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ABSTRACT: The realization of logic operations within passive crossbar memory arrays is a promising approach to expand the fields of application of such architectures. Material implication was recently suggested as the basic function of memristive crossbar junctions, and single bipolar resistive switches (BRS) as well as complementary resistive switches (CRS) were shown to be capable of realizing this logical functionality. Based on a systematic analysis of the Boolean functions, we demonstrate here that 14 of 16 Boolean functions can be realized with a single BRS or CRS cell in at most three sequential cycles. Since the read-out step is independent of the logic operation steps, the result of the logic operation is directly stored to memory, making logic-in-memory applications feasible.
Nanotechnology 07/2012; 23(30):305205. · 3.98 Impact Factor
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ABSTRACT: Complementary resistive switches (CRS) were recently suggested to solve the sneak path problem of larger passive memory arrays. CRS cells consist of an antiserial setup of two bipolar resistive switching cells. The conventional destructive readout for CRS cells is based on a current measurement which makes a considerable call on the switching endurance. Here, we report a new approach for a nondestructive readout (NDRO) based on a capacity measurement. We suggest a concept of an alternative setup of a CRS cell in which both resistive switching cells have similar switching properties but are distinguishable by different capacities. The new approach has the potential of an energy saving and fast readout procedure without decreasing cycling performance and is not limited by the switching kinetics for integrated passive memory arrays.
Nanotechnology 09/2011; 22(39):395203. · 3.98 Impact Factor
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Integrated Ferroelectrics 09/2010; 100(2008):254-262. · 0.30 Impact Factor
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ABSTRACT: This paper focuses on the deposition and electromechanical characterization of lanthanum-doped lead hafnate titanate (PLHT)
thin films as key material in piezoelectric microelectromechanical systems (pMEMS). PLHT (x/30/70) and PLHT(x/45/55) films with a thickness between 150nm and 250nm were deposited by chemical solution deposition (CSD). Thereby x varies between 0 and 10% La content. The electrical characterization shows that undoped (x=0) PLHT exhibit ferroelectric behavior similar to PZT of the same composition. La doping results in reduced ferroelectric
properties and also affects the electromechanical properties. Measurements using a double beam laser interferometer yield
a piezoelectric coefficient d
33 of 60pm/V, which stays constant with an increasing electric field. This leads to a linear displacement compared to undoped
PLHT or conventional PZT films used for MEMS applications.
Applied Physics A 01/2009; 94(4):739-745. · 1.63 Impact Factor
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ABSTRACT: A modified thermodynamic potential was derived to describe the phase states and dielectric properties of (110) oriented epitaxial films grown on orthorhombic substrates.
Applied Physics Letters 01/2007; 90(3):036101-036101-2. · 3.84 Impact Factor
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ABSTRACT: The influences of the Zr content on the structural, electrical, and electromechanical properties of Pb[Zr(x),Ti(1−x)]O3 [PZT(x/1−x)] thin films are investigated in detail. Additionally to measuring all major characteristics of the samples, the electromechanical large-signal behavior is modeled. Raising the Zr content increases the unit cell size and forces the preferred phase to become rhombohedral above the morphotropic phase boundary (MPB). The increased unit cell size changes the switching behavior and increases the intrinsic behavior of the unit cells. The intrinsic behavior is reduced by the phase change, which also introduces non-180° domain wall motion, improving the large-signal strain. Additionally, the domain configuration in saturation is more stable further away from the MPB. Finally, the most suitable materials will be selected for different applications.
Journal of Applied Physics. 12/2006; 100(12):124105-124105-8.
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ABSTRACT: PbZr1−xTixO3 (PZT) is one preferred ferroelectric material being used in nonvolatile ferroelectric random access memory devices. The use of oxide electrodes like IrO2 or SrRuO3 (SRO) is necessary to suppress the serious loss of polarization due to bipolar voltage cycling. Although, there are a number of models under discussion, the origin of the fatigue phenomenon is still not completely understood. In this paper, the fatigue effect of ferroelectric Pb(Zr0.40,Ti0.60)O3 thin films has been studied in detail. To achieve a deeper understanding of the effect, several PZT samples with different electrode materials were investigated. After determining the dependence of the single fatigue parameters, a simulation approach was made to analyze the fatigue effect qualitatively. A sample with SRO electrodes was measured up to 1013 cycles and no fatigue of the switchable polarization was observed.
Journal of Applied Physics 06/2006; 99(11):114104-114104-5. · 2.17 Impact Factor
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ABSTRACT: The effects of reversible and irreversible switching processes on the electromechanical large-signal strain S of tetragonal Pb(Zrx,Ti1−x)O3 thin films are investigated and discussed. Starting from electric small- and large-signal measurements, the percentage of switched unit cells cesw is calculated. The result is then used in combination with the measured electromechanical field-induced small-signal response to calculate the field-induced large-signal strain S. Enhanced models for this calculation are developed improving a known model. Differences between the calculated and measured large-signal strains are discussed in respect to parameter influences and irreversible contributions. In addition, detailed insight on the switching processes in respect to the electromechanical properties is given.
Journal of Applied Physics 12/2005; 98(12):124101-124101-5. · 2.17 Impact Factor
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ABSTRACT: Thin films of zirconium-substituted barium titanate were deposited by chemical solution deposition on platinum-coated silicon substrates at a temperature of 700C. The films showed a polycrystalline perovskite structure. The grain size was found to decrease with increase of Zr substitution. The effect of Zr substitution on the dielectric constant and the leakage was studied. It was found that with increasing Zr content the phase transition becomes diffuse and relaxor-like. The dielectric constant was also found to decrease with increasing amounts of Zr after an initial increase. The hysteresis loops became thinner and the remanent polarisation was found to decrease. The leakage behaviour was explained by Schottky theory. The barrier heights of the different films were calculated and found to vary between 1.12eV and 1.19eV.
Applied Physics A 05/2005; 81(1):25-29. · 1.63 Impact Factor
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ABSTRACT: The influence of grain boundaries on the dielectric properties of ferroelectric ceramics and polycrystalline thin films is described theoretically by the method of effective medium. Grain boundaries are modeled by low-permittivity (dead) layers, which do not exhibit ferroelectric instability. The effective permittivity of a polycrystalline material is calculated in the paraelectric regime above the transition temperature. The calculations are based on the solution of electrostatic problem for a spherical dielectric inclusion separated from the surrounding dissimilar matrix by a low-permittivity interface layer. For isotropic bulk ceramics, an analytic expression is derived for the effective permittivity as a function of the grain size, dead-layer thickness, and its permittivity. Temperature dependence of the aggregate dielectric response is calculated for BaTiO3 (BT) ceramics of different grain sizes and found to be in good agreement with measurements. It is shown that grain boundaries not only renormalize the Curie-Weiss temperature and constant, but may also cause deviations from the Curie-Weiss law. For BT polycrystalline thin films grown on dissimilar substrates, numerical calculations of the effective dielectric constants are performed, taking into account both the grain-boundary and substrate effects on the film anisotropic dielectric response. Theoretical predictions are compared with the grain size dependence of the permittivity of BT films grown on Pt-coated Si.
Journal of Electroceramics 01/2002; 9(1):5-16. · 1.19 Impact Factor
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ABSTRACT: For development and optimization of high density ferroelectric random access memory (FeRAM) devices, it is highly important to understand the polarization switching process. As demands on measurement hardware for these nonlinear devices rise with falling cycle time, the development of faster measurement equipment is desired for observation. We report on the direct investigation of the switching behaviour near device operation frequency of chemical solution deposition (CSD) prepared thin films of perovskite materials such as strontium bismuth tantalate SrBi 2 Ta 2 O 9 (SBT) and lead zirconate titanate Pb(Zr 0.3 ,T 0.7 )O 3 (PZT) with a newly developed measurement setup. In this work, high speed dynamic hysteresis measurements are performed to further explore the dynamic behaviour of polarization switching into the frequency domain. Virtual Ground measurements down to 100 ns cycle time of excitation signal were achieved, providing additional insight into device operation. A rise of Vc with a factor of 0.065 kV/decade between measurements at 10 Hz and 10 MHz of excitation frequency was confirmed.
Integrated Ferroelectrics 01/2002; 47(1):101-111. · 0.30 Impact Factor
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ABSTRACT: Experimental data on the dielectric hysteresis and the capacitance-voltage characteristics are analysed for polycrystalline Pb(ZrxTi1-x)O3 thin films. An analytical description of the effect of the domain structure, 90° rotation and 180° switching processes on the dielectric permittivity is proposed by taking into account the poling field characteristics of different domain types. A distinct correlation between these processes and an asymmetric behaviour of the dielectric permittivity of polydomain grains at E>0 and E<0 is theoretically established and compared with the experimental results.
Journal of Physics D Applied Physics 02/2001; 34(5):711. · 2.54 Impact Factor
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Integrated Ferroelectrics 01/2001; 32(1-4):93-99. · 0.30 Impact Factor
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ABSTRACT: In this letter, the reversible and irreversible polarization contributions in donor-doped Pb(Zr,Ti)O3 are investigated using conventional capacitance–voltage (C–V) and hysteresis measurements. The dependence of the Rayleigh coefficient in the subcoercive regime on the doping concentration is investigated and shown to be consistent with the assumption of an interaction of the domain walls with randomly distributed defects. © 2000 American Institute of Physics.
Applied Physics Letters 12/2000; 77(23):3830-3832. · 3.84 Impact Factor
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ABSTRACT: Three-dimensional (3D) piezoresponse force microscopy is applied in order to differentiate 90° and 180° domain switching in PbTiO3 (PTO) thin films. The 3D domain configuration is recorded both statically, revealing the surface crystallographic orientation of PTO films on the nanometer scale, and dynamically by simultaneously mapping the in-plane and out-of-plane hysteresis loops. We show that exclusively 180° switching occurs, also switching only half of the grain volume. © 2000 American Institute of Physics.
Applied Physics Letters 11/2000; 77(21):3444-3446. · 3.84 Impact Factor
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