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A reliable Ir diffusion barrier was prepared on polysilicon plugged substrate with a contact size of 0.6 μm. Using a Ti adhesion layer and stress-relief process, it was possible to integrate the Ir barrier into a high density 4 Mb ferroelectric random access memory device. After heat treating sol-gel derived Pb(Zr[sub 1-x]Ti[sub x])O[sub 3] (PZT) films at 700 °C, the Ir barrier contact displayed an ohmic behavior and showed a low resistance of 130 Ω per contact in 1k serial contact array. The PZT films on Pt/IrO[sub 2]/Ir poly-plugged substrate exhibited excellent ferroelectric properties such as remnant polarization and coercive voltage of 25 μC/cm2 and 1.15 V, respectively. Auger depth profile and transmission electron microscopy analyses confirmed that no appreciable oxidation was formed between the Ir barrier and the polysilicon plug. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report first-principles calculations on the antiferromagnetic spin ordering in graphene under biaxial strain. Using hybrid functional calculations, we found that the semimetallic graphene sheets undergo a transition to antiferromagnetic insulators at a biaxial strain of 7.7% and that the band gap rapidly increases after the onset of this transition before reaching 0.9 eV at a biaxial strain of 12%. We examined the competition of the antiferromagnetic spin ordering with two-dimensional Peierls distortions upon biaxial strain, and found that the preceding antiferromagnetic insulator phase impedes the Peierls insulator phase. The antiferromagnetic insulator phase is destabilized upon carrier filling but robust up to moderate carrier densities. This work indicates that biaxially strained graphene represents a noble system where the electron-electron and electron-lattice interactions compete with each other in a simple but nontrivial way. [ABSTRACT FROM AUTHOR]

We evaluate different switching behaviors of lead zirconate titanate (PZT) thin film capacitors with two different geometries: one, a square 100×100 μm; the second, a ribbon (1.6 μm width but with approximately the same total area), as a function of temperature T, and applied electric field E. The ribbon capacitor shows a stronger dependence (by ca. 70%) of activation field on T and E. This is interpreted as a chemical reduction of edge material in the long-perimeter ribbons due to plasma etching. In order to understand and model the different domain switching of these two types of PZT capacitor, we also investigate impedance spectra at various temperatures from 27 to 470 °C. From ac conductance spectra, both square- and ribbon-type capacitors have similar trap levels, 0.38±0.02 eV. From analysis of conductivity spectra, we find that the ribbon capacitor contains an additional 0.19±0.02 eV trap level attributed to H–O dipoles due to hydrogen reduction; the latter trap results in domain pinning, which is interpreted as the origin of the relatively strong dependence of the activation field on T and E in the ribbons compared to the square capacitors. The additional loss peak in the ribbon capacitors is also observed in real cell-type capacitors, but only when their edge/area ratio becomes large, as in submicron cells for megabit scale. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By replacing the traditional single magnetic free layer in magnetic random access memory (MRAM) with a synthetic antiferromagnetic (SAF) layer composed of two antiferromagnetically coupled layers, the possibility of the kink generation has been suppressed to a minimum level and the normalized free-layer shift has been reduced from 15% to less than 5%. These phenomena are thought to be from the reduction of the effective thickness and magnetic moment by introducing a SAF free layer. Since the SAF free layer decreases the magnetostatic interaction with the pinned layer, free-layer shift is also decreased. A SAF free layer forms a closed magnetic loop between two antiferromagnetically coupled layers. Therefore, it increases a tendency to become a single domain and its switching field distribution is enhanced. With the optimized SAF free layer, array quality factor [AQF, σ(Hc)/Hc] is increased to more than 10 and switching window could be obtained which is the area to be selectively switched in the memory cell array. When adopted in a 64-kb MRAM, it is confirmed that cells can be selectively switched without the disturbance to the other cells. [ABSTRACT FROM AUTHOR]

Despite several years of research into graphene electronics, sufficient on/off current ratio /on//off in graphene transistors with conventional device structures has been impossible to obtain. We report on a three-terminal active device, a graphene variable-barrier "barristor" (GB), in which the key is an atomically sharp interface between graphene and hydrogenated silicon. Large modulation on the device current (on/off ratio of 105) is achieved by adjusting the gate voltage to control the graphene-silicon Schottky barrier. The absence of Fermi-level pinning at the interface allows the barrier's height to be tuned to 0.2 electron volt by adjusting graphene's work function, which results in large shifts of diode threshold voltages. Fabricating GBs on respective 150-mm wafers and combining complementary p- and n-type GBs, we demonstrate inverter and half-adder logic circuits. [ABSTRACT FROM AUTHOR]