WO1998004002A1

WO1998004002A1 - Emitter and/or detector component for submillimetre wave radiation and method of producing said component

Info

Publication number: WO1998004002A1
Application number: PCT/DE1997/001558
Authority: WO
Inventors: Alfred Zehe
Original assignee: Oxxel Oxide Electronics Technology Gmbh
Priority date: 1996-07-23
Filing date: 1997-07-23
Publication date: 1998-01-29
Also published as: DE19629583A1; DE19629583C2; JP2000515322A; EP0931349A1

Abstract

The invention concerns a superconductive electronic component which displays specific properties of an emitter and/or detector for electromagnetic radiation in the submillimetre wave range. The component comprises a planar network of microbridges (webs) formed in a thin layer of a high-temperature superconductor. The latter is grown epitaxially on the substrate with the CuO2 planes either perpendicular or inclined at an angle Υ(1°∫Υ∫89°) to the substrate surface. In this way, each microbridge receives a sequence of stacks of superimposed (intrinsic) Josephson contacts. The invention also concerns superconductive connections (series and parallel) between individual microbridges, whereby switching circuit parameters, such as adaptation of the impedance to the radiation space and maximizing of the radiated output, can be optimized. The frequency and intensity, for example, of the radiation field can be influenced (e.g. modulated) by external means of an electronic control. In particular, this component can continuously cover the frequency range between the far infrared and the microwave range. The invention also concerns some applications of the proposed component, covering both the emission and detection of electromagnetic radiation.

Description

description

Emitter and or detector component for submillimeter-wave radiation and method for its production

Field of application of the invention

The invention relates to a superconducting component, production technologies and fields of application and, in particular, to a novel emitter and / or detector for the sub-millimeter wave area, as well as its diverse applications.

Characteristic of the known technical solutions

1. Arrangements of natural Josephson contacts

The first findings on the usability of Josephson contacts as tunable microwave emitters and detectors go back to the early work of B. Josephson and S. Shapiro. However, it was recognized at a very early stage that a single Josephson contact emits too little power and, moreover, has too wide a spectral distribution in order to find practical use as a microwave emitter. It is known that these shortcomings can be overcome by using stacking sequences of Josephson contacts [Jain et al. 1984; Bindslev Hansen and Lindelof 1 84; Lukens 1990].

As soon as the coupling between the Josephson contacts is strong enough, self-synchronization can occur with the effect of a coherent radiation emission from all contacts [Lukens 1990; Konopka 1994]. Possible coupling mechanisms and coupling strengths have already been examined in detail [Jain et al .; Lukens 1990]. The line width of the electromagnetic radiation emitted by the crystal stack decreases as the number of Josephson contacts in the array increases. It can become very small if there are a large number of Josephson contacts [Lukens 1990; Wiesenfeld and others 1994; Konopka 1994].

The power of the emitted radiation also increases with the number of Josephson contacts and can also be considerable in large arrangements (P> 1 mW), which is sufficient for many practical applications [Bindeslev Hansen and Lindelof 1984; Jain et al. 1984; Co- nopka et al. 1994, Wiesenfeld et al. 1994] It is important that a good impedance matching to the load resistance (eg the free space) is achieved, because otherwise the majority of the radiation does not emerge from the component, but is used up inside by multiple reflection

Another point of view are various loss mechanisms in the contacts. For example, the capacities of the contacts are responsible for a loss of power at higher frequencies [Lukens 1990, Wiesenfeld et al. 1994], which indicates the use of the smallest possible Josephson contacts. Small contact areas are also beneficial for reducing the noise and the spectral line width [Kunkel and Siegel 1994, Konopka 1994] The current flow through the contact becomes inhomogeneous as soon as between the width w of the transition and the Josephson penetration depth λ. the relationship exists, w ≥. 4λ,, [Kunkel and Siegel 1994] It is also clear that for optimal phase synchronization the critical currents (I _c ) through all Josephson contacts must be very similar. In general, a homogeneity of at least ± 5% in linear stack sequences is required [ Konopka 1994]

The high demands mentioned so far can be weakened somewhat if a distributed arrangement of acid-resistant Josephson contacts is chosen along a propagation line. However, the distance between the Josephson contacts and the selected radiation wavelength must match [Kükens 1990, Han et al. 1994] Apparently the tunability of the radiation frequency is severely curtailed, but in favor of a significantly increased emission power

There have been numerous experimental studies on the arrangement of Josephson junctions, and some remarkable results have been obtained. Most of them are based on conventional low-transition temperature superconductors, such as Nb / Al-AlO _x / Nb three-layer structures linear arrangements of 100 such Josephson contacts were detected [Han et al. 1993] In some cases, a broadband antenna (eg logarithmic spiral antenna etc.) was integrated on the chip, and the radiation emitted into the outside was measured. In other cases, another was used Josephson contact as detector coupled via a propagation line to the arrangement of the radiation emitters. Some of the best results achieved are as follows. An emission of P = 50μW at a frequency of v = 400-500 GHz was detected in a distributed arrangement of 500 Josephson contacts [ Han et al. 1994] in another circuit (Anordn of 10 x 10 contacts) is radiation with a line width of Δv = 10 kHz and a tunability of v - 53 - 230 GHz [Booi and Benz 1994] were measured.

With the discovery of high-temperature superconductors in La-Ba-Cu-O by G Bednorz and KA Müller in 1986, and the associated increase in the critical temperature in similar copper oxide (cuprate) compounds up to T _c > 160K enormous expectations for superconducting electronics at the temperature of liquid nitrogen and above arose. In fact, since then, dozens of research laboratories around the world have made Joseph-son contacts in these new materials using several different techniques. The radiation emission as a result of the Josephson alternating current in artificial Josephson contacts in high-temperature supercells was measured and analyzed [Kunkel and Siegel 1994]. In the same work, phase synchronization in step contacts over a broad frequency band of v = 80-500 GHz was demonstrated. In larger arrays, only a partial (up to 4 Josephson contacts) and also unstable phase synchronization could be achieved [Konopka 1994] Als Reason has been found to be a result of the inhomogeneity (dissimilarity) of such step contacts in high temperature superconductor-Josephson contacts where critical current variations of up to + 50% occur [Konopka 1990]. In another work, arrays of 5 and 10 Josephson transitions from adjacent step contacts are examined, again with only partial phase synchronization and very low radiation power [Kunkel and Siegel 1994].

In several publications, spectacular statements are made about promising future applications of grouped Josephson contacts. For example, applications as generators and detectors of radiation in the GHz and THz range are forecast [Jain et al. 1984], and even more specific ones in radio astronomy and radio Spectroscopy of heavy molecules [Konopka 1994], in voltage standards [Ono et al. 1995], etc. So far, all these applications have not been put into practice because of the difficulties mentioned above. It is generally assumed that a radiated power of 0 1 for spectroscopic applications - 1 mW is required for continuous tuning and this has not been possible to date [Konopka et al. 1994] US Pat. No. 3,725,213 describes a superconducting barrier component and its production technology which, in addition to other objectives, is also suitable as a generator and detector for millimeter-wave and sub-millimeter-wave radiation and is based on a granular structure of the superconducting material Sensitivity due to the summation of many Josephson contacts between crystal grains, there are few possibilities for reproducible production, electronic control, phase synchronization and impedance matching to the vacuum. This component can conduct normally between the two states via a current-pulse-induced magnetic field and are switched superconducting, however, no attempt is made to control the emitted radiation frequency via the magnetic field-dependent energy gap

A superconducting component is described in US Pat. No. 4,837,604, which uses vertical stacking sequences of Josephson contacts and a serial interconnection of stacking sequences. It is designed as a switch with 3 electrical contacts and is intended to be simple Josephson contacts or lateral arrangements of such contacts in analog and digital Switching arrangements without radiation emission is not a goal for the component, nor would its technical design allow such a goal

In US-PS 5, 1 14.912 a high-frequency oscillator is described, which is based on a flat arrangement of Josephson contacts. It is excited by a direct current source, and the frequency can be tuned by means of this direct current Choice of the number of Josephson contacts in the flat arrangement, or by connecting appropriate shunt resistors. As an application, a tunable DC-AC converter in the GHz range and even up to THz frequencies is specified

A disadvantage of this component is its expressive limitation to a 2-dimensional flat arrangement of adjacent Josephson contacts on a chip. Such a geometry implies a strict limitation of the maximum possible number of Josephson contacts. Specifically, the minimum area of a single contact is around 1 μm due to the limited performance of photolithography.The requirements for uniformity are high, a considerable critical current is required (not less than 1mA for optimal performance), which is also via lines with low On the other hand, supplying contact resistance limits the requirement for phase synchronization Longitudinal expansion of the component to about λ 4, a value that is about 75 μm for a frequency of 1 THz. If one allows small distances between the contacts, one can expect a maximum of one to two thousand such individual elements. In practice, arrangements of 10 x 10 = 100 contacts realized. As already explained, such a component design does not provide the minimum power of 0-1.1 mW required for interesting applications. It should be shown that the alternative designs proposed according to the invention allow a significantly higher packing density of Josephson contacts with the prospect of a significantly higher one emitted power and thus on a variety of new applications that are not possible with flat (planar) arrangements, as shown there

EP 446146 describes a three-layer Josephson contact which has superconducting electrodes on both sides, which consist of LyBa ₂ Cu ₃ O (Ly is Y or a rare earth metal, 6 <y <7). The non-superconducting barrier consists here from Bi ₂ Y Sr _y Cu _z O _w , 0 <x <2, 1 <y <3, 1 <z <3, and 6 <w <13 However, information on the properties of the component (such as BI _c , R „, IV characteristic, microwave modulation) or for the representation of lateral or vertical stack structures and their possible applications

A magnetic control mode for the emitted or detected radiation frequency is described in EP 513,557, where the component according to the invention consists of vertical stacking sequences of Josephson contacts, which also have side-mounted galvanic connections between each pair of adjacent superconductor / barrier / superconductor structures (SIS Structures), a further superconducting layer is provided, which is separated on both sides by an insulator layer from the adjacent Josephson contact. This layer is intended to control the individual component by passing a current through lateral contacts through this control layer (see also US Pat. No. 3,725,213). , a magnetic field is to be generated which influences the energy gap of the Josephson contact

This component has several disadvantages, which make its practical implementation impossible within the framework of the currently known material properties and available microfabrication technologies. In particular, (i) its manufacture requires the deposition of superconducting contacts of approximately 0.01 μm in width over insulating layers on two opposite side faces from perpendicular to it grown stack structures with Josephson contacts No technology is currently available for this. Furthermore, (ii) no superconductors are known which generate such large currents to generate the required high magnetic can withstand field strengths that would be required to reduce the energy gas in high-temperature superconductors within the limits of the required geometric component dimensions. Even assuming that this was somehow possible, (iii) the magnetic field of a particular control layer would affect more than just one Josephson contact, result in undesirable cross-talk between multiple Josephson contacts, and frustrate patent intent. Finally, (iv) the radiated power would be too low for many applications, since a circuit optimization of the Josephson contacts for matching the impedance to the outside is not provided.

2. Natural stacking sequences of Josephson contacts in copper oxide superconductors

In 1986, in the very first publication on copper oxide superconductors, JG Bednorz and KA Müller expressed the opinion that La-Ba-Cu-O is a quasi two-dimensional superconductor due to its distinctive layer structure. Subsequently, this hypothesis was confirmed by a large number of experimental results in various cuprate superconductors [eg Bozovic 1991], with direct evidence from the observation of superconductivity in Bi ₂ Sr ₂ CaCu ₂ Og layers the thickness of a unit cell [ Bozovic et al. 1994]. Furthermore, the critical current along the c-axis (ie perpendicular to the CuO ₂ layers) is much smaller than in the direction parallel to the CuO ₂ planes. It is not zero, ie a super current in the direction of the c- Axis flow. However, this implies the property that the planar 2-dimensional superconducting rods are weakly coupled via Josephson tunnels.

In other words, cuprate superconductors can be understood as natural (intrinsic) stacking sequences of Josephsen contacts with a distance of 6 .. 25 A. A theoretical model for a stacking sequence of Josephson-coupled superconducting layers was published 25 years ago [by Lawrence and Doniach 1971] and has been extensively investigated since then. The model's predictions relate to a non-linear current-voltage (I-V) characteristic, microwave radiation-induced I-V stages (Shapiro stages), and microwave emission by applying DC voltage.

In fact, all of these properties have been observed in cuprate superconductors, first in Bi ₂ Sr ₂ CaCu ₂ O _g [Kleiner et al. 1992] and then also in (Pb _y Biι. _Y ) ₂ Sr ₂ CaCu ₂ O ₈ , Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _ιo , etc. [Kleiner and Muller 1994, Muller 1994, 1996, as well as by other groups, Regi and others 1994, Irie and others 1994, Schmidl and others 1995, Yasuda and others 1996, Tanabe and others 1996, Yurgens and others 1996, Seidel and others 1996, Xiao and others 1996]. Most of these results were found in small single crystals, but mesa structures were also etched from single crystals or thin layers [Schlenga et al. 1995]. In some cases, phase synchronization of more than 1000 Josephson contacts was achieved [Schlenga et al. 1995], but in general only partially achieved, as is shown by the large number of branches in the IV characteristics (in all previous work). Specifically, if the Josephson contacts belonging to a stack are not all identical, ie if their critical current differs from contact to contact, they do not return to the normal conducting state at the same point on the characteristic as soon as the current flow is increased. As a result, the radiation emission must result as a superposition of coherent (narrow-band) radiation, which has also been observed [Schlenga et al. 1995, Müller 1996]. These differences in the properties of the Josephson contacts result from imperfect crystal growth and the lithography process to define the mesa structures, which also leads to differences in the cross-sectional area of the mesa structures. The highest frequency of emitted radiation measured so far is v = 95 GHz, which is, however, the result of inadequate laboratory detection technology [Müller 1996].

So far, no practically usable components or applications have been reported, although there are sufficient indications for the use of possible future emitters of submillimeter radiation [Schlenga 1995].

Although such mesa structures in thin cuprate layers showed nonlinear IU characteristics with numerous branches and switching between the branches, hysteresis, as well as Shapiro steps caused by microwave radiation, and even microwave emission, the IV characteristics and other properties of this mesa remain Structures far behind those of ideal phase-synchronized stacking sequences of Josephson contacts. In particular, the emitted microwave line is only in the pW range, which is equivalent to the fact that such stacking sequences are of no interest for practical applications.

There are three main reasons for this: (a) The Josephson contacts were not uniform in their values of I _c and R _N ; (b) The areas of the Josephson contacts were generally too large, typically about 30x30 μm ² »10 ^'5 ; and (c) the devices were not optimized in terms of their impedance matching to the free space. As a result of (a) and (b), phase synchronization is not perfect, unstable and random Natural Josephsonian contacts O

Cuprat superconductors have relatively large critical current densities in the c-axis direction (10 ⁴ -10 ⁶ A / cm ² ), so that such contacts have critical currents that are far too large, 100 mA and above. Large Josephson contacts show many complex excitation modes, supra-currents flowing in both directions, fluxon movement, etc. Although these problems are known, the scientists in the groups mentioned were unable to significantly reduce the contact area due to excessive electrical resistances. Excessive electrical contact resistances cause the stack sequences to heat up significantly, which makes phase synchronization more difficult and the critical currents become inhomogeneous. In extreme cases, the Josephson contacts burn out

3. thin layers of high-temperature superconductors with a-axis orientation

A current development that is suitable for practical implementation in a novel component is a technology for growing thin high-temperature cuprate superconductors in which the CuO ₂ planes are not arranged parallel to the substrate. These can actually be perpendicular to the substrate, and we want to refer to such a thin layer as an 'a-axis' oriented layer. This name is derived from the specific case that the single-crystal layer is grown in such an epitaxial relationship to the substrate that the a-axis is perpendicular to the surface of the substrate do not want to distinguish this case from the fact that the b-axis (in orthorhombic crystals with a ≠ b) is perpendicular to the substrate, and also if the a-axis is arbitrarily inclined, as long as only the c-axis runs parallel to the substrate surface, that is, as long as the CuO ₂ planes are perpendicular to the substrate surface

Using a similar commonly accepted (though inaccurate) terminology, we will refer to the whole set of epitaxial orientations where the CuO ₂ planes are at 90 ° or 0 ° angles to the substrate in the term "inclined a-axis" layer A more precise distinction and a more precise description is quite possible, for example using the concept of Miller's indices of substrate surface (on which the thin layer is to be deposited) and thin layer surface. However, this is not necessary for the discussion here

By far the largest group of high-quality superconductors produced and of high quality have the c-axis orientation (ie the CuO ₂ planes are parallel to the substrate surface). The reason for this is the strong anisotropy of phy- physical properties of layered cuprates, including growth rates in different crystallographic directions. Nevertheless, there is considerable effort directed to growing "a-axis" oriented and "inclined a-axis" layers, the main motive being the much greater coherence length towards the a-axis for three-layer Josephson -To use contacts. Some of the most successful breeding experiments of this type are presented below.

Thin Bi ₂ Sr ₂ CaCu ₂ O ₈ layers with CuO ₂ planes inclined by 45 ° have already been deposited on SrTiO ₃ substrates using magnetron sputtering technology, which deviated from the (110) direction at an angle of 5 °. MgO substrates with the same characteristics and additional buffer layers were also used. [Tanimura et al. 1993]. The desired inclined a-axis orientation was demonstrated by means of RHEED (diffraction of high-energy electrons in the reflection position) and TEM (transmission electron microscopy) in cross-sectional imaging and by measuring transport properties.

Essentially completely a-axis-oriented YBa ₂ Cu ₃ O ₇ layers were obtained on (100) -oriented LaSrCaO ₄ substrates with a PrBa ₂ Cu ₃ O ₇ buffer layer by means of single target sputtering [Suzuki et al. 1993]. Similar oriented films from Ndι _{+ x} Ba ₂ . _x Cu ₃ O ₇ .d were applied directly to (100) -oriented SrTiO ₃ substrates by means of laser vapor deposition, whereby special care was taken to set the growth parameters correctly [Badaye et al. 1995].

These examples demonstrate that it is technically possible to produce "a-axis" oriented and "inclined a-axis" layers of high quality from cuprate superconductors. An embodiment of the invention is based on the above facts.

Aim of the invention

The aim of the present invention is to provide means which allow the disadvantages and difficulties of known solutions discussed above to be avoided and to develop a component which avoids the disadvantages discussed.

It is a further object of the present invention to provide a novel radiation emitter and detector for electromagnetic radiation in the submillimeter wave range which simultaneously uses a plurality of stacking sequences of Josephson contacts in a flat (2-dimensional) arrangement so that the generation of microwave lines or the sensitivity for detecting microwave radiation is increased considerably.

It is a further object of the present invention to provide a novel radiation emitter in the submillimeter-wave range with such an impedance that impedance matching to the radiation-receiving space is achieved, whereby the radiated power takes maximum values.

It is a further object of the present invention to provide a novel radiation emitter in the sub-millimeter wave range which has a very small emission line width (less than one millionth part of the radiation frequency) within its sub-millimeter wave band reaching up to a few THz.

It is a further object of the present invention to provide a novel radiation emitter and detector in the submillimeter-wave range with an electronic control for continuously changing the emission frequency or the detection frequency over a wide spectral range.

It is a further object of the present invention to provide a novel radiation emitter and detector in the submillimeter-wave range, the emitted microwave radiation of which can be electronically modulated or switched on and off, which also corresponds to a fast electronic switch for superconducting electronics.

It is a further object of the present invention to provide a novel radiation emitter and detector in the submillimeter-wave range which enables the functions of emission and detection independently of one another, in channels with different frequencies or with electrically variable and controlled frequencies.

It is a further object of the present invention to provide a novel radiation emitter and detector in the sub-millimeter wave range which allows an inversion of the emission and detection mode with external electronic means

It is a further object of the present invention to provide a novel radiation emitter and detector in the sub-millimeter wave range which is suitable for inclusion in superconductor / semiconductor hybrid circuits

State the nature of the invention These objectives are achieved with the present invention of a two-dimensional network of superconducting microbridges with stacking sequences of (native) Josephson contacts, parts of the network being grouped and connected in series (serial, parallel) and operated via contacts with an external electronic control unit In particular, the object is achieved by the features specified in the characterizing part of claims 1 and 13. Advantageous refinements and applications of the invention are specified in claims 2 to 12 and 14 to 19

Embodiment

The invention will be explained in more detail using exemplary embodiments. The accompanying drawing shows

1 shows a unit cell of the crystal of a high-temperature superconductor, which contains a CuO ₂ plane,

Fig. 2. An "a-axis" oriented layer of a high-temperature superconductor. The CuO ₂ planes are perpendicular to the substrate

Fig. 3 A thin layer of a high-temperature superconductor with an "inclined a-axis". The CuO ₂ planes are inclined at an angle Θ with respect to the substrate

4 A, a microbridge which was produced from a high-temperature superconductor with an “a-axis” -oriented growth direction

FIG. 4B An equivalent circuit for the component shown in FIG. 4A. A simple, linear (serial) arrangement of Josephson transitions

Fig. 5. A microbridge made from a high temperature superconductor with "inclined a-axis" growth direction. The equivalent circuit corresponds to that of Fig. 4B

Fig 6 A. A parallel arrangement of micro bridges, each containing stacking sequences of natural Josephson contacts, produced from an epitaxial “a-axis” or “inclined a-axis” layer by chemical or ion etching of trenches that electrically isolate the micro bridges from one another

Fig. 6 B An equivalent circuit for the component from Fig. 6 A Parallel connection of two linear stack sequences of Josephson contacts Fig. 7.A A parallel connection of three identical groups (clusters), each with 10 microbeads

Fig. 7 B An equivalent circuit for the component of Fig. 7 A

Fig. 8 An arrangement of several groups of micro bridges, each containing stacking sequences of Josephson contacts, along a strip line. The distance between the individual segments of combined emitters corresponds to the wavelength λ of the electromagnetic radiation within the structure

Fig. 9 A basic structure of the device according to the invention, which contains a two-dimensional lateral arrangement of parallel micro-bridges (webs) (a) in a thin superconducting epitaxial layer, which are separated from one another by trenches (b) reaching down to the substrate and thus the current flow through the Steering micro-bridges or groups of micro-bridges Each micro-bridge contains a stacking sequence of Josephson contacts, the arrangement of which is explained in FIGS. 2 and 3. The electrical connections (c) and (d) allow a connection to external control electronics (e)

Based on an embodiment of the component according to the invention, the invention is described in more detail below, the basic structural unit of which, that is to say the linear stacking sequence of Josephson contacts, is formed in a thin layer of high quality of a high-temperature superconductor, the thin layer forming a special epitaxial relationship with the Substrate is located

1. Micro bridges in "a-axis oriented" and "inclined a-axis oriented" thin layers

For explanation it must be noted with reference to FIG. 1 that the crystallographic unit cell of all known cuprate superconductors represents an elongated parallelepiped with the side lengths a "b" 3 8Ä and c> a, b. For example c <6 5Ä in Lai -aSτ ₀ uCuO ₄ , c «l 1 7Ä in YBa ₂ Cu ₃ O ₇ , c« l 5 4Ä in Bi ₂ Sr ₂ CaCu ₂ θ8, etc [More specifically, the c-axis periodicity in Lai g ₅ Sr ₀ ιsCuO ₄ and Bi ₂ Sr ₂ CaCu ₂ O _g twice as large due to the presence of a sliding plane, although this fact is of little importance for the present discussion, as is that of a slight orthorhombic distortion with a ≠ b in YBa ₂ Cu O ₇ ]

All of the high temperature superconductors that have been considered to date have been grown with the c-axis perpendicular to the substrate (they are commonly referred to as “c-axes” for short oriented HTS layers "). This is the most common epitaxial relationship that usually occurs when high-temperature superconductors are grown on lattice-matched substrates, such as (100) -cut SrTiO ₃ , LaA10 ₃ , etc. In this case, run all CuO ₂ planes parallel to the large area of the substrate.

However, if specially cut substrates are used, it is possible to achieve other epitaxial arrangements in which the CuO ₂ planes are perpendicular to the large area of the substrate. In such a case, the a-axis of the cuprate superconductor (or the b-axis, which is completely equivalent) is arranged perpendicular to the large area of the substrate, as shown in FIG. 2. Such high-temperature superconductor thin layers are abbreviated as 'a-axis-oriented HTS layers'.

One way to achieve this orientation is as follows (here Lai.gsSro.isCuO. _» Is chosen as an example, where a« is 3.8 Ä and c _* 6.5 Ä):

The substrate and its "cut" (ie the direction of polishing or the orientation of the surface plane of the substrate) are selected so that the periodicity of the surface plane is 3.8 A x 6.5 A. Then there is the possibility that the layer with its a-axis grows perpendicular to the substrate. Another aspect is the number of "favorable contacts" between cations and anions of the layer and the substrate, which influence the energetic relationships in the interface. Of course, different substrates or at least substrate cuts are required for each different high-temperature superconductor.

For the present purpose, it is sufficient to state that such substrates and substrate sections for several cuprate high-temperature superconductors have already been discovered, and complete epitaxial a-axis growth has actually been demonstrated, namely for Laι. ₈₅ Sr ₀ .i ₅ CuO and YBa ₂ Cu ₃ O ₇ [Suzuki et al. 1993, Badaye et al. 1995].

Another embodiment of the present invention is provided by a possible other epitaxial relationship shown in FIG. 3. For this purpose, all CuO ₂ planes of the cuprate films are grown at an angle to the substrate which is different from 0 ° and 90 °. Such an angle depends on the substrate cut and can typically be 1 ° to 10 °, although larger or smaller angles are also possible. For the purpose of the present discussion, we assume that the angle is approximately 5 °. This requires the existence of steps in the substrate that are 3.8Ä high and have a distance of approximately d = 3.8 x tan 85 ° A. Epita xial growth of such inclined a-axis-oriented HTS layers has already been carried out [Tanimura et al. 1993, Kataoka et al. 1993],

As already stated, high-temperature cuprate superconductors, such as Bi ₂ Sr ₂ CaCu ₂ Og, Tl ₂ Ba2Ca ₂ Cu ₃ Oιo, HgBa2CaCu2θ6. ₂ , Laι.85, Sr ₀ .i5CuO ₄ , etc. are natural superconducting superlattices of SIS ..., or SINIS type. If one of the orientations of the thin layer is used, then simple microbridges of the type shown in FIG .A. and Fig. 5 type, and thus thus generate a stacking sequence of Josephson contacts. Such stacking sequences in micro bridges represent the basic structure for the component according to the invention. However, in order to set an optimal performance of the component, several such micro bridges must be connected together in a superconducting network, as described in the text below.

2. Interconnection of micro bridges: circuit optimization

A single stacking sequence of Josephson contacts is considered first. The maximum allowed critical current through a single contact is approximately

Larger values lead to very disturbed current-voltage characteristics due to the occurrence of special flow conditions. The Josephson contact behaves like a "long contact" with currents flowing back and forth at different locations. With the example of I _C R = 10mV and I _c = lmA, the typical lower limit for the electrical resistance R is obtained = 10Ω. Impedance matching of the component to the vacuum requires a total resistance Rτoτ ⁼ NR = 300 Ω. With R = 10Ω one obtains N = 30 as the value for the number of Josephson contacts to be inserted in the stacking sequence of a mesa structure. If I _e smaller would be less than 1mA, an even larger value for R and thus a smaller value for N. This value N would therefore be a lower limit for a single mesa structure with impedance matching to the vacuum.

The geometric dimensions of the contact are also already defined with the values mentioned. If ¹ = 10 A / cm ² , I _c = 1mA is the area of the Josephson contact

A = Iβ each = 10- ³ A / 10 A / m ² = 10 ^"7 cm ² = 10μm ² .

If square Josephson contacts were used, they should have an edge length of 3 μm. This value of j _c ^{1 =} 10 ⁴ A / cm ² relates to natural Josephson contacts in very anisotropic high-temperature superconductor materials, such as Bi ₂ Sr ₂ CaCu ₂ θ8. With less anisotropic high-temperature superconductor connections, j _e ¹ can assume higher values (up to 10 ⁶ A / cm ² in YBa ₂ Cu ₃ O ₇ ), which could result in even smaller contact cross-sectional areas.

However, the output power of such a simple stacking sequence is quite modest:

PM _AX ° ^U, = 1 / 8NI _C ² R = (1/8) X30X10 ⁶ X10A ² Ω = 5 x 10 ^ mW.

Higher radiated power can only be expected if more complex systems with series and parallel groups of mesa structures are used. Essentially, the idea is to increase the total current through the component without exceeding I _C ^MAX = 1 mA for a single contact by connecting several stack sequences in parallel (FIG. 6). A reduction in overall resistance can be easily compensated for by increasing the number of Josephson contacts in each stacking sequence.

For a parallel connection of M stack sequences, in which each contains N Josephson contacts in series connection, the total resistance is Rτoτ ⁼ (NM) R; For R _τθ τ = 300Ω and R = 10Ω we get N / M = 30 or N = 30 M.

The total current becomes I = ML., So the total power

Pτoτ ° = (l / 8) xlO- ⁶ x300xM ² A ² Ω * 0.4 x M ² mW arises.

It can thus be seen that the total radiated power is proportional to M ² , and it could appear that the power can be increased at will. However, restrictions are imposed by the maximum possible size of the network and of course the still acceptable dimensions of the individual batch sequences.

For a grouped arrangement of Josephson contacts in particular, phase synchronization can only be achieved over a distance of approximately λ / 4, where λ is the wavelength of the electromagnetic radiation emitted. If the desired radiated frequency were v = 3 THz, then λ = 100μ; for v = lTHz, one gets λ = 300μm.

To optimize component parameters (e.g. to adapt impedance to the vacuum and reduce the internal reflection of electromagnetic radiation at the 10

stall / vacuum interface), it is desirable to electrically combine micro bridges in any desired manner. However, the electrical connections should consist of superconductors and should not lead to the formation of 'weak links', which then act as Josephson contacts in series with the stacking sequence of Josephson contacts in the mesa structure. In other words, high temperature superconducting electrodes of the same type of superconducting material are required.

Both series and parallel connection of mesa structures is required in practically relevant cases. In the following section, a method will be explained with which the series switching of simple micro bridges or groups (clusters) vc-. Micro bridges are achieved that already exist as a parallel connection. Furthermore, realistic estimates of the maximum possible number of phase-locked Josephson contacts in such batch sequences and networks are given.

3rd example

An analysis of the realistic limits of linear stack sequences and their parallel and serial interconnection takes place in the following way: Assuming I _C R «25 mV and l ^^ = 1mA as given, then R = 25Ω is the resistance of a Josephson contact. This limits N to values of 10-15 if impedance matching to the vacuum is sought with R _T oτ = NR ≡ 300Ω. This is obviously not very favorable for a pure a-axis-oriented HTS layer (Fig. 2, Fig. 4. A), since in such a case the length of the microbridge (in a-axis layers is the name) "Microbridge" chosen for the previously designated "mesa structure" in c-axis layers). Would be less than 15 x 20 Å = 30θA, which is too small for common lithographic processes.

The situation improves for inclined a-axis oriented HTS layers (FIG. 3, FIG. 5), where the angle of inclination is relatively small (approximately 5 °). Here one gets an overall length L of the microbridge of d / tanθ for N = 15 and c = 15 Ä, where d is the layer thickness. For d = 1000 Å and θ = 5 ° one obtains L «10, OOOÄ = lμm, which represents a reasonable value for currently usual lithography processes. And this length can be increased further with increasing layer thicknesses. However, we also have to examine the required lateral dimensions. Restrictions come from the current density j _c . A typical current density for c-axis oriented layers is j _c = 10 ⁴ A / cm ² . With a desired critical current of L = 1mA one obtains the already mentioned contact area A = ljj _c = 10 ^' 3/10 ⁴ cm ² = 10μm ^{2. However} , it should be noted that the effective width is now equal to the layer thickness divided by the tangent of the angle of inclination, ie d / tanθ. With d = 1,000Ä and θ = 5 ° you get d / tanθ * lμm. This means that the width of the micro bridges should be 1 μm, which can certainly be achieved.

However, such a microbridge, which contains a stacking sequence of Josephson contacts, will only produce a relatively small output of emitted radiation, namely P _out = (l / 8) I _c ² R _TO τ = (1/8) (10 °) ² 300 W * 0.4mW.

In order to increase this power, a parallel connection of the M of such micro bridges is required again, since in this case P _ou ι = (1/8) (MI _C ) ² R _T oτ = M ² x 0.4 mW, provided that the number N of the natural Josephson contacts in each microbridge is set so that the impedance matching to the vacuum remains satisfied. For R _TOT ⁼ RN / M ≡ 300 and R = 15-30Ω we get N / M «10-20, or typically N = 15 M.

This provides the starting point for creating a very simple component, which is shown in FIG. 8 and consists of a parallel arrangement of M identical micro bridges. These are formed by simply creating a series of equidistant trenches down to the substrate by chemical or ion etching.

For N = 15 M one obtains micro-bridges which are elongated by M times. A pure a-axis oriented HTS film leads to a microbridge length of 15x30θA = 4,500Ä or 0.45μm, which is still a very small value and technologically difficult to manufacture. In contrast, the length of the microbridges in inclined a-axis-oriented HTS layers for d = 1,000A, N = 300 and θ = 5 ° will be approximately M μm.

We had already concluded above that for j _c = 10 A / cm ² and I _c = 1mA the contact area A = 10μm ² and the microbridge width was about 10 μm (our standard choice d = 1,000Ä and θ = 5 °). M is thus severely restricted, since the entire width of the component is 25μm for an emission frequency of v = 3THz (λ = 100μm), and for v = lTHz (λ = 300 μm) can be 75 μm. Hence one obtains for M = 3-7, which would correspond to a quite considerable output power of P ₀ "t = 1-20 mW.

Further improvements in emission performance could be obtained by choosing less anisotropic high temperature superconductors with a higher critical current density for the c-axis direction. For example, for YBa ₂ Cu O _7> j _c «10 ⁶ A / cm ² in the c-axis direction. In such a case, much smaller contact areas would have to be provided, say 0.1-1 μm ² , which results in much narrower trenches, an increased number of micro bridges and thus a higher emission power. A practical limit for the width of micro bridges could be 1 μm with very narrow trenches in between. At 3 THz this would result in an increase of around 25 for M and the considerable output power - / on around P «240 mW

Another possibility for improvement lies in the very short length of micro bridges (<lμm) for a-axis-oriented HTS layers. One could design a device according to FIG. 7. Using the available component length of 25 μm (for 3THz), three parallel segments (strips) of 10 parallel micro bridges each were connected together in this FIG. 7. The superconducting electrical connection between the 3 segments is parallel. One therefore has a total value M of micro-bridges, which results from the number of micro-bridges per segment multiplied by the number of segments. Realistic values can go up to 25 micro bridges per segment and up to 10 segments, which would correspond to an M = 250. Under ideal conditions, this would result in an immense emission output of

P = (250) ² 0.4 mW = 25W!

Although the previous value for the output power is certainly too high an estimate due to a number of other limiting factors, the potential that could be present in such a component is nevertheless visible. Also noteworthy is the simplicity of manufacture, which requires a single lithographic process cut without any particular alignment requirement.

Because of the greater width of the material strips perpendicular to the micro bridges, a higher current can flow here than in a single segment of micro bridges. The current flows in these strips along the CuO ₂ planes, which is the "simple" (ie more conductive) direction corresponds; j _c can in this direction (parallel to the a axis). 10 - 1000 times higher than in the "hard" (that is, c-axis) direction along which the current flows through the microbridge In this way, weak ^links' between avoided these contact paths and the micro bridges.

Finally, it should be noted that the electrical connection to the external electronics takes place via thick (0.5-1 μm) and large-area (1 mm ² ) normally conductive metal contacts (gold, silver, etc.) which have been deposited on the superconducting layer . Heating of the component due to the resistive behavior of these contacts is thereby considerably minimized. Connecting external connections is easy.

The embodiment of the component according to the invention discussed here has the additional advantage that the Josephson contacts have a very small cross-sectional area and thus a very small electrical capacitance C. A pure a-axis-oriented YBa ₂ Cu ₃ O ₇ film with a critical current in the c-direction of j _c = 10 ⁶ A / cm ² has a cross-sectional area of A = 10 ^"9 cm ² = 0 with an optimal current . lμ ^2. This also corresponds exactly to a layer thickness of 1,000 Å and the microbridge width of 1 μm, as already described above.

From the known material properties for cuprates and for insulating layers one can expect a capacitance of C 5 x 10 ^"15 F in such small contacts. [The specific capacitance of Nb / NbO _x / Nb-Josephson contacts is 50 fF / μm ² This value can be made 5 times lower if only 200 Å were used instead of the layer thickness of 1 μm, a disadvantage would then be the reduction in the maximum critical current density and a reduction in the radiated power.

On the other hand, such contacts have the advantage of critical damping. The McCumber parameter is ß = 2π I _C R ² C / Φ ₀ <1, where Φ ₀ = h / 2e = 2xl0 ^' l5 Vs is the flux quantum, h the Planck' see quantum of action and e is the electron charge. It is known that ß should be small (<1) when optimum radiated power and frequency tuning is required.

The above consideration is limited to the case of a single group (cluster) of Josephson contacts. In fact, it is possible to further increase the maximum radiated power by choosing a distributed arrangement of such groups. You can group Arrange the pen at an equidistant distance at distances of λ between them (let's say λ = 300μm for v = lTHz).

By covering the entire structure (layer) with an insulating material (e.g. SiO ₂ , MgO, CeO ₂ , etc.) and applying a metal layer (e.g. gold or silver), a transmission line can be created through which the electromagnetic radiation is conducted will (see Fig. 8).

Phase synchronization can be achieved in such structures over fairly long distances, whereby the radiated power can become considerable. The disadvantage of such lines is evident, however, that the operating frequency is quite fixed due to the group spacing λ. Higher performance can only be achieved at the price of reduced tunability.

Further aspects of optimization include the integration of an antenna, whereby the existing superconducting layer can conveniently be used for this.

4.Microwave radiation source

After a thin-film structure with an arrangement of micro bridges (generally in parallel and series connection) has been produced and connected to other standard components of microwave technology (antenna, propagation line), these can be connected to conventional control electronics with a controllable current source (up to 100 mA), control devices , Connect frequency and power displays, etc. This then represents a complete source for narrowband electromagnetic radiation, which can be tuned in a wide frequency range and up to high frequencies of 5-10 THz.

We call this component of the present invention the basic variant of the tunnel tron. It is shown in Figure 9.

5. Areas of application

The present invention can be used in almost all fields of application in which millimeter and submillimeter-wave radiation is emitted or detected. In addition, completely new fields of application open up, of which some examples are given below:

Some lasers and reverse wave tubes (carcinotrons) operate in the submillimeter wave range, but they are voluminous radiation sources with high power consumption. Solid state per oscillators, such as GUNN or IMPATT diodes, are limited to the millimeter wave range.

Josephson contacts, which are matched to the external resistance without reflection and combined to form a network, can be controlled via a voltage and cover a wide frequency range up to the terahertz range.

Quantum detection of electromagnetic radiation - a widely used concept in the visible and infrared spectral range - was previously only possible in the microwave and millimeter wave range in the narrow range of the spectrum, which is grouped around the resonance frequency of MASER amplifiers. The standard methods for detection in this frequency range use nonlinear electrical resistances, e.g. Schottky diodes as classic rectifiers and superimposed receivers. Their working principle is based on the conversion of received power between different frequency ranges, instead of the conversion of photons into electrical charge carriers, the functional principle of quantum detectors.

The abrupt non-linearity in the IU characteristic of SIS tunnel barriers for single-particle tunnels represents a useful property for resistive mixing. Superimposed receivers with Josephson contacts as such mixing stages have a sensitivity that approaches the quantum limit at frequencies up to several GHz. The function of a heterodyne receiver is to mix a weak useful signal of frequency v with the frequency of a local oscillator V ₀ , with an intermediate frequency vy = | V »-V _L0 | arises and is further processed electronically. A photon current with an arrival rate of one photon per nanosecond is a typical value of the detection sensitivity of such a receiver. Such light outputs are typical of radio astronomy, which examines interstellar matter in the millimeter and submillimeter wave range to explain the structure of the universe. Between 100 and 1000 μm wavelength, numerous lines of molecular rotation and vibration spectra appear, which can in principle be used to elucidate numerous physical properties in the universe. Research into the 115 GHz rotational vibration of the interstellar carbon monoxide (CO) with a receiver for λ = 2.6 mm also indicates the performance of such microwave spectrometers in other practical applications. Spectroscopy in its general meaning implies the study of absorption and emission of electromagnetic radiation from substances that are excited by an external source or emit themselves. The tunneltron component has the special property that it can be used as an excitation source for the medium to be spectroscoped and as a radiation receiver for the radiation emerging from the medium. To give one example: The tunnel tron enables the investigation of organic and inorganic compounds in vapors, liquids and solids with regard to their chemical composition and geometrical and energetic structure as well as interaction processes; All of this is possible as a function of various external parameters and in the time-resolved regime. There are numerous cases where spectroscopic measurements are of interest, e.g. for the detection of hidden substances of organic molecules and chemical compounds (biological substances, drugs and plastic substances, ...) after a suitable excitation in the submillimeter wave area, or also devices for Quality control for specific substances (eg water content or contamination in solid substances, fat layer thickness on meat underlays, etc.).

The tunnel tron as a coherent and tunable radiation source has properties of the wave field that e.g. come into play in interferometry and holography. In principle, holography is a method for producing a unique photographic image of a coherently exposed object, in which an undisturbed (direct) beam and the reflected beam originating from the object are brought into interference in a detection system. The reconstruction of this interference image provides a three-dimensional image of the object.

The possibility of frequency tuning of the coherent tunnel tron, as well as the possibility of propagation through media that are opaque to the human eye, but transparent to the submillimeter radiation of the tunnel tron, opens up numerous other applications.

Communication and data transmission is a further area of application of the component proposed here, a frequency band being accessible which is far above that which has been managed up to now by the ITU (Intern. Telecom. Union). The new frequency range enables a significant increase in the number of usable channels for both satellite and ground-based communication. [Looking at a channel width of 20 MHz, the frequency range up to 5 THz provides about 250,000 channels. This can be compared with for example 40 channels for satellite communication in the frequency band of 11.7. - 12.5 GHz, which was provided by the ITU for Region 1, Africa, Europe and the former Soviet Union together.] Assuming a 4 kHz channel width for voice communication, you would generate 2 billion voice channels on such Carrier could be transported.

Transmission to a high quality standard requires digital systems with pulse modulation (PCM - pulse code modulation), since frequency modulation would drive the noise power far beyond the level of 3 pW / km (about 52 dB), which was recommended by the CCIR as the upper noise limit.

Digital systems allow signals to be regenerated in intermediate stations, thereby avoiding the accumulation of errors.

It is itself grateful that a completely new wireless terrestrial microwave communication network, a broadband wireless link to the Internet and a broadband link to satellite communication with all the advantages mentioned of the high number of telephony channels and the additional benefit of a reduced radiation exposure as a result of the reduced Depth of absorption of the human skin for submillimeter radiation is created.

Imaging multifrequency microwave radiometer (MIMR) for the exploration of the near-earth area from satellites or other flying objects already has a high potential for use. Future remote sensing satellites will carry hyperspectral equipment suitable for imaging exploration in a large number of frequency channels, instead of the seven channels currently used with multispectral instruments.

Imaging close-up imaging is important for the safety and maneuverability of helicopters and the approach of aircraft.

The same applies to road traffic and even for robot applications with adverse environmental conditions. The basic requirement here is always a powerful, tunable, possibly monochromatic and coherent submillimeter-wave emitter (and corresponding detector), as is provided with the component of the present invention. As an 'on-chip' integrated or separate emitter and detector component, it is suitable for radar measurements in the most general sense, ie for location, navigation and early detection systems. The growing need for compact, low-power radar assemblies for civilian applications and for military use, the component according to the invention can be used to counter alarm or collision warning systems.

The tunnel tron can be an active sensor for SAR (synthetic aperture radar) application. A SAR system sends microwave radiation to the object (the earth when research satellites are the starting point) and receives the returning radiation. The fine tuning of the emitter allows the frequency to be positioned within the absorption band-min-ma of the atmosphere. The possibility of electronically changing the direction of the 'vellum field of the tunnel tron proves to be a further advantage for scanning the observation area

Biological and medical applications (tomography, imaging thermography, etc.) can easily be concluded in large numbers from the properties of the component according to the invention.

Claims

claims

1. Emitter <and / or detector component for submillimeter-wave radiation, consisting of a substrate, electrical leads (lines) to the electrodes, which are located on both sides of the component on a superconductor and are connected to an external power source, characterized in that that the component is created in a thin, single-crystalline and a-axis-oriented layer of a high-temperature superconductor (HTS) by forming micro bridges (a) and insulating trenches (b) in such a way that the micro bridges (a) on both sides of superconducting contacts ( c, d) of the high-temperature superconductor forming the layer, and can be combined in any manner in series and / or parallel connection and can be externally controlled individually or in groups by appropriately guiding the trenches (b).

2. Component according to claim 1, characterized in that the HTS layer has grown epitaxially with the c-axis parallel to the substrate surface, and the a-axis is inclined at an angle of 1 ° to 89 ° with respect to the normal direction on the substrate.

3. Component according to claim 1 or 2, characterized by an arrangement (array) of at least two to a few hundred micro bridges in parallel, each with two to a few hundred vertically stacked Josephson contacts per micro bridge, all micro bridges having common superconducting electrical contacts.

4. The component according to claim 3, characterized in that the electrical contacts allow voltage measurement for detector operation.

5. The component according to claim 3, characterized in that a plurality of parallel assemblies, which lead to the formation of a segment by a suitable trench guide, are connected in series.

6. The component according to one or more of the preceding claims, characterized by a distributed arrangement of complete groups of micro bridges along a microwave stripline to achieve a higher radiated power.

7. The component according to one or more of the preceding claims, characterized by a use for communication and data transmission.

8. The component according to one or more of the preceding claims, characterized by the use in radar systems

9. The component according to one or more of the preceding claims, characterized for applications as a multi-channel emitter and detector in satellite-based SAR (Synthetic Aperture Radar).

10. The component according to one or more of the preceding claims, characterized by the use in imaging multi-channel microwave radiometers.

11. The component according to one or more of the preceding claims, characterized by any type of spectroscopic application.

12. The component according to one or more of the preceding claims, characterized by the use as a local oscillator in superimposed receivers, for example for astronomical applications.

13. A method for producing an emitter and / or detector component for submillimeter-wave radiation according to one or more of the preceding claims, characterized in that the high-temperature superconductor (HTS) layer by molecular beam epitaxy (MBE) and analog methods, such as. atomic layer epitaxy (ALE), fine focus ion beam epitaxy (FIBE) is generated.

14. The method according to claim 13, characterized in that the molecular beam epitaxy (MBE) device has spectroscopic means for observing the interface and for controlling the growth of the HTS layer.

15. The method according to claim 13 and / or 14, characterized by the following process steps:

(a) Epitaxial growth of a HTS layer with an inclined a-axis, 100-500 nm thick, on a suitably cut wafer (substrate) with or without one or more buffer layers.

(b) Lithography for making the trenches.

(c) Ion etching down to the substrate surface.

(d) removal of the photoresist.

(e) attaching metal contacts to the HTS electrodes.

16. The method according to one or more of the preceding claims, characterized in that the HTS layer is produced by chemical vapor deposition (CVD) and analog methods.

17. The method according to one or more of the preceding claims, characterized in that the HTS layer by laser pulse deposition (PLD) and analog method her- is provided, including the case that the PLD device is equipped with spectroscopic means for interfacial observation and control of the growth process.

18. The method according to one or more of the preceding claims, characterized in that the HTS layer is produced by sputter deposition (SD) and analog methods, including the case that the SD device is equipped with spectroscopic means for interfacial observation and control of the growth process.

19. The method according to one or more of the preceding claim, characterized in that the component structure is produced using micromasks.