JP2630240B2 - Metal thin film resistors for superconducting integrated circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal thin film resistor in an Nb-based superconducting integrated circuit.

[0002]

2. Description of the Related Art The electric resistance value of a metal is determined by adding a term of residual resistance, a term of lattice vibration, and a term of magnetic order. In a resistor in a superconducting integrated circuit operating at a very low temperature, the residual resistance predominantly determines the resistance value.

In an Nb-based superconducting integrated circuit, a thin film of Mo is often used as a resistor. Mo has characteristics such as a small change over time in characteristics, a process that can be processed by a reactive ion etching method, and a small contact resistance with Nb, and is very easy to use as a resistor in a superconducting circuit. However, the residual resistance of Mo alone is small, and a long resistor is required to obtain a desired resistance, which hinders high integration of superconducting circuits.

[0004] Conversely, as an element having a high electric resistivity, for example, Zr is well known. However, I Triple E Transaction on Applied Superconductivity (IEEE Trans. On ASC) published in 1993 is known.
Journal, Vol. 3, No. 3, p. 3049,
Diffusion of oxygen at the contact interface between the resistor Zr and the superconducting wiring Nb is regarded as a problem, and handling as a resistor in a superconducting circuit becomes complicated. In addition, BINARY ALLOY PHASE
DIAGRAMS), 2nd edition, volume 3, page 2789, Zr-N
b The system phase diagram is shown in FIG. From this state diagram, Nb / Z
At the r interface, there is a possibility that a plurality of phases of α and β phases are generated in Zr, and it is expected that the characteristic change of the Nb / Zr interface due to diffusion is large.

Further, since the resistance of these resistors made of a single element such as Mo and Zr is constant, the resistance value is determined by the external dimensions such as the film thickness, pattern width and pattern length. Therefore, the degree of freedom in circuit design is low.

SUMMARY OF THE INVENTION An object of the present invention is to provide an alloy resistor for a superconducting integrated circuit which has a high resistivity, whose resistivity is variable in a wide composition range, and which is easy to handle. is there.

[0007]

According to the present invention, in an Nb-based superconducting integrated circuit, Mo or W is used as a base material, and the base material is selected from the group consisting of Mo, W, Ta, V, and Nb. A resistor characterized by being an all-solid-solution alloy constituted by adding at least one or more alloying elements different from the material is obtained.

[0008]

In general, the residual resistance of a metal can be increased by adding an alloy element. For a single alloy element, the relationship between residual resistance and concentration follows Nordheim's law. However, in reality, the concentration dependence of the resistance value is very complicated due to the formation of ordered phases, compounds, and the like.
It is used in dilute alloys of precious metals.

On the other hand, BINARY ALLOY PHASE DIAGRAMS, 2nd edition,
According to Volume 3, it can be seen that the five elements of Mo, W, Ta, V, and Nb are completely dissolved in each other, with the exception of the V-Ta system. Here, as an example, the phase diagram of the Mo-W system is cited in FIG. In the all-solid-solution alloy by these combinations,
Since there is no ordered phase or compound formation and a single phase in all composition ranges, a high residual resistance value is obtained in a wide composition range,
The residual resistance value can also be controlled by the composition ratio. In addition, a change in resistance with time due to diffusion or the like is small. Furthermore, since it is completely dissolved with Nb in the wiring layer,
Even at the interface between Nb and the alloy resistor, there is no generation of a compound or a different phase, so that the contact resistance is small and the change with time of the contact resistance is small.

[0010] By the way, solid Ta, V, and Nb undergo a superconducting transition at the temperature of liquid helium. However, when these elements are used as an additive element of the alloy, they have a size smaller than the coherence length in the base material. Therefore, the alloy resistance of the present invention does not cause a superconducting transition and has no adverse effect.

[0011] In addition, Mo, W, Ta, V , Nb is, F, such as SF ₆
It can be processed by a reactive ion etching method using a system gas, and the alloy resistor of the present invention can be processed using equipment that has processed a conventional resistor of Mo alone. Further, the etching end point of the base material Mo and W is 703.9 nm in wavelength.
Therefore, the controllability and reliability in the manufacturing process are high.

According to the present invention, a metal thin film resistor having a very stable and high resistance can be obtained. Further, since the resistance value can be controlled by the composition ratio, the degree of freedom in circuit design is increased. By using this resistor in a superconducting integrated circuit, high integration of the circuit has become possible.

[0013]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.
It is a -W system state diagram. BINARY ALLOY PHASE DIAGRAMS, 2nd edition,
Volume 3, p. 2685. It can be seen that Mo and W are completely dissolved in each other. Since the Mo-W alloy is an all-solid-solution alloy, there is no generation of ordered phases and compounds, and it is a single phase in all composition regions. Therefore, a high resistance value can be obtained in a wide composition range, and a change with time in the resistance value due to diffusion or the like is small. Further, since Mo and W are completely dissolved in Nb in the wiring layer, the contact resistance is small because no compound or heterophase is formed at the interface between the Nb in the wiring layer and the Mo-W alloy resistor. The change with time of the contact resistance is also small. High reliability,
As a result of using a high-resistance Mo-W alloy as a resistor in a superconducting integrated circuit, high integration of the superconducting circuit has become possible. Further, since the resistance value can be controlled by the composition ratio, the degree of freedom in circuit design is increased.

In this embodiment, a Mo-W alloy is described. However, the total ratio of Mo as a base material and addition of at least one or more alloying elements of Ta, V, and Nb is described. Solid solution alloy or W as base material, Ta, V, Nb
The same effect can be obtained with a full-rate solid solution alloy formed by adding at least one or more alloy elements.

[0015]

As described above, according to the present invention, it is possible to obtain an alloy resistor that is stable with little change with time and has a high resistance value, and that a superconducting circuit can be highly integrated. . Further, since the resistance value can be controlled by the composition ratio, the degree of freedom in circuit design is improved.

[Brief description of the drawings]

FIG. 1 is a Mo-W system state diagram for explaining one embodiment of the present invention.

FIG. 2 is a Zr—Nb system state diagram for explaining one of the conventional examples.

Claims (1)

(57) [Claims] In an Nb-based superconducting integrated circuit, Mo or Mo is used.
An alloy thin film resistor formed by using W as a base material and adding at least one or more alloy elements different from the base material among Mo, W, Ta, V, and Nb to the base material.