DE19629583C2 - Emitter and / or detector device for submillimeter-wave radiation with a multiplicity of Josephson contacts, method for its production and uses of the device - Google Patents

Description

The invention relates to an emitter and / or detector component for submillimeters wave radiation with a variety of Josephson contacts according to the generic term of claim 1, as is known from US 5 114 912 A. Also concerns the invention a method for producing the component and uses of the component.

US Pat. No. 5,114,912 A describes a high-frequency oscillator based on an arrangement of Josephson contacts lying in the surface establishes. He will excited by a DC power source, and the frequency can go through this Direct current can be tuned. Impedance matching can be done via the choice of Number of Josephson contacts in the flat arrangement or by connection corresponding shunt resistors can be achieved. As an application, a Tunable DC-AC converter in the GHz range and even up to THz frequencies.  

A disadvantage of this component is its express limitation to a two-dimensional planar arrangement of Josephson contacts lying next to one another on a chip. Such a geometry implies a strict limitation of the maximum possible number of Josephson contacts. In particular, the minimal area of a single contact is approximately 1 µm ² due to the limited performance of photolithography. The requirements for uniformity are high, a considerable critical current is required (not less than 1 mA for optimal performance), which is also to be supplied via lines with low contact resistance. On the other hand, the requirement for phase synchronization limits the longitudinal expansion of the component to approximately λ / 4, a value which is approximately 75 μm for a frequency of 1 THz. If you allow small distances between the contacts, you can expect a maximum of one to two thousand such individual elements. In practice, arrangements of 10 × 10 = 100 contacts were realized. 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 emitted power and thus of a multitude of new applications that do not have flat (planar) arrangements, as shown there possible are.

US Pat. No. 3,725,213 discloses a superconducting barrier component and its Manufacturing technology described, which as well as other objectives Generator and detector for millimeter wave and sub millimeter wave radiation is suitable and is based on a granular structure of the superconducting material. While a higher radiation power or sensitivity due to the summation many Josephson contacts between crystal grains, there are few opportunities for reproducible manufacturing, electronic Control, phase synchronization and impedance matching to the vacuum. This Device can use a current-pulse-induced magnetic field between the two States are switched normally and superconducting, however, one Control of the emitted radiation frequency via the magnetic field dependent Energy gap not tried.  

A magnetic control mode for the emitted or detected radiation Frequency is described in EP 0 513 557 A2, where the component is made of vertical stacking of Josephson contacts, which is also on the side have applied galvanic connections. Between every pair of neighboring superconductor / barrier / superconductor structures (SIS structures) is one further superconducting layer provided on both sides by an insulator layer is separated from the neighboring Josephson contact. This layer is intended to Control of the individual component serve: By passing a current over the side Conducting contacts through this control layer, a magnetic field is to be generated that affects the energy gap of the Josephson contact.

This component has several disadvantages that its practical implementation in the Under the currently known material properties and available Make microfabrication technologies impossible. In particular, (i) requires its Production of the deposition of superconducting contacts of about 0.01 µm in width insulating layers on two opposite side faces from perpendicular in addition grown stack structures with Josephson contacts. For that is against currently no technology available. Furthermore, (ii) they are not superconductors known to have such large currents to produce the high magnet required field strengths that can be used to reduce the energy gap in High temperature superconductors within the limits of the required geometric Component dimensions would need. Even assuming that this is would be somehow possible, (iii) the magnetic field of a particular control layer influence more than just a Josephson contact, to unwanted cross-talk between multiple Josephson contacts. After all, (iv) would be radiated power too low for many applications, because a circuit Optimization of the Josephson contacts for impedance matching to the outside is not provided.

According to DE 41 24 048 C2, cuprate superconductors can be used as natural (intrinsic) Stacking sequences of Josephson contacts with a distance of 0.6. . . 2.5 nm  and in some cases, phase synchronization was greater than 1000 Josephson contacts achieved, but generally only partially achieved, such as that Plenty of branches in the I-V characteristics (in all previous work) shows. Especially when the Josephson contacts belonging to a stack are not all are identical, d. i.e. when their critical current is from contact to contact is different, they do not fall at the same point in the characteristic curve in the normal conducting State as soon as the current flow is increased. As a result of this the radiation emission is a superposition of coherent (narrow-band) radiation surrender. These differences in the properties of the Josephson contacts affect from imperfect crystal growth and the lithography process for definition of the mesa structures, which also leads to differences in the cross-sectional area of the Mesa structures leads. The highest frequency so far emitted Radiation is at ν = 95 GHz, but this is the result of insufficient laboratory Detection technology is.

Although mesa structures in thin cuprate layers, non-linear I-U characteristics with numerous branches and switching between branches, hysteresis, as well also Shapiro steps caused by microwave radiation, and themselves Microwave emission showed the I-V characteristics and other properties remain of these mesa structures far behind those of ideal phase-locked ones Batch sequences of Josephson contacts back. In particular, the emitted Microwave power only in the pW range, which is equivalent to the fact that such Stack 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 30 x 30 µm ² ; and (c) the devices were not optimized for their impedance matching to the free space. As a result of (a) and (b), phase synchronization is not perfect, unstable and random. Natural Josephson contacts in cuprate 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, super 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.

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. In fact, these can all 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 monocrystalline layer is grown in such an epitaxial relationship to the substrate that the a-axis is perpendicular to the surface of the substrate. We 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, as well as if the a axis is arbitrarily inclined, as long as only the c axis is parallel to the substrate Surface runs, 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 sum up.

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. 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. Similarly oriented films made of Nd _{1 + 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.

A-axis oriented layers made of high temperature superconductors are from WO 92/22426 A1 and JP 5-291632 A known.

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

This object is achieved by the characterizing part of claim 1 and Claim 13 specified features solved. Advantageous configurations and Applications of the invention are set out in claims 2 to 12 and 14 to 19. With in other words, the present invention becomes a two-dimensional one Network of superconducting micro bridges with stacking sequences of (native) Josephson contacts created, parts of the network in predetermined Grouped and interconnected (serial, parallel), as well as via contacts with an external electronic control unit can be operated.  

The radiation emitter according to the invention in the submillimeter wave region has one Impedance with which an impedance matching to the one receiving the radiation Space is possible, whereby the radiated power assumes maximum values.

The radiation emitter according to the invention in the submillimeter wave region has one very narrow emission line width (less than one millionth of the radiation frequency) within its submillimeter wave Tape on.

The emission frequency or the detection frequency of the invention Radiation emitters and detectors in the submillimeter-wave range can be measured using a electronic control over a wide spectral range continuously to be changed.

The emitted microwave radiation of the radiation emitter according to the invention and -detectors in the submillimeter wave range can be electronically modulated or out and be turned on, which is also a fast electronic switch for Corresponds to superconducting electronics.

The functions of emission and detection are in the case of the invention Radiation emitter and detector in the submillimeter wave range independent from each other, in channels with different frequencies or electrically variable and controlled frequencies, possible.

The radiation emitter and detector according to the invention in submillimeter wave Area allows an inversion of the emission and detection mode with external ones electronic means.

The radiation emitter and detector according to the invention in submillimeter wave Field is for inclusion in superconductor / semiconductor hybrid circuits suitable.

The invention will be explained in more detail with the aid of exemplary embodiments. In the associated drawing shows:

Fig. 1 is a unit cell of the crystal of a high-temperature super conductor, 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 "inclined a-axis". The CuO ₂ planes are inclined at an angle Θ with respect to the substrate.

FIG. 4A is a microbridge of a high temperature superconductor having "a-axis" -oriented growing direction was prepared.

Fig. 4B An equivalent circuit for the device shown in Fig. 4A: A simple, linear (serial) arrangement of Josephson junctions.

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

Fig. 6A shows a parallel arrangement of microbridges, each containing stacking sequences of natural Josephson contacts, made from an epitaxial "a-axis" or "inclined a-axis" layer by chemical or ion etching of trenches that the Electrically isolate micro bridges from each other.

Fig. 6B is a equivalent circuit for the device of Figure 6A. Parallel connection of two linear stacking sequences of Jo sephson contacts.

FIG. 7A, a parallel circuit of three identical groups (clusters) with 10 microbridges.

Fig. 7B a equivalent circuit for the device of FIG. 7A.

Figure 8 shows an arrangement included. More groups of micro-bridges, each stacking sequences of Josephson junctions, 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, the layer in a thin superconducting epitaxy contains a two-dimensional lateral arrangement of parallel connected micro-bridges (webs) (a), which are separated from each other by trenches (b) extending to the substrate and thus the current flow steer through the micro bridges or groups of micro bridges. Each microbridge includes a stacking sequence of Josephson contacts whose Anord voltage in Fig. 2 and 3 is explained Fig.. 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 is the following described the invention in more detail, the basic structural unit, d. H. the linear stacking sequence of Josephson contacts, in a thin layer of high quality a high-temperature superconductor is formed, the thin layer in a special epitaxial relationship with the substrate.

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

Be noticed 1 for declaration must reference to FIG. That the crystallographic unit cell of all known cuprate superconductors is a long parallelepiped with sides a ≈ b ≈ 3.8 Å and c "b. For example, c ≈ 6.5 Å in La _1.85 Sr _0.15 CuO ₄ , c ≈ 11.7 Å in YBa ₂ Cu ₃ O ₇ , c ≈ 15.4 Å in Bi ₂ Sr ₂ CaCu ₂ O ₈ , etc. [More specifically, the c- Axis periodicity in La _1.85 Sr _0.15 CuO ₄ and Bi ₂ Sr ₂ Ca Cu ₂ O _{8 is} 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 ₃ O ₇ ].

If specially cut substrates are used, it is possible to achieve 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 referred to for short as "a-axis oriented HTS layers".

One way to achieve this orientation is as follows (here La _1.85 Sr _0.15 CuO ₄ is chosen as an example, where a ≈ 3.8 Å kund c ≈ 6.5 Å):

The substrate and its "cut" (ie the direction of polishing or the orientation of the surface plane of the substrate) are selected such that the periodicity of the surface plane is 3.8 Å × 6.5 Å. Then there is the possibility that the layer grows with its a-axis 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.

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 3.8 Å high and have a distance of approximately d = 3.8 × tan 85 ° Å.

As already stated, high-temperature cuprate superconductors such as Bi ₂ Sr ₂ CaCu ₂ O ₈ , Ti ₂ Ba ₂ Ca ₂ Cu ₃ O ₁₀ , HgBa ₂ CaCu ₂ O _6.2 , La _1.85 , Sr _0.15 CuO ₄ , etc. natural superconducting superlattices from SIS. , ., or SINIS type. If one of the orientations of the thin layer is used, then simple microbridges of the type shown in FIG. 4.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 operation of the component, several such micro bridges must be interconnected in a superconducting network, as described in the further text.

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 about I _c = 1 mA. 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 in different places. Using the example of I _c R = 10 mV and I _c = 1 mA, the typical lower limit for the electrical resistance is R = 10 Ω. The impedance matching of the component to the vacuum requires a total resistance R _TOT = NR ≅ 300 Ω. With R = 10 Ω you get N = 30 as the value for the number of Jo sephson contacts to be inserted in the stacking sequence of a mesa structure. If I _{c were} less than 1 mA, an even larger value for R and thus a smaller value for N would have occurred. As a result, this value N would 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 j _c ^┴ = 10 ⁴ A / cm ² , then I _c = 1 mA is the area of the Josephson contact

A = I _c / j _c = 10 ^-3 A / 10 ⁴ A / m ² = 10 ^-7 cm ² = 10 µm ² .

If you were to use square Josephson contacts, this should be one Have an edge length of 3 µm.

This value of j _c ^┴ = 10 ⁴ A / cm ² relates to natural Josephson contacts in very anisotropic high-temperature superconductor materials, such as. B. Bi ₂ Sr ₂ CaCu ₂ O ₈ . With less anisotropic high-temperature superconductor compounds, j _c ^┴ 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.

The output power of such a simple stacking sequence, however, is quite modest to: P _MAX ^out = 1 / 8Ni _c ² R = (1/8) × 30 × 10 ⁶ × 10 ² Ω A = 5 × 10 ^-4 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 R _TOT = (N / M) R. For R _TOT = 300 Ω and R = 10 Ω you get N / M = 30 or N = 30 M.

The total current is I = MI _c, so that the total power P _TOT ^out = (1/8) × 10 ^-6 × 300 × M ² A ² Ω ≈ 0.4 × 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.

In particular, for a grouped arrangement of Josephson contacts, phases can occur synchronization can only be achieved over a distance of approximately λ / 4, where λ is the wavelength of the emitted electromagnetic radiation. Would the desired radiated frequency ν = 3 THz, then λ = 100 µm; For ν = 1 THz gives λ = 300 µm.

To optimize component parameters (e.g. to match impedance to the Vacuum and a reduction in internal reflection from electromagnetic Radiation at the crystal / vacuum interface), it is desirable To combine micro bridges electrically in any desired way. Doing so however, the electrical connections consist of superconductors and not for Formation of 'weak links', which are then called Josephson contacts connected in series with the stacking sequence of Josephson Contacts work in the mesa structure. In other words, they are High temperature superconducting electrodes of the same type of superconducting Material required.

Both series and parallel connection of mesa structures is practical relevant cases required. A method is explained in the following section with the series connection of simple micro-bridges or groups (cluster) is achieved by micro bridges that already exist as a parallel connection. Furthermore, realistic estimates of the maximum possible number phase-locked Josephson contacts in such batch sequences and networks specified.

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 I _c ^MAX = 1 mA as given, then R = 25 Ω is the resistance of a Josephson contact . N is therefore limited to values of 10-15 if impedance matching to the vacuum is sought with R _TOT = NR ≅ 300 Ω. This is obviously not very favorable for a pure a-axis-oriented HTS layer ( Fig. 2, Fig. 4.A), because in such a case the length of the microbridge (in a-axis layers the term "microbridge "for the previously designated" mesa structure "in c-axis layers would be less than 15 × 20 Å = 300 Å, 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 (about 5 °). Here one gets a total length L of the microbridge of d / tanθ for N = 15 and c = 15 Å, where d is the layer thickness. For d = 1000 Å and θ = 5 ° one obtains L ≈ 10000 Å = 1 µm, which is a reasonable value for currently used 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 I _c = 1 mA, the aforementioned contact area A = I _c / j _c = 10 ^-3 / 10 ⁴ cm ² = 10 µm ^{2 is obtained} . 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 = 1000 Å and θ = 5 ° you get d / tanθ = 1 µm. This means that the width of the micro bridges should be 1 µm, which can certainly be achieved.

However, such a micro-bridge, which contains a stacking sequence of Josephson junctions will produce only a relatively small power emitted radiation, namely, P _out = (1/8) I _c ² R _TOT = (1/8) (10 ^{-3) 2} 300 W ≈ 0.4 mW.

In order to increase this performance, it again requires a parallel connection of M such micro-bridges, as in this case, P _out = (1/8) (MI _c) ² R _TOT = M is ² × 0.4 mW, provided that the number N of natural Josephson contacts in each microbridge is set so that the impedance matching to the vacuum remains fulfilled. For R _TOT = RN / M ≅ 300 and R = 15-30 Ω 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. 6 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 15 × 300 Å 4500 Å or 0.45 µm, which is still a very small value and technologically is difficult to manufacture. In contrast, the length of the microbridge is inclined a-axis oriented HTS layers for d = 1000 Å, N = 300 and θ = 5 ° approximately M µm.

We had already concluded above that for j _c = 10 ⁴ A / cm ² and I _c = 1 mA the contact area A = 10 µm ² and the microbridge width about 10 µm (our standard choice d = 1000 Å and θ = 5 ° is). M is thus severely restricted since the entire width of the component can be 25 µm for an emission frequency of ν = 3 THz (λ = 100 µm) and 75 µm for ν = 1 THz (λ = 300 µm). Consequently, for M = 3-7 one obtains, which would correspond to a quite considerable output power of P _out = 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 ₃ 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 lead to values for M of around 25 and the considerable output power of around P ≈ 240 mW.

Another possibility for improvement lies in the very short length of micro bridges (≦ 1 µm) for a-axis oriented HTS layers. One could design a device according to FIG. 7. Using the available component length of 25 μm (for 3 THz), three parallel segments (strips) of 10 parallel micro bridges each were interconnected 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 = 25 W!

Although the previous value for the output power certainly because of a number other limiting factors is too high an estimate, it will Potential visible that could be in such a component. Noteworthy is also the ease of manufacture that a single lithographic Process cutting without any special 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 corresponds to the "simple" (ie more conductive) direction; j _c can be 10-1000 times higher in this direction (parallel to the a-axis) than in the "hard" (ie c-axis) direction along which the current flows through the microbridges. In this way, weak links between these contact tracks and the micro bridges are avoided.

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. Bonding 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 have 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 = at an optimal current 0.1 µm ² . This corresponds exactly to a layer thickness of 1000 Å and the microbridge width of 1 µm, as already described above.

A capacitance of C ≈ 5 × 10 ^-15 F in such small contacts can be expected from the known material properties for cuprates and for insulating layers. [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 20 nm would be 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 β = 2πI _c R ² C / Φ ₀ ≦ 1, where Φ ₀ = h / 2e = 2 × 10 ^-15 Vs is the flux quantum, h the Planck quantum of action and e is the electron charge. It is known that β should be small (≦ 1) if optimal radiated power and frequency tuning is required.

The above consideration is in the case of a single group (cluster) of Josephson contacts limited. In fact, it is possible to get the maximum  radiated power can be further increased by using a distributed arrangement such groups chooses. Groups can be spaced equidistantly apart arrange the λ between them (let's say λ = 300 µm for ν = 1 THz).

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 transmitted (see Fig. 8).

Phase synchronization can take place in such structures over fairly long distances can be achieved, whereby the radiated power can be considerable. The The disadvantage of such lines is obviously that the operating frequency because of Group spacing λ is fairly fixed. Higher performance can only be achieved by Achieve price of reduced tunability. Other aspects of optimization include the integration of an antenna, which conveniently exist de superconducting layer can be used for this.

4. Microwave radiation source

After a thin film structure with an arrangement of micro bridges (in generally in parallel and series connection) and with others Standard components of microwave technology (antenna, propagation line) connected, you can connect this to a conventional control electronics with adjustable Power source (up to 100 mA), controls, displays for frequency and Connect power, etc. This then provides a complete source for narrowband ge electromagnetic radiation that is in a wide frequency range and up can be tuned 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 FIG. 9.

5. Areas of application

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

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

Josephson contacts that are adapted to the external resistance without reflection and too a network can be controlled by a voltage and a wide frequency range into the Terrahertz area cover up.

Quantum detection of electromagnetic radiation - a widely used one Concept in the visible and infrared spectral range - was previously in the microwave and millimeter wave range only possible in the narrow range of the spectrum is grouped around the resonance frequency of MASER amplifiers. The standard measure Methods for detection in this frequency range use nonlinear electrical Resistors, such as Schottky diodes as classic rectifiers and Overlay receiver. Their working principle is based on the transformation of received power between different frequency ranges instead of 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 the frequency ν _s with the frequency of a local oscillator ν _Lo , with an intermediate frequency ν _if = | ν _s - ν _Lo | 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. Numerous lines of molecular rotation and vibration spectra occur between 100 and 1000 µm wavelength, 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 Significance implies the study of absorption and emission electromagnetic radiation from substances excited by an external source or emit itself. The Tunneltron component has the special property that it is used as a source of excitation for the medium to be spectroscoped and as Radiation receiver used for the radiation emerging from the medium can be. To give an example: The tunnel tron enables the sub search for organic and inorganic compounds in vapors, liquids and solids with regard to their chemical composition and geometric and energetic structure as well as interaction processes; all of this is possible in function of various external parameters and in time-resolved Regime. There are numerous cases where spectroscopic measurements are of interest are, e.g. B. in 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 devices for quality control of specific substances (e.g. water content or Contamination in solid substances, fat layer thickness on meat underlays, etc.).  

The tunnel tron shows as a coherent and tunable radiation source Properties of the wave field on the z. B. in interferometry and holography come to fruition. In principle, holography is a method of generating a unique photographic illustration of a coherently exposed object in which an undisturbed (direct) beam and the reflected beam originating from the object are brought to interference in a detection system. The reconstruction this interference image provides a three-dimensional image of the object.

The possibility of frequency tuning of the coherent tunnel tron, as well also the possibility of spreading through media that is for the human eye opaque, 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 the 40 channels for satellite communication in the frequency band from 11.7-12.5 GHz, which was provided by the ITU for Region 1 , Africa, Europe and the former Soviet Union.] If you take a 4 kHz- Channel width for voice communication, one would generate 2 billion voice channels that could be transported on such a carrier.

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

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

It is even conceivable that a completely new wireless terrestrial microwave communication network, a broadband wireless link to the Internet and a Broadband link for satellite communication with all the advantages of high number of telephony channels and the added benefit of a reduced Radiation exposure due to the reduced absorption depth of the human Skin is created for submillimeter radiation.

Imaging multifrequency microwave radiometer (MIMR) for exploring the near-Earth area from satellites or other flying objects already has one high potential for use. Future remote sensing satellites will be hyperspec carry central devices with them, which are used for large-scale imaging exploration Number of frequency channels are suitable, instead of the seven channels that go against to be used with multispectral instruments.

Imaging all-round observation at close range is significant for the Safety and maneuverability of helicopters and the landing approach from Airplanes.

The same applies to road traffic and even for robotic Applications with adverse environmental conditions too. The basic requirement is always a powerful, tunable, as monochromatic as possible and coherent submillimeter wave emitter (and corresponding detector) such as that is provided with the device of the present invention.

It is an 'on-chip' integrated or separate emitter and detector component suitable for radar measurements in the most general sense, d. that is, for location, Naviga tion and early detection systems. The growing need for compact This is where low-power radar assemblies for civil and military use come in Component according to the invention. Alarm or collision warning Systems can be improved.  

The tunnel tron can be an active sensor for SAR (synthetic aperture radar) - Application. A SAR system sends microwave radiation onto the object (the Earth, if research satellites are the starting point), and receives the returning radiation. Fine-tuning the emitter leaves a position frequency within absorption band minima of the atmosphere. The Possibility to electronically control the direction of the tunnel tron's wave field change, proves to be a further advantage for scanning the observation area.

Biological and medical applications (tomography, imaging thermography phie etc.) are in large numbers from the properties of the invention Component easy to conclude.

Claims (19)

1. Emitter and / or detector component for submillimeter-wave radiation with a multiplicity of Josephson contacts, consisting of a substrate, electrical leads on electrodes, which are located on both sides of the component on a superconductor and can be connected to an external power source, characterized in that the component in a thin, single-crystal and a-axis-oriented or inclined a-axis-oriented layer of a high-temperature superconductor (HTS) by forming micro bridges (a) and insulating trenches (b) containing the Josephson contacts is created in such a way that the micro bridges (a) on both sides start from superconducting contacts (c, d) of the high-temperature superconductor forming the layer and are combined by appropriate routing of the trenches (b) in series and / or parallel connection and individually or in groups externally are controllable. 2. Component according to claim 1, characterized in that the inclined a-axis oriented HTS layer has grown epitaxially with the c-axis parallel to the substrate surface and the a- Axis at an angle of 1 ° to 89 ° with respect to the normal direction Substrate is inclined. 3. Component according to claim 1 or 2, characterized by an arrangement of at least two to a few hundred Micro bridges in parallel, each with two to a few hundred in the direction the c-axis stacked Josephson contacts per microbridge, all Micro bridges have common superconducting electrical contacts. 4. The component according to claim 3, characterized in that the electrical contacts measure a voltage Allow for detector operation.   5. The component according to claim 3, characterized in that several parallel assemblies, through a suitable trench routing lead to the formation of a segment, connected in series are. 6. Use a device according to one or more of the preceding the claims in a distributed arrangement of complete groups of micro bridges along a microwave strip line to achieve a higher radiation performance. 7. Use of a component according to one or more of the claims 1 to 5 for communication and data transmission. 8. Use of a component according to one or more of the claims 1 to 5 in radar systems. 9. Use of a component according to one or more of the claims 1 to 5 as multi-channel emitter and detector in satellite-based SAR (Synthetic Aperture Radar). 10. Use of a component according to one or more of the claims 1 to 5 in multi-channel microwave imaging radiometers. 11. Use of a component according to one or more of the claims 1 to 5 in spectroscopy. 12. Use of a component according to one or more of the claims 1 to 5 as a local oscillator in heterodyne 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 claims 1 to 5, 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 substrate with or without one or more buffer layers;
• b) lithography for the production of the trenches;
• c) ion etching up to the substrate surface;
• d) removing the photoresist from step (b); and
• e) attaching metal contacts to the HTS electrodes.

14. The method according to claim 13, characterized in that the high temperature superconductor (HTS) layer through Molecular beam epitaxy (MBE) or atomic position epitaxy (ALE) or fine focus Ion beam epitaxy (FIBE) is generated. 15. The method according to claim 14, characterized in that during the molecular beam epitaxy spectroscopy cal methods for monitoring the interface and for controlling the wax of the HTS layer. 16. The method according to claim 13, characterized in that the HTS layer is formed by chemical gas phase Deposition (CVD) is made. 17. The method according to claim 13, characterized in that the HTS layer by laser pulse deposition (PLD) is produced and that during the laser pulse deposition spectroscopic Interface monitoring and growth process control be used.   18. The method according to claim 13, characterized in that the HTS layer by sputter deposition (SD) is produced and that during the sputter deposition spectroscopic Interface monitoring and growth process control be used. 19. The method according to one or more of claims 13 to 18, characterized in that the component structure using Micromasks is generated.