JPH05267732A - Frequency variable resonator - Google Patents

Abstract

PURPOSE:To provide the title resonator capable of attaining the resonance frequency high in value reaching GHz zone as well as changing the frequency in low band not exceeding specific value. CONSTITUTION:The title frequency variable resonator is composed of a ring 5 comprising a superconductive thin film formed of a superconductive ground plane 2 formed on a substrate 1, a dielectric film 3 formed on the plane 2 and multiple Josephson junctions 6 formed on the dielectric film 3 having the same characteristics as those of the film 3 formed in series, a strip line 4 provided near the ring 5 as well as a magnetic field generating means 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microstrip type resonator used in a high frequency measuring instrument or the like, and more particularly to a resonator capable of changing a resonance frequency.

[0002]

2. Description of the Related Art FIGS. 3 (a), 3 (b) and 3 (c) show a conventional microstrip line type structure, in which (a) is a linear resonator and (b) is U. A type resonator, (c) is a disk resonator. These resonators include resonators 11a of various shapes in the vicinity of the strip line 10,
The resonance frequency is obtained by arranging 11b and 11c, but the resonance wavelength is a fixed resonator determined by the shape. In FIG. 4, a variable capacitor 11 is connected to one end of the strip line 10 and the resonance frequency is made variable by changing the capacitance thereof. Further, it is known that a frequency of about 800 MHz to 1 GHz is made variable by using a varactor diode.

[0003]

However, in the above-mentioned prior art, the one shown in FIG. 3 has a fixed resonance frequency, and it is difficult to obtain a resonance frequency having a high Q value in the one shown in FIG. There was a problem. There is also a report that a superconducting member is used to obtain a resonator with a high Q value. For example, in the case of a metallic superconducting film,
There is a problem that it is difficult to change the resonance frequency under the environment of 10K or less. The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a resonator capable of obtaining a high Q resonance frequency and changing the frequency even at 10 K or less.

[0004]

In order to solve the above problems, the present invention provides a superconducting ground plane formed on a substrate and a dielectric film formed on the superconducting ground plane. , A ring made of a superconducting thin film formed on this dielectric film and having a plurality of Josephson junctions having the same characteristics in series, a stripline provided in the vicinity of this ring, and above the ring. It is characterized in that a magnetic field generating means is provided at a predetermined distance.

[0005]

Since a plurality of Josephson junction equivalent inductances are formed in the ring, if the equivalent inductance is changed by an external magnetic field, the resonance frequency changes. And the magnetic field by the coil does not depend on temperature.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, (a) is a plan view,
(B) is AA sectional drawing of (a) figure. In these figures, 1 is a substrate having a low dielectric constant, such as MgO or LaAl ₂ O ₃ , 2 is a ground plane (GP) made of a superconducting member, and 3 is formed on GP. It is a dielectric film made of SiO ₂ or Al ₂ O ₃ . Reference numeral 4 is an input / output strip line made of a superconducting member, 5 is a ring made of a superconducting member, and a plurality of (five in the figure) Josephson junctions 6 are formed in the middle of the ring. 7
Is a magnetic field generating means (coil) arranged above the ring with a predetermined distance.

In the above structure, the radius of the ring 5 is a, and the inductance when there is no Josephson junction 6 is L
₀ , the capacitance of the ring is C, and the phase velocity of the electromagnetic wave at the strip line 4 is Vp, the relationship between the resonance frequency f ₀ and Vp in this case can be expressed by the following equation. f ₀ = Vp / λ = {Vp / (2πa)} · n ... λ; wavelength of resonance frequency (n = 1, 2, 3, ...) Vp = 1 / √ (L ₀ C)

Next, if a plurality of Josephson junctions are provided in series in the ring, the critical current of the Josephson junction is Ic, and the current and voltage flowing through the junctions are I and V, respectively, I = Ic from the Josephson effect. sin θ… V = (h ^' / 2e) (☆ θ / ☆ t)… θ; phase difference of the order parameter of Josephson junction h ^′ ; h / 2π (h is Planck's constant) e; electron Charge ☆; can be expressed as a partial differential symbol.

When the equation is differentiated with time, ☆ I / ☆ t = I _c cos θ (☆ θ / ☆ t) ... Therefore, V = (h '/ 2e) (1 / I _c cos θ) ・ ( ☆ I / ☆ t) = L _j (☆ I / ☆ t) ... L _j is defined as (h ^' / 2e) (1 / I _c cos θ)…, the Josephson junction equivalently has an inductance of L _j. I will be responsible.

Now, letting the inductance of the resonator be Lt, this inductance can be expressed as Lt (Φ _x ) = L ₀ + L _j (Φ _x ). Therefore, Φ _x
Thus, it is possible to change f ₀ by changing Vp.

Next, a superconducting ring including one Josephson junction is generally called an rf-SQUID. The magnetic flux in the ring is Φi according to the quantization condition of the magnetic flux in the ring.
When _{θ = 2π (Φi / Φ 0} + k) ...
k = 0,1,2 ... Φ ₀ = h / 2e; can be represented by a flux quantum. The relationship between Φi and the external magnetic flux Φ _x = is given by Φ _x = Φ _i + LI _c sin (2πΦ i / Φ ₀ ) ... L; the inductance of the ring.

FIG. 2 shows that α = 2πLIc / Φ₀The parameter
To Φ_xAnd Φi (α ... hysterisis
Parameters). In FIG. 2, when α ≦ 1, Φi is Φ_xTo
On the other hand, it is monovalent, and when α> 1, it is multivalent. Therefore α ≦ 1
The ring inductance L and critical current Ic
If θ is Φ _xIs uniquely determined for
Φ_xBy L_j Can be changed uniquely.

In the above description, one Josephson junction is provided in the ring, and in order to uniquely determine Φi with respect to Φ _x , the critical current Ic of the Josephson junction and the superconducting inductance L are The condition that the hysteresis parameter (α) is α = 2πLIc / Φ ₀ <1 is required between them.

However, under the above conditions, it is necessary to reduce L or Ic. If L is made small, the resonance frequency becomes extremely high, and if Ic is made small, the high-frequency current that can be flown is limited, and it is practically used. It becomes a problem. It is also possible to use α> 1, but in that case it is necessary to increase L or I _c . For example, when L is increased, L _j becomes relatively small, and when I _c is increased, L _j is decreased from the equation, and in any case, the amount of change in resonance frequency is decreased. The merit is small.

In the present invention, n Josephson junctions having equivalent characteristics are arranged in series in the ring. As a result, the equivalent inductance L ⁱ _j carried by the i-th Josephson junction is represented by L ⁱ _j ˜ (h ′ / 2e) (1 / I _c cos θi) per junction, and as a whole. Can be expressed as

Here, from the Hula-wide quantization condition, Σθ
i = 2π (Φi / Φ ₀ + k) k = 1, 2, 3 ... However, since the characteristics of n Josephson junctions are the same, Becomes Therefore, L _j = (h '/ 2e · Ic) {n / co
s (θ / n)}, for example, in the vicinity of θ to 0, L _j = nL ¹ _{j, which} is at least n times the equivalent inductance in the case of one Josephson junction. As a result, if n is properly selected, it can be made as large as the inductance L of the ring.

In this case, when α> 1 is used,
For that purpose, the amount of change in inductance can be increased by increasing L and increasing n accordingly. Thus, L can be set to an arbitrary value by appropriately selecting n. That is, the center frequency of the resonance frequency can be arbitrarily changed, which is a great practical advantage. Therefore, by partially sweeping the external magnetic field, the inductance of the junction can be largely changed and the change of the resonance frequency can be increased.

[0018]

According to the present invention as described in detail with reference to the above embodiments, since a plurality of equivalent Josephson junction inductances which are changed by an external magnetic field are formed in a ring type resonator, the ring inductance is reduced to the magnetic field. It is possible to realize a variable frequency resonator by changing the variable frequency, and to increase the inductance of the junction and increase the amount of change due to the magnetic field, so that the width of the resonant frequency to be swept can be increased. Moreover, since the critical current (I _c ) of the Josephson junction can be made large, the high frequency current that can be made to flow can also be made large. Furthermore, since the ring is made of a superconducting material, the loss is very small, so Q is essentially
The value will be high.

[0019]

[Brief description of drawings]

FIG. 1 is a plan view (a) and an AA cross-sectional view (b) of the (a) view showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship among a magnetic flux quantum Φ ₀ , a magnetic flux Φ _i in a ring, and an external magnetic flux Φ _x .

FIG. 3 is a configuration diagram of a conventional device.

FIG. 4 is another configuration diagram of a conventional device.

[Explanation of symbols]

 1 substrate 2 superconducting ground plane 3 dielectric film 4 stripline 5 ring 6 Josephson junction 7 magnetic field generating means (coil)

Claims (1)

[Claims] 1. A superconducting ground plane formed on a substrate, a dielectric film formed on the superconducting ground plane, and equivalent properties formed on the dielectric film. A ring composed of a superconducting thin film in which a plurality of Josephson junctions are formed in series, a stripline provided in the vicinity of the ring, and a magnetic field generating means are provided above the ring at a predetermined distance. Characteristic variable frequency resonator.