RU2347296C1 - Magnetically operated detector of shf radiation - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: magnetically operated detector of SHF radiation is related to SHF equipment and may be used in development of radio equipment for communication, radio location, in control instrumentation, in scientific instrument making. Magnetically operated detector of SHF radiation comprises detecting element on tunneling contact located in magnetic field. At that detecting element is made of magnetic granulated material with large set of magnetic tunneling contacts, to which offset current is supplied and which is installed in antinode of SHF radiation magnetic component. SHF radiation causes precession of some granules magnetisation, which are under effect of ferromagnetic resonance conditions, and at the same time it induces high frequency current in material.

EFFECT: increase of detector sensitivity with preservation of its frequency-selective properties controlled by magnetic field, simplification of design and technology of detecting device manufacture.

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Description

The invention relates to microwave technology and can be used to create radio equipment for communication, radar, in measuring equipment, in scientific instrumentation.

Microwave point pin detector diodes are well known [L.G. Gasanov, A.A. Lipatov, V.V. Markov, N. A. Mogilchenko. - M .: Radio and communications, 1988. - 288 p.]. By pressing a pointed wire from tungsten to a silicon crystal, a metal-semiconductor transition of a point diode is formed. The required current-voltage characteristics are achieved individually by selecting the contact point and adjusting the clamping force.

The pressure contact gives a wide variation in the transition parameters, is mechanically unreliable, diodes are sensitive to vibrations and shocks. The electric strength of the diode is small.

The best option for a microwave detector due to its speed is a Schottky barrier diode, obtained by vacuum deposition of metal on a semiconductor [V.I. Gaman, Physics of semiconductor devices. - Tomsk: Publishing House of NTD 2000. - 426 p.].

The steepness of the current-voltage characteristics and the electric strength of such a diode is higher than that of a point transition. High repeatability of the parameters of the diode on the Schottky barrier and their stability during operation are provided by modern epitaxial technology. The diode operates at a low level of the microwave signal and performs quadratic detection, i.e. the magnitude of the rectified voltage is proportional to the square of the amplitude of the microwave current.

The disadvantages of this device include its lack of controlled frequency selectivity, which is necessary for some applications.

However, magnetic tunneling contacts, in which a fundamentally new mechanism for detecting high-frequency current, based on the relationship of spin dynamics and spin-polarized transport [A.A. Tulapurkar, Y.Suzuki, A.Fukushima, H.Kubota, H.Maehara, are realized) , K. Tsunekawa, DD Djayaprawira, N. Watanabe & S. Yuasa, Spin-torque diode effect in magnetic tunnel junctions. Nature (London) v.438, N17, p.339-342, 2005, (prototype)].

The detecting element is a nanoscale layered structure - two thin magnetic layers with metal conductivity (electrodes), separated by a dielectric layer (tunnel barrier). Magnetic layers are characterized by different coercive fields, for a selected external magnetic field, the magnetization of an electrode with a higher coercivity (pined electrode) is directed at a certain angle to the direction of the field, the magnetization of an electrode with a lower coercivity (free electrode) has a direction that coincides with the magnetic field. If a high-frequency current I _ac with a frequency f is now passed through such a structure, it becomes spin polarized due to the ferromagnetic state of the electrodes. The resulting moment of forces from the spin-polarized conduction electrons acts on the magnetic moment of the free electrode [JCSlonczewski, Current-driven excitation of magnetic multilayers. J. Magn. Magn. Mater, v.159, p. L1-L7 (1996)], forcing it to precess with a frequency f if it is close to the frequency of the ferromagnetic resonance of the free electrode. Since the resistance of the structure depends on the mutual direction of the magnetization of its electrodes, a time-dependent resistance R (t) arises. Averaging the variable voltage component I _ac · R (t) over time over a period of high-frequency current gives a non-zero rectified voltage.

The disadvantages of the described detector should include: not very high sensitivity of the detector compared to the semiconductor diodes currently in use; the complexity of the manufacturing technology of the device - very high requirements for the accuracy and quality of manufacturing a nanoscale tunnel contact.

The technical result of the invention is to increase the sensitivity of the detector while maintaining its frequency-selective properties controlled by a magnetic field; in simplifying the design and manufacturing technology of the detecting device.

The specified technical result is achieved in that in a magnetically controlled microwave radiation detector, including a detecting element on a tunnel contact located in a magnetic field, it is new that the detecting element is made of granular magnetic material with a large set of magnetic tunnel contacts, to which a bias current is applied and which is installed in the antinode of the magnetic component of microwave radiation, the latter causes a precession of the magnetization of a part of the granules under ferromagnetic conditions onance, and at the same time induces a high-frequency current in the material.

In the inventive magnetically controlled microwave radiation detector as a detecting element located in a magnetic field, not a single magnetic tunnel structure is used, as in the prototype, but magnetic granular material, which implements a large set of magnetic tunnel contacts - pairs of ferromagnetic granules with metallic conductivity, separated by thin dielectric layers; the detecting element is located in the antinode of the magnetic component of the microwave radiation; the magnetic component of microwave radiation causes a precession of the magnetization of part of the granules under ferromagnetic resonance conditions, and at the same time induces a high-frequency current in the material, the rectification of which occurs at the tunneling contacts in the material; the design also provides the ability to set a constant bias current through the detecting element, which increases the sensitivity of the detecting device.

Comparative analysis with the prototype shows that the inventive device is characterized in that a fundamentally new material is used as a detecting element - granular magnetic medium; the device is installed in the antinode of the magnetic microwave field, which allows you to abandon special structural elements for exciting high-frequency current in the detecting element; in addition, the microwave magnetic field, and not the current, causes a precession of the magnetization of individual granules forming magnetic tunneling contacts, leading to a time-dependent resistance of the material and, as a consequence, to the effect of detecting high-frequency current; turning on a DC bias increases the sensitivity of the device. Thus, the claimed device meets the criteria of the invention of "novelty." When studying other well-known technical solutions in this technical field, the features that distinguish the claimed invention from the prototype were not identified, and therefore they provide the claimed technical solution with the criterion of "inventive step".

Figure 1 shows the design of a magnetically controlled microwave radiation detector (a): distribution of static H, high-frequency h _ac fields and high-frequency current I _ac in the detecting element; (b): 1 - short-circuited transmission line; 2 - a detecting element; 3 - electromagnet; 4 - contact pads; 5 - bias current source. Figure 2 shows a schematic drawing of two adjacent granules forming a magnetic tunnel contact, explaining the detection mechanism. S _i and S _j denote unit vectors along the magnetization direction of the i-th and j-th grains; in the field H S _i has a fixed direction, resonance conditions are satisfied for S _j and it precesses with a frequency f. Figure 3 shows the dependence of the detected voltage on the detector from an external magnetic field. The detecting element is a granular sample of La _0.7 Ca _0.3 MnO ₃ . Temperature T = 20 K, bias current I _dc = 0. Figure 4 presents the dependence of the detected voltage on the detector from an external magnetic field at various values of the bias current I _dc . The detecting element is a granular sample of La _0.7 Ca _0.3 MnO ₃ . Temperature T = 20 K.

Magnetically controlled microwave radiation detector contains: short-circuited transmission line 1; a detecting element 2, which is made of a magnetic granular material in the form of a thin plate (figa). The detecting element is mounted on the short-circuit wall of the transmission line at the antinode of the magnetic high-frequency field h _ac , which, in turn, induces a high-frequency current I _ac in the detecting element, Fig. 1 (b). A constant magnetic field H is created by an electromagnet 3. Using contact pads 4, conductors are attached to the plate of the detecting element to remove the detecting voltage V _dc and supply bias current I _dc to the detecting element from the current source 5.

The sensitive element is a material in which an extended network of magnetic tunnel junctions formed by ferromagnetic granules with metal conductivity with a thin dielectric layer between them is realized.

The mechanism of rectification of high-frequency current in a system of magnetic tunneling contacts is illustrated in figure 2 by the example of one contact formed by two granules. Each of the granules has its own coercive field and, therefore, the behavior of static magnetization and resonance conditions will differ for different granules. For a certain value of the magnetic field H, the direction of which coincides with the high-frequency current lines, the magnetic moment of the ith granule is directed at an angle α to the magnetic field, and the jth granule is under resonance conditions and its moment precesses with a frequency f around the direction of the external magnetic field . This precession causes a temporary dependence of the resistance of the magnetic tunnel junction

и

единичные векторы вдоль намагниченностей i-й и j-й гранул соответственно;here

and

unit vectors along the magnetizations of the ith and jth granules, respectively;

определяется как

equilibrium direction

defined as

на плоскость ху и

),where (ϕ is the angle between the projection

on the xy plane and

),

прецессирует как

(θ - угол прецессии);

precesses like

(θ is the angle of precession);

и

параллельны,R _↑↑ - transition resistance in the state when

and

parallel

ΔR = R _{↑ ↓} -R _↑↑ - increase in resistance when the state changes to antiparallel. Since the high-frequency magnetic field h _ac induces a high-frequency current

and I), протекающий через туннельный контакт, то напряжение на контакте V(t)=I(t)R(t) должно содержать член, включающий перемешивание I_ac и ΔR(t). Выпрямленное напряжение получаем усреднением по периоду колебанийI (t) = I _ac sin (2πft-δ) (δ is a possible phase shift between the oscillating

and I), flowing through the tunnel junction, then the voltage at the junction V (t) = I (t) R (t) must contain a term including mixing I _ac and ΔR (t). The rectified voltage is obtained by averaging over the oscillation period

индуцируются h_ac и, следовательно, имеют одну и ту же частоту f, пусть для простоты ϕ-δ=0, тогда сопротивление для тока, текущего из i-й в j-ю гранулу, будет меньше из-за меньшего угла между

и

, но для противоположного направления тока будет больше благодаря большему углу. Очевидно, что усреднение V(t) по периоду приведет к ненулевой величине выпрямленного напряжения V_dc.The straightening mechanism described has a simple qualitative explanation. High Frequency Current and Precession

h _{ac are} induced and, therefore, have the same frequency f, let for simplicity ϕ-δ = 0, then the resistance for the current flowing from the ith to the jth granule will be less due to the smaller angle between

and

but for the opposite direction the current will be larger due to the larger angle. Obviously, averaging V (t) over the period will lead to a nonzero value of the rectified voltage V _dc .

For the entire granular sample in which a random network of magnetic tunneling contacts is realized, the rectified voltage is the integral signal obtained by summing over all the contacts. Magnetic tunnel contacts are not identical, and differences in their characteristics are described by certain distribution functions. The behavior of V _dc depending on the magnetic field is determined by the distribution function for the resonance fields of individual granules involved in the formation of tunneling magnetic contacts.

The bias current I _dc , the value of which can be controlled, leads to the asymmetry of the tunnel junctions: an increase in I _dc causes a decrease in the Fermi level of one of the granules with respect to the other by eV _b , where e is the electron charge, and V _b is the corresponding voltage drop across the contact . Under these conditions, the probability of electron tunneling in the forward and reverse directions through the contact will differ, i.e. in fact, the contact resistance for the current flowing in the forward R _F and reverse R _B directions will be different. Formally, this can be taken into account, assuming that R _↑↑ , R _{↑ ↓} and, therefore, ΔR in equation (1) depends on the direction of the high-frequency current in the junction. A simple analysis shows that an increase in the bias current will lead to an increase in V _dc at a single contact and, as a consequence, over the entire granular sample.

The device operates as follows. Electromagnetic radiation with a frequency f, falling into the detecting device, induces a constant voltage V _dc on the detecting element. An external magnetic field allows you to adjust the sensitivity of the detector, so figure 3 shows the dependence of the rectified voltage on the detector V _dc with a detecting element based on a granular sample of La _0.7 Ca _0.3 MnO ₃ , magnetic field H, and granular metal-dielectric alloys based on Co can be used -Al-O; Fe-Al-O. The inclusion of a bias current through the detecting element also allows you to adjust the sensitivity of the detector: at a fixed microwave power, an increase in I _dc to 2 mA leads to a 20-fold increase in V _dc , Fig. 4. Moreover, the bias does not affect the dependence of the rectified voltage V _dc on the magnetic field.

Considering that, in accordance with the detection mechanism, the dependence of V _dc on the magnetic field is determined by the distribution of the resonant fields of the granules of the detecting element, for different frequencies of microwave radiation, the maximum sensitivity of the detector will be observed at different magnetic fields. Thus, it becomes possible to adjust the frequency selectivity of the detector by selecting an external magnetic field.

Claims (1)

A magnetically controlled microwave radiation detector including a detecting element on a tunnel contact located in a magnetic field, characterized in that the detecting element is made of granular magnetic material with a large set of magnetic tunnel contacts, to which a bias current is supplied and which is set in antinode of the magnetic component of microwave radiation, the latter causes a precession of the magnetization of a part of the granules under ferromagnetic resonance conditions, and at the same time induces a high-frequency current in ateriale.

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