JPH04302180A - Superconductive connecting structure - Google Patents

Abstract

PURPOSE:To enable Nb superconductors to be superconductively joined together without fail by a method wherein an NbN layer is formed adjacent to the joining interface of a superconductive joint where the Nb superconductors are jointed together. CONSTITUTION:An NbN layer 7 is formed adjacent to a joining interface between a lower Nb superconductive thin film 2 and an upper Nb superconductive thin film 3 in a through-hole 6. As NbN is superconductor which is stable and high in critical temperature, the upper Nb superconductive thin film 3 and the lower Nb superconductive thin film 2 are superconductively connected together without fail owing to the presence of the NbN layer 7 even if NbO or the like is left more or less on the interface due to the cleaning of the surface. Therefore, an element of laminar structure composed of laminated Nb thin films can be enhanced in yield.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a superconducting connection structure, and is suitable for connecting an Nb superconductor thin film and a lead made of Nb superconductor in, for example, SQUID used for biomagnetic field measurement or micromagnetic detection. The present invention relates to a superconducting connection structure suitable for application.

0002

[Prior art] SQUID (superconducting quantum interference device)
When measuring biomagnetic fields using a magnetometer, high sensitivity can be achieved by integrating the SQUID element body made of Nb superconductor thin film, the detection coil, the input coil, etc. on a single substrate using thin film fabrication technology. Techniques to achieve this have already been proposed (for example, IEICE Transactions '90/7)
Vol. J73-D-II No. 7).

In such cases, various coils made of Nb thin film and the SQUID element body are laminated with an insulating film interposed therebetween. It is superconductingly connected to thin films, etc.

0004

[Problems to be Solved by the Invention] By the way, the surface of Nb is significantly oxidized, and when making through-holes for connection as described above, the surface of the Nb thin film in the upper layer is usually cleaned after cleaning by reverse sputtering on the surface of the Nb thin film in the lower layer. By forming a film, superconducting contact with the upper Nb thin film is achieved. However, at this time, NbO remains on the surface of the underlying Nb thin film or adhesion of impurities impedes the flow of superconducting current at the connection interface, which causes a decrease in yield. There is.

[0005] The present invention was made in view of the above points, and aims to provide a superconducting connection structure that can reliably connect Nb superconductors and thereby improve the yield of devices such as SQUIDs. There is.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an Nb
It is characterized by the formation of N.

[0007]

[Function] NbN is a stable superconductor with a high critical temperature.
By forming this, a stable superconducting connection becomes possible. Here, when making a superconducting connection between Nb thin films, after the same thin film fabrication process as before, unstable NbO near the bonding interface is replaced with NbN by ion implantation of N2 from the surface with high energy. The superconducting connection structure of the present invention described above can be obtained by the following methods.

[0008]

Embodiment FIG. 1 is a sectional view showing a schematic structure of an embodiment of the present invention. The lower layer Nb superconducting thin film 2 formed on the substrate 1 constitutes, for example, a detection coil of a SQUID, and the upper layer Nb superconducting thin film 3 is a superconducting lead for connecting this detection coil to others. The surrounding part of the lower layer Nb superconducting thin film 2 is covered with a SiO insulating film 4, and the upper part is covered with a SiO2 insulating film 5.
A through hole 6 is formed in the iO2 insulating film 5. The upper layer Nb superconducting thin film 3 enters into this through hole 6 and is interconnected with the lower layer Nb superconducting thin film 2.

N of the lower layer and upper layer in the through hole 6
Near the junction interface between the b superconducting thin films 2 and 3 is a NbN layer 7. NbN is a superconductor with a stable and high critical temperature, and according to the structure of the embodiment of the present invention described above, NbN
Due to the presence of the bN layer 7, the upper layer Nb superconducting thin film 3 and the lower layer Nb superconducting thin film 2 are reliably connected to each other by superconductivity, and in elements such as SQUIDs having a stacked structure of Nb thin films, superconducting connections are required at points where superconducting connections are required. By employing the above structure, the yield of devices is improved.

Next, the manufacturing method of the above embodiment of the present invention will be described. FIG. 2 is an explanatory diagram of the manufacturing procedure. First, as shown in (A), an Nb thin film is formed on a substrate 1 by sputtering, and then a desired patterning is performed by reactive ion etching etc.
A superconducting thin film 2 is formed, and SiO 2 is deposited on the pattern through a photoresist to form an SiO 2 insulating film 4 filling the periphery of the Nb superconducting thin film 2 and flattening the surface.

Next, as shown in (B), Si is uniformly applied to the surface.
After depositing the O2 insulating film 5, a through hole 6 for contact is formed in a predetermined portion of the SiO2 insulating film 5 by reactive ion etching. Thereafter, as shown in (C), the surface is irradiated with Ar+ to clean the surface, and then, as shown in (D), an upper Nb superconducting thin film 3 that will become a lead layer is formed.

Finally, as shown in (E), N2 ions are implanted from the surface at a high energy of, for example, Mev order, so that the center of the range is at the interface between the lower and upper Nb superconducting thin films 2 and 3. do. As a result, the N2 ions react with Nb, as shown in FIG. 3, which shows a schematic enlarged cross-sectional view (A) and a graph (B) showing the NbN production ratio.
A stable NbN layer 7 with a high critical temperature is formed in the region sandwiching the interface b between the lower and upper Nb superconducting thin films 2 and 3.
b The superconducting thin films 2 and 3 are reliably connected superconductingly.

[0013]

Effects of the Invention As explained above, according to the present invention, NbN, which is a stable compound with a high critical temperature, is formed near the connection interface of the Nb-Nb superconducting connection, so that it can be easily removed even by surface cleaning etc. Some N at the interface
Even if bO and the like remain, the two are reliably connected superconductingly, and by applying the present invention to elements such as SQUIDs having a stacked structure, it is possible to improve the yield.

[Brief explanation of drawings]

[Figure 1] Cross-sectional view showing a schematic structure of an embodiment of the present invention

[
Figure 2: An explanatory diagram of an example of the manufacturing procedure of the embodiment of the present invention

[Figure 3
] Schematic enlarged cross-sectional view (A) near the interface in Figure 2 (E)
Graph showing the creation rate of NbN

[Explanation of symbols]

1... Board 2... Lower layer Nb superconducting thin film 3... Upper layer Nb superconducting thin film 4...SiO insulating film 5...SiO2 insulation film 6...Through hole 7...NbN layer

Claims (1)

[Claims] 1. A superconducting connection structure characterized in that NbN is formed near the connection interface at a superconducting connection point where Nb superconductors and Nb superconductors are connected to each other.