JP5449764B2 - Superconducting material for high frequency, high frequency transmission line - Google Patents

Description

  The present invention relates to a high-frequency superconducting member for forming a line for transmitting a high frequency of MHz or higher, a high-frequency transmission line using the same, and a method for manufacturing a high-frequency superconducting member.

  If a superconducting member is used, a resonator having a small material loss and a high Q value can be made small. A superconducting filter using such a resonator can realize a steep skirt characteristic that cannot be realized by a conventional filter. For this reason, in the field of high-frequency filters of MHz or higher, superconducting filters are being put into practical use.

Among the superconducting materials used for the superconducting filter, ReBa ₂ Cu ₃ O _7-δ (Re is La, Y, Sm, Eu, Gd, Dy, Yb) having a superconducting transition temperature of about 90 K and showing a high critical current value. , Nd, Ho, Er) is expected as a promising material. Hereinafter, ReBa ₂ Cu ₃ O _7-δ is also expressed as ReBCO.

  The sapphire substrate is inexpensive as a large-area single crystal substrate, has an appropriate dielectric constant necessary for manufacturing a high-frequency circuit of MHz or higher, has high mechanical strength, and has low thermal conductivity. Therefore, it is most suitable as a substrate for forming a superconducting material when a high frequency filter circuit is manufactured.

  However, it is very difficult to directly form ReBCO having excellent high-frequency characteristics on a sapphire substrate, and no successful example has been reported at this stage. As a solution to this problem, a technique of growing a buffer layer on a sapphire substrate and growing a superconducting thin film thereon is widely used.

In this case, the lattice matching with the superconducting material, on the R plane of the sapphire substrate (1 1 02) or A-face (11 2 0), ceria: a superconducting material such as (CeO ₂ cerium oxide) and YSZ A method of forming a ReBCO thin film after forming a buffer layer having a close lattice constant is generally used (Patent Documents 1 and 2). Since this buffer layer functions as a base of the superconducting layer laminated on the upper part, it can be easily estimated that the crystal structure and the surface shape have a great influence on the upper superconducting layer.

Conventionally, in order to form a ReBCO thin film having excellent high frequency characteristics, a CuO two-dimensional network composed of Cu and O, which is considered to bear the superconducting characteristics of the ReBCO superconductor, so as not to impair the superconducting characteristics of ReBCO. It has been considered necessary to realize a state in which the structure is well maintained. In order to maintain this two-dimensional network structure satisfactorily, it has been considered that the buffer layer serving as the base requires a structure with a flat surface and good crystallinity with few crystal defects. And the device which realizes such a structure has been advanced. (Patent Document 1, Patent Document 3)
JP 2004-303846 A JP 2004-180203 A JP 2004-244263 A

  The present invention has been made in consideration of the above circumstances, and the object of the present invention is to provide a superconducting member for high frequency comprising a superconducting layer that realizes high surface conductivity in a high frequency band of MHz or higher on a sapphire substrate. Another object of the present invention is to provide a method for manufacturing a high-frequency transmission line using the same and a superconducting member for high frequency.

The high-frequency superconducting member according to the first aspect of the present invention is formed on an R-plane sapphire substrate and one or both surfaces of the substrate, and has a half-value width of 0.00 in a (002) peak rocking curve measurement using XRD. 8 or more It has a ceria buffer layer which is 0 or less, and a superconducting layer on the buffer layer.

In the high-frequency superconducting member according to the first aspect, the superconducting layer is ReBa ₂ Cu ₃ O _7-δ (Re is at least one selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) It is desirable that the element be formed of

  In the high-frequency superconducting member of the first aspect, it is desirable that the superconducting layer has a thickness of 350 nm or more and 1100 nm or less.

  In the high-frequency superconducting member according to the first aspect, it is desirable that the buffer layer has a thickness of 50 nm to 180 nm.

The high-frequency superconducting member according to the first aspect of the present invention is formed on an R-plane sapphire substrate and one or both surfaces of the substrate, and has a half-value width of 0.00 in a (002) peak rocking curve measurement using XRD. 8 or more It has a ceria buffer layer which is 0 or less, and a superconducting layer on the buffer layer.

In the high-frequency transmission line according to the second aspect, the superconducting layer is ReBa ₂ Cu ₃ O _7-δ (Re is at least one selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb). Element).

  In the high-frequency transmission line according to the second aspect, it is desirable that the superconducting layer has a thickness of 350 nm to 1100 nm.

  According to the present invention, on a sapphire substrate, a high-frequency superconducting member comprising a superconducting layer that realizes high surface conductivity in a high-frequency band of MHz or higher, a high-frequency transmission line using the same, and a method for manufacturing a high-frequency superconducting member Can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)

  The high-frequency superconducting member of the present embodiment is formed on an R-plane sapphire substrate and one or both surfaces of this substrate, and has a half-width of 0. 0 in a (002) peak rocking curve measurement using XRD (X-ray Diffraction). It has a ceria buffer layer of 7 or more and 1.1 or less and a superconducting layer on the buffer layer.

  FIG. 1 is a cross-sectional view of the high-frequency superconducting member of the present embodiment. In the high-frequency superconducting member 10, buffer layers 14 are formed on both surfaces of an R-plane sapphire substrate 12.

The buffer layer 14 is made of ceria (CeO ₂ : cerium oxide). The ceria of the buffer layer 14 has a half width of 0.7 or more and 1.1 or less in the (002) peak rocking curve measurement using XRD.

A superconducting layer 16 is formed on the buffer layer 14. The superconducting layer 16 is a copper oxide superconductor, for example, ReBa ₂ Cu ₃ O _7-δ (Re is at least one selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb. Element).

  In order to achieve a high Q value in a superconducting resonator using a high-frequency superconducting member, the high-frequency superconducting member needs to have a high surface conductivity. The high-frequency superconducting member 10 of the present embodiment uses ceria having a half-value width of 0.7 or more and 1.1 or less as the buffer layer 14 in the (002) peak rocking curve measurement using XRD. Rate can be realized.

  FIG. 2 is a diagram showing the relationship between the surface conductivity and the ceria half width. The full width at half maximum is based on the rocking curve measurement of the (002) peak using XRD.

  The surface conductivity is calculated by creating a resonator that resonates at 2 GHz using the high-frequency superconducting member 10 of the present embodiment and measuring the Q value of the resonator.

The thickness of the buffer layer 14 is 120 nm. The superconducting layer 16 is YBa ₂ Cu ₃ O _7-δ having a thickness of 500 nm.

In order for the superconducting resonator to occupy characteristics superior to those of the normal conducting resonator, the surface conductivity σ _s is required to be 1 × 10 ¹³ (S) or more. As shown in FIG. 2, the surface conductivity σ _s has a high value in a region where the half-value width is 0.7 or more and 1.1 or less, and is 1 × 10 ¹³ (S) or more.

And it is more desirable that the half width is 0.8 or more and 1.0 or less. This is because a high surface conductivity σ _s can be obtained stably.

FIG. 3 is a graph showing the relationship between the surface conductivity and the thickness of the ceria buffer layer. The superconducting layer 16 is YBa ₂ Cu ₃ O _7-δ having a thickness of 500 nm. The half width of the ceria buffer layer 14 is in the range of 0.7 to 1.1.

As apparent from FIG. 3, the surface conductivity depends on the thickness of the ceria buffer layer 14, and the surface conductivity σ _s has a high value when the thickness of the buffer layer 14 is in the range of 50 nm to 180 nm. . Therefore, from the viewpoint of realizing high surface conductivity, the thickness of the buffer layer 14 is desirably 50 nm or more and 180 nm or less.

Furthermore, from the viewpoint of realizing a high surface conductivity of 3 × 10 ¹³ (S) or more, the thickness of the buffer layer 14 is more preferably 80 nm or more and 150 nm or less. When the thickness is 120 nm, the surface conductivity σ _s can be 5 × 10 ¹³ (S) or more.

FIG. 4 is a diagram showing the relationship between the surface conductivity and the thickness of the superconducting layer. The thickness of the buffer layer 14 is 120 nm. The superconducting layer 16 is YBa ₂ Cu ₃ O _7-δ . The half width of the ceria buffer layer 14 is in the range of 0.7 to 1.1.

As is clear from FIG. 4, the surface conductivity depends on the thickness of the superconducting layer 16, and the surface conductivity σ _s has a high value when the thickness of the superconducting layer 16 is in the range of 350 nm to 1100 nm. Therefore, from the viewpoint of realizing high surface conductivity, the thickness of the superconducting layer 16 is desirably 350 nm or more and 1100 nm or less.

Furthermore, from the viewpoint of stably realizing a high surface conductivity of 4 × 10 ¹³ (S) or more, the thickness of the superconducting layer 16 is more preferably 500 nm or more and 800 nm or less. When the thickness is 600 nm, the surface conductivity σ _s can be 5 × 10 ¹³ (S) or more.

  Next, a method for manufacturing the high frequency superconducting member of the present embodiment shown in FIG. 1 will be described. This manufacturing method includes a step of preparing an R-plane sapphire substrate, a surface temperature of the substrate of 710 ° C. or higher and 820 ° C. or lower, an oxygen partial pressure of 20 Pa or lower, and an average film formation rate of 50 nm / min or higher and 150 nm. The step of forming a ceria buffer layer under the condition of / min or less and the step of forming a superconducting layer on the buffer layer are included.

  First, a sapphire substrate cut at the R plane, that is, an R plane sapphire substrate 12 is prepared. The R-plane sapphire substrate 12 is generally available at a low cost.

  A ceria buffer layer 14 is formed on one surface of the R-plane sapphire substrate 12 by, for example, laser ablation. At this time, the surface temperature of the substrate immediately after the start of film formation is set to 710 ° C. or higher and 820 ° C. or lower.

  The oxygen partial pressure in the film formation chamber is set to 20 Pa or less. Further, the average film formation rate is set to 50 nm / min or more and 150 nm / min or less. By controlling the repetition frequency of the laser pulse during film formation to be 50 Hz or more and 150 Hz or less, the average film formation rate can be realized.

  Here, it is not preferable that the surface temperature of the substrate falls below the range of 710 ° C. or more and 820 ° C. or less because the half width of ceria becomes larger than 1.1. On the other hand, if the above range is exceeded, the ceria half width is less than 0.7, which is not preferable.

  Moreover, if the oxygen partial pressure is higher than 20 Pa, the ceria half-width is less than 0.7, which is not preferable.

  Moreover, it is not preferable that the average film formation rate falls below the range of 50 nm / min to 150 nm / min because the half width of ceria is smaller than 0.7. On the other hand, if it exceeds the above range, the ceria half-width becomes larger than 1.1, which is not preferable.

  After forming ceria on one surface of the R-plane sapphire substrate 12, ceria is formed on the other surface under the same conditions, and the buffer layers 14 are formed on both surfaces of the R-plane sapphire substrate 12.

  Thereafter, the superconducting layer 16 is formed on the buffer layer 14 by, for example, sputtering.

In this manufacturing method, the superconducting layer is formed of ReBa ₂ Cu ₃ O _7-δ (Re is at least one element selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb). It is preferable from the viewpoint of obtaining high conductive properties.

Further, from the viewpoint of realizing a high surface conductivity σ _s as described above, the thickness of the ceria buffer layer 14 is desirably 50 nm or more and 180 nm or less, and more desirably 80 nm or more and 150 nm or less.

Further, from the viewpoint of realizing a high surface conductivity σ _s as described above, the thickness of the superconducting layer 16 is desirably 350 nm or more and 1100 nm or less, and more desirably 500 nm or more and 800 nm or less.

In the high-frequency superconducting member 10 of the present embodiment, the superconducting layer 16 is particularly selected from ReBa ₂ Cu ₃ O _7-δ (Re is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). High surface conductivity σ _{s of} 4 × 10 ¹³ (S) or more can be realized. Furthermore, when Re = Y or Re = Dy, the surface conductivity σ _s can be 5 × 10 ¹³ (S) or more.

  Here, the case where the buffer layer 14 and the superconducting layer 16 are formed on both surfaces of the R-plane sapphire substrate 12 has been described as an example. In forming a microstrip device, the buffer layer 14 and the superconducting layer 16 need to be formed on both sides of the substrate. However, in forming a coplanar device, the buffer layer 14 and the superconducting layer 16 need only be formed on one side of the R-plane sapphire substrate 12. Therefore, the buffer layer 14 and the superconducting layer 16 may be formed on only one side of the R-plane sapphire substrate 12.

(Second Embodiment)

  The high-frequency transmission line of the present embodiment is formed on an R-plane sapphire substrate and one or both sides of this substrate, and has a half-width of 0.7 to 1.1 in the (002) peak rocking curve measurement using XRD. It has a ceria buffer layer and a line formed of a superconducting layer on the buffer layer. This high-frequency transmission line is a high-frequency transmission line formed by processing the high-frequency superconducting member of the first embodiment. Therefore, the description of the high-frequency superconducting member that is the same as in the first embodiment is omitted.

  FIG. 5 is a top view of the high-frequency transmission line of the present embodiment. The high-frequency transmission line 20 is a band pass filter formed by connecting a plurality of resonators.

  In this bandpass filter, ten resonators 22a, 22b, 22c, 22d, 22e, 22f, 22g, 22h, 22i, and 22j are connected in series to form a resonator group. On both sides of the resonator group, L-shaped lines are arranged close to the resonator, and are extended to the end of the substrate to form input / output lines 24a and 24b. Further, jump lines 26a and 26b are provided.

  6 is a cross-sectional view taken along the line A-A ′ of FIG. 5. As shown in FIG. 6, the high-frequency transmission line 20 is manufactured by patterning the superconducting layer 16 and the buffer layer 14 on the top surface of the R-plane sapphire substrate 12 of the high-frequency superconducting member 10 shown in FIG.

  The pattern formation can be performed by, for example, a known photoetching process and argon ion milling. The superconducting layer 16 on the lower surface of the R-plane sapphire substrate 12 functions as a ground plane.

By using a resonator having a high Q value using a high-frequency superconducting member having a high surface conductivity σ _s as in the present embodiment, a bandpass filter having a steep skirt characteristic and a small transmission loss Is possible.

  The embodiments of the present invention have been described above with reference to specific examples. In the description of the embodiment, the description of the high-frequency superconducting member, the high-frequency transmission line, the manufacturing method of the high-frequency superconducting member, and the like that are not directly necessary for the description of the present invention is omitted, but is required. The elements related to the manufacturing method of the high-frequency superconducting member, the high-frequency transmission line, and the high-frequency superconducting member can be appropriately selected and used.

  In addition, all high-frequency superconducting members, high-frequency transmission lines, and high-frequency superconducting member manufacturing methods that include elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention. The scope of the present invention is defined by the appended claims and equivalents thereof.

  A bandpass filter having the structure described in the second embodiment was created. First, a ceria buffer layer was formed on both surfaces of an R-plane sapphire substrate using a laser ablation method.

  The growth conditions of the buffer layer were set such that the substrate surface temperature was 740 ° C., the oxygen partial pressure in the deposition chamber during growth was 15 Pa, and the repetition frequency of the laser pulse was 60 Hz. The average film formation rate on the substrate was 60 nm / min. As a result, the full width at half maximum was in the range of 0.8 to 1.0 so as to obtain a high-frequency surface conductivity.

The thickness of the buffer layer was 120 nm. A YBa ₂ Cu ₃ O _7-δ thin film was laminated on the ceria buffer layer at 600 nm.

  Next, an Au electrode was vapor-deposited to about 300 nm on the entire surface of one side to be the input / output line connection portion and the ground plane layer. Then, the circuit pattern of the band pass filter shown in FIG. 5 was produced on the surface opposite to the ground plane layer. A photo-etching process and an argon ion milling process were used for processing the circuit pattern of the band-pass filter.

  FIG. 7 is a diagram showing the pass characteristic (S21) and reflection characteristic (S11) of the prototype bandpass filter. Thus, a bandpass filter having a steep skirt characteristic and a small transmission loss was realized.

It is sectional drawing of the superconducting member for high frequencies of 1st Embodiment. It is a figure which shows the relationship between the surface conductivity of 1st Embodiment, and the half value width of a ceria. It is a figure which shows the relationship between the surface conductivity of 1st Embodiment, and the thickness of the ceria buffer layer. It is a figure which shows the relationship between the surface conductivity of 1st Embodiment, and the thickness of a superconducting layer. It is a top view of the high frequency transmission line of a 2nd embodiment. It is A-A 'sectional drawing of FIG. It is a figure which shows the pass characteristic and reflection characteristic of the band pass filter of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 High frequency superconducting member 12 R surface sapphire substrate 14 Buffer layer 16 Superconducting layer 20 High frequency transmission line 22a-j Resonator 24a, b Input / output line 26a, b Jump line

Claims (7)

An R-plane sapphire substrate;
Formed on one side or both sides of the substrate, the half-value width of 0.1 in the rocking curve measurement of the (002) peak using XRD. 8 or more A ceria buffer layer that is less than or equal to 0 ;
A superconducting layer on the buffer layer;
A high-frequency superconducting member characterized by comprising: The superconducting layer is formed of ReBa ₂ Cu ₃ O _7-δ (Re is at least one element selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb). The superconducting member for high frequency according to claim 1.   The high-frequency superconducting member according to claim 1 or 2, wherein the superconducting layer has a thickness of 350 nm or more and 1100 nm or less.   The high-frequency superconducting member according to any one of claims 1 to 3, wherein the buffer layer has a thickness of 50 nm or more and 180 nm or less. An R-plane sapphire substrate;
Formed on one side or both sides of the substrate, the half-value width of 0.1 in the rocking curve measurement of the (002) peak using XRD. 8 or more A ceria buffer layer that is less than or equal to 0 ;
A line formed of a superconducting layer on the buffer layer;
A high-frequency transmission line characterized by comprising: The superconducting layer is formed of ReBa ₂ Cu ₃ O _7-δ (Re is at least one element selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb). The high-frequency transmission line according to claim 5.   7. The high-frequency transmission line according to claim 5, wherein the superconducting layer has a thickness of 350 nm to 1100 nm.

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