films possess a saturation ferroelectric hysteresis loop, butterfly-shape C-V curve and low leakage current density. These results show that BaTiO3 films with favorable electrical performance could be epitaxially grown on GaN using SrRuO3/TiO2 bufferlayer.
    Ferroelectrics 10/2010; 406(1):56-61. DOI:10.1080/00150193.2010.484334 · 0.38 Impact Factor
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    ABSTRACT: LiNbO3 film (LNO)/AlGaN/GaN heterostructure was fabricated and its memory characteristics were studied. The heterostructure exhibited a wide range clockwise hysteresis (0.3–12.1 V) likely due to the electrons trapping and distrapping from the Li vacancies in the LNO film. After 10 years retention, 10% of the window could remain. In addition, a slight decrease for the memory window happened after 105 cycles. These results indicated that LNO film combined with AlGaN/GaN would hold promise for next-generation nonvolatile memory devices. Possible operating mechanism for the memory effect in the heterostructure was explained qualitatively by the energy band diagram.
    Applied Physics Letters 01/2010; 96(3):032103-032103-3. DOI:10.1063/1.3294308 · 3.52 Impact Factor
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    ABSTRACT: Epitaxial SrTiO <sub>3</sub> films were fabricated by laser molecular beam epitaxy on bare and TiO <sub>2</sub> buffered GaN(0002), respectively. The whole deposition processes were in situ monitored by reflection high energy electron diffraction (RHEED). X-ray diffraction (XRD) was carried out to study the growth orientation and crystalline quality of STO films. The interfacial characters and epitaxial relationships were also investigated by high revolution transition electron microscope and selected area electron diffraction (SAED). According to the RHEED observation, the lowest epitaxy temperature of STO on TiO <sub>2</sub> buffered GaN was decreased compared with the direct deposited one. The epitaxial relationship was (111)[1 1 0] STO //(0002)[11 2 0] GaN in both cases as confirmed by RHEED, XRD, and SAED. The full width at half maximum of ω -scan and Φ -scan of STO on TiO <sub>2</sub> buffered GaN was reduced compared with that deposited on bare GaN, indicating that epitaxial quality of STO film is improved by inserting TiO <sub>2</sub> layer. In summary, the lattice mismatch was reduced by inserting rutile TiO <sub>2</sub> . As a result, the crystalline temperature was reduced and enhanced epitaxial quality of STO thin film was obtained.
    Journal of Applied Physics 12/2009; 106(10-106):104120 - 104120-4. DOI:10.1063/1.3257259 · 2.19 Impact Factor
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    ABSTRACT: Hf-doped Bi{sub 4}Ti{sub 3}O{sub 12} (BTH) ferroelectric films with excellent electrical properties were epitaxially integrated with GaN semiconductor using (111) SrTiO{sub 3} (STO)/rutile (200) TiO{sub 2} as buffer layer. The STO/TiO{sub 2} buffer layer was deposited by laser molecular beam epitaxy. The structural characteristics of the buffer layer were in situ and ex situ characterized by reflective high energy electron diffraction, x-ray diffraction (XRD), and high resolution transmission microscopy. The overlaying SrRuO{sub 3} (SRO) and BTH films were then deposited by pulsed laser deposition. XRD spectra, including theta-2theta and PHI scans, show that the (208) BTH films were epitaxially grown on GaN, and the BTH films inherit the in-plane twin-domain of STO buffer layer. Electrical measurements demonstrate that the non-c axis BTH films possess a large remnant polarization (2P{sub r}=45 muC/cm{sup 2}), excellent fatigue endurance (10.2% degradation after 1.1x10{sup 10} switching cycles), and a low leakage current density (1.94x10{sup -7} A/cm{sup 2} at an electric field of 200 kV/cm). These results reveal that the (208) BTH films with favorable electrical performance could be epitaxially grown on GaN template using STO/TiO{sub 2} buffer layer.
    Journal of Applied Physics 05/2009; 105(10). DOI:10.1063/1.3126717 · 2.19 Impact Factor
  • J. Zhu, W. B. Luo, Y. R. Li
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    ABSTRACT: BiFeO3 (BFO) films have been epitaxially grown on SrTiO3(001) and SrTiO3(111) substrates with a LaNiO3 conductive layer as a template using pulsed laser deposition. X-ray diffraction θ–2θ and Φ scanning revealed that the epitaxial relationship is BFO[100]//LNO[100]//STO[100]; BFO(001)//LNO(001)//STO(001) and BFO[112¯]//LNO[112¯]//STO[112¯]; BFO(111)//LNO(111)//STO(111) on SrTiO3(001) and SrTiO3(111) substrates, respectively. The epitaxial relationship was also confirmed by ex situ reflective high-energy electron reflection (RHEED). From P–E measurements, both samples showed typical ferroelectric hysteresis loops, indicating good electrical properties. Furthermore, it was found that the remanent polarization (2Pr) under the same applied electrical field of the epitaxial BFO(111) thin film on the LNO-coated (111) STO substrate is much larger than that of the BFO(100) film on the LNO-coated STO(100) substrate. The larger polarization of BFO(111) films may be caused by that the easy polarization axis lays close to [111] direction, indicating the anisotropic ferroelectric property for BFO films. Thus, with the epitaxial LNO electrode template layers, the epitaxial BFO films exhibit high-quality structure and good electrical properties.
    Applied Surface Science 12/2008; 255(5):3466-3469. DOI:10.1016/j.apsusc.2008.09.008 · 2.54 Impact Factor