U.S. patent application number 09/275187 was filed with the patent office on 2001-06-07 for squid formed on a sapphire substrate and method for manufacturing the same.
Invention is credited to NAGAISHI, TATSUOKI.
Application Number | 20010003118 09/275187 |
Document ID | / |
Family ID | 14099925 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010003118 |
Kind Code |
A1 |
NAGAISHI, TATSUOKI |
June 7, 2001 |
SQUID FORMED ON A SAPPHIRE SUBSTRATE AND METHOD FOR MANUFACTURING
THE SAME
Abstract
The present invention relates to a SQUID made of an oxide
superconducting thin film is formed on a sapphire substrate.
CeO.sub.2 film, RBa.sub.2Cu.sub.3O.sub.7-x film ("R" indicates a
rare earth element chosen among a group formed Yb, Er, Ho, Y, Dy,
Gd, Eu, Sm and Nd) and SrTiO.sub.3 film are deposited the substrate
top of sapphire successively. Furthermore, an oxide superconducting
thin film to be a SQUID is deposited on the SrTiO.sub.3 film.
Inventors: |
NAGAISHI, TATSUOKI;
(ITAMI-SHI, JP) |
Correspondence
Address: |
FOLEY AND LARDNER
SUITE 500
3000 K STREET NW
WASHINGTON
DC
200075109
|
Family ID: |
14099925 |
Appl. No.: |
09/275187 |
Filed: |
March 23, 1999 |
Current U.S.
Class: |
505/162 ;
257/E39.015; 427/62; 427/63 |
Current CPC
Class: |
Y10S 428/93 20130101;
H01L 39/2496 20130101; H01L 39/225 20130101; Y10S 505/701
20130101 |
Class at
Publication: |
505/162 ; 427/62;
427/63 |
International
Class: |
B05D 005/12; F41C
003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 1998 |
JP |
10-64057 |
Claims
1. A method for manufacturing a SQUID formed of oxide
superconducting thin film comprising following each processes; (1)
CeO.sub.2 film, RBa.sub.2Cu.sub.3O.sub.7-x film and SrTiO.sub.3
film are deposited on a sapphire substrate in sequence, ("R"
indicates a rare earth element chosen among a group formed Yb, Er,
Ho, Y, Dy, Gd, Eu, Sm and Nd) (2) A physical step is formed on said
SrTiO.sub.3 film, (3) A second RBa.sub.2Cu.sub.3O.sub.7-x film is
formed on said SrTiO.sub.3 film, ("R" indicates as same as the
above) and (4) An oxide superconducting thin film is patronized to
be a SQUID.
2. A method mentioned in claim 1, said CeO.sub.2 film is a
CeO.sub.2 film oriented (100), said RBa.sub.2Cu.sub.3O.sub.7-x film
is a RBa.sub.2Cu.sub.3O.sub.7-x film oriented (001) ("R" indicates
as same as the above) and said SrTiO.sub.3 film is a SrTiO.sub.3
film oriented (100).
3. A method mentioned in claim 2, said CeO.sub.2 film is deposited
by a laser beam vapor deposition method in an atmosphere less than
50 m Torr.
4. A method mentioned in claim 3, said SrTiO.sub.3 film is
deposited by a laser beam vapor deposition method in an atmosphere
less than 50 m Torr.
5. A method mentioned in claim 1, several SQUIDs are formed on one
sapphire substrate simultaneously.
6. A SQUID formed of oxide superconducting thin film comprising; a
sapphire substrate, a CeO.sub.2 film, a RBa.sub.2Cu.sub.3O.sub.7-x
film and a SrTiO.sub.3 film repeated on said sapphire substrate and
a second RBa.sub.2Cu.sub.3O.sub.7-x film ("R" indicates a rare
earth element chosen among a group formed Yb, Er, Ho, Y, Dy, Gd,
Eu, Sm and Nd) that is an oxide superconducting thin film and
formed to be a SQUID.
7. A SQUID mentioned in claim 6, said CeO.sub.2 film is a CeO.sub.2
film oriented (100), said RBa.sub.2Cu.sub.3O.sub.7-x film is a
RBa.sub.2Cu.sub.3O.sub.7-x film oriented (001) ("R" indicates as
same as the above) and said SrTiO.sub.3 film is a SrTiO.sub.3 film
oriented (100).
Description
DETAILED DESCRIPTION OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to of SQUID. The present
invention is related to a configuration of SQUID and a method for
manufacturing the same. More specifically, tie present invention is
related to a SQUID formed of an oxide superconducting thin film on
a sapphire substrate.
[0003] 2. Description of related art
[0004] Generally, a SQUID comprises a circular current road for
superconducting current, including one or two Josefson
conjugation(s). The SQUID related to the present invention is a
SQUID formed of an oxide superconducting thin film in particular
that has the composition "RBa.sub.2Cu.sub.3O.sub.7-x ("R" indicates
a rare earth element chosen among a group formed Yb, Er, Ho, Y, Dy,
Gd, Eu, Sm and Nd)". The oxide superconducting thin film of this
kind has high critical temperature and is to be effective by
cooling by liquid nitrogen.
[0005] However, a specified crystal structure is required so that
the oxide thin film obtains superconducting state. Accordingly, in
most case, an oxide superconducting thin film is formed on a MgO
single crystal substrate or SrTiO.sub.3 single crystal substrate.
These substrate materials have well matching of cell to the oxide
superconducting thin film and preferable arrangement of crystal is
provided.
[0006] However, MgO single crystal substrate and SrTiO.sub.3 single
crystal substrate are very expensive. And, these substrates having
large area are hard to be obtained. As the result, SQUID formed of
an oxide superconducting thin film tends to be expensive.
[0007] On the other hand, Si single crystal substrate or sapphire
substrate is obtained easily and cheep. However, an oxide
superconducting thin film is hard to be formed on them.
SUMMARY OF THE INVENTION
[0008] The problems mentioned above will be solved by the present
invention. In manufacture method of the present invention, sapphire
substrate is used as a substrate material and oxide superconducting
thin film of high quality is formed at the same time.
[0009] Characteristic of the present invention is not simple
displacement of substrate material. Namely, when a SrTiO.sub.3 film
is formed directly on a sapphire substrate, SrTiO.sub.3 film (100)
is never formed. However, the method according to the present
invention contains peculiar characteristic 3 phases production
process.
[0010] As the first process, a CeO.sub.2 (100) film is formed on
the sapphire substrate. As the second process forms, a
RBa.sub.2Cu.sub.3O.sub.7-x (001) film ("R" indicates a rare earth
element chosen among a group formed Yb, Er, Ho, Y, Dy, Gd, Eu, Sm
and Nd) is formed on the CeO.sub.2 (100) film. As the third
process, SrTiO.sub.3 (100) film is formed, on the
RBa.sub.2Cu.sub.3O.sub.7-x (001) film. At last, the oxide
superconducting thin film to be a SQUID is formed on this
SrTiO.sub.3 (100) film.
[0011] Such processes bring the following effect.
[0012] Each film sticks well mutually. The oxide superconducting
thin film can be formed on SrTiO.sub.3 film that is oriented (100).
Accordingly, high quality oxide superconducting thin film is
provided on a sapphire substrate. The quality of the oxide
superconducting thin film is equal to the one of an oxide
superconducting thin film on MgO substrate or SrTiO.sub.3 substrate
Acquisition of a sapphire substrate is easy, different from MgO
substrate or SrTiO.sub.3 plate
[0013] Furthermore, an advantage is not simply confined to
reduction of material cost. A sapphire substrate having large area
is easy to provided. Accordingly, several SQUIDs can be formed on
one substrate and production of SQUID becomes in large
quantities
[0014] In other words, high performance and inexpensive SQUID is to
be supplied by the present invention.
[0015] The above and other objects, features and advantages of the
present invention will be apparent from the following description
of preferred embodiments of the invention with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows diagrammatic sectional views for illustrating
each process of the method of the present invention.
[0017] FIG. 2 shows a birdseye view of one of embodiments of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Embodiment 1
[0019] At first, as shown in FIG. 1A, CeO.sub.2 film 2 is deposited
the whole surface of the sapphire substrate 1 having a flat R
principal surface. As shown in FIG. 1B, a
RBa.sub.2Cu.sub.3O.sub.7-x ("R" indicates a rare earth element
chosen among a group formed Yb, Er, Ho, Y, Dy, Gd, Eu, Sm and Nd)
film 3 and a SrTiO.sub.3 film 4 deposited on the CeO.sub.2 film 2
successively. Each process of these series processes can be done by
pulsed laser deposition for example.
[0020] Successively, the surface of the SrTiO.sub.3 film is
processed to form a physical step by the following process.
[0021] At first, as shown in FIG. 1C, resist 5 is deposited on the
whole surface of the SrTiO.sub.3 film 4. Successively, as shown in
FIG. 1D, after a part of this resist has exposed, unnecessary
domain of the resist is removed. As shown in FIG. 1E, the resist 5
left is used as a mask while a part of the SrTiO.sub.3 film 4 is
removed by Ar ion-milling. Finally, as shown in FIG. 1F, the resist
layer 5 left on the SrTiO.sub.3 film 4 is removed with appropriate
solvent. A kind of solvent is selected according to a kind of
resist, for example, a solvent can be an acetone.
[0022] Then, after series of the process, a physical step is formed
on the surface of the SrTiO.sub.3 film 4. This SrTiO.sub.3 film 4
becomes a substrate of an oxide superconducting thin film.
[0023] As shown in FIG. 1G, an oxide superconducting thin film 6 is
deposited on the SrTiO.sub.3 film 4. This oxide superconducting
thin film 6 has a composition RBa.sub.2Cu.sub.3O.sub.7-x. ("R"
indicates a rare earth element chosen among a group formed Yb, Er,
Ho, Y, Dy, Gd, Eu, Sm and Nd)
[0024] Furthermore, as shown in FIG. 1H, a pair of electrode 7a, 7b
is formed on the oxide superconducting thin film 6. The electrode
7a, 7b is formed by using a metal mask for example and formed of Au
membrane and Ag membrane laminating each other for example.
[0025] Finally, the oxide superconducting thin film 6 is processed
precision at the point as same as the step. The oxide
superconducting thin film processed forms a Josefson junction. This
minute processing can be enforced by standard photolithography
technology.
[0026] Thus, the process of manufacturing the SQUID has completed
in this way. Orientation of each film is shown in Table 1.
1TABLE 1 CeO.sub.2 RBa.sub.2Cu.sub.3O.sub.7-x SrTiO.sub.3 (100)
(001) (100)
[0027] We made a SQUID actually by the method mentioned above.
Deposition of each film was done by laser beam vapor deposition.
Common condition is shown in Table 2 and individual condition is
shown in Table 3.
2 TABLE 2 Substrate and distance of target 100 mm Energy density of
laser beam 2.5 J/cm.sup.2 Exposure area 2 mm .times. 4 mm
[0028]
3TABLE 3 Composition of film CeO.sub.2 RBa.sub.2Cu.sub.3O.sub.7-x
SrTiO.sub.3 temperature of substrate (.degree. C.) 680 700 700
oxygen pressure (mTorr) 10 400 100 film thickness (nm) 20 100
300
[0029] It was identified by a test that the condition mentioned
above is effective when any chemical element is selected as an
element "R". ("R" indicates a rare earth element chosen among a
group formed Yb, Er, Ho, Y, Dy, Gd, Eu, Sm and Nd)
[0030] The height of the step formed on the SrTiO.sub.3 film was
160 nm. Thickness of the oxide superconducting thin film was 220
nm. The width of the superconducting thin film at the Josefson
junction was 5 .mu.m. The configuration of SQUID was 5 mm square.
The inductance of SQUID was turned into 40 pH.
[0031] Current/voltage characteristic and magnetic field/voltage
characteristic of this SQUID provided were measured by quadrupole
method. As a result, 21c was 100 .mu.A, and current potential
characteristic of RSJ type was observed. These results mean that
the conjugation is good condition. Furthermore, width of voltage
modulation by having hanged magnetic field was more than 10
.mu.V.
[0032] Then, we understood that the SQUID formed on the sapphire
substrate worked as a magnetism sensor and confirmed good
characteristic of the SQUID from these resultant.
[0033] Embodiment 2
[0034] Sapphire substrate having large sapphire is ordinary
supplied. Accordingly, in case that sapphire substrate is used as a
substrate for SQUID, as shown in FIG. 2, several SQUID can be put
on one substrate 1. In this case, manufacture time for one SQUID is
shortened. Dimension of each element drawn in FIG. 2 is exaggerated
so that characteristic of each element is easy to be understood. At
the same time, in FIG. 2, the reference number given for each
element is the same as one corresponding in FIG. 1.
* * * * *