JPH1065402A - Low pass filter adopting microstrip open stub line system and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the low pass filter adopting the microstrip open stub line system in which an unevenness of a passing rate at a pass band is reduced and a flatness degree is improved. SOLUTION: The low pass filter adopting the microstrip open stub line system includes a filter pattern consisting of a single crystal substrate 4 with an excellent microwave characteristic, of an input terminal 1a for signal transmission formed to one side corner on the single crystal substrate 4, of an output terminal 1b for signal transmission formed to the other side corner opposite to the one side corner at which the input terminal 1a for signal transmission on the single crystal substrate 4 is formed, of five stub conductors 3 filtering a signal and formed perpendicularly to the signal progress direction between the input terminal 1a and the output terminal 1b on the single crystal substrate 4, and of four strip conductors 2 formed perpendicularly to the stub conductor 3, and a ground conductor 5 (Ti/Ag) formed under the single crystal substrate 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pass filter (low-pass filter) used for a transmitting / receiving system for communication.
filter), in particular, a cutoff frequency (cuto).
ff frequency is about 3-33 GHz, and a low band of a microstrip open stub line system capable of improving a skirt characteristic up to a stop band and a loss characteristic in a pass band. Pass filter (Microstrip o
pen-stub line type lowpass filters) and a method for producing the same.

[0002]

2. Description of the Related Art The demand for high-quality radio services has exploded from fields that use radio resources, such as mobile communications and satellite communications (satellite broadcasting), and the desire for large-capacity, high-quality information has diversified. And personalization.

[0003]

Problems to be solved to solve this problem include, for example, improving characteristics and reducing the size of various core components constituting a microwave (high frequency) communication system. is there. Therefore, in order to utilize limited radio wave resources efficiently, it is necessary not only to develop materials (superconducting materials and dielectric materials) that exhibit extremely excellent microwave characteristics, but also to achieve high performance and high reliability. In this situation, it is very necessary to develop microwave components that can be miniaturized.

For this reason, a high degree of goodness (Q-factor)
r), and forming a microwave element using a high-temperature superconductor having lossless and no-resistance characteristics is a microwave component for communication that can be reduced in size and improved in performance. It is expected to be highly feasible. For example, Mg, LaAlO ₃ , N
A high-quality high-temperature superconducting epitaxy thin film is grown on a substrate such as dGaO _3, and a microwave element / circuit optimally provided by using the grown thin film (for example, a high-temperature superconducting MMIC that is easy to manufacture). And microstrip filters for development).

On the other hand, in order to create an excellent microwave element / circuit for use as a core component for a microwave communication system, an element manufactured through design, manufacture, and evaluation must have a theoretical value (design value). Should exhibit microwave loss characteristics that almost match

[0006] After all, to summarize the problems to be solved,
First, the growth of a high-temperature superconducting epitaxial thin film having excellent microwave characteristics and development of a dielectric single crystal substrate for manufacturing the thin film. Second, lithography and etching for increasing the sharpness of a circuit pattern. The third step is the development of a test jig for measuring the characteristics of microwaves at a low temperature, and the fourth step is the development of a microminiature low-temperature cooling device. The developed high-temperature superconducting filter should be actively used in advanced technology for microwave band radio waves.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a microstrip open stub line type low-pass filter capable of reducing unevenness of a pass rate in a pass band and improving flatness, and a method of manufacturing the same. is there.

Another object of the present invention is to provide a microstrip open stub line type low-pass filter capable of improving the skirt characteristic up to the stop band, that is, having a steeper slope up to the stop band. And a method for manufacturing the same.

[0009]

In order to achieve the above object, according to the present invention, there is provided a single crystal substrate having excellent microwave characteristics, and a signal transmission device formed on one side of the upper portion of the single crystal substrate. An input end, an output end for signal transmission formed on the other side opposite to the input end for signal transmission on the upper side of the single crystal substrate, and the input on the upper side of the single crystal substrate. It is composed of five stub conductors and four strip conductors formed so as to be perpendicular to the stub conductor and formed between the end and the output end to be perpendicular to the signal traveling direction and filter the signal. A low-pass filter of a microstrip open stub line type including a filter pattern formed and a ground conductor formed below the single crystal substrate.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
A first embodiment of the present invention will be described.

FIGS. 1 and 2 show a stub conductor and a strip conductor according to the present invention, respectively.
A plan view showing a modified 9-ultra low-pass filter (FIG. 1: tilted strip conductor structure) and a non-deformed 9-ultra low-pass filter (FIG. 2: in the signal transmission direction) (A parallel strip conductor structure).

In the microstrip open stub line type 9-ultra low-pass filter, MgO,
A signal transmission input terminal 1a and an output terminal 1b are formed on both sides of an upper portion of a single crystal substrate 10 having excellent microwave characteristics, such as LaAlO ₃ or sapphire.

[0013] Five stub conductors 3 formed between the signal transmission input terminal 1a and the output terminal 1b to be perpendicular to the signal traveling direction and appropriately filter the signal; A filter pattern is formed by the four strip conductors 2 formed to be vertical, and a ground conductor 14 (ground plate) made of a Ti / Ag metal thin film (2 μm) is formed below the single crystal substrate 10. It is formed. The stub conductor 3 and the strip conductor 2
, A single-crystal substrate 10 and a ground conductor 14, a microstrip line having an open stub (microstrip open stub line) is configured.

The input terminal 1a and the output terminal 1b are connected to YB
a ₂ Cu ₃ O _7-d (δ is represented by d due to restrictions on usable characters in an electronic application) (hereinafter referred to as YBCO)
Microstrip line using high temperature superconducting epitaxial thin film such as
e: 50 ohm) and a test jig (test-j)
ig) is contacted with a K-type connector pin attached to the housing. When MgO is used in the single crystal substrate 10, the line width of the input terminal 1a and the output terminal 1b is 0.4
9 mm.

The filter pattern is a strip conductor 2
And the stub conductor 3, the number of poles (pol) depends on the number of strip conductors 2 and stub conductors 3.
number) is determined. For example, the cutoff frequency (cuto) of the filter pattern configured as described above
(ff frequency) is 8 GHz. In the pass band, the signal passes with almost no loss, and in the stop band equal to or higher than the cutoff frequency, signal transmission is blocked. In the above pass band, the insertion loss was within 0.5 dB, the amplitude of the irregularities was about 0.02 dB, and the flatness of the pass band was very good.

The number of poles in the filter pattern is nine.
The increased skirt improves the characteristics of the skirt in the stop band and provides a steeper slope to the stop band.

Further, by selecting the shape of the filter pattern, the cutoff frequency can be set between 3 and 33 GHz.

When a low-pass filter is designed, these elements are composed of a strip conductor and a stub.
b) Since it is based on a conductor, a design is first made on the basis of a design theory for a lumped element type prototype low-pass filter in a low frequency band.

In a microwave band of several GHz or more, the capacitance (c) between the microstrip transmission line and the open-stub (open-stub) line is determined.
and a low-pass filter of a microwave distributed element type.

When designing such a circuit interpretation, the dielectric constant and thickness (0.5 mm) of the substrate to be used (mainly MgO) and the high-temperature superconducting YBCO epitaxial layer grown on the substrate are used. Thin film thickness (450n
m), the line width, interval, length, etc. of the input / output end (transmission line) and the stub conductor are determined in consideration of the superconductivity, the cutoff frequency of the low-pass filter, the input power (power), and the like.

Subsequently, several simulations (si
through which the optimal circuit pattern of the 9-ultra low pass filter is obtained.

The MgO single crystal substrate 10 used in the present invention has excellent microwave characteristics. Also,
The electrical characteristics and surface characteristics of the high-temperature superconducting YBCO epitaxial thin film manufactured on the single crystal substrate 10 are also very good.

The ground conductor 14 is formed below the single crystal substrate 10 and is formed of Ti / Ti so as to make excellent electrical matching and contact with the bottom inside the test jig.
The Ag double thin film is uniformly deposited by an electron beam evaporator. Further, the ground conductor 14 has very good adhesion to the MgO single crystal substrate 10.

FIGS. 3 to 8 are views showing the manufacturing process of the microstrip open stub line type high temperature superconducting 9-ultra low pass filter of FIG.

First, a pretreatment process for flattening the surface of the substrate is performed. In the pre-treatment process, ECR (Elec
tron Cyclotron Resonance)
Etching by ion milling, or surface etching for a short time using an etchant. Then, the MgO
A high-temperature superconducting epitaxial thin film (YBCO) 11 is grown on a single crystal substrate 10 by a pulsed laser deposition method, and an Au thin film 12 for a pad is deposited. Thus, the configuration is as shown in FIG.

As shown in FIG. 4, a photoresistor (P
R) The film 13 is coated with a spin coater (Spincoat)
er), and as shown in FIG. 5, a circuit pattern is transferred and an exposure process is performed to remove the photoresist film 13 of the exposed circuit pattern. Thereafter, as shown in FIG.
Is patterned with a circuit pattern of a strip conductor and a stub conductor. As shown in FIG. 7, the remaining PR film 13 is removed, and an Au-pat 12 is formed (formation) for excellent contact with the connector pins.
Subsequently, unnecessary impurities are washed.

As shown in FIG. 8, a ground conductor 14 is formed by depositing a Ti / Ag double thin film on the back surface of the substrate 10 using an electron beam evaporator. Here, the single crystal substrate 10
Good high-temperature superconducting YB with good microwave characteristics
An MgO single crystal having a size of 20 mm × 20 mm × 0.5 mm (t) capable of growing the CO epitaxial thin film 11 on a substrate is used.

On the upper surface of the single-crystal substrate 10, a high-temperature superconducting epitaxial thin film 11 of YBCO or the like is grown by a pulse laser deposition method. At this time, the excimer laser (exc)
imer laser) (wavelength: 308 nm)
The substrate is grown at a temperature of 750 ° C. and a partial pressure of oxygen of 200 mTorr in a deposition chamber. As described above, after the pulse laser is deposited, oxygen is injected at 550 ° C., and the epitaxial thin film 11 is grown by heat treatment for about one hour (without breaking vacuum). Tc of the high temperature superconductor YBCO / MgO epitaxial thin film thus manufactured
(Critical temperature) was 89K.

In the step shown in FIG. 5, a photoresist layer 13 can be formed on the epitaxial thin film 11 by a spin coating method and soft baking can be performed. Hereinafter, the procedure will be described.

After aligning an electron beam mask on the photoresistor 13, a UV light source for 10W (source) is used.
For 3 minutes. The exposed sample is treated with a sea pre-developer (developer, MT-318) for 3 minutes to remove the exposed portion of the photoresist 13 and expose the epitaxial thin film 11, and then to distilled water (D
The surface of the element is washed once with I-water). Thereafter, the exposed portion of the epitaxial thin film 11 is etched,
Form a filter pattern.

At the time of the above-mentioned etching, in the case of wet etching, etching is performed by using EDTA (acetic acid) (chemical etching), and in the case of dry etching, etching is performed by an ECR-ion milling apparatus.

The pattern obtained by forming the epitaxial thin film 11 has an input terminal 1a for signal transmission and an output terminal 1a.
b, and a filter pattern composed of the strip conductor 2 and the stub conductor 3. In addition, the Au pad 12 is formed so that the contact with the connector pin can be enhanced. Then, the sharpness of the filter pattern (s
After increasing the harness, washing with distilled water (DI-water) and washing with acetone are performed so as to remove the photoresist 13 used for the mask and other impurities, and then hard baking (hard). baking) process for about 3 minutes,
The patterning process of the high temperature superconducting 9-ultra low pass filter is completed.

In the process shown in FIG. 8, a ground conductor 14 is formed below the single crystal substrate 10. Ground conductor 1
No. 4 is a vacuum chamber (10 ^-2 To
(rr, 500 ° C.), a Ti / Ag double thin film can be continuously deposited and formed.

The Ti / Ag double thin film, which is the ground conductor 14, has excellent adhesion to the MgO single crystal substrate 10 and is easy to deposit a thin film. In particular, silver (Ag) is a high-temperature superconducting Y
In the pattern formed by the BCO epitaxial thin film 11,
There is also an advantage that contamination of other substances can be prevented since it has no influence. Since the silver thin film has not only excellent microwave characteristics but also excellent electrical conductivity, a test jig (test) is required when measuring the microwave characteristics.
It is also an advantage to have a good contact and consistency with the inner bottom of -jig).

By performing the above-described steps of the present invention, a high-temperature superconducting epitaxial thin film having excellent microwave characteristics can be formed on a substrate.

As described above, the present invention utilizes a high-temperature superconducting epitaxial thin film (including a substrate) having excellent microwave characteristics, and is used for a radio automation system, a radio device, a remote sensing device, a sensor in the field of radar, a radio wave measurement and Elements that constitute core components of various microwaves / millimeter waves used in radio astronomy and the like (element devices)
es) to strip conductor, stub conductor, gold (A
u) New structure /
High temperature superconductivity with new functions and improved properties 9
It is possible to provide a very low-pass filter;

[0037]

As described above, according to the present invention, it is possible to reduce the size of a subsystem of a microwave communication system related to an advanced technology for utilizing radio resources. Further, the effect of improving the performance of the information communication system and the microwave component can be obtained.

If a high-temperature superconducting epitaxial thin film is used as the strip conductor and the stub conductor, it is possible to manufacture a communication component having a small size, a small size, and a high performance. It can also have a great effect on the creation of elements / circuits and subsystems of functions and microwaves with new structures.
It can actively respond to the rapidly increasing demand for high-definition radio services.

Since the number of poles of the filter pattern increases, the amplitude of the unevenness in the pass band is also reduced to within 0.02 dB, so that the flatness in the pass band can be improved and the stop band can be improved. There is an advantage that the skirt characteristic can be improved and the stop band can be increased.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a 9-ultra low-pass filter according to a first embodiment of the present invention, which has an inclined strip conductor structure.

FIG. 2 is an explanatory diagram showing a configuration of a 9-ultra low-pass filter of the first embodiment of the present invention having a strip conductor structure parallel to the signal transmission direction.

FIG. 3 is a view showing a manufacturing process of the high-temperature superconducting 9-ultra low-pass filter of the microstrip open stub type shown in FIG. 1, which includes pretreatment for planarizing the surface of the substrate, formation of an epitaxial thin film, and Au. It is sectional drawing which shows the process of thin film formation.

FIG. 4 is a cross-sectional view illustrating a process of manufacturing a high-temperature superconducting 9-ultra low-pass filter using the microstrip open stub method of FIG. 1 and applying a photoresist (PR) film.

FIG. 5 is a cross-sectional view illustrating a manufacturing process of the microstrip open stub high-temperature superconducting 9-ultra low-pass filter of FIG.

6 is a cross-sectional view illustrating a manufacturing process of the high-temperature superconducting 9-ultra low-pass filter of the microstrip open stub type of FIG. 1 and illustrating an etching process.

FIG. 7 is a cross-sectional view illustrating a process of manufacturing the high-temperature superconducting 9-ultra low-pass filter of the microstrip open stub type in FIG. 1 and illustrating a process of removing a PR film.

FIG. 8 is a cross-sectional view illustrating a process of manufacturing a high-temperature superconducting 9-ultra low-pass filter of the microstrip open stub type of FIG. 1 and depositing a Ti / Ag double thin film.

[Explanation of symbols]

 1a: input terminal, 1b: output terminal, 2: strip conductor, 3: stub conductor, 4, 10: single crystal substrate, 5, 14: ground conductor, 11: epitaxial thin film layer, 12: Au pad (Au thin film), 13 ... Photoresist film.

Continued on the front page (72) Inventor Jeha Kim Korea, Daejeon, Yusung, Jun Min-dong 464-1, Expo Apartments 101-603

Claims (11)

[Claims] A single crystal substrate having microwave characteristics; input and output terminals for signal transmission formed on both sides of an upper surface of the single crystal substrate; and an input terminal and an output terminal on an upper portion of the single crystal substrate. A strip conductor between which a signal is transmitted, and a strip conductor formed so as to be perpendicular to a traveling direction of a signal transmitted through the strip conductor, and a plurality of strip conductors between an input end and an output end are formed; A microstrip open stub line type low-pass filter comprising: a plurality of stub conductors for controlling and filtering a signal; and a ground conductor formed under the single crystal substrate. 2. The microstrip open stub line according to claim 1, wherein the strip conductor has a form parallel or inclined to a traveling direction of a signal transmitted between an input terminal and an output terminal. Low pass filter. 3. The cut-off frequency (fc) of a low-pass filter according to claim 1, wherein the filter pattern includes a strip conductor and a stub conductor.
Is in the range of 3-33 GHz. 4. The low-pass filter according to claim 1, wherein the single crystal substrate is an MgO substrate. 5. The method according to claim 1, wherein the low-pass filter pattern is a high-temperature superconducting YBa.
₂ Cu ₃ O _7-d (δ is represented by d due to restrictions on usable characters in an electronic application) A microstrip open stub line type low-pass filter comprising a thin film. 6. The low-pass filter according to claim 1, wherein the ground conductor is a double metal thin film of Ti / Ag. 7. A pre-treatment step for flattening the surface of a single crystal substrate (10); and growing a high temperature superconducting epitaxial thin film (11) on the single crystal substrate (10) to form an Au thin film for pad (12). Forming a photoresist (PR) film (13); exposing the photoresist film (13) to patterning; and performing an etching process to form the epitaxial thin film (1).
1) patterning into a strip conductor and stub conductor circuit pattern, removing the remaining PR film (13), and forming the Au pad (12) for contact with a connector pin (Fo)
and a step of forming a Ti / Ag double thin film (14) on the bottom surface of the single crystal substrate (10). Manufacturing method. 8. The method according to claim 7, further comprising a photolithographic process, wherein the circuit pattern is patterned by ECR-ion milling dry etching.
After removing the R film, the surface of the filter pattern and the surface of the contaminated substrate are further cleaned to improve the sharpness of the filter pattern. Production method. 9. The method according to claim 7, wherein the high-temperature superconducting thin film (11) is made of YBa ₂ Cu ₃ O.
_7-d (Due to restrictions on available characters in electronic applications, δ
Is represented by d. A) a method of manufacturing a low-pass filter using a microstrip open stub line, wherein the ground conductor is formed by forming a Ti / Ag double metal thin film; 10. The low-pass filter according to claim 1, wherein at least one of the strip conductor and the stub conductor is made of a superconductor. 11. The low-pass filter according to claim 10, wherein the superconductor is a high-temperature superconductor.