JPH1079640A - Piezoelectric device, its manufacture and mobile communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy confinement type piezoelectric device suppressive in undesired spurious radiation, lower in impedance and capable of coping with higher frequency by suppressing reflection of vibration at the end of an electrode and conforming thickness vibration by a projection substantially provided in a piezoelectric substrate thereby making possible free electrode design with less restriction and selection of a wider electrode material and to provide the method for manufacturing the device easily. SOLUTION: Projections 4a, 4b, 4c, 4d are provided in a piezoelectric substrate 1, upper destinations are divided into excitation electrodes 2a, 2b and a dummy electrode 2c, a very small interval is provided between respective split electrodes and the electrodes are insulated electrically. Thus, reflection is not almost caused to the thickness vibration and the confinement of the vibration energy of the thickness vibration is conducted substantially by the projections provided to the piezoelectric substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric device which can be used for an energy trapped thickness resonant piezoelectric device such as a piezoelectric resonator used for high frequency clock generation and a multi-mode piezoelectric filter used for high frequency signal processing. And a method of manufacturing the same, and a mobile communication device using the same.

[0002]

2. Description of the Related Art In recent years, the processing speed and data transfer speed of information devices such as computers and their peripheral devices have been remarkably increased, and accordingly, generation of a high-frequency clock is required. A high-frequency clock generation uses an energy-trapping type of oscillator, typified by a crystal oscillator, and a high-frequency oscillator is required. When a high frequency stability is required for a change due to an environmental temperature or a change with time, an AT-cut quartz crystal is exclusively used as a piezoelectric body. AT-cut quartz oscillator
It has excellent temperature stability on the order of ppm. When frequency stability is not required, an energy trap type vibrator made of piezoelectric ceramic is used.

[0003] Regarding an energy trap type vibrator,
This will be described with reference to FIGS. 10 (A) to 10 (D).
10A is a top view, FIG. 10B is a cross-sectional view, and FIG.
(C) is an amplitude distribution diagram of a substitute confined thickness resonance mode. A piezoelectric substrate 51 and excitation electrodes 52 and 5 formed on the front and back surfaces thereof in a range narrower than the piezoelectric substrate.
3. For the theory of energy confinement, see Elastic Wave Device Technology Handbook, pp. 82-89 (edited by the 150th Committee of the JSPS Acoustic Wave Device Technology, 1991).
Issued by Ohm on November 30, 2008). The propagation of the thickness vibration along the plate surface of the thickness vibration
The energy of the vibration mode that satisfies the conditions of propagation and attenuation at the surrounding electrodeless portion 55 is confined in the excitation electrode portion 54. Since the vibration does not propagate to the end face of the piezoelectric substrate 51, it is possible to easily hold the piezoelectric substrate 51 in the package at the end face. Since vibration energy does not leak to the holding unit, a high Q value can be realized, and there is an advantage that the effect of holding on the characteristics is small. The difference between the propagation constants of the excitation electrode portion 54 and the non-electrode portion 55 is due to both effects of (1) a decrease in cutoff frequency due to a mass load such as an electrode and (2) a decrease in cutoff frequency of the electrode portion due to a piezoelectric effect. Done by In the case of a piezoelectric substrate having a small electromechanical coupling coefficient such as a thickness shear resonator of an AT-cut quartz crystal, energy is confined mainly by the mass load of the excitation electrode provided, and in a piezoelectric ceramic having a large electromechanical coupling coefficient,
The piezoelectric effect exerts an overwhelmingly large confinement effect.

FIG. 10D is a frequency chart of a typical resonance mode in the case where the thickness vibration propagates above the cutoff frequency with the cutoff frequency as a boundary. The vertical axis represents the frequency, fc is the cutoff frequency of the non-electrode portion, and fc 'is the cutoff frequency of the electrode portion. The horizontal axis represents the degree of energy confinement. The excitation electrode length (L / H) standardized by the thickness H of the piezoelectric body and the standardized frequency decrease amount Δ = (fc−fc ′) / It is a value represented by fc. The curves in the chart show the transition of the frequency of each resonance mode according to the degree of energy confinement. S0 and A0 are the fundamental resonances of the symmetric and oblique modes, and Sn and An (where n is the thickness resonance order and n> 1) represent the higher modes of the symmetric and oblique symmetry. . In the electromechanical coupling in the obliquely symmetric mode, the integrated value over the entire surface of the excitation electrode becomes zero, so that the vibrator having a symmetric configuration is not electrically excited. In other words, in the case of a vibrator having a symmetric excitation electrode pattern, the obliquely symmetric mode is not excited. This is because the electromechanical coupling on the entire excitation section is completely canceled. Vibrator with broken symmetry,
In the case of a filter described later, an oblique symmetric mode is excited.

[0005] Here, consider the conditions under which each vibration mode is confined. The thickness vibration having a frequency lower than the cutoff frequency of both the electrode portion and the non-electrode portion cannot be propagated in the electrode portion or the non-electrode portion, and thus cannot be confined. Further, the thickness vibration having a frequency higher than the cutoff frequency of both the electrode portion and the non-electrode portion propagates through both the electrode portion and the non-electrode portion, and is not confined. Therefore, only when the frequency of the thickness vibration is lower than the cut-off frequency of the non-electrode portion and higher than the cut-off frequency of the electrode portion, the vibration is confined in the electrode portion and resonance appears.

For example, when the confinement amount is A in the figure, S
0 is confined and resonates, but S1 is higher than the cut-off frequency of the non-electrode portion and propagates to the non-electrode portion, so it is not confined and does not resonate. When the amount of confinement is increased to B,
Not only S0 but also S1 and S2 are confined and resonate. That is, if the confinement amount is an appropriate value such as A, the main resonance is only S0, and an excellent vibrator without unnecessary resonance and spurious can be obtained. On the other hand, if the amount of confinement is further increased by increasing the amount of frequency drop or increasing the electrode length, spurious resonance, which is unnecessary resonance, appears. The spurious causes a frequency jump and unstable operation in the clock oscillator. Therefore, it is necessary to select the amount of frequency reduction and the electrode length so as to suppress the spurious.

[0007] Next, with the spread of personal mobile communication devices such as mobile phones and pagers in recent years, energy trap type piezoelectric filters have been in increasing demand. Surface acoustic wave filters, dielectric filters,
The 1st-IF has a surface acoustic wave filter and a crystal filter,
The 2nd-IF uses a multi-stage filter such as a ceramic filter. Among these, the energy trapping type multi-mode piezoelectric filter is a part of a crystal filter and a ceramic filter.To construct a system with as few stages as possible, each filter must have a high channel selectivity and a manufacturing method with stable characteristics. Desired. Also,
Due to the rapid increase of subscribers such as mobile phones, the number of channels becomes insufficient, and higher RF frequencies will be used.
Along with this, IF filters having higher frequencies are required.

Here, a quartz crystal MCF (monolithic crystal filter) will be described as an example of a conventional energy trap type multi-mode piezoelectric filter with reference to FIG. An input electrode 92a and an output electrode 92 divided into two on the front side using AT-cut quartz as the piezoelectric substrate 91.
The common ground electrode 93 is provided on the back surface corresponding to the input / output electrodes 92a and 92b. The crystal substrate 91 is fixed to pins 95a, 95b, and 95c provided on a base 94 of the can package with a conductive paste 96, and input / output and ground electrodes are drawn out. Finally, a metal cap 97 is welded to the base 94 to perform sealing.

The filter also uses the principle of energy confinement similarly to the vibrator, and the thickness vibration energy is confined in the portion where the electrode is formed due to the mass load of the electrode. The portions of the input electrode 92a and the output electrode 92b form separate energy confinement oscillators. When these two vibrators are arranged at an appropriate distance and the leaked vibrations are coupled, both the symmetric mode in which the input side and the output side vibrate in the same phase and the oblique symmetric mode in which the input side and the output side vibrate in the opposite phase are excited. Become like A desired filter characteristic is obtained by controlling both symmetric and oblique symmetric modes that propagate from the input side to the output side.

A filter is required to have a stricter electrode design than a vibrator. In the case of a vibrator, it is sufficient to avoid high-order mode spurs to some extent, but in the case of a filter, the electrode film thickness and size must be such that only the basic symmetric mode and oblique symmetric mode in the input and output electrodes are confined. Basically, if the electrode is made heavier or the electrode area is made larger, a higher-order mode having a higher frequency is reflected at the end of the electrode and resonates to cause spurious. Therefore, there is an upper limit to the possible electrode thickness and electrode size, which severely limits the degree of freedom in filter design.

[0011] For both conventional vibrators and filters, gold is used for those requiring high frequency stability as an electrode material, and an underlayer such as chromium is used. Otherwise, silver is used to reduce costs. In the case of a high frequency, a metal such as aluminum having a small specific gravity is also used.

As an inexpensive method of forming an electrode thin film on a piezoelectric substrate, a metal mask having holes of the same shape as the electrode to be formed is generally used as a mask material. In specifications where higher frequencies are required, better filter characteristics and a stable manufacturing method are required, high electrode processing accuracy is required, and processing using photolithography instead of metal masks is also performed. Has become. In such a strict specification, it is necessary to accurately match the pattern of the front electrode and the back electrode, and the manufacturing cost increases.

Although a can package has been described as a mounting form, a small vibrator / filter has been required with the miniaturization of equipment, and a large number of packages mounted with a piezoelectric substrate lying in a surface mount package have been increasing. Is coming.

[0014]

As can be seen from the above description, in the energy trapping piezoelectric device,
The biggest challenge is how to control spurious levels.

When the piezoelectric device is a vibrator, the spurious causes a jump in the oscillation frequency of the vibrator and an unstable excitation state. In addition, when the piezoelectric device is a filter, the thickness vibration having a frequency higher than the pass band easily propagates from the input to the output when the piezoelectric device is a filter. A band is formed. As described above, the conditions of the electrode thickness and the electrode length that do not cause spurious are required, but are not always feasible.

For example, it is required that both the vibrator and the filter have low impedance. This is because the oscillator is used for stable oscillation, and the filter is used for facilitating impedance matching with a circuit. Although it is possible to reduce the impedance by increasing the electrode area, resonance occurs up to higher-order modes, which causes spurious. It is possible to increase the electrode size by reducing the electrode film thickness, but as the electrode film thickness is reduced, an unstable state is formed in which fine electrode particles are locally connected. There was also a limit. Although the lower limit of the electrode film thickness depends on the electrode material, a film thickness of at least 50 nm is necessary to obtain a practically stable electrode film. In addition, it is possible to reduce the mass load by making a high specific gravity electrode such as gold or silver a metal such as aluminum having a low specific gravity.
The electrodes tend to change more easily than gold or silver, and there is a problem in long-term reliability. Furthermore, when a piezoelectric substrate with a large electromechanical coupling coefficient, such as piezoelectric ceramic, lithium tantalate, or lithium niobate, is used, even if the mass load on the electrodes is zero, a certain amount of energy is trapped by the piezoelectric effect, and spurious emissions are generated. The upper limit of the electrode size is significantly smaller. Therefore, there is a problem that there is a limit in reducing impedance in a range where stable operation can be guaranteed without spurious.

When the frequency is further increased, the wavelength of the thickness vibration is shortened, so that it is necessary to relatively reduce the mass load on the electrode. Therefore, it is necessary to reduce the electrode thickness or to reduce the electrode area when the electrode thickness cannot be so reduced to suppress the spurious.

Further, in the conventional energy trapping piezoelectric device, since the lead portion of the electrode also becomes a mass load, a problem that the thickness vibration propagates through the lead portion of the electrode and is reflected at an unexpected portion to cause spurious noise. there were.
Further, in the conventional case, it is difficult to analytically design the behavior of the drawer portion, so that it is necessary to repeat design trial production and determine it empirically.

The present invention has been made in consideration of the above-mentioned conventional problems, and can suppress unnecessary spurious components.
A piezoelectric device capable of designing an electrode with a higher degree of freedom than ever before in a confinement design of a piezoelectric device corresponding to a higher frequency, a method of manufacturing a piezoelectric device capable of manufacturing the electrode more easily, and a mobile communication using the same It is intended to provide a device.

[0020]

According to a first aspect of the present invention, there is provided a piezoelectric substrate used for thickness vibration, and one or more sets of excitation electrodes provided on both sides of the piezoelectric substrate for performing the thickness vibration. And an energy trapping load that substantially traps vibration energy generated by the thickness vibration, wherein the energy trapping load is a piezoelectric device provided inside or outside the excitation electrode.

According to a twelfth aspect of the present invention, there is provided a step of providing an energy confinement load for substantially confining vibration energy generated by the thickness vibration at a portion on the piezoelectric substrate where the thickness vibration occurs, wherein the energy confinement load is Providing one or more sets of excitation electrodes for performing the thickness vibration on both surfaces of the provided piezoelectric substrate.

According to a thirteenth aspect of the present invention, there is provided a step of providing one or more sets of excitation electrodes for performing thickness vibration on both surfaces of a piezoelectric substrate, and generating the excitation electrodes on the provided excitation electrodes by the thickness vibration. Providing a load for confining energy that substantially confines the vibration energy to be generated.

25. The method according to claim 25, wherein a step of providing an energy trapping load pattern for substantially trapping vibration energy generated by the thickness vibration is provided on at least one side of the piezoelectric substrate where the thickness vibration occurs. Providing a pattern of excitation electrodes for performing the thickness vibration on both sides of the piezoelectric device.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Hereinafter, an energy trapping piezoelectric device according to an embodiment of the piezoelectric device of the present invention will be described with reference to FIGS. 1 (A) to 1 (C).

FIGS. 1A to 1C show an example of the structure of a multimode piezoelectric filter according to a first embodiment of the present invention. FIG. 1A is a top view of the present multimode piezoelectric filter. 1B is a cross-sectional view taken along the line AA ′ in FIG. 1A, and FIG. 1C is a view as viewed from below.

As shown in FIG. 1, 1 is a piezoelectric substrate, 2a is an input electrode, 2b is an output electrode, 2c is a top ground electrode,
Are projections formed on the upper and lower surfaces of the piezoelectric substrate 1. These projections correspond to the energy trapping projections of the present invention.
These projections also correspond to the energy confining load of the present invention. The input electrode 2a, the output electrode 2b, and the upper surface ground electrode 2c cover almost the entire upper surface of the piezoelectric substrate 1 with a very small electrode gap of several μm, and the lower electrode 3 substantially covers the lower surface of the piezoelectric substrate 1. The entire surface is covered, and the electrode 2 c is electrically connected to the lower surface ground electrode 3 via the side surface of the piezoelectric substrate 1.

The input electrode 2a, the output electrode 2b, and the upper surface ground electrode 2c are collectively referred to as the upper surface electrode 2. Further, the upper surface ground electrode 2c corresponds to the reflection suppressing dummy electrode of the present invention. Also, a set of excitation electrodes formed by the input electrode 2a and the lower surface ground electrode 3 and another set of excitation electrodes formed by the output electrode 2b and the lower surface ground electrode 3 are formed on the piezoelectric substrate of the present invention. Corresponding to a plurality of sets of excitation electrodes.

As described above, the protrusions 4a and 4c are
a and the projections 4b, 4
Since d is in contact with the inner surface of the output electrode 2 b and the inner surface of the lower surface ground electrode 3, the piezoelectric device according to the present embodiment has a configuration in which the energy trapping protrusions have the excitation electrode based on the thickness direction of the piezoelectric substrate 1. Corresponds to a piezoelectric device of the type provided inside.

Although the thickness vibration is reflected on the end face of the electrode which is present alone as in the related art, the electrode is arranged immediately near the end face of the electrode and the distance between the electrodes is reduced as in the first embodiment. The reflection at the electrode end surface can be suppressed, and the vibration is not confined by the electrode.

On the other hand, the projections 4a, 4a provided on the piezoelectric substrate 1
b, 4c, and 4d are provided at positions where the thickness vibration is excited by the input / output electrodes 2a and 2b and the lower surface ground electrode 3 on the upper and lower surfaces, and are substantially provided by the mass load effect of the projection. The fundamental symmetrical mode and obliquely symmetrical mode vibration are confined.

In the conventional piezoelectric filter, as described with reference to FIG. 11, the input electrode 92a and the common ground electrode 93, and the output electrode 92b and the common ground electrode 9
3 was used to confine the vibration.

On the other hand, in the piezoelectric filter of the present embodiment, the vibration is substantially confined by the projections 4a to 4d provided on the piezoelectric substrate 1. Therefore, the confinement design to confine the basic symmetric mode and the oblique symmetric mode and prevent higher-order modes from being confined can be performed by adjusting the shape and thickness of the projections, and the electrodes can be confined. Dependencies are reduced. Therefore, the degree of freedom in electrode design such as the size and thickness of the electrode and the electrode material is increased.

In the present embodiment, FIGS.
As shown in (C), the respective areas of the input electrode 2a and the output electrode 2b are set to be larger than the respective areas of the protrusions 4a and 4b. Therefore, it is possible to effectively excite the vibration component leaking to the surroundings from the vibration confinement by the protrusion, and it is possible to configure an efficient filter having lower input / output impedance.

Further, suppose that the structure of the conventional piezoelectric device is
That is, in the configuration utilizing the confinement of vibration due to the mass load of the electrode, a very light mass load is required as an electrode thin film that cannot be actually realized. According to the configuration of the embodiment, it can be realized. That is, according to the configuration of the present embodiment, the mass load of the energy trapping projections 4a to 4d is reduced,
It is possible to widen the vibration area (corresponding to each area of the energy confinement projections 4a to 4d) and reduce the input / output impedance.

Further, in the conventional configuration, even when aluminum must be used as the electrode material, according to the present embodiment, a stable electrode film such as gold or silver can be used, and the electrode thickness can be reduced. It is possible to increase the thickness up to a film thickness with stable characteristics.

In the first embodiment, since the electrodes are provided on almost the entire surface including the extraction electrode portion, reflection of thickness vibration by the extraction electrode and the like, which is a conventional problem, hardly occurs, and is caused by the electrode. Spurious generation can be suppressed, and the electrodes can be freely routed.
The reflection at the electrode end becomes smaller as the electrode spacing becomes smaller. However, as a guide, the electrode spacing at which the reflection suppression at the electrode end is larger than the spurious suppression for the pass band required as the filter characteristic. It is desirable that In addition, it is necessary to consider all spurious components in the frequency band to be suppressed when the reflection is suppressed by the electrode ends.

In a conventional energy trapping piezoelectric device, when a piezoelectric substrate having a large coupling coefficient is used, even if the electrode mass is zero, the frequency drop of the electrode portion due to the piezoelectric effect is large, and it is inevitable to suppress spurious. It is necessary to reduce the size of the electrode, and there is a limit to lowering the impedance. By minimizing the distance between the divided electrodes as in the present invention, the amount of frequency reduction between the divided electrodes is the same, and the non-electrode portion having a high cutoff frequency can be defined as a micro minute section. The reflection at the electrode end due to the effect can also be suppressed. That is, even if the substrate has a large coupling coefficient, the confinement design can be performed only by the mass load of the protrusion.

Further, as described in this embodiment, by dropping the reflection suppressing dummy electrode provided around the input electrode and the output electrode to the ground, the stray capacitance between the input electrode and the output electrode is reduced. Electric signal transmission can be reduced.

It is to be noted that the vibrations due to the mass load can be confined without the protrusions 4c and 4d on the lower surface only by the protrusions 4a and 4b on the upper surface, and the effect of the present invention can be obtained. By forming protrusions at the same position on both sides,
The balance of thickness vibration confinement is improved, and it becomes easier to suppress the generation of unnecessary spurious vibration.

Next, an example of a method for manufacturing a piezoelectric device according to the present invention will be described with reference to FIGS. 2 (A) to 2 (F).

FIGS. 2A to 2F are flow charts showing the flow of steps for manufacturing the multi-mode piezoelectric filter according to the first embodiment. 2 (A) to 2
(F) corresponds to the AA ′ cross section of FIG.

That is, each manufacturing process will be sequentially described with reference to the following drawings.

As shown in FIG. 2A, an AT-cut crystal having a zero-frequency temperature coefficient was used as the piezoelectric substrate 1, and a photoresist 5 was applied to both surfaces thereof and dried.

As shown in FIG. 2 (B), a photomask is brought into close contact with the upper surface of the piezoelectric substrate 1 and substantially parallel ultraviolet light is irradiated from the upper surface side to collectively expose and develop the photoresist 5 on both sides of the quartz crystal. Thus, the same photoresist pattern was formed on both surfaces of the quartz crystal 1.

As shown in FIG. 2C, the quartz crystal 1 is etched on both sides with an aqueous solution of ammonium bifluoride using the photoresist pattern 5 as a mask material, and the projections 4a, 4a are formed on both sides.
b and 4c, 4d were formed.

As shown in FIG. 2D, after the photoresist 5 was peeled off, a gold thin film having a thickness of 100 nm was formed on both surfaces of the quartz crystal 1 as a top electrode 2 and a bottom electrode 3 using chromium as a base.

As shown in FIG. 2E, a photoresist pattern 6 was formed on the upper electrode 2 by a photolithography process.

As shown in FIG. 2F, by using the photoresist 6 as a mask, the interelectrode gap of the upper electrode 2 was removed by etching to form electrode patterns 2a, 2b and 2c.

Although FIGS. 1A and 2A show one rectangular piezoelectric substrate, the present invention is not limited to this. For example, a plurality of piezoelectric substrates may be manufactured at once. Of course, such a configuration is also acceptable. That is, in this case, using a rectangular piezoelectric substrate having a larger size than the piezoelectric substrate shown in FIGS. 1A and 2A, a structure similar to the structure shown in FIG. After manufacturing, the piezoelectric device may be cut into the size of the piezoelectric device shown in FIG. 1A and mounted in a ceramic package for surface mounting using a conductive paste.

According to the manufacturing method of the first embodiment, if the piezoelectric substrate is transparent to the light source for exposing the photoresist 6, the projections 4a, 4b and 4c, 4d are formed at the same position on both surfaces of the piezoelectric substrate. Can be formed. Further, by using photolithography for forming the electrode pattern, the gap between the electrodes can be made extremely small, and the reflection of thickness vibration by the electrodes can be suppressed.

In the conventional example, the electrode pattern is formed by using a metal mask. However, the accuracy is at most several tens of μm.
Is also possible. Therefore, according to the present embodiment, it is possible to satisfy the recently required high filter accuracy and realize high production stability.

In the metal mask, the positioning of the electrodes on the upper and lower surfaces is not easy, which causes a manufacturing variation. However, the positioning can be accurately performed by using photolithography.

In general, the pattern formation using photolithography is higher in manufacturing cost than a metal mask.
If a large number of filters are collectively manufactured on a large-sized piezoelectric substrate as in the first embodiment, photolithography with good workability becomes more advantageous.

Further, in the first embodiment, the pattern forming step is simplified by using the lower surface electrode 3 as the entire surface ground electrode. In the configuration of the conventional example, the entire lower surface can be grounded, but the confinement effect by the electrode on the lower surface is lost. On the other hand, in the configuration of the present invention, the protrusions 4a, 4b,
Vibration confinement can be performed in 4c and 4d, and the entire surface can be used as a ground electrode without changing confinement conditions.

The method of forming the energy confinement load is not limited to the case where the piezoelectric substrate 1 is formed by etching. For example, a method of directly forming the energy confinement thin film pattern on the piezoelectric substrate 1 may be used. . Thus, by forming the energy confinement load with a thin film pattern different from the electrodes, the present invention can be applied to a piezoelectric substrate that is difficult to etch. (Embodiment 2) Hereinafter, an energy trapping piezoelectric device according to an embodiment of the piezoelectric device of the present invention will be described with reference to FIGS. 3 (A) to 3 (C) and FIGS. 4 (A) to 4 (C). I will explain while.

FIGS. 3A to 3C show an example of the structure of a multi-mode piezoelectric filter according to a second embodiment of the present invention. FIG. 3A is a top view, and FIG. Figure 3 (A)
FIG. 3C is a cross-sectional view taken along line AA ′ of FIG. FIGS. 4A to 4C show the second embodiment.
3 is a flow chart showing a method for manufacturing the semiconductor device of FIG.
It corresponds to the A 'section. Next, each manufacturing process will be sequentially described with reference to the drawings.

As shown in FIG. 4A, a single crystal of lithium tantalate was used as the piezoelectric substrate 1, and a gold thin film having a chromium base as an upper electrode 2 and a lower electrode 3 was formed on both surfaces thereof.
A film was formed to a thickness of 00 nm.

As shown in FIG. 4B, electrode patterns 2a, 2b, and 2c for dividing the electrode 2 at a small interval were formed by a photolithography process.

As shown in FIG. 4C, the projections 4a, 4b
As 4c and 4d, a silicon oxide thin film pattern was formed by aligning the positions on both surfaces of the portion for confining the vibration.
These projections 4a, 4b and 4c, 4d correspond to the energy trapping thin film of the present invention. In addition, these projections 4
a, 4b and 4c, 4d correspond to the energy confinement loads of the present invention.

The main structural difference between the second embodiment and the first embodiment is that the projections 4a, 4b and 4c,
d is formed by a thin film pattern, and a part 2d of the ground electrode 2c is arranged between the input electrode 2a and the output electrode 2b in the pattern of the upper surface electrode.

As described above, the protrusions 4 formed by the thin film
a, 4c are provided on the outer surface of the input electrode 2a and the lower surface earth electrode 3, and projections 4b, 4d formed of thin films are provided on the outer surface of the output electrode 2b and the lower surface earth electrode 3, respectively. Therefore, the piezoelectric device according to the present embodiment corresponds to a piezoelectric device in which the energy trapping projection is provided outside the excitation electrode with reference to the thickness direction of the piezoelectric substrate 1.

As described above, the protrusions 4a, 4b and 4c, 4c
By forming d in a thin film pattern, it is possible to confine thickness vibration even on a piezoelectric substrate made of a material that is difficult to etch such as lithium tantalate, thereby expanding the range of substrate materials to which the present invention can be applied. Can be.

In the second embodiment, the projections are formed on the electrodes, but this has the effect of protecting the electrode in the portion where the thickness vibration occurs. For example, when an electrode material that easily changes with time such as aluminum is used, if there is a stable protrusion such as silicon oxide on the excitation electrode, the oxidation of aluminum can be suppressed, and the change in filter characteristics with time can be suppressed. it can.

The projections 4a, 4b, 4c, and 4d of the present embodiment are formed in the same manner as the method of directly forming the energy trapping thin film pattern on the piezoelectric substrate 1 described at the end of the first embodiment. May of course be formed. Even in that case, the same effect as described above can be obtained.

In the case of this configuration, if both the piezoelectric substrate and the projections are transparent, the projections on both surfaces can be formed at the same position with high precision by the same process as in the first embodiment.

Next, by providing the ground pattern 2d between the input / output electrodes 2a and 2b, a signal is electrically propagated by the stray capacitance between the input / output electrodes, which has been a problem in the conventional electrode configuration, and the input / output electrodes 2a and 2b have a problem. The problem that isolation between outputs cannot be obtained can be solved. That is, the input electrode 2a is 2
Since the output electrode 2b is grounded by the stray capacitance between the terminals a and d and the output electrode 2b is grounded by the stray capacitance between the terminals 2b and 2d, direct electrical coupling can be reduced. It is possible to provide such a ground electrode with a conventional filter, but by providing a ground electrode, a new mass load has been applied between the input and output vibrators, and the conditions for confining vibration have changed. I will. It is presumed to cause new spurs. On the other hand, in the present invention, since the distance between the electrodes is extremely small and the substantial vibration confinement is performed by the projections 4a, 4b, 4c, and 4d, the vibration confinement conditions are also used in the electrode configuration of the second embodiment. Does not change, and a higher-performance filter can be realized. (Embodiment 3) Hereinafter, an energy trapping piezoelectric device which is an embodiment of the piezoelectric device of the present invention will be described with reference to FIGS. 5 (A) to 5 (C).

FIGS. 5A to 5C show an example of the structure of a multimode piezoelectric filter according to a third embodiment of the present invention. FIG. 5A is a top view thereof, and FIG. ) Is FIG.
FIG. 5A is a cross-sectional view taken along line AA ′, and FIG. As shown in FIG.
a is an input electrode, 2b is an output electrode, 2c is a top ground electrode, 3 is a bottom ground electrode, 4a, 4b, 4c, 4d, 4
e, 4f are projections formed on the upper and lower surfaces of the piezoelectric substrate 1,
Are inter-electrode protrusions formed between the upper and lower electrodes. The feature of the first and second embodiments is that the gap between the upper electrodes 2a, 2b, and 2c is filled with an inter-electrode projection 7 having a thickness given by a formula generally described later.
Here, the second anti-reflection projection or the second anti-reflection thin film of the present invention corresponds to the inter-electrode projection 7. FIG. 5B
FIG. 6 is a diagram in a case where the inter-electrode projection 7 corresponds to the second reflection suppression projection of the present invention. The configuration when the inter-electrode projection 7 corresponds to the second reflection suppressing thin film of the present invention is shown in FIGS.
FIG. 7D and FIGS. 8A to 8D.

As described above, the thickness of the inter-electrode projection 7 is adjusted so as to satisfy the following equation.

The amount of frequency decrease due to the mass load of the inter-electrode protrusion = the amount of frequency decrease due to the mass load of the electrode + the amount of frequency decrease due to the piezoelectric effect of the electrode portion. The cutoff frequency can be made substantially the same at the boundary between the electrode portion and the non-electrode portion. As described above with reference to FIG. 10D, the thickness vibration to be confined has a frequency between fc and fc ′, and there is no difference between the cutoff frequencies at the boundary between the electrode portion and the non-electrode portion. That means
This means that there is virtually no vibration mode reflected and confined at the end of the electrode. Therefore, spurious due to the electrode end can be suppressed.

Here, the cut-off frequency is the resonance frequency of the thickness vibration of an infinite flat plate, assuming that the target portion is infinitely widened.

According to the structure of the third embodiment, the reflection of thickness vibration at the interface between the electrode portion and the non-electrode portion can be suppressed to an extremely small value. That is, the thickness vibration is confined by the protrusion 4
a, 4b, 4c, 4d, 4e, and 4f, and the excitation electrode can be designed more freely.

For example, in order to minimize the reflection of the thickness vibration at the electrode end portions described in the first and second embodiments, the gap between the electrodes (for example, the input electrode 2a in FIG.
And the distance between the output electrode 2b and the ground electrode 2c).

On the other hand, in the third embodiment, as described above, the second reflection suppressing projection or the second reflection suppressing thin film is arranged without any gap between the electrodes. In addition, the reflection of the thickness vibration at the electrode end can be suppressed. Therefore, it is not always necessary to make a fine interval between the electrodes.

That is, as long as the second anti-reflection projection or the second anti-reflection thin film is arranged between these electrodes, the generation of spurious due to the reflection of the thickness vibration at the end of the electrode can be avoided. Design can be performed For example, as shown in FIGS. 5 (A) to 5 (C), the input / output electrodes 2a, 2b
Even if the ground electrode 2c is not disposed in the immediate vicinity of each of the extraction electrode portions, the reflection of the thickness vibration at the electrode end portion or the extraction electrode portion can be sufficiently suppressed in any of these cases.
Therefore, it is not necessary to process the electrodes very finely, and simpler manufacturing can be realized without using a fine pitch photolithography apparatus.

As in the configuration of the first embodiment, the excitation electrode 2
If the lower electrode 3 also exists on the back surface of the extraction electrodes a and 2b, an extra stray capacitance is added between the extraction electrode and the lower electrode, the capacitance ratio as a vibrator increases, and the range of the filter that can be designed is limited. And there is a possibility that unnecessary thickness vibration may be excited also at the intersection of the extraction electrode and the lower electrode. According to the third embodiment, as shown in FIGS. 5 (A) to 5 (C), even if the intersection between each of the extraction electrode portions of the input / output electrodes 2a and 2b and the lower surface electrode 3 is eliminated, the extraction electrode Since the reflection of the thickness vibration can be sufficiently suppressed, there is more design freedom than in the first embodiment, and unnecessary resonance can be suppressed.

The configuration shown in FIG. 5 is different from the projections 4a, 4b, 4
This is a so-called three-pole structure filter in which three energy confinement oscillators composed of c, 4d, 4e, and 4f are coupled. The fundamental symmetric mode and the oblique symmetric mode, and the phase of only the center oscillator is inverted. The filter is configured using three vibration modes of the symmetric mode. As described above, the effect of the present invention is not limited to the number of vibrators and the number of modes used in the filter, but can be applied to a piezoelectric filter having a larger number of poles.

The upper surface ground electrode 2c in the piezoelectric filter of the present embodiment does not have the role of the dummy electrode 2c described in the first and second embodiments. That is, the upper surface ground electrode 2c of the present embodiment has only the role of the ground electrode as one of the excitation electrodes.

Next, as one embodiment of the method of manufacturing the piezoelectric device of the present invention, a method of manufacturing the above-described piezoelectric filter of Embodiment 3 will be described with reference to FIGS.
(D), FIGS. 7 (A) to 7 (D), FIGS. 8 (A) to 8
Three examples will be described using (D).

Here, FIGS. 6A to 6D correspond to FIGS.
It is a flowchart which shows the flow of the process for manufacturing the multi-mode piezoelectric filter which is Embodiment 3 described with (A) -FIG.5 (C). This figure corresponds to the cross-sectional view taken along the line AA ′ of FIG.

First, a first example of the manufacturing method will be sequentially described with reference to FIG.

As shown in FIG. 6A, using an AT-cut quartz as the piezoelectric substrate 1, the quartz is etched by photolithography, and the projections 4a, 4b, 4c, 4d, 4d are formed.
e, 4f were formed.

As shown in FIG. 6B, a photoresist pattern 8 corresponding to the electrode gap is formed on each of the upper and lower surfaces of the quartz crystal 1, and the inter-electrode protrusion 7 is formed by etching the quartz crystal.
Was formed.

As shown in FIG. 6 (C), a gold thin film having a base of chromium was formed to a thickness of 100 nm on both surfaces.

As shown in FIG. 6 (D), the electrodes were lifted off by removing and cleaning the photoresist 8, thereby forming electrode film patterns 2a, 2b, 2c and 3 on both surfaces.

Next, a second example will be described with reference to FIGS. 7A to 7D.

Here, FIGS. 7A to 7D are cross-sectional views showing a flow chart of a process for manufacturing the multi-mode piezoelectric filter described in the third embodiment.

As shown in FIG. 7A, a silicon oxide thin film 9 is formed on both sides by using lithium tantalate as the piezoelectric substrate 1, and the silicon oxide film is etched by using a photolithography method to form the projections 4a. 4b, 4c, 4d, 4e, 4f
Was formed.

As shown in FIG. 7B, a photoresist pattern 8 corresponding to the electrode gap was formed on each of the upper and lower surfaces of the piezoelectric substrate 1, and the inter-electrode projections 7 were formed by etching the silicon oxide thin film.

As shown in FIG. 7C, a gold thin film having a base of chromium was formed to a thickness of 100 nm on both surfaces.

As shown in FIG. 7D, the electrodes are lifted off by removing and cleaning the photoresists 53 and 54,
Electrode film patterns 2a, 2b, 2c and 3 on both surfaces were formed.

Next, a third example will be described with reference to FIGS. 8A to 8D.

FIGS. 8A to 8D are cross-sectional views showing a flow chart of a process for manufacturing a multimode piezoelectric filter having the structure of the third embodiment.

As shown in FIG. 8A, using an AT-cut quartz as the piezoelectric substrate 1, the quartz is etched by photolithography, and the projections 4a, 4b, 4c, 4d, 4d are formed.
e, 4f were formed.

As shown in FIG. 8B, a gold thin film having a base of chromium was formed to a thickness of 100 nm on both surfaces of the quartz crystal 1 to form a photoresist pattern 10 corresponding to the electrode pattern.

As shown in FIG. 8C, the electrodes were etched using the photoresist 10 as a mask, and silicon oxide thin films 11 were formed on both surfaces.

As shown in FIG. 8D, the silicon oxide film 11 was lifted off by removing and cleaning the photoresist 10, and the inter-electrode protrusions 7 on both surfaces were formed.

According to the above-described three manufacturing methods, since the space between the electrode patterns is completely filled with the inter-electrode projections, vibration reflection at the electrode end can be suppressed over the entire surface on both surfaces of the element, and the spurious Very few multimode piezoelectric filters can be realized. Fourth Embodiment In the first to third embodiments, an example of a multi-mode piezoelectric filter in which the vibrations of a plurality of vibrators are coupled has been described as the energy trapping piezoelectric device of the present invention. The same effect can be obtained by applying the present invention to the present invention.

Hereinafter, an energy trapping piezoelectric vibrator, which is one embodiment of the piezoelectric device of the present invention, will be described with reference to FIGS. 9A to 9C, and the manufacturing process will be described at the same time.

FIG. 9A is a top view of the energy trapping piezoelectric vibrator of the present embodiment, and FIG. 9B is FIG. 9A.
3 is a sectional view taken along line AA ′ of FIG.

FIG. 9 (C) is another example of the energy trapping piezoelectric vibrator of FIG. 9 (A), and shows a case where both the dummy electrode and the inter-electrode projection are provided. A) A)
It is sectional drawing corresponding to -A '.

As shown in FIG. 9 (A), a single crystal of lithium tantalate was used as the piezoelectric substrate 1, and a gold thin film with chromium as the underlayer was used as the upper electrode 2 and the lower electrode 3 on both surfaces thereof.
A film was formed to a thickness of 00 nm.

As shown in FIG. 9B, electrode patterns 2a and 2c for dividing the electrode 2 at very small intervals were formed by a photolithographic process. Here, the electrode pattern 2c corresponds to the reflection suppressing dummy electrode of the present invention which is electrically insulated from the excitation electrode and formed on the piezoelectric substrate with a predetermined gap from the excitation electrode.

As shown in FIG. 9C, the projections 4a, 4c
As a result, a silicon oxide thin film pattern was formed by aligning the positions on both surfaces of a portion for confining vibration. FIG. 9 (C)
The piezoelectric vibrator having the configuration shown in (1) corresponds to a piezoelectric device of the type including the anti-reflection dummy electrode of the present invention and the first anti-reflection thin film. In FIG. 9C, the projections 4a and 4c corresponding to the energy confinement load of the present invention are:
FIG. 9B also shows that a thin film is formed on a piezoelectric substrate.
Configuration.

In FIGS. 9A to 9C, the electrode 2a and the lower electrode 3 correspond to a pair of excitation electrodes of the present invention.

FIGS. 9A and 9B are examples in which the configuration and the manufacturing method of the second embodiment are applied to a piezoelectric vibrator. The upper surface electrode 2 is divided into an excitation electrode, an extraction electrode 2a, and a dummy electrode 2c at a small interval.
Vibration reflection on the end face of the electrode 2a can be suppressed.
Therefore, substantial energy confinement is performed by the projections 4a and 4c. The protrusions 4a and 4c may be provided directly on the piezoelectric substrate 1, and the protrusions 4a and 4c may be provided by etching the piezoelectric substrate as in the first embodiment. Is obtained.

On the other hand, the configuration of FIG.
7 (A) to 7 (D) are applied to the piezoelectric vibrator, and interelectrode protrusions 7 are provided in the electrode gap.

That is, in the configuration of FIG.
By providing an interelectrode protrusion between the fine gap between the excitation electrode and the dummy electrode described in the above, reflection of vibration at the electrode end can be further suppressed as in the third embodiment.

In the structure shown in FIG. 9C, the protrusions 4a, 4a
Although the case where c is formed as a thin film on the piezoelectric substrate has been described, the present invention is not limited to this. For example, as shown in FIG. 9B, a thin film as an energy trapping load is formed on the excitation electrode. Of course, such a configuration is also acceptable. In this case, it can be manufactured by providing an energy confinement load after forming the electrode patterns on both surfaces in substantially the same manner as the contents shown in FIG. 4C of the second embodiment.

In any of the above arrangements, the energy confinement of the piezoelectric vibrator is substantially performed by the projections 4a and 4c. And the dependence on the electrodes is reduced.

Therefore, the degree of freedom in electrode design such as electrode size, film thickness, electrode material and the like is expanded. Exciting electrode 2a is projected 4a
The vibration component leaking to the surroundings from the vibration confinement by the protrusion can be effectively excited, and the impedance can be further reduced.

Further, according to the present invention, it is possible to achieve a very light mass load that cannot be realized as an electrode thin film by the conventional method of confining the vibration by the mass load of the electrode, and to increase the vibration area by reducing the mass load. It is possible to lower the impedance.

Furthermore, even when aluminum must be used conventionally, a stable electrode film such as gold or silver can be used, and the thickness of the electrode can be increased to a thickness with stable characteristics.

Further, since the electrodes are provided on almost the entire surface including the extraction electrode portion, reflection of thickness vibration by the extraction electrode and the like, which is a problem in the conventional structure, is less likely to occur, and spurious noise caused by the electrodes is reduced. Generation can be suppressed and the electrodes can be freely drawn.

Although the reflection at the electrode end becomes smaller as the electrode spacing becomes smaller, as a guide, the electrode spacing is such that the amount of reflection suppression at the electrode end is larger than the required amount of spurious suppression. Is desirable. In addition, it is necessary to consider all spurious components in the frequency band to be suppressed when the reflection is suppressed by the electrode ends.

Conventionally, in a piezoelectric substrate having a large coupling coefficient, the confinement due to the piezoelectric effect is large, and it is necessary to reduce the size of the electrodes.
According to the present invention, since the frequency reduction amount of the excitation electrode portion and the dummy electrode portion is the same, the confinement design can be performed only by the mass load of the protrusion.

As described above, as described in the fourth embodiment, the effects of the first to third embodiments are not limited to the multi-mode piezoelectric filter, but can be widely applied to an energy trapping piezoelectric device such as a vibrator. Similar effects can be obtained.

Further, by using the piezoelectric filter having the above configuration in a wireless communication device such as a portable telephone, unnecessary high frequency components can be suppressed, and the high frequency section can be formed by a filter having a large degree of freedom in design and excellent characteristics. Therefore, it is possible to realize a wireless communication device in which the selectivity of the adjacent channel is large and is hardly affected by an interference wave. By using the piezoelectric vibrator having the above configuration in an information device or a communication device, a clock can be generated by a vibrator having stable characteristics with less spurious, so that an information device or a communication device having a stable reference frequency and operation can be realized.

Further, according to the above-described embodiment, the configuration for confining the energy confining piezoelectric device can be made easier than in the past, so that an electrode design with a higher degree of freedom and a wider range of electrode materials can be used. You can choose.
In addition, unnecessary spurious components can be easily suppressed, and a piezoelectric device with lower impedance and higher frequency can be realized. Moreover, in the filter, an energy trapping piezoelectric device having excellent channel selectivity can be realized. Further, the manufacturing method is much easier than before.

In the first to fourth embodiments, quartz, lithium tantalate, and lithium niobate are used as the piezoelectric material. However, the present invention is not limited to the piezoelectric material, and is not limited to the piezoelectric material. Has the same effect in the piezoelectric material constituting the above.

Further, in the above-described embodiment, the configuration in the case where the load for energy confinement is provided together with the load for energy confinement, such as a dummy electrode, a reflection suppressing protrusion, or a reflection suppressing thin film, is described. Not limited to, for example,
The reflection suppressing load may be omitted. That is, compared to the conventional configuration in which energy is confined by the excitation electrode, the piezoelectric device having the above-described energy confinement load reduces unnecessary spurious vibrations. Therefore, the reflection suppressing load is not necessarily required.

In the above embodiment, the configuration in which the electrodes on both surfaces of the piezoelectric substrate are divided has been described. However, the present invention is not limited to this. For example, even if only one of the electrodes is divided. Of course it is good.

Further, in the above-described embodiment, the configuration in which the energy confining load is always formed on the surface of the piezoelectric substrate on which the electrode is divided has been described. A configuration in which the energy confinement load is formed only on the surface on which the unformed electrode is formed may be used.

In the above embodiment, the reflection suppressing dummy electrode of the present invention is formed using the same electrode material as the excitation electrode. However, the present invention is not limited to this. For example, another electrode material or an insulating material may be used. Of course, it may be formed of a completely different material.

In the above embodiment, the energy confinement load of the present invention is set larger than the area of the excitation electrode. However, the present invention is not limited to this. For example, the load may be the same as the area of the excitation electrode. .

[0125]

As is apparent from the above description, the present invention has an advantage that a design having a higher degree of freedom can be achieved as compared with the prior art. In addition, it has an advantage that its manufacture can be performed more easily. Also, it has the advantage of having excellent channel selectivity.

[Brief description of the drawings]

FIG. 1A is a top view showing an energy trapping piezoelectric device according to a first embodiment of the present invention. FIG. 1B is a cross-sectional view showing the piezoelectric device. FIG. 1C is a back view showing the piezoelectric device.

FIGS. 2A to 2F are flowcharts showing a method of manufacturing the energy trapping piezoelectric device according to the first embodiment of the present invention.

3A is a top view showing an energy trapping piezoelectric device according to a second embodiment of the present invention. FIG. 3B is a cross-sectional view showing the piezoelectric device. FIG. 3C is a back view showing the piezoelectric device.

FIGS. 4A to 4C are flowcharts showing a method of manufacturing an energy trapping piezoelectric device according to a second embodiment of the present invention.

5A is a top view illustrating an energy trapping piezoelectric device according to Embodiment 3 of the present invention. FIG. 5B is a cross-sectional view illustrating the piezoelectric device. FIG. 5C is a rear view illustrating the piezoelectric device.

FIGS. 6A to 6D are flowcharts showing a method for manufacturing an energy trapping piezoelectric device according to a third embodiment of the present invention.

FIGS. 7A to 7D are flowcharts showing a method for manufacturing an energy trapping piezoelectric device according to a third embodiment of the present invention.

FIGS. 8A to 8D are flowcharts showing a method of manufacturing an energy trapping piezoelectric device according to a third embodiment of the present invention.

9A is a top view illustrating an energy trapping piezoelectric device according to Embodiment 4 of the present invention. FIG. 9B is a cross-sectional view illustrating the piezoelectric device. FIG. 9C is a cross-sectional view illustrating another configuration of the piezoelectric device.

10A is a top view illustrating a conventional energy trapping piezoelectric vibrator. FIG. 10B is a cross-sectional view illustrating the piezoelectric vibrator. FIG. 10C is an amplitude distribution diagram of each vibration mode of the piezoelectric vibrator. ): Frequency chart of each vibration mode of the piezoelectric vibrator

FIG. 11 is a perspective view showing a conventional energy trapping piezoelectric filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Upper surface electrode 2a Input electrode 2b Output electrode 3 Lower surface electrode 4a-4d Projection 7 Projection between electrodes

Continuation of the front page (72) Inventor Shinji Itamochi 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (27)

[Claims] 1. A piezoelectric substrate used for thickness vibration, one or more sets of excitation electrodes provided on both sides of the piezoelectric substrate for performing the thickness vibration, and a vibration energy generated by the thickness vibration is substantially generated. A piezoelectric device, comprising: a load for confining energy to be confined; and the load for confining energy is provided inside or outside the excitation electrode. 2. The energy confining load comprises: (1)
An energy trapping projection or a thin film provided inside the excitation electrode and on at least one surface of the piezoelectric substrate, or (2) outside the excitation electrode and the piezoelectric substrate 2. The piezoelectric device according to claim 1, wherein the piezoelectric device is an energy trapping thin film provided on an excitation electrode formed on at least one surface of the piezoelectric device. 3. A load for suppressing reflection, which suppresses reflection of thickness vibration at an outer peripheral end portion of the excitation electrode, is applied to all or a part of a region on the piezoelectric substrate other than a region where the excitation electrode is provided. The piezoelectric device according to claim 2, wherein the piezoelectric device is provided in an area. 4. The reflection suppressing load is a reflection suppressing dummy electrode which is electrically insulated from the excitation electrode and is provided on the piezoelectric substrate with a predetermined gap from the excitation electrode. The piezoelectric device according to claim 3, wherein: 5. The reflection suppressing load includes: (1) a reflection suppressing dummy electrode electrically insulated from the excitation electrode and provided on the piezoelectric substrate at a predetermined distance from the excitation electrode. And (2) a first reflection suppression protrusion or a first reflection suppression thin film provided between the excitation electrode and the reflection suppression dummy electrode spaced apart from each other, The cutoff frequency of the thickness vibration at the portion of the reflection suppressing protrusion or the first reflection suppressing thin film is practically the same as the cutoff frequency of the thickness vibration at the portion of the excitation electrode and the portion of the dummy electrode for reflection suppression. The piezoelectric device according to claim 3, wherein 6. The anti-reflection load is a second anti-reflection projection provided substantially adjacent to the excitation electrode.
The cutoff frequency of the thickness vibration at the portion of the second reflection suppressing projection or the portion of the second reflection suppressing thin film is different from the cutoff frequency of the thickness vibration at the portion of the excitation electrode. The piezoelectric device according to claim 3, wherein the piezoelectric device is the same. 7. An end of both the excitation electrode and the reflection suppressing dummy electrode facing each other at the predetermined interval, the reflection of a vibration mode which is not an object of confinement in the energy confinement load is suppressed. The piezoelectric device according to claim 4, wherein: 8. A frequency reduction amount of a cutoff frequency due to a mass load of the reflection suppressing projection is defined as F1, and a frequency reduction amount of a cutoff frequency due to a mass load of the excitation electrode is defined as F1.
2, the height H of the reflection suppressing projection from the reference plane is set to a value that satisfies F1 = F2 + F3, where F3 is the frequency reduction amount of the cutoff frequency due to the piezoelectric effect of the excitation electrode. 7. The piezoelectric device according to claim 5, wherein: 9. The piezoelectric device according to claim 2, wherein the energy confining loads are formed at substantially the same position on both sides of the piezoelectric substrate. 10. The piezoelectric device according to claim 1, wherein a plurality of the excitation electrodes are provided on the piezoelectric substrate, and the plurality of the excitation electrodes have a filter function. 11. An earth electrode provided between the electrodes of the plurality of sets of excitation electrodes at a predetermined interval from the excitation electrodes, wherein both of the excitation electrode and the earth electrode which are close to each other, The reflection of a vibration mode which is not a target of confinement in the energy confinement load is suppressed at an end portion facing at a predetermined interval.
0. The piezoelectric device according to 0. 12. The method according to claim 12, wherein a portion on the piezoelectric substrate where the thickness vibration occurs is
Providing an energy confining load for substantially confining the vibration energy generated by the thickness vibration; and one or more sets of excitation electrodes for performing the thickness vibration on both surfaces of the piezoelectric substrate on which the energy confining load is provided. Providing a piezoelectric device. 13. A step of providing one or more sets of excitation electrodes for performing thickness vibration on both surfaces of a piezoelectric substrate, and substantially confining vibration energy generated by the thickness vibration on the provided excitation electrodes. Providing a load for confining energy. 14. The energy confinement load is an energy confinement projection, and after etching-resistant masking is performed on a portion of the piezoelectric substrate where the projection is to be formed, portions other than the predetermined portion are removed. 13. The method according to claim 12, wherein the protrusions are formed by thinning by etching. 15. The piezoelectric device according to claim 12, wherein the energy confinement load is an energy confinement thin film, and the thin film is formed on the piezoelectric substrate or on the excitation electrode. Method. 16. The method according to claim 16, wherein the step of providing the excitation electrode includes forming an electrode film on both sides of the piezoelectric substrate on which the energy trapping load is formed, and forming the electrode film on both sides of the piezoelectric substrate. 13. The method according to claim 12, further comprising a dividing step of dividing an electrode film formed on at least one surface into a region for the excitation electrode and a region for the dummy electrode. 17. The step of providing an excitation electrode includes: forming an electrode film on both surfaces of the piezoelectric substrate; forming at least one of the electrode films formed on both surfaces of the piezoelectric substrate. 14. The method according to claim 13, further comprising: a dividing step of dividing the divided electrode film into a region of the excitation electrode and a region of the dummy electrode. 18. In the dividing step, a predetermined gap is formed between the excitation electrode and the dummy electrode, and the predetermined gap has a reflection of a vibration mode which is not a target of confinement in the energy confinement load. 18. The method according to claim 16, wherein the excitation electrode and the dummy electrode are adjusted so as to be substantially insulated and electrically insulated from the dummy electrode. 19. A plurality of sets of said excitation electrodes are formed on both sides of said piezoelectric substrate, and at least on one side of said piezoelectric substrate at a position between said excitation electrodes formed at a predetermined interval. Or, reflection suppression for forming a reflection suppressing load for suppressing reflection of thickness vibration at a position between excitation electrodes to be formed at a predetermined interval on at least one surface of the piezoelectric substrate. 14. The method for manufacturing a piezoelectric device according to claim 12, further comprising a load forming step. 20. The reflection suppressing load is a reflection suppressing projection, forms a photoresist pattern corresponding to the pattern shape between the excitation electrodes, and etches the piezoelectric substrate using the photoresist pattern as a mask. Forming the reflection suppressing protrusions, forming an electrode film on the piezoelectric substrate on which the reflection suppressing protrusions are formed, removing and cleaning the photoresist, and lifting off the electrode film on the photoresist. 20. The method for manufacturing a piezoelectric device according to claim 19, wherein: 21. The reflection suppressing load is a reflection suppressing insulating thin film, an insulating thin film is formed on the piezoelectric substrate, and a photoresist pattern corresponding to a pattern shape between the excitation electrodes is formed. Forming, etching the insulating thin film using the photoresist pattern as a mask to form the reflection suppressing insulating thin film, and forming an electrode film on the piezoelectric substrate on which the reflection suppressing insulating thin film is formed. 20. The method of manufacturing a piezoelectric device according to claim 19, wherein the photoresist is peeled and washed to lift off the electrode film on the photoresist. 22. The reflection suppressing load is a reflection suppressing insulating thin film, forming an electrode film, forming a photoresist pattern corresponding to the pattern shape of the excitation electrode on the electrode film, Etching the electrode film using a photoresist pattern as a mask, after the etching, further forming an insulating thin film, peeling and cleaning the photoresist, and lifting off the insulating thin film on the photoresist, 20. The method for manufacturing a piezoelectric device according to claim 19, wherein an insulating thin film for suppressing reflection is formed. 23. The piezoelectric substrate is a substantially transparent substrate. When forming the energy trapping projection or the reflection suppressing projection on both surfaces of the piezoelectric substrate, a photoresist is applied to both surfaces of the piezoelectric substrate, The projections having the same shape are formed on both surfaces by simultaneously exposing the photoresist on both surfaces with a light beam, forming the same photoresist pattern on the both surfaces, and performing etching. 20. The method for manufacturing a piezoelectric device according to 12, 13, or 19. 24. A dummy electrode forming step of forming a dummy electrode on the piezoelectric substrate in a region other than the region of the excitation electrode at a predetermined distance from the excitation electrode; In the position between the dummy electrode,
14. The method for manufacturing a piezoelectric device according to claim 12, further comprising: a reflection suppressing load forming step of forming a reflection suppressing load for suppressing reflection of thickness vibration. 25. A step of providing an energy trapping load pattern for substantially confining vibration energy generated by the thickness vibration on at least one side of the piezoelectric substrate on which the thickness vibration occurs; Providing a pattern of an excitation electrode for performing the following. 26. A mobile communication device using the piezoelectric device according to claim 1. Description: 27. A mobile communication device using a piezoelectric device manufactured by the method of manufacturing a piezoelectric device according to claim 12.