JP4469809B2 - Superconducting filter device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a superconducting filter device, and more particularly to a superconducting transmission filter applied to a transmission system of a cryogenic RF front end of a mobile communication base station.

  In recent years, with the spread and development of mobile phones, high-speed and large-capacity transmission technology has become indispensable. Superconductors have a very low surface resistance in the high-frequency region as compared with ordinary good electrical conductors, and therefore can be expected to have low-loss and high-Q resonators and are promising as filters for mobile communication base stations. Has been.

  For example, as shown in FIG. 1, an RF signal received via an antenna 151 is converted into a band filter (BPF) 152R, a low noise amplifier (LNA) 153, and a down converter (D / C) that constitute a reception system front end. 154 and demodulator (DEMOD) 155, and baseband processing is performed by the baseband unit 156.

  In the transmission system, the signal processed by the baseband unit 156 passes through a modulator (MOD) 157, an up converter (U / C) 158, a high power amplifier (HPA) 159, and a band filter (BPF) 152T, and then an RF signal. As radiated from the antenna 151.

  When the superconducting filter is applied to the band filter 152R on the receiving side, a transmission loss is small and a steep frequency cutoff characteristic is expected. On the other hand, when applied to the band filter 152T on the transmission side, an effect of removing distortion generated by the high power amplifier 159 can be expected, but a large amount of power is required to transmit a high-frequency signal, miniaturization and good power characteristics. This is the current challenge.

  When a superconducting filter is used in a mobile communication application, a frequency tuning capability is required. In order to make the superconducting filter tunable, a plate on which a conductor layer is formed via a space is arranged above the superconducting resonator pattern so that the conductor layer faces the resonator pattern. There has been proposed a method of adjusting the distance between the resonator pattern and the conductor layer by inserting a piezoelectric element between the plates (see, for example, Patent Document 1).

  2 (a) to 2 (c) show the configuration of the known tunable filter described above. Strip type resonator patterns 77 a to 77 d arranged in a spiral shape are formed on the filter circuit board 71. A plate 72 is disposed above the filter circuit board 71. A conductor layer 72b is formed on the entire surface of the plate 72 facing the resonator patterns 77a to 77d. Piezoelectric elements 74 a to 74 d are inserted between the base 75 holding the filter circuit board 71 and the plate 72. A voltage applying wire 82 extending from the tuning connector 81 is connected to the piezoelectric elements 74a to 74d, and a tuning voltage is applied thereto. The distance of the space is changed by the expansion and contraction of the piezoelectric element by voltage application, and the center frequency of the filter can be tuned.

However, this superconducting filter can tune the center frequency, but cannot adjust its bandwidth. In addition, since it is a so-called microstrip type filter, there is a problem that loss increases when high RF power is input on the transmission side. This is because high frequencies such as microwaves tend to concentrate on the edge portion of the conductor, and current concentrates on the edge or corner portion of the microstrip line, and the current density exceeds the critical current density of the superconductor.
Japanese translation of PCT publication No. 2003-516079

  In order to alleviate the concentration of current on the superconducting resonator pattern, a plane pattern type (circular, elliptical, polygonal, etc.) resonator pattern with few corners and edges is formed as a transmission filter. It is conceivable to realize a large power response. Further, it is conceivable that a coupling corresponding to a desired bandwidth is generated by arranging a conductor pattern having a predetermined shape via a laminated dielectric above the planar figure type superconducting resonator pattern. Two resonator modes (a so-called “dual mode”) are generated by one resonator, thereby preventing current concentration and contributing to miniaturization.

  However, a deviation from the design simulation result occurs depending on the material characteristics and mounting state of the laminated dielectric and the material characteristics and position of the conductor pattern for generating the dual mode. When adjusting the material, film thickness, mounting state, etc. in order to adjust the deviation, several parameters also move at the same time, which makes adjustment difficult.

  Therefore, it is an object to provide a configuration that can adjust both the center frequency and the bandwidth of a superconducting resonator filter with a simple configuration.

  In order to solve the above problems, the present invention inserts a plurality of piezoelectric elements between a base substrate on which a superconducting resonator pattern is formed and a laminated dielectric on which a conductor pattern for generating a dual mode is formed. Then, a voltage is applied to each piezoelectric element independently to adjust the distance between the laminated dielectric and the resonator pattern.

Specifically, the superconducting filter device includes a first dielectric substrate, said first dielectric co oscillator pattern formed on the superconducting material substrate, situated above the resonator pattern A second dielectric substrate having a dual-mode generating conductor pattern for generating two resonance modes in the resonator pattern; and a piezoelectric element inserted between the first and second dielectric substrates; Is provided.

  As one configuration example, the piezoelectric element further includes a voltage applying unit that is inserted at four corners between the first and second dielectric substrates and individually applies a voltage to each piezoelectric element.

  In the dual mode type superconducting filter, the center frequency and the bandwidth can be adjusted with high accuracy.

  FIG. 3 shows a configuration of a superconducting filter device 10 according to an embodiment of the present invention. FIG. 3A is a top view, and FIG. 3B is a cross-sectional view. The superconducting filter device 10 is mounted on a metal package 21 for use in a transmission filter of a base station of a mobile communication system, for example.

  The superconducting device 10 includes a dielectric base substrate 11 such as an MgO single crystal substrate, a superconducting resonator pattern 12 formed in a predetermined shape with a superconducting material on the surface of the dielectric base substrate 11, and a superconducting resonator. A signal input / output line (feeder) 13 extending in the vicinity of the pattern 12, a second dielectric substrate 14 mounted on the dielectric substrate 11, and a circular or elliptical conductor pattern formed on the laminated dielectric substrate 14 15 and a piezoelectric element 16 inserted between the dielectric base substrate 11 and the laminated dielectric substrate 14.

  In the example of FIG. 3, a YBCO (Y-Ba-Cu-O-based) material is used as a superconductive material, and the superconductive resonator pattern 12 is formed as a two-dimensional circuit pattern (disk pattern).

  In the present specification and claims, the term “two-dimensional circuit pattern” or “two-dimensional circuit type pattern” is distinguished from a strip-shaped or line-shaped (one-dimensional) pattern, and is circular, elliptical, It shall mean a plane figure type pattern such as a square.

  As the dielectric base substrate 11, any dielectric substrate having a dielectric constant of 8 to 10 at a frequency of 3 to 5 GHz can be used other than the MgO single crystal substrate.

  One of the input / output feeders 13 is used as a signal input, and the other is used as a signal output. These feeders 13 are respectively connected to an input connector and an output connector 22 provided on the metal package 21. A ground electrode (ground film) 24 is formed on the back surface of the dielectric base substrate 11.

  A second dielectric substrate 14 such as a LaAlO 3 single crystal is mounted on top of the dielectric base substrate 11 (hereinafter referred to as “laminated dielectric substrate 14”). A conductive disk pattern 15 for coupling or dual mode generation is formed on one surface of the laminated dielectric substrate 14 (on the upper surface side in the example of FIG. 3B).

  As the laminated dielectric substrate 14, any substrate having a dielectric constant exceeding 20 can be used other than the LaAlO3 single crystal substrate. Further, it is desirable that both surfaces of the substrate are smooth and have a thermal expansion coefficient similar to that of the dielectric base substrate 11 at a low temperature.

  A piezoelectric element 16 is provided on the other surface of the multilayer dielectric substrate 14. In the example of FIG. 3A, the piezoelectric elements 16 are provided at the four corners of the laminated dielectric substrate 14 and are connected to the bias voltage applying wires 19, respectively. The bias voltage applying wire 19 is connected to an external voltage applying means (not shown) through a through hole (not shown) formed in the metal package 22. A voltage is independently applied to the piezoelectric elements 16 via the corresponding bias voltage application wires 19 to control the distance between the superconducting resonator pattern 12 and the laminated dielectric substrate 14.

  FIG. 4 shows a configuration example of the piezoelectric element 16. FIG. 4A shows a piezoelectric element using a thickness expansion / contraction mode. A piezoelectric film 17 is sandwiched between the pair of electrode films 18. The electrode film 18 is made of Pt or SrRuO3, and the piezoelectric film 17 is made of PZT or BaTiO3. This piezoelectric element expands and contracts in the thickness direction of the piezoelectric film as indicated by an arrow when a voltage is applied.

  FIG. 4B shows a stacked piezoelectric element. A plurality of piezoelectric thin plates 17 are laminated, and each piece is alternately laminated and fixed so that the polarization in the thickness direction is reversed. The internal electrodes 18b extend from the pair of external electrodes 18a in an interdigital manner parallel to the piezoelectric (ceramic) layers 17. By reducing the thickness per layer of the piezoelectric layer 17, the voltage can be lowered, and by stacking, the total amount of displacement can be earned. The displacement direction due to the application of voltage is the stacking direction indicated by the arrows.

The displacement amount ΔL in this case is
ΔL = d ₃₃ × n × V
It is represented by Here d ₃₃ is the piezoelectric constant of the longitudinal effect, n represents the number of lamination, V is a driving voltage. If a material having a large piezoelectric constant is used, the total number of stacked layers and the driving voltage can be reduced compared to the case where the same displacement can be obtained, which is advantageous for downsizing.

As a material capable of obtaining a large piezoelectric constant, PZT + 3.60 × 10 ¹² m / V, Pb (Ni _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃ solid solution (PNN-PT-PZ) +5 70 × 10 ¹² m / V is obtained. When the latter is used, the actual film thickness is 20 μm as a single film, and the film thickness of the electrode is 1 to 2 μm. When the driving voltage is about 20 V, 100 layers are required to obtain a displacement of 1 μm or more, and the piezoelectric element 16 is formed by forming a metal film having a thickness of 101 to 202 μm on a total of 2 mm of the piezoelectric film.

  In order to accommodate the thickness of the piezoelectric element 16, as shown in FIG. 4 (b), a concave portion 11a is formed at a corresponding portion of the dielectric base substrate 11 and / or the laminated dielectric substrate 14, and the concave portion 11a is formed in the concave portion 11a. The piezoelectric element 16 is disposed.

  In the embodiment, piezoelectric elements 16 are provided at the four corners of the laminated dielectric substrate 14 and mounted on the dielectric base substrate 11. As a manufacturing process of the superconducting filter device 10 in this case, a two-dimensional circuit type resonator pattern 12 is formed of a superconducting material on the dielectric base substrate 11. On the other hand, a conductor pattern 15 for generating a dual mode (or coupling) is formed on one surface of the multilayer dielectric substrate 14, and a piezoelectric element 16 is formed or disposed on the other surface. Then, the laminated dielectric substrate 14 is mounted on the dielectric base substrate so that the surface on which the piezoelectric element 16 is formed faces the superconducting resonator pattern 12.

  Alternatively, the piezoelectric element 16 may be provided on the dielectric base substrate 11 on which the superconducting resonator pattern 12 is formed. In this case, a two-dimensional circuit type resonator pattern 12 is formed of a superconducting material on the dielectric base substrate 11, and a plurality of resonator patterns 12 are formed around the resonator pattern 12 (for example, four corners on the substrate 11). The piezoelectric element 16 is formed or arranged. On the other hand, a conductor pattern 15 for generating a dual mode (or coupling) is formed on the laminated dielectric substrate 14. Then, the laminated dielectric substrate 14 is mounted on the piezoelectric element 16.

  When the latter method is employed, if alignment marks are formed at the four corners of the multilayer electric substrate 14 on the formation surface side of the dual mode generating conductor pattern 15, the dual mode generating conductor pattern 15 also has an alignment function.

  When the distance between the laminated dielectric substrate 14 on which the dual-mode generating conductor 15 is formed and the superconducting resonator pattern 12 changes due to expansion and contraction of the piezoelectric element, the degree of interference between the center frequency and the electromagnetic field modes of each other (Coupling), that is, the bandwidth is different.

  5 and 6 are graphs showing filter characteristics when the distance between the laminated dielectric substrate 14 on which the dual-mode generating conductor pattern 15 is formed and the superconducting resonator pattern 12 is changed. In the simulation, an 18 × 18 × 0.5 mm LaAlO 3 single layer is formed above a sample in which a disk-type superconducting resonator pattern 12 having a diameter of 12.8 mm is formed on a 20 × 20 × 0.5 mm MgO single crystal substrate 11. A sample in which a disk-type dual mode generating conductor pattern 15 having a diameter of 3.8 mm was formed on the crystal substrate 14, and the distance between the superconducting resonator pattern 12 and the LaAlO3 single crystal substrate was changed.

  FIGS. 5A to 5D show the case where the distance between the multilayer dielectric substrate 14 on which the dual mode generating conductor 15 is formed and the superconducting resonator pattern 12 is 0 μm, 1 μm, 3 μm, and 5 μm, respectively. 6 (a) to 6 (d) are filter characteristics when the intervals are set to 7 μm, 10 μm, 15 μm, and 20 μm, respectively. In each graph, practice shows reflection characteristics (S11), and wavy lines show transmission characteristics (S21).

  It can be seen that as the laminated dielectric substrate 14 is moved away, the center frequency increases and the bandwidth decreases. This is because the effective dielectric constant of the filter is lowered by separating the multilayer dielectric 14 having the dual mode generating conductor pattern 15 from the superconducting resonator pattern 12, and the influence of coupling between two degenerate modes is increased. It means smaller.

  When this is used, for example, the laminated piezoelectric element 16 shown in FIG. 4B is accommodated in the recess 11a provided in the dielectric base substrate 11 or the laminated dielectric substrate 14, and the voltage applied to each piezoelectric element is set. By controlling, the center frequency and the bandwidth can be finely adjusted.

  As described above, according to the present invention, in the superconducting filter device, not only the center frequency but also the bandwidth can be adjusted with high accuracy, so that desired filter characteristics can be obtained. In addition to improving the manufacturing yield, there is an effect that the range of application to the tunable filter is expanded.

  Although the present invention has been described based on specific embodiments, the present invention is not limited to these examples.

  For example, in the embodiment, a YBCO thin film is used as the superconducting material, but any oxide superconducting material can be used. For example, an RBCO (R—Ba—Cu—O) -based thin film, that is, a superconducting material using Nd, Sm, Gd, Dy, and Ho instead of Y (yttrium) as the R element may be used. Also, BSCCO (Bi-Sr-Ca-Cu-O) system, PBSCCO (Pb-Bi-Sr-Ca-Cu-O) system, CBCCO (Cu-Bap-Caq-Cur-Ox, 1.5 <p <2.5, 2.5 <q <3.5, 3.5 <r <4.5) may be used for the superconducting material.

  The dielectric base substrate 11 is not limited to the MgO single crystal substrate, and for example, a LaAlO 3 substrate, a sapphire substrate, or the like may be used. The laminated dielectric substrate 14 is not limited to a LaAlO 3 substrate, and may be, for example, an NdGaO 3 substrate, an LSAT substrate, a LaSrGaO 4 substrate, a LaGaO 3 substrate, a YSZ substrate, or the like.

Finally, the following notes are disclosed regarding the above description.
(Appendix 1) a first dielectric substrate;
A two-dimensional circuit type resonator pattern formed of a superconducting material on the first dielectric substrate;
A second dielectric substrate positioned above the resonator pattern and having a conductor pattern for generating coupling;
A superconducting filter device comprising: a piezoelectric element inserted between the first and second dielectric substrates.
(Appendix 2) The piezoelectric elements are located at four corners between the first and second dielectric substrates,
The superconducting filter device according to appendix 1, further comprising voltage applying means for individually applying a voltage to each piezoelectric element.
(Additional remark 3) It further has a means to apply a voltage to the said piezoelectric element, The distance between the said 2nd dielectric substrate and the said resonator pattern is changed by the voltage application to the said piezoelectric element, and, thereby, a filter The superconducting filter device according to appendix 1, wherein a center frequency and a bandwidth of the superconducting filter are controlled.
(Supplementary Note 4) The piezoelectric element is a laminated piezoelectric element,
The superconducting filter device according to appendix 1, wherein at least one of the first dielectric substrate and the second dielectric substrate has a recess for accommodating the thickness of the piezoelectric element.
(Supplementary Note 5) The superconducting device according to any one of Supplementary Notes 1 to 4, wherein the conductor pattern that generates the coupling is formed of a superconducting material.
(Appendix 6) A two-dimensional circuit type resonator pattern is formed on a first dielectric substrate with a superconducting material,
A conductor pattern for generating coupling is formed on one surface of the second dielectric substrate, and a piezoelectric element is formed on the other surface;
A method of manufacturing a superconducting filter device, wherein the second dielectric substrate is mounted on the first dielectric substrate so that a surface on which the piezoelectric element is formed faces the resonator pattern. .
(Appendix 7) On a first dielectric substrate, a superconducting material is used to form a two-dimensional circuit type resonator pattern and a plurality of piezoelectric elements positioned around the resonator pattern,
Forming a conductor pattern for generating coupling on the second dielectric substrate;
A method of manufacturing a superconducting filter device, wherein the second dielectric substrate is mounted on the piezoelectric element.
(Supplementary note 8) The method for producing a superconducting filter device according to supplementary note 7, wherein an alignment mark is formed on the surface of the second dielectric substrate 14 on which the conductor pattern 15 is formed.
(Supplementary Note 9) A two-dimensional circuit type resonator pattern is formed of a superconducting material on a first dielectric substrate,
Forming a conductor pattern for generating coupling on the second dielectric substrate;
Forming a recess in a plurality of locations of at least one of the first dielectric substrate and the second dielectric substrate;
A laminated piezoelectric element is disposed in the recess,
A method of manufacturing a superconducting filter device, wherein the second dielectric substrate is mounted on the first dielectric substrate.

It is a schematic block diagram of RF front end of a mobile communication base station. It is a block diagram of the conventional tunable superconducting filter. It is a schematic block diagram of the superconducting filter which concerns on one Embodiment of this invention. It is a figure which shows the structural example of the piezoelectric element provided in the superconducting filter of FIG. It is the simulation result (the 1) which shows the filter characteristic when the distance between a superconducting resonator pattern and a laminated dielectric substrate is changed. It is the simulation result (the 1) which shows the filter characteristic when the distance between a superconducting resonator pattern and a laminated dielectric substrate is changed.

Explanation of symbols

10 Superconducting filter device 11 Dielectric base substrate (first dielectric substrate)
11a Concave portion 12 Superconducting resonator pattern 13 Feeder (signal input / output line)
14 Multilayer dielectric substrate (second dielectric substrate)
15 Dual-mode (coupling) generating conductor pattern 16 Piezoelectric element

Claims (5)

A first dielectric substrate;
Co vibrator pattern formed of a superconducting material on said first dielectric substrate,
A second dielectric substrate positioned above the resonator pattern and having a dual-mode generating conductor pattern for generating two resonance modes in the resonator pattern;
A superconducting filter device comprising: a piezoelectric element inserted between the first and second dielectric substrates. The piezoelectric elements are located at four corners between the first and second dielectric substrates,
2. The superconducting filter device according to claim 1, further comprising voltage applying means for individually applying a voltage to each of the piezoelectric elements. The superconducting device according to claim 1, wherein the conductor pattern for generating the dual mode is made of a superconducting material. A first dielectric substrate to form a co-acoustic transducer pattern of a superconducting material,
A conductor pattern for generating a dual mode for generating two resonance modes in the resonator pattern is formed on one surface of the second dielectric substrate, and a piezoelectric element is formed on the other surface;
A method of manufacturing a superconducting filter device, wherein the second dielectric substrate is mounted on the first dielectric substrate so that a surface on which the piezoelectric element is formed faces the resonator pattern. . A first dielectric substrate, a co-acoustic transducer pattern in superconducting material, a plurality of piezoelectric elements located around the resonator pattern formed,
Forming a dual-mode generating conductor pattern on the second dielectric substrate for generating two resonance modes in the resonator pattern;
A method of manufacturing a superconducting filter device, wherein the second dielectric substrate is mounted on the piezoelectric element.

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