Josephson junction array device, and manufacture thereof

Abstract

A superconductive device is disclosed, which has specific characteristics of a generator and/or detector of sub-millimeter wavelength radiation, comprising a two-dimensional lateral array of mesas (column-shaped elements) each containing vertically stacked Josephson junctions on top of one another. This device is capable of covering the entire frequency range between the microwave and far infrared spectral regions, in a plurality of applications, where radiation emission and detection is involved. According to its various embodiments, thin columns (stacks) of Josephson junctions are monolithically built between superconducting electrical top and bottom contact layers. Mutually isolated segments cut out of the contact layers allow for optimization of circuit parameters such as impedance matching to load and maximizing the output power. External electronic control allows modulation of the radiation field and other operation modes of the device. The specification also describes special applications of the disclosed device.

Description

[0001] (a) Field of the Invention[0002] The invention relates to superconducting devices, corresponding technologies and application fields, and more specifically to a novel generator and detector of sub-millimeter electromagnetic radiation, and its multiple applications.[0003] (b) Description of the Related Art[0004] 1. Arrays of Artificial Junctions[0005] The first realization of potential usefulness of Josephson junctions as tunable microwave sources and detectors can be traced back to the earliest works of B. Josephson and S. Shapiro. It was also understood very early that a single Josephson junction emits with too little power and too broad linewidth to be useful as a practical microwave source. These deficiencies can be removed by using arrays of Josephson junctions [Jain et al. 1984; Bindslev Hansen and Lindelof 1984; Lukens 1990]. If the coupling between the junctions is strong enough, phase locking may occur between them; in this cases, the array emits coherent radiation [L...

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Benefits of technology

0039] It is therefore an object of the present invention to pr

Problems solved by technology

No such applications have been realized (i.e., reduced to practice) so far, because of technical difficulties expounded above.

While enhanced radiation emission or sensitivity is intended by the summation of many Josephson junction-containing grains, there is little control and reproducibility, no phase locking, and complete load mismatch to vacuum.

Although this device is capable of switching between the superconducting and normal conductivity state by means of a magnetic field, generated by an electrical pulse through a layer adjacent to the Josephson junction, no intention has been made to control the radiation emission frequency by virtue of the effect the magnetic field might have on the energy gap of the superconductor.

One drawback of this device is that it is explicitly restricted to two-dimensional planar arrangements of Josephson junctions, which are placed next to one another on the chip.

This geometry introduces severe limitations on the maximum possible number of junctions in such an array.

As we will discuss in Section V (vii) below, this design does not allow for out-of-chip power of emitted microwave radiation at a level interesting for conceivable applications i.e. at least 0.1-1 mW.

This device has several drawbacks, some of which make its reduction to practice impossible within the constraints of currently known materials parameters and available microfabrication technologies.

In particular, that patent description does not teach one how to fabricate the (series) superconducting contacts between superconducting electrodes of stacked SIS Josephson junctions, which is the critical technological step required to fabricate the device.

There is no known technology today capable of performing such a task.

That, however, clashes with the current limitations for epitaxial growth of high-quality high-T.sub.c superconductor films (no more than few hundred nm).

To fabricate a stack of several such devices would be even less possible.

However, apart from losing the advantages of a high T.sub.c (such as the possibility to avoid expen

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