WO2002035704A1

WO2002035704A1 - Logic circuit

Info

Publication number: WO2002035704A1
Application number: PCT/DE2001/003936
Authority: WO
Inventors: Joachim Bangert; Ralf Richter
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-10-26
Filing date: 2001-10-15
Publication date: 2002-05-02
Also published as: DE10053206C1

Abstract

The invention relates to a logic circuit, comprising at least one magnetoresistive element to which a conductor with at least two signal connections is allocated. Said conductor, when carrying a current, enables the generation of a magnetic field which acts on said magnetoresistive element and by which means the magnetisation of a soft magnetic layer of the magnetoresistive element can be switched. Means are provided for generating another magnetic field that is essentially perpendicular to the magnetisation of the soft magnetic layer, according to necessity.

Description

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In order to solve this problem, a logic circuit arrangement of the type mentioned at the beginning provides according to the invention that means are provided for generating a further magnetic field which is essentially perpendicular to the magnetization of the soft magnetic layer, as required.

The magnetic field which can be generated with the means provided according to the invention and which is perpendicular to the magnetization of the soft magnetic layer, which can be rotated with a sufficiently high magnetic field via the field which can be generated via the conductor with the signal connections, is particularly advantageously possible for rotating or switching the magnetization of the soft magnetic layer to reduce the required coercive force. This means that a lower magnetic field that can be generated by the signal currents carried over the conductor is required for switching. The rotating process in the magnetic layer also occurs faster than the switching in the logic circuit arrangement described in the publication mentioned at the beginning.

If there is no vertical magnetic field, the coercive field strength required for switching is high. In order to turn the magnetization, signals have to be given via both signal connections so that additively a sufficiently high current flows over the conductor, which generates a sufficiently high magnetic field that has a field strength that is equal to or greater than the coercive field strength. In this case, AND logic is implemented. If the vertical magnetic field is now generated, the magnetic field is reduced

Coercive field strength. For turning it is already sufficient if only one signal and thus only half the current flows through the conductor, ie a lower magnetic field is sufficient for switching. In this case, an OR function would be implemented (since each of the signals is sufficient for switching individually). tsJ tsJ F ¹

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The means, for example the further conductor, is expediently assigned a switching or control element, via which the generation of the further magnetic field can be controlled. Any such element can be used as such a switching or control element which makes it possible to conduct a current over the conductor which is connected to a corresponding current source when it is necessary. An MRAM memory cell, that is to say a magnetic random access memory cell, can be expediently used as such a switching or control element, the state of which is used to define the current supply operation of the further conductor. A switching or control element with non-volatile switching or control information is expediently used.

According to an advantageous embodiment of the invention it can be provided that the means for generating a low bias magnetic field, which acts essentially continuously on the magnetoresistive element, and a higher magnetic field. The bias magnetic field lowers the

Coercive field strength, too, but only slightly, which is advantageous in that the hysteresis curve becomes "more homogeneous". One approaches ideal switching behavior, switching is possible more quickly. The magnetoresistive element or reference element is therefore somewhat pretensioned The magnetic field that actually defines the function of the logic circuit arrangement is significantly higher and significantly reduces the coercive field strength.

It may furthermore be expedient if an amplifier element is assigned to a magnetoresistive element - of whatever type - in order to amplify the output signal, so that it can be used as an input signal for other logic elements.

As already described, the logic circuit arrangement according to the invention enables the construction of a basic logic element comprising only one magnetoresistive element with associated arranged. Head and other head, the assignment of a reference element is optional. The simplicity of the construction consequently enables the likewise simple and substantially smaller construction of a larger logic circuit arrangement which comprises a multiplicity of magnetoresistive elements arranged in the manner of an array, optionally assigned reference elements, with assigned conductors and further conductors and optionally amplifier elements. Field-programmable logic arrays can thus be formed in a simple manner, which can be used together with integrated circuits.

GMR (giant magnetoresistive) or TMR (tunneling magnetoresistive) elements can expediently be used as magnetoresistive elements or reference elements.

Furthermore, according to the invention, the means can comprise a plurality of further conductors which are assigned to the magnetoresistive element, are located one above the other and / or next to one another and are electrically insulated from one another and are energized together to generate the perpendicularly acting magnetic field.

An alternative to the invention for using separate further conductors which are electrically insulated with respect to the magnetoresistive element provides that the current lines of the magnetoresistive element serve as further conductors. A tunnel current is applied to the magnetoresistive element during operation. The lines provided for this purpose can expediently also serve as additional conductors for generating this perpendicular magnetic field.

Finally, it can be provided according to the invention that the hard magnetic reference layer of a magnetoresistive element can be remagnetized via the field that can be generated when the conductor is energized with the signal connections. This offers the possibility to change the basic function of the logic circuit, which depends on the orientation of the Magnetization of the reference layer is. If high currents are conducted through the signal connections, which of course must be significantly higher than the normal signals, since the reference layer magnetization must of course not change during normal operation, it is possible, for example, to

Change circuit function from an "OR" to an "NA D" function.

Further advantages, features and details of the invention emerge from the exemplary embodiments described below and from the drawings. Show:

1 is a schematic diagram of a logic circuit arrangement of a first embodiment,

Fig. 2 is a schematic diagram of an idealized switching curve of a magnetoresistive element with asteroid switching behavior, and

Fig. 3 shows a second embodiment of a logic circuit arrangement according to the invention with a reference element.

1 shows a logic circuit arrangement 1 according to the invention consisting of a magnetoresistive element 2, for example a GMR or a TMR element. This magnetoresistive element can be supplied with a measuring current I ₀ via suitable feed lines, the size of the measuring voltages which can be tapped depending on how the magnetization of the soft magnetic layer of the magnetoresistive element relates to the magnetization of the hard magnetic reference layer. The basic function of a GMR or TMR element is well known, it does not need to be discussed here.

Electrically insulated, a conductor 3, which can also be energized, runs across the magnetoresistive element 2 and, when energized, a magnetic field at the location of the soft magnetic see layer of magnetoresistive element 2 generated. The current I _A / _B in conductor 3 is added up from the individual currents of the two logic inputs A and B, to which corresponding logic signals can be applied. The voltage drop U across the magnetoresistive element is the logic output.

The current-voltage curve of a magnetoresistive element 2 follows directly from the hysteresis curve of the soft magnetic layer of the magnetoresistive element and ideally assumes two discrete values at constant I ₀ , which define a logical "0" (U ₀ ) and a logical "1" (Ui) serve. The basic principle or the basic course is shown in FIG. 2 on the basis of the extended hysteresis curve.

Two discrete current values of logic inputs A and B are defined as logic "1" (1 (1)) and logic "0" (1 (0)). Depending on the current combinations or the resulting currents and thus magnetic fields across the magnetoresistive element 2, the magnetization of the soft magnetic layer and thus the change in the voltage U from logical "0" to logical "1" is defined Logic circuit as 0R, NOR, AND or NAND function.

Once 1 (0), 1 (1), U (0) and U (l) are defined globally, then the switching behavior and specifically the coercive field strength H of the soft magnetic layer of the magnetoresistive element 2 define the function of the logic circuit. If H _{c is} small, so that a logical "1" at one of the inputs A, B is sufficient to switch from U (0) to U (l), then there is an OR function (switches the element from U ( l) according to U (0), there is a NOR function.) If H _{c is} so large that a logical "1" must be present at both logic inputs so that the magnetic field generated via conductor 3 is sufficiently large for the magnetoresistive element 2 and thus switches the voltage, there is an AND function (and accordingly a NAND function when switching from U (l) to U (0)). > UJ to bO P ¹ P>

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Function can be reprogrammed by the external magnetic field, reprogramming from a NAND to a NOR function is also possible, depending on the definition of the inputs and outputs.

This is expressed in the current-voltage curve by the fact that - see idealized in FIG. 2 - the hysteresis curve becomes narrower. The idealized switching curve is obtained if I _P = 0. If a current I _P = I ^{X is conducted} over the further conductor 4, the required switching current decreases, as indicated by the dashed line. If the sum of the two signals present at inputs A and B is still required for the solid curve (AND function), only a signal present at one of the inputs A or B is required to switch over according to the broken line.

The information as to whether the further conductor 4 is energized and thus a magnetic field H _P is to be applied or not is specified via a switching or control element 6, in the example shown an M-RAM memory cell 7. An amplifier element 8 serves for signal amplification in order to be able to control one or more logic inputs of other logic functions.

Below is an example of how the logic inputs and outputs can be defined to define NAND functions:

The logical inputs are defined:

logical "1": 1 (1) = 1 * logical "0": I (0) = - 0.5 I *

The logical outputs are defined:

logical "1": U {l) = Uι logical "0": U (0) = U ₀ . Before a logic function is carried out, the magnetoresistive element 2 must be brought into a defined initial state, a logic 0 being applied to both inputs in this exemplary embodiment (reset function). There is therefore a current of 1 (0) = -0.5 I * at both inputs. According to the above definition and the astroid switching behavior described with reference to FIG. 2, it follows that if I _P = 0 there is a NAND function, if I _P = I ^{λ there} is a NOR function.

3 shows a further embodiment of a logic circuit 9 according to the invention. In this respect, it corresponds to the logic circuit according to FIG. 1, but here a second magnetoresistive reference element 2 ^{X is} provided, above which a conductor 3 also runs in an electrically insulated manner, so that also this reference element 2 'is switched with a magnetic field like the actual measuring element 2. Via the magnetoresistive reference element 2', in which a constant current 1 (0) is also present, a reference voltage U _{R is} tapped in the same way ideally, in the range ≤ U _max U _R <U _m i _n, said U _max, U _m i _n the maximum and minimum voltage drop across the element 2 in stream 1 (0).

In summary, it should be noted that the invention specifies a field-programmable logic circuit arrangement that requires considerably fewer elements and can therefore be built up on a smaller area on a wafer. Furthermore, its function can be switched over at any time in a simple manner. Switching takes place in a rotation process that allows faster signal processing.

Claims

claims

1. logic circuit arrangement with at least one magnetoresistive element to which a conductor with at least two signal connections is assigned, by means of which a magnetic field acting on the magnetoresistive element can be generated in the current-carrying state, by means of which the magnetization of a soft magnetic layer of the magnetoresistive element can be switched over, characterized in that means are provided for generating a further magnetic field (H _p ) which is essentially perpendicular to the magnetization of the soft magnetic layer.

2. Logic circuit arrangement according to claim 1, so that the means comprise at least one further current-carrying conductor (4).

3. Logic circuit according to claim 2, so that the further conductor (4) is dimensioned and arranged in such a way that the magnetic field that can be generated by it acts essentially homogeneously on the magnetoresistive element (2).

4. Logic circuit arrangement according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that one or more magnetoresistive elements (2) is assigned a magnetoresistive reference element (2 ') with its own assigned means.

5. Logic circuit arrangement according to one of the preceding claims, characterized in that the means is assigned a switching or control element (6) via which the generation of the further magnetic field (H _p ) can be controlled.

6. Logic circuit arrangement according to claim 5, which also means that it is a switching or control element with non-volatile stored control information.

7. Logic circuit arrangement according to claim 5 or 6, that the switch or control element (6) is an MRAM memory cell (7).

8. Logic circuit arrangement according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the means for generating a low bias magnetic field, which acts essentially continuously on the magnetoresistive element, and a higher magnetic field is formed.

9. Logic circuit arrangement according to one of the preceding claims, d a d u r c h g e k e n n z e i c h - n e t that a magnetoresistive element (2, 2 ') is associated with an amplifier element (8).

10. Logic circuit arrangement according to one of the preceding claims, characterized in that it comprises a plurality of magnetoresistive elements (2) arranged in an array-like manner and optionally reference elements (2 ') with assigned conductors (3) and further conductors (4) and optionally amplifier elements ( 8).

11. Logic circuit arrangement according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the magnetoresistive element (2) or reference element (2 ') is a GMR or a TMR element.

12. Logic circuit according to one of claims 2 to 11, characterized in that the means several more, the magnetoresistive element (2) zu- orderly, superimposed and / or juxtaposed and electrically insulated conductors.

13. Logic circuit according to one of claims 2 to 12, d a d u r c h g e k e n n z e i c h n e t that the current lines of the magnetoresistive element serve as further conductors.

14. Logic circuit according to one of the preceding claims, so that the hard magnetic reference layer of a magnetoresistive element can be remagnetized via the field that can be generated when the conductor is energized with the signal connections, if necessary.