JP3221037B2 - Current modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed and large-current current modulator suitable for the field of microelectronics and power electronics (power).

[0002]

2. Description of the Related Art A device using a superconductor is a typical example of a current modulator aiming at high speed and large current capacity.

A current modulator using this superconductor can be generally classified into a two-terminal element and a three-terminal element. Here, a three-terminal element is considered.

A three-terminal device basically has a structure in which a channel junction is provided between two electrode superconductors, and a control electrode is attached to the channel junction. As the channel junction, an insulator, a semiconductor, a normal conductor, or a superconductor is used. Now, a current modulation device using a superconductor as a channel junction, in other words, a current modulation device having a structure of an electrode superconductor, a channel superconductor, and an electrode superconductor is a current modulation device using another channel junction. Compared with the device, there is an advantage that the size of the channel assembly is hardly limited, the control electrode can be easily attached, and the current capacity can be increased. This means that when another channel junction is used, a tunnel effect or a proximity effect of several Å to several hundreds
効果 Effects that are effective only at the following size dominates device characteristics, whereas when using a superconductor as a channel junction, the effect that the superconducting carrier of the channel superconductor is modulated by the control electrode signal Dominate the element characteristics. Therefore, the only three-terminal element that can be manufactured with a pattern rule on the order of microns or more that can be used by ordinary photolithography technology is only a current modulator having a structure of electrode superconductor, channel superconductor, and electrode superconductor.

[0005]

However, the current modulator having the structure of the conventional electrode superconductor / channel superconductor / electrode superconductor has the advantage that it is easy to manufacture as described above. , Low controllability by control electrode signal,
There is a disadvantage that the switching characteristic is inferior to a current modulator using another channel junction, particularly a current modulator using a semiconductor for the channel junction. Poor switching characteristics impose great restrictions on the application of the current modulator, which means that the application field in which the advantage of easy manufacturing can be utilized is limited. So this is a big problem.

An object of the present invention is to solve the above-mentioned problems. An object of the present invention is to provide a current source which can be manufactured according to a pattern rule on the order of microns and has good controllability by control electrode signals and sufficient switching characteristics. A modulation device is provided.

[0007]

A current modulator according to the present invention comprises a first electrode superconductor, a channel superconductor,
A second electrode superconductor, and a control electrode, for controlling a current flowing between the first electrode superconductor and the second electrode superconductor through the channel superconductor. In the current modulation device, the first electrode superconductor and the second electrode superconductor formed of an oxide superconducting thin film are formed on the substrate, and the first electrode superconductor is A circumscribed normal conductor or a circumscribed superconductor made of an oxide superconducting thin film is formed so as to cover a part of the second electrode superconductor, and oxidized on the circumscribed normal conductor or the circumscribed superconductor. The channel superconductor formed of a superconducting thin film is formed, and the control electrode is formed on the channel superconductor.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.

(Embodiment 1) FIG. 1 is a diagram showing a cross-sectional structure of a current modulator according to a first embodiment of the present invention. FIG.
In the current modulation device, the first electrode superconductor 1 and the second electrode superconductor 1
, Electrode superconductor 2, channel superconductor 3, circumscribed superconductor 4 (or circumscribed normal conductor 4), dielectric 5, control electrode 6,
And the substrate 7. At this time, the circumscribed superconductor 4
Has a structure sandwiched between a first superconductor 1, a second superconductor 2 and a channel superconductor 3.

The process and materials for manufacturing the current modulator of this embodiment are as follows. First, a film having a thickness of 50 on a substrate 7 made of strontium titanate single crystal.
Forming the NdBa ₂ Cu ₃ O _7-X-based oxide superconducting thin film of 0A～1000A. The critical temperature of this NdBa ₂ Cu ₃ O _{7 -X} film is 88K. The substrate is not limited to strontium titanate as long as the substrate does not react with the superconducting thin film and has good lattice constant matching. Next, after forming the superconducting thin film, patterning is performed using photolithography to obtain the first electrode superconductor 1 and the second electrode superconductor 2 at the same time. The distance between the first electrode superconductor 1 and the second electrode superconductor 2 is 5 μm.

Next, Nd having a film thickness of about 20 ° to 120 °
_1.85 Ce _0.15 CuO _4-X-based oxide superconductor thin film and the thickness and patterned after continuously formed La _1.85 Ba _0.15 CuO _4-X-based oxide superconductor thin film of 50Å~200Å circumscribed superconductors 4 (or the circumscribed normal conductor 4, depending on the operating temperature) and the channel superconductor 3 are formed. The critical temperatures of the circumscribed superconductor 4 and the channel superconductor 3 are each 22 K
And 30K. Thereafter, a dielectric 5 and a control electrode 6 are formed and patterned. The current modulator is obtained by the above process.

The switching ratio of the obtained current modulator was examined. The measurement temperatures are 20K and 25K. Since the critical temperature of the formed Nd _1.85 Ce _0.15 CuO _4-x- based oxide superconductor is 22K, the circumscriber adjacent to the channel superconductor 3 becomes the circumscribed superconductor 4 when the measurement temperature is 20K.
At 5K, it becomes the circumscribed normal conductor 4. The switching ratio is the ratio of the current flowing between the first superconducting electrode 1 and the second superconducting electrode 2 when a voltage is applied to the control electrode 6 and when the voltage is not applied (J
con / Jc off). Table 1 shows the results together with comparative examples in which the circumscribed normal conductor 4 or the circumscribed superconductor 4 was not formed.

[0013]

[Table 1]

As can be seen from the table, a channel superconductor (here, a hole-doped type: p-type) and a circumscribed normal conductor or a circumscribed superconductor of different carrier types (here, an electron-doped type: n)
) Is formed adjacent to the periphery of the channel superconductor, thereby significantly improving the switching ratio.

This is because the circumscribed normal conductor or the circumscribed superconductor of the electron-doped type and the channel superconductor of the hole-doped type are adjacent to each other to reduce carriers in the channel superconductor and facilitate modulation. It is thought that there is. In addition, comparing the circumscribed normal conductor and the circumscribed superconductor, it can be seen that the circumscribed superconductor is more preferable because the improvement of the switching ratio is more remarkable. It is considered that the circumscriber also needs to have an appropriate electronic state (energy gap) in order to efficiently reduce the carrier density in the channel superconductor 3.

(Embodiment 2) In the same structure and the same process as Embodiment 1, YBa ₂ having a critical temperature of 80 K is applied to the channel superconductor 3.
The Cu ₄ O ₈ superconductor, a first superconducting electrode 1 and the second superconducting YBa electrode critical temperature 2 is 90K ₂ Cu ₃ 0 _7-X superconductor, circumscribed normal conductor 4 Nd _1.85 Ce _0.15 CuO _4-X
A current modulator is obtained using a normal oxide-based conductor.

At a measurement temperature of 77 K (liquid nitrogen temperature), the thickness of the circumscribed normal conductor 4 was changed and the switching ratio was examined. The results are shown in FIG. By forming the circumscribed normal conductor 4 as in the first embodiment, the switching ratio is significantly improved. The thickness of the circumscribed normal conductor 4 has an appropriate value.
It is understood that the range of 0 ° to 120 ° is preferable. Especially 1
If the angle exceeds 20 °, the switching ratio will be reduced.

(Embodiment 3) FIG. 2 is a diagram showing a sectional structure of a current modulator according to a third embodiment of the present invention. FIG.
In the current modulation device, the first electrode superconductor 1 and the second electrode superconductor 1
, A channel superconductor 3, a circumscribing normal conductor 4, a dielectric 5, a control electrode 6, and a substrate 7. The components are the same as those of the second embodiment, but a major difference is that the circumscribed normal conductor 4 is not sandwiched between the first superconductor 1, the second superconductor 2, and the channel superconductor 3.

The process and materials for manufacturing the current modulator of this embodiment are as follows. On the substrate 7 made of strontium titanate single crystal, a film thickness of
A Nd _1.85 Ce _0.15 CuO _4-x- based oxide film of 00% is formed to form a circumscribed normal conductor. Then circumscribed normal conductor 4 thickness on to YBa ₂ Cu ₃ 0 _7-X first formed and patterned superconducting electrode 1 and the second superconducting electrodes made of a superconductor of 500A～1000A. The distance between the first superconducting electrode 1 and the second superconducting electrode 2 is 5 μm. Next, a channel superconductor 3 made of a YBa ₂ Cu ₄ O ₈ superconductor thin film, a dielectric 5 and a control electrode 6 are formed and patterned between the first superconducting electrode 1 and the second superconducting electrode 2. The current modulator is obtained by the above process.

The switching ratio of the obtained current modulator at 77K was examined. The results are shown in FIG. The switching ratio is significantly improved by forming the circumscribed normal conductor 4. The thickness of the circumscribed normal conductor 4 is less dependent on the thickness of 20 mm.
If it is Å50 ° or more, there is almost no change. Comparing the characteristics with the second embodiment, the second embodiment has less dependency on the film thickness and is easy to manufacture. On the other hand, the effect of improving the switching ratio is slightly lowered.

As a comparative example, instead of the circumscribed normal conductor 4 of an n-type oxide having a carrier type different from that of the channel superconductor 3 of the present embodiment, an n-type Si substrate and the same carrier type as the channel superconductor 3 are used. Table 2 shows the switching ratio when a p-type oxide made of La _1.85 Ba _0.15 CuO _4-X was used.

From Table 2, it can be seen that the circumscribing normal conductor 4 is most preferably an n-type oxide. On the contrary, when the n-type Si substrate is used, the switching ratio is lowered. This is because the switching ratio is low when the channel superconductor and the first electrode superconductor 1 and the second electrode superconductor 2 are formed. This is because Si diffuses into the crystal, and Si is oxidized to deteriorate the mutual crystal structure. Also, as is well known, oxide superconductors have a strong anisotropy and a short coherent length, so it is necessary to suppress the generation of grain boundaries as much as possible and to orient the crystals. It is also a big problem that this point cannot be largely solved.

[0023]

[Table 2]

In the three embodiments described above, the circumscribed normal conductor 4 or the circumscribed superconductor 4 is provided with Nd _1.85 Ce _0.15 CuO
_{A 4-X} type oxide film was used, but Nd _1.85 Th _0.15 CuO _4-y ,
Pr _1.85 Ce _0.15 CuO _4-y , Pr _1.85 Th _0.15 CuO
_4-y , Sm _1.85 Ce _0.15 CuO _4-y equal channel superconductor 3
Any material having a carrier type different from that described above may be used. Note that an oxide having a similar crystal structure (having a close lattice constant and low mismatch) is more preferable. Further, as shown in FIG. 3, the structure may be such that the first electrode 1 and the second electrode are formed on the circumscribed superconductor 4 and the channel superconductor 3, and the current control method is quasiparticle injection or current injection type. There is no problem even if it is.

[0025]

As described above, according to the present invention, a first electrode superconductor, an intermediate superconductor, a second electrode superconductor, and a control electrode are provided. In a current modulator for controlling a current flowing between a first electrode superconductor and a second electrode superconductor through a body by a control electrode signal, the channel superconductor is circumscribed around a channel superconductor periphery. A circumscribing normal conductor or circumscribing superconductor having different injection carrier types (holes or electrons) can be formed from a micron order size or more, and the controllability by the control electrode signal is good and sufficient. A current modulation device having switching characteristics can be provided.

If the present invention is applied to a current modulator using an oxide superconductor, a three-terminal element having good controllability and capable of coping with a large current capacity and having a limited use environment can be formed by using ordinary photolithography technology. The effect is extremely large because it can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a current modulation device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure of a current modulation device according to a third embodiment of the present invention.

FIG. 3 is a diagram showing a sectional structure of a current modulation device other than the embodiment according to the present invention.

FIG. 4 is a graph showing the dependency of the switching ratio of Example 2 and Example 3 on the film thickness of the circumscribed normal conductor 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st electrode superconductor 2 ... 2nd electrode superconductor 3 ... Channel superconductor 4 ... Circumscribed normal conductor or circumscribed normal conductor 5 ... Dielectric 6 ... Control electrode 7 ... Substrate

Continuation of the front page (72) Inventor Tatsuya Shimoda 3-5-5 Yamato, Suwa-shi, Nagano Seiko Epson Corporation (56) References JP-A-63-283177 (JP, A) JP-A-64-53474 ( JP, A) JP-A-3-41783 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/22-39/24 H01L 39/00

Claims (1)

(57) [Claims] A first electrode superconductor, a channel superconductor, a second electrode superconductor, and a control electrode on a substrate, wherein the first electrode superconductor is provided via the channel superconductor. A current modulator for controlling a current flowing between an electrode superconductor and the second electrode superconductor, wherein the first electrode superconductor comprising an oxide superconducting thin film on the substrate and the second electrode superconductor And a circumscribed normal conductor or circumscribed superconductor made of an oxide superconducting thin film so as to cover a part of the first electrode superconductor and a part of the second electrode superconductor. A conductor is formed, the channel superconductor made of an oxide superconducting thin film is formed on the circumscribed normal conductor or the circumscribed superconductor, and the control electrode is formed on the channel superconductor. A current modulator characterized by being performed.