JPS61190990A - Superconductive element - Google Patents

Abstract

PURPOSE:To increase gains at a time when controlling the state of coupling between superconducting electrodes by applied voltage by changing the distribution of impurity concentration in semiconductor layers forming the superconducting electrodes. CONSTITUTION:When negative voltage is applied to a control electrode 5, the storage layer of positive charges easily extends into a low impurity- concentration layer 3. Consequently, the state of superconductive coupling between a first superconducting electrode 6 and a second superconducting electrode 7 can be changed by a small control signal of approximately 10mV at that time, thus making gains larger than the uniform distribution of an impurity by approximately 2.5-3 times. When positive voltage is applied to the control electrode 5, the inversion layer of negative charges hardly extends at small control voltage. When fixed voltage or more is applied, the inversion layer expands to the low impurity-concentration layer 3 first, and the state of superconductive coupling between the first and second superconducting electrodes 6, 7 begins to change rapidly. Accordingly, a superconductive element having a function of large gains is acquired.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a superconducting device that operates at extremely low temperatures, and in particular to controlling the number of superconducting or normal conducting electrons tunneling through a semiconductor by a voltage applied to a control electrode. The present invention relates to superconducting elements.

[Background of the invention]

Superconducting devices that use semiconductors and have electrodes to control device characteristics include T and D.

Phys, ) 2736.51 (1980) and is well known. In a JOFET, should an electrode made of a superconductor be formed on a heavily doped semiconductor substrate?

Alternatively, a doped layer is formed on a high-purity buffer layer, and an electrode made of a superconductor is formed thereon.

In this case, the device characteristics are controlled by applying a voltage to the control electrode to spread one inversion layer from the control electrode side to the semiconductor side. In this case, because the impurity concentration of the semiconductor layer directly under the control electrode is high, the voltage that should be applied to the control electrode reaches several hundred millivolts, whereas the voltage obtained as an output is about the same level or even higher. small,
It was not possible to use circuits similar to those used in conventional semiconductor technology.

[Purpose of the invention]

An object of the present invention is to provide a superconducting element that has a large gain when controlling the coupling state between superconducting electrodes using an applied voltage.

[Summary of the invention]

The present invention provides at least two superconducting electrodes in contact with a semiconductor layer (or substrate), and at least one electrode that controls the current flowing between the superconducting electrodes (changes the superconducting weak coupling state between the superconducting electrodes). and configured such that the distribution of impurities contained in the semiconductor layer consists of at least one high impurity concentration part having an impurity concentration above the average and at least one low impurity concentration part having an impurity concentration below the average. It is. Namely.

The above object is achieved by varying the concentration distribution of impurities contained in the semiconductor layer forming the superconducting electrode.

The semiconductor layer in a conventional superconducting device uniformly contains impurities at a high concentration, so the spread of the charge accumulation layer or inversion layer is small compared to the voltage applied to the control electrode. In the present invention, since the distribution of impurities is varied, the spread of the charge accumulation layer or inversion layer is different from that in the case where impurities are uniformly contained, and even with a small applied voltage, the accumulation layer or inversion layer can be easily formed. can be expanded and the gain can be increased.

For example, in one recommended embodiment of the present invention, two superconducting electrodes are provided on one side of the semiconductor layer, and a control electrode is provided on the other side of the semiconductor layer with an insulating film interposed therebetween, and the concentration distribution is adjusted in the depth direction of the semiconductor layer. In order to achieve this, the impurity concentration in the semiconductor on the side closer to the control electrode is increased, and the impurity concentration in the semiconductor on the side closer to the superconducting electrode is lowered. In the case of such an impurity distribution, a charge accumulation layer can easily spread from a high impurity concentration layer to a low impurity concentration layer even with a small control voltage. Therefore, by utilizing such characteristics, the superconducting weakly coupled state can be easily changed with a small control voltage, and the gain can be increased. On the other hand, regarding the inversion layer, the inversion layer does not spread easily until the control voltage exceeds a certain value (that is, until the inversion layer spreads to the high impurity concentration layer), but at a voltage that causes the inversion layer to spread to the low impurity concentration layer, The inversion layer then expands easily even with a small increase in voltage. Therefore, by utilizing these characteristics, it is possible to create a high-gain superconducting element in which the characteristics hardly change until the control voltage reaches a certain value, and then the device characteristics suddenly change when the control voltage exceeds a certain value. can get.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention.

Boron ions were implanted into a (100)-oriented Si single crystal substrate 1 at a density of 10 cm at an acceleration voltage of 70 KeV, and annealed at 900° C. in nitrogen for 35 minutes. Through this treatment, a high impurity concentration layer 2 with a thickness of about 200 nm is formed. After cleaning the surface, boron is added as an impurity by molecular beam epitaxy or vapor phase epitaxy.
A low impurity concentration layer 3 containing a certain amount of impurity is formed. The amount of impurity boron contained in the low impurity concentration layer 3 is selected to be smaller than the amount of impurity boron contained in the high impurity concentration layer 2. When the semiconductor is Si, the impurity concentration is 1014~10 for the low impurity concentration layer. Desirably, it is about 10"an-', and about 101' to 101s in a high impurity concentration layer.

Next, the Si single crystal substrate 1 is etched from the back side using a chemical such as KOH using SiO2 or the like formed by normal pressure vapor phase growth as a mask. In this etching, since the etching rate of the (100) plane of the Si single crystal is higher than the etching rate of the (111) plane, the shape shown in FIG. 1 can be obtained. Subsequently, the surface of the Si single-crystal substrate 1 is oxidized in pure oxygen at 1000°C to a thickness of approximately 40°C.
A SiOx layer 4 with a thickness of about 500 nm was formed, and then AQ was deposited to a thickness of about 500 nm using a resistance heating evaporation method to form a control electrode 5.

When the Si layer 4 is formed, a Si oxide film is also grown on the surface of the low impurity concentration layer 30, so this is removed by chemical etching to clean the surface of the low impurity concentration layer 3. On this cleaned low impurity concentration layer 3, a thickness of approximately 3.
00 nm of Nb was deposited by DC magnetron sputtering, and this was processed by reactive ion etching using an electron beam resist pattern with a thickness of about 350 nm as a mask to form the first superconducting electrode 6 and the second superconducting electrode 7. And so. The distance between the first and second superconducting electrodes is 0.2 when the semiconductor material is Si.
It is desirable that it is less than μm. Through the above steps, the superconducting element of the present invention could be manufactured. This superconducting element was cooled to liquid helium temperature and operated. When a negative voltage is applied to the control electrode, a positive charge accumulation layer easily spreads into the low impurity concentration layer 3. Therefore, in this case, 10
The first superconducting electrode 6 is activated by a small control signal on the order of mV.
It is possible to change the superconducting bonding state between the superconducting electrode 7 and the second superconducting electrode 7, and the gain can be increased by about 2.5 to 3 times compared to the case where impurities are uniformly distributed.

When a positive voltage is applied to the control electrode, the negative charge inversion layer hardly spreads at a small control voltage, and when the voltage exceeds a certain level, the inversion layer spreads for the first time in the low impurity concentration layer 3, and the first Then, the superconducting coupling state between the second superconducting electrodes 6 and 7 suddenly begins to change. Therefore, in this case,
Compared to a case where impurities are uniformly distributed, a superconducting element can be obtained that has a constant non-zero threshold for starting operation and also has a large gain.

In this example, a high impurity concentration layer was provided on the side closer to the control electrode and a low impurity concentration layer was provided on the side closer to the superconducting electrode, but by reversing this, a low impurity concentration layer was provided on the side closer to the control electrode. , a high impurity concentration layer may be provided on the side closer to the superconducting electrode. In this case as well, the charge inversion layer or accumulation layer can easily spread to the low impurity concentration layer with a small control voltage, so that the gain can be increased. In this case, when the voltage exceeds a certain level, the inversion layer/accumulation layer begins to spread through the high impurity concentration layer, so the inversion layer/accumulation layer becomes difficult to wave any further, and changes in device characteristics are small. It has the property of becoming. In addition, when the impurity concentration on the superconducting electrode side is high, the height and width of the Schottky barrier that exists at the interface between the semiconductor and the superconductor is reduced, making it easier for electrons to seep from the superconducting electrode into the semiconductor. produces the effect of

In this case, the spatial distance between the first and second superconducting electrodes can be made longer than before, making it easier to manufacture the device.

FIG. 2 shows another embodiment of the invention. In this embodiment, the portion with low impurity concentration is located at the center of the semiconductor layer. That is, a high impurity concentration layer 3' is formed by molecular beam epitaxy or the like on a low impurity concentration layer 2 formed in the same manner as in the embodiment shown in FIG. In the case of this example, the effects of the two previous examples (an example in which a high impurity concentration layer is provided on the control electrode side, a low impurity concentration layer on the superconducting electrode side, and an example with the opposite structure) are obtained. have both,
That is, the gain is large and the device can be easily manufactured.

FIG. 3 shows another embodiment of the present invention, in which a control electrode is provided on the same side as the surface of the semiconductor layer forming the superconducting electrode. On a Si substrate 301 containing 10 am-' of phosphorus as an impurity, 10 am-' of phosphorus was added by molecular beam epitaxy.
an-"Low impurity concentration layer 302 containing phosphorus IQ"
am-” high impurity concentration layer 303, 10”a of phosphorus
A low impurity concentration layer 302' containing m-" is formed. Next, a SiO□ layer is formed at a low temperature of 500 DEG C. and patterned. Using this as a mask, phosphorus is ion-implanted.

Approximately 200n of Nb was added onto the surface into which phosphorous was ion-implanted.
After m sputtering, the Sin2 layer used as a mask is removed by etching. In this way, superconducting electrodes 306 and 307 are formed. Next, a Si film 304 is formed by 02 plasma oxidation, and finally a film 304 with a thickness of 500 nm is formed.
A control electrode 305 made of an AQ vapor-deposited film of m is formed.

Even in the case of this embodiment, by applying a voltage to the W control electrode 305, the accumulation layer or the inversion layer is changed to the low impurity concentration layer 305.
2', the gain can be increased as in the previous embodiment.

In the embodiments described so far, a case has been described in which two superconducting electrodes are included, but the number of superconducting electrodes may be three or more, and the same applies to the number of control electrodes. For example, the effects of the present invention can be obtained even in the case of a superconducting element having three superconducting electrodes as shown in FIG. Such a superconducting element can be manufactured by the same process as the embodiment described in FIG. 1, except for the shape of the superconducting electrode formed and processed. 406°406'
4 corresponds to a source superconducting electrode, and 407 corresponds to a drain superconducting electrode. Such a device has the advantage that one element has the same effect as two elements connected in parallel, and can improve the degree of circuit integration.

Further, in the above embodiments, a case was described in which a difference in impurity concentration was provided over the entire layer, but a low impurity concentration portion or a high impurity concentration portion may be provided only in a certain portion of the semiconductor layer6. A similar effect can be obtained by providing a high impurity concentration area or a low impurity concentration area in a limited area including directly below the superconducting electrode. Further, the same effect can be obtained even if the difference in impurity concentration is not provided stepwise but is provided so as to gradually change.

Furthermore, in the embodiments described above, Si single crystal was used as the semiconductor material, but amorphous or polycrystalline S
The purpose of the present invention can also be achieved using i. Also, G8 + GaAs was used instead of Si.

Materials such as InAs, InP, and InSb may be used. In addition to Nb, pb and pb may be used as materials for the superconducting electrode.
Alloy whose main component is + N b N , Nb, Sn,
Similar effects can be obtained by using Nb compounds such as Nb5A Q , Nb, and Gs.

The material of the control electrode is not limited to AQ, and the same effect can be obtained by using a superconducting metal such as Pb. Further, although the control electrode is provided through an insulating film, the control electrode may be formed through a Schottky barrier.

FIG. 5 shows an example of use of the superconducting element according to the present invention for reference.

The superconducting element of the present invention is used in an extremely low temperature environment at or near liquid helium temperature, and can realize high-speed switching with low power consumption. Therefore, if an arithmetic unit is made using the superconducting element of the present invention, it is possible to realize compact and high-speed processing. FIG. 5 shows an image signal processing device for a human body medical diagnostic device using nuclear magnetic resonance, which is constructed by taking advantage of this feature. In this diagnostic device, a superconducting magnet 21 using liquid helium is used to generate a magnetic field, and a small liquid helium refrigerator 22 is used to supply the liquid helium. If the arithmetic device 24 using the superconducting element of the present invention, which is housed in the insulator 23, is used in this device, the processing of complex image signals will be 5 to 10 times faster than when using a conventional arithmetic device using semiconductor elements.
The speed is about twice as fast, reducing the time required to diagnose a patient, and it also becomes possible to process more sophisticated images and provide more appropriate information for diagnosis. Further, the amount of liquid helium used in the arithmetic device at this time is increased by an almost negligible amount. In FIG. 5, liquid helium is supplied from the refrigerator 22 through pipes 31 and 32.

Further, the nuclear magnetic resonance signal 34 is sent from the signal detector 25 to the arithmetic unit 24, and the processed image signal is output to the display 26 through the cable 35. Also, magnet 21
is also controlled by sending a signal 33 from the arithmetic unit 24. In this usage example, the magnet 21 and the computing device 24 are housed in separate heat-insulating containers, but they may be housed in the same heat-insulating container. In this usage example,
Although a medical diagnostic device has been described, similar effects can generally be obtained for control of devices using liquid helium or signal processing.

[Effects of the Invention] According to the present invention, since the impurity concentration distribution in the semiconductor layer forming the superconducting electrode is varied, the gain when controlling the bonding state between the superconducting electrodes by the applied voltage can be increased. can do.

[Brief explanation of drawings]

Figures 1 to 3 are cross-sectional views of a superconducting element that is an embodiment of the present invention, Figure 4 is a plan view of a superconducting element that is an embodiment of the present invention, and Figure 5 is a method according to the present invention. It is a block diagram showing a reference example of the working power of a superconducting element.

Claims (1)

[Claims] 1. A semiconductor layer comprising a semiconductor layer, at least two superconducting electrodes provided in contact with the semiconductor layer, and at least one control electrode for controlling a current flowing between the superconducting electrodes, The distribution of impurities contained in the semiconductor layer is characterized by comprising at least one high impurity concentration region having an impurity concentration above the average and at least one low impurity concentration region having an impurity concentration below the average. Superconducting element. 2. A superconducting element according to claim 1, wherein the superconducting electrode is provided on one side of the semiconductor layer, and the control electrode is provided on the other side of the semiconductor layer. 3. A superconducting element according to claim 1 or 2, wherein the high impurity concentration portion is present in contact with a control electrode. 4. The superconducting element according to claim 1 or 2, wherein the high impurity concentration portion is present in contact with the superconducting electrode. 5. The superconductor according to claim 1 or 2, characterized in that the high impurity concentration portion consists of a portion that is in contact with the control electrode and a portion that is in contact with the superconducting electrode. element.