JP3015754B2 - Trimming method of superconducting resonance circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for trimming a superconducting resonance circuit, and more particularly to a method for trimming a superconducting resonance circuit. The present invention relates to a method for trimming a superconducting resonance circuit that forms various frequency filters such as band rejection and band elimination (these are collectively referred to as filters). In addition,
Although the name "resonance circuit" is generally used in a lumped-constant type bandpass filter, the present invention is not limited to this. The term (resonator or resonator) indicating one unit of a distributed constant type resonance circuit is also included.

[0002]

2. Description of the Related Art In order to improve the performance of a radio system, an attempt has been made to construct a filter of a receiving head (a part close to an antenna) with a high temperature superconductor (HTS). This is because the electrical resistance of the HTS is extremely small, and a sharp filter characteristic can be realized while suppressing a signal loss to be small, so that a signal-to-noise (S / N) ratio can be improved.

The prototype of this type of filter is a microstrip transmission line having a structure in which a dielectric substrate is sandwiched between a strip conductor and a ground conductor, and is arranged by arranging adjacent resonance circuits so as to be side-coupled. , And a band-pass filter. In this specification,
The one in which the resonance circuit is formed by the HTS is called an "HTS bandpass filter" for convenience. Note that the ground electrode may be formed of HTS.

In general, when a bandpass filter having a narrow band (a value of the bandwidth / center frequency is small; usually 3% or less) or a steep cutoff characteristic is required, the resonance frequencies of the individual resonance circuits must be strictly adjusted. Therefore, trimming for correcting the length of the resonator, the area of the electrode, and the like is performed. In particular, in an HTS bandpass filter, a narrower band and a steeper cutoff characteristic are required, and such a trimming operation is indispensable.

[0005]

The conventional trimming is
Fine adjustment of the length, area, etc. of each resonance circuit while observing the overall pass characteristics of the band-pass filter.However, because each resonance circuit is complicatedly electromagnetically coupled, adjustment by trial and error In addition, it may take time, and in some cases, the filter may become unusable due to excessive trimming. In addition, in the case of the HTS bandpass filter, the operation is performed at a low temperature, so that However, there is a problem that adjustment by trial and error cannot be applied even by trial and error.

Accordingly, an object of the present invention is to provide a novel trimming method capable of avoiding trial-and-error adjustment and excessive trimming.

[0007]

SUMMARY OF THE INVENTION The above object is, when trimming a plurality of high-temperature superconductor resonator circuit on a dielectric substrate individually, a particular resonant circuits sufficiently lower temperature than the critical temperature (Tk) of ( Ta) and the other resonance circuit is cooled to temperature.
Temperature (Tb) higher than Ta and lower than critical temperature
This can be achieved by trimming the specific resonance circuit while heating .

According to this, the skin resistance of a specific resonance circuit is an extremely small value (1/10 of a metal) specific to the superconducting state.
0), but the skin resistance of the other resonant circuits is in a superconducting state, but is maintained at a temperature close to the critical temperature, but is a large value (however, much smaller than in the normal conducting state) As a result, a large difference occurs between the R components, and the Q of the circuit differs, so that the characteristics of a specific resonance circuit can be easily identified.

FIG. 1A is a characteristic diagram in the case where the temperatures of all resonance circuits are cooled to a temperature (Ta) sufficiently lower than the critical temperature ( Tk) . FIG. Cool to a temperature Ta sufficiently lower than the temperature Tk, and apply another resonance circuit to a temperature higher than Ta and lower than Tk.
It is a characteristic diagram in the case where the heat.

In general, the ideal characteristic of a band-pass filter is flat as shown in FIG. 1A (for convenience, a pass-type characteristic is shown). One peak is observed as shown in FIG. This is because the temperature of a specific resonance circuit was maintained at a temperature sufficiently lower than the critical temperature, and the temperature of another resonance circuit was maintained at a temperature close to the critical temperature. Because it appeared. Therefore, the characteristics of the specific resonance circuit can be easily identified from the entire frequency characteristics, so that the trimming of the specific resonance circuit can be performed without causing excessive trial and error adjustment and trimming. .

Incidentally, the no-load Qu of the resonance circuit is Qu = A
/ B. Here, A is energy stored in the resonance circuit, and B is energy lost in one cycle of resonance. Practically, if the impedance of the resonance circuit is Z and the resistance is R, it can be expressed as Qu = Z / R.
Is SQRT (L / C), and Z = ωL = 1 / ω
Since C, ω ² = 1 / LC is the basic equation of the resonance circuit. The load Q (so-called circuit Q) is represented by Q = A / B '. B 'is the energy that "passes" within one cycle of resonance.

In the case of a wide band filter, a so-called staggering method for shifting the resonance frequency of each resonator is often used to obtain flat characteristics. On the other hand, in the case of a narrow band filter, the resonance frequencies of the individual resonators are precisely matched, and the degree of coupling between the resonators is finely adjusted (Butterworth characteristics, Chebyshev characteristics, etc. according to a function that determines the degree of coupling). In particular, the application of the invention of the present application is useful because the required shut-off characteristics are obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 7 are views showing one embodiment of a method for trimming a superconducting resonance circuit according to the present invention. FIG.
, 1 is an HTS bandpass filter (hereinafter abbreviated as a bandpass filter). This bandpass filter 1 has a dielectric substrate 4 having a ground conductor 3 placed on a heat diffusion plate 2 and an HT
Many (three in the figure, for convenience) resonance circuits 5
7 and input / output wirings 8, 9 are formed.
Electromagnetic field coupling is performed between the resonance circuits 5 to 7 and the input / output wirings 8 and 9, and one of the input / output wirings 8 and the connector 10 are electrically connected, and the other input / output wiring 9 is connected to the connector 11 are electrically connected to each other.

In such a configuration, the heat diffusion plate 2 is
While cooling to a very low temperature of about 0K, one connector 1
0, a signal generator is connected to the other connector 11 and a spectrum analyzer is connected to the other connector 11 to sweep (sweep) the signal frequency. Is displayed. For example, in the case of a band-pass filter of the pass type, the overall characteristic with the minimum pass loss at a predetermined frequency fo can be obtained. In general, the pass frequency of a bandpass filter (cutoff frequency for a cutoff type) is fo ± Δf
(± Δf is a so-called filter bandwidth). The ideal filter characteristic has a constant loss of fo ± Δf. For example, in the case of a pass type, a flat trapezoidal overall characteristic having fo ± Δf as a pass bandwidth can be obtained.

The reason for providing multiple stages of resonance circuits is to obtain a flat ideal trapezoidal overall characteristic as described above. That is, although only one resonance circuit can provide only a mountain-shaped frequency characteristic (hereinafter referred to as an individual characteristic), an ideal overall characteristic can be obtained as a whole by finely adjusting the resonance frequency of each resonance circuit. It is. Trimming is an operation of adjusting the resonance frequency of each resonance circuit. Specifically, it is a work to adjust the length and area of the resonance circuit, but it is extremely difficult to separate and identify the individual characteristics of the resonance circuit to be trimmed from the overall characteristics. I have to become.

Therefore, the present embodiment has the following characteristic items in order to separate and identify the individual characteristics of the resonance circuit to be trimmed from the overall characteristics. That is, the plurality of resonance circuits 5 to 7 on the dielectric substrate 4
Are individually cooled , the temperature of a specific resonance circuit (for convenience, the resonance circuit 6) is cooled to a temperature sufficiently lower than the critical temperature Tk , and another resonance circuit (for convenience, resonance circuits 5, 7) is used. ) At a temperature higher than Ta and lower than Tk
The point is to heat so that Critical temperature
The (Tk), is generally the temperature at which the DC resistance of the superconducting material becomes zero. The skin resistance Rs has a very small value at a temperature Ta sufficiently lower than the critical temperature (for convenience, R
a) (Note 1), but at a higher temperature Tb, R
At a temperature higher than the critical temperature (Tc for convenience), the value becomes much larger than Rb (for convenience, Rc ). In this embodiment, T
c is not used. This is because if Rc having an excessive value is used, the band-pass filter does not operate at all. On the other hand, both Ta and Tb are temperatures below the critical temperature,
Ra and Rb are also common in that they are skin resistance in a superconducting state, but differ in that Ta is at a lower temperature than Tb. From this difference, it is the relationship of Ra <Rb is obtained.

Therefore, according to this embodiment, the resonance circuit
6 becomes Ra, and the other resonance circuits 5, 7
Of the resonance circuit 6 becomes Rb.
As a result of the Q of the other resonance circuits 5 and 7 being reduced by the difference of the skin resistance (R), it is possible to have a shape specificity between the individual characteristics of the resonance circuit 6 and the other individual characteristics, Overall characteristics
Can be almost regarded as the individual characteristics of the resonance circuit 6. Therefore, the trimming of the specific resonance circuit 6 can be performed while observing the individual characteristics of the specific resonance circuit 6, and a particularly advantageous effect that adjustment by trial and error and excessive trimming can be avoided can be obtained.

Note 1: In direct current, the resistance of the superconductor is the critical temperature
Although it becomes zero below the degree (Tk) , the resistance value does not become zero even at Tk or less in an alternating current, and shows a very small resistance value. Although this phenomenon is explained by a two-fluid model, not all carriers are in a superconducting state but a mixture of two types of carriers, superconducting and normal conducting. In direct current, only superconducting carriers act to achieve zero resistance, but in alternating current, normally conducting carriers are also driven by an electric field and cause loss. The ratio of the carriers in the superconducting state and the normal state changes depending on the temperature. As the temperature decreases, the ratio in the superconducting state increases. Therefore, the surface resistance changes over a wide range depending on the temperature.

FIG. 3 is a conceptual diagram showing a preferred embodiment applied to the above characteristic items. In the figure,
20 is a dielectric substrate, 21 is an input wiring, 22 to 26 are resonance circuits, 27 is an output wiring, and the input / output wirings 21 and 27 and the resonance circuits 22 to 26 are formed of HTS. Now, assuming that the center resonance circuit 24 (hereinafter referred to as a resonance circuit of interest) is a resonance circuit to be trimmed,
Therefore, the temperature of the resonance circuit of interest 24 is maintained at Ta, and the temperatures of the other resonance circuits 22, 23, 25, and 26 are maintained at T.
b must be maintained. For this purpose, first, in a state where all the resonance circuits 22 to 26 and the input / output signal lines 21 and 27 are cooled to extremely low temperature, appropriate portions of the other resonance circuits 22, 23, 25 and 26 except for the resonance circuit 24 of interest. (X mark) is locally heated. Only the skin resistance of the unheated target resonance circuit 24 becomes Ra, and the other resonance circuits 22, 23, 25, and 2
6 is Rb, the individual characteristics of the resonance circuit 24 of interest can be separated and identified from the total characteristics between the input wiring 21 and the output wiring 27, due to the difference in Q. The trimming of the resonance circuit of interest 24 can be performed while avoiding excessive trimming.

The means for local heating may be any means that can precisely heat the target location at the intended temperature at the intended temperature. For example, non-contact heating such as charged particles such as ion beams or high energy density lasers. However, since these means are mainly dominated by physical processing (heating is followed), non-contact heating such as low energy density laser light is suitable. When processing an actual circuit pattern, there are a method of shaving with a particle such as ion milling, and a method of evaporating the surface with a strongly converged laser beam. For heating, the convergence of light may be at a level that localizes the heating.

FIG. 4 is an image diagram of local heating. Here, assuming that the cooling temperature of the heat diffusion plate is 70 K, the thickness of the ground conductor is 100 μm, the thickness of the dielectric substrate 20 is 500 μm, and the thickness of the resonance circuit 22 is 0.5 μm. The appropriate heating temperature and heating area that do not have a thermal effect on the area were investigated. In this case, if the heating temperature is 90 K and the heating area is about 100 μm to 200 μm, the influence on the adjacent resonance circuit can be avoided.

The hatched portions 23a to 25a of the resonance circuits 23 to 25 are metal pads for trimming.
By removing a part of this metal pad using a charged particle beam such as an ion beam or a trimming beam such as laser ablation, the required trimming can be performed without affecting the portion formed by the HTS of the resonance circuit. Can be.

Next, the actual trimming will be described with reference to FIG. First, the resonance frequency of each resonance circuit of the bandpass filter is shifted in consideration of the variation in the resonance frequency of the resonance circuit before trimming. The causes of the error in the resonance frequency include variations in the thickness of the substrate, variations in the dielectric constant of the substrate material, errors in the crystal azimuth angle of the substrate, variations in dimensions due to the photoprocess conditions of the resonance circuit, and HT.
These include variations in the high-frequency impedance of the S thin film pattern, variations in the substrate temperature setting, and the like.

Next, with the bandpass filter cooled to a predetermined temperature, the measurement starts with measuring the passing signal levels on both sides of the center frequency (step 30). next,
In the same state, the resonance circuits are individually heated, and the heating conditions (temperature, etc.) and the passing signal level are recorded (step 3).
1). Next, in order to equalize the contribution of the individual resonance circuits to the attenuation, the entire resonance circuit of the bandpass filter is heated so as to have a predetermined attenuation (step 3).
2). Next, the heating of the resonance circuit to be trimmed is stopped, and the signal level is measured. The difference between this measured value and the case where all the resonance circuits are heated becomes the resonance frequency of the resonance circuit to be trimmed (step 33).

Next, it is determined whether or not trimming of the target resonance circuit is possible. For example, if the metal pads 23a to 25a of FIG. 3 remain, trimming is possible (step 34). If possible, trimming (coarse trimming) of the resonance circuit is performed, and the resonance frequency is roughly approximated to the target frequency (step 35). The above steps 32 to 35 are repeated for all the resonance circuits,
The resonance frequency of the entire band-pass filter is brought close to an intermediate target value (step 36). Then, finally, the above steps 32 to 35 are repeated again for all the resonance circuits, and the trimming of all the resonance circuits is performed precisely to bring the resonance frequency of the entire bandpass filter close to the final target value, thus completing the operation ( Step 37).

In the above embodiment, the trimming is performed by processing with an ion beam or laser ablation, but the present invention is not limited to this. For example, a dielectric may be deposited on or beside the resonant circuit. Deposition of the dielectric can be performed by various methods.
It is suitable for trimming performed while examining high-frequency characteristics in a vacuum and in a low-temperature environment, and is easier to realize than ion beam processing or laser ablation.

Although not described in the above embodiment, attention should be paid to the direction of frequency adjustment during trimming. In bidirectional trimming (for example, after adjusting from a low frequency to a high frequency, then adjusting again from a high frequency to a low frequency), the same element is repeatedly trimmed in the opposite direction, which may deteriorate the characteristics. Because it will be higher
In practice, it is desirable to perform unidirectional trimming (for example, either adjustment from a low frequency to a high frequency or adjustment from a low frequency to a high frequency).

In the above embodiment, coarse trimming is performed in the first stage (FIG. 5: step 36), and fine trimming is performed after confirming the overall result (FIG. 5:
Step 37) is because if the adjustment up to the final stage is performed for one resonance circuit at a time, the optimum adjustment cannot be performed due to the interaction of each resonance circuit.

In the above embodiment, the trimming portion (see reference numerals 23a to 25a in FIG. 3) is provided at the end of the resonance circuit. The reason is as follows. That is,
In the case of a 定 数 wavelength distributed constant type resonance circuit, the current distribution is maximum at the center of the resonance circuit and minimum (zero) at both ends, so that the center of the resonance circuit, which is the current concentration part, is trimmed. First, the trimming of this part (current concentrated part) reduces the pattern width.
In particular, it is impossible to deny the possibility of damage due to current concentration on the HTS thin film. Incidentally, even when trimming the carbon film resistor, if a cut is made in the current concentrated portion, the current is concentrated at the end of the cut and the pattern is likely to be destroyed, so it is common to trim the portion with a small current density. It is. In particular, in the case of the HTS thin film, the problem with the current concentration is larger than that of the resistor, so that
It is necessary to set the trimming portion avoiding the current concentration portion.

Further, in the above embodiment, a metal pad provided at the end of the resonance circuit (see reference numerals 23a to 25a in FIG. 3).
Is used as the trimming part, for the following reason. In other words, the end of the resonance circuit acts as a capacitor to be connected to the ground electrode, and the electric field is large, but almost no current flows. Therefore, by providing a trimming pattern in this portion, if the HTS thin film is damaged or critical current This is because the effect on the characteristics is not so large even if the surface resistance decreases or the surface resistance increases. Moreover, even if the metal pad is shaved by laser ablation, ion milling, or the like, there is little possibility that an altered layer is formed. As described above, since a small amount of current flows through the longitudinal end of the resonance circuit, there is little problem even if the end of the HTS thin film is replaced with metal.

In addition to the above-described respective trimming methods, the following trimming can be considered. In general, the superconducting transition temperature of an HTS thin film changes depending on the oxygen content in the film. When the oxygen content is large, the superconducting transition occurs at a high temperature, and a smaller surface resistance value can be obtained at the same temperature. For this reason, annealing is performed in a high-concentration oxygen atmosphere after film formation in order to “increase the oxygen content”.
It is known that when the S thin film is heated in a vacuum, oxygen in the film escapes to the outside and “oxygen content is reduced”, so that trimming utilizing this reduced oxygen content is also possible. That is, as described above, a decrease in the oxygen content causes a decrease in the superconducting transition temperature. Therefore, if the escape amount of oxygen is appropriately controlled, the normal temperature of the HTS thin film (6
(Approximately 0-77 K), a portion that becomes a normal conduction state can be selectively created, and trimming can be performed by adjusting the size of the portion. This trimming is performed in the resistance (several hundred Ω / □) in the region of the HTS thin film in the normal conduction state.
Degree) and surface resistance in superconducting state (less than 1mΩ / □)
This is the one that actively used the difference between the two. Of course, an increase in the resistance value leads to an increase in the loss, and there is some degree of heating.
Needless to say, the temperature must be appropriate so as not to affect the surroundings.

Next, the simulation results of the above embodiment will be described. The specifications of the band-pass filter are as follows: “Center frequency: 1.5 GHz, bandwidth: 15 MHz, number of stages: 9
Step, characteristics: Chebyshev, ripple: 0.1 db ”, and the Q and gk values of the circuits of each resonance circuit are as shown in Table 1 below. Specific bandwidth of bandpass filter (bandwidth / center frequency)
Is 1%, Qu for each resonance circuit is basically the reciprocal of 100. The gk value is a coefficient of the Q of each resonance circuit with respect to the normalized Qu. The gk value depends on the function used by the bandpass filter,
The value of a band-pass filter having a large attenuation such as a Chebyshev type is larger. The loss of each resonance circuit of the bandpass filter is proportional to Q / Qu of each resonance circuit. The loss of the entire bandpass filter is the sum of the loss of each resonance circuit. In a normal band-pass filter, the same resonance circuit is used, and a required degree of coupling is obtained by changing the distance between the resonance circuits. In that case, Q
u will be equal. The contribution ratio of each resonance circuit to the insertion loss is grasped by the gk value. For example, in Table 1, the gk value at the fifth stage is the largest, so the maximum contribution ratio is at the fifth stage.

FIG. 6 is a graph showing simulation results when Qu of each resonance circuit is reduced uniformly for the sake of simplicity. According to this graph, as a trimming target, the characteristic of a central resonance circuit (hereinafter, a resonance circuit of interest) in which heating is turned on and off is clearly shown. The three curves A, B, and C at the top of the graph uniformly lower the Qu of other resonance circuits other than the resonance circuit of interest (Qu = 8).
4) and the Qu of the resonance circuit of interest is set to 40000. That is, by the “local heating” described in the above embodiment, Qu of another resonance circuit is made smaller than Qu of the resonance circuit of interest. The peak frequency (resonance frequency) of each curve is f _A = 1.4978GH from the left.
z, f _B = 1.5 GHz and f _C = 1.5023 GHz.

The two curves D and E below the graph are the pass characteristics of the filter when the Qu of all the resonance circuits is reduced (84), and are approximately equal to those of the three curves A to C above the graph. The level is reduced by about 10 db. Curve D shows the case where the resonance frequency of the resonance circuit of interest is 1.4978 GHz, and curve E shows the case where the resonance frequency is 1.5023 GHz. When Qu decreases uniformly, the difference in resonance frequency with respect to the overall characteristics is very small. From the above, the resonance frequency of the resonance circuit of interest is determined by the pass characteristics on the lower side of the graph (pass characteristics when Qu of all the resonance circuits are uniformly reduced) and the transmission characteristics on the upper side of the graph (Qu of the resonance circuit of interest). The measurement can be accurately performed by determining the difference from the transmission characteristic when only the height is increased.

[0035]

According to the present invention, only the skin resistance of a specific resonance circuit has a very small value, and the skin resistance of the other resonance circuits has a slightly larger value.
There is a difference in minutes, and there is a difference in Q of the circuit. Therefore, the characteristic of the specific resonance circuit can be easily identified from the entire frequency characteristics, and the trimming of the specific resonance circuit can be performed without causing excessive trial and error adjustment and trimming. A particularly advantageous effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a structural diagram of a bandpass filter according to one embodiment.

FIG. 3 is a plan view of a bandpass filter according to one embodiment.

FIG. 4 is an image diagram of local heating of a bandpass filter of one embodiment.

FIG. 5 is a flowchart of a trimming operation according to an embodiment.

FIG. 6 is a simulation characteristic diagram of one embodiment.

[Explanation of symbols]

 4: Dielectric substrate 5-7: Resonant circuit 20: Dielectric substrate 22-26: Resonant circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01P 1/203 ZAA H01P 7/08 ZAA

Claims (1)

(57) [Claims] To 1. A when trimming individually a plurality of high-temperature superconductor resonator circuit on a dielectric substrate, cooling the specific resonant circuits to sufficiently lower temperature than the critical temperature (Ta), and the other resonance Temperature of the circuit above the temperature Ta and below the critical temperature
A method for trimming a superconducting resonance circuit, wherein the specific resonance circuit is trimmed while being heated to become (Tb) .