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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 375-382 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electrodes can impact the device performance of ferroelectric capacitors in several ways. The present controlled studies on Pb (Nb, Zr, Ti)O3 with Pt, (La, Sr)CoO3 and SrRuO3 is a clear demonstration of the role of electrodes in impacting the leakage current mechanism of the ferroelectric capacitors and their reliability properties. The oxide electrode capacitors show predominantly nonblocking contact and good fatigue and imprint properties. Pt electrode capacitors show blocking contacts, long term leakage current relaxation, and poor fatigue and imprint properties. The nature of the temperature and voltage dependence of leakage current relaxation in Pt capacitors indicates trapping of charge carriers to be the cause for the observed relaxation. A good correlation between leakage current relaxation and the rate of polarization loss during fatigue and the similarity in their voltage and temperature dependence suggests trapping (of charged carriers/domains, respectively) as common to both phenomena. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3194-3196 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Interfaces and hence electrodes determine the performance of (Ba,Sr)TiO3 (BST) capacitors for ultralarge scale integration dynamic random access memories. Electrode materials forming a rectifying contact on BST drastically reduce the dielectric constant and hence the capacitance and charge storage density of the capacitor, when the dielectric thickness is reduced. This can limit the role of Pt as an electrode material for gigabit dynamic random access memories (DRAM). The conducting oxide, La0.5Sr0.5CoO3 (LSCO) with its perovskite structure, has structural and chemical compatibility with BST. Our results in LSCO/BST/LSCO capacitor show that the mechanism of conduction is not interface limited but predominantly bulk limited. A 75 nm BST film with LSCO electrodes shows a leakage current density of 1×10−7 A/cm2 at 1 V, 85 °C. The dielectric constant at 1 V, 105 Hz is 350, making LSCO a potential contact electrode for DRAM memories. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3023-3025 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The ferroelectric properties of Pb(Zr,Ti)O3 films are known to degrade when subjected to forming gas anneals. In an earlier publication we established that although there may be loss of oxygen and lead during forming gas anneal, the primary mechanism for loss of ferroelectricity is the incorporation of hydrogen and subsequent formation of [OH]−1 bonds between the ionized hydrogen and oxygen ions along the polarization axis in the octahedra. In this study, we show that (La,Sr)CoO3 oxide electrodes can act as a diffusion barrier to hydrogen during forming gas anneals. Forming gas anneal at lower temperatures such as 200 and 300 °C does not lead to a measurable loss of polarization. There is some loss of polarization during forming gas anneals at 450 °C for 〈fraction SHAPE="CASE"〉12 h, however the capacitors still exhibit ferroelectric properties. The capacitors show no fatigue up to 1011 cycles, no imprint, good logic state retention characteristics, and similar slopes for the pulse width dependent polarization values before and after forming gas anneal in the measured range. More importantly, we have demonstrated that even a bare La0.5Sr0.5CoO3 top electrode can prevent the complete loss of ferroelectricity during forming gas treatment. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3366-3368 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the activation field characteristics of (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 capacitors with areas varying from 13 to 9600 μm2. Switching properties such as maximum current and switching time depend on the capacitor area and measuring circuit elements, but the activation field is independent of capacitor area and measuring circuit parameters. Area independence of activation fields is also confirmed in (Pb,La)(Zr,Ti)O3 thin film capacitors. Two different approaches have been used to determine the activation field, yielding similar results. It is concluded that activation field is an intrinsic property and is a good quantitative measure of the ferroelectric switching properties. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of heteroepitaxy-induced constraint on the structure and piezoelectric properties of the relaxor ferroelectric lead magnesium niobate–lead titanate (PMN–PT) were investigated. Relaxor PMN–PT epitaxial thin films with oxide electrodes were grown by pulsed-laser deposition on (100) LaAlO3 substrates. We observe a systematic decrease in the phase transition temperature (temperature at which a maximum in dielectric response occurs), from around 250 to around 60 °C as the relaxor thickness is increased from 100 to 400 nm. This is accompanied by an increase in the relative dielectric constant (εr), measured at room temperature and 10 kHz, from 300 to 2000. The piezoelectric coefficient d33 measured using a scanned probe microscope, increase by almost an order of magnitude with increasing film thickness. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1787-1789 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report on ferroelectric properties of polycrystalline sol-gel derived Pb(Nb, Zr, Ti)O3 (PNZT) thin films with SrRuO3 (SRO) electrodes. The processing temperature of the bottom electrode was varied between 550 and 850 °C. The polarization of the ferroelectric capacitors was dependent on the processing temperature of the bottom electrode. The capacitors exhibit low switching fields (40 kV/cm), high resistivity (1011 Ω cm at 3 V) and high remanent polarization values (19 μC/cm2 at 3 V), desirable properties for high-density ferroelectric memories. The activation field for these capacitors was measured to be ∼350 kV/cm and the polarization values exhibited a shallow dependence on the pulse width from 1 s to 1 μs. Fatigue, logic state retention, and dynamic imprint tests indicate robust capacitors from a memory viewpoint. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 438-440 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of various substrates on the electrical and electromechanical properties of 100-nm-thick epitaxial 0.9[Pb(Mg1/3Nb2/3)O3]–0.1[PbTiO3](0.9PMN–0.1PT) thin films is investigated. (001) 0.9PMN–0.1PT films are grown on (001)LaAlO3(LAO), (La, Sr)(Al, Ta)O3(LSAT), SrTiO3(STO), and MgO substrates with 40-nm-thick top and bottom La0.5Sr0.5CoO3 electrodes by pulsed laser deposition. X-ray diffraction results indicate that the films on LAO, LSAT, and STO are stressed biaxially in compression in the film-substrate interface whereas the films on MgO are stressed in tension. A decrease in the temperature of dielectric maximum (Tm) together with an increase in the dielectric constant and the longitudinal piezomodulus is observed with decreasing in-plane epitaxial stresses for LAO, LSAT, and STO substrates. The films on MgO substrates have the highest dielectric constant and piezomodulus with Tm below room temperature. The variation in Tm may be attributed to the shift in the transformation temperature from the paraelectric state to the relaxor state due to internal stresses in the film-substrate interface. Electrical and electromechanical properties should depend strongly on internal stresses in the vicinity of the phase transformation, which is reflected in our experimental observations. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 716-718 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this letter, we report on the influence of lead content on thin-film ferroelectric properties of lead niobium zirconate titanate. These films were prepared by the sol-gel technique and deposited on (La,Sr)CoO3 electrodes. It was determined that 7% excess lead in the sol was required to obtain nominally stoichiometric films. Lead deficiency in the film results in lead vacancies and excess lead is accommodated by forming octahedral site vacancies. Further amounts of lead in the sol leads to second phase PbO, which then coexists with the perovskite phase. The charged vacancies are compensated by mobile holes, which can interact with domains during switching. Under applied field and short pulse widths, the films with larger number of holes exhibited poor switching. Significant polarization relaxation was measured for films with excess lead, which is attributed to interaction of ionic defects with domains. Our results indicate that lead excess leads to poor reliability properties,whereas lead deficiency suppresses the polarization of the capacitors. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    Standort Signatur Einschränkungen Verfügbarkeit
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