JPH10163804A - Wide band dual mode piezoelectric filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric filter which has a wide pass band range and can suppress the spurious on the higher frequency side by forming integrally a vibration part of an extra-thin plate and a thick circular surrounding part which holds the vibration part at its periphery and placing two electrodes on both vibration and surrounding parts with a prescribed space set between them together with the specific size and shape set for the vibration part. SOLUTION: A piezoelectric substrate 1 includes a vibration part 2 of a very thin plate which is formed by the photoetching and a thick circular surrounding part 3 which is formed integrally with the part 2 at its periphery. Then two electrodes 4a and 4b having width W and length L are provided on the upper surface of the substrate 1 with a space (g) set between both electrodes, and an electrode 5 is deposited on an entire rear surface of the substrate 1. The lead wires 6 are led from the electrodes 4a and 4b toward their peripheral thick end parts, and the electrode 5 serves as a lead electrode at the recess side. When the dimensions of the part 2 is set at A=(A1+A2)/2 in its electrode placing direction and at B in the vertical direction respectively, A/(2W+g) is set at 1.4 to 1.8 with B/L set at 1.3 to 1.7 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dual mode piezoelectric filter (hereinafter, referred to as MCF) frequently used in portable radio equipment and the like, and more particularly to an ultra-thin filter which suppresses spurious components generated near the high frequency side of the pass band of a wide band MCF. It relates to a plate MCF.

[0002]

2. Description of the Related Art Ultra-thin plate MCFs are widely used in wireless devices such as mobile phones because of their excellent features such as miniaturization, low loss and impact resistance. FIG. 4A shows a conventional ultra-thin plate M
FIG. 2B is a plan view of the CF element, and FIG. A
Using a photo-etching means, a T-cut quartz substrate is integrally formed with a vibrating portion 12 of an ultra-thin plate and a thick annular surrounding portion 13 for holding the vibrating portion 12 therearound.
And the electrodes 14a, 1a are separated by a gap g on the plane side of the substrate.
4b is disposed, and an electrode 15 is attached to the entire surface of the recessed portion by vapor deposition or the like. Lead electrodes 16a and 16b extend from the electrodes 14a and 14b toward the peripheral thick ends, and the entire surface electrode 15 also serves as a lead electrode on the concave side.

[0003] An ultra-thin MCF is constructed using two modes, a first mode and a second mode, resulting from acoustic coupling between two pairs of electrodes 14a, 15 and 14b, 15. As is well known, the pass band width of the ultra-thin plate MCF is almost twice the difference between the resonance frequencies of the primary mode and the secondary mode. The degree of coupling between the two modes, that is, the difference between the resonance frequencies of the two modes, depends on the elastic constant of the piezoelectric substrate 11, the electrode shape, the electrode thickness, and the gap g between the two pairs of electrodes. The pass bandwidth of the filter is widened.

In general, in an ultra-thin MCF using an AT-cut quartz substrate, the cutting angle of the quartz substrate 11 is determined from desired temperature characteristics of the filter, and as a result, the elastic constant of the quartz substrate 11 is necessarily determined. . Further, since the shape of the electrode of the ultra-thin plate MCF is determined from the desired termination condition, only the film thickness of the electrode and the gap g between the two pairs of electrodes are the parameters that influence the degree of coupling between the two modes. In the means for reducing the film thickness of the electrode as a method of expanding the bandwidth of the ultra-thin MCF, if the film thickness is too small, the two vibration modes do not sufficiently confine to the electrode portion, and a part of the vibration energy is reduced. Leakage to the periphery degrades the Q value of the two modes, increasing the insertion loss of the filter. Therefore, the thickness of the electrode needs to be a thickness that keeps the insertion loss of the filter to a minimum and suppresses spurious near the passband, and thus the thickness of the electrode is limited. Therefore, as a means for determining the pass band width of the ultra-thin plate MCF, it is general to adjust the electrode gap g.

[0005]

However, when an attempt is made to widen the band by using an ultra-thin MCF, spurs occur,
There is a defect that desired attenuation region characteristics cannot be obtained. Here, the coordinate axis of FIG. 4A is taken as shown in the lower left corner of the figure, and in the vibrating section 12 of the quartz substrate 11, the dimension of the upper end of the vibrating section 12 in the Z′-axis direction in the figure is A1, and the lower side in the figure is A1. Assuming that the size of the end in the Z′-axis direction is A2, the size A of the center of the substrate 11 in the Z′-axis direction is A = (A1 + A2) / 2. Further, the dimension of the vibrating part 12 in the X-axis direction is B. The dimension W ′ in the Z′-axis direction of the electrodes 14 a and 14 b and the gap g arranged in the vibrating section 12 is W ′ = (2W + g),
Let L be the dimension of the a and b in the X-axis direction. For example, FIG.
7 shows an example of the filtering characteristics of an ultra-thin plate MCF prototyped under the conditions of a center frequency of 71 MHz, a pass band width of 3 dB ± 80 kHz used for GSM and the like. Here, the vibration area dimension A = 1.3 m
m, B = 1.0 mm, electrode dimension W '= 0.684 mm
(W = 0.32 mm, g = 0.044 mm), L = 0.
54 mm, electrode thickness 1000 Å (angstrom)
And the dimensional ratio of the width W ′ of the electrode part to the width A of the vibration part 12 is A / W ′ = 1.9, and the length L of the electrode part in the X-axis direction and the length B of the vibration part 2 are The dimensional ratio is B / L = 1.85.
In GSM applications, the need for spurious suppression is f ₀ + 400k
20 dB in the frequency range from Hz to +600 kHz,
f ₀ is 30 dB in the frequency range of +600 kHz to +800 kHz, whereas the ultra-thin MC
In F, spurious components S1, S2, S3, etc. are generated as shown in FIG. 5, and the spurious components cannot be satisfied at the above-mentioned respective frequency ranges of 10 dB and 20 dB.

In order to suppress spurious (increase the amount of spurious attenuation), generally, the electrode area of the MCF is increased, the impedance of the filter is reduced, and the impedance ratio of the termination impedance to the inharmonic mode is increased to increase the spurious. How to increase the amount of attenuation,
There is a means for reducing the thickness of the electrode to prevent the inharmonic mode from being confined under the electrode. However, the former is disadvantageous in terms of miniaturization, and the latter has an Al electrode thickness of 500 to 500 because Al bonding is performed for connection with a package. If the angle is less than 600Å (angstrom), there is a problem in the bonding strength.
There is a problem to put it to practical use.

However, since the terminal impedance of the ultra-thin plate MCF is proportional to the bandwidth, the specific bandwidth is 0.1%.
In order to increase the bandwidth as described above, the input / output terminal impedance becomes as large as several kΩ. On the other hand, the amount of spurious attenuation due to the inharmonic mode is approximately determined by the ratio between the terminal impedance and the impedance in the inharmonic mode. In the ultra-thin MCF, the impedance of the inharmonic mode is almost determined by the shape of the electrode and its film thickness. Therefore, unless the conditions are changed, the impedance becomes almost the same. Therefore, when the ultra-thin MCF is terminated with high impedance, the spurious attenuation is reduced. The amount is smaller. As described above, in the case of the ultra-thin plate MCF having a high impedance termination, there is no spurious suppression means, which is a big problem. SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional multi-mode piezoelectric filter, and provides an ultra-thin plate MCF having a wide pass bandwidth and suppressing spurious components generated on a high frequency side. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a vibrating portion of an ultra-thin plate and a thick annular surrounding portion for holding the vibrating portion around the vibrating portion. In a dual-mode piezoelectric filter in which two electrodes having a width W and a length L are arranged on the upper surface of a piezoelectric substrate integrally formed with a gap g and all electrodes are attached to the back surface, When the dimension in the electrode arrangement direction is A at the center of the portion and the dimension in the vertical direction is B, A / (2W + g) is from 1.4 to 1.
8, a broadband double mode piezoelectric filter characterized by selecting B / L in the range of 1.3 to 1.7 to suppress spurious. According to a second aspect of the present invention, there is provided a double mode piezoelectric filter in which the double mode piezoelectric filter according to the first aspect is cascaded in multiple stages.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 (a) is a schematic plan view showing an embodiment of a wide band ultra-thin sheet MCF according to the present invention. A thick annular surrounding portion 3 for holding the vibrating portion is integrally formed in the periphery, the electrodes 4a and 4b are arranged with a gap g on the plane side of the substrate, and the electrode 5 is deposited on the entire surface of the concave portion. Adhere with etc. Lead electrodes 6, 6 extend from the electrodes 4a, 4b toward the peripheral thick ends, and the entire surface electrode 5 also serves as a lead electrode on the concave side. FIG. 1B is a cross-sectional view taken along the line ZZ ′ of FIG. 1A, and shows the structure of the plane side, the electrodes 4a and 4b, the concave side, and the entire surface electrode 5.

In FIG. 1A, a vibrating part 2 of a piezoelectric substrate 1 is shown.
Primary mode, secondary mode, and tertiary mode having a substantially sinusoidal or cosine-shaped displacement intensity distribution along the Z'-axis direction (electrode arrangement direction) by the two electrodes 4a, 4b and the electrode 5 provided above. A standing wave such as a mode is excited. In addition, even in the X-axis direction, standing waves of odd-numbered modes such as a first-order resonance mode, a third-order mode, and a fifth-order mode having a substantially sinusoidal or cosine-wave displacement intensity distribution are generated. The reason that the even-order mode is not excited in the X-axis direction is that the generated charges in the even-order resonance mode are offset by the electrode arrangement in the X-axis direction. For ultra-thin MCF, Z '
Since it is configured using two resonance modes in which the displacement in the axial direction is primary and secondary, respectively, and the displacement in the X-axis direction is primary, the other higher-order modes are the inharmonic mode. These are collectively referred to as unnecessary modes, which cause the appearance of the spurs S1, S2, S3, and the like.

In FIG. 5, a spurious component S1 closest to the center frequency is a tertiary mode excited along the Z'-axis direction, a primary resonance mode in the X-axis direction, and spurious components S2 and S3 are Higher-order modes excited along the X-axis direction are assumed to be primary and secondary modes excited along the Z′-axis direction, respectively, and are assumed to be tertiary resonance modes in the X-axis direction. The vibrating unit 2 for suppressing spurious S2 and S3 based on the inharmonic mode
Various experiments were performed using the dimension B in the X-axis direction as a parameter. The reason is that the displacement distribution of the third-order inharmonic mode excited along the X-axis direction is smaller in the X-axis direction than the displacement of the two main vibrations (primary in the X-axis direction) used for the ultra-thin MCF. Since the displacement is distributed further along the outer side, the vibrating portion does not affect the main vibration, substantially affects only the foot portion of the vibration displacement distribution of the third-order inharmonic mode, and has a large resonance impedance. 2 structure. In other words, only the two main vibration modes are set to the energy confinement mode, and the tertiary inharmonic mode is not set to the confinement mode, but the vibration energy of these modes is leaked to the periphery to increase the impedance of the inharmonic mode. Is a means for suppressing spurious.

FIG. 3A is a graph showing the results of an example of an experiment conducted under various conditions. The standardized dimension A / W ′ in the Z′-axis direction is set to a constant value of 1.9, and Is standardized by the electrode dimension L in the X-axis direction to be B / L, and when the B / L is changed, the spurs S1, S2
And changes in insertion loss. It can be seen that the spurious S2, which is the tertiary mode in the X-axis direction, is affected by the dimension in the X-direction, and that the smaller the B / L, the greater the spurious attenuation. FIG. 3A shows that B / L is 1.3.
In the range of ~ 1.7, the two main vibrations are in the confinement mode, so that the insertion loss is small.
The next mode does not become the confinement mode sufficiently, and a part of the vibration energy leaks to the peripheral part. Therefore, since the resonance impedance of the mode increases, the spurious S2 can be suppressed. If the dimension in the X-axis direction is too small, the two main vibration modes are not confined and Q
Values will degrade, which will significantly increase the insertion loss value. Therefore, it is desirable that B / L be 1.3 or more.

Next, the spurious S1 appearing in the tertiary inharmonic mode in the Z 'axis direction is
By reducing the central dimension A in the direction, it is possible to suppress for the same reason as described above. That is, only the two main vibrations are in the energy confined state, and the third-order inharmonic mode excited along the Z′-axis direction is not the confined mode, but the vibration energy is leaked to the peripheral portion, so that The spurious S1 is suppressed by increasing the resonance impedance. FIG. 3B is a graph showing the results of an example of an experiment performed under various conditions.
When L is a constant value of 1.48, the dimension A in the Z′-axis direction of the vibrating part 2 is standardized by the electrode part dimension W ′ = (2W + g) to be A / W ′, and the A / W ′ is changed. FIG. 5 illustrates spurs S1 and S2 and insertion loss when the operation is performed.
As is clear from the figure, the value of A / W 'is 1.4 to
In the case of the range of 1.8, the two main vibrations are sufficiently in the confinement mode, but the spurious S1 is not in the confinement mode in the vibrating part 2, and the vibration energy leaks to the peripheral portion, and the spurious S1 is removed. It becomes possible to suppress.

FIG. 2 shows an example of the filtering characteristics of an ultra-thin MCF having a center frequency of 71 MHz, a 3 dB pass band width of ± 80 kHz, and constructed according to the present invention. Assuming that the center dimension of the vibrating part 2 in the Z′-axis direction is A = 1.1 mm and the dimension of the vibrating part 2 in the X-axis direction is B = 0.80 mm, the standardized dimension of the electrode part versus the vibrating part is A / W. '= 1.61, and the ratio of the electrode dimension to the vibrating portion in the X-axis direction is B / L = 1.48, which are values within the range of the present invention. The electrode film thickness and electrode dimensions are the same as the parameters in the case of FIG. As apparent from FIG. 2 f ₀ +
20d in the frequency range of 400kHz to + 600kHz
B, f ₀ The requirement of 30 dB is satisfied in the frequency range of +600 kHz to +800 kHz.

Further, an ultra-thin sheet MC constructed using the present invention
Needless to say, an ultra-thin plate MCF having a steeper attenuation characteristic can be formed by cascade-connecting a plurality of Fs. Further, it is obvious that the present invention can be applied to a piezoelectric substrate other than a quartz substrate, for example, a piezoelectric substrate such as LITaO3, LiNbO3, LBO, and langasite.

[0016]

As described above, the present invention is constructed as described above, so that the conventional means can reduce the thickness of the ultrathin plate M having a pass band width of 0.1% or more.
When manufacturing CF, spurious on the high frequency side could not be suppressed. However, by appropriately setting the vibration part dimensions of the ultra-thin quartz substrate according to the present invention, the resonance impedance of unnecessary inharmonic mode was increased. By doing so, it is possible to suppress spurious due to higher-order inharmonic modes near the passband, and to realize an ultra-thin sheet MCF improved by 5 to 10 dB or more compared to the conventional ultra-thin sheet MCF, It has a remarkable effect when used in portable radios.

[Brief description of the drawings]

FIG. 1 (a) is an ultra-thin MCF showing one embodiment of the present invention.
FIG. 2B is a schematic view showing the configuration of the piezoelectric substrate and the electrodes, and FIG. 2B is a cross-sectional view taken along the line CC ′ in FIG.

FIG. 2 shows a filtering characteristic of an embodiment according to the present invention.

3A is a diagram showing spurious emissions S1 and S2 when the dimension in the X-axis direction is used as a parameter and the amount of attenuation of insertion loss. FIG. 3B is a diagram showing spurious noise when the dimension in the Z′-axis direction is used as a parameter. It is a figure which shows S1, S2, and the attenuation of insertion loss.

FIG. 4A is a plan view of a conventional ultra-thin sheet MCF, and FIG.
FIG. 4 is a cross-sectional view taken along the line CC ′ in FIG.

FIG. 5 is a diagram showing the filtering characteristics of a conventional ultra-thin plate MCF.

[Explanation of symbols]

 1. Piezoelectric substrate 2. Vibrating part 3. Annular surrounding part 4a, 4b. Electrode 5. Full-surface electrode 6. Lead electrode 7. Electrode for bonding pad A1, A2, B. Vibrating part dimensions W ..Electrode width L..Electrode length g..Gap Z, Z '.. Cutting line

Claims (2)

[Claims] 1. An electrode having a width W and a length L on an upper surface of a piezoelectric substrate integrally formed with a vibrating portion of an ultra-thin plate and a thick annular surrounding portion for holding the vibrating portion around the vibrating portion. Are arranged with a gap g, and the entire surface of the electrode is attached to the back surface. In a dual mode piezoelectric filter, the dimension in the electrode arrangement direction at the center of the vibrating portion is A, and the dimension in the vertical direction is B. ,
A / (2W + g) is 1.4 to 1.8, and B / L is 1.3.
A broadband dual-mode piezoelectric filter selected from the range of 1.7 to 1.7 to suppress spurious. 2. A wide-band double-mode piezoelectric filter comprising the double-mode piezoelectric filter according to claim 1 connected in multiple stages.