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Imprint, the preferential orientation of the polarization of a ferroelectric device subjected to elevated temperatures, is a primary reliability concern afflicting data retention in ferroelectric RAM. In this paper, we demonstrate Preisach-based hysteresis modeling, which can be used to predict imprint behavior in ferroelectric thin films. A method was developed for capturing imprint in the context of a Preisach model and a numerical approach for evaluating the Preisach distribution was expanded upon. Interpolation and curve fitting were used to make predictions of the Preisach distributions of imprinted ferroelectric hafnium zirconium oxide devices after short-duration bakes at 23–260 °C and long-term bakes at 85 and 125 °C. In the case of long-term bakes, imprint-induced coercive shifts were modeled as shifts in the derivative of the top and bottom hysteretic polarization curves. The shift in the curves is modeled by fitting experimental data to a commonly used empirically logarithmic relationship reported in the literature. Simulations give remanent polarizations and coercive fields within <5.0 μC/cm2 and 0.1 V, respectively, of the raw data average. [ABSTRACT FROM AUTHOR]

In this work, we study the interlayer exchange coupling, J, between two NiFe and FeCo layers in a series of NiFe / Ru 1 − x B x (d) / FeCo synthetic antiferromagnet (SAF) samples, where the thickness of the spacer layer, d, is varied from 0.4 nm to 0.9 nm, and the boron concentration, x, is varied from 0 to 15 at. %. The samples are studied as deposited and after being annealed at 250 ° C. B is deposited into the Ru spacer layer to investigate what occurs after annealing a FeCoB/Ru/FeCoB SAF structure, which is commonly used in modern nanoscale magnetic devices, in which the FeCoB layer crystallizes to FeCo and B diffuses to adjacent layers. We find that J in as-deposited samples is relatively unaffected by adding up to 15% B into the Ru spacer layer. However, after annealing at 250 ° C , J changes the sign from antiferromagnetic coupling to ferromagnetic coupling for spacer layers thinner than 0.45 nm for 5% and 10% B and thinner than 0.525 nm for 15% B. We used transmission electron microscopy energy-dispersive x-ray spectroscopy in order to investigate the diffusion of atoms within a similar Ta (2.5 nm) / NiFe (0.8 nm) / Ru 1 − x B x (23 nm) layer structure. We find that after annealing at 250 ° C , the sample containing 15% B within the Ru 85 B 15 layer had significantly more diffusion of Fe into the Ru 85 B 15 layer, from the NiFe layer, as compared to the sample with 0% B. Thus, the presence of B within the spacer layer enhances diffusion of Fe into the spacer layer. [ABSTRACT FROM AUTHOR]

We successfully measured not only the tunneling properties but also the magnetic properties of a magnetic tunnel junction without patterning the magnetic tunnel junction stack itself by the current-in-plane tunneling method. Arrays of in-line four-point-probe sets with different spacings defined on the wafer made it possible to evaluate film tunneling properties. The estimated results differed little from those estimated by the commercial instrument. The small standard deviations of measured magnetic properties prove that our method is indeed reliable. Even though the properties for a less than submicron spacing were not available, we could successfully estimate the major characteristics of magnetic tunnel junctions. Our method can be applied in any environment, even in air without any clean-room facilities, and completed in as little as a day. [ABSTRACT FROM AUTHOR]

Using the concept of the Preisach model for a ferroelectric capacitor, we have analyzed the behavior of frequency (f)-dependent polarization reversal in surface-stabilized ferroelectric liquid crystals (SSFLCs) under an external field. At a fixed temperature, the peak height of the capacitance-voltage hysteresis loop is found to be decreasing with an increasing number of polarization cycles up to a certain typical value of frequency (e.g., fc) being different for different ferroelectric liquid crystals (FLCs). We also observed an inversion (a well instead of a peak) in the hysteresis loops appearing above a typical higher frequency denoted fi. The values of capacitance of the FLC capacitors became almost independent of the voltage for the frequencies between fc and fi. The frequency dependence of dielectric biaxiality in the SSFLCs is directly attributed to the appearance of such behavior. [ABSTRACT FROM AUTHOR]

We present a review on the subject of Conductive Bridging Random Access Memory (CBRAM) based on copper- or silver-doped silicon dioxide. CBRAM is a promising type of resistive non-volatile memory which relies on metal ion transport and redox reactions to form a persistent conducting filament in a high resistance film. This effect may be reversed to return the device to a high resistance state. Such control over resistance can be used to represent digital information (e.g., high =0, low =1) or produce multiple discrete or even continuous analog values as required by advanced storage and computing concepts. Many materials have been used in CBRAM devices but we concentrate in this paper on silicon dioxide as the ion conducting layer. The primary benefits of this approach lie with the CMOS process compatibility and the ubiquity of this material in integrated circuits which greatly lower the barrier for widespread usage and permit integration of memory with silicon-based devices. Our discussion covers materials and electrochemical theory, including the role of counter charge in these devices, as well as the current understanding of the nature of the filament growth. Theory of operation is supported by descriptions of physical and electrical analyses of devices, including in-situ microscopy and impedance spectroscopy. We also provide insight into memory arrays and other advanced applications, particularly in neuromorphic computing. The radiation tolerance of these devices is also described. [ABSTRACT FROM AUTHOR]

Conventional spin transfer torque MRAM sensing circuits suffer from a small sensing margin and a large sensing margin variation in deep submicron technologies. The small sensing margin issue becomes worse in the low-leakage process technology due to the higher threshold voltage. In this brief, the self-body biasing (self-BB) scheme is proposed to resolve the small sensing margin issue. In the self-BB scheme, the threshold voltage of load pMOS is adaptively controlled by body bias. Although leakage current flows through the body due to the positive junction bias voltage, it is well suppressed to less than 1% (0.3 \muA ) of the sensing current and flows only during the sensing operation. To reduce large sensing margin variation, the source degeneration scheme with the longer channel length is used for the load pMOS. The HSPICE simulation results obtained using low-leakage 45-nm model parameters show that the proposed sensing circuit achieves a probability of the read access pass yield (PRAPY\_Memory) of 100%, whereas the sensing circuit without BB scheme has an PRAPY\_Memory of 5.8% for a 32-Mb memory with a sensing time of 2 ns. [ABSTRACT FROM AUTHOR]

Programmable metallization cell (PMC) memory, also known as conductive bridging RAM (CBRAM), is a resistive-switching memory based on non-volatile formation and dissolution of a conductive filament (CF) in a solid electrolyte. Although ease of fabrication, promising performance and multilevel (ML) capability make the PMC a possible candidate for post-Flash non-volatile memories, further physical understanding is required to better assess its true potential. In this work, we investigate the kinetics involved in the programming operation (i.e., transition from the high resistance to the low resistance state), which occurs by voltage-driven ion migration and electrochemical deposition, and results in CF formation and growth. The main kinetic parameters control-ling the programming operation are extracted from our electrical data. Also, CF growth and corresponding resistance decrease is shown to be controllable with reasonable accuracy in pulse mode by employing a variable load resistance which can dynamically control the programming kinetics. A semi-analytical physical model is shown to account for experimental data and allows for the engineering of fast and reliable ML programming in one transistor - one resistor (1T-1R) devices. [ABSTRACT FROM AUTHOR]

This paper provides an in-depth review of the magnetoresistive random access memory technology and its developments over the past decade. Both the traditional field-driven and more recent spin torque transfer driven designs are discussed. By pointing out key technical challenges, important aspects and characteristics of various designs are used to illustrate mechanisms that overcome the technical obstacles. A significant portion of this paper is devoted to the principles of various designs based on spin torque transfer effect, including memory elements with in-plane and perpendicular magnetic electrodes. [ABSTRACT FROM AUTHOR]

We report the effects of the rotational motion of the director around the chiral smectic cone on the dielectric relaxation and polarization reversal process in a surface stabilized ferroelectric liquid crystal cell. Measurement was made at a fixed temperature (40°C), far below the SmA–SmC* transition temperature (62°C) of the ferroelectric liquid crystal material (CS‐1027). The amount of switchable polarization (ASP), during the polarization reversal, is found to decrease with increasing frequency of the applied signal until a typical value of frequency (fl) is reached. This behaviour is considered to be due to the time‐dependent rotational motion of the director. The ASP value was calculated by measuring polarization–voltage (P–V) and capacitance–voltage (C–V) hysteresis loops as a function of the applied signal frequency and then following the Preisach model for the ferroelectric capacitor. The peaks of the C–V hysteresis loop, which correspond to the reversal of polarization, are gradually converted into wells for frequencies greater than a critical value (fi). The hysteresis loops shows ‘frustrated’ behaviour for frequencies between fl and fi. The inversion of the C–V hysteresis loop at higher frequencies (>fi) is attributed to the inversion of the dielectric biaxiality and the corresponding ‘frustrated’ behaviour arising due to competition between the dielectric and ferroelectric torques. A suitable equivalent circuit can be designed to represent the frequency‐dependent C–V and magnitude of admittance (conductance) –voltage (G–V) hysteresis behavior. [ABSTRACT FROM AUTHOR]

A sensing technique using a voltage-mode architecture, noise-shaping modulator, and digital filter (a counter) is presented for use with cross-point MRAM arrays and magnetic tunnel junction memory cells. The presented technique eliminates the need for precision components, the use of calibrations, and reduces the effects of power supply noise. To obviate the effects of cell-to-cell variations in the array, a digital self-referencing scheme using the counter is presented. Measured experimental results in a 180-nm CMOS process indicate an RMS sensing noise of 20 μV for a 5-μs sense time. Further increases in sense time are shown to increase the signal-to-noise ratio. The current used by the sense amplifier and counter was measured as 10 μA when running at 100 MHz or 10 mA when 1000 sense amplifiers are used with a memory subarray having 1000 bitlines. [ABSTRACT FROM AUTHOR]

We show that magnetization damping in Permalloy, Ni80Fe20, can be enhanced sufficiently to reduce postswitching magnetization precession to an acceptable level by alloying with the transition metal Os (osmium). The damping increases monotonically upon raising the Os concentration in Permalloy, at least up to 9% of Os. Other effects of alloying with Os are suppression of magnetization and enhancement of in-plane anisotropy. Magnetization damping also increases significantly upon alloying with the five other transition metals included in this study (4d elements: Nb, Ru, Rh; 5d elements: Ta, Pt) but never as strongly as with Os. [ABSTRACT FROM AUTHOR]

We demonstrate a method for measuring magnetoresistance (MR) and resistance area product (RA) of unpatterned magnetic tunnel junction film stacks. The RA is measured by making a series of four point probe resistance measurements on the surface of an unpatterned wafer at various probe spacings. The key to this technique is in placing the probes at the appropriate spacings, on the order of microns for typical applications. The MR is obtained by repeating the measurement at different magnetic fields. A simple conceptual model and an exact analytical solution in good agreement with experimental data are presented. The current-in-plane tunneling method requires no processing, is fast, and provides reliable data which are reflective of the deposition only. [ABSTRACT FROM AUTHOR]

Memristive devices are hardware components for applications in neuromorphic computing, memories, and logic computation. This work contributes to the ongoing debate on the switching mechanism of eightwise polarity in SrTiO3‐based resistive switches. Specifically the effect of atmospheric humidity on the materials defect chemistry and switching properties is considered. Asymmetric devices are designed by exchanging the top and bottom positions of Pt and LaNiO3 electrodes allowing for a separate analysis of the top and the bottom metal‐oxide interfaces. Under dry atmospheres the switching hysteresis is enhanced with a top Pt contact and suppressed with a bottom Pt contact. It is argued that the buried position and dense microstructure of the bottom platinum impedes an oxygen vacancy driven switching mechanism. Under humid atmospheres eightwise switching occurs in both devices suggesting the presence of two switching mechanisms within the same eightwise switching polarity, namely, oxygen vacancy and hydroxide ion enabled switching. The findings help develop strategies to suppress eightwise switching by burying the active metal‐oxide interface and ensuring dense electrode microstructures. Suppression of switching mechanisms relying on exchange with the environment is desirable for technological implementation of resistive switches and for strategies in stacking of memristive devices for memory and for neuromorphic hardware. [ABSTRACT FROM AUTHOR]

We investigate the chemical state and electronic structure of boron in the MgO layer in CoFeB/MgO/CoFeB magnetic tunnel junctions by synchrotron radiation X-ray photoelectron spectroscopy and first-principles calculations. In the top CoFeB, we observe three boron 1s peaks corresponding to oxidic, intermediate, and metallic boron. As the annealed films were etched, the B2O3 starts to appear together with the Mg 2p peak, indicating that boron atoms diffuse into the MgO barrier. Our calculations show that B impurities in the MgO barrier do not create any midgap states but reduce the MgO barrier height with the increase of boron concentration. [ABSTRACT FROM AUTHOR]