JP2008301453A - Thin film piezoelectric resonator, and filter circuit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress dissipating vibrational energy of a piezoelectric resonant part from a portion supporting a piezoelectric body at the end of a cavity section to a substrate side so as to enhance a Q value as a quality factor of the thin film piezoelectric resonator. <P>SOLUTION: This thin film piezoelectric resonator includes a piezoelectric resonant part 11 of which the piezoelectric film 6 is sandwiched with a lower electrode 5 and an upper electrode 7, a substrate 1 disposed opposite to the piezoelectric resonant part 11 through a space and in a lower electrode 5 side, at least a high acoustic impedance layer made from material with an acoustic impedance higher than that of the substrate 1 and the piezoelectric film 6, and a support 3 of a cyclic structure which connects an end or its vicinity of the piezoelectric resonant part 11 with the substrate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thin film piezoelectric resonator and a filter circuit using the same.

In recent years, wireless-centric technology has made great strides, and further development aimed at high-speed transmission continues. As the amount of information transmitted increases, the frequency is further increased, and there is a strong demand for further miniaturization and weight reduction of high-frequency communication devices. Wireless devices are generally high frequency (RF: Radi).
o Frequency (RF) processing and a baseband (BB) base for digital signal processing.

Of these, the BB portion is a portion that performs signal modulation / demodulation by digital signal processing, and can basically be configured by an LSI chip, so that it can be easily downsized. In contrast, R
The F part is a part that amplifies or exchanges frequency using a high frequency signal as an analog signal.
It is difficult to configure only with a chip, and the configuration is complicated including many passive components such as an oscillator and a filter.

Conventionally, RF and IF (Intermediate Frequency) in mobile communication devices
As an energy filter, a surface acoustic wave (SAW) is used.
Wave) elements are commonly used. However, the resonance frequency of the SAW element is inversely proportional to the distance between the comb electrodes, and in the frequency region exceeding 1 GHz, the distance between the comb electrodes is 1 μm or less, and the use frequency that has been required in recent years is increased. It is difficult to respond to Further, since a special substrate such as LiTaO3 is used, it is basically an individual component, and there is a difficulty in miniaturization.

A thin film piezoelectric resonator (FBAR: Film Bulk Acoustic) using a longitudinal vibration mode in the thickness direction of a piezoelectric thin film as a resonator that has attracted attention in recent years instead of a SAW element.
Resonator). This thin film piezoelectric resonator has a bulk ultrasonic wave (BAW: Bulk).
It is also called an “Acoustic Wave” element. In this thin film piezoelectric resonator, the resonance frequency is determined by the sound speed and film thickness of the piezoelectric body, and usually corresponds to 2 GHz with a film thickness of 1 to 2 μm, and corresponds to 5 GHz with a film thickness of 0.4 to 0.8 μm, High frequency up to several tens of GHz is possible. Further, it is relatively easy to form on a Si substrate, and there is a merit for the demand for downsizing.

As this type of thin film piezoelectric resonator, for example, a piezoelectric resonator unit in which a piezoelectric body is sandwiched between a lower electrode and an upper electrode is arranged on a substrate having a hollow portion in the ring, and the piezoelectric resonator unit, the substrate, S during
There is a structure in which a hollow template layer made of an oxide material such as iO2 or a nitride material such as Si3N4 is provided (for example, see Patent Document 1).

Also, an air bridge type thin film piezoelectric resonator is provided. A piezoelectric resonator having a piezoelectric film sandwiched between a lower electrode and an upper electrode is disposed on a substrate via a cavity, and the piezoelectric resonator There is a structure in which a support layer made of silicon nitride or the like is provided between a substrate and the like (see, for example, Patent Document 2).

However, in the thin film piezoelectric resonator having the above structure, the piezoelectric resonator unit and the substrate are connected by a support such as a hollow template layer and a support layer, but vibration energy is dissipated from the connection portion to the substrate side. Therefore, the Q value which is the quality factor of the resonator is deteriorated. The deterioration of the Q value causes deterioration of characteristics such as a decrease in bandwidth and an increase in insertion loss when a band-pass filter is formed by a thin film piezoelectric resonator.
JP2005-252851 JP 2005-45694 A

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide vibration energy of the piezoelectric resonator in the thin film piezoelectric resonator from the portion connecting the piezoelectric resonator to the substrate. Dissipation is suppressed, thereby improving the Q value, which is a quality factor of the thin film piezoelectric resonator.

In order to achieve the above object, a thin film piezoelectric resonator according to an aspect of the present invention has a piezoelectric resonator having a piezoelectric film sandwiched between a lower electrode and an upper electrode, and is disposed oppositely on the substrate. Formed in an annular structure having a cavity in the ring and disposed between the substrate and the piezoelectric resonator, and most of the piezoelectric resonator is disposed on the cavity. A support member having at least a portion connecting the substrate to the substrate, and a portion of the support that connects the end of the piezoelectric resonator and the substrate. Includes at least a high acoustic impedance layer made of a material having higher acoustic impedance than the substrate and the piezoelectric film.

A thin film piezoelectric resonator according to another aspect of the present invention includes a substrate having an annular structure having a cavity in a ring, a piezoelectric resonator having a piezoelectric film sandwiched between a lower electrode and an upper electrode, and A large portion of the piezoelectric resonator unit is disposed on the cavity of the substrate, and a part of an end of the piezoelectric resonator unit is at least superimposed on the substrate and supported by the substrate; A support body that is disposed between the overlapping portions and connects the end portion of the piezoelectric resonator unit and the substrate, and includes the end portion of the piezoelectric resonator portion and the substrate of the support member. The connecting portion includes at least a high acoustic impedance layer made of a material having an acoustic impedance higher than that of the substrate and the piezoelectric film.

According to the present invention, a support including at least a high acoustic impedance layer made of a material having a higher acoustic impedance than the substrate and the piezoelectric film, and dissipating from the connection by connecting the piezoelectric resonator and the substrate. Therefore, the Q value can be improved in the thin film piezoelectric resonator.

In general, in a thin film piezoelectric resonator having a structure in which a piezoelectric resonator and a substrate are connected by a support,
At the connection portion between the piezoelectric resonator and the support, the vibration energy of the piezoelectric resonator 11 propagates through the support and is dissipated toward the substrate, and the piezoelectric resonator forms a capacitor. In addition, it is considered that this connection portion becomes unnecessary parasitic capacitance, which deteriorates the characteristics as a resonator.

The resonance characteristics of the thin film piezoelectric resonator include an electromechanical coupling coefficient kt ² that is an index of the strength of piezoelectricity, and a Q value (also referred to as a quality factor) representing the sharpness of resonance. Further, with respect to the Q value, there are a Q value at a resonance point where the electrical impedance of the thin film piezoelectric resonator is minimized, and a Q value at an anti-resonance point where the electrical impedance is maximized.

Case where the filter circuit by combining the FBAR, the bandwidth of the filter circuit is proportional to the electromechanical coupling coefficient kt ^2, the insertion loss within a band is expressed by the product of electromechanical coupling factor kt ² and Q values Inversely proportional to the figure of merit. The electromechanical coupling coefficient kt ² is a value specific to the material,
Maximize crystal purity by improving crystal orientation in the polarization direction, adjusting the film thickness using electrode material with high acoustic impedance, and improving the resonance characteristics of the thin film piezoelectric resonator using electrodes Although it is possible, it is limited because of the inherent value of the material.

Therefore, in order to further reduce the insertion loss of the filter circuit, it is necessary to increase the Q value of the thin film piezoelectric resonator as much as possible. Here, the filter circuit is basically a single bandpass filter or a duplexer in which a plurality of these are combined. Speaking of the band of the filter circuit, it refers to the band of each bandpass filter which is a basic configuration.

Factors affecting the Q value of the resonance point of the thin film piezoelectric resonator are the elastic loss of the piezoelectric film, the elastic loss of the lower electrode and the upper electrode, and the series resistance, while affecting the Q value of the antiresonance point. The affecting factors are the elastic loss of the piezoelectric film, the elastic loss of the lower electrode and the upper electrode, the conductance of the substrate,
This is the dielectric loss of the piezoelectric film.

According to the analysis of the experimental data by the present inventors, the origin of the Q value at the resonance point is the largest proportion of the series resistance of the lower electrode, while the Q value at the anti-resonance point is about the piezoelectric film. It was found that the elastic loss and vibrational energy dissipation to the substrate are dominant. Furthermore, the dissipation of vibration energy is caused by the connection between the piezoelectric resonator unit composed of the lower electrode, the piezoelectric film, and the upper electrode and the support, and the boundary between this connected part and the non-connected part (in the cavity region). It has been found that it occurs in a region up to a point separated by several μm on the non-supporting portion side of the piezoelectric resonance portion.

Based on this knowledge, by dissipating the vibration energy at the anti-resonance point to the substrate, the support is made of a piezoelectric film, a sacrificial layer and a material having a higher acoustic impedance than the substrate (high acoustic impedance layer). Has been found to be suppressed as follows.

That is, a part of the vibration propagating from the piezoelectric resonator to the support is reflected (first reflection) toward the piezoelectric resonator at the interface between the piezoelectric resonator and the support, and the rest is applied to the support. It propagates toward the substrate and is reflected (second reflection) toward the piezoelectric resonator at the interface between the support and the substrate. Here, since the first reflection and the second reflection are out of phase by 180 °, the thickness of the support made of the high acoustic impedance layer is reduced to a quarter of the acoustic wavelength of the anti-resonance frequency. By setting the thickness, it is considered that the first reflection and the second reflection have the same phase and are strengthened in the piezoelectric resonator, and the dissipation of vibration energy from the piezoelectric resonator is suppressed.

As a result, in the thin film piezoelectric resonator in which the high acoustic impedance layer is provided at the connecting portion between the piezoelectric resonator and the substrate in the support, the Q value of the antiresonance point is higher than that of the conventional thin film piezoelectric resonator. improves. Further, if a bandpass filter is configured using this thin film piezoelectric resonator, the insertion loss can be reduced as compared with a conventional bandpass filter using a thin film piezoelectric resonator. The intensity of the first reflection and the second reflection increases as the difference in acoustic impedance between the piezoelectric film and the support and between the support and the substrate increases.

As described above, in the thin film piezoelectric resonator, when a high acoustic impedance layer is used as the support, reflection due to the acoustic impedance difference occurs, so that the Q value is improved as compared with the conventional thin film piezoelectric resonator. Further, the thickness of the high acoustic impedance layer is set to a quarter of the acoustic wavelength of the antiresonance frequency of the resonator, and between the piezoelectric film and the high acoustic impedance layer and between the high acoustic impedance layer and the substrate. If each acoustic impedance difference is made large, the reflectivity for vibration energy leaking from the piezoelectric resonator to the support can be further increased.
Further, the Q value is improved.

The frequency dependence of the acoustic impedance of each of the piezoelectric body, the high acoustic impedance layer, and the substrate is sufficiently negligible with respect to the difference between the resonance frequency and the antiresonance frequency of the piezoelectric body resonance portion (each acoustic impedance is The frequency used as a reference when designing the thickness of the high acoustic impedance layer (which is defined as the design frequency) strictly specifies the anti-resonance frequency of the piezoelectric resonator as described above. There is no need. If the frequency band from the resonance frequency to the anti-resonance frequency and a frequency in the vicinity thereof are used, the characteristics of the thin film piezoelectric resonator are not greatly affected.

For example, when a thin film piezoelectric resonator is created for a ladder filter circuit, the thickness of the high acoustic impedance layer 3 may be set with the center frequency in the passband of the filter circuit to be created as the design frequency. In this case, although it deviates a little from the frequency band from the resonance frequency to the antiresonance frequency in each series-parallel thin film piezoelectric resonator, the difference in each acoustic impedance can be regarded as constant as described above.

In the simulation analysis in which the Q value is calculated by changing the design frequency of the high acoustic impedance layer, the band around 4 times the frequency difference between the resonance frequency of the piezoelectric body resonance part and the anti-resonance frequency is centered on the anti-resonance frequency. It was confirmed that there was a sufficient improvement in Q value. Therefore, in both the case of designing as a single resonator and the case of forming a filter, the frequency difference between the resonance frequency of the piezoelectric resonator and the antiresonance frequency is about four times, centering on the antiresonance frequency of the piezoelectric resonator. In this band, the design frequency of the high acoustic impedance layer may be set.

When designing a ladder type filter circuit using this thin film piezoelectric resonator, thin film piezoelectric resonators having different resonance frequencies are used for the series resonator and the parallel resonator of the filter circuit, respectively. The resonance frequencies of both thin film piezoelectric resonators are designed within a band that is about four times the frequency difference between the resonance frequency and the anti-resonance frequency of the piezoelectric body resonance part, centering on the center frequency of the band of the filter circuit. Therefore, if the thickness of the high acoustic impedance layer of both thin film piezoelectric resonators is designed to be a quarter of the acoustic wavelength of the center frequency of the filter circuit, a ladder type using a conventional thin film piezoelectric resonator is used. A band-pass filter with less insertion loss can be obtained by improving the Q value at the antiresonance point of both thin film piezoelectric resonators than the filter.

  Embodiments of the present invention will be described below with reference to the drawings.

Example 1
FIG. 1 is a plan view of the thin film piezoelectric resonator according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view of the cross section taken along the line AA in FIG. For convenience of explanation, in FIG. 1, the upper electrode protective film 8 of FIG. 2 is omitted.

As shown in FIGS. 1 and 2, the thin film piezoelectric resonator according to the first embodiment of the present invention is provided with a support 3 on a substrate 1. The support 3 is formed in an annular structure, and the lower part thereof is partially embedded in the substrate 1. In this embodiment, the support 3 has a substantially rectangular annular structure with four corners protruding outward in order to form etching vias 9 for etching and forming a cavity 10 described later. The shape of the support 3 is not limited to a quadrangle.

A sacrificial layer 2 is formed on the substrate 1 outside the support 3, and the upper surface of the sacrificial layer 3 is formed so as to be substantially flush with the upper surface of the support 3.

A cavity 10 surrounded by the support 3 is formed on the substrate 1 inside the annular structure of the support 3.
A protective layer 4 is formed on the entire surface of the sacrificial layer 2 including the support 3 so as to cover the cavity 10. On this protective layer 4, the lower electrode 5 has a cavity 10 excluding the peripheral region of the etching via 9.
The lower electrode 5 formed so as to include the planar structure of the support 3 is patterned into a rectangular shape, and the end of the lower electrode 5 except for the periphery of the etching via 9 is a hollow portion. It is formed so as not to be disposed above. This is because if the cavity 10 exists below the end of the lower electrode 5, the piezoelectric film 6 formed on the end of the lower electrode 5 is likely to crack. Further, a part of the lower electrode 5 extends to the periphery of the substrate 1, here the left side in FIG. 1, in order to draw out the lower electrode.

A piezoelectric film 6 is formed on the entire surface of the protective layer 4 including the lower electrode 5, and an upper electrode 7 patterned in a rectangular shape is formed on the piezoelectric film 6 in the region of the cavity 10. A part of the upper electrode 7 extends to the outside of the cavity 10, in this case, to the right in FIG.

A protective layer 8 is formed on the entire surface of the piezoelectric film 6 including the upper electrode 7. Further, etching vias 9 are formed at the four corners in the annular structure of the support 3 where the lower electrode 5 and the upper electrode 7 are not formed. The etching via 9 passes through the protective layer 8 and the piezoelectric film 6 and communicates with the cavity 10.

In the thin film piezoelectric resonator, the laminated body 12 composed of the lower electrode 5, the piezoelectric film 6 and the upper electrode 7.
The laminated body 12 is supported on the cavity 10 by the support 3 and the sacrificial layer 2 via the protective layer 4, so that the piezoelectric film 6 is sandwiched between the lower electrode 5 and the upper electrode 7. The piezoelectric resonator 11 is supported above the cavity 10 in a hollow manner. Here, the piezoelectric resonator unit 11 is
A portion where the lower electrode 5, the piezoelectric film 6 and the upper electrode 7 are completely overlapped to form a capacitor.

The piezoelectric resonator unit 11 has a structure in which most of the piezoelectric resonator unit 11 is above the cavity 10 and is supported in a hollow state. However, for the convenience of forming the lower electrode 5 and pulling out the upper electrode, the piezoelectric resonator unit 11.
Is supported by a part of the support 3 having an annular structure via the protective film 4 at the end of the cavity 10 and connected to the substrate 1. Hereinafter, a connection portion between the end of the piezoelectric resonator 11 and the support 3 is simply referred to as a connection portion.

In this example, in the thin film piezoelectric resonator having the above structure, the entire support 3 having the annular structure is made of tungsten (W) having a higher acoustic impedance than the piezoelectric film 6, the sacrificial layer 2, and the substrate 1.
), And the thickness of the support 3 made of the high acoustic impedance layer is ¼ of the acoustic wavelength of the anti-resonance frequency.

In addition, as high acoustic impedance materials other than W, Mo, Ta, Ru, Rh, Pd,
Ir, Pt, etc. can be used. These materials are optimal because they have a considerably high acoustic impedance with respect to the piezoelectric film 6 and the substrate 1. Co, Au, diamond, Cr, Ni, Cu, LiTaO3, Sr are materials having lower acoustic impedance than these materials.
TiO3, NbN, VN, and TiN can also be used because their acoustic impedance is higher than that of the piezoelectric film 6 and the substrate 1.

An example of the manufacturing process of the thin film piezoelectric resonator of this embodiment will be described with reference to FIG. 1 is a cross-sectional view of the AA cross section of FIG. 1 as viewed in the direction of the arrow.

As shown in FIG. 2A, the SOG (Sp) is formed on the entire surface of the high resistance Si (100) substrate 1.
glass applied by in On Glass method, or CVD (Chemical)
TEOS (Tetraeth) formed by the Vapor Deposition method
An oxysilane) film (SiO 2) is formed as a sacrificial layer 2 (which will be treated as a TEOS film in the following description) to a thickness of 0.5 μm, and is patterned by photolithography and reactive ion etching (RIE). Etching is performed until the Si substrate 1 is exposed at the bottom, thereby forming a substantially rectangular annular structure trench 31 protruding at the four corners shown in FIG. These four corner protrusions are provided to form etching vias 9 later. The shape of the bottom of the trench 31 is shown as flat in the drawing, but may be a curved shape as well as a flat shape.

The thickness of the sacrificial layer 2 and the depth of the trench 31 are determined depending on the sound speed of the high acoustic impedance layer to be embedded later in the trench 31 as the support 3 and the antiresonance frequency of the thin film piezoelectric resonator. Is set to the optimum thickness. The optimum thickness of the high acoustic impedance layer is a quarter of the acoustic wavelength of the anti-resonance frequency of the thin film piezoelectric resonator, so that the reflection characteristic of vibration energy is most improved, and the piezoelectric resonator unit 11 is Dissipation of vibration energy can be suppressed at the support portion of the support 3 to be supported.

In this embodiment, as described later, tungsten (W) is used as the high acoustic impedance layer 3, and an optimum thickness of the high acoustic impedance layer is 0.65 μm in order to produce a 2.0 GHz thin film piezoelectric resonator. Therefore, the depth of the trench 31 is set to 0.65 μm. In addition, although the thickness of the sacrificial layer 2 is 0.5 μm, the sacrificial layer 2 is formed so that the Si substrate 1 is exposed at the bottom of the trench 31. . However, since the height of the cavity 10 to be formed later is the same as the thickness of the sacrificial layer 2, if the sacrificial layer 2 is too thin, the height of the cavity 10 becomes too low and the piezoelectric resonator 11 bends. As a result, a defect that partially contacts the substrate 1 occurs. The minimum required height of the cavity 10 is determined by the material used for the piezoelectric film 6 and the design of the thin film piezoelectric resonator, and therefore the thickness of the sacrificial layer 2 may be set to be larger than this.

Thereafter, selective growth of W is performed using tungsten hexafluoride (WF6) and silane (SiH4) by a cold wall LPCVD apparatus. At this time, growth does not occur on the TEOS film of the sacrificial layer 2 on the surface of the substrate 1, but the growth is selectively performed only on the Si of the substrate 1 at the bottom of the trench 31. The high acoustic impedance layer to be embedded is formed, and the support body 3 having a substantially rectangular annular structure reflecting the annular structure of the trench 31 is formed. Thereby, the depth of the trench 31 becomes the thickness of the high acoustic impedance layer. When a material other than W is used as the high acoustic impedance layer, the depth of the trench 31 may be appropriately changed according to the sound speed of the material.

Here, W was selectively grown. However, after W is buried and grown in the trench 31 by a normal CVD method or sputtering method, an unnecessary W portion other than the trench 31 is subjected to CMP (C
A method of polishing and planarizing by a mechanical mechanical polishing method is also possible. Of course, even in the case of the selective growth described above, when a W buried layer protrudes above the trench 31, planarization processing by CMP is performed. In addition, when a high acoustic impedance material other than W, which is difficult to be selectively grown, can be formed by this method.

Here, W is buried directly in the trench 31, but as shown in FIG. 4, after a Ti or Ti / TiN laminated body is previously formed on the inner wall of the trench 31 as the adhesion layer 51, W is buried. The support 3 may be formed. Thereby, the adhesiveness of the board | substrate 2 and the support body 3 of W can be reinforced.

After the W is buried, as shown in FIG. 3B, a protective layer 4 made of polycrystalline silicon is formed by CVD on the entire surface of the sacrificial layer 2 including the support 3 having a ring structure. Here, polycrystalline silicon is used as the protective layer 4, but amorphous silicon or the like can also be used. Further, an insulating material capable of taking a selective ratio between the sacrificial layer 2 and the etching as the protective layer 4, for example,
SiCN, Al2O3, or the like may be used. The substrate 1, the sacrificial layer 2, the support 3 and the protective layer 4
The material used for may be appropriately changed so that only the sacrificial layer 2 is selectively etched.

Next, an Al film having a thickness of 200 nm is formed on the entire surface of the protective layer 4 by RF sputtering. Thereafter, the Al film is patterned by lithography and reactive ion etching (RIE) to form the lower electrode 5. As shown in FIGS. 1 and 3C, the lower electrode 5 is formed in a rectangular shape including the upper portion of the support 3 having an annular structure, except for the peripheral region of the etching via 9. A part extends to the periphery of the substrate 1 to draw out the lower electrode.

On the entire surface of the protective layer 4 including the lower electrode 5, an AlN film having a thickness of 1.7 μm is formed as a piezoelectric film 6 by a reactive sputtering method using Ar and N 2 gas. afterwards,
A Mo film having a thickness of 250 nm is formed on the entire surface of the piezoelectric film 6 by sputtering or the like, and this Mo film is patterned by photolithography and RIE using a fluorine-based gas to form the upper electrode 7. The upper electrode 7 is composed of a sacrificial layer 2 surrounded by a support 3 having an annular structure.
It is formed in a rectangular shape so as to fit on the region of the piezoelectric film 6 above. Further, a part of the upper electrode 7 is formed so as to cross the support body 3 and reach the outside from the inside surrounded by the annular structure of the support body 3 for wiring extraction.

A thickness of 50 nm is formed by plasma CVD so as to cover the upper electrode 7 and the piezoelectric film 6.
The SiN film is formed as the upper electrode protective layer 8 on the entire surface.

Thereafter, by using photolithography and RIE, the upper electrode protective layer 8 and the piezoelectric film 6 are opened to form extraction portions for the lower electrode 5 and the upper electrode 7 (not shown).

As shown in FIG. 1, the sacrifice that reaches the sacrifice layer 2 through the upper electrode protection layer 8, the piezoelectric film 6, and the protection layer 4 above the protrusions at the four corners of the sacrifice layer 2 surrounded by the support 3. Etching vias 9 for layer removal are formed. In the case of the present embodiment, the etching vias 9 are formed at four places, but may be formed at one place or a plurality of places as appropriate according to the shape of the annular structure of the support 3, or
A slit-like etching via may be used.

Next, the sacrificial layer 2 in the region surrounded by the support 3 is selectively removed by wet etching using buffered hydrofluoric acid (HF + NH 4 F) through the etching via 9. In this wet etching, Si of the substrate 1 and the protective layer 4 and W of the support 3 are hardly etched. As a result, the cavity 10 is formed in the region surrounded by the support 3 as shown in FIG. 2, and the thin film piezoelectric resonator is completed.

In the thin film piezoelectric resonator of the above-described embodiment, the following effects were obtained. That is, as a comparative example, a thin film piezoelectric resonator having the same structure as that of the above-described embodiment in which the support 3 is not made a high acoustic impedance layer but is embedded with polycrystalline silicon was manufactured, and the resonance characteristics were evaluated using a vector network analyzer. As a result, in this comparative example, the resonance frequency was 2.0 GHz, the quality factor Q at the resonance point was 950, the electromechanical coupling factor kt ² was 6.7%, and the quality factor Q at the antiresonance point was 400.

On the other hand, in the thin film piezoelectric resonator of this example, the resonance frequency is about 2.0 GHz, the electromechanical coupling coefficient kt ² is 6.7%, and the quality factor Q of the resonance point is 950, which is the same value as the comparative example. There are
The quality factor at the anti-resonance point was 800, twice that of the comparative example, and the resonance characteristics were improved.

In this embodiment, the side wall of the trench 31 is formed perpendicular to the substrate 1 in the drawing. However, the trench 31 may have a slight inclination or a curved surface, and has an opening width upward. Even if it has a taper shape that spreads, the same effect as the above-described embodiment can be obtained.

In this embodiment, the protective layer 4 protects the lower electrode 5 and the piezoelectric film 6 from being etched when the cavity 10 is formed by etching. However, the protective layer 4 is not necessarily required when the lower electrode 5 and the piezoelectric film 6 are made of a material that is not damaged by etching or when an etching solution that does not etch them is used. If the protective layer 4 is formed thin, the presence or absence of the protective layer 4 does not significantly affect the resonance characteristics of the thin film piezoelectric resonator.

In the present embodiment, as an example, as shown in the cross-sectional view of FIG. 2, the support 3 made of the high acoustic impedance layer is the end of the lower electrode 5 of the piezoelectric resonator 11 (the right end in FIG. 2). Although it is arranged closer to the cavity 10, it is preferable that the support 3 is covered from the end portion of the lower electrode 5 to the position of the perpendicular line dropped on the substrate 1. As the distance in the plane from the end of the lower electrode 5 to the support 3 increases, the area where the piezoelectric resonator 11 is not supported by the support 3 increases, and vibration energy from the piezoelectric resonator 11 to the substrate 1 increases. This is because leakage increases.

In this embodiment, AlN is used as the piezoelectric film, but if it is replaced with ZnO or another piezoelectric film having piezoelectricity, the same effects as in this embodiment can be obtained.

(Modification of Example 1)
A plan view of a thin film piezoelectric resonator according to a modification of the first embodiment is shown in FIG. 5 is the same as FIG.
Similarly, the upper electrode protective layer 8 is omitted. Further, the cross section viewed in the direction of the arrow along the line AA in the figure is the same as the cross section of the first embodiment shown in FIG. The modification differs from the first embodiment in that a slit-like etching via 62 as shown in FIG. 5 is used in place of the etching via 9 of the first embodiment. In addition, according to this, the planar shape of the cavity 10 and the support 3 is a square.

By adopting the structure of this modification example, when the sacrificial layer 2 is etched through the etching via 62 to form the cavity 10, the etching time is shortened compared to the first embodiment, and the etching process is facilitated. Become. Also in the thin film piezoelectric resonator of this modification, the same effect as in the above embodiment can be obtained.

(Another Modification of Example 1)
FIG. 6 is a cross-sectional view showing a manufacturing process of a thin film piezoelectric resonator of another modification of the first embodiment. FIG. 6 corresponds to a cross-sectional view of the cross section taken along the line AA in FIG. This modification differs from the first embodiment in that a support 3 having an annular structure is embedded in the substrate 1, a recess 40 is formed inside the support 3 and sacrificed in the recess. The purpose is to create a thin film piezoelectric resonator by embedding the layer 41. The plan view of the thin film piezoelectric resonator obtained by this modification is shown in FIG.
This embodiment is the same as the first embodiment except that the sacrificial layer 2 on the substrate 1 outside the support 3 having the annular structure is replaced with the substrate 1.

As shown in FIG. 6A, an annular trench 31 having the same shape as that of the first embodiment is formed on the Si substrate 1 by lithography and RIE, and a high acoustic impedance layer made of W is formed by CVD. After being embedded in the trench 31 having an annular structure, W is shaved by CMP to planarize until Si of the substrate 1 is exposed. As a result, an annular support 3 made of W is formed in the substrate 1.

Next, as shown in FIG. 2B, a recess 40 is formed inside the support 3 along the support 3 having the annular structure by photolithography and RIE. This recess 40 is finally the cavity 1
0. In this figure, the recess 40 has a depth that does not reach the bottom of the support 3.
Depending on the design, the depth is adjusted so that the required height of the cavity 10 is obtained. Also, this depression 40
Even if the depth becomes deeper than the bottom of the support 3, there is no problem in the selective etching of the sacrificial layer embedded in the recess 40 thereafter.

PSG (Phospho-Silicate-Gl) is embedded so as to embed the recess 40.
ass) as a sacrificial layer 41, and an extra PS until the substrate 1 is exposed by CMP.
The protective layer 4 made of polycrystalline silicon having a thickness of 50 nm is formed by CVD on the entire upper surface of the substrate 1 including the sacrificial layer 41 made of PSG and the support 3.

Thereafter, as shown in FIG. 6C, the lower electrode 5, the piezoelectric film 6,
After forming the upper electrode 7, the upper electrode protective layer 8 and the etching via 9, the etching via 9
Then, the sacrificial layer 41 made of PSG is etched to form the cavity 10.

In the thin film piezoelectric resonator according to this modification, the same resonance characteristics as in the first embodiment can be obtained.

(Example 2)
FIG. 7 is a cross-sectional view showing the manufacturing process of the thin film piezoelectric resonator according to the second embodiment of the present invention. As shown in FIG. 7C, the present embodiment differs from the first embodiment in that the sacrificial layer 2 is thick, the trench 31 is deep, and the support 3 has a high acoustic impedance layer 3b and a low acoustic impedance. The point is a two-stage structure composed of the layers 3a, and the point that the height of the cavity 10 is high. In addition, the same location as Example 1 is shown with the same code | symbol. The plan view of the thin film piezoelectric resonator of the present embodiment is the same as FIG.

As shown in FIG. 7A, an annular structure trench 31 is formed in the sacrificial layer 2 in the same manner as in the first embodiment, and polycrystalline silicon is formed in the trench 31 as a low acoustic impedance layer 3a by CVD. After embedding, the unnecessary portion of polycrystalline silicon is polished by CMP,
The surface of the substrate 1 is flattened. Here, the thickness of the sacrificial layer 2 is 2 μm as compared with the first embodiment.
The trench 31 was formed as deep as 2.5 μm.

Thereafter, only the upper end portion of the low acoustic impedance layer 3a in the trench 31 is selectively etched without etching the SiO 2 of the sacrificial layer 2 by CDE (Chemical Dry Etching) method, and the bottom of the trench 31 is annularly formed. The low acoustic impedance layer 3a of the structure is left. This selective etching is performed so that the depth from the surface of the sacrificial layer 2 to the upper surface of the low acoustic impedance layer 3a is 0.65 μm, which is the same as in the first embodiment.
Similar to the first embodiment, this depth is the thickness of the high acoustic impedance layer to be embedded later.

A method of selectively etching only Si without etching SiO 2 is as follows.
Besides the DE method, KOH solution and TMAH (Tetra Methyl Ammonium
Hydroxyide) can also be performed by wet etching using an etchant.

Instead of the etching, when the polycrystalline silicon as the low acoustic impedance layer 3a is embedded in the trench 31 by CVD, the depth from the surface of the sacrificial layer 2 is 0.65.
The film formation is stopped when polycrystalline silicon is deposited on the bottom of the trench 31 so as to be μm.
Unnecessary polycrystalline silicon deposited on the sacrificial layer 2 may be removed in advance by CMP, and the polycrystalline silicon of the high acoustic impedance layer 3b is subsequently embedded on the low acoustic impedance layer 3a in the trench 31. Thereafter, when unnecessary polycrystalline silicon of the high acoustic impedance layer 3b deposited on the sacrificial layer 2 is removed by CMP, it may be removed together.
Thereby, it is also possible to form the low acoustic impedance layer 3 a having a ring structure of polycrystalline silicon at the bottom of the trench 31.

Thereafter, as in the first embodiment, W is embedded as a high acoustic impedance layer 3b on the low acoustic impedance layer 3a in the trench 31, and unnecessary W deposited on the sacrificial layer 2 is CM.
By removing by planarization by the P method, the high acoustic impedance layer 3b having an annular structure embedded in the trench 31 is formed.

As described above, the unnecessary low acoustic impedance layer 3 a deposited on the sacrificial layer 2.
When the polycrystalline silicon of the high acoustic impedance layer 3b is buried in the trench 31 without removing the polycrystalline silicon, an unnecessary high acoustic impedance layer 3b on the sacrificial layer 2 is formed.
When the polycrystalline silicon is removed by CMP, unnecessary polycrystalline silicon of the low acoustic impedance layer 3a on the sacrificial layer 2 is removed together.

The annular structure support 3 is formed by the annular low acoustic impedance layer 3a and the annular high acoustic impedance layer 3b formed thereon. Thereafter, as shown in FIG. 7B, the protective layer 4 is formed on the entire surface of the sacrificial layer 2 including the high acoustic impedance layer 3b having an annular structure.

Thereafter, the lower electrode 5, the piezoelectric film 6, the upper electrode 7, the upper electrode protective layer 8, the etching via 9 and the cavity 10 are formed in the same manner as in the first embodiment, and the thin film shown in FIG. A piezoelectric resonator is obtained. Here, when the sacrificial layer 2 is etched to form the cavity 10, the low acoustic impedance layer 3 a of the annular structure of the annular support 3 is exposed to the etching solution. Crystalline silicon has a high etching selectivity with respect to the sacrificial layer 2 and is not etched.

In this example, the height of the cavity 10 is higher than that of Example 1 and the sacrificial layer 2 is formed thick, but the thickness of the high acoustic impedance layer 3b is the same as that of Example 1 above. Since the material occupying the upper and lower portions of the high acoustic impedance layer 3b is the same as in the first embodiment, the same effect as in the first embodiment can be obtained.

This example is particularly useful when a thin film piezoelectric resonator having a high cavity portion is formed.

In the present embodiment, polycrystalline silicon is used as the low acoustic impedance layer 3a. However, similarly to the protective layer 4 in the first embodiment, amorphous silicon can be used. In addition to these materials, other materials can be used as long as they have a high etching selectivity with the sacrificial layer 2 and a lower acoustic impedance than the high acoustic impedance layer 3b.

(Example 3)
A manufacturing process of the thin film piezoelectric resonator according to the third embodiment of the present invention will be described with reference to FIGS. 8 is a cross-sectional view of the AA cross section of FIG. 9 as viewed in the direction of the arrow, and FIG. 9 omits the uppermost upper electrode protective layer 8.

In this embodiment, the etching via 9 is formed and the sacrificial layer 2 is etched and the cavity 10 is not formed as in the first embodiment, but etching is performed until the protective layer 4 is reached from the bottom of the substrate 1. An opening 72 penetrating the substrate 1 and a cavity 1 that is continuous and surrounded by the support 3
It differs from the said Example 1 by the point which forms 0. The same parts as those in the first embodiment are denoted by the same reference numerals, and only the characteristic portions of the present embodiment will be described.

First, as shown in FIG. 8A, a thermal oxide film (SiO 2) is formed on a high resistance Si (100) substrate 1.
) 71 is formed to a thickness of 0.5 μm. Thereafter, in the same manner as in Example 1, a high acoustic impedance layer having a ring structure made of W having a thickness of 0.65 μm is embedded as the support 3, and the protective layer 4 is thermally oxidized including the upper surface of the support 3. It is formed on the entire surface of the film 71.

Further, as shown in FIG. 5B, the lower electrode 5, the piezoelectric film 6, the upper electrode 7 and the upper electrode protective layer 8 are formed in exactly the same manner as in Example 1, and then the Si substrate 1 is formed. The lower part is polished by back grinding and dry polishing so that the thickness of the Si substrate 1 becomes 0.2 μm.

As shown in FIG. 4C, a mask pattern having an opening along the annular structure of the support 3 is formed on the polished surface by photolithography, and RIE using a fluoride-based gas is performed from the opening. Thus, the Si substrate 1 is etched toward the piezoelectric film 6 and the etching is stopped by the thermal oxide film 71, thereby forming an opening 72 penetrating the Si substrate 1 in the Si substrate 1. Thereafter, the thermal oxide film 71 exposed in the opening 72 of the Si substrate 1 is removed by etching along the inner surface of the support 3 using wet etching and RIE using a fluoride-based gas. Etching is stopped by the protective layer 4 made of the material, and the cavity 10 that is continuous with the opening 72 of the Si substrate 1 and is surrounded by the support 3 is formed. Thereafter, the mask below the Si substrate 1 is removed.

In this embodiment, it is possible to use W, Ta, Mo, or the like for the high acoustic impedance layer of the support 3, but more preferably a material that can withstand fluoride-based dry etching, for example,
It is desirable to use Ru, Rh, Pd, Ir, Pt or the like. As a result, the support 3 made of the high acoustic impedance layer is etched from the lower part of the substrate 1 to open the opening 72.
After forming the film, it acts as a guide when forming the cavity 10, and it is possible to suppress displacement from the surface pattern at the bottom of the substrate 1.

As a result of evaluating the resonance characteristics of the thin film piezoelectric resonator thus obtained using a vector network analyzer, the resonance frequency is about 2.0 GHz, the electromechanical coupling coefficient is 6.7%, and the quality factor Q is resonance. The point was 940, and the antiresonance point was 820, and almost the same characteristics as in Example 1 were obtained.

In the present embodiment, in order to form the cavity from the lower part of the substrate, as shown in the plan view of FIG.

(Modification of Example 3)
Next, a modification of the third embodiment is shown in FIG. In the step shown in FIG. 8A of the third embodiment, the thickness of the thermal oxide film 71 formed on the substrate 1 is reduced to about 50 nm, and the upper protective layer 4 is not provided. Through the same steps as in Example 3, the thin film piezoelectric resonator shown in FIG. 10 is obtained. Here, when forming the cavity 10, the substrate 1 is dry-etched or wet-etched from the lower part of the substrate 1 to reach the bottom of the support 3 and has an opening 72 having a shape along the annular structure of the support 3. Form. Etching is continued as it is, and the substrate 1 is further etched along the inner surface of the support 3 to stop the etching at the thermal oxide film 71. Thereafter, the thermal oxide film 71 is etched with buffered hydrofluoric acid or the like, and the etching is stopped when reaching the lower electrode 5, thereby forming the cavity 10 continuous with the opening 72 in the annular structure of the support 3. To do.

In the modified example as described above, the same effect as in the third embodiment can be obtained. In the above-described modification, when the lower electrode 5 and the piezoelectric film 6 are materials that may be etched when the thermal oxide film 71 is etched, a structure in which the thermal oxide film 71 is left as it is may be employed. Since the thickness of the thermal oxide film 71 is reduced to about 50 nm, the characteristics of the thin film piezoelectric resonator are not changed even in this case.

Example 4
A thin film piezoelectric resonator according to a fourth embodiment of the present invention is shown in FIG. FIG. 2A is a plan view thereof, and FIG. 2B is a cross-sectional view of the A-A cross section in FIG.

The difference between the fourth embodiment and the first embodiment is that in the first embodiment, the support 3 that forms the side wall of the cavity 10 is entirely formed of a high acoustic impedance layer. FIG.
As shown in FIG. 1, in the support 3 having an annular structure, a portion connecting the piezoelectric resonator 11 and the Si substrate 1 is formed by the high acoustic impedance layer 3 b, and other portions are formed by the high acoustic impedance layer 3 b. This is a point formed from a low acoustic impedance layer 3c made of a material having low acoustic impedance. The low acoustic impedance layer 3c may be formed of polycrystalline silicon or amorphous silicon which is the same material as the low acoustic impedance layer of the second embodiment, or may be formed of a different material. In addition, the low acoustic impedance layer 3c in the present embodiment is merely for embedding the support 3 with a material different from that of the high acoustic impedance layer, and has a function of an etching stop layer when the cavity 10 is formed by etching. If you do it, it's enough.

The difference in the manufacturing process from Example 1 is as follows. Similar to Example 1 above, FIG.
As shown in (a), after reaching the Si substrate 1 in the sacrificial layer 2 and forming a trench 31 having an annular structure having a depth of 0.65 μm, unlike the first embodiment, the annular structure is formed by CVD or the like. A polycrystalline silicon film is formed on the sacrificial layer 2 so as to fill the entire interior of the trench 31. afterwards,
By polishing the excess polycrystalline silicon by CMP until the sacrificial layer 2 is exposed and flattening the surface of the sacrificial layer 2, an annular low acoustic impedance layer 3c made of polycrystalline silicon is embedded in the trench 31. The

Thereafter, a mask pattern is formed so that the region where the high acoustic impedance layer 3b is to be formed is an opening shown in the plan view of FIG. Only the low acoustic impedance layer 3c exposed at the opening is selectively etched by wet etching using CDE, KOH solution, or TMAH solution to partially expose the inner surface of the trench 31, and then the trench 31 is exposed. A high acoustic impedance layer made of W is formed on the entire surface of the sacrificial layer 2 by CVD or the like so as to embed the exposed portion of the inner surface, and excess W is polished by CMP to flatten the surface of the sacrificial layer 2.

When the depth of the trench 31 needs to be deeper than 0.65 μm as in the second embodiment, the selective etching of the low acoustic impedance layer 3c embedded in the trench 31 is etched. Etching may be stopped when the upper surface of the low acoustic impedance layer 3c reaches a depth of 0.65 μm from the surface of the sacrificial layer 2.

Thereafter, through the same process as in the first embodiment, the portion connecting the end of the piezoelectric resonator 11 and the Si substrate 1 as shown in FIG. 11 is the high acoustic impedance layer 3b, and the other portions. A thin film piezoelectric resonator having a ring-shaped support 3 made of a low acoustic impedance layer 3c is obtained. Here, the thickness of the high acoustic impedance layer 3b made of embedded W is determined by the depth of the trench 31, and is 0.65 μm as in the first embodiment.

In the thin-film piezoelectric resonator described above, since leakage of vibration energy from the piezoelectric body 11 to the substrate originally does not occur in the portion of the support 3 where the piezoelectric resonator 11 and the substrate 1 are not connected. The acoustic impedance layer 3b is not disposed, and the portion of the support 3 that connects the piezoelectric resonator 11 where the vibration energy leaks and the substrate 1 is composed of a high acoustic impedance layer. Vibration energy leaking to the substrate 1 through the body 3 can be suppressed. Therefore, also in the present embodiment, the same effect as in the first embodiment can be obtained.

(Example 5)
FIG. 12 shows a thin film piezoelectric resonator according to a fifth embodiment of the present invention. The figure (b) is a plan view.
A cross-sectional view of the A-A cross section viewed in the direction of the arrow is FIG. In this embodiment, FIG.
In the thin-film piezoelectric resonator of the third embodiment shown in FIG. 3, the portion of the support 3 in which the piezoelectric resonator 11 and the substrate 1 are not connected to each other hardly leaks vibration energy from the piezoelectric member 11 to the substrate. While removing the support 3, the low acoustic impedance layer 81 a and the high acoustic impedance layer 81 b are connected to the portion connecting the piezoelectric resonator unit 11 and the substrate 1 from which vibration energy leaks.
And a support body 81 having a laminated structure. Hereinafter, the same parts as those in the third embodiment are denoted by the same reference numerals, and only the characteristic portions of the present embodiment will be described.

That is, as shown in FIG. 12, a rectangular opening 72 is formed in the lower part of the Si substrate 1, embedded in the Si substrate 1, and upward toward the substrate 1 along one side of the opening 72. An extending support 81 is formed, and a cavity 10 is formed along the support 81 from the opening 72 upward in the Si substrate 1. Except for the support 81, a thermal oxide film 71 (SiO 2) is formed on the upper surface of the Si substrate 1 so as to be substantially flush with the upper surface of the support 81. A protective film 4, a lower electrode 5, a piezoelectric film 6, an upper electrode 7 and a protective film 8 are sequentially formed so as to cover the cavity 10, the upper surface of the support 81 and the upper surface of the thermal oxide film 71. The piezoelectric body resonance portion 11 composed of the piezoelectric film 6 and the upper electrode 7 has a cavity portion 10 except that a part of the end portion (the end portion of the lower electrode 5) is supported by the support body 81 below. It is formed so as to be entirely included in the planar area.

The support 81 is composed of an acoustic mirror layer in which a low acoustic impedance layer 81a made of SiO 2 having a thickness of 0.73 μm and a high acoustic impedance layer 81b made of W having a thickness of 0.65 μm are alternately laminated in two periods as upper and lower layers, respectively. . The thickness of both layers is set to a thickness that is ¼ of the acoustic wavelength of the anti-resonance frequency of the thin film piezoelectric resonator, and the vibration propagating from the piezoelectric resonator 11 is efficient by the principle of the Bragg reflection layer. It is often reflected toward the piezoelectric body resonance part 11. Also according to the present embodiment, a thin film piezoelectric resonator having good resonance characteristics can be obtained by the effect of the present invention.

Further, in this embodiment, the support body 81 is an acoustic mirror layer having a two-period structure of a low acoustic impedance layer 81a and a high acoustic impedance layer 81b. An acoustic mirror layer having a structure may be used. Alternatively, an acoustic mirror layer having two or more cycles can be used. However, since the reflection capability as the acoustic mirror layer is saturated even if the period is increased, the number of periods of the acoustic mirror layer may be appropriately selected depending on the structure of the thin film piezoelectric resonator and the process.

The manufacturing process may be created according to Example 3 as an example. In Example 3, the depth of the trench that penetrates the thermal oxide film (SiO 2) 71 and reaches the substrate 1 is the height of the high acoustic impedance layer made of W. Although it was the same as the thickness, in the case of the present example, as shown in FIG. 12A, the total thickness of each layer of the acoustic mirror layer described above is obtained.

In addition, the low acoustic impedance layer 81a and the high acoustic impedance layer 81b are provided inside the trench.
In order to embed the layers alternately, film formation techniques such as CVD and sputtering are used, and when the design thickness is reached, the film formation of each layer is stopped and the layers are alternately stacked. An extra layer deposited around the trench may be polished and planarized by CMP after each layer is deposited or after all layers are deposited. In this case, although not shown in FIG. 12, the laminated structure of the high acoustic impedance layer is also formed on the inner surface of the trench (side surface of the support 81), but with respect to the width in the in-plane direction of the support 81. It is negligible, and the influence on the thin film piezoelectric resonator is almost negligible.

In addition to the above, after the acoustic mirror layer is first formed on the Si substrate 1, the acoustic mirror layer is removed except for the portion corresponding to the support 81, and then SiO2 or the like is applied to the entire surface of the Si substrate 1. The above structure can also be realized by a method of depositing and finally polishing and flattening SiO 2 until the upper surface of the acoustic mirror layer is exposed by CMP.

(Example 6)
A cross-sectional view of a thin film piezoelectric resonator according to a sixth embodiment of the present invention is shown in FIG. This example
In the structure of the same thin film piezoelectric resonator as that of the third embodiment shown in FIG. 8C, the support 3 is formed so that the high acoustic impedance layer is embedded in the trench.
As shown in FIG. 3, a support 82 is disposed between the piezoelectric resonator 11 and the Si substrate 1 at the end of the lower electrode 5 of the piezoelectric resonator 11. The support 82 is a high acoustic impedance layer made of W having a thickness of 0.65 μm as in the third embodiment.

In the present embodiment, a trench is formed in the thermal oxide film 71 on the substrate 1 shown in the third embodiment, and a high acoustic impedance layer made of W is embedded and grown therein, and then the thermal oxide film 71 is exposed. As shown in FIG. 13, after forming the protective layer 4 on the thermal oxide film 71 on the substrate 1 instead of the step of removing the excess W by the CMP method to planarize the surface and forming the protective layer 4. A high acoustic impedance layer made of W is patterned into a desired shape to form the support 82. The subsequent steps are the same as those in Example 3.

Also in the present embodiment, the leakage of vibration energy from the piezoelectric body resonance portion 11 toward the substrate 1 can be suppressed by reflection of vibration energy by the support 82 formed of the high acoustic impedance layer, and good resonance can be achieved. A thin film piezoelectric resonator having characteristics can be created.

(Example 7)
FIG. 14 shows an embodiment in which a ladder-type bandpass filter is formed using the thin film piezoelectric resonator according to the first embodiment of the present invention.

FIG. 14A is a plan view of a chip of the ladder type filter circuit 101 formed by the thin film piezoelectric resonators F1 to F7. The planar pattern is simplified and only the substrate 1, the lower electrode 5, the piezoelectric film 6, and the upper electrode 7 necessary for explanation of the circuit are shown for the sake of simplicity. Also,
For simplicity, each electrode is drawn out of the piezoelectric film 6 and exposed on the substrate 1. Each thin film piezoelectric resonator indicates a region where the piezoelectric film 6 is sandwiched between the lower electrode 5 and the upper electrode 6 in the figure, and is denoted by F1 to F7, respectively.

The individual thin film piezoelectric resonators are as shown in the first embodiment, and the thickness and pattern shape of each layer of each thin film piezoelectric resonator are finely adjusted according to the design of the filter circuit. Figure (b)
Shows a circuit diagram of the ladder type filter circuit of FIG.

The correspondence relationship of each electrode between the ladder type filter circuit shown in FIG. 6A and the circuit diagram of FIG. The upper electrode 7 and the lower electrode 5 of the thin film piezoelectric resonator F2 are connected to the input terminals 102 and 103, respectively, and the upper electrode 7 of the thin film piezoelectric resonator F2 and the upper electrode 7 of the thin film piezoelectric resonator F1 are connected. The lower electrode 5 of the thin film piezoelectric resonator F1 is connected to the lower electrodes 5 of the thin film piezoelectric resonators F3 and F4, and the upper electrode 7 of the thin film piezoelectric resonator F3 is connected to the thin film piezoelectric resonators F5 and F6.
The lower electrode 5 of the thin film piezoelectric resonator F5 is monolithically formed on the same substrate 1 so as to be connected to the lower electrode 5 of the thin film piezoelectric resonator F7.

The output terminal 104 is connected to the lower electrode 5 of the thin film piezoelectric resonator F5, and the output terminal 105 is connected to the upper electrode 7 of the thin film piezoelectric resonator F7. The lower electrode 5 of F2, the upper electrode 7 of F4, the lower electrode 5 of F6 and the upper electrode 7 of F7 are connected together.

Using the thin film piezoelectric resonator according to the first embodiment which is an aspect of the present invention, the above-described 3.5-stage ladder filter is configured, and the filter characteristics are measured by a vector network analyzer. 0.0GHz, insertion loss is -1.0d over 80MHz bandwidth
It turned out that the favorable filter characteristic which is B is acquired.

The configuration of the filter circuit according to the present embodiment is merely an example, the thin film piezoelectric resonators of the above-described embodiments and modifications are used, and the present invention is not limited to the ladder filter circuit illustrated in the present embodiment. The present invention can also be applied to ladder filter circuits, lattice filter circuits, duplexers using these, RF filter circuits, and IF filter circuits. As other applications, the present invention can also be applied to a reference vibrator, a voltage controlled oscillator (VCO), and the like.

As mentioned above, although the form of the invention which concerns on this invention was demonstrated using the said each Example and its modification, it combines with each of these Examples and the modification, and it is the structure shown in each Example and the modification. Of course, each constituent material, the thickness of each layer, the pattern shape, and the like may be changed without departing from the scope of the present invention.

Of course, it is possible to use the acoustic mirror layer of Example 7 for the entire support of the other examples and its modifications, or for the part of the support that connects the piezoelectric resonator and the substrate. At that time, the number of periods of the acoustic mirror layer may be appropriately set according to the design.

1 is a plan view of a thin film piezoelectric resonator according to a first embodiment of the present invention. Sectional drawing of the thin film piezoelectric resonator of Example 1 of this invention. Sectional drawing which shows the manufacturing process of the thin film resonator of Example 1 of this invention. Sectional drawing which showed the example which embeds W using the contact | adherence layer in Example 1 of this invention. The top view of the thin film piezoelectric resonator in the modification of Example 1 of this invention. Sectional drawing which shows the manufacturing process of the thin film piezoelectric resonator in another modification of Example 1 of this invention. Sectional drawing which shows the manufacturing process of the thin film piezoelectric resonator of Example 2 of this invention. Sectional drawing which shows the manufacturing process of the thin film piezoelectric resonator of Example 3 of this invention. The top view of the thin film piezoelectric resonator of Example 3 of this invention. Sectional drawing of the thin film piezoelectric resonator of the modification of Example 3 of this invention. The top view and sectional drawing of the thin film piezoelectric resonator of Example 4 of this invention. The top view and sectional drawing of the thin film piezoelectric resonator of Example 5 of this invention. Sectional drawing of the thin film piezoelectric resonator of Example 6 of this invention. The figure which shows the filter circuit using the thin film piezoelectric resonator of Example 7 of this invention.

Explanation of symbols

1 substrate,
2, 41 Sacrificial layers 3, 81, 82 Supports 3a, 3c, 81a Low acoustic impedance layers 3b, 81b High acoustic impedance layers 4 Protective layer 5 Lower electrode 6 Piezoelectric film 7 Upper electrode 8 Upper electrode protective layers 9, 62 Etching Via 10 Cavity 11 Piezoelectric Resonance Unit 12 Laminate 31 Trench 40 Depression 51 Adhesion Layer 71 Thermal Oxide Film 72 Opening 101 Ladder Type Filter Circuit 102, 103 Input Terminal 104, 105 Output Terminal

Claims (9)

A substrate,
A piezoelectric body having a piezoelectric resonance part sandwiched between a lower electrode and an upper electrode, and a laminated body disposed oppositely on the substrate;
Formed in an annular structure having a cavity in the ring and disposed between the substrate and the piezoelectric resonator, and most of the piezoelectric resonator is disposed on the cavity, and at least the piezoelectric resonance A support having a part connecting a part of the end of the part and the substrate,
The portion of the support that connects the end of the piezoelectric resonator and the substrate includes at least a high acoustic impedance layer made of a material having an acoustic impedance higher than that of the substrate and the piezoelectric film. Thin film piezoelectric resonator. An annular substrate having a cavity in the ring;
The piezoelectric film has a piezoelectric resonance part sandwiched between a lower electrode and an upper electrode, and most of the piezoelectric resonance part is disposed on the cavity of the substrate, and the end of the piezoelectric resonance part is A part of which is stacked on at least the substrate and supported by the substrate;
A support body that is disposed at least between the overlapping portions and connects an end of the piezoelectric resonator unit and the substrate;
Of the support, the portion connecting the end of the piezoelectric resonator and the substrate includes at least a high acoustic impedance layer made of a material having higher acoustic impedance than the substrate and the piezoelectric film. A thin film piezoelectric resonator. The thin film piezoelectric resonator according to claim 2, wherein the support has an annular structure formed along an inner surface of the substrate. The portion of the support that connects the piezoelectric resonator and the substrate has a low acoustic impedance layer made of a material having an acoustic impedance lower than that of the high acoustic impedance layer, and the piezoelectric resonator resonates from the substrate to the substrate. The thin film piezoelectric resonator according to claim 1, wherein the thin acoustic wave resonator is formed in a two-stage structure of the high acoustic impedance layer and the low acoustic impedance layer. 5. The thin film piezoelectric resonator according to claim 4, wherein the low acoustic impedance layer is made of polycrystalline silicon or amorphous silicon. The thickness of the high acoustic impedance layer has a thickness of a quarter of an acoustic wavelength of a design frequency that is greater than or equal to a resonance frequency of the piezoelectric resonator and less than or equal to an antiresonance frequency. 6. The thin film piezoelectric resonator according to any one of 5 above. The portion of the support that connects the piezoelectric resonator and the substrate further includes a low acoustic impedance layer made of a material having an acoustic impedance lower than that of the high acoustic impedance layer, and the high acoustic impedance layer and the low acoustic impedance layer 4. The thin film piezoelectric resonator according to claim 1, comprising an acoustic mirror layer in which acoustic impedance layers are alternately stacked. Each of the high acoustic impedance layer and the low acoustic impedance layer has a thickness of a quarter of an acoustic wavelength of a design frequency that is greater than or equal to a resonance frequency of the piezoelectric resonator and less than or equal to an antiresonance frequency. The thin film piezoelectric resonator according to claim 7.   A filter circuit using the thin film piezoelectric resonator according to claim 1.

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