Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors

Photoluminescence and photocurrent characteristics of Eu^{2 +} activated MAl₂O₄ (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured simultaneously on the same samples within a specially designed measuring box. Composition effects, such as a presence of Dy^{3 +} as a co-activator and Al-rich composition on the PL and PC characteristics have been investigated. Also, sensing characteristics on UV and visual light have been tested. The simultaneous measurement of PL and PC on the same sample clearly indicated that the presence of co-activator and vacant site, namely Al-rich composition, acted as a hole trap; the introduction of co-activator and vacant site decreased the PC and increased the PL during and after UV and visible light irradiation, whose PC was much lower than that of MAl₂O₄ with only Eu^{2 +} as an activator. The electrical intensity affected on the PL characteristics after UV and visual light irradiation(afterglow); with increasing in the electrical intensity, the afterglow lasted more longer and intensively. The PC of MAl₂O₄ showed a good proportional relationship to UV and visible light intensity. Especially, SrAl₂O₄ showed an excellent linearity within 1–5 mW/cm², but showed somewhat delayed response and hysterisis as seen in CdS photoelectric cell.     

Film Thickness Dependence of Electrical Properties for Pb(Zr,Ti)O3 Thin Films Prepared on (111)Ir/TiO2/SiO2/Si and (111)Pt/TiO2/SiO2/Si Substrates by Pulsed-Metalorganic Chemical Vapor Deposition

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films with various film thicknesses were deposited on (111)Ir/TiO₂/SiO₂/Si and (111)Pt/TiO₂/SiO₂/Si substrates at 540°C by source-gas-pulsed metalorganic chemical vapor deposition (pulsed-MOCVD). PZT films deposited on (111)Ir/TiO₂/SiO₂/Si substrates showed good surface flatness and lower leakage current density. The rate of the decrease of remanent polarization (P _r ) and the rate of increase of coercive field (E _c ) for the films with decreasing the film thickness smaller on (111)Ir/TiO₂/SiO₂/Si substrates than those of (111)Pt/TiO₂/SiO₂/Si substrates. In addition, P _r and E _c values saturated at low voltage when the film thickness was the same. As a result, good ferroelectricity with P _r and E _c values of 40 μC/cm² and 140 kV/cm were obtained for 35 nm-thick films prepared on (111)Ir/TiO₂/SiO₂/Si substrates by pulsed-MOCVD.     

Effect of CeO2 and Nd2O3 on the Microstructure and Microwave Dielectric Properties of (Zr0.8,Sn0.2)TiO4 Ceramics

(Zr_0.8,Sn_0.2)TiO₄ (ZST) ceramics were prepared by solid-state reaction method with 1 wt% ZnO and 0.5–1.5 wt% CeO₂ or Nd₂O₃ as sintering aids. The effect of processing parameters and additive concentration on the structure, microstructure and microwave dielectric properties of ZST ceramics were investigated. The dielectric constant (?_r) and temperature coefficient of the resonance frequency (τ_f) were not significantly affected by the addition of these additives. The unloaded quality factors (Q_u) were effectively promoted by CeO₂ and Nd₂O₃ additions. ?_r values of 40 and 38.3, Qxf_o values of 57,500 and 59,300 were obtained for the samples sintered with 1.5 and 0.5 wt% of CeO₂ and Nd₂O₃ respectively. The improvement in Qxf_o value is primarily attributed to the increase in uniform grain size and density.     

Water-Immersible Micromachined Pb(Zr, Ti)O3 Thin Film Actuators

We demonstrate a water-immersible thin film lead zirconate titanate, Pb(Zr, Ti)O₃, [PZT] actuator, without special passivation layer, towards in-vivo or in-vitro scanning probe microscope (SPM) measurements of living cells in water or biological fluids. In order to be water-immersible, the electrodes need to be electrically insulated and the piezoelectric layer needs to be protected against direct water contact. This paper describes our design solution with a simple fabrication process for a water-immersible piezoelectric device, which separates the bottom electrode from the top electrode by having a narrow ditch covered with PZT film. The PZT film is then encapsulated with the top metal electrode without insulation layer. In this structure, the PZT is sandwiched between the top and bottom metal electrodes to prevent water permeation. The device is fabricated using lift-off processing for the bottom and top electrodes, sol-gel spinning for the PZT thin film and wet etching for the PZT patterning. The piezoelectric constant, d₃₁, is about –100 pC/N. The dielectric polarization and fatigue properties of the devices were measured in air and water. The spontaneous polarization, remnant polarization, coercive field and dielectric constant are 54 C/cm², 15 C/cm², 60 kV/cm and 1200, respectively. The polarization property of the device was unchanged in either air or water up to 1 × 10⁹ continuous cycles.     

Electrical and Magnetic Properties of Some Rare Earth Orthoferrites (RFeO3 where R = Y,Ho, Er) Systems

The electrical and magnetic characteristics of some rare earth orthoferrites (RFeO₃, where R = Y, Ho & Er) have been discussed. These two characteristics suggest that such system can be categorized under multiferroic with different Curie and Neel temperature. The electrical characteristics shows relaxation phenomenon with Curie temperature varies with change in frequency. The Curie temperature is in the range of 340–480°C, whereas Neel temperature is about 370°C.     

Optimum Reflection-Type Phase Shifter Using (Ba,Sr)TiO3 Thin Film

In this paper, in order to obtain a large differential phase shift with a little change in applied voltage, a ferroelectric reflective load circuit has been designed on top of barium strontium titanate (Ba,Sr)TiO₃ [BST] thin film. The design of the ferroelectric reflection-type phase shifter is based on a reflection theory of terminating circuit, which has a reflection-type analogue phase shifter with two ports terminated in symmetric phase-controllable reflective networks. To achieve large amounts of phase shift in low bias-voltage range, the effects of change of capacitance and transmission line connected with two coupled ports of a 3-dB 90° branch-line hybrid coupler have been investigated. A large phase shift with a small capacitance change in the parallel terminating circuit has been demonstrated in the paper.     

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO₃ (BFO) and the gadolinium and transition metal ions co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ (TM?=?Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2P _r ), low coercive field (2E _c ), and reduced leakage current density, which are 136 μC/cm², 1360 kV/cm at 1470 kV/cm, and 5.14?×?10^-6 A/cm² at 100 kV/cm, respectively.     

Chemical Processing and Properties of (Sr,Ca) 2 (Nb,Ta) 2 O 7 Thin Films

Ca-doped Sr 2 (Nb,Ta) 2 O 7 thin films have been synthesized by the chemical solution deposition. Homogeneous and stable (Sr,Ca) 2 (Nb,Ta) 2 O 7 precursor solutions were prepared by optimizing the reaction of starting metal alkoxides in ethanol with a key additive of 2-ethoxyethanol. The improvement of ferroelectric properties of the Sr 2 (Nb,Ta) 2 O 7 based films were achieved through the Ca substitution into Sr 2 (Nb 0.3 Ta 0.7 ) 2 O 7 as well as the optimization of heating conditions. The crystallization temperature of the layered perovskite (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films on Pt/Ir/Ti/SiO 2 /Si substrates was found to be above 750C. (Sr 0.9 Ca 0.1 ) 2 (Nb 0.3 Ta 0.7 ) 2 O 7 thin films crystallized at 750C exhibited P r of 0.51 w C/cm 2 and E c of 69 kV/cm.     

Measurement of Microwave Dielectric Properties of (Sr,Ba)Nb2O6 Thin Films

(001) oriented (Sr,Ba)Nb₂O₆ (SBN) thin films were deposited on MgO (001) single crystal substrates by the pulsed laser deposition method. Structural properties of SBN films were investigated using X-ray diffractometer. The microwave dielectric properties of SBN films were examined by calculating the scattering parameter obtained using a HP 8510C vector network analyzer with the frequency range 0.5–20 GHz at room temperature under the dc bias field of 0–80 kV/cm for interdigital capacitors (IDT) and coplanar waveguide (CPW) device based on SBN/MgO layer structure. Thick metal electrode patterns were fabricated by dc sputtering deposition, photolithography and etching process. The IDT device based on (001) oriented SBN films exhibited about 40% capacitance tunability with an electric field change of 80 kV/cm at room temperature, and the dielectric quality factor was about 20 at 12 GHz with no dc bias.     

Ferroelectric-Gate Field Effect Transistors Using (Y,Yb)MnO3/Y2O3/Si(111) Structures for 1T-Type FeRAMs

Fabrication and characterization of metal-ferroelectric-insulator-semiconductor field-effect-transistors (MFIS FETs) using (Y,Yb)MnO₃/Y₂O₃/Si structures were introduced for the first time. P-channel MFIS FETs were fabricated on n-type Si(111) substrates, in which an Y_0.5Yb_0.5MnO₃(200 nm)/Y₂O₃(25 nm) structure was used as gate insulator. The Y_0.5Yb_0.5MnO₃ and Y₂O₃ films were prepared by chemical solution deposition. A fabricated MFIS FETs showed the hysteresis loop due to spontaneous polarization in the I_D-V_GS characteristic, in which the memory window was about 0.9V when the applied gate voltage was swept between 8 V and ?8 V. Especially, the alternative drain current was retained after applying a single voltage pulse with a magnitude of +9 V or ?9 V.     

Polarization Switching in (100)/(001) Oriented Epitaxial Pb(Zr, Ti)O3 Thin Films

Thin films made of (100)/(001)-oriented Pb(Zr, Ti)O₃ (PZT) were deposited by liquid-delivery metal-organic chemical vapor deposition on Ir/MgAl₂O₄/SiO₂/Si(100) substrates. For comparison, PZT thin films were also deposited on Ir/MgO(100) substrates. The X-ray scan spectra for the (202) reflections revealed that the PZT films have four-fold symmetry. It indicates that the PZT films were epitaxially grown as a cube-on-cube structure on both substrates. The switchable polarization (Q_sw) of the PZT capacitors on the silicon substrate was only 23 C/cm² at 1.8 V; however, Q_sw of PZT capacitors on MgO was 99 C/cm². In the case of PZT films deposited on silicon, the volume fraction of (001)-oriented domains (which contribute to polarization switching) was 15.1% (calculated from an XRD pattern). This result is due to the lower Q_sw of PZT capacitors on silicon. By piezoresponse-force microscopy, switchable and unswitchable domains could be identified by imaging color contrast, namely, (001) and (100) domains, respectively. Consequently, domain distribution of the PZT film on a silicon substrate indicates that the (001) domain exists in the (100) domain matrix.     

Slow Dielectric Relaxation in Pb(Zr,Ti)O3 and (Ba,Sr)TiO3 Ferroelectric Thin Films

An impedance analysis of Ni/Pb(Zr,Ti)O₃/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO₃ thin films between SrRuO₃ electrodes.     

(La1-xTbx)2/3Sr1/3MnO3薄膜的巨磁电阻效应

利用脉冲激光沉积法制备了（La1-xTbx)2/3Sr1/3MnO3系列薄膜样品。在77－300K的温度范围内,对样品的微观结构、磁化强度、电阻率和巨磁电阻效应等物理性质进行了系统研究。随着Tb含量x的增大,铁磁－顺磁转变温度随之下降,在x=0. 33样品中,最大磁化场μ0H=1.2T时,观察到34％的巨磁电阻。本文对其机理进行了研究和讨论。     

Sm的氧化对Sm2(Co,Fe,Cu,Zr)17磁体微观结构及磁性能的影响

用粉末冶金法制备了Sm2(Co,Fe,Cu,Zr)17磁体,研究了工艺过程Sm的氧化对材料性能影响。微观分析表明,Sm的氧化主要以Sm2O3形成析出孔洞,破坏了材料的组织结构,从而影响材料的性能。     

Characterization in a Wide Frequency Range (40 MHz–67 GHz) of a KTa0.65Nb0.35O3 Thin Film for Tunable Applications

A (100) oriented KTa_0.65Nb_0.35O₃ 400 nm-thin film has been deposited by Pulsed Laser Deposition on MgO substrate. Microwave measurements, performed on InterDigitated Capacitors, show a paraelectric phase at room temperature with a tunability for the devices of 64% under an electric field of 400 kV/cm. Then, using a specific de-embedding method, the complex permittivity of the KTN thin film has been extracted from 40 MHz up to 67 GHz on coplanar waveguides. As promising applications are pointed out at 60 GHz, such as indoor communications, material characterizations are expected in this spectrum.     

Pb(Mg1/3Nb2/3)0.97Ti0.03O3 Ferroelectric Thin Films, Deposited by Laser Ablation on TiN Bottom Electrodes

Pb(Mg_1/3Nb_2/3)_0.97Ti_0.03O₃ (PMNT) polycrystalline thin films were deposited on Titanium Nitride electrode at different temperatures by laser ablation, using a wavelength of 248 nm. The morphology of the films was analyzed by scanning electron microscopy (SEM). The nature of the ferroelectric layer-electrode interface is studied by transmission electron microscopy (TEM) as well as the effect of its characteristics in the performance of the multilayer system. The influence of the annealing temperature on the dielectric properties was studied by hysteresis and fatigue measurements.     

An Effective Interlayer Dielectric and Passivation Scheme Using Reactively Sputtered AL 2 O 3 for (Ba,Sr)TiO 3 Capacitors

Interlayer dielectric and passivation layers for BST capacitors are often very hydrogen rich as a result of the by-products generated during the fabrication process. This hydrogen is well known to significantly degrade the leakage characteristics of the underlying BST capacitors. [1] While it is possible to focus on modifying interlayer dielectric (ILD) or passivation processes to minimize hydrogen exposure, it is preferable to maintain standard process modules available in silicon fabrication lines for case of manufacturing. However, post-deposition annealing is frequently required to reduce the effects of hydrogen, which may migrate into the capacitor during these deposition processes. It is known that Al 2 O 3 films provide an effective barrier to hydrogen migration, even at high temperatures. This paper discusses the integration of a reactively sputtered Al 2 O 3 barrier layer into the interlayer dielectric and passivation process flows of BST thin film capacitors to reduce device degradation during backend processing. Reactively sputtered Al 2 O 3 films were integrated into the production ILD process flow for BST thin film capacitors. Results indicate significant reduction in the post-deposition annealing time is possible while maintaining stable I-V characteristics on the finished devices. The barrier layer can also be etched by standard RIE tools used to etch other common oxides in silicon processing. Aggressive backend passivation schemes were also evaluated to determine the process window available for robust backend integration.     

正极材料Li2MSiO4(M=Fe、Mn)的研究进展

对近年来有关正极材料Li2MSiO4(M=Fe、Mn)的结构特征、电化学性能中存在的问题(如电导率低、容量衰减等)及性能改善的方法(如掺杂、包覆等)进行了综述.总结了对结构认识存在分歧的原因及合成方法对材料性能的影响.     

Preparation of Pb(Ti,Zr)O3/RuO2 multilayers in situ by pulsed laser ablation deposition

Abstract

RuO₂/PbZr_0.52Ti_0.48O₃ multilayers have been prepared by pulsed laser deposition and characterised by Grazing Incident Angle Bragg Diffraction and scanning electron microscopy. The results are correlated with the different deposition conditions and post-growth thermal annealing. The structure of the paraelectric pyrochlore phase (Pb₂(Zr,Ti)₂O₆) and its stability relative to the ferroelectric perovskite is discussed.