JP2008258799A - Thin film piezoelectric resonator - Google Patents

Abstract

A thin film piezoelectric resonator having excellent resonance characteristics is provided.
A substrate provided with a cavity, a lower electrode provided on the substrate so as to cover the cavity, a piezoelectric film provided on the lower electrode, and a piezoelectric film provided on the piezoelectric film. A thin film piezoelectric device comprising: an upper electrode; and a mass load portion provided on the upper electrode, wherein the mass load portion is provided so as to straddle an edge of the cavity. A resonator is provided.
[Selection] Figure 1

Description

  The present invention relates to a thin film piezoelectric resonator.

  With the recent enhancement in performance and functionality of mobile radio terminals, the number of parts used in mobile radio terminals has increased significantly, and miniaturization and modularization of parts have become important. Here, the filter occupies a large space in the wireless circuit, and in order to reduce the size of the wireless circuit and the number of parts, the filter must be downsized and modularized.

  Conventionally used filters include, for example, a dielectric filter, a surface acoustic wave (SAW) filter, and an LC filter. In recent years, a plurality of thin film bulk acoustic wave resonators (thin film piezoelectrics) A resonator filter including a resonator is considered to be most promising for downsizing and modularization of the filter.

  A thin film bulk acoustic wave resonator (thin film piezoelectric resonator) (hereinafter referred to as a thin film piezoelectric resonator) includes a lower electrode provided on a substrate, an upper electrode provided to face the lower electrode, an upper electrode and a lower electrode, And a cavity provided below the lower electrode.

In such a thin film piezoelectric resonator, parasitic capacitance occurs when the upper electrode and the lower electrode face each other on the substrate outside the cavity region. When a thin film piezoelectric resonator is used as a resonator filter, parasitic capacitance becomes a cause of filter characteristic deterioration. For this reason, a technique is disclosed in which the width of the portion where the upper electrode is drawn out of the cavity region is narrowed to suppress the generation of parasitic capacitance (see, for example, Patent Document 1).
Moreover, in order to ensure electrical connection between the upper electrode and the upper electrode wiring, a technique is disclosed in which the upper electrode and the upper electrode wiring are overlapped outside the cavity region (see, for example, Patent Document 2).

However, in the techniques disclosed in Patent Documents 1 and 2, suppression of vibration energy leaking to the substrate side through the lower electrode is not considered, and there is a problem in improving resonance characteristics.
JP-T-2006-503448 JP 2004-120494 A

  The present invention provides a thin film piezoelectric resonator having excellent resonance characteristics.

  According to one aspect of the present invention, a substrate provided with a cavity, a lower electrode provided on the substrate so as to cover the cavity, a piezoelectric film provided on the lower electrode, and the piezoelectric film An upper electrode provided on the upper electrode, and a mass load portion provided on the upper electrode, wherein the mass load portion is provided so as to straddle the edge of the cavity. A thin film piezoelectric resonator is provided.

  According to the present invention, a thin film piezoelectric resonator having excellent resonance characteristics is provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view for illustrating a thin film piezoelectric resonator according to a first embodiment of the invention.
FIG. 2 is a schematic diagram for illustrating the thin film piezoelectric resonator according to the first comparative example.

First, the first comparative example shown in FIG. 2 will be described.
FIG. 2A is a schematic partial cross-sectional view for illustrating the thin film piezoelectric resonator 10 according to the first comparative example.
As shown in FIG. 2A, on the upper surface of the substrate 2, a thermal oxide film (not shown), a passivation film (not shown), an amorphous base film (not shown), a lower electrode 3, a piezoelectric film 5, an upper electrode 4, not shown. The upper passivation film is formed from the lower layer in this order. The substrate 2 is provided with a cavity 6 penetrating the substrate 2, and a lower electrode 3 is provided so as to cover the opening on the substrate upper surface side of the cavity 6. An upper electrode 4 is provided so as to face the lower electrode 3, and a piezoelectric film 5 is provided between the lower electrode 3 and the upper electrode 4. Note that the portion where the upper electrode 4 and the lower electrode 3 overlap each other immediately above the cavity 6 is referred to as a resonator unit 7. In addition, a portion where the upper electrode 4 and the lower electrode 3 overlap each other on the substrate 2 outside the cavity 6 region is referred to as a parasitic capacitance portion 8.

Here, if the material of each part is exemplified, for example, the substrate 2 is silicon (Si), the thermal oxide film (not shown) is silicon oxide (SiO ₂ ), the passivation film (not shown) is silicon nitride (SiN), and not shown. The amorphous base film is tantalum aluminum (TaAl), the lower electrode 3 is aluminum (Al), the piezoelectric film 5 is aluminum nitride (AlN), the upper electrode 4 is molybdenum (Mo), and the upper passivation film (not shown) is silicon nitride (SiN). ). In addition, it is not necessarily limited to these materials, It can change suitably.

  The thin film piezoelectric resonator 10 has an action of filtering an input signal using the piezoelectric effect of the piezoelectric film 5. A signal input to an input terminal (not shown) is output from the upper electrode 4 connected to the input terminal (not shown) to the lower electrode 3 via the piezoelectric film 5. At this time, the piezoelectric film 5 vibrates in the thickness direction due to the inverse piezoelectric effect, but the laminated body composed of the upper electrode 4, the piezoelectric film 5, and the lower electrode 3 has a constant resonance frequency with respect to the vibration generated in the piezoelectric film 5. Therefore, only the signal that matches this resonance frequency among the input signals is output. Therefore, a resonator filter can be configured by using at least one thin film piezoelectric resonator 10 having such a filtering function.

  Here, when the upper electrode 4 and the lower electrode 3 face each other outside the cavity region, parasitic capacitance is generated at that portion, and vibration energy leaks to the substrate 2 through the lower electrode 3. For example, parasitic capacitance is generated in the parasitic capacitance section 8 shown in FIG. 2A, and vibration energy leaks.

  Further, for example, a resonator filter for mobile radio terminals is composed of a plurality of thin film piezoelectric resonators having a resonance frequency of 1 to 5 GHz. In such a thin film piezoelectric resonator, for example, when aluminum nitride (AlN) is used as the piezoelectric film, the film thickness of the piezoelectric film is 1-2 μm, whereas the film thickness of the electrode is 0.2-0. It becomes about 5 μm. Compared to ceramic resonators and quartz resonators that are composed of piezoelectric plates of several tens to several hundreds of micrometers and electrodes of several micrometers or less, thin film piezoelectric resonators having a resonance frequency of several GHz band The ratio of the film thickness of the electrode to the thickness is 10 to 60%, which is very large. For this reason, the influence of the electrode material, film thickness, and laminated structure on the resonance characteristics is extremely large.

  In this case, for example, when aluminum (Al) is used as the lower electrode 3, an aluminum nitride (AlN) piezoelectric film 5 having excellent orientation can be obtained. In addition, since the resistance value can be kept low, the Q value (Qr) at the resonance frequency can be improved. Therefore, a material mainly composed of aluminum (Al) or copper (Cu) is used as the material of the lower electrode 3.

  However, since aluminum (Al) has a small elastic constant, vibration energy is likely to be accumulated in the lower electrode 3, and the portion where the upper and lower electrodes face each other outside the cavity 6 region (parasitic capacitance portion 8) as described above. There is a problem that vibration energy is dissipated to the substrate 2 and as a result, the Q value (Qa) of the antiresonance frequency is lowered. This becomes more conspicuous for a material having a lower acoustic impedance such as aluminum (Al).

  FIG. 2B is a schematic diagram for illustrating the distribution of vibration energy at the anti-resonance frequency, and the distribution of vibration energy is obtained by simulation using the finite element method. FIG. 2B shows that the brighter the color tone, the higher the vibration energy. As can be seen from FIG. 2 (b), the vibration energy accumulated in the lower electrode 3 leaks into the substrate 2 along the edge of the cavity 6. In addition, the arrow in a figure has shown the flow (leakage) direction of vibration energy.

  As a result of the study, the present inventor obtained the knowledge that if the mass load portion 9 is provided on the upper electrode 4 so as to straddle the edge of the cavity 6, leakage of vibration energy can be suppressed. .

FIG. 1A is a schematic partial cross-sectional view for illustrating the thin film piezoelectric resonator according to the first embodiment of the invention. In addition, the same code | symbol is attached | subjected to the part similar to what was demonstrated in FIG. 2, and the description is abbreviate | omitted.
As shown in FIG. 1A, a mass load portion 9 is provided on the upper electrode 4 of the thin film piezoelectric resonator 1. The mass load portion 9 is provided so as to straddle directly above the edge of the cavity 6.

  When such a mass load portion 9 is provided, the center position of the vibration energy distribution in the thickness direction can be shifted to the upper electrode 4 side. Therefore, the vibration energy accumulated in the lower electrode 3 can be reduced accordingly. As a result, the vibration energy leaking from the lower electrode 3 to the substrate 2 can be suppressed, and the Q value (Qa) at the antiresonance frequency can be improved. The mass load part 9 is preferably provided so as to straddle the edge of the cavity 6, one end thereof being provided immediately above the resonator part 7, and the other end being provided immediately above the parasitic capacitance part 8.

  FIG. 1B is a schematic diagram for illustrating the distribution of vibration energy at the anti-resonance frequency, and the distribution of vibration energy is obtained by simulation using the finite element method. Here, FIG. 1B shows that the brighter the color tone, the higher the vibration energy. As can be seen from FIG. 1B, the vibration energy distribution is shifted to the upper electrode 4 side, and the vibration energy accumulated in the lower electrode 3 is greatly reduced. Further, the vibration energy leaking from the lower electrode 3 to the substrate 2 along the edge of the cavity 6 is also greatly reduced.

  Here, according to the experiment conducted by the present inventor, the Q value (Qa) 550 at the anti-resonance frequency of the comparative example shown in FIG. . In this case, the material of the mass load portion 9 is aluminum (Al). The thickness was set to 1 μm, and the position of one end of the mass load portion 9 was set to 5 μm on the cavity 6 side beyond just above the edge of the cavity 6. The width dimension is the same as that of the upper electrode 4.

FIG. 3 is a graph for illustrating impedance characteristics.
The waveform of F1 in FIG. 3 is that of the comparative example shown in FIG. 2, and the waveform of F2 is obtained by providing the aforementioned mass load portion 9. FIG. 3 shows that the resonance peak at the antiresonance frequency of F2 is sharper than the resonance peak at the antiresonance frequency of F1, and the Q value (Qa) at the antiresonance frequency is improved.

FIG. 4 is a Smith chart for illustrating impedance characteristics.
The waveform of F1 in FIG. 4 is that of the comparative example shown in FIG. 2, and the waveform of F2 is the one provided with the aforementioned mass load portion 9. From FIG. 4, it can be seen that F2 is closer to the outer circle than F1, and there is less energy loss (vibration energy leakage).

The material of the mass load portion 9 may be any material that can load an appropriate mass on the upper electrode 4. For example, aluminum (Al), aluminum nitride (AlN), copper (Cu), silicon nitride (SiN), silicon oxide (SiO ₂ ), molybdenum (Mo), tungsten (W), indium (In), gold (Au) And resin (for example, photosensitive polyimide resin, photosensitive epoxy resin, etc.). However, it is not necessarily limited to these and can be changed as appropriate.

In this case, for example, aluminum (Al) or the like can be selected in consideration of workability, and aluminum (Al), copper (Cu), or gold (Au) can be selected in consideration of integral formation with an upper electrode wiring described later. Etc. can be selected.
Further, if a material having an acoustic impedance lower than that of the upper electrode 4 is selected, vibration energy can be confined to the upper electrode 4, so that the Q value (Qa) at the antiresonance frequency can be further improved.

In addition, it is not always necessary to cover the entire area of the parasitic capacitance portion 8, but if the entire area is covered, leakage of vibration energy can be reduced.
Further, the thickness, length, and width are not limited to those described above, and can be appropriately changed depending on, for example, the material of the mass load portion 9 or the resonance frequency of the thin film piezoelectric resonator. Also, the thickness and width need not be constant. For example, the thickness and width may be gradually reduced or gradually increased. Also, the outer shape need not be a rectangular parallelepiped or a cube, and can be changed as appropriate. Further, the number of mass load portions 9 is not necessarily one, and a plurality of mass load portions 9 may be provided.
Note that the position of one end of the mass load unit 9 on the resonator unit 7 side (the amount of protrusion to the cavity 6 side immediately above the edge of the cavity 6) is not limited to the above-mentioned ones. It will be described later.

FIG. 5 is a schematic view for illustrating a thin film piezoelectric resonator according to a second embodiment of the invention.
FIG. 5A is a schematic plan view, and FIG. 5B is a schematic cross-sectional view. In addition, the same code | symbol is attached | subjected to the part similar to what was demonstrated in FIG. 2, and the description is abbreviate | omitted.
As shown in FIG. 5A, a mass load portion 9 a is provided on the upper electrode 4 of the thin film piezoelectric resonator 20. The mass load portion 9 a is provided so as to exceed the position immediately above the edge of the cavity 6 by the dimension X. The mass load portion 9a and the upper electrode wiring 9b are integrally joined.
In addition, the case where it forms integrally is also included in integral joining.

The upper electrode wiring 9 b is a bonding pad wiring and is electrically connected to the upper electrode 4. Then, external devices and the upper electrode 4 are electrically connected by wire bonding to the upper electrode wiring 9b. A lower electrode wiring (not shown) is also electrically connected to the lower electrode 3, and an external device and the lower electrode 3 are electrically connected.
The mass load portion 9a, the upper electrode wiring 9b, and the lower electrode wiring (not shown) are made of a conductive material, and can be, for example, aluminum (Al), copper (Cu), gold (Au), or the like. However, it is not limited to these and can be changed as appropriate.

Further, if the mass load portion 9a and the upper electrode wiring 9b are integrally formed, the productivity is high and the yield can be improved.
Even when the mass load portion 9a and the upper electrode wiring 9b are integrally joined, one of them can be formed first.
Further, the mass load portion 9a and the upper electrode wiring 9b may be formed separately without being integrally joined.
Further, the material can be changed between the mass load portion 9a and the upper electrode wiring 9b, or different materials can be joined together.
Further, the upper surfaces of the mass load portion 9a and the upper electrode wiring 9b (opposite surfaces that are in contact with the upper electrode 4) are not necessarily flush with each other.

Next, the amount of protrusion of the mass load portion 9a toward the cavity 6 immediately above the edge of the cavity 6 will be described.
FIG. 6 is a graph for illustrating the influence of the thickness of the protruding portion.
Each graph in FIG. 6 represents frequency-reflected wave coefficient (S ₁₁ ) characteristics, where the horizontal axis represents frequency and the vertical axis represents reflected wave coefficient (S ₁₁ ). Incidentally, the hatched portion in the figure shows a region between the resonance frequency Fr and the anti-resonance frequency Fa.
In FIG. 6, the mass load portion 9a and the upper electrode wiring 9b are integrally formed, and the material thereof is aluminum (Al). Further, the protruding amount (dimension X in FIG. 5B) is set to 5 μm, and the thickness of the mass load portion 9a is changed.

Here, since the reflected wave coefficient (S ₁₁ ) indicates the degree to which the incident wave is reflected to the original port, there is no loss when the upper end of the graph (S ₁₁ = 0 dB), and the lower part of the graph The more you go, the bigger the loss.

FIG. 6A shows frequency-reflected wave coefficient (S ₁₁ ) characteristics when the thickness of the protruding portion is 0 μm, that is, when there is no protruding portion (one end is directly above the edge of the cavity 6). It is. From FIG. 6A, it can be seen that the loss is large in the region between the resonance frequency Fr and the anti-resonance frequency Fa, and a protruding portion is necessary.

6 (b) shows a case where the thickness of the protruding portion is 0.2 μm, FIG. 6 (c) shows a case where the thickness of the protruding portion is 0.5 μm, and FIG. This is a frequency-reflected wave coefficient (S ₁₁ ) characteristic when the thickness of the tension portion is 1 μm.
6B to 6D show that there is little loss in the region between the resonance frequency Fr and the anti-resonance frequency Fa, and the vibration energy leakage suppression effect by the mass load portion 9a is high.

FIG. 6E shows frequency-reflected wave coefficient (S ₁₁ ) characteristics when the thickness of the protruding portion is 3 μm.
From FIG. 6 (e), it can be seen that the loss increases in the region between the resonance frequency Fr and the anti-resonance frequency Fa.
Although this is not necessarily clear, it is considered that spurious vibrations are generated if the mass load is excessively increased.

From the above, when the material of the mass load portion 9a is aluminum (Al), the thickness can be 0.2 μm or more and 1 μm or less. Then, a thin film piezoelectric resonator having excellent resonance characteristics can be obtained.
In the case of a material other than aluminum (Al), the appropriate thickness range may be changed in inverse proportion to the density.

FIG. 7 is a graph for illustrating the influence of the length of the protruding portion.
Each graph in FIG. 7 represents frequency-reflected wave coefficient (S ₁₁ ) characteristics, with the horizontal axis representing frequency and the vertical axis representing reflected wave coefficient (S ₁₁ ). Incidentally, the hatched portion in the figure indicates a region between the resonance frequency Fr and the anti-resonance frequency Fa.
In FIG. 7, the mass load portion 9a and the upper electrode wiring 9b are integrally formed, and the material thereof is aluminum (Al). Further, the thickness of the mass load portion 9a is set to 1 μm, and the amount of protrusion (dimension X in FIG. 5B) is changed.

Here, since the reflected wave coefficient (S ₁₁ ) indicates the degree to which the incident wave is reflected to the original port, there is no loss when the upper end of the graph (S ₁₁ = 0 dB), and the lower part of the graph The more you go, the bigger the loss.

FIG. 7A shows the frequency-reflected wave coefficient (S ₁₁ ) characteristic when the length of the protruding portion is 0 μm, that is, when there is no protruding portion (one end is directly above the edge of the cavity 6). It is. From FIG. 7A, it can be seen that the loss is large in the region between the resonance frequency Fr and the anti-resonance frequency Fa, and a protruding portion is necessary.

FIG. 7B shows frequency-reflected wave coefficient (S ₁₁ ) characteristics when the length of the protruding portion is 1 μm.
From FIG. 7B, it can be seen that the loss is large in the region between the resonance frequency Fr and the anti-resonance frequency Fa.

FIG. 7C shows the frequency-reflected wave coefficient (S ₁₁ ) characteristics when the length of the protruding portion is 3 μm, and FIG. 7D shows the frequency-reflected wave coefficient (S ₁₁ ) characteristics when the length of the protruding portion is 5 μm. .
7C and 7D show that there is little loss in the region between the resonance frequency Fr and the anti-resonance frequency Fa, and the vibration energy leakage suppression effect by the mass load portion 9a is high.

FIG. 7E shows frequency-reflected wave coefficient (S ₁₁ ) characteristics when the length of the protruding portion is 10 μm.
From FIG. 7 (e), it can be seen that the loss increases in the region between the resonance frequency Fr and the anti-resonance frequency Fa.
Although this is not necessarily clear, it is considered that spurious vibrations are generated if the load mass is excessively increased.

From the above, when the material of the mass load portion 9a is aluminum (Al), the length of the protruding portion can be set to 3 μm or more and 5 μm or less. Then, a thin film piezoelectric resonator having excellent resonance characteristics can be obtained.
In the case of a material other than aluminum (Al), the appropriate range of the length of the protruding portion may be changed in inverse proportion to the density.

FIG. 8 is a schematic plan view for illustrating a thin film piezoelectric resonator according to the third embodiment of the invention.
FIG. 9 is a schematic plan view for illustrating a thin film piezoelectric resonator according to a second comparative example. In addition, the same code | symbol is attached | subjected to the part similar to what was demonstrated in FIG. 2, and description is abbreviate | omitted.

First, the second comparative example shown in FIG. 9 will be described.
In the thin film piezoelectric resonator 30 shown in FIG. 9A, the lower electrode 3 covers the entire cavity 6. Further, one side of the upper electrode 4 (the lower side in FIG. 9A) extends outside the cavity 6 region. The upper electrode 4 and the upper electrode wiring 90b are electrically connected. In the thin film piezoelectric resonator 30 having such a configuration, the parasitic capacitance portion 8 exists on one side (the lower side in FIG. 9A) of the four sides of the upper electrode 4.

As described above, vibration energy leaks from the parasitic capacitance portion 8, but if the area of the parasitic capacitance portion 8 is large, the leakage of vibration energy is large.
In the thin film piezoelectric resonator 30 having a large leakage of vibration energy, the Q value (Qr) at the resonance frequency is as high as about 1100, but the Q value (Qa) at the antiresonance frequency is about 540, and the resonance characteristics deteriorate. .

  Also in the thin film piezoelectric resonator 31 shown in FIG. 9B, one side of the upper electrode 4 (the lower side in FIG. 9B) extends out of the cavity 6 region. However, unlike FIG. 9A, the width of the upper electrode 4 is made narrower than the width of the lower electrode 3 in a portion (parasitic capacitance portion 8 a) extending outside the cavity 6 region. In this way, since the area of the parasitic capacitance portion 8a can be reduced, leakage of vibration energy can be suppressed.

Therefore, in the thin film piezoelectric resonator 31, the Q value (Qa) at the antiresonance frequency can be improved from about 540 to about 640.
However, in the thin film piezoelectric resonator 31 having such a configuration, it has been found that the Q value (Qr) at the resonance frequency decreases from about 1100 to about 640, and the resonance characteristics cannot be improved. This is considered to be caused by the following.

  In consideration of resonance characteristics, generally, the material of the upper electrode 4 has a large specific resistance value, and the thickness of the upper electrode 4 is also thin (for example, about 200 to 300 nm). For this reason, if the width of the portion extending outside the cavity 6 is narrowed, the electrical resistance of this portion increases. When the electrical resistance of this portion increases, the Q value (Qr) at the resonance frequency decreases.

In the thin film piezoelectric resonator 32 shown in FIG. 9C, the upper electrode wiring 90b is overlaid on the aforementioned narrowed portion. In this case, the tip of the overlapped portion was prevented from coming out to the resonator portion (directly above the cavity 6).
The material of the upper electrode wiring 90b has a small specific resistance value (for example, aluminum) and a large thickness (for example, about 1 μm). Therefore, the increase in the electrical resistance can be suppressed by overlapping the upper electrode wiring 90b. In this case, the Q value (Qa) at the anti-resonance frequency could be about 610, and the Q value (Qr) at the resonance frequency could be about 740.

  As a result of the study, the present inventor has determined that the Q value (Qa) at the antiresonance frequency and the Q value (Qr) at the resonance frequency can be obtained by extending the tip of the overlapped portion into the resonator portion (directly above the cavity 6). The knowledge that it can improve further was acquired.

In the thin film piezoelectric resonator 40 shown in FIG. 8A, the tip of the overlapped portion is extended into the resonator portion (directly above the cavity 6).
Further, in the thin film piezoelectric resonator 41 shown in FIG. 8B, one side of the upper electrode 4 is not extended outside the cavity 6, but the upper electrode wiring 90b is extended.
In these cases, the portion extending into the resonator portion (immediately above the cavity 6) is the above-described mass load portion 90a.
With such a configuration, the leakage of vibration energy can be further reduced by reducing the area of the parasitic capacitance portion 8a and the effect of the action of the mass load portion 90a. In addition, since the upper electrode wiring 90b extends to the cavity 6, the contact area between the upper electrode wiring 90b and the upper electrode 4 can be increased, and the electrical resistance can be reduced. As a result, the Q value (Qa) at the anti-resonance frequency and the Q value (Qr) at the resonance frequency can be further improved.

  For example, in the thin film piezoelectric resonator 40 shown in FIG. 8A, the Q value (Qa) at the antiresonance frequency can be set to about 670, and the Q value (Qr) at the resonance frequency can be set to about 1040. In the thin film piezoelectric resonator 41 shown in FIG. 8B, the Q value (Qa) at the anti-resonance frequency can be set to about 640, and the Q value (Qr) at the resonance frequency can be set to about 1010.

FIG. 10 is a graph showing the Q value (Qa) at the anti-resonance frequency, and FIG. 11 is a graph showing the Q value (Qr) at the resonance frequency.
In each graph, the horizontal axis A is the thin film piezoelectric resonator 30 shown in FIG. 9A, B is the thin film piezoelectric resonator 31 shown in FIG. 9B, and C is the thin film piezoelectric resonator shown in FIG. 9C. 32 and D are thin film piezoelectric resonators 40 shown in FIG. 8A, and E is a thin film piezoelectric resonator 41 shown in FIG. 8B.

  10 and 11, the Q value (Qa) at the antiresonance frequency is improved by providing the mass load portion 90a by extending the upper electrode wiring 90b into the resonator portion (directly above the cavity 6). It can be seen that the Q value (Qr) at the resonance frequency can also be improved. Therefore, a thin film piezoelectric resonator having excellent resonance characteristics can be obtained. In addition, since the dimension of the mass load part 90a, a form, material, etc. are the same as that of the case of the mass load part 9a mentioned above, the description is abbreviate | omitted.

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.
As for the above-described specific examples, those skilled in the art appropriately modified the design are included in the scope of the present invention as long as they have the characteristics of the present invention.

  For example, the shape, size, material, arrangement, and the like of each element included in the thin film piezoelectric resonator 1, the thin film piezoelectric resonator 20, the thin film piezoelectric resonator 40, and the like are not limited to those illustrated, but may be changed as appropriate. it can.

  Moreover, each element with which each specific example mentioned above is provided can be combined as much as possible, and what combined these is also included in the scope of the present invention as long as the gist of the present invention is included.

1 is a schematic diagram for illustrating a thin film piezoelectric resonator according to a first embodiment of the invention. It is a schematic diagram for illustrating the thin film piezoelectric resonator according to the first comparative example. It is a graph for demonstrating an impedance characteristic. It is a Smith chart for illustrating an impedance characteristic. FIG. 6 is a schematic diagram for illustrating a thin film piezoelectric resonator according to a second embodiment of the invention. It is a graph for demonstrating the influence of the thickness of a protruding part. It is a graph for demonstrating the influence of the length of a protruding part. FIG. 6 is a schematic plan view for illustrating a thin film piezoelectric resonator according to a third embodiment of the invention. It is a schematic plan view for illustrating a thin film piezoelectric resonator according to a second comparative example. It is a graph showing Q value (Qa) in an antiresonance frequency. It is a graph showing Q value (Qr) in a resonant frequency.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Thin film piezoelectric resonator, 2 Substrate, 3 Lower electrode, 4 Upper electrode, 5 Piezoelectric film, 6 Cavity, 7 Resonator part, 8 Parasitic capacitance part, 9 Mass load part, 9a Mass load part, 9b Upper electrode wiring, 10 Thin film piezoelectric resonator, 20 Thin film piezoelectric resonator, 30 Thin film piezoelectric resonator, 31 Thin film piezoelectric resonator, 32 Thin film piezoelectric resonator, 40 Thin film piezoelectric resonator, 41 Thin film piezoelectric resonator, Fa Antiresonance frequency, Fr Resonance frequency, Qa Q value at anti-resonance frequency, Qr Q value at resonance point

Claims (5)

A substrate provided with a cavity;
A lower electrode provided on the substrate so as to cover the cavity;
A piezoelectric film provided on the lower electrode;
An upper electrode provided on the piezoelectric film;
A mass load provided on the upper electrode;
With
The thin film piezoelectric resonator according to claim 1, wherein the mass load portion is provided so as to straddle directly above the edge of the cavity.   2. The thin film piezoelectric resonator according to claim 1, wherein one end of the mass load portion is provided immediately above the resonator portion, and the other end is provided immediately above the parasitic capacitance portion.   The thin film piezoelectric resonator according to claim 1, wherein the mass load portion is integrally joined to the upper electrode wiring.   The thin film piezoelectric resonator according to claim 1, wherein the mass load portion is made of a material having an acoustic impedance lower than that of the material of the upper electrode.   5. The thin film piezoelectric resonator according to claim 1, wherein in the parasitic capacitance portion, a width of the upper electrode is narrower than a width of the lower electrode.