JP2002204139A - Elastic surface-wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic surface wave filter having a good insertion loss and a wide passing band width. SOLUTION: The elastic surface wave filter comprises one or more electrode groups, each comprising a plurality of IDT electrodes (2, 3 and 4) arranged in one row in the propagating direction of elastic surface wave between two reflector electrodes 7 and 7, arranged on a piezoelectric substrate 1. Average electrode-finger width from the central electrode finger of an arbitrary IDT electrode (e.g. 3) to the central electrode finger of an adjacent IDT electrode (e.g. 2) in the electrode group is set smaller than the average electrode finger width from an electrode finger located in the center of IDT electrodes (3 and 4) adjacent, respectively, to two reflector electrodes 7 and 7 and an electrode finger located at the end on the adjacent reflector electrode 7 side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a surface acoustic wave filter including a T electrode and a reflector electrode.

[0002]

2. Description of the Related Art In recent years, a surface acoustic wave filter has been used in various communication devices, and plays a role in miniaturization and no adjustment. As the frequency and function of communication devices increase, the demand for a wider surface acoustic wave filter has been increasing. For example, 900MH
As a filter for a z-band mobile phone, the effective pass bandwidth is 3
There is a demand for a high-performance broadband filter of 5 MHz or more (fractional bandwidth of about 3.7% or more). Note that the fractional bandwidth BR
Is BR = BW / fc (BW has an in-band insertion loss of 3 dB
And fc can be represented by the center frequency of the pass band when the in-band insertion loss is 3 dB.

[0003] In order to realize such a wide band, various methods have been conventionally proposed. For example, three IDs
T (Inter Digital Transduction)
r) Electrode (electrode in which a pair of comb-shaped electrodes are opposed to each other)
And a so-called double mode surface acoustic wave resonator filter using a first-order longitudinal mode and a third-order longitudinal mode is known.

FIG. 7 is a plan view showing such a surface acoustic wave filter. ID arranged on the piezoelectric substrate 101
The T electrode 102 applies an alternating electric field to a pair of opposing comb-toothed electrodes, and generates a surface acoustic wave (hereinafter, also referred to as SAW).
To excite. According to the principle, by applying an input signal to the IDT electrode 102, the excited SAW is positioned on both sides of the IDT electrode 102, and the ID for the output signal is output.
The SAW is propagated to the T electrodes 103 and 104, and is reflected by the reflector electrodes 107 located at both ends, and becomes a standing wave between the reflector electrodes 107 and 107. The modes of the standing wave include a primary mode and its higher-order (third-order) mode by three IDT electrodes. Since the pass characteristics can be obtained at the resonance frequencies generated in these modes, the pass band can be widened by controlling the interval between the resonance frequencies. In the drawing, 105 and 106 are portions between the IDT electrodes, 108 is a portion between the IDT electrode and the reflector electrode, 111 is an input signal terminal, 112 is an input ground terminal, and 113 and 115.
Is an output signal terminal, and 114 and 116 are output ground terminals.

Conventionally, frequency control between the modes is performed by:
All the IDT electrodes have the same pitch L, and the frequency between the modes is controlled by controlling the distance d between the center of the electrode fingers at the ends of the IDT electrodes located at the center and on both sides thereof (portion between the IDT electrodes). The way to do it was taken.
Further, the frequency is controlled by adding a capacitor to the IDT electrode for the output signal.

For this reason, in a conventional dual mode surface acoustic wave resonator filter, for example, LiTaO3 is used as a piezoelectric substrate.
When a single crystal substrate is used, the relative bandwidth (the value of the pass band width with respect to the center frequency) is about 0.40% (Japanese Patent Laid-Open No.
No. 231417), or only about 2% at most (see Japanese Patent Application Laid-Open No. 4-40705). Although 3.7% is realized with the maximum bandwidth (see Japanese Patent Application Laid-Open No. 7-58581), as described above, the ratio of the occupied bandwidth of the system is 3.7%. Since a filter needs to have a frequency corresponding to a temperature variation and a variation variation at the time of fabrication, there is a problem in application to a communication device such as a mobile phone which requires a wide pass band width.

In recent years, in order to reduce the size, weight, and cost of mobile communication devices and the like, the number of components used has been reduced, and it has been required to add new functions to surface acoustic wave filters. One of the demands is to be able to configure an unbalanced input-balanced output type or a balanced input-unbalanced output type. Here, the balanced input or balanced output means a signal that is input or output as a potential difference between two signal lines, and the signals on each signal line have the same amplitude and opposite phases. On the other hand, an unbalanced input or an unbalanced output means that a signal is input or output as a potential of one line with respect to a ground potential.

A conventional SAW filter is generally an unbalanced input-unbalanced output type SAW filter (hereinafter referred to as an unbalanced type SW filter).
Therefore, if circuits and electronic components connected to the subsequent stage of the SAW filter are of a balanced input type, an unbalanced-balanced converter (hereinafter referred to as a balun) is provided between the SAW filter and the subsequent stage. (Also referred to as "). Similarly, when the circuits and electronic components in the preceding stage of the SAW filter are of a balanced output type, the circuit configuration has a balun inserted between the preceding stage and the SAW filter.

At present, an unbalanced-to-balanced output type SAW filter or a balanced-to-unbalanced output type in which a SAW filter is provided with an unbalanced-balanced conversion function or a balanced-unbalanced conversion function in order to eliminate a balun. SAW filter
(Hereinafter referred to as a balanced SAW filter) is being put to practical use.

For example, SA of a plurality of IDT electrodes arranged side by side
In a resonator-type electrode pattern provided with a reflector for efficiently resonating the SAW at both ends of the W propagation path, the driving frequency and the pass band are increased to several hundred MHz to several GHz, and at the same time, the low frequency in the pass band is reduced. Although there is a demand for insertion loss and high attenuation outside the pass band, there is a problem that insertion loss is large. Although studies are being made to widen the pass band of the filter characteristic, in unbalanced input-balanced output or balanced input-unbalanced output,
The impedance on the balanced input / output side is, for example, 100Ω,
A surface acoustic wave filter other than the normal 50Ω such as 150Ω and 200Ω is required, and there has been no surface acoustic wave filter that can be suitably used without deteriorating the filter characteristics.

Therefore, the present invention provides good insertion loss,
It is an object of the present invention to provide a surface acoustic wave filter having a wide pass band, and an excellent surface acoustic wave filter which can operate as a balanced type, has good filter characteristics, and can function as a high quality balanced type surface acoustic wave filter. .

[0012]

In order to achieve the above object, a surface acoustic wave device according to the present invention comprises a plurality of IDT electrodes arranged in a line between two reflector electrodes on a piezoelectric substrate. And at least one electrode group located at the center of an arbitrary IDT electrode in the electrode group.
The average electrode finger width from the electrode finger located at the center of the electrode to the electrode located at the end of the adjacent reflector electrode from the electrode finger located at the center of the IDT electrode adjacent to each of the two reflector electrodes It is characterized in that it is smaller than the average electrode finger width up to the finger.

[0013] Further, at least three IDT electrodes are arranged between the two reflector electrodes, and an IDT electrode located at the center of the three IDT electrodes is used as an unbalanced input portion or an unbalanced output portion, and IDs located at both ends
The T electrode is a balanced output section or a balanced input section. Further, in such a structure, the following equation:
95 ≦ N1 / N2 ≦ 1.30, 11 ≦ N1
≤ 18 (where N1 is the logarithm of the IDT electrode located at the center, and N2 is the logarithm of the IDT electrodes located at both ends).

The IDT electrodes located at both ends may be used as an unbalanced input portion or an unbalanced output portion, and the IDT electrode located at the center may be used as a balanced output portion or a balanced input portion. Further, in such a configuration,
The following equation, 1.00 ≦ N1 / N2 ≦ 1.25, 12
≤ N1 ≤ 16 (where N1 is the logarithm of the IDT electrode located at the center and N2 is the logarithm of the IDT electrodes located at both ends).

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings schematically showing the embodiments.

FIG. 1 is a plan view of a surface acoustic wave filter according to the present invention. It is the same as arranging a plurality of IDT electrodes having a conventional structure and mounting reflector electrodes on both ends thereof. However, in the structure of the present invention, an electrode is provided between an arbitrary IDT electrode and an adjacent IDT electrode. The width of the finger and the space width thereof are reduced (the pitch L is reduced) to control the standing wave mode frequency. As shown in the figure, the pitch L is, from one electrode finger group (comb-shaped electrode) constituting the IDT electrode, from the line width center of an arbitrary electrode finger to the line width center of the next electrode finger. Means the distance.

That is, an electrode group in which a plurality of IDT electrodes (2, 3, 4) are arranged in a row in the direction of surface acoustic wave propagation between two reflector electrodes 7, 7 on the piezoelectric substrate 1. Are arranged, and the average electrode finger width from the electrode finger located at the center of an arbitrary IDT electrode (eg, 3) to the electrode finger located at the center of an adjacent IDT electrode (eg, 2) in this electrode group Is the ID adjacent to each of the two reflector electrodes 7
It is characterized in that it is smaller than the average electrode finger width from the electrode finger located at the center of the T electrode (3, 4) to the electrode finger located at the end of the adjacent reflector electrode 7 side. In the figure,
5 and 6 are portions between the IDT electrodes, 8 is a portion between the IDT electrode and the reflector electrode, 11 is an input signal terminal, 12 is an input ground terminal,
13 and 15 are output signal terminals, and 14 and 16 are output ground terminals. In addition, since the number of electrode fingers of the IDT electrodes 2, 3, 4 and the reflector electrode ranges from several to several hundred, their shapes are simplified. Hereinafter, in the drawings showing the surface acoustic wave filters, all of them are similarly simplified and shown.

Here, among the three IDT electrodes 2 to 4,
The IDT electrode 2 arranged at the center is an IDT electrode for unbalanced input or unbalanced output, and the IDT electrodes 3 and 4 arranged at both ends are IDT electrodes for balanced input or balanced output, respectively. If one of the pair of electrodes forming the output IDT electrode is output 1, the other is output 2 having the same amplitude and the opposite phase to output 1, and is balanced. Performs a type filter operation.

Conventionally, as shown in FIG. 7, a surface acoustic wave is propagated between IDT electrodes at a discontinuous gap d. However, by changing this to a continuous variable pitch as in the present invention. The loss due to the discontinuous gap can be reduced as much as possible, and the insertion loss can be improved.

Next, the optimum range for frequency control between modes will be described. By controlling the distance G (center distance between IDT electrodes) between the center positions of adjacent IDT electrodes in FIG. 1, the pass bandwidth can be controlled to the maximum. As the range, an equation of the IDT electrode center interval G = n · λ + ΔG (where n is a natural number, and λ is a constant pitch L in the IDT electrodes 3 and 4 on the reflector electrodes 7 and 7 side in FIG. 1). FIG. 2 shows the relationship between ΔG and the fractional bandwidth.

As shown in FIG. 2, the range where 3.7% or more of the conventional system bandwidth can be obtained is ΔG of 0.78.
It turns out that it is 〜0.84, which can be said to be a good range. Furthermore, since the required specific bandwidth is required to be 4.1% or more as the device temperature and manufacturing deviation, ΔG
It can be seen that the range of 0.785 to 0.82 is a more effective range.

The graph shown in FIG. 2 is a measurement result when a lithium tantalate single crystal is used as the piezoelectric substrate, but the same tendency is obtained with other substrate materials.

Next, modified examples of the electrode configuration of the present invention are shown in FIGS.
11 is shown. Each of them is based on the configuration of the IDT electrode shown in FIG. 1 and has two reflector electrodes 27, 27 (FIG. 1).
At 0, 11, at least three IDT electrodes 22, 23, 24 (27, 27 and 47, 47) (FIGS. 10, 11).
Now, the first IDT groups 22 to 24, the second IDT groups 42 to
44), the IDT electrode located at the center of these three IDT electrodes is used as an unbalanced input or unbalanced output, and the IDT electrodes located at both ends are used as a balanced output or a balanced input. It is characterized by the following.

For example, in the case of the surface acoustic wave filter shown in FIG. 8, IDT electrodes 22 to 24 are juxtaposed along the SAW propagation direction, and reflector electrodes 27 and 27 are arranged so as to sandwich these IDT electrodes 22 to 24. And a single-stage resonator-type electrode pattern. Also, the IDT located in the center
The electrode 22 is an unbalanced input or unbalanced output, and is connected to the unbalanced input / output terminal 31 and the ground terminal 34. Further, the IDT electrodes 23 and 24 located at both ends are used as a balanced output unit or a balanced input unit, and the IDT electrodes 2 and
4 to the first balanced input / output terminal 32 and the ground terminal 34,
The IDT electrode 23 located at the bottom of the figure is connected to the second balanced input / output terminal 33 and the ground terminal 34. According to the electrode pattern shown in FIG. 8, a single resonator pattern is provided, so that a low-loss filter characteristic can be obtained. Further, since the configuration is simple, the size can be reduced.

In the case of the surface acoustic wave filter shown in FIG. 9, three IDT electrodes are arranged in parallel in the SAW propagation direction as in FIG. 8, and reflector electrodes are arranged so as to sandwich the IDT electrode. An electrode pattern having a step configuration is provided, but the IDT electrodes 24 and 23 located at both ends are used as unbalanced input portions or unbalanced output portions, and the unbalanced input / output terminal 31 and the ground terminal 34 are provided.
, And the IDT electrode 22 located at the center is used as a balanced output portion or a balanced input portion, and the first balanced input / output terminal 32 and the second
Connected to balanced input / output terminal 33. The surface acoustic wave filter shown in FIG. 9 is advantageous in that low-loss filter characteristics can be obtained similarly to the surface acoustic wave device filter shown in FIG.

In the case of the surface acoustic wave filter shown in FIG. 10, three IDT electrodes are juxtaposed along the SAW propagation direction.
This is a two-stage electrode pattern called a resonator type in which reflector electrodes are arranged so as to sandwich an IDT electrode. In one resonator type electrode pattern, I
The DT electrodes 23 and 24 are unbalanced input portions or unbalanced output portions, and both IDT electrodes are connected to the unbalanced input / output terminal 31 and the ground terminal 34. And the ID located in the center
The T electrode 22 is connected to the ground electrode 34 and the IDT electrode 42 located at the center of the other resonator type electrode pattern. IDs located at both ends of the other resonator-type electrode pattern
T electrodes 43 and 44 are used as a balanced input section or a balanced output section,
The IDT electrode 44 located on the upper side of the figure is connected to the first balanced input / output terminal 32 and the ground terminal 34, and the IDT electrode 44 located on the lower side of the figure is connected.
The electrode 43 is connected to the second balanced input / output terminal 33 and the ground terminal. The IDT electrode 42 located at the center is connected to the ground electrode 34. Since the surface acoustic wave filter shown in FIG. 10 has two resonator patterns, it is particularly advantageous in that a filter characteristic having a high attenuation can be obtained.

In the case of the surface acoustic wave filter shown in FIG. 11, three IDT electrodes are used in the SAW filter as in the case of the filter shown in FIG.
A two-stage electrode pattern called a resonator type in which reflectors are arranged side by side along the propagation direction and a reflector is arranged so as to sandwich these IDT electrodes. The IDT electrode 22 located at the center of one of the resonator-type electrode patterns is used as an unbalanced input portion or an output portion, and is connected to the unbalanced input / output terminal 31 and the ground terminal. Then, the IDT electrodes 23 located at both ends,
24 is connected to a ground terminal 34 and IDT electrodes 43 and 44 located at both ends of the other resonator type electrode pattern. Also, the ID located at the center of the other resonator type electrode pattern
The T electrode 42 is a balanced input or a balanced output, and is connected to the first balanced input / output terminal 32 and the second balanced input / output terminal 33. The IDT electrodes 43 and 44 located at both ends are both connected to the ground electrode 34. The surface acoustic wave filter shown in FIG. 11 is also advantageous in that a filter characteristic having a high attenuation can be obtained because it has two resonator patterns.

The characteristics of the surface acoustic wave filters shown in FIGS. 8 to 11 are that the width of the electrode finger between the IDT electrodes and the width of the space between the IDT electrodes and the space width thereof are reduced to control the standing wave mode frequency. It is in. In other words, in the IDT electrode adjacent to the reflector electrode, the pitch of the adjacent IDT electrode is a fixed portion, but the electrode finger portion where the IDT electrodes are arranged is changed by changing the electrode finger width and the space width thereof. Inter-frequency can be controlled. Conventionally, surface acoustic waves are propagated through discontinuous gaps between IDT electrodes, but by making this a continuous variable pitch according to the present invention,
The loss due to the discontinuous gap can be reduced, and the insertion loss can be improved.

Further, according to the present invention, the filter characteristic is broadened and the VSWR is reduced (ratio for evaluating the magnitude of the reflected signal: Voltage Standing Wave R).
atio) to provide the optimum number of central IDT electrode pairs, the number of IDT electrode pairs at both ends, and the optimum film thickness. In other words, by changing the number of IDT electrode pairs, the excited SAW changes, and the combination of the logarithms of the central IDT electrode and the IDT electrodes at both ends makes it possible to realize a wider band and lower VSWR.

FIG. 12 shows the logarithmic ratio Ni / No of the logarithm Ni of the IDT electrode located at the center and the logarithm No of the IDT electrodes located at both ends in the surface acoustic wave filter of FIGS.
6 is a graph showing a change in a fractional bandwidth due to the above. To obtain a ratio bandwidth of 3.7% or more from this graph, Ni / No
It has been found that it must be ≦ 1.30.

FIG. 13 shows the logarithm N of the IDT electrode located at the center in the surface acoustic wave filter shown in FIGS.
Logarithmic ratio Ni of i and log No of IDT electrodes located at both ends
5 is a graph showing a change in VSWR according to / No. From this graph, it is 0.95 to reduce VSWR to 3.0 or less.
≦ Ni / No ≦ 1.30.

FIG. 14 shows the surface acoustic wave filter shown in FIGS.
FIG. 7 is a diagram showing a change in a fractional bandwidth due to the following. From this figure, it has been found that a condition of 11 ≦ Ni ≦ 18 is necessary to obtain a fractional bandwidth of 3.7% or more.

To summarize the above, the following equations (1) and (2)
If a filter that meets
A good filter having a VSWR of 3.0 or less can be obtained. 0.95 ≦ N1 / N2 ≦ 1.30 (1) 11 ≦ N1 ≦ 18 (2) Furthermore, when the IDT electrode is formed so as to satisfy the condition of Ni / No ≦ 1.25 from FIG. 4.2%
It has been found that the above characteristics are obtained, and that the filter is more excellent in quality. Also, from FIG. 13, 1.0 ≦ Ni / N
When an IDT electrode is formed so as to satisfy the condition of o ≦ 1.25, it has been found that a characteristic having a VSWR of 2.5 or less is obtained, and a filter having better quality is obtained. FIG.
It has been found that, when the IDT electrode is formed so as to satisfy the condition of 12 ≦ Ni ≦ 16, characteristics with a specific bandwidth of 4.2% or more are obtained, and the filter is more excellent in quality.

In summary, the following equations (3) and (4)
If a filter that satisfies is satisfied, the specific bandwidth is 4.2% or more,
A more excellent filter having a VSWR of 2.5 or less can be obtained. 1.00 ≦ N1 / N2 ≦ 1.25 (3) 12 ≦ N1 ≦ 16 (4) According to the surface acoustic wave filter having the IDT electrode structure satisfying the above conditions, the number of IDT electrode pairs is optimized. As a result, it is possible to manufacture a filter having excellent characteristics of the relative bandwidth and the ripple and having excellent quality.

In FIG. 1, the surface acoustic wave filter is composed of one section of resonator. However, the present invention is not limited to this. For example, a surface acoustic wave filter having two or more resonators connected in cascade or an IDT electrode may be used. The present invention can be applied to five or more surface acoustic wave filters. Also, the electrode structure of the surface acoustic wave filter of FIGS. 8 to 11 is not limited to this, and at least three IDT electrodes are arranged between two reflector electrodes, and the three IDT electrodes ID located at the center
As long as the T electrode is used as an unbalanced input or unbalanced output and the IDT electrodes located at both ends are used as a balanced output or a balanced input, a multistage configuration can be used.

As the piezoelectric substrate 1 for the SAW filter, 36 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal, 42 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal, 64 ° ± 3 ° Y Cut X propagation lithium niobate single crystal, 41 ° ± 3 ° Y cut X propagation lithium single crystal,
A 45 ° ± 3 ° X-cut Z-propagating lithium tetraborate single crystal is preferable as a piezoelectric substrate because it has a large electromechanical coupling coefficient and a small frequency temperature coefficient. The thickness of the piezoelectric substrate is preferably about 0.1 mm to 0.5 mm. If the thickness is less than 0.1 mm, the piezoelectric substrate becomes brittle. If the thickness exceeds 0.5 mm, the material cost and component dimensions increase, and the piezoelectric substrate cannot be used.

The IDT electrodes 2, 3, and 4 are made of Al or an Al alloy (Al—Cu, Al—Ti) and are formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. Electrode thickness is 0.1μm ~ 0.5μ
It is preferable to set it to about m in order to obtain characteristics as a SAW filter.

Further, the electrode of the SAW filter according to the present invention and the SAW propagation portion on the piezoelectric substrate are provided with Si, SiO 2,
SiNx and Al2O3 may be formed as a protective film to prevent conduction by a conductive foreign substance and improve power resistance.

[0039]

<Example 1> An example in which a surface acoustic wave filter according to the present invention is concretely manufactured will be described.

LiTaO3 propagated at 36 ° Y-cut X-direction
An Al (98w) as shown in FIG.
(t%)-Cu (2 wt%) to form a fine electrode pattern. For pattern production, a sputtering apparatus, a reduction projection exposure machine (stepper), and an RIE (React)
Photolithography was performed using an Ion Etching apparatus.

First, the substrate material was subjected to ultrasonic cleaning with acetone, IPA or the like to remove organic components. Next, after the substrate was sufficiently dried by a clean oven, an electrode was formed. A sputtering apparatus was used for forming the electrodes, and a material made of an Al-Cu alloy was used. At this time, the electrode film thickness was about 0.2 μm.

Next, a photoresist is spin-coated to a thickness of about 0.5 μm, patterned into a desired shape by a reduction projection exposure apparatus (stepper), and an unnecessary portion of the photoresist is dissolved with an alkali developing solution by a developing apparatus. After the desired pattern is exposed, RIE (Reacti
The patterning was completed by etching the electrode film with a Ve Ion Etching (Ve Ion Etching) apparatus to obtain an electrode pattern of a surface acoustic wave resonator constituting a ladder type surface acoustic wave filter.

Thereafter, a protective film was formed on a predetermined region of the electrode. That is, next, CVD (Chemical
By using a Vapor Deposition device, about 0.02 μm of SiO 2 was deposited on the electrode pattern and the piezoelectric substrate.
m was formed. Thereafter, the photoresist was patterned by photolithography, and the window opening for wire bonding was etched by an RIE apparatus or the like to complete a protective film pattern.

Next, the substrate was diced along dicing lines, and divided into chips. Then, each chip was picked up by a die bonding apparatus and bonded in a package using a resin containing a silicone resin as a main component. Thereafter, drying and curing were performed at a temperature of about 160 ° C. The package used was a 3 mm square laminated structure.

Next, a 30 μm φ Au wire was ball-bonded on the electrode portion of the package and the Al electrode pad on the chip, and then the lid was covered on the package, and the package was welded and sealed with a sealing machine to complete a surface acoustic wave filter. . In addition,
The ground electrodes on the chip were separately wired and bonded to the ground electrodes on the package by Au ball bonding.

The surface acoustic wave resonator constituting the ladder type surface acoustic wave filter has 5 to 25 comb electrodes and a cross width of 15 to 150 λ, and the line width varies between the IDT electrodes. However, the line width was set to approximately 1 μm. The number of reflector electrodes was 100.

FIG. 3 shows the measurement results of the transmission amount in this embodiment.
Shown in Please tell us about the measurement conditions (including the number of samples, etc.) and the measuring equipment (model number). A signal of 0 dBm is input and the frequency is 842.5 MHz to 1042.5 MHz.
The measurement was performed under the conditions of z, the number of measurement points: 801 points, the frequency of 10 MHz to 6 GHz, and the number of measurement points: 401 points. The number of samples was 30, and the measuring instrument used was a network analyzer 8753D manufactured by Agilent Technologies. Here, ΔG is an electrical characteristic at 0.81, and good electrical characteristics with a minimum insertion loss of 1.7 dB and a specific bandwidth of 4.7% were obtained. On the other hand, FIGS. 4 to 6 are electric characteristic diagrams when ΔG is 0.62, 0.90, and 1.00, and good characteristics were not obtained.

Example 2 First, a SAW device having a center frequency in a 900 MHz band was manufactured. It was fabricated by forming an electrode pattern having the structure shown in FIG. 11 on a piezoelectric substrate made of lithium tantalate single crystal propagating in the 36 ° Y-cut X direction.

First, an electrode made of an Al—Cu alloy was formed on the cleaned substrate by sputtering in the same manner as in Example 1. The film thickness was about 0.3 μm.

Next, a photoresist was applied to a thickness of about 1 μm and baked in a nitrogen (N 2) atmosphere. Next, a large number of resist positive patterns of a SAW filter were formed on the substrate by a photolithography method using a reduction projection exposure apparatus using ultraviolet rays. Minimum line width is about 1.0μm
And Next, dry etching was performed using an RIE apparatus to form an electrode pattern.

Next, CVD (Chemical Vap)
or Deposition apparatus, about 0.02 μm of SiO 2 was formed on the electrode pattern and the piezoelectric substrate. Next, a resist was applied to a thickness of about 1 μm and baked in an N 2 atmosphere. Next, a resist pattern was formed so that a protective film of SiO2 on the SAW resonator could be formed by a photolithography method using a reduction projection exposure apparatus using ultraviolet rays. Next, dry etching was performed by an RIE apparatus to form a protective film pattern of SiO2.
Next, an Al thin film of about 0.6 μm was formed by a sputtering method on the electrode pattern for bump formation connecting the electrode pattern and the electrode terminal of the package. Next, the resist applied at the time of forming the SiO2 protective film and unnecessary electrodes were simultaneously removed by a lift-off method to form an electrode pattern having a desired shape.

Next, Au bumps were formed on the bump forming electrode patterns by a bump forming apparatus. Next, the SAW elements were individually cut out by dicing. next,
S individually cut out from a 2.5 × 2.0 mm square ceramic package by a flip chip bonding apparatus
One AW element is adhered in a ceramic package, and N
Baking was performed in two atmospheres. Next, the package was covered with a metal cap by a sealing device to seal the inside of the package, thereby producing a surface acoustic wave filter.

Thereafter, the surface acoustic wave filter was connected to the same network analyzer as in Example 1, and the frequency characteristics of insertion loss were measured. 0dBm signal is input and the frequency 84
2.5MHz to 1042.5MHz, number of measurement points:
801 point conditions and frequency 10MHz to 6GH
z, number of measurement points: Measured under the conditions of 401 points. The number of samples was 30, and the measuring instrument was a network analyzer 8753D manufactured by Agilent Technologies. FIG. 15 shows a frequency characteristic graph near the pass band. It was confirmed that the filter characteristics of the product of the present invention were very wide and about 5 MHz larger than the conventional one. It was confirmed that the VSWR was about 0.5 smaller than the conventional one. That is, the bandwidth is 42 MHz, and the VSWR is 2.4.
Met. Further, as shown in FIG. 16, good amplitude balance and phase balance characteristics were obtained.

The results show that the filter characteristic of the present invention has a pass band width of about 10 to 15% as compared with the conventional filter,
Was improved by 14% to 18%.

[0055]

As described above, the surface acoustic wave filter according to the present invention has a structure in which the electrode group located on the center of an arbitrary IDT electrode in an electrode group disposed on a piezoelectric substrate is located at a position adjacent to an electrode finger located at the center.
The average electrode finger width from the electrode finger located at the center of the DT electrode to the electrode located at the end of the adjacent reflector electrode from the electrode finger located at the center of the IDT electrode adjacent to each of the two reflector electrodes Since it is smaller than the average electrode finger width up to the finger, it is possible to obtain a surface acoustic wave device filter having a wide pass band. Further, it is possible to reduce the loss due to the conventional discontinuous gap, and to provide an excellent surface acoustic wave filter with improved insertion loss.

Further, at least three IDT electrodes are arranged between the two reflector electrodes, and the three IDT electrodes are arranged.
The IDT electrode located at the center of the DT electrodes is used as an unbalanced input portion or an unbalanced output portion, and the IDT electrodes located at both ends are used.
Since the electrode is a balanced output section or a balanced input section and the configuration of the IDT electrode is optimized, a surface acoustic wave filter which can operate as a balanced type and has excellent characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a configuration example of a surface acoustic wave filter according to the present invention.

FIG. 2 is a diagram showing a correlation between an IDT electrode center interval ΔG and a fractional bandwidth of the surface acoustic wave filter according to the present invention.

FIG. 3 shows an optimum ΔG of the surface acoustic wave filter according to the present invention.
It is an electrical characteristic figure in the range of.

FIG. 4 is an electrical characteristic diagram outside an optimum ΔG range.

FIG. 5 is an electrical characteristic diagram outside the range of the optimum ΔG.

FIG. 6 is an electrical characteristic diagram outside the range of the optimum ΔG.

FIG. 7 is a plan view showing a configuration example of a conventional surface acoustic wave filter.

FIG. 8 is a schematic electrode configuration diagram of a one-stage SAW filter according to the present invention.

FIG. 9 is a schematic electrode configuration diagram of a one-stage SAW filter according to the present invention.

FIG. 10 is a schematic electrode configuration diagram of a two-stage connected SAW filter according to the present invention.

FIG. 11 is a schematic electrode configuration diagram of a two-stage connected SAW filter according to the present invention.

FIG. 12 is a graph showing the relationship between the logarithmic ratio Ni / No and the relative bandwidth.

FIG. 13 is a graph showing the relationship between logarithmic ratio Ni / No and VSWR.

FIG. 14 is a graph showing a relationship between a logarithmic Ni and a fractional bandwidth.

FIG. 15 is a graph showing frequency characteristics near a pass band in the SAW filter of the present invention.

FIG. 16 is a graph showing amplitude and phase balance characteristics near a pass band in the SAW filter of the present invention.

[Explanation of symbols]

1: Piezoelectric substrate 2, 3, 4, 22, 23, 24, 42, 43, 44:
IDT electrodes 5, 6: IDT electrode portion 7, 27, 47: Reflector electrode 8: IDT electrode and reflector electrode portion 11: Input signal terminal 12: Input ground terminal 13, 15: Output signal terminal 14, 16: Output ground terminal 31: Unbalanced input / output terminal 32: First balanced input / output terminal 33: Second balanced input / output terminal 34: Ground terminal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shigehiko Nagamine 3-5-3 Kodai, Seika-cho, Soraku-gun, Kyoto F-term in Kyocera Corporation Central Research Laboratory 5J097 AA01 AA06 AA12 AA19 BB14 CC03 CC08 DD04 DD13 DD29 FF01 FF03 GG01 GG03 GG04 GG05 HA02 KK04

Claims (5)

[Claims] 1. One or more electrode groups each including a plurality of IDT electrodes arranged in a line between two reflector electrodes on a piezoelectric substrate, and a center of an arbitrary IDT electrode in the electrode group. The average electrode finger width from the electrode finger located at the center of the adjacent IDT electrode to the electrode finger located at the center of the adjacent IDT electrode is determined by calculating the average electrode finger width from the electrode finger located at the center of the IDT electrode adjacent to each of the two reflector electrodes A surface acoustic wave filter characterized by being smaller than an average electrode finger width up to an electrode finger located at an end on the electrode side. 2. An electrode group comprising: at least three IDT electrodes disposed between two reflector electrodes; and a centrally located IDT electrode among the three IDT electrodes is connected to an unbalanced input portion or an unbalanced output. 2. A surface acoustic wave filter according to claim 1, wherein the IDT electrodes located at both ends are a balanced output section or a balanced input section. 3. The surface acoustic wave filter according to claim 2, wherein the following expressions (1) and (2) are satisfied. 0.95 ≦ N1 / N2 ≦ 1.30 (1) 11 ≦ N1 ≦ 18 (2) (where N1 is the number of IDT electrodes located at the center, N
2 is the number of IDT electrodes located at both ends) 4. An IDT electrode located at both ends is an unbalanced input or unbalanced output, and the IDT electrode located at the center is a balanced output or a balanced input. 3. The surface acoustic wave filter according to 1. 5. The surface acoustic wave filter according to claim 2, wherein the following expressions (3) and (4) are satisfied. 1.00 ≦ N1 / N2 ≦ 1.25 (3) 12 ≦ N1 ≦ 16 (4) (where N1 is the number of IDT electrodes located at the center, N
2 is the number of IDT electrodes located at both ends)