JPH07122790A - Thin film device - Google Patents

Abstract

PURPOSE:To enable a thin film device to be set in I/V characteristics as required by a method wherein an impedance device is connected in parallel with a superconduction weak junction, and a means capable of controlling the impedance device in impedance is provided. CONSTITUTION:A Josephson device 12 and a transistor 13 are formed on a substrate 11 for the formation of a thin film device, wherein the Josephson device 12 is an SIS Josephson device composed of a first superconductor, an insulator, and a second superconductor which are connected in this sequence. The transistor 13 is a MOS field-effect transistor where Si is utilized, wherein control signals are inputted through a gate electrode G to control a resistive component between a source and a drain. The Josephson device 12 and the resistive component between the source and the drain of the transistor 13 are made to constitute a parallel circuit. As mentioned above, a resistance between the source and the drain of a MOS field-effect transistor is used as an impedance so as to finely control a thin film device of this constitution in I/V characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a switch, a memory,
The present invention relates to thin film elements used in electronic circuits as elements such as mixers and sensors, and particularly to thin film elements using superconducting weak coupling.

[0002]

2. Description of the Related Art A thin film element using superconducting weak coupling has attracted attention and expectation as an element which operates at high speed and low power consumption. In the past, its operation was extremely cold, so its range of applications was quite limited. However, recent discoveries of high-temperature oxide superconductors have made it possible to operate at liquid nitrogen temperature (77K), the refrigeration technology is reduced, and its application range is expanding.

A thin-film element using superconducting weak coupling is mainly a two-terminal Josephson element, and its electrical equivalent circuit can be described by a parallel circuit of a Josephson junction, a resistance component, and a capacitance component. A model based on this equivalent circuit is RSJ (Res-istive Sh
It is known that the I / V characteristics of the Josephson device can be understood almost quantitatively by conducting analysis using an unjunction model. According to the RSJ model, an I / V characteristic having a hysteresis is obtained when the capacitance component is large and dominant, and also a hysteresis is obtained when the resistance component is small and dominant. It is possible to obtain a stable I / V characteristic. The former characteristic is generally obtained by a Josephson device composed of a thin insulator sandwiched between two superconductors, that is, a SIS structure. Therefore, the characteristic will be referred to as a SIS Josephson characteristic hereinafter. On the other hand, the latter characteristic is generally obtained by a Josephson device having a structure in which a normal conductor is sandwiched between two superconductors, that is, an SNS structure. therefore,
Hereinafter, the characteristic will be referred to as an SNS Josephson characteristic. When neither the capacitive component nor the resistive component can be said to be dominant, an intermediate property between the SIS Josephson characteristic and the SNS Josephson characteristic, that is, a characteristic that hysteresis exists but is small is obtained.

The resistance component and the capacitance component of the Josephson element are determined by the element structure, element material and manufacturing conditions. Therefore, the I / V characteristic of the conventional Josephson device, that is, the thin film device using the conventional superconductor is uniquely determined by its structure, material, and manufacturing conditions.

[0005]

However, the conventional thin film element using weak superconducting coupling has a drawback that its I / V characteristics cannot be adjusted to desired characteristics according to the purpose. This drawback will be explained more concretely as follows. For example, when the thin film element is applied to a memory, the SIS Josephson characteristic having a hysteresis is necessary, and when the thin film element is applied to an electromagnetic wave detector, the SNS Josephson characteristic with a small contribution of the capacitance component is desirable. , And so on, depending on the purpose I
/ V characteristic is required. As described above, it has been difficult for a conventional thin film device using weak superconducting coupling to be applied to a plurality of target fields with one kind of thin film device for various required characteristics. Therefore, with respect to the conventional thin film element using the superconducting weak coupling, there has been a problem that the element structure, the element material, and the manufacturing conditions must be individually examined and the technology must be established according to the purpose of use. Further, when the thin film element is applied to an electromagnetic wave detector, it is known that the output voltage of the detector can be increased and the sensitivity can be improved by using a plurality of thin film elements connected in series. In this case, it is necessary to make the I / V characteristics of the plurality of thin film elements uniform. Therefore, in this case, it is desirable to correct the variation in the I / V characteristics of each thin film element, but it is impossible to perform this correction in the conventional thin film element using weak superconducting coupling.

The inability to match the I / V characteristics is a further significant drawback, especially in thin film devices using high temperature oxide superconductors. One of the reasons is that high-temperature oxide superconductors have poorer processing accuracy than metal superconductors and it is difficult to control the size and shape. It is difficult to reduce the variation in characteristics of each thin film element when used as a thin film. Another reason is that when an oxide high temperature superconductor is used, it is difficult to form a thin insulating layer (I layer), so that the Josephson element in which the capacitance component is dominant is a Josephson element in which the resistance component is dominant. The production yield is lower than that of, and therefore, the application of the thin film element using the oxide high temperature superconductor to the application field where the SIS Josephson characteristic is required is greatly restricted.

[0007]

SUMMARY OF THE INVENTION The present invention provides a superconducting thin film device capable of adjusting the I / V characteristic to a desired characteristic by eliminating the above-mentioned drawbacks. In the thin film element provided, the impedance element is connected in parallel to the superconducting weak coupling, the means for controlling the impedance of the impedance element is provided, and the main component of the controlled impedance is the resistance. , The property of superconducting weak coupling is that the superconducting tunnel effect is dominant, and the superconducting weak coupling is the first superconductor,
It has a structure in which an insulator and a second superconductor are connected in this order, and an impedance is connected in parallel to the superconducting weak coupling, and the impedance is composed of a series connection structure of a plurality of impedance elements. Alternatively, the superconducting weak coupling is connected in parallel with an impedance composed of a series connection structure of a plurality of impedance elements, and at least one of the plurality of impedance elements forming the series connection structure is fixed. At least one of them has means for controlling the impedance, and further, the impedance is connected in parallel to the superconducting weak coupling, and the impedance is connected in series. The structure consists of multiple structures connected in parallel. At least one of the impedance elements has a fixed impedance, and the other at least one has a means for controlling impedance, and the impedance control of the impedance element having means for controlling impedance has a series connection structure. Can be performed independently for each, and if necessary, the main component of the impedance element with fixed impedance is capacitance, and the main component of the impedance element equipped with means for controlling impedance is resistance. The superconducting proximity effect is dominant in the characteristics of superconducting weak coupling. The Josephson junction has a structure in which a first superconductor, a normal conductor, and a second superconductor are connected in this order. The impedance element having means for controlling impedance must be a semiconductor element. And superconductors constituting the superconducting weak coupling is characterized in that an oxide superconductor.

[0008]

EXAMPLES The present invention will be described in detail below based on examples.

(Embodiment 1) FIG. 1 is a plan view of a thin film element in Embodiment 1 of the present invention. The thin film element is composed of a Josephson element 12 and a transistor 13 on a substrate 11.
Is formed by forming.

The Josephson element 12 is a first superconductor,
This is a SIS Josephson device having a structure in which an insulator and a second superconductor are connected in this order. The first and second superconductors are YBCO oxide superconductors and have a critical temperature of 90K. The Josephson element 12 alone exhibits tunnel type Josephson characteristics. This is because the capacitance component is large and its normal resistance is high. The transistor 13 is a MOS field effect transistor using Si, and symbols S, D, and G described on the periphery thereof are source, drain, and gate electrodes, respectively. A control signal is input to the gate electrode G to control the resistance component between the source and drain. Transistor 13
Is a normally-off type, and its source-drain resistance is much larger than the normal resistance of the Josephson element 12 when the gate voltage is zero, and becomes smaller as the gate voltage is applied. As shown in FIG. 1, the Josephson device 12 and the resistance component between the source and drain of the transistor 13 form a parallel circuit.

Using the thin film element shown in FIG. 1, the I / V characteristic between both terminals of a parallel circuit composed of a SIS Josephson element and a MOS field effect transistor was measured and the relationship with the gate voltage of the MOS field effect transistor was measured. Was evaluated. The measurement was performed in a helium gas atmosphere at a temperature of 60K.

FIG. 2 is a diagram showing the gate voltage dependence of the I / V characteristic of the thin film element. FIG. 2 shows that the I / V characteristic of the thin film element continuously changes from the SIS Josephson characteristic to the SNS Josephson characteristic as the gate voltage is increased. The reason is that the resistance between the source and drain of the MOS field effect transistor decreases as the gate voltage increases. That is, when the gate voltage increases, the equivalent circuit of the thin film element can be described as a parallel circuit of a tunnel type Josephson junction and a resistor. The above results can be quantitatively explained by numerical calculation based on the RSJ model.

In this embodiment, the normally-off type is used as the MOS field effect transistor, but it goes without saying that the normally-on type can be used to control the I / V characteristics as in the case of the present embodiment.

In this embodiment, the impedance is MOS
The I / V characteristics were finely controlled by using the source-drain resistance of the field effect transistor. However, if the fine control is not necessary, the SIS Josephson element is simply used for SN control.
When it is desired to obtain the S Josephson characteristic, a resistance element may be used instead of the MOS field effect transistor.

(Embodiment 2) FIG. 3 is a plan structural view of a thin film element in Embodiment 2 of the present invention. This thin film element is composed of a substrate 21, a Josephson element 22, and a transistor 2.
3 and then by forming the capacitor 24.

The Josephson element 22 is a first superconductor,
It is an SNS Josephson device having a structure in which a normal conductor and a second superconductor are connected in this order. The first and second superconductors are YBCO oxide superconductors and have a critical temperature of 90K. The Josephson element 22 alone exhibits a proximity effect type Josephson characteristic. This is because the capacitance component is small and the normal resistance is low. The transistor 23 is a MOS field effect transistor using Si, and symbols S, D, and G described on the periphery thereof are source, drain, and gate electrodes, respectively. A control signal is input to the gate electrode G to control the resistance component between the source and drain. Transistor 23
Is a normally-off type, and its source-drain resistance is much larger than the normal resistance of the Josephson element 22 when the gate voltage is zero, and becomes smaller as the gate voltage is applied. As shown in FIG. 3, the Josephson element 22 and the capacitor 24 form a parallel circuit through the source and drain of the transistor 23.

Using the thin film element shown in FIG. 3, the on / off state of the MOS field effect transistor was controlled by the gate voltage, and the I / V characteristic in each state was measured. The measurement was performed in a helium gas atmosphere at a temperature of 60K.

FIG. 4 is a diagram showing the I / V characteristics of the thin film element in each of the off and on states of the transistor controlled by the gate voltage. FIG. 4 shows that the I / V characteristic of the thin film element is the SNS Josephson characteristic when the transistor is off, and the SIS Josephson characteristic when the transistor is on. The reason is that the resistance between the source and drain is almost infinite when the gate voltage is zero, and the capacitor is disconnected. On the other hand, when the gate voltage is applied, the source is drained.・ Drain resistance is almost zero, and the capacitor is in parallel with the SNS Josephson device. That is, this characteristic control is based on the control of the capacitance component connected in parallel with the SNS Josephson element by the gate voltage. As is clear from the above description, the transistor in this case functions as a switch.

When the gate voltage is an intermediate voltage between the above two cases, an intermediate characteristic of both the SIS Josephson characteristic and the SNS Josephson characteristic is shown. This characteristic cannot be quantitatively explained by an ordinary RSJ model, but if the resistance component is variable using a model in which the capacitance component of the RSJ model is replaced by a resistance component and a series connection of the capacitance component, numerical calculation is performed. It can be explained quantitatively.

In this embodiment, the normally-off type is used as the MOS field effect transistor, but it goes without saying that the normally-on type can be used to control the I / V characteristics as in the case of the present embodiment.

In this embodiment, the capacitance component of the capacitor and the MO
A series connection structure of the source-drain resistance of the S field effect transistor is connected in parallel to the Josephson element to form an I / V.
Although the characteristics are controlled, if no control is required, a resistance element may be used instead of the MOS field effect transistor. Further, when it is desired to obtain the SIS Josephson characteristics by simply using the SNS Josephson element, the MOS field effect transistor may be removed and only the capacitor may be connected in parallel to the Josephson element.

(Embodiment 3) In Embodiment 2, only one structure composed of a capacitor and a transistor is connected in parallel to one Josephson element. The thin film element of this embodiment is obtained by forming a structure in which a plurality of structures each including a capacitor and a transistor are connected in parallel, and connecting them in parallel to one Josephson element. Figure 5
FIG. 4 is a diagram showing an equivalent circuit of a thin film element in this example. Explaining the symbols shown in FIG. 5, JJ is a superconducting weak junction composed of Josephson junction, R
Is the resistance associated with superconducting weak coupling, C is the capacitance, and S, D, and G are the source, drain, and gate electrodes of the transistor, respectively. In this embodiment, the gate voltage of each transistor is controlled independently.
As a result, the I / V characteristic corresponding to the stepwise change of the capacitance component is obtained.

[0023]

As described above, according to the present invention, in a thin film element having a superconducting weak coupling, an impedance element is connected in parallel to the superconducting weak coupling, and the impedance of the impedance element is That the main component of the controlled impedance is resistance, that the characteristics of the superconducting weak coupling are dominated by the superconducting tunnel effect, and that the superconducting weak coupling is A structure in which a superconductor, an insulator, and a second superconductor are connected in this order, and impedance is connected in parallel to the superconducting weak coupling, and the impedance is a series connection of a plurality of impedance elements. The structure is composed of multiple impedance elements connected in parallel to the superconducting weak coupling. In addition, at least one of the plurality of impedance elements forming the series connection structure has a fixed impedance, and at least one of the other impedance elements has a means for controlling the impedance. Impedances are connected in parallel, and the impedance is composed of a structure in which a plurality of series connection structures of a plurality of impedance elements are connected in parallel, and at least one of the plurality of impedance elements forming each series connection structure is Has a fixed impedance,
At least one of the other has a means for controlling impedance, and impedance control of the impedance element having means for controlling impedance can be performed independently for each series connection structure. If necessary, the main component of the impedance element having a fixed impedance is capacitance, the main component of the impedance element having means for controlling impedance is resistance, and the characteristic of superconducting weak coupling is the superconducting proximity effect. Is dominant, the Josephson junction has a structure in which a first superconductor, a normal conductor, and a second superconductor are connected in this order, and the impedance element having means for controlling impedance is a semiconductor. Be an element,
Since the superconductor that constitutes the superconducting weak bond is an oxide superconductor, the I / V characteristic of the Josephson device is
Since it is possible to match the desired characteristics of the S Josephson element characteristics and the SNS Josephson element characteristics, there is an effect that the optimum characteristics can be freely selected according to the application purpose.

Further, if the present invention is applied to a field where it is desired to connect and use a plurality of detecting elements having the same characteristics, such as an electromagnetic wave detector using a superconducting element,
Since the characteristic variations of the element due to manufacturing or the like can be corrected and made uniform, the effect is large.

[Brief description of drawings]

FIG. 1 is a plan structure diagram of a thin film element in Example 1 of the present invention.

FIG. 2 is a diagram showing gate voltage dependence of I / V characteristics of a thin film element.

FIG. 3 is a plan structural view of a thin film element in Example 2 of the present invention.

FIG. 4 is an I / V of a thin film element in each of an on state and an off state of a transistor controlled by a gate voltage.
The figure which shows a characteristic.

FIG. 5 is a diagram showing an equivalent circuit of a thin film element in Example 3 of the present invention.

[Explanation of symbols]

 11 substrate 12 Josephson device 13 transistor 21 substrate 22 Josephson device 23 transistor 24 capacitor

Continuation of the front page (72) Inventor Tatsuya Shimoda 3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (14)

[Claims] 1. A thin-film element having a superconducting weak coupling, wherein an impedance element is connected in parallel to the superconducting weak coupling. 2. A means for controlling the impedance of the impedance element is provided.
The thin film element described. 3. The thin film element according to claim 2, wherein the main component of controlled impedance is resistance. 4. The thin film element according to claim 1, wherein the superconducting weak coupling property is dominated by the superconducting tunnel effect. 5. The thin film element according to claim 4, wherein the weak superconducting bond has a structure in which a first superconductor, an insulator, and a second superconductor are connected in this order. 6. A thin film element, wherein an impedance is connected in parallel to the superconducting weak coupling, and the impedance is composed of a series connection structure of a plurality of impedance elements. 7. The superconducting weak coupling is connected in parallel with an impedance composed of a series connection structure of a plurality of impedance elements, and at least one of the plurality of impedance elements forming the series connection structure is a fixed impedance. And at least one other comprises means for controlling impedance. 8. A thin film element, wherein an impedance is connected in parallel to the superconducting weak coupling, and the impedance is composed of a structure in which a plurality of series connection structures of a plurality of impedance elements are connected in parallel. 9. A means for controlling impedance, wherein at least one of a plurality of impedance elements forming each series connection structure has a fixed impedance, and at least one of the other impedance elements comprises means for controlling impedance. 9. The thin film element according to claim 8, wherein the impedance control of the impedance element including the element can be performed independently for each series connection structure. 10. The thin film according to claim 7, wherein the main component of the impedance element having a fixed impedance is capacitance, and the main component of the impedance element having means for controlling impedance is resistance. element. 11. The thin film element according to claim 10, wherein the superconducting weak coupling property is dominated by the superconducting proximity effect. 12. The thin film element according to claim 11, wherein the weak superconducting bond has a structure in which a first superconductor, a normal conductor and a second superconductor are connected in this order. 13. The thin-film element according to claim 2, claim 3, claim 7, claim 9, or claim 10, wherein the impedance element having means for controlling impedance is a semiconductor element. 14. The thin film element according to claim 1, wherein the superconductor constituting the superconducting weak bond is an oxide superconductor.