Piezoelectric oscillation element and piezoelectric oscillation component using the same

A piezoelectric oscillation element (1) comprising a piezoelectric substrate (10), a first conductor film (21) formed on one main surface of the piezoelectric substrate (10), a second conductor film (22) formed on the other main surface, and grounding terminals (31a, 31b) formed on the side surfaces of the piezoelectric substrate (10). Specified capacitances are respectively formed between the first and second conductor films (21, 22) formed on the main surfaces of the piezoelectric substrate (10) and the grounding terminals (31a, 31b) formed on the side surfaces thereof. Larger capacitances can be formed than when electrodes are disposed on the same main surface in proximity of each other to form a capacitance, whereby no adverse effect is given to thickness vibration occurring between the first and second conductor films (21, 22).

TECHNICAL FIELD

The present invention relates to a small-sized and high-performance piezoelectric oscillation element including a built-in load capacitance, and a piezoelectric oscillation component using the same.

BACKGROUND ART

Conventionally, microcomputers are widely used for communication devices and electronic devices, and as a clock source of such a microcomputer, a piezoelectric oscillation element having a built-in load capacitance has attracted attention. This piezoelectric oscillation element is structured so that load capacitances are connected between input and output terminals of the piezoelectric oscillation element and a ground potential.

As such a piezoelectric oscillation element, there is available one having a vibration electrode and a capacitance electrode on the same main surface of a piezoelectric substrate and a capacitance formed between the oscillation electrode and the capacitance electrode (for example, refer to Patent Document 1). The capacitance electrode is connected to a ground electrode provided on a side surface of the piezoelectric substrate.

With this structure, it becomes unnecessary to provide lamination of a capacitor substrate for forming a capacitance, and the piezoelectric oscillation element can be made thin.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, in the above-described conventional piezoelectric element, a capacitance is formed between the oscillation electrode and the capacitance electrode formed on the same main surface of the piezoelectric substrate, so that a region in which thickness vibration is generated and a region in which a capacitance is generated are close to each other.

Therefore, the electric field of the region in which a capacitance is generated influences the electric field of the region in which thickness vibration of the piezoelectric substrate is generated, and may suppress thickness vibration and deteriorate the resonance characteristics.

An object of the present invention is to provide a small-sized thin piezoelectric oscillation element which has a built-in load capacitance and excellent resonance characteristics for thickness vibration and suppresses undesired vibration, and a piezoelectric oscillation component using the same.

Means for Solving the Problem

A piezoelectric oscillation element of the present invention includes a piezoelectric substrate, a first conductor film formed on one main surface of the piezoelectric substrate, a second conductor film formed on the other main surface of the piezoelectric substrate, and ground terminals formed on side surfaces of the piezoelectric substrate, wherein predetermined capacitances are formed between the first and second conductor films and the ground terminals.

In this structure, a capacitance is formed between the first conductor film formed on the one main surface of the piezoelectric substrate and the ground terminal formed on the side surface, and a capacitance is formed between the second conductor film formed on the other main surface of the piezoelectric substrate and the ground terminal formed on the side surface. Therefore, when it is assumed that the gaps of the ends closest to each other of the electrodes are equal to each other, in comparison with the case where the electrodes on the same main surface are formed close to each other and a capacitance is formed, a larger capacitance can be formed. In addition, the first and second conductor films and the ground terminals do not surface-face each other across the piezoelectric substrate, so that thickness vibration is hardly excited there between. Therefore, there is no harmful influence on desired thickness vibration generated between the first and second conductor films, so that the oscillation stability is not lost.

In the piezoelectric oscillation element of the present invention, first and second input/output terminals are formed at positions where the ground terminals are arranged between the first and second input/output terminals on the side surfaces of the piezoelectric substrate, and connection is made between the first conductor film and the first input/output terminal and between the second conductor film and the second input/output terminal.

Therefore, capacitances are generated between the first and second input/output terminals and the ground terminals, and load capacitances necessary for oscillation can be efficiently formed.

Furthermore, the piezoelectric oscillation element of the present invention is structured so that the first conductor film has a first vibration electrode and a first capacitance electrode, and the second conductor film has a second vibration electrode and a second capacitance electrode, and the first and second vibration electrodes face each other by sandwiching the piezoelectric substrate there between.

Thereby, in the region in which the first and second vibration electrodes face each other, thickness vibration can be generated, and a capacitance can be formed between the capacitance electrode and the ground terminal at a position away from the vibration region, so that it can be effectively prevented that desired thickness vibration in the vibration region is suppressed by the electric field formed between the capacitance electrode and the ground terminal and the resonance characteristic is deteriorated.

Insulators may be deposited on the piezoelectric substrate at positions between the first and second capacitance electrodes and the ground terminals. These insulators effectively prevent electrical short circuits between the first and second capacitance electrodes and the ground terminals. Thereby, it becomes possible to narrow the distances between the first and second capacitance electrodes and the ground terminals, and larger capacitances can be formed.

In the piezoelectric oscillation element of the present invention, it is preferable that no electrode is formed in a region facing the first capacitance electrode via the piezoelectric substrate, and no electrode is formed in a region facing the second capacitance electrode via the piezoelectric substrate. That is, the capacitance electrodes have no electrodes facing them via the piezoelectric substrate.

Therefore, the central portion of the facing region most greatly vibrates, and the vibration becomes smaller toward the outside from the facing region. The capacitance electrode and the ground electrode form a capacitance in a region out of the facing region, so that even when an electric field is generated in this remote region, this does not suppress the thickness vibration in the facing region.

A structure may be alternatively employed in which a first auxiliary capacitance electrode is formed in the region facing the first capacitance electrode via the piezoelectric substrate, and a second auxiliary capacitance electrode is formed in the region facing the second capacitance electrode via the piezoelectric substrate. Thereby, much larger capacitances can be formed between the first and second capacitance electrodes and the ground terminals.

In this case, the first auxiliary capacitance electrode is not basically different in potential from the first capacitance electrode, and the second auxiliary capacitance electrode is not basically different in potential from the second capacitance electrode. With these potentials, an electric field is generated neither between the first auxiliary capacitance electrode and the first capacitance electrode nor between the second auxiliary capacitance electrode and the second capacitance electrode. Therefore, the thickness vibration generated in a region in which the first and second vibration electrodes face each other is prevented from being suppressed.

Another structure may be employed in which insulators are deposited on the piezoelectric substrate at positions between the first and second capacitance electrodes and the ground terminals, and insulators are deposited on the piezoelectric substrate at positions between the first and second auxiliary capacitance electrodes and the ground terminals. Thereby, between the first and second capacitance electrodes and the ground terminals and between the first and second auxiliary capacitance electrodes and the ground terminals, electrical short circuits can be effectively prevented. Thereby, the distances between the first and second capacitance electrodes and the ground terminals and between the first and second auxiliary capacitance electrodes and the ground terminals can be narrowed, so that larger capacitances can be formed.

The ground terminals may be made of an elastic material having conductivity. It becomes possible to effectively damp (deaden) undesired vibration generated by electric fields between the capacitance electrodes or auxiliary capacitance electrodes and the ground terminals by the elastic ground terminals, and the problem of deterioration in stability of oscillation due to spurious components generated by undesired vibration can be effectively prevented.

In addition, a first dielectric layer covering apart of the first conductor film and a second dielectric layer covering a part of the second conductor film may further be included, and the ground terminals may be connected to a first ground electrode facing the first conductor film via the first dielectric layer and a second ground electrode facing the second dielectric layer via the second dielectric layer.

With this structure, the first conductor film and the first ground electrode face each other via the first dielectric layer, and the second conductor film and the second ground electrode face each other via the second dielectric layer. Therefore, by forming the first and second dielectric layers so as to be thin by using a high dielectric constant material, large capacitances can be easily formed between the first conductor film and the first ground electrode and between the second conductor film and the second ground electrode. Most of the electric field generated between the first conductor film and the first ground electrode exists in the first dielectric layer, and most of the electric field generated between the second conductor film and the second ground electrode exists in the second dielectric layer, so that the electric fields hardly leak into the piezoelectric substrate. Therefore, electric fields can be effectively suppressed from leaking into the vibration region in which the first and second vibration electrodes face each other across the piezoelectric substrate.

It is a preferable structure in which the first conductor film has the first vibration electrode and the first capacitance electrode, and the second conductor film has the second vibration electrode and the second capacitance electrode, and the first and second vibration electrodes face each other via the piezoelectric substrate.

In this case, it is preferable that the first dielectric layer covers apart of the first capacitance electrode, and that the second dielectric layer covers a part of the second capacitance electrode.

It is also allowed that on one main surface of the piezoelectric substrate, a first auxiliary ground electrode to be connected to the ground terminal is formed between the first capacitance electrode and a side end of the piezoelectric substrate, and that a second auxiliary ground electrode to be connected to the ground terminal is formed between the second capacitance electrode and a side end of the piezoelectric substrate on the other main surface of the piezoelectric substrate. With this structure, in addition to the capacitance formed between the first capacitance electrode and the first ground electrode, a capacitance is also formed between the first capacitance electrode and the first auxiliary ground electrode. In addition to the capacitance formed between the second capacitance electrode and the second ground electrode, a capacitance is also formed between the second capacitance electrode and the second auxiliary ground electrode, so that the overall capacitance can be increased.

The piezoelectric oscillation element of the present invention may have insulation plates deposited so as to cover at least a part of the first ground electrode and at least a part of the second ground electrode. This deposition of the insulators can suppress electrical short circuits between the first and second capacitance electrodes and the first and second ground electrodes.

When the insulation plates have openings surrounding the first and second vibration electrodes, vibration spaces can be secured due to these insulators, so that a piezoelectric oscillation element with excellent resonance characteristics can be obtained.

A piezoelectric oscillation component of the present invention is structured so that the piezoelectric oscillation element structured as described above is sandwiched between protective substrates provided on and under the component. By thus hermetically sealing the piezoelectric oscillation element with the protective substrates, a highly reliable piezoelectric oscillation component can be manufactured.

In further detail, the first conductor film has a first vibration electrode and a first capacitance electrode, the second conductor film has a second vibration electrode and a second capacitance electrode, the upper and lower surfaces of the piezoelectric oscillation element are sandwiched by insulation plates having openings formed so as to surround the first and second vibration electrodes, and protective substrates are deposited on the upper and lower surfaces of the piezoelectric oscillation element via the insulation plates. By employing this structure, a piezoelectric oscillation component which is small in size and excellent in electrical characteristics and reliability can be obtained.

The above-described and other advantages, features, and effects of the present invention will be made clear by the following description of embodiments with reference to the accompanying drawings.

DESCRIPTION OF SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the piezoelectric oscillation element of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1is an external perspective view of a piezoelectric oscillation element of an embodiment of the present invention,FIG. 2is a plan view observed from above, andFIG. 3is a sectional view along A-A.

The piezoelectric oscillation element1includes a piezoelectric substrate10, a first conductor film21(synthesis of21a,21b, and21cin the drawings) deposited on one main surface of the piezoelectric substrate10, a second conductor film22(synthesis of22a,22b, and22cin the drawings) deposited on the other main surface of the piezoelectric substrate10, ground terminals31aand31bdeposited on side surfaces of the piezoelectric substrate10, and first input/output terminals32aand32band second input/output terminals33aand33bdeposited on the side surfaces of the piezoelectric substrate10.

The piezoelectric substrate10is made of piezoelectric ceramics including a base material such as lead zirconate titanate (PZT), lead titanate (PT), potassium sodium niobate (Na1-xKxNbO3), bismuth layer-structured compound (for example, MBi4Ti4O15, M: bivalent alkaline earth metal), or piezoelectric single crystal such as crystal or lithium tantalate. In order to realize a small size and excellent mounting performance on a circuit board, it is desirable that the piezoelectric substrate is in a rectangular parallelepiped shape having a length of 0.6 to 5 mm, a width of 0.3 to 5 mm, and a thickness of 40 μm (micrometers) to 1 mm.

The piezoelectric substrate10does not always have to have an even thickness on the entire surface thereof, and for the purpose of improving the resonance characteristics of thickness vibration for energy confinement, for example, it is allowed that the thickness of the vibration region can be made thin or thick.

Preferably, the value of the relative permittivity of the piezoelectric substrate10is not more than 1000 for excellent resonance characteristics of a high-frequency region.

When the piezoelectric substrate10is made of a ceramic material, it is formed into a sheet according to a method in which a binder is added to a raw material powder and pressed, a method in which the raw material powder is mixed with water and a dispersant and dried by using a ball mill and added with a binder, a solvent, and a plasticizer, etc., and molded according to a doctor blade method, or the like. Next, calcination is performed at a peak temperature of 1100 to 1400° C. for 0.5 to 8 hours, and then polarization is applied by applying a voltage of 3 to 6 kV/mm in the thickness direction at a temperature of 80 to 200° C., whereby a piezoelectric substrate10with desired piezoelectric characteristics is obtained.

When the piezoelectric substrate10is made of a piezoelectric single crystal material, by cutting an ingot (base metal) of the piezoelectric single crystal material which becomes the piezoelectric substrate10so as to have a predetermined crystal direction, a piezoelectric substrate10having desired piezoelectric characteristics is obtained.

The first conductor film21is deposited on the one main surface of the piezoelectric substrate10, and includes a first vibration electrode21a, a first capacitance electrode21bextended from the first vibration electrode21atoward the ground terminal31a, and a connection electrode21cfor electrically connecting the first vibration electrode21aand the first input/output terminals32aand32b.

Similarly, the second capacitance electrode22is deposited on the other main surface of the piezoelectric substrate10, and includes a second vibration electrode22a, a second capacitance electrode22bextended from the second vibration electrode22atoward the ground terminal31b, and a connection electrode22cfor electrically connecting the second vibration electrode22aand the second input/output terminals33aand33b.

The first vibration electrode21aand the second vibration electrode22aare arranged so as to face each other by sandwiching the piezoelectric substrate10therebetween. The region in which these first and second vibration electrodes21aand22aface each other is referred to as a “facing region.”

In regions facing the first capacitance electrode21band the connection electrode21cvia the piezoelectric substrate10, no electrode is formed to prevent excitation of extra thickness vibration.

In the regions facing the second capacitance electrode22band the connection electrode22c, no electrode is formed, either, to prevent excitation of extra thickness vibration.

In the facing region, an electric field is applied between the first vibration electrode21aand the second vibration electrode22a, and energy confinement type thickness vibration is excited. For the thickness vibration, a fundamental wave of the thickness longitudinal vibration or higher harmonic can be used. A region in which this thickness vibration is excited is referred to as a “vibration region.” The vibration region includes the facing region in which the first vibration electrode21aand the second vibration electrode22aface each other and regions near the facing region (seeFIG. 3).

Preferably, the first conductor film21and the second conductor film22are formed of a metal film of gold, silver, copper, aluminum, etc. in terms of conductivity, and desirably, its thickness is in a range of 0.1 μm to 3 μm. If the metal film is thinner than 0.1 μm, the conductivity deteriorates due to oxidation caused when the piezoelectric substrate10is exposed to a high temperature in the atmosphere, and if the metal film is made thicker than 3 μm, the film easily peels off.

For forming the metal film, coating and baking by vacuum deposition, PVD, sputtering, or thick-film printing can be used. For increasing the adhesion to the piezoelectric substrate10, for example, an underlying electrode layer with high adhesion to the ceramic substrate, such as Cr, may be formed in advance, and a desired metal film may be formed thereon.

After depositing the metal film on both entire main surfaces of the piezoelectric substrate10, a photoresist film with a thickness of 1 to 10 μm is formed on the piezoelectric substrate10by spin coating, etc., and patterned by photo etching to form electrodes.

The ground terminals31aand31bare deposited near the centers of the side surfaces of the piezoelectric substrate10, and the ground terminal31ais arranged near the first capacitance electrode21band the ground terminal31bis arranged near the second capacitance electrode22b, and these are both connected to a ground potential.

The first input/output terminals32aand32band the second input/output terminals33aand33bare deposited on the both side surfaces of the piezoelectric substrate10.

The first input/output terminal32aand the second input/output terminal33aare arranged so as to sandwich the ground terminal31a, and the first input/output terminal32band the second input/output terminal33bare arranged so as to sandwich the ground terminal31b. The first input/output terminals32aand32bare connected via the connection electrode21c, and the second input/output terminals33aand33bare connected via the connection electrode22c.

These ground terminals31aand31b, first input/output terminals32aand32b, and second input/output terminals33aand33bare used for electrical connection and mechanical fixture of the piezoelectric oscillation element1to the outside.

The ground terminals31aand31band the input/output terminals32a,32b,33aand33bare desirably made of an elastic material having conductivity such as a conductive resin.

By using a conductive resin, it becomes possible to damp undesired vibration excited between the first and second capacitance electrodes21band22bprovided on the outer peripheral edge of the main surfaces of the piezoelectric substrate10and the ground terminals31aand31bprovided on the side surfaces of the piezoelectric substrate10, and a piezoelectric oscillation element1with more excellent resonance characteristics can be obtained.

It is desirable that the thickness of the conductive resin is not less than 5 μm in terms of the high effect of damping undesired vibration. However, if it is excessively made thick, the resin becomes easy to peel off from the piezoelectric substrate10due to a stress working at mounting, so that the range of 10 μm to 60 μm is especially desirable. The elastic modulus of the conductive resin in a range of 2 to 60 GPa can bring about a sufficient damping effect.

For forming such a conductive resin, a thermosetting or photo-curable conductive resin may be applied by using screen printing, roller transfer or the like and cured by heating or ultra violet irradiation. As a foundation layer of the conductive resin, a metal film of gold, silver, copper, aluminum, etc. may be formed. Furthermore, on the surface of the conductive resin, at least one kind of plating film using Cu, Ni, Sn, Au, etc. is formed, whereby a piezoelectric oscillation element excellent in solderability is obtained.

In terms of excellent conductivity and easiness in plating film formation, it is desirable that the conductive resin contains at least one kind of metal filler using Ag, Cu, Ni, etc., and it is desirable that the amount of the metal filler in the conductive resin is 75 to 95 weight %. In terms of improvement in solder wettability of the plating film, in order to make the conductive resin surface smooth, the particle diameter of the metal filler is preferably smaller. For example, it is desirable that its average particle diameter is 0.5 to 2 μm.

When an alternating voltage is applied to the input/output terminals32a,32b,33aand33bof this piezoelectric oscillation element1, energy confinement type thickness vibration is excited in the vibration region sandwiched between the first vibration electrode21aand the second vibration electrode22aof the piezoelectric substrate10, and a resonance peak caused by the vibration appears in the frequency characteristics. The piezoelectric oscillation element1of the present invention uses the resonance phenomenon caused by such thickness vibration.

FIG. 4is an equivalent circuit diagram of the piezoelectric oscillation element.

The capacitance between the first capacitance electrode21band the ground terminal31a, the capacitance between the first input/output terminal32aand the ground terminal31a, and the capacitance between the first input/output terminal32band the ground terminal31bform a load capacitance c1shown inFIG. 4.

The capacitance between the second capacitance electrode22band the ground terminal31b, the capacitance between the second input/output terminal33aand the ground terminal31a, and the capacitance between the second input/output terminal33band the ground terminal31bform a load capacitance c2shown inFIG. 4.

Thus, between the input/output terminals32a,32b,33aand33band the ground terminals31aand31b, load capacitances c1and c2are formed, and a piezoelectric oscillation element including a load capacitance as a whole is obtained.

The piezoelectric oscillation element1of this embodiment can form a larger capacitance when the gaps of the electrode ends closest to each other are equal to each other in comparison with the case where a capacitance is formed by arranging electrodes close to each other on the same main surface of the piezoelectric substrate. Therefore, the piezoelectric oscillation element1has a larger load capacitance.

As shown inFIG. 3, at positions away from the vibration region in which the first and second vibration electrodes21aand22aare formed, capacitances are formed between the first and second capacitance electrodes21band22band the ground terminals31aand31b, so that it is effectively prevented that the electric fields formed between these electrodes suppress desired vibration in the vibration region to deteriorate the resonance characteristics.

Furthermore, in the piezoelectric oscillation element1of this embodiment, on the side surfaces of the piezoelectric substrate10, the input/output terminals32aand33aare formed so as to sandwich the ground terminal31a, and the input/output terminals32band33bare formed so as to sandwich the ground terminal31b, so that capacitances are generated even between the ground terminals31aand31band the input/output terminals32a,32b,33aand33b, so that a load capacitance necessary for oscillation can be increased.

In this piezoelectric oscillation element1, as described above, a large load capacitance can be structurally formed, so that it becomes possible to use a PT (PbTiO3)-based material whose relative permittivity is small although its Qm is high, and a high-performance piezoelectric element having a built-in load capacitance can be obtained.

FIG. 5is an external perspective view showing a piezoelectric oscillation element having another structure,FIG. 6is a plan view observed from above, andFIG. 7is a sectional view along B-B. Only differences from the above-described embodiment will be described, and description of the same components will be omitted by using the same reference numerals (the same applies to the following).

A structural difference of this piezoelectric oscillation element from the piezoelectric oscillation element shown inFIG. 1throughFIG. 3is that an insulator24ais deposited on the piezoelectric substrate10at a position between the first capacitance electrode21band the ground terminal31a, and an insulator24bis deposited on the piezoelectric substrate10at a position between the second capacitance electrode22band the ground terminal31b.

For the insulators24aand24b, a resin material such as phenol-based resin, polyimide-based resin, and epoxy-based resin can be used. An epoxy-based resin is desirably used due to its excellent insulation, adhesion to ceramic, and excellent moisture resistance. Preferably, the epoxy-based resin is a curable type which does not cause hydrolysis, and epoxy-based resin added with particles of rutile type titanium oxide, etc. for the purpose of lowering water permeability, added with 2-4 diamino-6 vinyl-S triamine and isocyanuric acid for the purpose of improving insulation, and added with a proper amount of carbon black for the purpose of preventing permeation of moisture due to cleaving of the main chain of the resin may be used.

When a resin material is used as the insulators24aand24b, for example, a thermosetting or photo-curable resin is applied with a thickness of 1 to 80 μm onto the piezoelectric substrate10by screen printing, etc., and cured by heating or ultra violet irradiation.

By thus depositing the insulators24aand24bon the piezoelectric substrate10, electrical short circuits due to insulation breakdown, migration or manufacturing failures between the first and second capacitance electrodes21band22band the ground terminals31aand31bcan be effectively prevented. Thereby, without fearing short circuits, the distances between the first and second capacitance electrodes21band22band the ground terminals31aand31bcan be further narrowed, whereby a large capacitance can be formed.

FIG. 8is a plan view observed from above a piezoelectric oscillation element according to another embodiment of the present invention.

In the piezoelectric oscillation element1shown inFIG. 8, on one main surface of the piezoelectric substrate10, a first capacitance electrode21dis provided so as to extend from the connection electrode21cof the first conductor film21, and on the other main surface of the piezoelectric substrate10, a second capacitance electrode22dis provided so as to extend from the connection electrode22cof the second conductor film22. The first capacitance electrode21dis closer to the ground terminal31a, and the second capacitance electrode22dis closer to the ground terminal31b. No electrode is formed in the region facing the first capacitance electrode21dvia the piezoelectric substrate10. No electrode is formed also in the region facing the second capacitance electrode22d.

In this structure, the function of forming capacitances by the capacitance electrodes21dand22dbetween the same and the ground terminals31aand31bis the same as in the capacitance electrodes21band22b.

With this structure, the capacitance between the ground terminal31aand the first input/output terminal32acan be increased, and the capacitance between the ground terminal31band the second input/output terminal33bcan be increased.

With this structure, it becomes unnecessary to form an extra electrode pattern near the vibration region, and it becomes possible to reduce harmful influence of the electrode mass effect and the like on the desired thickness vibration.

FIG. 9is a perspective view of the piezoelectric oscillation element according to a variation ofFIG. 8, andFIG. 10is a sectional view along C—C.

A first auxiliary capacitance electrode23ais formed in the region facing the first capacitance electrode21dvia the piezoelectric substrate10, and a second auxiliary capacitance electrode23bis formed in a region facing the second capacitance electrode22d. The first auxiliary capacitance electrode23ais connected to the first input/output terminal32a, and the second auxiliary capacitance electrode23bis electrically connected to the second input/output terminal33b. Therefore, the first auxiliary capacitance electrode23abasically becomes equal in potential to the first capacitance electrode21d, and the second auxiliary capacitance electrode23bbasically becomes equal in potential to the second capacitance electrode22d.

With this structure, in comparison with the structure ofFIG. 8, due to addition of the auxiliary capacitance electrodes23aand23b, capacitances are also formed between the auxiliary capacitance electrodes23aand23band the ground terminals31aand31b, so that the load capacitances c1and c2in the equivalent circuit diagram shown inFIG. 4can be made much larger.

An electric field is generated neither between the first auxiliary capacitance electrode23aand the first capacitance electrode21dnor between the second auxiliary capacitance electrode23band the second capacitance electrode22d. Therefore, no electric field leaks into the vibration region in which the first and second vibration electrodes21dand22dface each other across the piezoelectric substrate10.

FIG. 11is a perspective view of a piezoelectric oscillation element obtained by adding insulators to the piezoelectric oscillation element ofFIG. 9, andFIG. 12is a sectional view along D-D.

In this piezoelectric oscillation element, on one main surface of the piezoelectric substrate10, an insulator24ais deposited on the piezoelectric substrate10at a position between the first capacitance electrode21dand the ground terminal31a, and an insulator24bis deposited on the piezoelectric substrate10at a position between the second auxiliary capacitance electrode23band the ground terminal31b. Also on the other main surface of the piezoelectric substrate10, an insulator24cis deposited on the piezoelectric substrate10at a position between the first auxiliary capacitance electrode23aand the ground terminal31a, and an insulator24dis deposited on the piezoelectric substrate10at a position between the second capacitance electrode22dand the ground terminal31b.

In this structure, electrical short circuits of the first and second capacitance electrodes21dand22dand the first and second auxiliary capacitance electrodes23aand23bwith the ground terminals31aand31bcan be effectively prevented.

In addition, it becomes possible to effectively narrow the distances from the first and second capacitance electrodes21dand22dand the first and second auxiliary capacitance electrodes23aand23bto the ground terminals31aand31b, so that a larger capacitance can be formed.

FIG. 13is an external perspective view showing a piezoelectric oscillation component using the piezoelectric oscillation element of the present invention,FIG. 14is a plan view observed from below, andFIG. 15andFIG. 16are exploded perspective views.

In the piezoelectric oscillation component5having this structure, protective substrates50aand50bare deposited on upper and lower surfaces of the piezoelectric oscillation element1via insulation plates40aand40b.

These insulation plates40aand40bhave a function of effectively preventing electrical short circuits due to insulation breakdown, migration, manufacturing failures or the like between the first and second capacitance elements21band22band the ground terminals31aand31bsimilar to the above-described insulators24aand24b.

For the insulation plates40aand40b, a resin material using, for example, a phenol-based resin, a polyimide-based resin, an epoxy-based resin, etc. as a base material can be used. A base material of an epoxy-based resin is desirably used due to its excellent insulation, high adhesion to ceramic, and excellent moisture resistance and heat resistance. Preferably, the epoxy-based resin is a curable type which does not cause hydrolysis, and if required, the epoxy-based resin may be added with rutile type titanium oxide for the purpose of lowering water permeability, added with 2-4 diamino-6 vinyl-S triamine and isocyanuric acid for the purpose of improving insulation, or added with a proper amount of carbon black for the purpose of preventing permeation of moisture due to cleaving of the main chain of the resin.

With respect to such a resin material, for example, a thermosetting or light-curable resin is applied with a thickness of 1 to 80 μm onto the piezoelectric substrate10by screen printing, transfer, etc., and only a desired part is cured by heating, ultra violet irradiation or the like to form insulation plates40aand40bin desired shapes.

For the protective substrates50aand50b, a dielectric ceramic material such as alumina, titanium oxide, magnesium oxide, barium titanate, etc. can be used, so that it becomes possible to form a large capacitance by using the protective substrates50aand50b. In this case, desirably, dielectric ceramic with a relative permittivity of about 200 to 2500 is used.

Furthermore, on the lower surface of the piezoelectric oscillation component5, external electrodes (general term: external electrode60) including a plurality of electrodes60athrough60care deposited. The terminals of the external electrode60aare connected to the first input/output terminals32aand32b, the external electrode60bis connected to the ground terminals31aand31b, and the external electrode60cis connected to the second input/output terminals33aand33b, respectively.

Therefore, the capacitance formed between the external electrodes60aand60bis added to the load capacitance c1ofFIG. 2, and the capacitance formed between the external electrodes60cand60bis added to the load capacitance c2ofFIG. 2, so that a much larger total load capacitance can be formed.

When the protective substrates50aand50bare made of a ceramic material, the external electrode60may be formed of a favorable conductor film of Ag, etc. by vapor deposition, sputtering or the like, formed by baking a conductive paste, or formed by using a conductive resin.

Not only the external electrode60but also the input/output terminals32aand32b, the input/output terminals33aand33b, and the ground terminals31aand31bcan be formed by depositing a conductive resin.

For deposition of this conductive resin, a thermosetting or light-curable conductive resin is applied by screen printing, roller transfer or the like, and cured by heating or ultra violet irradiation. By forming at least one kind of plating film using Cu, Ni, Sn, Au, etc. on the surface of the conductive resin, a piezoelectric oscillation component excellent in solderability can be obtained.

For realizing excellent conductivity and easy formation of plating film, it is desirable that the conductive resin contains at least one kind of metal filler using Ag, Cu, Ni, etc., and that the amount of the metal filler contained in the conductive resin is 75 to 95 weight %. For smoothing the surface of the conductive resin to improve the solder wettability of the plating film, the particle size of the metal filler is preferably smaller, and for example, a metal filler with an average particle size of 0.5 to 2 μm is desirably used.

In the piezoelectric oscillation component5of this embodiment, as shown inFIG. 13andFIG. 15, protective substrates50aand50bare deposited on both main surfaces of the piezoelectric oscillation element1via annular insulation plates40aand40bformed so as to surround the first and second vibration electrodes21aand22a.

Therefore, in the vicinity of centers of the insulation plates40aand40b, openings41aand41bare formed. While vibration spaces are secured by these openings41aand41b, hermetic sealing can be realized by the protective substrates50aand50b, so that a piezoelectric oscillation component which can be used independently without separately preparing an airtight package is obtained.

In addition, the insulation plates40aand40balso function to prevent electrical short circuits between the capacitance electrodes and auxiliary capacitance electrodes and the ground terminals, whereby a piezoelectric oscillation component small in size and excellent in electrical characteristics and reliability can be obtained.

In this piezoelectric oscillation component5, when protective substrates50aand50bmade of ceramics with a high relative permittivity are used, it becomes possible to make thin the protective substrates50aand50b, so that the piezoelectric oscillation component5can be made thin.

In the above-described embodiment, a ceramic material is used for the protective substrates50aand50b. However, if the ceramic material is made thin for making the protective substrates thin, an extra step is needed in polishing. If the substrate is reduced in thickness to 100 μm or less, the substrate becomes easy to crack and handling thereof becomes difficult.

Therefore, when the piezoelectric oscillation component5is made thin, a resin sheet material which does not crack even when it is made thin and is low in cost may be used for the protective substrates50aand50b.

A resin sheet material with a thickness of not more than 100 μm is generally usable and reduction in cost can be realized.

As the resin sheet material, an epoxy-based resin, polyimide-based resin, liquid crystal polymer (LCP), polyethyletherketone (PEEK), etc., may be used. In terms of realizing a reduction in thickness and airtightness of the piezoelectricoscillation component5, the thickness of the resin sheet material is desirably 20 to 100 μm.

When the thin resin sheet material is used, for the purpose of improving the mechanical strength as the protective substrate, if required, a resin sheet material containing a needle-like filler or fiber material made of an inorganic or organic material may be used.

In order to prevent the resin sheet material from being deformed or torn by an external force from above or below, it is especially desirable to use a resin sheet material (prepreg) obtained by impregnating an epoxy-based resin, a polyimide-based resin or the like in a fabric made of glass fibers or aramid fibers, and the mechanical strength of the resin sheet material can be significantly improved by these fibers.

By forming the protective substrates50aand50bof resin sheets and forming the ground terminals31a,31b, the input/output terminals32a,32b,33aand33band the external electrode60from a conductive resin, both of these are made of resin materials, so that adhesion there between is increased, and as a result, terminals and electrodes excellent in adhesion are formed.

In the piezoelectric oscillation component5of the above-described embodiment, the protective substrates50aand50bare made of dielectric ceramic or resin sheet materials. However, it is also allowed that, for example, the upper protective substrate50ais formed of a thin resin sheet material, and that the lower protective substrate50bis made of dielectric ceramics with a low relative permittivity of 10 or less and a high strength such as alumina. Thereby, a load capacitance of the component can be secured, and the component can be improved in mechanical strength while it is made thin.

When the upper protective substrate50ais formed of a thin resin sheet material, and the lower protective substrate50bis made of dielectric ceramics with low strength although having a high relative permittivity of 200 or more such as barium titanate, a component made thin can be obtained while a large load capacitance of the component is secured.

Furthermore, as shown inFIG. 16, it is also allowed that a protective substrate50cis further disposed between the lower protective substrate50band the insulation plate40b, the protective substrates50aand50care formed of resin sheet materials, and the protective substrate50bis made of dielectric ceramic. With this structure, even if the protective substrate50bmade of the above-described dielectric ceramics should crack due to an external force, the airtightness of the vibration space can be maintained by the resin sheet50c, and a flux can be prevented from intruding at solder-mounting.

FIG. 17is an external perspective view showing a piezoelectric oscillation element of another embodiment of the present invention,FIG. 18is a plan view observed from above, andFIG. 19is a sectional view along E-E.

This piezoelectric oscillation element is basically the same in structure as the piezoelectric oscillation elements described with reference toFIG. 1throughFIG. 3, except for the following points.

In this piezoelectric oscillation element1, a first dielectric layer35acovering a part of the first capacitance electrode21band a second dielectric layer35bcovering a part of the second capacitance electrode22bare deposited on both main surfaces of the piezoelectric substrate.

In order to prevent attenuation of desired thickness vibration, it is desirable that these dielectric layers35aand35bare provided away from the region in which the first vibration electrode21aand the second vibration electrode22aface each other and a vibration region near the region.

As the dielectric material forming the dielectric layers35aand35b, a polymer-based dielectric material is preferably used since it can be formed according to an easy method such as screen printing. For example, by means of using a polymer-dispersed type dielectric material obtained by mixing inorganic particles (average particle size: 0.5 to 5 μm) of a dielectric material having a high relative permittivity (not less than 1500) such as barium titanate with a resin such as epoxy-based resin or melamine-based resin and dispersing them, or a polymer-composite type dielectric material obtained by chemically decorating the surfaces of inorganic particles (average particle size: 30 to 200 nm (nanometers)) formed by reducing the particle size of a dielectric material with a high relative permittivity (not less than 1500) such as barium titanate and evenly filling these at high concentration in a resin such as an epoxy-based resin, a high relative permittivity can be realized. In terms of the high relative permittivity, a glass-baked type dielectric material obtained by dispersing inorganic particles (average particle diameter: 0.2 to 5 μm) of a dielectric material with a high relative permittivity (not less than 1500) such as barium titanate in a glass base material is also usable. Furthermore, a dielectric film of barium titanate, etc. may be formed by sputtering, aerosol deposition, or molecular collision.

In case of using the polymer-based dielectric material, if the thicknesses of the first dielectric layer35aand the second dielectric layer35bare excessively made thin the voltage resistance thereof deteriorates, and if these are excessively made thick, the capacitance value thereof lowers. Desirably, the film thickness when using the polymer-dispersed type dielectric as the dielectric material is in a range of 8 to 20 μm, and the film thickness when using the polymer-composite type dielectric is in a range of 4 to 50 μm. When the glass-baked type dielectric material is used as the dielectric material, for the same reason as described above, it is desirable that the film thickness is in a range of 8 to 20 μm. Furthermore, when a ceramic film is used as the dielectric material, if the film is thin, the voltage resistance deteriorates, and if the film is thick, it takes time to form the film and the cost increases, so that the film thickness is desirably in a range of 1 to 5 μm.

The ground terminal31adeposited near the center of one side surface of the piezoelectric substrate10extends on one main surface of the piezoelectric substrate10and forms a first ground electrode31c. This first ground electrode31cfaces the first capacitance electrode21bvia the first dielectric layer35a. Thereby, a predetermined capacitance is formed between the same and the first capacitance electrode21b.

The ground terminal31bdeposited near the center of the other side surface of the piezoelectric substrate10extends on the other main surface of the piezoelectric substrate10and forms a second ground electrode31d. This second ground electrode31dfaces the second capacitance electrode22bvia the second dielectric layer35b. Thereby, between the same and the second capacitance electrode22b, a predetermined capacitance is formed.

The ground terminal31aand the first ground electrode31care electrically connected, and the ground terminal31band the second ground electrode31dare electrically connected.

In terms of conductivity, it is preferable that the ground terminal31a, the ground terminal31b, the first ground electrode31c, and the second ground electrode31dare formed of metal films of gold, silver, copper, aluminum, etc., and that thicknesses are in a range of 0.1 to 3 μm. If the metal film is thinner than 0.1 μm, for example, when it is exposed to a high temperature in the atmosphere, its conductivity deteriorates due to oxidation, and if the metal film is thicker than 3 μm, it becomes easy to peel off. Vacuum deposition or sputtering can be used for deposition of the metal film.

The ground terminal31a, the ground terminal31b, the first ground electrode31c, and the second ground electrode31dmay be formed by using a conductive resin such as an epoxy-based resin for the reason that it can be easily formed by a simple device for screen printing. In particular, when a polymer-based material is used for the first dielectric layer35aand the second dielectric layer35b, a conductive resin such as an epoxy-based resin is preferably used because of its excellent adhesive strength to the dielectric layer.

As the conductive resin, a thermosetting or light-curable conductive resin is usable, and desirably, it contains at least one kind of metal filler using Ag, Cu, Ni, etc., and the amount of the metal filler in the conductive resin is desirably 75 to 95 weight %. In particular, when a conductive resin is formed to be thin, the smaller particle diameters of the metal filler are preferable, and a conductive resin film with a thickness of 5 to 15 μm can be formed by using a metal filler with an average particle size of 0.5 to 2 μm and by using screen printing, roller transfer, etc.

When ceramic films are used as the first dielectric layer35aand the second dielectric layer35b, either of a metal film or a conductive resin may be used as an electrode material.

In the piezoelectric oscillation element1of this embodiment, the first and second dielectric layers35aand35bare formed to be thin by using a dielectric material with high permittivity, whereby a large capacitance can be easily formed between the first capacitance electrode21band the first ground electrode31cand between the second capacitance electrode22band the second ground electrode31d.

Most of the electric field generated between the first capacitance electrode21band the first ground electrode31cexists in the first dielectric layer35a, and most of the electric field generated between the second capacitance electrode22band the second ground electrode31dexists in the second dielectric layer35b, so that the electric fields hardly leak into the piezoelectric substrate10.

Therefore, suppression of desired vibration and resulting deterioration in oscillation due to electric fields leaking into a vibration region in which the first and second vibration electrodes21aand21bface each other via the piezoelectric substrate10can be effectively prevented. In addition, deterioration in stability of the oscillation due to undesired vibration generated by the electric fields leaking into other regions of the piezoelectric substrate10can be effectively prevented.

Next, piezoelectric oscillation elements of other embodiments of the present invention are shown inFIG. 20throughFIG. 26.

FIG. 20is an external perspective view showing a piezoelectric oscillation element according to another embodiment, andFIG. 21is a plan view observed from above.

The characteristic portions of the piezoelectric oscillation element1of this embodiment are a first capacitance electrode21dformed so as to extend from the connection electrode21ctoward the ground terminal31con one main surface of the piezoelectric substrate10, and a second capacitance electrode22dformed so as to extend from the connection electrode22ctoward the ground terminal31bon the other main surface of the piezoelectric substrate10.

These capacitance electrodes21dand22dface the ground electrode31cand the ground electrode31dvia the first dielectric layer35aand the second dielectric layer35b.

With this structure, as in the case of the embodiment ofFIG. 17throughFIG. 19, it becomes unnecessary to form an extra electrode pattern near the vibration region, and a failure that harmfully influences the desired thickness vibration due to mass effect of the electrode and the like can be effectively prevented.

FIG. 22is an external perspective view showing a piezoelectric oscillation element according to another embodiment,FIG. 23is a plan view observed from above, andFIG. 24is a sectional view along F-F.

The characteristic portions of the piezoelectric oscillation element1of this embodiment are a first auxiliary ground electrode31eto be connected to the ground terminal31a, formed between the first capacitance electrode21bon one main surface of the piezoelectric substrate10and the side end of the piezoelectric substrate10, and a second auxiliary ground electrode31fto be connected to the second ground terminal31b, formed between the second capacitance electrode22bon the other main surface of the piezoelectric substrate10and the side end of the piezoelectric substrate10.

Thereby, as shown inFIG. 24, a capacitance is also formed between the first capacitance electrode21band the first auxiliary ground electrode31eand between the second capacitance electrode22band the second auxiliary ground electrode31f, and it becomes possible to more efficiently form load capacitances forming an oscillation circuit.

FIG. 25is an external perspective view showing a piezoelectric oscillation element of still another embodiment, andFIG. 26is a plan view observed from above.

The characteristic portions of the piezoelectric oscillation element1of this embodiment are an insulation plate40adeposited so as to cover the upper portion of the piezoelectric oscillation element1shown inFIG. 17throughFIG. 19, and an insulation plate40bdeposited so as to cover the lower portion of this piezoelectric oscillation element1.

The insulation plates40aand40bare thus deposited so as to cover the first and second ground electrodes31cand31d, so that the ground electrodes31cand31dcan be protected from conductive foreign bodies and moisture. Therefore, between the first and second capacitance electrodes21band22band the ground electrodes31cand31d, electrical short circuits due to adhesion of conductive foreign bodies or ion migration can be effectively prevented.

The material of the insulation plates40aand40bis the same as described above with reference toFIG. 13throughFIG. 16.

In the piezoelectric oscillation element1of this embodiment, the insulation plates40aand40bare formed annularly so as to surround the vibration regions. That is, the insulation plate40ahas an opening41a, and the insulation plate40bhas an opening41b. Accordingly, due to the openings41aand41b, vibration spaces are secured, and it becomes possible to easily mount the piezoelectric oscillation element1inside an airtight package, etc.

In addition, the insulation plates40aand40bperforms two functions of preventing short circuits and securing vibration spaces, so that the piezoelectric oscillation element1can be small-sized and reduced in the number of constituting parts.

FIG. 27throughFIG. 30are drawings showing a piezoelectric oscillation component using the piezoelectric oscillation element of the present invention, andFIG. 27is an external perspective view,FIG. 28is a plan view observed from below, andFIG. 29andFIG. 30are exploded perspective views.

In the piezoelectric oscillation component5of this embodiment, protective substrates50aand50bare deposited on upper and lower surfaces of the piezoelectric oscillation element1shown inFIG. 25andFIG. 26via insulation plates40aand40b.

Furthermore, on the lower surface of the protective oscillation component5, external electrodes60athrough60care deposited as shown inFIG. 28. The external electrode60ais connected to the first input/output terminals32aand32b, the external electrode60bis connected to the ground terminals31aand31b, and the external electrode60cis connected to the second input/output terminals33aand33b.

Therefore, a capacitance formed between the external electrodes60aand60bis added to the capacitance c1shown inFIG. 4, and a capacitance formed between the external electrodes60cand60bis added to the capacitance c2shown inFIG. 4, so that a larger load capacitance can be formed as a whole.

As the external electrodes60athrough60c, a conductive resin is preferably used. However, when the protective substrates50aand50bare made of a ceramic material, for example, the external electrodes60athrough60cmay be formed by deposition, sputtering or the like of a favorable conductor film of, for example, Ag, or formed by baking a conductive paste.

In the piezoelectric oscillation component5of this embodiment, the protective substrates50aand50bare deposited on the both main surfaces of the piezoelectric oscillation element1via the annular insulation plates40formed so as to surround first and second vibration electrodes21aand22a. Therefore, the piezoelectric oscillation element1can be hermetically sealed by the protective substrates50aand50bwhile vibration spaces are secured by openings41aand41bformed near the centers of the insulation plates40, so that the piezoelectric oscillation component which can be used independently without separately preparing an airtight package is obtained.

In addition, the insulation plates40aand40balso perform the function of preventing electrical short circuits between the first and second capacitance electrodes21band22band the first and second ground electrodes31cand31d, so that a piezoelectric oscillation component which is small in size and excellent in reliability can be obtained.

In the piezoelectric oscillation component5of the above-described embodiment, the protective substrates50aand50bare made of dielectric ceramic or resin sheet material. However, alternatively, for example, the upper protective substrate50ais formed of a thin resin sheet material and the lower protective substrate50bis made of dielectric ceramic having a low relative permittivity of not more than 10 and having high strength such as alumina, whereby the load capacitance of the component is secured and the mechanical strength of the component can be improved while the component is made thin.

Furthermore, the upper protective substrate50ais made of a thin resin sheet material, and the lower protective substrate50bis made of low-strength dielectric ceramic while having a high relative permittivity of not less than 200 such as barium titanate, whereby the component can be made thin while a large load capacitance can be secured.

Furthermore, it is also allowed that a protective substrate50cis disposed between the lower protective substrate50band the insulation plate40bas shown inFIG. 30and the protective substrates50aand50care formed of resin sheet materials and the protective substrate50bis made of dielectric ceramic. With this structure, even if the protective substrate50bmade of dielectric ceramic should crack due to an external force, airtightness of the vibration space can be maintained by the protective substrate50cformed of a resin sheet, so that fluxing can be prevented from intruding at solder-mounting.

The present invention is not limited to the above-described embodiments, and can be variously varied and modified without deviating from the spirit of the present invention.

For example, in the piezoelectric oscillation element1shown inFIG. 1throughFIG. 3andFIG. 5throughFIG. 7, the first and second capacitance electrodes21band22bwhich are constant in width are formed from the first and second vibration electrodes21aand22atoward the ground terminals31aand31b. However, the present invention is not limited to this form.

As shown inFIG. 31, the first and second capacitance electrodes21band22bmay be widened near the ground terminals31aand31b. This makes it possible to form a larger capacitance.

In the piezoelectric oscillation element1shown inFIG. 17throughFIG. 26, the first dielectric35aand the first ground electrode31care each laminated as one layer on the first capacitance electrode21b, and the second dielectric35band the second ground electrode31dare each laminated as one layer on the second capacitance electrode22b.

However, without limiting to this, a plurality of layers may be laminated alternately, such as a dielectric layer, a ground electrode, a capacitance electrode, a dielectric layer, a ground electrode, and so on in order, on the first and second capacitance electrodes. This makes it possible to easily form a larger capacitance.

The piezoelectricoscillation element1shown inFIG. 17throughFIG. 26shows an example in which no electrode is formed on portions that face the connection electrodes21cand22cvia the piezoelectric substrate10. However, on these portions, electrodes with the same potential as that of the connection electrode21cor22cmay be formed.

The material of the insulation plates40aand40bof the piezoelectric oscillation component5is not limited to a resin material, and they may be made of a glass-based material to a thickness of 5 to 80 μm, or may be made of an oxide film of Al2O3or SiO2to a thickness of 0.1 to 10 μm. On these insulators, insulators made of a resin material may be formed so as to surround the first and second vibration electrodes21aand22a.