JP2005006045A - High frequency signal filter device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency signal filter device which can continuously change the filter characteristics, and moreover, is small and high in efficiency. <P>SOLUTION: The high frequency signal filter device 1 is provided with a first voltage variable capacitor FC1 on the signal line 10 of a micro strip line provided on a substrate, and a second voltage variable capacitor FC2 inserted between the signal line 10 of the micro strip line and a grounding face 20. Also, the electronic equipment is provided with the high frequency signal filter device 1, and a control means for controlling the opening/closing of the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 of the high frequency signal filter device 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for filtering signals, and more particularly to a dielectric resonator and a waveguide device (for example, a planar microstrip line) provided on a dielectric or a semiconductor substrate coated with the dielectric. The present invention relates to a high-frequency signal filter device and an electronic apparatus.
[0002]
[Prior art]
In recent years, the center frequency of a carrier wave exceeds 10 GHz as a filter for filtering a transmission signal from a signal generator to an antenna, filtering a reception signal from an antenna to a receiver, or bidirectional filtering in a multi-channel communication system. Development of a high-frequency signal filter device that is applied to a high-frequency signal and filters a signal having a desired band is desired.
[0003]
Conventionally, a trial production report of a filter having a signal frequency of about 10 GHz using an electro-acoustic conversion element has been made (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP 2000-502231A [0005]
[Problems to be solved by the invention]
However, with such a high-frequency signal filter device, it is impossible to control the pass characteristics of the filter with an external signal. Many prototypes of filters using planar cross-finger electrodes whose filter characteristics in the band exceeding 10 GHz can be controlled from the outside have been reported, but the efficiency is poor and sufficiently steep signal passing characteristics are obtained. However, there is a disadvantage that the element area is large.
[0006]
[Means for Solving the Problems]
The present invention has been made to solve such problems. That is, according to the present invention, the first voltage variable capacitor provided on the signal line of the micro strip line provided on the substrate and the second voltage inserted between the signal line of the micro strip line and the ground plane. A high-frequency signal filter device including a variable capacitor. Further, the electronic apparatus includes the high-frequency signal filter device and a control unit that controls voltage application to the first voltage variable capacitor and the second voltage variable capacitor of the high-frequency signal filter device.
[0007]
In the present invention as described above, the first voltage variable capacitor plays a role of transmitting a signal in a specific signal band, and the second voltage variable capacitor short-circuits a signal in a specific signal band to the ground side. Play a role. In addition, the first voltage variable capacitor is inserted in series in the signal line of the micro strip line, thereby controlling the voltage application to the first voltage variable capacitor, thereby increasing the signal band that can pass through the signal line. Change continuously.
[0008]
On the other hand, when the second voltage variable capacitor is inserted between the signal line of the micro strip line and the ground plane, the signal applied to the second voltage variable capacitor is controlled and short-circuited to the ground side. The bandwidth of is continuously changed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic plan view illustrating a high-frequency signal filter device according to this embodiment. That is, the high-frequency signal filter device 1 includes a planar micro strip line. The first voltage variable capacitor FC1 provided on the signal line 10 of the micro strip line and the signal of the micro strip line are provided. The second voltage variable capacitor FC2 is inserted between the line 10 and the ground surface 20 provided on the back surface of the substrate.
[0010]
The first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 have a capacitor (capacitance) variable by applying a DC voltage, and best control the signal transmission characteristics of these two voltage variable capacitors. Thus, the signal transmission band characteristics (transmission bandwidth, center value of the transmission band) of the high-frequency signal filter device 1 according to the present embodiment can be controlled.
[0011]
The first voltage variable capacitor FC1 is inserted in series on the signal line 10. The first voltage variable capacitor FC1 is a high-pass filter composed of a capacitor (capacitance) and an inductor. The capacitor is composed of a dielectric film (a BST thin film to be described later) provided corresponding to the break K of the signal line 10 and the upper electrode D, and the inductor applies a DC voltage to the signal line 10 between the two breaks K. It is comprised by the wiring 11 for applying.
[0012]
By applying a DC voltage from the wiring 11 of the first voltage variable capacitor FC1, a signal band that can pass through the signal line 10 is changed, and only a signal in a specific band can selectively flow. Therefore, the signal band that can pass through the signal line 10 can be continuously varied within a certain range depending on the magnitude of the DC voltage applied from the wiring 11.
[0013]
The second voltage variable capacitor FC2 is inserted in series on the branch line 10a that branches from the signal line 10 to the ground plane 20. Similarly to the first voltage variable capacitor FC1, the second voltage variable capacitor FC2 is also a high-pass filter composed of a capacitor and an inductor. That is, the capacitor is composed of a dielectric thin film provided corresponding to the break K of the branch line 10a and the upper electrode D, and the inductor is for applying a DC voltage to the branch line 10a between the two breaks K. The wiring 11 is used.
[0014]
By applying a DC voltage from the wiring 11 of the second voltage variable capacitor FC2, a signal band that can pass through the branch line 10a can be changed, and only a signal in a specific band can be short-circuited to the ground plane 20 side. Therefore, the attenuation band of the high-frequency signal flowing through the signal line 10 can be continuously varied within a certain range depending on the magnitude of the DC voltage applied from the wiring 11.
[0015]
That is, in the high-frequency signal filter device 1 according to the present embodiment, a combination of two types of voltage variable capacitors in which the capacitors and the inductances in the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 are appropriately adjusted is used. It is possible to switch between different types of filter operations such as a pass filter, a high pass filter, and a notch filter, and to continuously change the filter characteristics.
[0016]
Examples of the dielectric thin film constituting the capacitor C of the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 include (Ba _x Sr _1-x ) TiO ₃ (x = 0 to 0.7) (hereinafter referred to as “Ba _x Sr _1-x” ) The capacity is changed depending on the DC voltage when a DC voltage is applied to the BST thin film.
[0017]
Therefore, a terminal for applying a DC voltage is connected to each of the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2, and the first voltage variable capacitor FC1 and the second voltage variable capacitor. Before and after the signal line 10 and the branch line 10a to which the FC 2 is connected, a break (capacitance) K for insulating the applied DC voltage is provided.
[0018]
The first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 are mainly composed of a BST thin film and an upper electrode D. Further, the signal line 10, the branch line 10a, and the ground plane 20 are configured using Cu, Au, or the like that is a good conductor.
[0019]
For the substrate on which the signal line 10 and the like are formed, SiO ₂ , Al ₂ O ₃ , a polymer material having a good insulating property, a composite material of polymer and SiO ₂ , Al ₂ O ₃ , or the like is used. In order to ensure the quality of the BST thin film, Pt may be used as a film formation base.
[0020]
FIG. 2 is a schematic plan view of the high-frequency signal filter device according to the present embodiment. This figure is a plan view of the front surface side of the substrate 2, and a ground plane 20 is provided on the back surface of the substrate 2. A signal line 10 is provided on the surface of the substrate 2, and a first voltage variable capacitor FC <b> 1 is formed in series with the signal line 10.
[0021]
A second voltage variable capacitor FC <b> 2 is formed between the signal line 10 and the ground plane 20. The second voltage variable capacitor FC2 is provided in series with the branch line 10a from the signal line 10, and the end of the branch line 10a is connected to the grounding surface 20 on the back surface through the substrate 2. Note that the pad P is electrically connected to the ground surface 20 on the back surface of the substrate 2, and when it is desired to obtain electrical continuity with the ground surface 20, the pad P is electrically connected as necessary.
[0022]
3A and 3B are diagrams showing an equivalent circuit of the high-frequency signal filter device according to the present embodiment, where FIG. 3A is an overall view, FIG. 3B is an equivalent circuit of a first voltage variable capacitor, and FIG. 3C is a second voltage. There is an equivalent circuit of variable capacitance.
[0023]
In both the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2, the capacitor is configured as a stray capacitance with the ground plane, and the inductor is configured by a wiring for DC voltage input.
[0024]
The high-frequency signal filter device 1 of the present embodiment shown in FIG. 1 has a minimum configuration, and for example, a circuit network may be formed using a plurality of voltage variable capacitors as shown in FIG. That is, the signal line 10 is branched and each of the first voltage variable capacitors FC11, FC12, FC13 is provided to form a parallel switch, and a plurality of lines from the signal line 10 to the ground plane 20 are provided to each of the second voltage switches. The voltage variable capacitors FC21, FC22, FC23 are connected.
[0025]
With such a configuration, a ladder type filter or a signal branching element such as a duplexer can be configured as necessary. When a plurality of voltage variable capacitors are arranged in parallel, it is desirable to have a symmetrical line structure so that the line length of each switch group is the same in consideration of signal delay. That is, the line lengths of the voltage variable capacitors FC11, FC12, FC13 from the branch point a to the connection point b of the switch group by the first voltage variable capacitors FC11, FC12, FC13 are the same, and the second voltage variable capacitor The voltage variable capacitors FC21, FC22, and FC23 have the same line length from the branch point c to the connection point d of the switch group of FC21, FC22, and FC23.
[0026]
5A and 5B are schematic cross-sectional views for explaining the structure of the first voltage variable capacitor. FIG. 5A is a schematic cross-sectional view in a direction perpendicular to the line, and FIG. 5B is a schematic cross-sectional view in a direction parallel to the line. It is.
[0027]
The first voltage variable capacitor FC1 is provided on the signal line 10 of the micro strip line configured by the signal line 10 provided on the surface of the substrate 2 and the ground plane 20 provided on the back surface of the substrate 2. A wiring 11 for applying a variable DC voltage is connected.
[0028]
A BST thin film 21 is formed on the two cuts K of the signal line 10 and on the signal line 10 corresponding to the position, and the upper electrode is formed on the BST thin film 21 so as to cover the upper part of the two cuts K from the signal line 10. Each D is provided.
[0029]
Therefore, by applying a DC voltage from the wiring 11 to the signal line 10 between the two breaks K, the relative dielectric constant of the BST thin film 21 changes according to the applied voltage, and a high frequency band that passes through the signal line 10. It becomes possible to change the characteristics.
[0030]
Although not shown, the second voltage variable capacitor FC2 has the same configuration as the first voltage variable capacitor FC1. In this case, the signal line 10 used in the description of the first voltage variable capacitor FC1 becomes a branch line connected from the signal line 10 to the ground plane 20.
[0031]
In the present embodiment, the DC voltage application to the first and second voltage variable capacitors FC1 and FC2 is controlled by a control means (not shown), so that a band-pass filter is obtained by a combination of switch operations. It is possible to configure an electronic device that can switch different types of filter operations such as a high-pass filter and a notch filter.
[0032]
Here, an example of the line design of the high-frequency signal filter device according to the present embodiment will be described.
[0033]
The characteristic impedance (Z) of the line is expressed by the following equation according to the thickness (h), relative dielectric constant (εr), and signal line width (w) of the dielectric film provided between the ground plane and the signal line. Therefore, it is determined.
[0034]
Z = 377 / (w / h) (εr) ^1/2 [1+ (1.735εr ^−0.0724 ) (w / h) ^−0.836 ]
[0035]
For example, when Al ₂ O ₃ having a relative dielectric constant of 9.8 is used in a 50Ω line, w / h = 0.9. For example, when the thickness of the substrate 2 is 0.525 mm, the signal line 10 The width (line width) w is 0.473 mm.
[0036]
The relative dielectric constant of the BST thin film formed on Pt is, for example, 1 by applying a voltage of 0 to ± 10 V between the crossed finger electrodes with a spacing of 250 μm in a film having a thickness of 77 K and a thickness of 0.27 μm. Go down to / 6. In order to increase the efficiency, it is desirable to lower the temperature of the element, but the same phenomenon occurs even at room temperature.
[0037]
For the high-frequency line, the width of the upper electrode D not exceeding the line width (widths w1 and w2 of each upper electrode D corresponding to each cut K shown in FIG. 5, lengths L1 and L2 of the upper electrode D), BST thin film A capacitance determined by a relative dielectric constant (εr) of 21 and a film thickness h is inserted in series.
[0038]
The first voltage variable capacitor FC1 is inserted in series between the input side and the output side of the signal line 10, and the second voltage variable capacitor FC2 is inserted between the signal line 10 and the ground plane 20, When functioning as a high pass filter and the effects of both are combined, a band pass filter can be constructed.
[0039]
In this case, the first voltage variable capacitor FC1 and the inductor determine the cut-off frequency on the low frequency side, and the second voltage variable capacitor FC2 and the inductor determine the cut-off frequency on the high frequency side. Each cutoff frequency 2πf ₀ is given by √ (4 / LC). Therefore, desired characteristics can be obtained by appropriately selecting the capacitance and the inductor value. Further, since the relative permittivity changes depending on the applied voltage, the filter characteristics can be continuously controlled from the external terminal of the DC voltage.
[0040]
For example, if it is desired to obtain a cutoff frequency of about 20 GHz and the inductance is selected to be 30 pH, the required capacitance value is about 10 pF. The relative dielectric constant of the BST thin film 21 can be expected to be about 120. If the thickness h of the BST thin film 21 shown in FIG. 5 is 0.2 μm and the width (w1, w2) of the upper electrode D is about 0.3 mm, the length (L1, L2) of the upper electrode D shown in FIG. ) May be about 0.7 mm. Actually, since two cuts (capacitance) are inserted in series, each of L1 and L2 needs to have a length of about 1.4 mm.
[0041]
Here, when a band-pass filter operation is to be performed using a filter composed of two capacitors, the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2, an electric field is applied to the first voltage variable capacitor. Then, the capacitor may be lowered to about 80%. Further, the capacity portions of the first voltage variable capacitor FC1 and the second voltage variable capacitor FC2 are low-pass filters as viewed from the DC input pad, and a DC voltage can be applied.
[0042]
Next, a method for manufacturing the high-frequency signal filter device according to this embodiment will be described. 6 to 7 are schematic cross-sectional views (mainly a portion of the first voltage variable capacitor) for sequentially explaining the manufacturing method. 6 and 7 are schematic cross-sectional views in the direction perpendicular to the signal lines.
[0043]
First, an insulating substrate 2 (for example, a semiconductor substrate coated with alumina or a part of a low dielectric constant film) provided with connection holes at appropriate intervals is cleaned and plated by Ni / Au or Ni / Films are formed in the order of Au / Pt. Using a method such as milling or dry etching, a flat microstrip line having a thickness of 0.5 μm is formed.
[0044]
FIG. 6A shows a state in which a micro strip line having a ground plane 20 on the back surface of the substrate 2 and a signal line 10 on the front surface is formed. The signal line 10 on the substrate 2 is patterned with a wiring 11 that is a meander line for applying a DC voltage. In this state, the BST thin film 21 is deposited on the entire surface of the substrate 2 on which the line pattern is formed by sputtering.
[0045]
Next, as shown in FIG. 6B, a hole is made in a part of the deposited BST thin film 21. This drilling uses milling, dry etching, or the like. Then, as shown in FIG. 6 (c), a conductor film D ′ such as gold (Au), which will be the upper electrode, is produced in the formed hole by sputtering, vapor deposition or the like, and further patterned by milling, dry etching or the like. Thus, the upper electrode D as shown in FIG. 7A is formed in the hole on the signal line 10.
[0046]
FIG. 7B shows a schematic cross section of a capacitor component portion by the BST thin film 21 after the upper electrode D is patterned. Next, the entire surface of the formed line pattern is covered with a polymer thin film having a good insulating property or a SiO ₂ thin film. Then, the insulating film on the signal line 10, the ground plane 20, and the DC voltage application wiring 11 is removed, and a signal can be connected to an external circuit.
[0047]
【The invention's effect】
As described above, the present invention has the following effects. That is, according to the present invention, a filter is formed by a planar micro stripline element, a first voltage variable capacitor provided on a signal line, and a second voltage variable capacitor inserted between the signal line and the ground plane. A structure capable of continuously changing characteristics can be realized. Further, such a configuration makes it possible to achieve a very small size as compared with a high frequency filter using a crossed finger type electrode. In addition, by applying a control bias voltage using a relatively simple control means, continuous control of the transmission characteristics and cutoff characteristics of the filter can be realized. It is also possible to make.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a high-frequency signal filter device according to an embodiment.
FIG. 2 is a schematic plan view of the high-frequency signal filter device according to the present embodiment.
FIG. 3 is a diagram showing an equivalent circuit of the high-frequency signal filter device according to the present embodiment.
FIG. 4 is a schematic diagram showing an example of a network using a plurality of voltage variable capacitors.
FIG. 5 is a schematic cross-sectional view for explaining the structure of a first voltage variable capacitor FC1.
FIG. 6 is a schematic cross-sectional view (part 1) for sequentially explaining the manufacturing method;
FIG. 7 is a schematic cross-sectional view (part 2) for sequentially explaining the manufacturing method;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... High frequency signal filter apparatus, 2 ... Board | substrate, 10 ... Signal line, 10a ... Branch line, 20 ... Ground plane, 21 ... BST thin film, D ... Upper electrode, FC1 ... 1st voltage variable capacitor, FC2 ... 2nd Voltage variable capacity

Claims (7)

A first voltage variable capacitor provided on a signal line of a micro strip line provided on a substrate;
A high frequency signal filter device comprising: a second voltage variable capacitor inserted between a signal line of the micro strip line and a ground plane. 2. The high-frequency signal filter device according to claim 1, wherein a line corresponding to each of the first voltage variable capacitor and the second voltage variable capacitor is provided with a break that insulates the application of a DC voltage. . 2. The signal line of the micro strip line is branched into a plurality of lines, and each of the branched signal lines is provided with the first voltage variable capacitor to form a parallel switch. High frequency signal filter device. 2. The high frequency signal filter device according to claim 1, wherein a plurality of the second voltage variable capacitors are provided between a signal line of the micro strip line and a ground plane. The dielectric that constitutes the first voltage variable capacitor and the second voltage variable capacitor uses (Ba _x Sr _1-x ) TiO ₃ (x = 0 to 0.7). 1. The high-frequency signal filter device according to 1. 2. The high frequency signal filter device according to claim 1, wherein the substrate is made of a semiconductor substrate partially coated with a low dielectric constant film. The high-frequency signal filter device according to any one of claims 1 to 6,
An electronic apparatus comprising: the first voltage variable capacitor of the high-frequency signal filter device; and a control unit that controls voltage application to the voltage variable capacitor.

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