Multi-valued Memory Research Articles

Use of the Asymmetric Planar Hall Resistance of an Fe Film for Possible Multi-Value Memory Device Applications

Systematic planar Hall measurements have been performed on a ferromagnetic Fe film grown on a standard (001) GaAs substrate at room temperature. The angular dependence of the planar Hall effect revealed the presence of both four-fold (cubic) and two-fold (uniaxial) anisotropies in the 7 nm thick Fe film. The dominance of the four-fold symmetric anisotropy, however, provided four magnetic easy axes near the (100) direction, which results in a two step switching phenomenon in the magnetization reversal process. An interesting asymmetric hysteresis loop was observed in the planar Hall resistance (PHR) when the turning point of the field scan is set at the value in the region of the second transition. The intermediate resistance states appearing in the asymmetric PHR loop were understood in terms of mutli-domain structures formed during the second switching of magnetization. Such multi-domain structure of the Fe film showing robust time stability provided additional Hall resistance states, which can be used for multi-valued memory device applications.

Magnetic Anisotropy of GaMnAs Film and Its Application in Multi-valued Memory Devices

The magnetic anisotropy of GaMnAs ferromagnetic semiconductor film was investigated by magneto-transport measurements. Values of cubic and uniaxial anisotropies were obtained by analyzing the angular dependences of Hall effects based on magnetic free energy. The presence of strong cubic anisotropy gave four magnetic easy axes in the film's plane, resulting in two-step switching behavior in field scans of the planar Hall effect. Asymmetric loops containing four resistance plateaus were observed in minor scans of the planar Hall effect owing to the formation of stable multi-domain structures during magnetization reversal. Four-valued memory function based on the four observed Hall resistance states was demonstrated by using appropriate sequences of magnetic field pulses.

Magnetic Anisotropy of GaMnAs Film and Its Application in Multi-valued Memory Devices

Magnetic Anisotropy of GaMnAs Film and Its Application in Multi-valued Memory Devices

Theoretical modeling of spin quantum cross structure devices with noncollinear ferromagnetic electrodes

Recently, we have proposed a spin quantum cross structure (SQCS) device toward the realization of novel switching devices. The SQCS device consists of two ferromagnetic metal thin films with their edges facing each other at an angle of θ, and sandwiches a few molecules and atoms. In this paper, the calculation of electronic transport has been performed for SQCS devices with the Ni noncollinear magnetic films as both electrodes within the framework of the Anderson Hamiltonian, taking into consideration both polar angle θ, and azimuthal angle ϕ. We have obtained the general noncollinear spin transport formula, and the polar angle dependence of current-voltage characteristics of SQCS devices. The noncollinear spin transport is determined only by the angle θ defined by the inner product of two spins. Also, it is implied that SQCS devices can serve as multivalued memory devices by varying the angle θ.

Nonvolatile multivalued memory effects in electronic phase-change manganites controlled by Joule heating

Non-volatile multivalued memory effects caused by magnetic fields, currents, and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and (Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic region between ferromagnetic metallic and charge-ordered insulating states. The current/voltage effects observed in this study are explained by the self-heating effect, which enable us to control the colossal electroresistance effects. This thermal-cycle induced switching between electronic solid and liquid states can be regarded as electronic version of atomic crystal/amorphous transitions in phase-change chalcogenides.

A novel network of chaotic elements and its application in multi-valued associative memory

We give a novel chaotic element model whose activation function composed of Gauss and Sigmoid function. It is shown that the model may exhibit a complex dynamic behavior. The most significant bifurcation processes, leading to chaos, are investigated through the computation of the Lyapunov exponents. Based on this model, we propose a novel network of chaotic elements, which can be applied in associative memory, and then investigate its dynamic behavior. It is worth noting that multi-valued associative memory can also be realized by this network.

A novel multi-valued BAM model with improved error-correcting capability

A Hyperbolic Tangent multi-valued Bi-directional Associative Memory (HTBAM) model is proposed in this letter. Two general energy functions are defined to prove the stability of one class of multi-valued Bi-directional Associative Memorys(BAMs), with HTBAM being the special case. Simulation results show that HTBAM has a competitive storage capacity and much more error-correcting capability than other multi-valued BAMs.

Production and control of planar microwave plasmas for materials processing

The paper is a review of the current understanding for the operation of the non-magnetized large-area planar microwave plasma sources with emphasis on the high-density surface-wave plasmas. The paper starts with a review of the various plasma source designs currently in use and short comparison of microwave and lower-frequency RF plasmas. Then the most important phenomena in such plasmas (occurrence of standing-wave eigenmode resonance densities, density dependence of the impedance, energy balance, stability, multi-valued power-density dependence, mode jumps, memory and hysteresis loops, self-tuning ability, local plasma resonance, non-collisional heating) are revisited with simple two-dimensional models. For each phenomenon references to more detailed theoretical treatment and experimental studies are given and a few key experimental curves are reproduced. At the end some unresolved problems are listed.

Design of an inner-product processor for hardware realization of multi-valued exponential bidirectional associative memory

Inner-product calculations are often required in digital neural computing. The critical path of the inner product of two vectors is the carry propagation delay generated from individual product terms. In this work, a novel and high-speed realization of an inner-product processor for the multi-valued exponential bidirectional associative memory (MV-eBAM) is presented in order to reduce the carry propagation delay, wherein the treatment of inner product of two vectors is given. Notably, a systolic-like architecture of digital compressors is used to reduce the carry propagation delay in the critical path of the inner product of two vectors. The architecture we propose here might offer a sub-optimal solution for the digital hardware realization of the inner-product computation.

A deterministic capacity-finding method for multi-valued exponential BAM

The multi-valued exponential bidirectional associative memory (MV-eBAM) has been proposed and proved to be asymptotically stable under certain constraints. Although multi-valued eBAM has been verified to possess high capacity by thorough simulations, the capacity is still unable to be solved analytically. In the paper, an algorithm is proposed to derive the capacity. Some important characteristics, including the absolute lower bound of the radix, and the approximate capacity are also discussed. The result shows that the multi-valued eBAM indeed possesses high capacity.

A multivalued bidirectional associative memory operating on a complex domain

A bidirectional associative memory (BAM) with complex states and connection weights is investigated in this paper. The states are represented by quantization values defined on the unit circle of the complex plane. A given Lyapunov function indicates that the proposed complex domain BAM (CDBAM) is bidirectionally stable no matter which operation (synchronous or asynchronous) is used. We also prove that all the equilibrium (fixed) points of CDBAM correspond to local energy minima so that the design problem can be solved by a gradient descent algorithm. Finally, a gradient descent algorithm in the complex domain is derived to design the weight matrix of CDBAM. Several computer simulations are performed to illustrate the validity, capacity, attractivity and the applications of the CDBAM.

Complex-valued multistate neural associative memory

A model of a multivalued associative memory is presented. This memory has the form of a fully connected attractor neural network composed of multistate complex-valued neurons. Such a network is able to perform the task of storing and recalling gray-scale images. It is also shown that the complex-valued fully connected neural network may be considered as a generalization of a Hopfield network containing real-valued neurons. A computational energy function is introduced and evaluated in order to prove network stability for asynchronous dynamics. Storage capacity as related to the number of accessible neuron states is also estimated.

Capacity analysis of the asymptotically stable multi-valued exponential bidirectional associative memory

The exponential bidirectional associative memory (eBAM) has been proposed and proved to be a stable and high capacity associative neural network. However, the intrinsic structure and the evolution functions of this network restrict the representation of patterns to be either bipolar or binary vectors. We consider the promising development of multi-valued systems and then design a multi-valued discrete eBAM (MV-eBAM). The multi-valued eBAM has been proved to be asymptotically stable under certain constraints. Although MV-eBAM is also verified to possess high capacity by thorough simulations, there are important characteristics to be explored, including the absolute lower bound of the radix, and the approximate capacity. In order to estimate the capacity of the MV-eBAM, a modified evolution equation is also proposed. Hence, an analytic solution is derived. Besides, a radix searching algorithm is presented such that the absolute lower bound of the radix for this MV-eBAM can be found.

Multivalued associative memories based on recurrent networks

A multivalued neural associative memory model based on a recurrent network structure is proposed. This model adopts the same principle proposed in the authors' previous work, the exponential correlation associative memories (ECAM). The model also has a very high storage capacity and strong error-correction capability. The major components of the new model include a weighted average process and some similarity-measure computation. As in ECAM, in order to enhance the differences among the weights and make the largest weights more overwhelming, the new model incorporates a nonlinear function in the calculation of weights. Several possible similarity measures suitable for this model are suggested. Simulation results of the performance of the new model with different measures show that, loaded with 500 64-component patterns, the model can sustain noise with power about one fifth to three fifths of the average signal power.

Nine-state resonant tunneling diode memory

The authors demonstrate an epitaxial series combination of eight pseudomorphic AlAs/In/sub 0.53/Ga/sub 0.47/As/InAs resonant tunneling diodes (RTDs) grown by molecular beam epitaxy on InP. This series RTD produces an eight-peak multiple negative differential resistance characteristic with a peak-to-valley current ratio (PVR) exceeding 2 per peak at a peak current density of approximately 6 kA/cm/sup 2/. Hysteresis in the current-voltage characteristic is reduced by uniformly Si doping the double-barrier resonant tunneling region at a density of 5*10/sup 16/ cm/sup -3/. Using this multiple-peak RTD in series with a field-effect transistor load, a nine-state multivalued memory circuit is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field programmable analogue array based on MOSFET transconductors

An area efficient and parasitic insensitive technique for the implementation of a field programmable analogue array is proposed. The connections between configurable analogue blocks are realised using MOSFET transconductors. The conductance is controlled by varying the gate voltages defined by a multivalued memory system or external/internal signals.

A new resonant-tunnel diode-based multivalued memory circuit using a MESFET depletion load

A resonant-tunnel-diode-based (RTD-based) multivalued memory (MVM) circuit using a depletion-load MESFET is described. Compared with the commonly used resistor load in multivalued logic (MVL) circuits, this circuit design offers better noise margins, lower power dissipation, and easier integration. SPICE was used to simulate a three-state memory circuit, functioning as a MVL cell and consisting of a series connection of two RTDs and a MESFET depletion load. It is shown that the simulated multipeak I-V curve for this MVM cell is in good agreement with the measurement results from the two discrete RTDs connected in series. The signal write and read operations for this MVM circuit are also successfully simulated, and these operations were reliable and showed fast response. Some important effects on the MVM circuit due to the parasitic resistor and capacitor in the RTD are discussed. This MVM cell structure can be easily extended to implement more states in a memory circuit. >

Multivalued SRAM cell using resonant tunneling diodes

A multivalued SRAM cell using a vertically integrated multipeak resonant tunneling diode (RTD) pair is described. Two RTDs in series can have 2N+1 stable states. With this concept, a five-stable-state memory cell has been implemented with two 2-peak RTDs. Several designs are presented for a high-speed static random access multivalued memory using the folding characteristics of RTDs. The different designs are described and studied by comparing their power consumption under different conditions of device parameters and switching speed. The authors show that the proposed memory cell using a pair of multipeak RTDs yields the best result from the standpoint of size, power dissipation, and speed among the RTD memory cells discussed. >

Error correction technique for multivalued MOS memory

An error correction technique is proposed to increase the noise margin of a multivalued MOS memory. The stored voltage information is first converted to a binary representation. The noise margin of the store voltage is then increased by storing and comparing the least significant bits of the binary representation.

Implementation and applications of multivalued decoders

A synthesis procedure is described for multivalued threshold decoders and their application to the implementation of multivalued functions. This method is based on the definition of inversion and extreme functions. Decoders are obtained using only the very simple blocks which synthesize inversion functions. This general design procedure may be used for any integrated circuit technology. As an example, the method is applied to the synthesis of an integrated CMOS quaternary decoder. Both the layout and the timing of the integrated circuit, and their application to the synthesis of multivalued functions and multistable memory elements, are shown.