JPS60198788A - Structure of josephson ic - Google Patents

Abstract

PURPOSE:To reduce influences of a magnetic field generated by earth current by a method wherein a ground plane is arranged in insulation from earth terminals by providing earth lines connected to the earth terminals of an IC. CONSTITUTION:In a Josephson IC chip 201, an earth plate 207 to pass earth currents of ICs 203-206 is formed on an Si substrate 202 by using an Nb film. An insulation layer 209 is produced except the aperture of the earth terminals 208 connecting the earth plate 207 to the earth lines 213 of the ICs 203-206. A shield plate 210 is formed out of an Nb film where the apertures of the earth terminals 208 have been removed with accelerated Ar atoms, and an insulation layer 211 is produced except the apertures of the earth terminals 208 so as to cover the shield plate 210. The ICs 203-206 are produced after formation of superconductive films 212 (Pb alloy) to fill the apertures of the earth terminals 208 and of the earth lines 213 (Pb alloy). The earth plate 207 is connected to a bonding pad 217.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a Josephson integrated circuit used in a Josephson computer and the like, and particularly to a structure suitable for a highly reliable integrated circuit.

BACKGROUND OF THE INVENTION Conventional Josephson integrated circuits (e.g. IBM Journal
al of Re5earch and Develo
pment, Vol 24Na2130~142.1
95 to 205), a ground plane having a shielding function is used as a substitute for the ground plate for draining the ground current of the circuit. A conventional example is shown in FIG.

In the Josephson integrated circuit chip 101, the ground plane 102 used as a shield plate for protecting the circuit from external magnetism such as earth's magnetism is formed of a superconductor. This is because the superconductor shields magnetism, and the ground plane is connected to the bonding pad portion 103,
It is fabricated on almost the entire surface of the chip except for 112. Josephson circuits 104 to 107 are supplied with power from pad 108 through power supply line 109. The ground current of the Josephson circuits 104-107 is then passed through the ground terminals 110. Passing through the ground plane 102, the bonding pad 11
2.

In such a structure, Josephson integrated circuits 104-1
07 earth current 111 is Josephson circuit circuit 107
It will flow under the surface. (7) As a result, the magnetic field generated by the earth current 111
This has the disadvantage that the threshold curve of the 07 switching element fluctuates, and in extreme cases it switches to a voltage state, causing the integrated circuit to malfunction.

[Object of the Invention] An object of the present invention is to provide a structure of a Josephson integrated circuit that prevents malfunctions caused by ground current in the Josephson integrated circuit and improves the reliability of the integrated circuit.

[Summary of the Invention] The present invention eliminates the above-mentioned drawbacks by employing a structure that can isolate the integrated circuit from the magnetic field generated by the ground current of the Josephson integrated circuit. Specifically, the two functions of a conventional ground plane are fulfilled by an independently provided ground wire and shield plate. This configuration can reduce circuit malfunctions caused by ground current.

[Embodiments of the invention] The present invention will be explained in detail below.

The first embodiment is shown in FIGS. 2(a) and 2(b). A shield plate 210 for magnetic shielding and a ground wire 207 (hereinafter referred to as a ground plate since it is formed in a plate shape in the drawing) for flowing a ground current are connected to an insulating layer 20.
This is an embodiment in which a two-layer structure is provided through a cylindrical layer 9. More specifically, an insulating layer 2 is provided under the shield plate 210.
This is an embodiment of a structure in which a grounding plate 207 is provided through the grounding plate 09, and a shielding plate 210 blocks the magnetic field generated by the grounding current.

FIG. 2(a) is a plan view of the circuit chip 201, and FIG. 2(b) is a plan view of the circuit chip 201.
) shows a cross-sectional view taken along line AA' of the ground terminal portion 208. In the Josephson integrated circuit chip 201, thermally oxidized St
A grounding plate 207 through which grounding currents of the integrated circuits 203 to 206 flow is formed on the substrate 202 using an Nb film produced by DC magnetron sputtering. Next, except for the opening of the ground terminal 208 that connects the ground plate 207 and the ground wires 213 of the integrated circuits 203 to 206,
An insulating layer (for example, 5 inches) 209 is fabricated by a normal lift-off method. Furthermore, Nb removed (ion etched) by accelerated Ar atoms from the opening of the ground terminal 208.
A shield plate 210 is formed of a film, and an insulating layer 211 is produced in the same manner as the insulating layer 209 so as to cover the shield plate 210 except for the opening of the ground terminal 208. Next, a superconducting film 212 for filling the opening of the ground terminal 208 and a ground wire 213 on the same layer as the base electrode of the switching element.
are formed of, for example, a Pb alloy, and then the integrated circuits 203 to 20
6 is prepared. The integrated circuits 203 to 206 are supplied with power from a bonding pad 214 through a power line 215, and the ground plate 207 is connected to the bonding pad 217.

In an integrated circuit having such a structure, the integrated circuits 203 to 20
The grounding current 216 of No. 6 passes through the grounding wire 213 and the hole-filling superconducting film 212, flows out to the grounding plate 207, and connects to the bonding pad? 17 and passes under the integrated circuit 205. However, since the shield plate 210 is provided on the upper surface of the earth plate 207, the magnetic field generated by the earth current 216 is shielded by the shield plate 210. As a result, for example, the threshold curve of the integrated circuit 205 does not change and malfunctions do not occur.

As explained above, according to the embodiment, the magnetic field caused by the earth current can be shielded by the shield plate, which has the effect of preventing malfunction of the integrated circuit.

The second embodiment will be explained with reference to FIGS. 3(a) and 3(b).

Incidentally, FIG. 2(b) shows a BB' cross section of the ground end wire 313. This is a case of a two-layer structure in which a shield plate 303 and a ground wire 305 are provided with an insulating layer 304 interposed therebetween.

Specifically, this is an example in which a ground wire 305 is provided on the upper surface of the shield plate 303, and the magnetism generated by the current flowing through the ground wire 305 is concentrated directly under the ground wire and is separated from the ground wire 305 even if only a little. Since the magnetic field suddenly becomes smaller, the integrated circuit is not affected by the magnetic field.

In the Josephson integrated circuit chip 301, a shield plate 303 is formed of a Nb film on a thermally oxidized Si substrate 302, and its surface is oxidized to form an oxide film 314 (Nb 20g).
After forming an insulating layer (for example, 5iO) 304, a ground 41305 is made of the same material (for example, Pb alloy) as the base electrode of the switching element. Thereafter, integrated circuits 308 to 311 are manufactured in which the power line 306 is connected to the bonding pad 307, and the ground line 305 is connected to the bonding pad 312.

In an integrated circuit having such a structure, all of the ground current 313 of the integrated circuit gathers on the ground wire 305 and flows out to the bonding pad 312, and does not pass through the bottom surfaces of the integrated circuits 308-311. Furthermore, the ground wire 305 and the integrated circuit 308~
If the distance of 311 is set to, for example, 40 to 50 μm, the magnetic field due to the ground current 313 will be approximately 115 μm directly below the ground wire 305.
00. Therefore, the integrated circuit will not malfunction due to the magnetic field generated by the earth current.

As explained above, according to the second embodiment, the ground wire can be provided independently in the same process as the integrated circuit of the stem,
Since the ground current does not pass through the bottom surface of the integrated circuit, it is effective in preventing malfunction of the integrated circuit due to the ground current.

Further, a third embodiment will be explained with reference to FIGS. 4(a) and 4(b). In addition, FIG. 4B is a cc' cross-sectional view of the ground terminal 406. This is an example in which the shield plate 404 and the ground plate 403 (or the ground wire) are composed of a single layer of divided superconducting film.

In the Josephson integrated circuit chip 401, a Nb film was formed on a thermally oxidized Si substrate 402 by direct current magnetron sputtering, and then diluted with hydrofluoric acid.

The earth wire 403 and the shield plate 404 are separated by etching with a mixture of nitric acid and water. Next, a superconducting film (for example, a pb gold alloy 406) for connecting the ground wire 403 and the base electrode 405 of the switch element is fabricated.
The integrated circuits (409 to 412) are formed by a normal process, and the integrated circuit 4 is connected to the bonding pad 407 and the power supply [408].
Wire so that power can be supplied to 09 to 412, and connect the ground wire 40
3 connects to the bonding pad 414. Furthermore, layer 41
Reference numeral 5 is an oxide film obtained by oxidizing the surface of the shield plate 404, and layer 416 is an insulating film of SiO.

In an integrated circuit having such a structure, integrated circuits 409 to 41
The ground current 413 of No. 2 collects on the ground wire 403 and flows to the bonding pad 414. Therefore, since the integrated circuit ground current 413 does not pass through the bottom surface of the integrated circuit, the magnetic field generated by the ground current does not affect the integrated circuit.

As described above, according to the third embodiment, by separating the ground wire and the shield plate and providing them independently in the same layer, there is an effect of preventing malfunctions of the integrated circuit due to ground current.

[Effects of the Invention] According to the present invention, it is possible to reduce the influence of a magnetic field generated by a ground current, prevent a Josephson element from malfunctioning due to a ground current, and improve the reliability of an integrated circuit.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional integrated circuit, and FIG. 3 and 4 each show a different embodiment of an integrated circuit chip according to the invention. 101.201, 301, 401... Josephson integrated circuit chip, 203-206, 308-311.40
9-412...Josephson integrated circuit, 208.40
6... Earth terminal, 207,303°404... Shield plate, 207,305,403... Earth wire. Patent applicant Hirobe Kawata, Director of the Agency of Industrial Science and Technology

Claims (1)

[Claims] 1. A Josephson integrated circuit is provided on a substrate, and a ground plane for external magnetic shielding formed of a superconductor is provided on the lower layer of the substrate, in which a grounding terminal of the integrated circuit is provided. A structure of a Josephson integrated circuit, characterized in that a connected ground wire is provided, and the ground plane is arranged insulated from the ground terminal. 2. In item 1, the ground wire is provided below the shield plate via an insulating layer, an opening is provided in the shield plate below the ground terminal of the integrated circuit, and the ground wire is connected to the ground through the opening. A structure of a Josephson integrated circuit characterized in that a terminal and the ground wire are connected. 3. The structure of the Josephson integrated circuit according to item 1, wherein the ground wire and the shield plate are constructed by dividing a superconductor film formed on the substrate by etching.