JP3292168B2 - Filter adjustment method and adjustment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave passive circuit device which is a superconducting application technology in a satellite communication field, a mobile communication field and the like.

[0002]

2. Description of the Related Art As a microwave passive circuit device used in a microwave communication device, a microwave waveguide or a microstrip circuit formed on a dielectric substrate is used. Since the microwave waveguide has a small loss, it is used for a passive circuit requiring high Q characteristics such as a narrow band filter. However, a waveguide having a three-dimensional shape is generally used, and is not suitable for the purpose of forming a hybrid circuit with a semiconductor to reduce the size of a communication device.

[0003] The use of a planar circuit such as a microstrip circuit in a microwave passive circuit device can be hybridized with a semiconductor element, and has the advantage that the microwave circuit device can be reduced in size and weight. Generally applied widely. However, in this case, the effect of conductor loss is greater than in the case of a waveguide, so that it is not suitable for use in a microwave circuit device that requires a high Q value and low loss. There's a problem.

Therefore, use of a microwave circuit device using a high-temperature superconducting material for a conductor portion of a microstrip circuit has been considered. Since the high-temperature superconducting material has a surface resistance in the microwave band that is at least two orders of magnitude lower than that of a normal metal such as gold, the high-temperature superconducting material has a feature that the microwave circuit can have a high Q value or low loss. For example, by using the filter as a reception filter for a mobile communication base station, it is possible to realize a high-performance filter having a small insertion loss in a pass band and a steep out-of-band attenuation characteristic. For this reason, it is attracting attention as a new technology capable of improving the performance of microwave passive circuits.

[0005]

In a conventional high-temperature superconducting filter using a microstrip circuit, a high-temperature superconductor is formed on both surfaces of a dielectric substrate, and a filter circuit is formed on one surface by, for example, etching. Is formed as a ground conductor. In this type of filter, it is essential that the frequency characteristics can be adjusted. At that time, it is most important for the filter to adjust the center frequency to the required frequency. Methods for adjusting the frequency characteristics of a high-temperature superconducting filter are already known, and various methods are used. First
Is a method of changing the length of the microstrip line. This is, for example, a method of cutting a part of the microstrip line by etching or a laser beam to change the length. However, this adjustment method is irreversible, and there is a problem that the filter cannot be used again if the resection is performed too much. In addition, it has been pointed out that when ablation is performed by a laser beam, it is difficult to perform fine adjustment in units of several microns, and that the characteristics of the high-temperature superconductor portion irradiated with the laser are deteriorated. .

As a second method for adjusting the electrical characteristics of the high-temperature superconducting filter, a screw is provided on a package in which a microstrip circuit is installed, and the distance between the screw and the microstrip circuit is adjusted to reduce the impedance of the circuit. There is a way to change it. In this method, it is pointed out that when the screw is brought close to the microstrip line made of a high-temperature superconducting material, the Q value of the filter is reduced, and the filter characteristics are deteriorated.

A third method is disclosed in Japanese Unexamined Patent Publication No.
JP-A-107570 discloses a method described in “Method for Adjusting Electric Characteristics of Distributed Constant Print Filter and Filter Apparatus Used for the Method”. This method is applied to a filter using a conventional normal conductor for a microstrip line, but the impedance is changed by placing a dielectric wafer on the microstrip line to adjust the electrical characteristics of the filter. How to In this method, the frequency can be arbitrarily changed by changing the thickness of the dielectric to be installed. This adjustment method can be applied to a high-temperature superconducting filter.

However, it is difficult to adjust the electrical characteristics of these high-temperature superconducting filters because the high-temperature superconducting filters operate at a low temperature of 100 K or less and must be installed in a refrigerator and cooled. That is, high performance filter characteristics cannot be obtained. For this reason, in the first and third methods, the frequency characteristics are measured by cooling the filter once, and then the temperature is returned to room temperature to adjust the length of the line, or to install a dielectric. After adjustment, the sample is cooled and measured again. Then, since this process is repeated many times to gradually adjust to the target frequency, a very long and patient work is required.

Next, in the second method, if the screw is adjusted from the outside by devising a refrigerator, the filter is maintained at the operating temperature of the high-temperature superconducting material and the electric characteristics are monitored while monitoring the filter characteristics. Target characteristics can be adjusted. However, as described above, there is a problem that the filter characteristics deteriorate due to the effect of the loss of the screw portion.

As described above, the high-temperature superconducting filter has a feature that the conductor loss of the microstrip circuit is reduced, so that the high-temperature superconducting filter is small and lightweight and has high-performance filter characteristics. There was a problem that was difficult. That is, while a conventional filter using a normal conductor can be adjusted while monitoring the frequency characteristics at room temperature, a high-temperature superconducting filter operating at a low temperature does not deteriorate the filter characteristics and has a low frequency characteristic. It was difficult to adjust while monitoring.

In view of the above problems, an object of the present invention is to provide a method capable of easily and accurately adjusting the electrical characteristics of a high-temperature superconducting filter in a refrigerator without deteriorating the filter characteristics. .

[0012]

In order to achieve the above object, a method for adjusting a filter according to the present invention comprises: installing a high-temperature superconducting microstrip filter formed on a dielectric substrate in a refrigerator for evaluation; The frequency characteristic of the high-temperature superconducting filter is monitored by connecting it to a filter characteristic measuring device while being cooled to a low temperature of 90 K or less. In this state, a method of adjusting a high-temperature superconducting filter is characterized in that a dielectric thin film is deposited on a filter circuit to adjust electric characteristics of the filter, particularly, a center frequency.

At this time, a dielectric target is set in the refrigerator chamber, and a target component of an organic material or an inorganic material is deposited on the filter by irradiating the target with a laser beam introduced from the outside. This is a method for adjusting a filter. Further, the refrigerator chamber is provided with a mechanism capable of opening and closing the lid of the package in which the filter is installed from the outside of the refrigerator chamber, so that electrical adjustment can be performed while opening and closing the lid of the package. This is a method for adjusting a characteristic filter.

The high-temperature superconducting material is characterized in that the surface resistance in the frequency range of the microwave band used for communication equipment such as mobile communication and satellite communication is at least two orders of magnitude smaller than that of a normal metal such as gold. are doing. In addition, since the critical temperature for superconductivity is higher than the boiling point of liquid nitrogen, 77 K , superconductivity can be obtained with a simple and inexpensive small refrigerator. It is expected to be applied to equipment. However, as described above, there is a problem that it is difficult to adjust the electrical characteristics such as the center frequency due to the low-temperature operation.

According to the present invention, the high-temperature superconducting microstrip filter formed on the dielectric substrate as described above is installed in a refrigerator for evaluation and cooled to a low temperature of 90 K or less. While monitoring the frequency characteristics of the above, a dielectric thin film is deposited. By depositing this dielectric thin film on the filter circuit, the characteristic impedance of the filter changes, and the electrical characteristics of the filter, in particular,
The center frequency can be adjusted. At this time, since the dielectric thin film can be deposited while monitoring the filter characteristics, the center frequency of the filter can be adjusted to the set value by terminating the deposition when the target frequency is reached.

The dielectric thin film is deposited on a filter circuit by placing a dielectric target in a refrigerator chamber, irradiating the target with laser light introduced from the outside, and evaporating the target components. Here, the reason that the sputtering method or the evaporation method generally used for the deposition of the dielectric thin film was not used is that, for example, in the sputtering method, the filter circuit was exposed to plasma during the deposition and was damaged, or the vacuum was applied. This is because in the vapor deposition method, the temperature of the filter circuit rises due to radiant heat of the evaporation source, which may deteriorate the superconducting characteristics of the high-temperature superconducting thin film forming the filter circuit.

On the other hand, in the irradiation by the laser beam of the present invention, the target temperature rise is small, so that the temperature of the filter does not rise, and it is not exposed to plasma unlike sputtering, so that the superconducting property is reduced. Deterioration does not occur, and the dielectric thin film can be deposited while maintaining the temperature of the filter at a desired temperature.

The dielectric thin film to be deposited is, for example, Al ₂ O ₃
As a result, a material having a small dielectric loss is selected.
This is because when a material having a large dielectric loss is used, the Q value is reduced due to the influence of the dielectric loss, which leads to deterioration of the filter performance. The electrical characteristics of the filter depend on the type of dielectric,
That is, the characteristics to be set can be continuously adjusted by changing the dielectric constant and the film thickness.

Generally, the frequency characteristics of the microstrip filter are slightly different when the package lid is closed and when it is opened. Therefore, it is necessary to finally adjust the electrical characteristics with the lid closed. Therefore, by providing a mechanism for opening and closing the package lid where the filter is installed from the outside of the refrigerator chamber, it is necessary to close the package lid immediately after depositing the dielectric thin film and monitor the frequency characteristics of the filter. Can be.

[0020]

FIG. 1 is an overall configuration diagram of an apparatus for adjusting a filter characteristic according to an embodiment of the present invention. In FIG. 1, a filter installed in a package 1 is set on a cooling stage 2. This cooling stage 2
Is located in the vacuum vessel 3 and can be cooled by the Stirling refrigerator 4 to about 50 K, which is lower than the operating temperature of the high-temperature superconducting material.

During the adjustment of the electrical characteristics, the temperature of the filter is
It can be maintained within ± 1 degree by temperature control.
Further, a dielectric target 5 is provided so as to face the filter, and a laser beam 6 is introduced through a laser window 7 and irradiated on the dielectric target 5. As a result, the target component evaporates and a dielectric thin film can be deposited on the filter circuit. A mask 8 is provided between the filter and the target. As a result, the dielectric thin film can be formed only in a necessary area of the filter circuit.

The filter is connected to a filter characteristic measuring device 10 by a coaxial cable 9. Therefore, the frequency characteristic of the filter can be monitored even during the deposition of the dielectric thin film. Further, since a mechanism capable of opening and closing the package lid 11 from the outside is provided in the vacuum container, the frequency characteristics of the filter can be measured with the package lid closed after the vapor deposition is completed.

FIG. 2 shows an example of a microstrip filter circuit manufactured to apply the filter adjustment method of the present invention. This filter has a center frequency of 9.8 GH
z, a 2% Chebyshev type band-pass filter having a 2% bandwidth. The microstrip line 12 constituting the filter circuit is a high-temperature superconducting thin film having a thickness of about 500 nm, and is formed on a dielectric substrate 13. The size of the substrate is 25 mm × 6.5 mm, and the thickness is 0.5 mm.

FIG. 3 shows a cross-sectional shape of the microstrip filter. As shown, a ground conductor 14 made of a high-temperature superconducting thin film is provided on the back surface of the dielectric substrate 13. In this example, a YBa ₂ Cu ₃ O _x (YBCO) thin film having a critical temperature of 90 K was used as the high-temperature superconducting thin film.
In addition, a single crystal MgO having a small dielectric loss was used for the dielectric substrate. This filter is set in a gold plated package.

The high-temperature superconducting filter manufactured in this manner is set on the cooling stage 2 in the refrigerator, and the package 1
The coaxial cable 9 is connected to the connector part of the above, and a preparation is made so that the frequency characteristic can be measured by the filter characteristic measuring device 10. As the filter characteristic measuring device 10, for example, a vector network analyzer can be used. The lid 11 of the package can be opened and closed from the outside of the refrigerator 3 by being set in an opening / closing mechanism. With the lid 11 of the package 1 closed, the inside of the vacuum container 3 is evacuated. . Next, the cooling of the filter is started by turning on the power of the refrigerator 4. The filter reaches 60 K in about 30 minutes to 1 hour and is then maintained at this temperature. At this stage, the frequency characteristics of the filter are measured.

FIG. 4 shows the measured pass characteristics of the filter. The frequency characteristic 16 in an unadjusted state shows a flat and symmetrical pass characteristic in the pass band. Further, the insertion loss in the pass band was a very small value of about 0.1 dB, and it was confirmed that the low-loss characteristic characteristic of the high-temperature superconducting filter was obtained. However, the center frequency of the filter is slightly shifted from the center frequency 17 to be set as shown in FIG.

Then, the lid 11 of the package 1 is placed in the refrigerator.
Is opened so that the dielectric thin film 15 can be deposited on the filter circuit. The relative permittivity is 1 as the dielectric target 5
An Al ₂ O ₃ target of about 0 is used. When an excimer laser (KrF, wavelength: 248 nm) is irradiated on the target surface from the outside of the refrigerator chamber 3 through a laser window 7, the target component of the laser-irradiated portion is instantaneously ejected, and is placed on the filter circuit as shown in FIG. Is deposited as a dielectric thin film 15 shown in FIG.

The deposition rate was about 1 nm / sec.
Since the effective dielectric constant increases when a dielectric thin film is deposited,
The center frequency of the filter shifts to the lower frequency side. And, as the film thickness increases, the effective permittivity increases.
The width of adjustment of the center frequency can be changed by changing the thickness of the dielectric thin film.

FIG. 4 shows a frequency characteristic 18 when the thickness of the dielectric thin film is 2 μm, and a frequency characteristic 1 when the thickness of the dielectric thin film is 4 μm.
9 is shown. The pass band shape is almost unchanged, and the film thickness 2
In the case of μm, the center frequency shifted slightly to the lower frequency side like B. Further, it can be seen that, as the film thickness increases to 4 μm, the center frequency shifts further to the lower frequency side as shown by C, and is substantially equal to the set frequency.

In this embodiment, as described above, the filter can be held at 60 K on the cooling stage as shown in FIG. 1, and the dielectric thin film can be deposited while monitoring the frequency characteristics of the filter with a network analyzer. For,
When the film thickness became 4 μm and the frequency could be adjusted to the set frequency, the excimer laser was turned off to terminate the vapor deposition. It should be noted that since the insertion loss in the pass band does not increase even after the deposition of the dielectric thin film, it is considered that the dielectric loss of the thin film has almost no influence. Therefore, it can be seen that the desired center frequency can be easily adjusted without lowering the filter characteristics.

Further, the YBCO thin film used for the microstrip line shows almost no change in the critical temperature even after the deposition of the dielectric thin film, and the characteristic deterioration of the high-temperature superconducting thin film expected by the sputtering method or the evaporation method. It was confirmed that almost no occurrences occurred. Further, even when the package lid was closed, the center frequency of the filter hardly changed, so that the final filter characteristics could be set to the intended specifications.

Next, a dielectric material Al ₂ O ₃ is used as a target.
When Teflon having a relative dielectric constant of about 2 is used as an organic material instead of Teflon, Teflon has a relative dielectric constant of Al ₂ O
_Since it is as low as about 1/5 of ₃ , the increase in the effective dielectric constant of the filter when deposited on the filter circuit is also small. Therefore, the shift amount of the center frequency after the deposition of a 2 μm-thick film is
It was about 1/5 of that of the Al ₂ O ₃ thin film. Also, in the case of the Teflon thin film, no decrease in filter characteristics such as an increase in insertion loss in the pass band was observed. As described above, using a Teflon thin film having a small relative dielectric constant also has a feature that the center frequency can be adjusted more accurately.

After depositing the oxide dielectric thin film,
It is natural that the electrical characteristics can be adjusted by depositing an organic thin film to form a multilayer.

[0034]

According to the present invention, a high-temperature superconducting microstrip filter formed on a dielectric substrate is placed in a refrigerator for element evaluation and cooled to a low temperature of 90 K or less. Since the dielectric thin film is deposited while monitoring the frequency characteristics, the electrical characteristics of the filter, especially,
The center frequency can be adjusted easily and accurately in a short time.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a filter characteristic adjusting device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a microstrip filter circuit to which the present invention is applied.

FIG. 3 is a diagram showing a cross-sectional structure of the microstrip filter shown in FIG.

FIG. 4 is a diagram for explaining a frequency characteristic adjusting method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Package 2 Cooling stage 3 Vacuum container 4 Stirling refrigerator 5 Dielectric target 6 Laser light 7 Laser introduction window 8 Mask 9 Coaxial cable 10 Filter characteristic measuring device 11 Package lid 12 Microstrip line 13 Dielectric substrate 14 Ground conductor 15 Dielectric thin film 16 Unadjusted filter characteristic 17 Set center frequency 18 Filter characteristic when dielectric thin film thickness is 2 μm 19 Filter characteristic when dielectric thin film thickness is 4 μm

Claims (9)

(57) [Claims] 1. A microstrip filter comprising a high-temperature superconducting thin film formed on a dielectric substrate,
A method for adjusting the electrical characteristics of the filter installed in the refrigerator for evaluation, wherein the filter is provided in a refrigerator chamber having a mechanism capable of opening and closing a lid of a package in which the filter is installed from the outside of the refrigerator chamber. A method for adjusting a filter, comprising adjusting an electrical characteristic of the filter while depositing a dielectric thin film thereon. 2. The filter adjusting method according to claim 1, wherein the adjusted electrical characteristic is a center frequency of the filter. 3. A dielectric target and the filter are set in a refrigerator chamber, and a laser beam introduced from the outside is irradiated on the dielectric target, so that the dielectric target component is deposited on the filter circuit. 3. The method for adjusting a filter according to claim 1, wherein the filter is adjusted. 4. An organic material or an inorganic material is used as said dielectric target.
The method for adjusting a filter according to any one of the above. 5. The method for adjusting a filter according to claim 1, wherein the electrical adjustment is performed by changing the thickness of a dielectric thin film deposited on the filter. 6. The method for adjusting a filter according to claim 1, wherein the electric adjustment is performed by changing a dielectric constant of a dielectric thin film deposited on the filter. 7. During the deposition of the dielectric thin film, the filter installed on a cooling stage in the refrigerator for evaluation is 9
The method for adjusting a filter according to any one of claims 1 to 6, wherein the filter is cooled to a low temperature of 0 K or less. 8. During the deposition of the dielectric thin film, a filter installed on a cooling stage in the refrigerator for evaluation has a pressure of 90 K.
Wherein the dielectric thin film is deposited while being cooled to a low temperature below, and connected to a filter characteristic measuring device to measure its frequency characteristic.
8. The method for adjusting a filter according to any one of 7. 9. A device for adjusting a microstrip filter comprising a high-temperature superconducting thin film formed on a dielectric substrate, wherein a cooling stage for cooling the filter installed in a package and a dielectric thin film are provided on the filter. A vacuum container having a dielectric target for depositing a laser beam and a window for introducing a laser beam from the outside to the dielectric target, and a package lid on which the filter is installed can be opened and closed from the outside of the vacuum container. An adjustment device for a filter characteristic, comprising: an opening / closing mechanism; and a measurement circuit for measuring a frequency characteristic of the filter.