Analog spectrum analyzer

Abstract

A spectrum analyzer for a signal I.sub.RF comprising a plurality of frequencies f.sub.i comprises N entities each made up of a structure formed by a stack of magnetic and non-magnetic layers having in at least one of the magnetic layers a magnetic configuration in the shape of a vortex, the excitation modes of the magnetic configuration being suitable for detecting the frequencies contained in an incident signal in real time, each entity having a first lower electrode and a second upper electrode, a voltage-measuring device suitable for measuring an electric voltage showing the presence of a frequency f.sub.k in the analyzed signal I.sub.RF, the device being connected to the lower electrode and to the upper electrode, a measurement-processing device suitable for determining the value of the frequencies f.sub.k in the signal I.sub.RF, and a line carrying the signal to be analyzed to each of the entities.

Claims

1. A spectrum analyzer for a signal I.sub.RF comprising a number of frequencies f.sub.i, comprising: N entities, N being non-zero, each consisting of a structure formed by a stacking of magnetic and non-magnetic layers having, in at least one of the magnetic layers, a vortex-form magnetic configuration and at least two of the N entities having a different geometry with an oscillation frequency of an entity being associated with a geometry of the entity, excitation modes of the magnetic configuration being configured to detect in real time frequencies contained in an incident signal, each entity having a bottom first electrode and a top second electrode, a voltage measurement device configured to measure an electrical voltage representative of a presence of a frequency f.sub.k in an analyzed signal I.sub.RF, the voltage measurement device being linked to the bottom first electrode and to the top second electrode of each entity, and a measurement processing device configured to determine a value of the frequency f.sub.k present in the signal I.sub.RF, lines bringing signals to be analyzed from the voltage measurement device, which are connected to each of the entities, wherein said entities are arranged in series, a first entity is linked to the voltage measurement device and to an injection circuit via a first connection circuit, the top second electrode is connected to the first connection circuit by a first connection wire, the bottom first electrode is linked to the voltage measurement device by a second connection wire, a transmission line brings the signal I.sub.RF to the first connection circuit, a nodal point situated on the second connection wire makes it possible to connect the voltage measurement device to the bottom first electrode and to a second connection circuit of a next entity, the entity being linked to a polarization and the voltage measurement device by means of the second connection circuit at a level of its top second electrode and by a line comprising the nodal point at a level of its bottom first electrode, the nodal point being linked with the second connection circuit of the next entity, and so on to a last entity.

2. The spectrum analyzer as claimed in claim 1, wherein said entities are arranged in parallel, a transmission line bringing the signal to be analyzed I.sub.RF to a divider configured for dividing a RF power of the signal to be analyzed and for distributing the signal on N transmission sublines, each subline being connected to a connection circuit linking the top second electrode to the voltage measurement device configured for measuring a voltage V.sub.n the between the bottom first electrode and the top second electrode, the bottom first electrode being linked to a ground point common to all the entities and to the voltage measurement device.

3. The spectrum analyzer as claimed in claim 2, wherein the connection circuit connected to an entity comprises: a connection wire connecting a junction point to the top second electrode of said entity via a connection wire, a connection wire which connects the junction point to the voltage measurement device via the connection wire, a connection wire linking the junction point to a first wall of a capacitor, a connection wire linking a second wall of the capacitor to a connection wire bringing the signal to be analyzed.

4. The spectrum analyzer as claimed in claim 1, wherein the first connection circuit comprises: a connection wire which connects a junction point to the top second electrode of said entity via a connection wire, a connection wire which connects the junction point to the voltage measurement device via the connection wire, a connection wire linking the junction point to a first wall of a capacitor, a connection wire linking a second wall of the capacitor to a connection wire.

5. The analyzer as claimed in claim 1 wherein the entities are arranged in parallel, the top second electrode being linked to the voltage measurement device configured for measuring the value of a voltage V.sub.n between the bottom first electrode and the top second electrode, the bottom first electrode being linked to a ground point common to all the entities, a radiating magnetic line making it possible to inductively couple to a detector of the signal to be analyzed I.sub.RF at each of the entities.

6. The analyzer as claimed in claim 1, wherein the device also consists of N polarization lines configured for injecting a direct current I.sub.n between two nodal points connected respectively to the bottom first electrode and to the top second electrode of the entity and configured for varying a frequency that the entities are capable of detecting through the measurement of the value of a voltage V.sub.n between the bottom first electrode and the top second electrode, a first one of the nodal points is connected via the first connection wire to a first inductor in turn connected to the second connection wire, second one of the nodal points is connected via the second connection wire to a second inductor in turn connected to the first connection wire.

7. The analyzer as claimed in claim 1, wherein the voltage measurement device consists of a current source linked by a main connection to a division device configured for dividing the current and for distributing it over N connection sublines, each subline being connected to a node.

8. The spectrum analyzer as claimed in claim 1, wherein the entities are devices in a form of pillars having a structure chosen from the following list: a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic type, a non-magnetic intermediate layer, an active layer containing a magnetic vortex and a top electrode, a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic type, a non-magnetic intermediate layer, an active layer containing a magnetic vortex, a second non-magnetic intermediate layer, a perpendicular magnetic polarizer and a top electrode, a stacking consisting of: a bottom electrode, a first active layer containing a magnetic vortex, a magnetic intermediate layer, a second active layer containing a vortex and a top electrode, and a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic type, a non-magnetic intermediate layer, a first active layer containing a magnetic vortex, a second non-magnetic intermediate layer, a second active layer containing a magnetic vortex and a top electrode.

9. The spectrum analyzer as claimed in claim 1, wherein the voltage measurement device is a voltmeter for measuring a voltage V.sub.n at terminals of each entity and the measurement processing device consists of N comparators of the voltage V.sub.n to a threshold value.

10. The spectrum analyzer as claimed in claim 1, wherein the entity has an ellipsoidal, square or rectangular form.

11. The spectrum analyzer as claimed in claim 1, comprising a number of circular entities or junctions having different diameters variable between 50 nm and 1 m in order to adjust a frequency over a range of frequencies lying between 30 MHz and 2 GHz.

12. The spectrum analyzer as claimed in claim 1, wherein the entities have a structure configured for producing a magnetic configuration corresponding to a coreless magnetic vortex of C-state type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the method and the device according to the invention will become more apparent on reading the following description of an exemplary embodiment given by way of nonlimiting illustration, with attached figures which represent:

(2) FIGS. 1A and 1B, an illustration of a junction used to implement the invention,

(3) FIG. 2, a first diagram of a device according to the invention for which the elements are arranged in parallel with direct electrical coupling by a transmission line,

(4) FIG. 3, a second example of a device for which the elements are arranged in series with direct electrical coupling by transmission line,

(5) FIG. 4, a third example for which the elements are excited by magnetic coupling by virtue of an inductive line, and

(6) FIG. 5, an exemplary embodiment for the polarization and measurement device.

DETAILED DESCRIPTION

(7) Before giving a few examples of embodiments of a spectrum analysis device according to the invention, a recap on the elements used to detect the frequencies present in a frequency spectrum will be given.

(8) FIGS. 1A and 1B represent an example of a basic building block for the implementation of the invention: a spintronic device having a vortex configuration, i.e. vortex junction. This junction is constructed from a cylindrical stacking of at least two thin ferromagnetic layers 1, 2 separated by an intermediate layer 3 (that can be metallic or insulating). For simplicity, a circular cylinder is considered. Without departing from the scope of the invention, it is possible to use other forms, for example an elliptical cylinder. For at least one of the two magnetic layers, called active layer corresponding to the top layer 1 of FIG. 1, the fundamental state or remanent magnetic configuration is characterized by a non-uniform magnetization, for example a vortex configuration or a C-state configuration, known to those skilled in the art. A detailed description of the magnetic vortex and also of the terminology used for this field are described in the patent application WO201307797. The thickness of the active layer is denoted h and its diameter . In a first configuration, the second magnetic layer, the bottom layer 2, is called trapped, and is characterized by a uniform magnetization.

(9) The materials envisaged for the production of the magnetic layers 1 and 2 can be, for example, iron Fe, cobalt Co, nickel Ni, alloys comprising at least one of these elements (CoFeB for example) and also Heusler alloys. The thickness of each layer can vary between 0.5 and 40 nm.

(10) Turning now to the intermediate layer, it is possible to envisage, for example, insulating materials such as MgO with a thickness of approximately 1 nm, or else metallic layers such as gold Au or copper Cu, or ruthenium Ru, the thicknesses of which can vary from 1 to 10 nm.

(11) Each layer can consist of a stacking of sublayers in order to improve the magnetic characteristics of the object concerned. For example, the trapped layer can be a so-called synthetic antiferromagnetic (SAF) layer, i.e. formed by a stacking of an antiferromagnetic layer of IrMn or of PtMn of 10 nm, a layer of ferromagnetic materials in direct contact with the antiferromagnetic layer, 2.5 nm of CoFeB for example, and a last magnetic layer, for example 3 nm of CoFeB, separated by a layer of non-magnetic materials, 0.85 nm of Ru for example.

(12) It is also possible to improve the magneto-resistive properties of the tunnel barrier defined by the intermediate layer by inserting magnetic sublayers such as CoFe of approximately 1 nm between the intermediate layer and the active layer.

(13) This junction also comprises, on each of its faces, so-called electrical contact layers (top and bottom electrodes), not represented in FIG. 1, that make it possible to electrically connect the junction to a current or voltage source in order to make a current of electrons circulate through the junction and/or an electrical voltage measurement device such as, for example, a voltmeter or an ammeter.

(14) The structure of the analyzer can comprise a number of entities (20.sub.n) in the form of pillars having a structure chosen from the following list: a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic (SAF) type, a non-magnetic intermediate layer, an active layer containing a magnetic vortex and a top electrode, a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic (SAF) type, a non-magnetic intermediate layer, an active layer containing a magnetic vortex, a second non-magnetic intermediate layer, a perpendicular magnetic polarizer and a top electrode, a stacking consisting of: a bottom electrode, a first active layer containing a magnetic vortex, a magnetic intermediate layer, a second active layer containing a vortex and a top electrode, and a stacking consisting of: a bottom electrode, a magnetic multilayer of synthetic antiferromagnetic (SAF) type, a non-magnetic intermediate layer, a first active layer containing a magnetic vortex, a second non-magnetic intermediate layer, a second active layer containing a magnetic vortex and a top electrode.

(15) A nonlimiting example of materials that can be used to produce the electrodes can be as follows: the top electrode is formed by 7 nm of Ta, 6 nm of Ru, 5 nm of Cr and 200 nm of Au, the bottom electrode is formed from 3 nm of Ta and 2 nm of Ru. The electrodes are obtained by a number of micro/nano fabrication steps according to a technique known by those skilled in the art and described for example in the patent application US20080150643.

(16) An important geometrical parameter for defining the radiofrequency properties of the junction is its diameter; it can vary, for example, between a few tens of nanometers and a few microns, while the overall thickness can be of the order of some tens of nanometers. In general, all the layers of the junction (except for the electrodes) have the same diameter as that of the active layer. There can however be variants in which the diameter of the junction is not constant over its entire height.

(17) Typically, the junction is deposited on a substrate, for example of SiO.sub.2 type.

(18) If no external force acts on the active layer, the vortex is stable in its position of equilibrium (generally at the disk center, FIG. 1A). If a spin-polarized electrical current is injected through the junction, by virtue of the spin transfer phenomenon, the core of the magnetic vortex can be gyrated about its position of equilibrium (FIG. 1B). The gyration frequency is determined by the geometrical parameters and by the materials used. For example, if a circular layer of NiFe with a diameter of 500 nm and a thickness of 5 nm is considered, the gyration frequency will be of the order of 140 MHz. By magneto-resistive effect, this vortex magnetization dynamic is converted into an oscillation of the electrical voltage at the terminals of the junction with a characteristic frequency, called natural frequency of the junction, which depends on the thickness/diameter ratio (h/) of the active layer. This dependency of the oscillation frequency on the ratio (h/) is typical of the vortex mode.

(19) When an alternating signal I.sub.RF is injected with a frequency close to the natural frequency of the system (that is to say of the order of the ray width of the resonance signal), there is a modification of the voltage V.sub.dc at the terminals of the junction. More directly, the electrical resistance of the junction changes characteristically when the frequency of the injected RF signal is close to the natural frequency of the junction. This voltage (or resistance) variation is the discriminator for detecting the signal and the frequencies of the RF signal.

(20) Different junction structures can be envisaged in the context of the invention.

(21) A first, so-called 1 standard vortex structure consists of the following stacking: a bottom electrode; SAF; an intermediate layer of MgO; an active layer; a top electrode.

(22) A second, so-called 1 hybrid vortex structure comprises, for example, a bottom electrode, SAF, an intermediate layer of MgO, an active layer; a few nm of Cu; a perpendicular polarizer formed by a succession of sublayers: for example [Co0.2/Ni0.5]*10; a top electrode.

(23) A third, so-called 2 hybrid vortex structure is composed of a bottom electrode, SAF; an intermediate layer of MgO; a first active layer; a few nm of Cu; a second active layer; a top electrode.

(24) A fourth, so-called 2 standard vortex structure is composed of a bottom electrode, a first active layer; an intermediate layer of MgO; a second active layer; a top electrode.

(25) As an illustrative and nonlimiting example, a network of circular junctions with a diameter varying from 50 nm to 1 m makes it possible to adjust the frequency over a range of approximately 2 GHz to 30 MHz.

(26) The resonance frequency f.sub.R of the junction is also dependent on two other parameters that are the intensity of the direct current circulating through the pillar and the perpendicular component of the magnetic field possibly applied thereto. It is therefore possible to make a very accurate adjustment of the frequency by acting on these two parameters. For example, if a scan of one of these external parameters is carried out, the frequency resolution of the detector can be improved; furthermore, with this scan it is possible to extract an additional item of information: the amplitude of the RF signal. However, such information is obtained at the cost of the loss of the real time nature of the detection.

(27) FIG. 2 illustrates a first example of a device according to the invention. The device comprises N junctions or entities 20.sub.n connected in parallel to which a signal to be analyzed I.sub.RF by direct electrical coupling is injected. This junction 20.sub.n is characterized by a specific structure, for example that described in FIG. 1 or even one of the four structures described previously, with a diameter .sub.n and a thickness h.sub.n of the active layer. With this junction structure is associated a resonance frequency fr.sub.n. All the junctions are deposited on a substrate 4.

(28) The bottom electrode 21.sub.n of a junction 20.sub.n is connected via a transmission line 42.sub.n to a ground point 41 common to all the junctions and, via a connection wire 24.sub.n, to a measurement device 6a adapted for measuring a voltage value. The current which will be distributed at each junction can be of direct or alternating type. The top electrode 22.sub.n of the junction 20.sub.n, is connected via a connection wire 23.sub.n to a connection circuit 3.sub.n which separates the alternating side (alternating current injection circuit 5 connected via a connection wire 25.sub.n) from the direct side (measurement device 6a connected via a connection wire 26.sub.n).

(29) The connection circuit 3.sub.n comprises, for example: a connection wire 33.sub.n which connects a junction point 30.sub.n, at the node, to the top electrode 22.sub.n of the junction 20.sub.n via a connection wire 23.sub.n, a connection wire 36.sub.n which connects the node 30.sub.n to the voltage measurement device 6a via the connection wire 26.sub.n, a connection wire 31.sub.n linking the node 30.sub.n to a first side 34.sub.n1 of a capacitor 34.sub.n, a connection wire 35.sub.n linking the second side 34.sub.n2 of the capacitor 34.sub.n to the alternating current injection circuit 5 via the connection wire 25.sub.n.

(30) In the alternating current injection circuit 5, a main transmission line 53 brings the signal I.sub.RF to be analyzed 52 to a splitter device, which can be an active or passive element. The splitter 54 divides the RF power of the signal to be analyzed, and distributes the signal I.sub.RF over N transmission sublines, 55.sub.n. Each subline 55.sub.n is connected to the connection circuit 3.sub.n via the connection wire 25.sub.n In this way, the signal I.sub.RF to be analyzed 52 is injected on each junction 20.sub.n, via each of the sublines.

(31) The voltage measurement device 6a makes it possible to measure the voltage V.sub.n measured between the bottom electrode and the top electrode of each junction (subcircuit 6.sub.a). It can also be used to inject a direct current DC (subcircuit 6.sub.b). This voltage measurement device is connected to the bottom electrode 21.sub.n via the connection wire 24.sub.n and to the connection circuit 3.sub.n via the connection wire 26.sub.n. Two inductors (67.sub.n1 and 67.sub.n2) prevent the passage of alternating current in the voltage measurement device 6a.

(32) The subcircuit 6.sub.a consists of N measurement devices 68.sub.n each adapted for measuring the voltage V.sub.n at the terminals of each junction, for example a voltmeter. The voltage V.sub.n is measured between two nodal points 60.sub.n1 and 60.sub.n2 connected respectively to the bottom electrode and to the top electrode of the junction.

(33) According to a first example, the subcircuit 6.sub.b consists of a parallel arrangement of a number of polarization lines 69.sub.n each delivering a particular current intensity I.sub.n between the two nodal points 60.sub.n1 and 60.sub.n2, connected respectively to the bottom electrode (21.sub.n) and to the top electrode (22.sub.n) of the entity 20.sub.n, and making it possible to vary the frequency that the entities (20.sub.n) can detect through the measurement of the value of the voltage V.sub.n between the bottom electrode (21.sub.n) and the top electrode (22.sub.n). The first node 60.sub.n1 is connected via a first connection wire 61.sub.n1 to a first inductor 67.sub.n1 which is connected to the connection wire 24.sub.n via the connection wire 64.sub.n; the second node 60.sub.n2 is connected via a second connection wire 61.sub.n2 to a second inductor 67.sub.n2 that is connected to the connection wire 26.sub.n via the connection wire 66.sub.n.

(34) It is also possible to have a single common polarization line and adjust the current I.sub.n individually by the addition of an active or passive element in series between the main polarization line and the junction 20.sub.n. In this second version of subcircuit 6.sub.b (see FIG. 5), a main connection wire 63 brings the current I.sub.dc 62 to a division device 69 or splitter, which can be an active or passive element. The splitter 69 divides the current I.sub.dc 62 and distributes it over N connection wires 65.sub.n. Each subline 65.sub.n is connected to the node 61.sub.n via an element Z.sub.n. The element Z.sub.n can be active or passive (diodes, resistor, etc.). The nodes 60.sub.n1 and 60.sub.n2 are connected respectively to the inductors 67.sub.n1 and 67.sub.n2 in the same way as the preceding example.

(35) The voltage measurement subcircuit 6.sub.a is itself linked to a value processing device 7. The device 7 can be a comparator of the voltage values measured for each junction relative to one or more reference values, threshold values, in order to determine whether a frequency f.sub.k corresponding to the resonance frequency of the junction 20.sub.n is present in the signal currently being analyzed. The presence of a frequency f.sub.k of the analyzed signal I.sub.RF can be memorized written and stored in a memory and/or displayed on a screen 8. Another way of proceeding for the device 7 is to use a set of analog/digital converters.

(36) With all working independently and having very small dimensions, within the hundred nanometers range, a massive parallel arranging of these unitary detection entities or junctions makes it possible, within a very small volume, to produce an instantaneous analog spectrum analyzer function for a signal I.sub.RF. The resonance frequency band of each junction [f.sub.0f.sub.0, f.sub.0+f] is adjusted by acting on the thickness/diameter ratio (h/) of the active layer. The diameter .sub.n is, for example, adjusted in order for the resonance frequencies to be juxtaposed and thus create a network for detecting frequencies without holes for analyzing a signal. In this way, it is possible to detect the frequencies present in a signal I.sub.RF.

(37) The frequency analyzer device according to the invention will act as follows: when a signal I.sub.RF to be analyzed containing, for example, three frequencies, f.sub.1, f.sub.2, f.sub.3, is coupled to the device, only the junctions having the structure adapted for resonating on these three frequencies will resonate around f.sub.1, f.sub.2, f.sub.3, so as to simultaneously give the information that the spectrum is occupied around these three frequencies.

(38) In this first example (junctions connected in parallel by direct electrical coupling), the number of sublines 55.sub.n is equal to the numbers of junctions. This approach facilitates the control of the impedance matching of the network but to the detriment of sensitivity since the incident power is divided into a number of sublines. It is for example used in the case where the requirement is to detect frequencies with few channels and also of high powers.

(39) Another way of proceeding is to consider junctions connected in series. FIG. 3 represents a variant embodiment where the entities or junctions are connected in series. This arrangement allows for a relatively good control of the sensitivity to the detriment of the facility to match impedance.

(40) In this variant embodiment, each junction 20.sub.n of the network is linked to the connection circuit 3.sub.n in a way identical to that described in FIG. 2, that is to say, the top electrode 22.sub.n is connected to the connection circuit 3.sub.n via the connection wire 23.sub.n. Similarly, the voltage measurement circuit 6a is connected to the connection circuit 3.sub.n via the connection wire 26.sub.n. However, the top electrode 21.sub.n is linked differently as will be described hereinbelow. The aim of this variant embodiment is to connect the junctions in series. The alternating current injection circuit 5 is therefore simplified. A main transmission line 53 brings the signal I.sub.RF 52 directly to the connection circuit of the first junction 3.sub.1 via the connection wire 25.sub.1. Each junction, in this example, is separated electrically from the other junctions. To obtain a series connection, each junction 20.sub.n is connected to the next junction 20.sub.n+1. For each junction, there is a nodal point 27.sub.n which makes it possible to link the voltage measurement circuit 6a (via the connection wire 24.sub.n), the bottom electrode of the pillar 21.sub.n (via the connection wire 28.sub.n), and the connection circuit 3.sub.n+1 of the successive junction 20.sub.n+1 (via the connection wire 25.sub.n+1). In this way, the signal to be analyzed or alternating current I.sub.RF is injected in series into the pillar, while a direct current I.sub.n is applied to each pillar and its voltage V.sub.n is measured separately.

(41) FIG. 4 schematically represents another possible variant embodiment for the device according to the invention. In this case, the signal I.sub.RF to be analyzed 52 is routed by a radiating magnetic coupling line 53. The alternating current I.sub.RF generates an alternating field which, by inductive coupling, will act on each junction. The amplitude of the alternating signal felt by the junction 20.sub.n depends on the distance between the line 53 and the junction itself. The typical values are of the order of a few hundred nanometers. The line can be placed below the junction or to the side depending on the type of junction considered. As in the first embodiment (see FIG. 2), the bottom electrode 21.sub.n of a junction 20.sub.n is connected via a transmission line 42.sub.n to a ground point 41 common to all the junctions and via a connection wire 24.sub.n to the voltage measurement device 6a. On the other hand, the top electrode 22.sub.n is connected directly to the voltage measurement device 6a via the connection wire 23.sub.n. The voltage measurement device 6a, and consequently the value processing device 7 and the screen 8 with all their variants, are identical to those described in the first variant embodiment (see FIGS. 2 and 5).

ADVANTAGES

(42) The parallel reading of a network of the magnetic junctions makes it possible to obtain instantaneous information on a range of frequencies present in an incident radiofrequency signal. By virtue of the use of nano objects having the form of a cylindrical magnetic stacking of nanometric size in which the resonance frequencies can be induced to make the detection, the dimensions of the device are extremely reduced.