JPH04368006A - Oxide superconducting microwave component - Google Patents

Abstract

PURPOSE:To easily adjust and control a frequency or a delay time externally by controlling a gap between an upper board and an intermediate board with expansion/contraction of a piezoelectric lamination ceramics. CONSTITUTION:Ground planes 12a, 12b made of an oxide superconducting thin film are directed to the outside respectively and a prescribed gap 16 is provided between opposed faces and 1st and 2nd boards 13, 14 are opposed to each other, a center conductor 11 is formed to the side of the opposite face of the board 13, e.g. with the oxide superconducting material while leaving the gap 16 partly, and a piezo element 17 is provided to, e.g. the ground plane 12a of any board (e.g. the board 14). Then the gap 16 between the oxide superconducting boards 12a, 12b having a high dielectric constant is controlled by the piezoelectric lamination ceramics 17 to vary the effective dielectric constant in the vicinity of the center conductor 11, resulting that a phase speed and a group speed of a microwave propagating through the center conductor 11 are controlled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting microwave component using an oxide superconducting thin film capable of frequency control or delay time control.

0002

2. Description of the Related Art Conventionally, passive components such as various filters, resonators, and delay lines used in the microwave region have been made of normal conductive metals with low surface resistance, such as oxygen-free copper and gold. Surface resistance, which dominates conductor loss in microwave components, increases in proportion to the 1/2 power of the frequency in normal conductive metals and in proportion to the square of the frequency in superconducting materials.

[0003] Superconducting materials have less resistance loss than copper in the range of several hundred GHz or less, and the resistance loss can be further reduced as the frequency becomes lower. However, in the past, metal-based superconducting materials such as niobium that exhibit superconductivity at extremely low temperatures have been applied only to a few special fields due to problems such as cooling.

[0004] In recent years, oxide superconducting materials such as yottrium-based, bismuth-based, and thallium-based materials have been discovered, and the technology for forming thin films of these materials is also making great progress. As a result, we can expect small superconducting microwave components that have much lower resistance loss than conventional normal metals and utilize low dispersion, and can operate at 77K, making them cooler than metallic superconducting materials. It has the characteristic of being easy to implement. Therefore, research into microwave components using oxide superconducting thin films is being actively pursued.

Microwave components basically consist of a center conductor and a ground plane. Their basic configuration is shown in FIG. FIG. 6(a) shows a microtrip type, and FIG. 6(b) shows a stripline type. In FIG. 6, 1 is the center conductor, 2a is the lower ground plane, 3 is the intermediate board containing the center conductor 1, and 4 is the upper ground plane 2.
5 is a lower substrate including the lower ground plane 2a, and 6 is a gap between the intermediate substrate 3 and the upper substrate 4.

Currently, the microstrip type is most commonly used in MICs, MMICs, etc., and in order to suppress radiation loss and conductor loss, it is necessary to surround the center conductor 1 with a ground plane to approximate the stripline type. This is particularly important for superconducting microwave components that utilize low loss.

When the ground plane is also formed of a superconducting material, two layers are required for the microstrip type and three layers for the strip line type, since it is currently not possible to form an oxide superconducting thin film with good high frequency characteristics on the front and back surfaces of the substrate. It is constructed by overlapping two substrates. In the future, if a technology is developed that allows superconducting thin films to be formed on the front and back surfaces of a substrate, the center conductor 1 and the lower ground plane 2a can be formed on the same substrate, but the center conductor 1 will need to be patterned. 1 and the upper substrate 4 including the upper ground plane 2b must be separate.

[0008]

[Problem to be Solved by the Invention] Therefore, when constructing a stripline structure advantageous for a low-loss superconducting device using an oxide superconducting thin film, it is necessary to avoid the gap 6 between the upper substrate 4 and the intermediate substrate 3. Can not. Generally, oxide superconducting thin films for microwave components are formed on MgO and LaAlO3 substrates, and the dielectric constants of these are as large as 9 and 25, respectively. Therefore, there was a problem in that the air gap between the intermediate substrate 3 and the lower substrate 5 in particular greatly changed the effective permittivity near the center conductor, causing the phase velocity and group velocity of the microwave propagating through the center conductor to shift from the designed values. .

FIG. 7 shows the center conductor pattern of a typical oxide superconducting passive device. FIG. 7(a) shows a resonator,
(b) is a Chebyshev type band-pass filter, (c) is a delay line, and 1 means the center conductor as in FIG. 6. Shifts in phase velocity and group velocity due to changes in the effective dielectric constant in these passive devices cause a very sharp frequency shift of the resonance peak in a resonator, and a shift in the center frequency of the passband in a filter. The advantageous narrow band pass characteristics cannot be utilized.

Another problem with the delay line is that the delay time deviates from the designed value. As described above, since superconducting microwave components have extremely sharp frequency characteristics by their nature, they are extremely useful for application to high-Q resonators and ultra-narrow band filters. On the other hand, adjusting to the designed center frequency is extremely complicated and difficult. Furthermore, since superconducting microwaves have a large surface resistance above the critical temperature and sufficient microwave characteristics cannot be expected, it is almost impossible to adjust them at room temperature.

[0011]Therefore, in superconducting microwave components, there has been a strong desire for a component structure that allows easy adjustment even after cooling. Sweeping and modulating phase information, such as sweeping the frequency and modulating the delay time, was also strongly desired from the perspective of adding functionality.

The present invention has been made in view of the above situation, and by controlling the gap between substrates having a high dielectric constant in a strip line structure using piezoelectric laminated ceramics provided outside the ground plane, the frequency can be increased. Another object of the present invention is to provide a high-performance, highly reliable device with new functionality that allows the delay time to be easily adjusted and controlled from the outside.

[0013]

[Means for Solving the Problems] In order to solve these problems, the present invention proposes that if the gap between the upper substrate and the intermediate substrate can be controlled in some way, the effective permittivity near the center conductor can be changed arbitrarily. This is based on the idea that the phase velocity and group velocity of the microwave propagating through the center conductor can be controlled from the outside. Specifically, first ground planes made of conductive material are arranged facing outward and with a predetermined gap between them on opposing surfaces.
and a second substrate, a center conductor formed with an oxide superconducting material on the opposing surface side of one substrate while leaving a portion of the gap, and a piezo element provided on the ground plane side of one of the substrates. It is composed of

[0014]

[Operation] By controlling the gap between oxide superconducting substrates with high dielectric constants in a stripline structure using piezoelectric laminated ceramics, the effective dielectric constant near the center conductor is changed, and as a result, propagation occurs through the center conductor. By controlling the phase velocity and group velocity of the microwave, the frequency or delay time of the oxide superconducting microwave component can be easily controlled from the outside, and the oxidation process can be easily adjusted and controlled even after cooling. A structure suitable for superconducting microwave components has been realized.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the structure of an oxide superconducting microwave device to which the present invention is applied. 11 in Figure 1
12a is an upper ground plane made of an oxide superconducting thin film, 12b is a lower ground plane made of an oxide superconducting thin film, and 13 is a crystal intermediate substrate of MgO or LaAlO3 containing the central conductor pattern 11. , 14 is a single crystal upper substrate including an upper ground plane 12a, 15 is a single crystal lower substrate including a lower ground plane 12b, and 16 is an intermediate substrate 13 and an upper substrate 1.
4, 17 is a piezoelectric laminated ceramic element mechanically brought into close contact with the upper end surface of the upper substrate 14, 18a is a surface that mechanically supports the piezoelectric ceramic element 17, which is one of the piezo elements, and 18b is a lower substrate. This is a surface that mechanically supports 15.

That is, in this device, the first substrate 13 and the second substrate 14 are connected with the ground planes 12a and 12b formed of oxide superconducting thin films facing outward and with a predetermined gap 16 provided on the opposing surfaces. For example, the substrate 1
A center conductor 11 is formed with a gap 16 partially left on the opposing surface of the substrate 3, and a piezo element 17 is provided on the ground plane 12a side of one of the substrates (substrate 14 in this example). be done. εs is the dielectric constant in the gap (spacing) between the upper substrate 14 and the intermediate substrate 13, and in this example, since the filling material is air, the dielectric constant is 1.

The intermediate substrate 13 and the lower substrate 15 are fixed to the lower mechanical support surface 18a with an adhesive or a spring material so as to prevent losses such as dielectric loss. On the other hand, the upper substrate 14
is fixed to the upper mechanical support surface 18b via the piezoelectric laminated ceramics 17. The center of gravity A of the upper substrate 14 is displaced in the direction of the arrow by supplying a DC voltage to the piezoelectric ceramic element 17. Accordingly, the spacing can be varied within a maximum range of 0.5 to 1.9 μm.

FIG. 2 shows the relationship between the displacement of the piezoelectric laminated ceramic element 17 and the voltage. The elements a and b have element lengths of 18 and 9 mm, respectively. It can be seen from the figure that with a DC voltage of 0 to 150 V, the longitudinal displacement, ie the spacing, of approximately 19.8 μm, respectively, can be controlled in the range of 0.5 to 19 μm.

FIG. 3 is an example of the relationship between the rate of change in effective dielectric constant and spacing obtained by computer simulation. The substrate is a 0.5 mm thick MgO (εr=9.1) single crystal substrate or a 0.5 mm thick LaAlO3 (εr
r=25) Using a single crystal substrate, the center conductor width is 500,1
The thickness is 60 μm, and the numerical analysis is performed using a thickness of 0.5 μm. The gap (spacing) assumes air (εs=1),
The maximum displacement is 8 μm, which corresponds to the element b in FIG.

When the center conductor width is 500 μm, when the spacing is expanded to 8 μm, the MgO substrate has a loss of about -10%,
A LaLlO3 substrate shows an effective dielectric constant change of about -20%. When the center conductor width is shortened to 160 μm in a LaAlO3 substrate, the change in dielectric constant becomes even more remarkable.

The resonance or center frequency of a resonator or bandpass filter varies greatly depending on the effective dielectric constant near the center conductor. Further, the delay time in the delay line is also determined by the group velocity (Vg) of the macrowave propagating through the center conductor, and at this time also varies greatly depending on the effective dielectric constant near the center conductor. When there is no gap in the strip line structure, the effective dielectric constant is given by the dielectric constant εr of the substrate, but when there is a gap such as air, the effective permittivity εr decreases by the gap.

The rate of change in dielectric constant (δεr/εr) is calculated as the rate of change in frequency (δf/f)=−0.5×(δεr/εr
), and the rate of change in group speed, which is important in the delay line, is similarly expressed as (δVg/Vg)=-0.5×(δεr/
There is a relationship of εr). For example, if the apparent rate of change in dielectric constant (δεr/εr) becomes -20% due to air gaps, etc., this will result in a +10% frequency shift or a +10% change in group speed.

By using the piezoelectric element with symbol b shown in FIG. 2, the spacing can be controlled within a maximum range of 8 μm.
As a result, the effective dielectric constant changes by approximately -10% in the MgO substrate and by approximately -20% in the LaLlO3 substrate. Therefore, MgO
The phase velocity and grouping velocity can be controlled within a range of approximately +5% for the substrate and approximately +10% for the LaAlO3 substrate.

[0024] In the narrow band pass filter using superconductivity,
For example, center frequency 10GHz, passband 1000MHz
(1%), and this specification makes frequency adjustment significantly difficult, but if adjustment and control are performed using the present invention, MgO can achieve ±250MHz and LaAlO3 can achieve ±250MHz.
Since adjustment of 500 MHz can be easily performed, it is not only possible to easily adjust the frequency after cooling, but also to sweep and modulate the frequency by external input.

[0025] This also applies to resonators, and in the case of resonators, the shift of the resonant frequency due to temperature changes is a problem, but with the structure according to the present invention, the resonant frequency is used as a control signal and fed back to the piezoelectric laminated ceramics. By incorporating control, it is possible to suppress temperature changes in the resonant frequency.

On the other hand, even in a delay line that is effective as a superconducting microwave component, it is difficult to change the delay time in an analog manner, so the delay time is changed in steps by switching the delay line. In the present invention, the grouping speed can be controlled by ±2.5% with the MgO substrate and ±5% with the LaLlO3 substrate. In other words, it is possible to change the delay time within this range, and use the delay time as a control signal,
By incorporating a feedback system into piezoelectric ceramics, it is possible to stabilize the delay time or to create a variable delay line within the above range.

FIG. 4 shows a conceptual diagram of a basic control loop using phase information as a control signal in such an oxide superconducting microwave component. (a) shows a frequency and delay time adjustment/stabilization control system, and (b) shows a sweep/modulation control system.

FIG. 5 shows a computer simulation of the relationship between characteristic impedance and spacing. The model conditions are the same as in FIG. In the case of a center conductor width of 500 μm, even if the spacing is increased to 8 μm, the resistance remains within 1 Ω, but with a width of 160 μm, the resistance changes by nearly 4 Ω. However, overall, even if the spacing is increased to 8 μm, the characteristic impedance does not change significantly. However, these are 20Ω and 30Ω systems, and filters,
There is no problem in the case of a resonator, but in the case of a delay line, it is necessary to provide a transformer or the like to connect to the 50Ω system.

[0029] In the above embodiments, the ground plane was also explained as being made of superconducting material, but although superconducting material has better characteristics, it may be made of normal conducting material if it does not mind deteriorating the characteristics. .

[0030]

Effects of the Invention As explained above, the present invention controls the gap between the upper substrate and the intermediate substrate by expanding and contracting the piezoelectric laminated ceramic, thereby reducing the effective dielectric constant by 10 to 20% without changing the characteristic impedance much. The degree can be reduced. Therefore, it becomes possible to change the propagation speed of microwaves propagating through the center conductor by 5 to 10%. In other words, maximum ±
Not only can the center frequency and delay time be adjusted and stabilized within a range of 5%, but by feedback controlling the spacing using the frequency and delay time as a control signal, it is possible to sweep and modulate the frequency and delay time. As a result, it is easy to adjust even after cooling. Furthermore, by constructing an appropriate feedback system, it becomes possible to create oxide superconducting microwave devices with new functions such as frequency sweep and modulation.

[Brief explanation of drawings]

FIG. 1: Oxide superconducting microwave device according to the present invention

[Figure 2] Diagram showing the relationship between displacement and voltage in piezoelectric ceramics

[Figure 3] Diagram showing the relationship between the rate of change in effective permittivity and spacing

[Figure 4] Conceptual diagram of basic control loop

[Figure 5] Diagram showing the relationship between characteristic impedance and spacing

[Figure 6] Diagram showing an example of the structure of microwave components

[Figure 7] Diagram showing the center conductor pattern of a typical microwave component

[Explanation of symbols]

1 Center conductor 2 Ground plane 3 Intermediate board 4 Upper board 5 Lower board 6 Gap 7 Piezoelectric laminated ceramics 8 Support surface

Claims (2)

[Claims] 1. First and second substrates each having a ground plane formed of a conductive material facing outward and with a predetermined gap provided on opposing surfaces; An oxide superconducting microwave component comprising a center conductor formed of a superconducting material with a portion of the gap remaining, and a piezo element provided on the ground plane side of any of the substrates. 2. In claim 1, a control means is provided which uses phase information such as frequency, phase velocity, group velocity, delay time, etc. as a control signal and feeds back a difference between the control signal and a reference setting signal to the piezoelectric laminated ceramic. Microwave parts characterized by: