WO2000059051A1

WO2000059051A1 - Microelectronic device with tunnel junctions, memory network sensor comprising such devices

Info

Publication number: WO2000059051A1
Application number: PCT/FR2000/000648
Authority: WO
Inventors: Kamel Ounadjela; Michel Hehn
Original assignee: Universite Louis Pasteur (Etablissement Public A Caractere Scientifique, Culturel Et Professionnel)
Priority date: 1999-03-31
Filing date: 2000-03-16
Publication date: 2000-10-05
Also published as: AU3299400A; FR2791814A1

Abstract

The present invention relates to a microelectronic device with tunnel junctions in addition to a memory network and a sensor comprising such devices. The microelectronic device has three electric connection terminals and is formed by stacking two magnetoresistive tunnel junctions, whereby each junction consists of two conducting electrodes (1,3; 3,5) separated by a layer of insulating material (2 or 4) forming a tunnel barrier. Said stack has a median electrode (3) that is common to both junctions. The inventive device is characterized in that it comprises one electrode (1,3 or 5) made from a magnetic or semi-magnetic material and at least one second electrode (1,3 or 5) made from a magnetic or semi-magnetic material or at least one tunnel barrier (2 or 4) in the form of a tunnel barrier that filters electron spins, whereby each electrode (1,3,5) made from a magnetic material or semi-magnetic material has its own coercitive field.

Description

Microelectronic device with tunnel junctions and memory array and sensor comprising such devices

The present invention relates to the field of electronic circuits, in particular integrated circuits, and relates to a microelectronic or nanoelectronic device, in particular of the transistor type, with tunnel junctions, as well as memories or sensors integrating at least one such device.

The miniaturization of electronic devices as well as the increase in their density of integration have not stopped increasing for several years. Limited at first by the techniques of microelectronics, the reduction in the size of the components should come up against a much more fundamental, unavoidable limit in the years to come, beyond which the functioning of traditional components becomes obsolete. This limit, fixed by quantum mechanics, is reached when the mean free path of the electrons is equal to or greater than the characteristic lengths of the device. Thus, the operation of conventional MOSFET transistors Si, for example, will be disturbed when the length of the gates becomes less than 50 nm.

Instead of circumventing these difficulties, these quantum effects were first used to produce logic circuits with high integration density (for example Coulomb blocking devices). However, these new devices are, on the one hand, confronted with the current limits of lithography techniques which do not allow the manufacture of systems operating at ambient temperature and, on the other hand, limited to the storage of information only. In order to provide the other logical functions necessary for the development of sub-micronic electronics, and to circumvent the limits of the resolution of mass production lithography techniques, research has focused on hybrid components for which metals have been integrated in the active areas of the component, other than the polarization of a grid. Thus, the geometry of the components could be modified and the quantum effects could be bypassed, on the one hand, the electron then no longer moves in the plane of the hetero-structure but perpendicular to this plane and, from on the other hand, by the use of metallic materials, its average free path is approximately ten times smaller.

The new generation of transistors, resulting from this modification, is generally based either on the use of a Schottky Metal / Si tunnel diode whose height is modulated by the application of a grid voltage, or by two Schottky diodes Si / Metal / Metal / Si for which the transmission is regulated by the ratio of the bias voltages of the Si / Metal diode and of the Si / Si assembly.

Nevertheless, the possibilities of evolution of this type of systems are limited, on the one hand, by the need to use a semiconductor composed of a single crystal and, on the other hand, by the reduced range of height and barrier width accessible at the Semiconductor / Metal interface.

Apparently, some of these limitations have been removed by replacing the semiconductor with an insulator and by stacking two tunnel diodes composed of a single crystal (cf. S. Muratake et al, Electronics Letters 28, 1002; 1992). Tests carried out at low temperature on a structure of the Metal / Insulator / Metal / Insulator / Metal type have shown the existence of a transistor effect linked to the tunnel transport of hot electrons from one diode to another.

So far, these achievements have however been limited by controlling the growth of insulating layers whose thickness must be of the order of a few nanometers.

In addition, in the example cited above, the barrier must be composed of a single crystal to maintain a significant barrier height, which limits the number of metals which can be used as electrodes and the number of insulators which can be used as a barrier.

In addition, for several years, a new category of components has emerged with the emergence of a new discipline: spin electronics. Coming from research on metallic thin films, giant magneto-resistance (MRG) systems aroused keen interest as soon as they were discovered by the fields of applications they open up, particularly in the field of read heads and storage. of data. Reduced to its simplest expression, such a system consists of two thin ferromagnetic metallic layers separated by a non-magnetic metallic layer. According to the relative orientation of the magnetizations of the two ferromagnetic layers, the probability of transmission of the electrons will depend on the orientation of their spin. Passing a configuration of parallel antiparallel magnetization, induced by the application of an external magnetic field, results in a variation in resistance (or magnetoresistance) of more than 50% at room temperature.

The use of the electron spin is at the origin of the development of new "transistor" type devices, the oldest of which, composed only of metallic layers, was proposed by M. Johnson (Science 260, 320 , 1993).

However, the possibilities of application of the “all metal transistor” developed by Mr. Johnson are reduced given the amplitude of the signals and the impedance of the system and its use is limited essentially to logic electronics.

More recent types of transistors have been developed from two Schottky Si / Metal / Metal / Si diodes where the metal layer has been replaced by a magneto-resistive multilayer (MC) (cf. DJ. Monsma et al, Phys. Rev. Lett. 74, 5260; 1995). The transmission can then be regulated by the ratio of the bias voltages of the Si / MC diode and of the Si / Si assembly, but also by modifying the relative orientation of the magnetizations of each magnetic layer.

However, the performance of this type of structure seems to be very limited. Indeed, obtaining crystalline growth of semiconductors on a magnetic metal, necessary for obtaining Schottky barriers, is far from being controlled to date.

To overcome this crucial step, the manufacturing method proposed by D.J. Monsma et al. consists in bonding under ultra-vacuum two Si substrates each covered with a multilayer deposit. However, this technique is not suitable for mass production and becomes a major constraint for the development of such a transistor.

On the other hand, in order to limit all the parasitic leakage currents to allow a maximum rate of variation (depending on the temperature and the nature of the materials of the multilayer), the implementations and the tests were carried out at 77K with a Co / Cu multilayer, thus limiting the operating range of the transistor obtained and maximizing the variation of the signal. The other limitations formulated above for the Si / Metal / Si transistor are also applicable for this latter development. Finally, we also know the Magneto Tunnel Junctions.

Resistives (JTMR). In its most simplified form, a JTMR consists of two ferromagnetic electrodes having different coercive fields separated by an insulating barrier (see in particular US-A-5,640,343 and US-A-5,650,958). Its operation takes advantage of the asymmetry of the density of states of the energy bands of the electrons of spin +1/2 and spin -1/2 of a ferromagnetic material. By neglecting the diffusion of spins, the tunnel probability of a polarized electron depends on the relative orientation of the magnetizations of the layers. In the parallel configuration, there is a maximum agreement between the number of states occupied in one electrode and the number of states available in the other; the tunnel current is therefore maximum. On the contrary, in the antiparallel configuration, the tunnel effect takes place between majority states in one electrode and minority states in the other. This variance implies a minimum of current and therefore a maximum of resistance. This new hybrid technology, combining metallic materials with insulating materials, makes it possible to increase the performance of junctions while retaining a high and adjustable magnetoresistance (60% for CoFe electrodes) dependent on the relative orientation of the magnetization of the two. electrodes.

The transport process in such junctions is enriched by tunnel transport which makes it possible to increase the resistance of the element, varying from a few ohms to a few MΩ, and therefore the measured signals can reach a few tenths of a Volt. Since the probability of tunnel transmission in a tunnel junction depends exponentially on the height and width of the tunnel diode, a small change in the shape of the barrier, induced by a slight change in the bias voltage, can cause a big change in the transmitted current.

However, the embodiments proposed to date on the basis of magneto-resistive tunnel junctions relate only to two-terminal components such as in particular diodes, magnetic field sensors or memory cells, applications in which they are substituted for current structures without however making an advantageous constitutive modification.

The present invention aims in particular to overcome the aforementioned drawbacks. For this purpose, its main object is a microelectronic device with three electrical connection terminals, formed by a stack of two magneto-resistive tunnel junctions, each of which is composed of two conductive electrodes separated by a layer of insulating material forming a tunnel barrier, said stack having a central electrode common to the two junctions, characterized in that it comprises, on the one hand, an electrode made of a magnetic material or half -metallic (material whose magnetic polarization is equal to 100%) and, on the other hand, either at least a second electrode made of a magnetic or semi-metallic material, or at least one tunnel barrier in the form of tunnel barrier filtering the spins of electrons, each electrode of a magnetic or semi-metallic material having its own coercive field.

The present invention also relates to a transistor in the form of a microelectronic device as described above, the gain of which is controlled by means of the bias voltages applied to its different electrodes and / or by the intermediate the orientations of the respective magnetizations of each magnetic or semi-metallic electrode.

The present invention also relates to an elementary memory cell which may have two or more magnetic states, characterized in that it is constituted by a microelectronic device, the information being stored in the form of determined orientations of the magnetizations of the electrodes 1, 3, 5 in a magnetic or semi-metallic material or in the form of determined orientations of the magnetizations of the electrodes 1, 3 or 5 with respect to a spin filter barrier.

Finally, the present invention also relates to an array of elementary memories, characterized in that it consists of a set of elementary memory cells of the aforementioned type connected to each other and to external control circuits 6, 7, 8 by means a network of transmission lines 6 ′, 7 ′, 8 ′ making it possible to apply a particular polarization to each of the electrodes 1, 3, 5 of each of the elementary memory cells in order to read the information stored in each of them.

The invention will be better understood from the description below, which relates to preferred embodiments, given by way of nonlimiting example, and explained with reference to the appended schematic drawings, in which: FIG. 1 is a schematic representation of a microelectronic device according to the invention used as a magnetic transistor with tunnel junctions in a common emitter assembly; FIG. 2 is a schematic representation of the potential profile seen by the electrons inside the device of FIG. 1 when it is subjected to the electrical connections for a mode of operation as a common emitter; FIGS. 3A and 3B are schematic representations of the device of FIG. 1 and of the potential profile and of the corresponding simplified band structure seen by the electrons inside the transistor when the electrodes of the base / collector tunnel diode are composed of a semi-metallic material whose polarization is 100%, the figures showing the evolution of the strip structure as a function of the relative orientation of the magnetizations of the two electrodes (base, collector) for a respectively parallel configuration (figure 3A) and anti parallel (Figure 3B); FIGS. 4A and 4B are schematic representations of the device of FIG. 1 and of the potential profile and of the corresponding simplified band structure seen by the electrons inside the transistor when the electrodes of the emitter / base tunnel diode are composed of a semi-metallic material whose polarization is 100%, the figures showing the evolution of the strip structure as a function of the relative orientation of the magnetizations of the two electrodes (emitter, base) for a respectively parallel configuration (figure 4 A) and anti parallel (Figure 4b); FIGS. 5A and 5B are schematic representations of the device of FIG. 1 and of the potential profile and of the corresponding simplified band structure seen by the electrons inside the transistor when the emitter and collector electrodes of the transistor are composed of a semi-metallic material whose polarization is 100%, the figures showing the evolution of the strip structure as a function of the relative orientation of the magnetizations of the two electrodes (emitter, collector) for a respectively parallel configuration (FIG. 5A) and anti parallel (Figure 5B); FIG. 6A is a schematic representation of a matrix of random access magnetic memories composed of microelectronic devices according to the invention; Figure 6B is a schematic view on a different scale of the detail X in Figure 6 A; FIG. 6C represents the potential profile of a memory cell of FIG. 6A waiting to read information; FIG. 7A is a schematic representation of a memory matrix similar to that represented in FIG. 6A, the cells of which have been identified by numbering; FIG. 7B represents the potential profile of the memory cell 14 of the matrix shown in FIG. 7 A during an operation of reading the latter; FIGS. 7C to 7E represent the potential profiles of the other memory cells of the matrix of FIG. 7 A during the read operation of cell 14; FIG. 8 represents the matrix of FIG. 7A during a write operation relating to the cell referenced 14; FIG. 9 is a side elevation view of a multilayer structure constituting the starting point for the production of a microelectronic device according to the invention, and, FIGS. 10A to 10E represent the successive stages of lithography and of etching carried out on the multilayer structure of FIG. 9 to lead to a microelectronic device according to the invention, each of said FIGS. 10A to 10E comprising a top view and a side elevation view, and, FIG. 10F is a top view through the mask used for the current step, the pattern of which is shown in hatching of the device shown in FIG. 10E after depositing the electrical connections at the electrodes. According to the invention, and as shown in particular in Figures 1 to 6, 9 and 10 of the accompanying drawings, the microelectronic device with three electrical connection terminals is formed by a stack of two magneto-resistive tunnel junctions, each of which is composed two conductive electrodes 1, 3; 3, 5 separated by a layer of insulating material forming a tunnel barrier, said stack having a middle electrode 3 common to the two junctions. This device is characterized in that it comprises, on the one hand, an electrode 1, 3 or 5 made of a magnetic or semi-metallic material and, on the other hand, either at least a second electrode 1, 3 or 5 made of a magnetic or semi-metallic material, or at least one tunnel barrier 2 or 4 in the form of a tunnel barrier filtering the spins of electrons, each electrode 1, 3, 5 in a magnetic or semi-metallic material having its own coercive field . The electrodes 1, 3 and 5 can be made of a conductive material whose crystalline quality is arbitrary (crystalline, textured or amorphous), the first electrode 1 (lower in the stacking structure) being deposited directly on a substrate or a buffer layer, possibly multilayer, of any crystalline quality, the second electrode 3 (middle) being deposited on the first insulating layer

2 forming a tunnel barrier directly in contact with the latter and the third electrode 5 (upper in the stacking structure) being deposited on the second insulating layer 4 forming a tunnel barrier, directly in contact with the latter.

The first and second tunnel barriers 2 and 4 are made of insulating materials whose respective crystalline qualities are arbitrary (crystalline, textured or amorphous) and are deposited directly in contact on the layers forming corresponding electrodes 1 and 3. These layers 2 and 4 forming a barrier can be formed by depositing an insulating material or by depositing a conductive material rendered insulating by a subsequent treatment, the choice of the material and of the treatment depending on the characteristics desired for the insulating barrier considered (height , width). The entire multilayer structure forming the microelectronic device according to the invention may be coated with protective layer (s) against chemical and or mechanical alterations and to preserve the properties of the different layers during the subsequent treatment steps. According to a first embodiment of the invention, allowing in particular a transistor type operation, the middle electrode 3 of the microelectronic device advantageously has a thickness less than or equal to the limit value e \ allowing the electrons coming from one of the two other electrodes 1 or 5 to pass to the other of said two other electrodes 1 or 5 while retaining an energy greater than that of the Fermi level of said median electrode 3.

When this latter arrangement is verified, the electrodes 1,

3 and / or 5 can be polarized so as to obtain a transistor type operation allowing the amplification of a current injected into one of the electrodes 1, 3, 5 by an artificial current source formed by the polarization of one of the two tunnel junctions 1, 2, 3; 3, 4, 5, the operating conditions also being controlled by the guidelines respective magnetizations of magnetic or semi-metallic electrodes 1, 3 and / or 5.

In operation in common emitter mode and for given electrode voltages, the gain of the transistor and the maximum injected current are controlled and, if necessary, preprogrammed in a non-volatile manner, by means of the orientation of the magnetizations of the different magnetic or semi-metallic electrodes 1, 3, 5 under similar or reverse conditions, parallel or anti-parallel.

The operation of the transistor proposed above is based on the transport mechanism of the magnetic tunnel junctions. A spin-polarized tunnel current, pumped from a first tunnel diode by the application of a bias voltage across its terminals, is injected into the second diode, physically separated from the first by a thin metallic layer a few nanometers thick. or equal to ej (middle electrode 3). The electrons then behave like "hot electrons" whose energy is a function of the polarization voltages of the first and / or of the second diode. The transmission of spin-polarized electrons from the first diode to the second, i.e. the gain of the transistor, is controllable not only by the polarization voltages but also by the relative orientation of the magnetizations of each magnetic electrode or semi-metallic.

The possibilities of making transistors offered by the association of tunnel tunnel junctions are much more extensive than those proposed so far. Indeed, in such structures, the different layers do not need to be deposited epitaxially, which makes it possible to avoid the limitations linked to the crystal growth of a metal on a semiconductor or vice versa. This results in a possibility of arbitrary choice of the substrate (the silicon could be perfectly adapted, which allows the use of current microelectronics technologies for mass manufacturing) but also that of the different materials that make up the electrodes of the two tunnel diodes and barriers.

In the context of the invention, the Schottky barrier, requiring the use of a semiconductor composed of a single crystal, is replaced by a tunnel barrier which can be composed of polycrystalline or amorphous material. The free choice of the material making up the barrier makes it possible to modify the height of the barrier at will and to adjust the maximum operating temperature of such a microelectronic device. This the latter will no longer be limited by the lateral size of the active part of the component as is the case in other nano-electronic devices. In addition, the combination of a metal and an insulator is generally considered to be a good candidate for producing electronic devices with ultra fast response.

The different possibilities of constituting the microelectronic device described above will therefore make it possible to achieve different variants of hardware, some of which are described below in relation to operation in transistor. Thus, according to a first alternative embodiment, the emitting electrode 1 of the junction 1, 2, 3 is composed of a non-magnetic conductor and the other two electrodes 3 and 5 of the junction 3, 4, 5 are composed of a magnetic or semi-metallic conductor or a combination of the two with different coercive fields. The spin selection then takes place in junction 3, 4, 5 (Figure 3).

According to a second alternative embodiment, the emitting electrode 1 of the junction 1, 2. 3 as well as the collecting electrode 5 of the junction 3, 4, 5 are composed of a magnetic or semi-metallic conductor or a combination of two different coercive fields and the base electrode 3 is composed of a non-magnetic conductor. The spin selection then takes place at junction 3, 4, 5 (Figure 5).

According to a third alternative embodiment, the emitting electrodes 1 and base 3 of the junction 1, 2, 3 are composed of a magnetic or semi-metallic conductor or of a combination of the two of different coercive fields and the collecting electrode 5 is composed of a non-magnetic conductor. The spin selection is then made in junction 1, 2, 3 (Figure 4).

According to a fourth alternative embodiment, the three electrodes 1, 2, 3 are composed of a magnetic or semi-metallic conductor or of a combination of the two of different coercive fields. The spin selection is then made in the two junctions 1, 2, 3 and 3, 4, 5.

According to a fifth alternative embodiment, not shown in the accompanying drawings, it can also be provided that a pair of electrodes of a given junction is replaced by a pair (insulating barrier spin filter / electrode composed of a magnetic conductor or semi metallic), the barrier being in contact with a conductive electrode. The selection of spin then operates in the insulating barrier couple spin filter / electrode composed of a magnetic or semi-metallic conductor.

As Figure 1 illustrates, the transistor, formed of a microelectronic device according to the invention, is composed of two tunnel junctions or tunnel diodes stacked one on the other (diode n ° 1 = 1, 2, 3 and diode # 2 = 3, 4, 5). Each diode is composed of a pair of conductive electrodes, namely, (1, 3) for the diode n ° 1 and (3, 5) for the diode n ° 2, each pair of electrodes being separated by a barrier insulating (2 for diode n ° 1 and 4 for diode n ° 2). Depending on the type of transistor and the desired structure, at least two electrodes (1 and 5 or 3 and 5 or 1, 3 and 5) are composed of conductive materials allowing the spin polarization of the electrons during their passage through said electrodes ( magnetic or semi-metallic material) and having their own coercive field. The barriers 2 and 4, for their part, are composed of an insulating material which may possibly behave like a spin filter (in this case only a spin polarizing electrode is necessary). One of the essential parameters for the operation of the transistor relates to the thickness of the electrode 3 which must be sufficiently thin (of thickness less than or equal to ej) to allow the electrons emitted by the first barrier to remain hot (the hot electrons are sensitive to the densities of states above the Fermi level).

Electrical contacts 6 ', 7' and 8 'are taken on the electrodes (1, 5 and 3 respectively) in order to be able to apply a potential difference between the electrodes 1 and 3 (voltage generator 10) and the electrodes 1 and 5 (voltage generator 1 1) but also for connecting the transistor and inserting it into an electronic circuit. For measurement purposes, current indicators 9 and 12 can be inserted into the circuit in order to measure the electric currents and determine the amplification coefficients of the transistor. In addition, FIG. 1 also schematically shows means 13 making it possible to modify the magnetic state of each magnetic electrode 1, 3, 5 using either an external magnetic field or a magnetic field created by the passage of a current in a network of wires integrated on the transistor. The selection of the electrode to be modified is made using its particular coercive field. This modification leads to the variation of the impedance of the junction (s) 2, 4 whose electrodes are made of a material with magnetic properties. We will now describe, by way of illustrative examples and on the basis of FIGS. 2 to 5, different possibilities for implementing the microelectronic device according to the invention as a transistor in a mode of operation as a common emitter and or as switching. FIG. 2 shows the potential profile seen by the electrons inside the structure when it is subjected to the potential differences 10 and 11 around the operating point in the absence of a particular magnetic field at the level of the electrodes. This operating point will be chosen according to the heights and widths of the two barriers 2 and 4 tunnel, therefore of the materials used for the realization of these barriers. In FIG. 2, one can recognize the potential barriers linked to the presence of the insulating layers 2 and 4. The emitter / base diode 1, 2 and 3 is polarized directly using 10. It behaves like a source current whose flow is controlled by 10, 13 as well as the intrinsic parameters of the junction namely its height and its width. The base / collector diode 3, 4 and 5 is slightly reverse biased using 1 1 in order to limit the current I ^ which goes from 3 to 5 and from 5 to 3.

If the thickness of the base 3 is fairly thin (of the order of a few nanometers), the electrons from the emitter / base junction 1, 2 and 3 conserve their energy as the base passes. At the entry of the base / collector junction 3, 4 and 5, their energy, compared to the Fermi level of base 3, is equal to ex N _e b and these energetic electrons are generally designated by "hot electrons". The average potential that they encounter during the passage of the base / collector diode 3, 4 and 5 will therefore be reduced by the quantity ex N _e b relative to the electrons coming either from base 3 directly or from collector 5. This potential medium, equal to Φ ^ _c - (e / 2) x (Nec ⁺ eb) [Φbc corresponding to the intrinsic barrier height of the second tunnel junction] is small and allows a large transmission compared to that of the electrons injected into the base who see an average barrier height greater than Φ ^ c ⁺ (e / 2) x (V _e ^ - V _ec ). However, a variation of the base current I5 leads to a variation of the voltage V _ec . For a fixed voltage N _e b, the transmission of hot electrons will strongly change because it varies exponentially with Φ _DC - (e / 2) x N _ec . The current 1 ^ always remaining low, a small variation of l _j leads to a strong variation of the transmission of hot electrons and therefore a large variation of the current I _c , injected into the collector 5. Thus, the basic current Ib is amplified, the amplification coefficient depends on the characteristics of the two tunnel junctions 2 and 4 and for a given pair of junctions, it depends on the operating point, that is to say the bias voltages.

According to a second embodiment of the invention, the electrodes 1, 3 and 5 of the microelectronic device can be polarized so as to obtain switching operation, the middle electrode 3 possibly having a thickness greater than the thickness value limit e \ allowing the electrons coming from one of the two other electrodes 1 or 5 to transit to the other of the said two other electrodes 1 or 5 while conserving an energy higher than that of the Fermi level of said median electrode 3.

Indeed, the operation of the non-magnetic transistor in switching is made possible by the selective polarization of the three electrodes 1, 3, 5 of the device. In this particular application, the electrons injected into the base can be thermalized there. The relaxation of this constraint makes it possible to increase the thickness of the layer 3 constituting the base and to reduce the technological problems linked to making contact on this layer.

The implementation of a switching transistor consists in allowing or blocking the passage of information. It is possible, by playing on the polarizations of the electrodes, to allow the selective passage of a signal injected into the base, either in the emitter or in the collector.

This operating mode is described in more detail below with reference to FIG. 2.

When N _e b is placed at a positive polarization + N and V _ec at a polarization + 2xN, a signal injected into the base 3 (for example a current pulse) is transmitted only in the collector 5.

Conversely, when N _e b is placed at a negative polarization -N and N _ec at a negative polarization -2xV, a signal injected into the base 3 (for example a current pulse) is transmitted only in the transmitter 1 .

From the point of view of the signal injected into the base 3, the device according to the invention behaves like an open or closed door for transmission.

FIGS. 3 to 5 of the appended drawings illustrate the operation of the device according to the invention as a transistor in common emitter mode, influenced by the application of particular magnetic fields at the level of some of the electrodes 1, 3, 5. To describe the operation of the transistor under the influence of a magnetic field, it is necessary to take into account the band structure of the magnetic material which is used for each electrode 1, 3, 5. In order to simplify the understanding of the operation of the transistor under magnetic field, only structures of strips of semi-metallic materials whose magnetic polarization is equal to

100%. For such a material, the Fermi level is inside the minority spin band (24a for example) while the majority spin band (23a for example) is completely filled. The operating principle shown diagrammatically in FIGS. 3, 4 and

5, takes up the previous concept taking into account the state densities linked to the magnetic character of the electrodes. It should be noted that the operation which is described herein can be adapted to any material for which the band structures of the electrons of spin +1/2 ("spin up") and spin -1/2 ("spin down") ) are offset from each other. The operating points will then be chosen in order to obtain the greatest current variation.

Figures 3 to 5 of the accompanying drawings show different simple configurations which highlight the contribution of magnetism for additional functionality. The different functionalities are mentioned separately for the sake of clarity.

1) Variation of current amplification (Figures 3 and 5)

In this first example, the electrode 1 is made of a material which does not have asymmetry in its strip structure. The state densities of the spin + 1/2 21a and spin -1/2 22a electrons are identical. In the tunnel process, only electrons that find a place in base 3 are allowed to cross the barrier. Thus, by neglecting the diffusion of the spins, only the electrons coming from the band 22a pass through the band 24a. Base 3 acts as a spin filter for the hot electrons that will be injected into the second barrier and in base 3, the conduction electrons will all have a spin - 1/2.

In the parallel magnetization configuration (Figure 3A), the hot electrons, injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic base 3, find states available in the band 26a of the collector 5. The current of hot electrons transmitted in collector 5, amplifier of the basic current, is maximum in this magnetic configuration. In the anti-parallel magnetization configuration (Figure 3B), the hot electrons, injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic base 3, do not find a state available in the band 26b of the collector 5. Indeed, the band of spin electrons -1/2 26b is completely filled. The current of hot electrons transmitted in the collector 5, amplifier of the base current, is then reduced according to the relative orientation of the magnetizations of the base 3 and of the collector 5 and can be canceled for an anti-parallel orientation of the magnetizations. In this model with simplified band structures, the operation of the transistor according to the invention can be disturbed by the band structure of the base electrode 3. In fact, given the limited extension of the band of spin electrons - 1/2 24a, it is possible that, for a high bias voltage of the emitter / base junction (1. 2 and 3), the electrons injected from the emitter 1 do not find an available state in the base 3 because of their great energy.

In order to overcome this limitation, it is possible to favor the configuration described in FIG. 5 for which the emitter is made of a magnetic material and the base electrode is not magnetic but retains the spin of the hot electrons. The electrode 1 is then composed of a magnetic material which has an asymmetry in its band structure. Only the spin electrons -1/2 24a are injected into the band 22a of the base 3. These electrons find an available space in the base 3 and, given its small thickness compared to the spin diffusion length, retain the memory of their spin at the entrance to the barrier 4.

In the parallel magnetization configuration (FIG. 5A), the hot electrons, injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic emitter 1, find states available in the band 26a of the collector 5. The current of hot electrons transmitted in the collector 5, amplifier of the basic current, is maximum in this magnetic configuration.

In the anti-parallel magnetization configuration (Figure 5B), the hot electrons, injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic emitter 1, do not find an available state in the band 26b of the collector 5. Indeed, the band of spin electrons - 1/2 26b is completely filled. The electron current heat transmitted in the collector 5, amplifier of the basic current, is then zero. It can however be modulated by adjusting the relative orientation of the magnetizations of the emitter 1 and of the collector 5.

2) Variation of the maximum injected current (Figure 4) In this second example, the electrode 5, that is to say the collector, is made of a material which does not have asymmetry in its band structure. The state densities of the spin +1/2 21a and spin -1/2 22a electrons are identical. The other two electrodes, the emitter 1 and the base 3, are made of a material with an asymmetrical band structure. In the parallel magnetization configuration (FIG. 4A), the electrons, injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic emitter 1, find states available in the band 26a of the base 3. The limit current of hot electrons, transmitted in the collector 5, amplifier of the base current, is then maximum. In the anti-parallel magnetization configuration (Figure 4B). the electrons injected by the emitter / base diode (1, 2 and 3), polarized at 100% in the magnetic emitter 1. do not find an available state in the band 26b of the base 3. The electron limit current hot, transmitted in the collector 5, amplifier of the basic current, is then zero. It can however be modulated by adjusting the relative orientation of the magnetizations of the transmitter 1 and of the base 3.

3) Variation of the amplification of the current and the maximum injected current

The two functions described in the preceding paragraphs 1) and 2) can be combined in a single transistor device by using, for each electrode, a material with asymmetrical band structure. In this case, it will be possible, by adjusting the relative orientations of the magnetizations of each electrode, to modulate either the amplification of the current, or the maximum injected current, or both at the same time.

Of course, other configurations of polarization of the electrodes of the transistor device according to the invention, known to those skilled in the art, can be envisaged, in particular the modes of operation of the transistor in common base or common collector. For the sake of simplicity, the operation of the device according to the invention as a transistor has been described above in the case of the use of particular materials. Indeed, in more general cases, for example with ferromagnetic materials whose polarization is not 100%, the effects described above are verified with a lower intensity, in particular because the maximum currents injected as well as the amplification factors cannot be reduced to zero. However, modulation remains possible and strongly depends on the band structure of the materials chosen.

Furthermore, in addition to the characteristics of the strip structures of the materials constituting the electrodes described above, it is also possible to modify, in addition to the heights and widths of the barriers 2 and 4, the magnetic properties of said barriers.

It is for example possible to use, as already indicated previously, tunnel barriers which filter the spins of the electrons. In this case, and in particular for the above-mentioned examples, it is possible to replace a pair of magnetic electrodes separated by any insulating barrier with a spin filter barrier / magnetic electrode pair where the barrier is in contact with any conductive electrode.

It is also possible to use the microelectronic device according to the invention for the production of non-volatile programmable electronic components and, as already indicated above, of transistors operating in switching mode.

In the case of the use of conventional ferromagnetic metals, the control by the base of the current emitted in the collector does not allow a variation of current as important as indicated above. In particular, the collector current cannot be completely reduced to zero. This limitation can be taken advantage of to produce transistors whose gain is programmable and non-volatile.

Indeed, it must again be emphasized that the relative orientation of the magnetizations of the magnetic electrodes only depends on the magnetic history of the junction considered. This orientation is retained when the component is powered down. The gain of the transistor can then be increased or decreased simply by modifying the relative orientation of the magnetizations of the magnetic electrodes.

However, when the difference between the currents emitted in the collector in the different possible magnetization configurations is quite large, which is undoubtedly the case in the examples cited above, a two-state logic can be defined. According to the orientation relative magnetizations of magnetic electrodes (parallel or anti parallel), the collected current will be modified. The two states of this current can be associated with a passing and blocked state of the transistor and the microelectronic device then behaves like a transistor operating in switching mode.

The present invention also relates to an elementary memory cell which can have two or more magnetic states, characterized in that it is constituted by a microelectronic device as described above, the information being stored in the form of determined orientations of the magnetizations of the electrodes 1, 3, 5 of a magnetic or semi-metallic material, the information being read by selective polarization of the electrodes 1, 3, 5 of said cell (FIGS. 6A and 6B) or in the form of 'determined orientations of magnetizations of electrodes 1, 3 or 5 with respect to a spin filter barrier. As shown in Figure 8 of the accompanying drawings, the writing in this cell is carried out by sending a current pulse in a transmission line 8 'connected to the central electrode 3 forming the base and in one or more transmission lines 6' and / or 7 ′ connected to electrodes 1 and / or 5 forming an emitter and / or collector, the electrode 3 forming a base preferably having an easy magnetization axis perpendicular to the transmission line 8 ′ which is connected to it.

The invention also relates, as shown in particular in Figures 6 to 8 of the accompanying drawings, a network of elementary memories, characterized in that it consists of a set of elementary memory cells of the aforementioned type connected together and to external control circuits 6, 7, 8 by means of a network of transmission lines 6 ', 7', 8 'making it possible to apply a particular polarization to each of the electrodes 1, 3, 5 of each of the elementary memory cells to read the information stored in each of them. Advantageously, the external control circuits

6, 7, 8 are adapted to simultaneously send, to any of the elementary memory cells, current pulses through the transmission lines 6 ′, 7 ′, 8 ′ connected to the three electrodes 1, 3, 5 of the elementary memory cell concerned, so as to concomitantly generate a magnetic field in the vicinity of the magnetic layers, forming part of said cell, whose intensity and orientation are such that it results in a modification of their magnetic state, without affecting the state of the magnetic layers of the surrounding cells.

The invention finds a particularly advantageous application in the production of random access magnetic memory arrays (abbreviated to MRAM), composed of a plurality of microelectronic devices or of a plurality of elementary memory cells of the type described above.

As indicated previously, the stored information is coded by means of the relative orientation of the magnetic moment of one or more electrodes 1, 3, 5. This information is stable and non-volatile and it is therefore possible to dispense with refreshing the capacities necessary for conventional DRAM type memories.

In addition, and above all, the possibility of selective polarization of the three electrodes of each cell makes it possible to get rid of the diode put in series with each memory cell in all the architectures of MRAM proposed to date. This diode, essential to avoid leakage currents in memory cells close to that active for reading, is currently made of semiconductor material. The proper functioning of this diode requires a large diode surface and thereby limits the density of current MRAMs. Replacing the diode / elementary cell pair with the microelectronic device according to the invention overcomes the use of the diode and therefore pushes the current limits of storage density using magnetic memories. The device according to the invention being made up of two junctions stacked one on the other, it allows a considerable saving of space compared to conventional semiconductor memories where the various components of the memory are juxtaposed on the same plane.

In addition, each memory cell is made up of two stacked junctions whose resistance can be adjusted from a few Ohms to a few million Ohms depending on the characteristics of the junctions and these high resistances make it possible to create memories with low current consumption.

In addition, in a high density matrix embodiment, the use of the three electrodes makes it possible to overcome the problems of short-circuit intrinsic to the magneto-resistive memories, without introducing an additional diode or transistor expensive in space. Indeed, in substituting these components made of semiconductor materials by devices according to the invention, the surface of a memory cell is no longer imposed by the proper functioning of the cell but by the resolution of current lithography techniques. The use of the invention makes it possible to open up new perspectives for the storage of non-volatile data with high integration.

In addition, for this particular application, the electrons injected from the emitter into the base can be thermalized there. The relaxation of this constraint makes it possible to increase the thickness of the layer 3 constituting the base and to reduce the technological problems linked to making contact on this layer.

Before describing in detail the operation of the operations for reading and writing information in the aforementioned matrix network, it is preferable to define a possible composition of the transistor device used, by way of nonlimiting example.

Each active device forming a memory cell can operate by integrating one (in combination with a spin filter barrier). two or three magnetic electrodes, the main thing being to obtain a significant variation in the conductance according to the relative orientations of the magnetizations of the magnetic electrodes.

In the example described below, the electrodes 1 and 5 are made of a hard magnetic material with high coercivity having an asymmetry in their band structure. The base electrode 3, for its part, consists of a soft magnetic material having an asymmetry in its strip structure.

In the parallel magnetization configuration, the magnetizations of the three electrodes 1, 3 and 5 are aligned. According to the polarization states involved in the reading and writing processes, the electrons, injected by the emitter / base diode (1, 2 and 3) and polarized at 100%, in the emitter 1, find states available too both in the base 3 and in the collector 5. The limit electron current, transmitted in the collector 5, is then maximum. On the other hand, in the anti-parallel magnetization configuration, the magnetizations of the emitter 1 and collector 5 electrodes are anti-parallel, the electrons injected by the emitter diode polarized at 100%, do not find a state available in the base. The current transmitted in the base is then significantly reduced. Starting from this principle based on the variation in conductance linked to the relative orientations of the magnetizations of the three electrodes 1, 3 and 5, an example of application of the invention will be detailed below in a matrix of magnetic memories with random access ( MRAM). According to a preferred embodiment variant of the invention and as shown in FIGS. 6A, 7A and 8 of the appended drawings, each of said devices or each of said cells forming the MRAM is located at the intersection of three transmission lines 6 ', 7', 8 'isolated from each other, for example by oxide layers, the first 6' of which is part of the transmission lines connected to the electrodes 1 forming emitters, the second 8 'of which extends at 45 ° relative to the first, forms part of the transmission lines connected to the middle electrodes 3 forming bases and of which the third 7 ′, extending at 90 ° relative to the first, forms part of the transmission lines connected to the electrodes 5 forming collectors . In said FIGS. 6A, 7A and 8, the number of memory cells has been limited to nine for reasons of clarity and the cells subjected to identical potential differences bear identical reference numbers.

Thus, each memory cell is integrated into a network of conductive transmission lines 6 ', 7', 8 '; 15, 16, 17 which allow the selective polarization of its three electrodes 1, 3 and 5.

The emitters of the transistor devices forming memory cells are connected to the control circuit 6 of the transmitter lines 6 ', the collectors of the said transistor devices are connected to the control circuit 7 of the header lines 7', 17 and the bases of the said transistor devices are connected to the control circuit 8 of the lines of the bases 8 ′, 16. Since the relative orientation of the magnetizations of each electrode is independent of the polarization voltages, the stored information is retained even after the supply of the three electrodes is stopped 1, 3 and 5.

1) Reading of stored information

While waiting for the information to be read, all the memory cells made up of devices according to the invention are reverse biased (FIG. 6B): all the emitting lines 6 ′ of said cells are biased at a voltage -V volts, the lines of bases 8 'of said cells are biased at a voltage of 0 volts and all of the collector lines 7' of said cells are biased at voltage + V volts. This tension of polarization will be adjusted according to the properties of the tunnel junctions and in particular their barrier height. Since the resistances of the junctions are adjustable and can be high, this waiting step requires the use of little current. The potential barriers of the invention will therefore be deformed as shown in FIG. 6C.

The implementation of reading information follows a two-step process (Figure 7).

The first step consists in selecting the memory cell constituted by the invention whose content the user wants to know (in this example cell 14). This selection is made by polarizing the transistor 14 live as shown in FIG. 7 A. In order to read the information stored in the memory cell 14, the transmitting line 15 connected to the emitter of the transistor 14 is polarized at a voltage + V volts, the base line 16 connected to the base of the transistor 14 retains its polarization and the collector line 17 connected to the collector of the transistor 14 is polarized at a voltage -V volts. The potential barriers of transistor 14 will therefore be deformed as illustrated in FIG. 7B. The lines connected to the electrodes of the transistors 18 keep their polarization as indicated in FIG. 6B and 7C. However, the transistors 19 located on line 17 as well as the transistors 20 located on line 15 have seen a change in the bias voltage of their collector and emitter respectively. The potential barriers of the transistors 19 and 20 will therefore be deformed, they are shown in FIG. 7D for the transistors 19 and FIG. 7E for the transistors 20.

The second step consists in sending a signal (of the pulse type for example) on the base line 16. This signal will be transmitted in each transistor in a different way depending on the state of polarization. For transistor 14, the signal will be transmitted to its collector and therefore to line 17. The value of the signal emitted on line 17 by transistor 14 depends, for example, on the relative orientation of the magnetizations of the base and the collector and therefore information stored in the memory cell constituted by the transistor 14. There is no possible transmission to its emitter 15 because of the potential barrier whose height is artificially increased by the application of the voltage + V volt. For the transistors 18, the signal will be transmitted to their transmitter. There is no possible short circuit by the transistors 18 and 19 of the transmitter lines 7 no activated (bias voltage -V volt). The only signal emitted on line 17 can only come from the conduction of the basic signal 16 through transistor 14.

2) Writing information in an elementary cell (figure 8)

The selective writing of cell 14 (FIG. 7 A) consists in switching the magnetization of one or more of its magnetic layers without disturbing the information stored in the neighboring cells.

For this, the configuration of lines 6 ', 7', 8 '; 15, 16, 7 proves to be very advantageous. During the various technological structuring steps of the invention (FIG. 10), it is possible to orient the supply lines of the bases (lines 8; 16) of the cells perpendicular to the easy axis of magnetization of the different magnetic layers and supply lines for collectors and transmitters at +/- 45 degrees. It is indeed possible to promote an easy axis of magnetization of a magnetic layer in several ways and choose the direction of the line 8; 16 so that it is perpendicular to the direction of easy magnetization. One possibility is to make the layers grow in the presence of a magnetic field. This field will determine the easy direction of magnetization. Another possibility is to promote easy direction by choosing an adequate (tapered) shape of the transistor.

The writing consists in sending a current pulse on the lines connecting the base (Iwb), collecting (Iwc) and emitting (Iwe) electrodes which produces a magnetic field directed along the easy axis of the magnetic layers forming these electrodes (Hw ). The amplitude of the current pulse sent in line 8; 16 will be chosen so that the field created by the base electrode 3 alone does not make it possible to reverse the magnetization of the magnetic layer, the orientation of which makes it possible to modify the stored information. On the other hand, the two additional pulses sent in lines 6; 15 and 7; 17 will help to strengthen the field at the transistor 14 and return the magnetization of the soft layer of the transistor 14 without disturbing the nearest neighbors.

The use of three electrodes, compared to two, makes it possible to reduce the current emitted in each electrode. Finally, the present invention also relates to a magnetic field or current sensor constituted by at least one microelectronic device as described above, the modifications of the Characteristics, in particular the magnetic states of electrodes 1, 3 and 5, induced by an external magnetic field are known.

Indeed, knowing the characteristics of the transistor device, it is possible to find the characteristics of the current (passing through a wire and creating a magnetic field) or of the magnetic field which modifies the magnetic state of the electrodes and therefore the currents flowing in the different parts of the invention. For example, if the variation of the gain of the transistor as a function of the orientation of the magnetizations of the electrodes is known, a modification of the collector current gives access to the magnetic configuration of the electrodes of the invention and therefore to its magnetic environment. Given the tunnel nature of the transport process, this type of sensor is very sensitive.

As an example of a practical embodiment of a microelectronic device according to the invention, the following procedure, in conjunction with FIGS. 9 and 10A to 10F of the appended drawings, describes the six main consecutive lithography steps ( with the use of masks) and engraving allowing the production of such a device. The process for preparing said device will be carried out on a prefabricated multilayer (FIG. 9) using UN and / or electronic lithography techniques and dry and / or reactive ion etching.

During each step in this process, the lithography step initially consists in depositing a positive photosensitive resin on the multilayer. Then, the resin is insolated through a mask containing opaque patterns, the regions of the resin which have been exposed becoming more soluble than the non-exposed areas, in a determined solvent.

During the development, only the regions of the resin located below the mask patterns are preserved on the multilayer. The etching step consists in etching the parts of the sample not protected by the resin patterns.

(1) The first step of the process consists in clearing the contours of the microelectronic devices from the continuous layer. The patterns of each device are lithographs by exposing a first deposit of resin through a first mask. This pattern is then transferred into the multilayer by etching, the etching being stopped when the multilayer, between the patterns, is entirely pulverized (FIG. 10A). (2) The second step is to disengage the emitting electrode from the device. After the deposition of a new layer of resin, the latter is exposed through a second mask. This pattern is then transferred into the multilayer by etching, the etching being stopped in the buffer layer forming the first electrode 1. The electrical contact on said buffer layer will allow access to the emitting electrode (Figure 10B).

(3) The third step consists in disengaging the middle or base electrode 3. After the deposition of a new layer of resin, the latter is exposed through a third mask. This pattern protects the connection region of the emitting and collecting electrode. The unprotected part is then etched, the etching being stopped in the layer constituting the future base of the invention. The electrical contact on said layer will provide access to the base electrode 3 (Figure 10C). (4) The fourth step consists in protecting the future contact of the electrode of the collector 5. After the deposition of a new layer of resin, the latter is exposed through a fourth mask. This pattern protects the connection region of the collecting electrode 5 before depositing insulation on the entire sample (FIG. 10D). (5) The fifth step consists in opening contact sockets for the emitter and base electrodes in the insulating layer deposited at the end of the previous step. After the deposition of a new layer of resin, the latter is exposed through a fifth mask. This pattern of holes allows reactive etching of the Siθ2 to pierce holes in the insulating layer up to the base and emitting electrode (Figure 10E).

(6) The last step makes it possible to connect measurement pads to electrodes 1, 3 and 5. After the deposition of a new layer of resin, the latter is exposed through a sixth mask. This pattern of holes allows a deposit of a conductive material which contacts the emitter 1, the base 2 and the collector 3 (FIG. 10F).

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims

R E V E N D I C A T I O N S

1) Microelectronic device with three electrical connection terminals, formed by a stack of two magnetoresistive tunnel junctions each of which is composed of two conductive electrodes separated by a layer of an insulating material forming a tunnel barrier, said stack having a common middle electrode at the two junctions, characterized in that it comprises, on the one hand, an electrode (1, 3 or 5) made of a magnetic or semi-metallic material and, on the other hand, either at least a second electrode (1 , 3 or 5) made of a magnetic or semi-metallic material, or at least one tunnel barrier (2 or 4) in the form of a tunnel barrier filtering the spins of electrons, each electrode (1, 3, 5) of a magnetic material or semi-metallic with its own coercive field.

2) Microelectronic device according to claim 1, characterized in that the middle electrode (3) has a thickness less than or equal to the limit value (ej) allowing the electrons coming from one of the two other electrodes (1 or 5) to pass to the other of said two other electrodes (1 or 5) while retaining an energy greater than that of the Fermi level of said median electrode (3).

3) Microelectronic device according to claim 2, characterized in that the electrodes (1, 3, 5) are polarized so as to obtain an operation of the transistor type allowing the amplification of a current injected into one of the electrodes (1, 3 , 5) by an artificial current source formed by the polarization of one of the two tunnel junctions (1, 2, 3; 3, 4, 5), the operating conditions being also controlled by the respective orientations of the magnetizations of the electrodes magnetic or semi-metallic (1, 3, 5).

4) Microelectronic device according to claim 3, characterized in that, in operation in common emitter mode and for given electrode voltages, the gain of the transistor and the maximum injected current are controlled and, if necessary, preprogrammed, non-volatile manner, through the orientation of the magnetizations of the various magnetic or semi-metallic electrodes (1, 3, 5) under similar or inverse conditions, parallel or anti-parallel. 5) Microelectronic device according to claim 1 or 2, characterized in that the electrodes (1, 3, 5) are polarized so as to obtain a switching operation, the middle electrode (3) possibly having a thickness greater than the value of thickness limit (ej).

6) Microelectronic transistor, characterized in that it is constituted by a microelectronic device according to any one of claims 1 to 4, its gain, and if necessary its maximum current, being controlled by means of the applied bias voltages to its different electrodes (1, 3, 5) and / or through the orientations of the respective magnetizations of each magnetic and / or semi-metallic electrode (1, 3 and / or 5).

7) elementary memory cell which can have two or more magnetic states, characterized in that it is constituted by a microelectronic device according to any one of claims 1, 2 and 5, the information being stored in the form of determined orientations of the magnetizations of the electrodes (1, 3.5) in a magnetic or semi-metallic material, the reading of the information being effected by a selective polarization of the electrodes (1, 3, 5) of said cell or in the form of orientations determined magnetizations of electrodes 1, 3 or 5 with respect to a spin filter barrier.

8) Elementary memory cell according to claim 7, characterized in that the writing in this cell is carried out by sending a current pulse in a transmission line (8 ′) connected to the middle electrode (3) forming the base and in one or more transmission lines (6 'and / or 7') connected to the electrodes (1 and / or 5) forming an emitter and / or collector.

9) Elementary memory cell according to any one of claims 7 and 8, characterized in that the middle electrode (3) forming the base has an easy magnetization axis perpendicular to the transmission line (8 ') which is connected to it .

10) Network of elementary memories, characterized in that it consists of a set of elementary memory cells according to any one of claims 7 to 9 connected to each other and to external control circuits (6, 7. 8) at by means of a network of transmission lines (6 ', 7', 8 ') making it possible to apply a particular polarization to each of the electrodes (1, 3, 5) of each of the elementary memory cells for reading the information stored in each of them.

1 1) Network of elementary memories according to claim 10, characterized in that the external control circuits (6, 7, 8) are adapted to simultaneously send, to any one of the elementary memory cells, current pulses through the transmission lines (6 ', 7', 8 ') connected to the three electrodes (1, 3, 5) of the elementary memory cell concerned, so as to concomitantly generate a magnetic field in the vicinity of the magnetic layers, forming part of said cell, whose intensity and orientation are such that it results in a modification of their magnetic state, without affecting the state of the magnetic layers of the surrounding cells.

12) Array of random access magnetic memories composed of a plurality of microelectronic devices according to any one of claims 1, 2 and 5 or of a plurality of elementary memory cells according to any one of claims 7 to 9, each (e) of said devices or of said cells is located at the intersection of three transmission lines (6 ′, 7 ′, 8 ′) isolated from each other, for example by oxide layers, the first of which (6 ') is part of the transmission lines connected to the electrodes (1) forming transmitters, in the second (7'). extending at 45 ° with respect to the first, forms part of the transmission lines connected to the median electrodes (3) forming bases and of which the third (8 '), extending at 90 ° with respect to the first, forms part transmission lines connected to the electrodes (5) forming collectors. 13) Magnetic field or current sensor constituted by at least one microelectronic device according to any one of claims 1 to 5, the modifications of the characteristics of which, in particular the magnetic states of the electrodes (1, 3, 5), induced by a field external magnetic are known.