JP2929974B2 - Y-based high-temperature superconducting film structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Y-based high-temperature superconducting film structure for forming a microwave communication filter or the like.

[0002]

2. Description of the Related Art High temperature superconductivity (HTS)
Superconductors) When a thin film is applied to a microwave communication filter or the like, it is necessary to reduce insertion loss. The present inventors have created such a filter as shown in FIG. FIG. 1 is a schematic sectional view of the filter. In FIG. 1, an HTS
The film 2 is formed in a filter pattern, and a metal (for example, Au) film 3 is formed on the HTS film 2. Here, the metal film 3 in the electrode portion 4 of the filter is connected to the center electrode 7a of the connector 7 by a wire 6a. An HTS film 5 is also formed on the back surface of the substrate 1, and this HTS film 5 is grounded to the connector 7 by a wire 6b. The metal film 3 on the HTS film 2 other than the electrode part 4 functions as a protective film.

FIG. 2 shows a plan configuration of the filter pattern shown in FIG. The filters shown in FIGS. 1 and 2 constitute a distributed constant type filter. In such a filter, when the pass characteristics were simulated, the results shown in FIGS. 3 to 5 were obtained. 3, 4, and 5 show that the high-frequency surface resistance (Rs) is 1 mΩ,
The transmission characteristics at mΩ and 100 mΩ are shown. As is clear from these figures, as the surface resistance (Rs) increases, the transmission characteristics deteriorate, and the surface resistance (Rs) becomes 1
In the case of mΩ, the loss is almost zero. Therefore, if the surface resistance (Rs) is 1 mΩ, a filter with extremely small loss can be formed. For that purpose, it is necessary to form a high-quality HTS film 2.

[0004] From the standpoint of power handling capability, the contact resistance (R) between the HTS film 2 and the metal film 3 at the electrode portion 4 is increased for power supply.
c) must be sufficiently low.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to reduce both the surface resistance and the contact resistance at an electrode portion to improve the filter characteristics. And

[0006]

SUMMARY OF THE INVENTION The present inventors have focused on the crystal average grain size and the void ratio as the main factors of the film which affect the surface resistance value and the contact resistance value, and prepared samples having different crystal average grain sizes and void ratios. Then, a structure in which both the surface resistance value and the contact resistance value were reduced was clarified. The first aspect of the present invention based on such studies
Features, in which the HTS film of Y ₁ Ba ₂ Cu ₃ O _y composition was formed in the filter pattern on the substrate, and a metal film is laminated on at least the electrode portion on the film, the superconducting thin
The film contains voids (2b) and Y ₁ Ba ₂ Cu ₃ O _y
Has a structure in which plate-like crystals are two-dimensionally connected on a substrate,
The average crystal grain size d of the plate crystal of Y ₁ Ba ₂ Cu ₃ O _y satisfies the relationship of 1 ≦ d ≦ 3 (μm), and the ratio P of the voids in the two-dimensional plane on the substrate is It is characterized by satisfying the relationship of 3 ≦ P ≦ 10 (%).

The average crystal grain size mainly affects the surface resistance of the film, and the void ratio of the film mainly affects the contact resistance between the film and the metal. If the average crystal grain size is too small,
The grain boundary density is very high and the surface resistance increases. On the other hand, if the average crystal grain size is too large, the orientation of the crystal grains is poor, the surface flatness is deteriorated, and the surface resistance is increased. 1μ average crystal grain size
m to 3 μm or less, the surface resistance is 1 m
Ω or less.

On the other hand, if the void ratio is too small, the current flowing into the HTS film via the void is small, and the contact resistance increases. On the other hand, if the void ratio is too large, the contact resistance increases due to an increase in the surface resistance value or poor orientation of the crystal grains. By setting the void ratio to 3% or more and 10% or less, the contact resistance value could be extremely reduced.

A second feature of the present invention is that the thickness t of the HTS film is
1 satisfies 0.5 ≦ t1 ≦ 1.5 (μm).
Since the high-frequency current basically tends to flow near the surface of the film, if the film thickness is smaller than 0.5 μm, the surface resistance increases, and if the film thickness is larger than 1.5, the surface flatness of the film increases. It deteriorates and the surface resistance value deteriorates. Therefore, HTS
By setting the thickness of the film to 0.5 μm or more and 1.5 μm, an increase in surface resistance can be suppressed.

The third feature of the present invention is that the thickness t of the HTS film is
The relationship between 1 and the thickness t2 of the metal film is expressed as t1 + 0.2 ≦ t2
(Μm). If the thickness t2 of the metal film is too small with respect to the thickness t1 of the HTS film, the contact resistance increases because the laminated metal does not sufficiently enter the gaps in the film. Therefore, by setting the film thickness as described above, the metal can sufficiently penetrate deep into the gap, and a saturated small contact resistance value can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An HTS film was formed on a substrate by sputtering. Sputter deposition was performed using three parameters of the substrate temperature, the gas partial pressure, and the target applied power as parameters to prepare samples having different crystal average grain sizes and void ratios. Hereinafter, specific sputtering film forming conditions will be described. FIG. 6 shows an enlarged plan view of the HTS film thus formed, and FIG. 7 shows an AA ′ section thereof. FIG. 7 shows a state in which an Au film 3 is laminated as a metal film on the HTS film. As shown in FIG, HTS film,
It includes a gap 2b between the HTS crystal grains 2a, the HTS film
It has a structure in which columnar crystals are two-dimensionally connected on the substrate 1.

Among the three film forming parameters under the above film forming conditions, a film structure having a smaller crystal average grain size as the substrate temperature increases, the gas partial pressure increases, and the power applied to the target decreases. I was able to. In addition, as the substrate temperature increased, the gas partial pressure increased, and the target applied power increased, a film structure having a smaller void ratio could be obtained.

Note that the void ratio refers to the ratio of the area where voids are formed. The surface resistance value of the film obtained under the above film forming conditions was measured and evaluated by the dielectric resonator method. The contact resistance between the HTS film and the metal is 0.6 μm HT.
A 1.5 mm square Au pad having a thickness of 1 μm was formed on the S film and measured and evaluated. As a result of classifying and organizing the film structure and film characteristics obtained in this way, it was found that the main factor affecting the surface resistance was the average crystal grain size. FIG. 8 shows representative experimental results.

FIG. 8 shows that the average crystal grain size is 0.5 μm or less and that the average crystal grain size is 3.
It can be seen that at 4 μm or more, the surface resistance value has deteriorated more than 1 mΩ. It is considered that a film having an average crystal grain size of 0.5 μm or less has a very high grain boundary density, and this has caused an increase in surface resistance. On the other hand, a film having an average crystal grain size of 3.4 μm or more has poor orientation of crystal grains and deteriorates the surface flatness, and it is considered that this causes an increase in surface resistance.

Therefore, the average grain size of the crystal is 1 μm to 3 μm.
If it does below, the surface resistance value can be made 1 mΩ or less. Next, the obtained film structure and film characteristics were classified and arranged. As a result, it was found that the void ratio was the main factor affecting the contact resistance. FIG. 9 shows representative experimental results.

FIG. 9 shows that, regardless of the average crystal grain size, when the void ratio is 1% or less and when the void ratio is 15% or more, the contact resistance value is in the order of 10 ⁻² to 10 ⁻³ Ω · cm ² . It can be seen that it has deteriorated. In the c-axis oriented HTS film, the conductivity is better by one digit or more in the a and b axis directions (left and right directions in FIG. 7) than in the c axis direction perpendicular to the film (vertical direction in FIG. 7).
Here, since Au enters the gap of the film at the time of Au lamination, an effect of supplying a current along the a and b axes of the film through the original gap in which Au is embedded (hereinafter, referred to as an anchor effect). Cause.

For this reason, a film having a void ratio of 1% or less is
It is considered that the anchor effect after u-lamination was weak, and the contact resistance increased due to this. On the other hand, in a film having a void ratio of 15% or more, the conductive path of the HTS film is narrow, the orientation is poor, and the surface flatness is also deteriorated. .

Therefore, if the void ratio is set to 3% or more and 10% or less, the surface resistance is reduced and the ^density is reduced to 10 ^-4 Ω · cm.
Very low contact resistance values of ² or less can be achieved. As described above, when the contact resistance value is set to 10 ⁻⁴ Ω · cm ² or less, the filter characteristics can be sufficiently improved. Next, the thickness of the HTS film was examined with respect to the film having the average crystal grain size and the void ratio obtained as described above. FIG. 10 shows representative experimental results.

FIG. 10 shows that the HTS film thickness is less than 0.2 μm and the HT
It can be seen that when the S film thickness is 2.0 μm or more, the surface resistance value has deteriorated more than 1 mΩ. HTS film thickness 0.2μ
It is considered that the surface resistance of a film having a thickness of m or less is increased because the high-frequency current is excessively concentrated on the film surface due to the skin effect of the high-frequency current. On the other hand, a film having an HTS film thickness of 2.0 μm or more has poor orientation of crystal grains and deteriorates surface flatness, and it is considered that this causes an increase in surface resistance.

Therefore, it is preferable that the HTS film thickness be 0.5 μm or more and 1.5 μm or less. Next, the obtained HTS
The thickness of the Au laminated film was examined for the film having the thickness. FIG. 11 shows representative experimental results. From FIG.
Regarding two kinds of samples having different HTS film thicknesses, in any case, when the HTS film thickness is equal to the Au film thickness, the surface resistance is remarkably high, but when the Au film thickness is 0.2 μm or more, contact is made. It can be seen that the resistance value is small and saturated.

When the HTS film thickness is equal to the Au film thickness, the laminated Au does not sufficiently penetrate deep into the void, whereas when the Au film thickness is larger than the HTS film by 0.2 μm or more, the laminated Au film is laminated. It is considered that the contact resistance was saturated because Au sufficiently penetrated deep into the void. Therefore, if the Au film thickness is equal to or more than the HTS film thickness + 0.2 μm, 10 ⁻⁴ Ω ·
A very low contact resistance value saturated to less than cm ² can be obtained.

Based on the above study, Y ₁ Ba ₂
The Cu ₃ O _y HTS film 2 and the Au film 3 of the composition, Y ₁ B
a ₂ Cu _{3 Oy} plate-like crystal having an average crystal grain diameter d of 1 ≦ d
.Ltoreq.3 (.mu.m), percentage P of voids in a two-dimensional plane on substrate 1
Is 3 ≦ P ≦ 10 (%), and the thickness t1 of the HTS film 2 is
0.5 ≦ t1 ≦ 1.5 (μm), the thickness t1 and the thickness t2 of the Au film 3 satisfy the relationship of t1 + 0.2 ≦ t2 (μm), and the high-frequency surface resistance ( Rs) is 1 mΩ
Hereinafter, a filter having a contact resistance value (Rc) between the HTS film 2 and the Au film 3 of 10 ⁻⁴ Ω · cm ² or less could be formed.

The metal film of the electrode section 4 can be made of Ag or the like in addition to Au. Further, the filter may be not only a distributed constant type filter but also a lumped constant type filter.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a filter.

FIG. 2 is a plan view of a filter.

FIG. 3 is a characteristic diagram showing transmission characteristics when the surface resistance (Rs) is set to 1 mΩ.

FIG. 4 is a characteristic diagram showing transmission characteristics when the surface resistance (Rs) is set to 10 mΩ.

FIG. 5 is a characteristic diagram showing transmission characteristics when the surface resistance (Rs) is set to 100 mΩ.

FIG. 6 is a diagram illustrating a state in which the HTS film formed by sputtering is enlarged in a plane.

FIG. 7 is a sectional view taken along line A-A 'of FIG.

FIG. 8 is a diagram showing the relationship between surface resistance and average crystal grain size.

FIG. 9 is a diagram showing a relationship between a contact resistance and a void ratio.

FIG. 10 is a diagram showing the relationship between HTS film thickness and surface resistance.

FIG. 11 is a diagram showing a relationship between a film having an HTS film thickness and a film thickness of an Au laminated film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... HTS film, 2a ... HTS crystal particle, 2b
… Voids, 3… metal films, 4… electrode parts, 5… HTS films formed on the back surface of the substrate, 6a, 6b… wires, 7… connectors.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-208229 (JP, A) JP-A-6-37513 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 39/22-39/24 H01L 39/00 H01B 12/00-12/06 H01B 13/00 561-565 H01L 21/28-21/288 ZAA H01L 39/40-29/43 ZAA H01L 21/3205 ZAA C30B 29/22 501 H01P 1/203 ZAA C01G 1/00 C01G 3/00

Claims (3)

(57) [Claims] 1. A superconducting thin film (2) of Y ₁ Ba ₂ Cu ₃ O _y composition is formed in a filter pattern on a substrate (1), and a metal film (3) is formed on the film at least on an electrode part (4). in the stacked form the Y-based high temperature superconducting film structure, the superconducting thin film comprises voids (2b), and Y ₁ Ba
₂ Cu ₃ O plate crystals of _y has a two-dimensionally continuous structure on said substrate, said Y ₁ Ba ₂ Cu ₃ O _y crystal average particle size d of the plate-like crystals
But with satisfying the relation of 1 ≦ d ≦ 3 (μm) , and characterized in that the ratio P of the voids in a two-dimensional plane on the substrate, to satisfy the relationship of 3 ≦ P ≦ 10 (%) Y-based high-temperature superconducting film structure. 2. The Y according to claim 1, wherein the thickness t1 of the superconducting thin film (2) satisfies the relationship of 0.5 ≦ t1 ≦ 1.5 (μm).
Based high temperature superconducting film structure. 3. The film thickness t1 of the superconducting thin film (2) and the film thickness t2 of the metal film (3) satisfy a relationship of t1 + 0.2 ≦ t2 (μm). Y described in 2
Based high temperature superconducting film structure.