DE19639910C2 - Non-volatile analog value memory based on GMR layer systems - Google Patents

Description

The present invention relates to a static Analog value memory based on GMR (giant magneto resistive) layer systems, in particular as storage for Neural Networks.

A corresponding memory is the US 5,587,943 A.

For optimal hardware implementation of neural networks, non-volatile analog memory elements are required, for which the digital circuit technology common today has to be taken into account. As is known, a neural network is constructed in a matrix and has neurons at its crossing points, all of which are connected to one another in accordance with the matrix. Each individual neuron of this network has a large number of synapses, which _react to an incoming excitation S _k with a specific weight W _{ijk that} can be input. Here, i and j denote the rows and columns of the matrix and k denotes the respective component S _{k of} the excitation vector S considered. With its components, this vector S contains both such an external type and a feedback type. The basic function of the kth synapse can be z. B. by the equation

W _ijk (t + δt) = 1 - e _ij (t) W _ijk (t) + e _ij (t) S _k (t)

describe. The excitations e _ij (t) are a measure of the readiness of the network to adapt the vector S to the requests at time t. The value e = 0 means that the neuron of the network is not learning anything due to the lack of incoming excitation S. The value e = 1 means that the neuron forgets the previous state. For the functioning of a neural network, it is advantageous if the weights W _ijk can be stored analogously.

Analog storage magnetic layer systems are in print publications DE 42 30 981 A and DE 42 30 983 A described. There optically influenced magnetic layers are given in the selectable by the action of controlled laser radiation can be written. A disadvantage of these is known Storage layers that the intended laser scanning process at least not because of the required beam deflection can be miniaturized favorably.

The two publications mentioned show with their execution Example, such as within such a storage arrangement electrical conductor tracks serving for the control leads can be. Further from this state of the art known how and with which control the different analog level levels in the information-storing magnet layer can be adjusted.

From US 5,587,943 A mentioned at the outset is not a volatile memory with closed flow guidance to be removed men. This memory has an array of memory cells each of which also includes a magnetoresistive majority Layer system included, which is characterized by a so-called GMR (Giant Magnetoresistance) effect. This GMR Multi-layer system forms in analogy to well-known Storage rings together with three soft magnetic legs a closed, flow-guiding ring shape. By the central Opening of this ring shape are lines for storing, off read and control led. The structure of the well-known Spei Accordingly, chers is complex.

The object of the present invention is to provide a principle for the construction of a non-volatile analog memory with magneti specify memory effect, this memory and its associated control system with sensible technical Effort can be miniaturized. In particular, each Cell's memory can be capable of direct analog information to be able to save (as such) and be readable again.  

According to the patent claim, each cell of the invention analog memory from a GMR (giant magnetoresistive) Layer system constructed, as will be detailed below is explained in more detail.

For the principle of a GMR device, reference is also made to the publication DE 43 01 704 A, which relates to a device for detecting an angular position of an object. An MR sensor is described there, which serves the purpose of determining an angle of rotation of an object, such as, for. B. a magnet to detect or monitor quantitatively. This known device comprises a magnet rotatably arranged over a GMR magnetic layer structure. The magnetic field of this magnet acts in the GMR layer system. This consists of, as shown there in FIGS. 3 and 4, a plurality of layers lying one on top of the other made of magnetically differently sensitive materials. At least one layer of magnetic material with a relatively high coercive force is provided there, which serves as a bias layer and is effective. The magnetization M _B is effective for this layer structure as a constant orientation. This magnetization M _B is the reference direction for the other magnetic alignments. Another layer of far less coercive magnetic material is optionally separated by an intermediate layer on the already mentioned bias layer. In the so-called zero position, the magnetization in this second layer is oriented parallel or antiparallel to the bias layer in relation to the magnetization direction. By means of a magnetic field of the already mentioned rotatably arranged magnet, the magnetization M _M can be rotated out of the parallel or antiparallel orientation to the magnetization M _B in this MR layer system in accordance with the current orientation of the magnetic field of this magnet. An angle thus occurs between the directions of the magnetizations M _B and M _M.

Such a layer system usually consists of one Large number of alternating bias layers and magnetic field layers of magnetization mm.

Such an MR device has the physical property that the electrical resistance is clearly different from that mentioned Angle between the orientations of the bias layer and the Influenced magnetization layer is dependent. Here can the measuring current with which the respective electrical Resistance of the layer system for a given location is determined, perpendicular to the planes of the choice  Layers of the system or even directed at these levels be sent through the system. There are accordingly locally positioned electrode pairs for the Electricity input and output must be provided.

For the construction of such a known layer system still pointed out that both ferromagnetic as well antiferromagnetic coupling of adjacent layers is effective can be.

Further explanations of the invention are given in the Description to attached figures.

Fig. 1 shows the principle image shows a structure of an array according to the invention an analog-only memory, suitable for neurons with its individual memory cells in a matrix arrangement.

FIG. 2 shows the system of conductor tracks omitted in FIG. 1 but associated with the memory for detecting the respective resistance values of the individual memory cells.

Fig. 3 shows a circuit for writing the analog information.

In FIG. 1, 11 denotes the respective memory cells, which are known as layer systems known per se, consisting of magnetically soft layers (their magnetic orientation M _{M can be} influenced from the outside) and magnetically hard bias layers (which refer to the reference orientation M _B With reference to Fig. 1, these layers lie alternately with one another in the direction perpendicular to the representation of Fig. 1. The lines 12 shown in the figure and recognizable in Fig. 1 with regard to their arrangement principle and the corresponding lines 13 are used according to the invention for 1. Selective actuation of a selected cell 11 in the matrix array 1 of FIG. 1. With 14 , both the actuation lines and the actuation lines 13 are associated with return lines, a respective pair of branch lines 12 a and 13 a assigned to a respective cell the lines 12 and 13 thus run in, above or below the layer system the individual cell to be controlled, that due to the crosswise alignment of the branch lines 12 a and 13 a to each other, a 360 ° angle influence of the magnetization orientation M _M in the coercively weakly magnetically soft layer can be carried out selectively. This magnetically soft layer is thus coupled to the control system 12 , 13 , 12 a, 13 a for magnetization alignment in a selected cell. Since the coercive force / magnetization M _{B of} the magnetically hard layers is large, its magnetization M _B remains unchanged as the reference direction. The angle τ achieved by selected rotation of the magnetization M _{M of} the magnetically soft layers of the layer system, deviating from the unchanged orientation M _B , is the analog value of the written signal stored in the cell. By dimensioning and selecting the current direction of the currents in lines 12 and 13 , correspondingly graded angular settings τ can be achieved. These remain non-volatile in the activated cell even after the currents in lines 12 and 13 have been switched off .

Fig. 2 shows a conductor system of connection leads 21 and 22 for the above-mentioned measuring current, which is sent through the layer structure of the cell 11 to determine the respectively dependent angle τ dependent electrical resistance value of the cell 11 . The electrical resistance of the layer stack of the cell depends on the cosine of the angle between the orientation mm and the reference orientation M _B. The resistance is at a maximum if the magnetizations M _M and M _M are opposed to one another, ie are oriented antiparallel. Correspondingly minimal resistance can be determined when these magnetizations are aligned in parallel. The available range of the relative resistance change of cells of such a GMR system is typically between 5 and 70% of the maximum resistance.

FIG. 3 shows a circuit diagram for a preferred registration with currents in lines 12 and 13 . This advantageous registration takes the form of a feedback. The amount and the ratio between the two currents of the respectively selected lines 12 and 13 is varied according to the invention until the electrical resistance of the GMR cell has a resistance value corresponding to the value to be stored in the selected analog gradation of the available resistance value range. In itself, the circuit of FIG. 3 with the information contained therein is self-explanatory. The circuit contains the operational amplifier 31 , two further amplifiers 32 and 33 , the latter with the output connections for driving the lines 12 and 13 . The amplifier 32 works as a subtractor and the amplifier 33 as a controller. A fixed resistor is denoted by 34 and by 35 the selected GMR cell to be driven is indicated. According to the selected control, the connections 112 , 212 on the one hand and the connections 113 , 213 on the other hand are connected to one another. The electrical current I flowing through the electrical resistance of the cell 11 , which also flows through the fixed resistor 34 and generates a voltage drop there, is a respective measure of the analog value stored in the cell.

Claims (3)

1. Non-volatile analog value memory, in particular for neural networks, with an array ( 1 ) with memory cells arranged in a matrix, these cells being a layer system with magnetically soft (M _M ) (low coercive force) and magnetically hard (M _M ) (high coercive force) Have layers and wherein the array ( 1 ) is assigned a first matrix-shaped interconnect system ( 12 , 13 , 14 ), which for the optional control of the individual cells ( 11 ) of this array for each cell ( 11 ) has a pair of branch lines ( 12 a , 13 a) be seated and in such a respective pair in the area of the respective individual cell ( 11 ) these branch lines ( 12 a, 13 a) cross and the array ( 1 ) has a second matrix-shaped interconnect system ( 21 , 22 ) is assigned to the layer system of the individual cells ( 11 ) adjacent electrode pairs re, optionally controllable via this conductor track system ( 21 , 22 ) and the electrode pairs of a current electrical resistance value of the individual cell ( 11 ) can be determined. 2. Analog value memory according to claim 1, wherein the layer system of the individual cells ( 11 ) is a GMR (giant magnetoresistive) layer system. 3. Analog value memory according to claim 1 or 2, with an assigned to the first conductor track system ( 12 , 13 , 14 ) electronic circuit ( Fig. 3) with which the amount of the individual drive currents and their relationship to one another can be determined by means of current value variations with feedback.