JP2005311849A - Piezoelectric membrane resonator, filter and method for manufacturing piezoelectric membrane resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a piezoelectric membrane resonator having high frequency selectivity by reducing a change in a temperature characteristic even when the temperature changes and preventing a resonance frequency from being deviated. <P>SOLUTION: This piezoelectric membrane resonator is provided with a silicon substrate 11, a laminated resonant body 12 consisting of a lower electrode film provided over the silicon substrate 11, a piezoelectric film 15 overlapped on the lower electrode film 13 and an upper electrode film 14 overlapped on the piezoelectric film 15. A lower temperature correction film 16 having a temperature characteristic reverse to a temperature characteristic for a resonance frequency of the lower electrode film 13 is provided between the silicon substrate 11 and the lower electrode film 13, and an upper temperature correction film 17 having the temperature characteristic reverse to the temperature characteristic for the resonance frequency of the an upper electrode film 14 is provided on the top face of the upper electrode film 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention comprises several types of piezoelectric thin film resonators belonging to a vibrator provided with an acoustic reflection multilayer film called a so-called Fbar (Film Bulk Acoustic Resonator) or SMR (Solid Mounted Resonator). The present invention relates to a filter used mainly in the GHz band and a method for manufacturing a piezoelectric thin film resonator.

In general, a piezoelectric thin film resonator called FBAR includes a substrate and a laminated resonator provided on the substrate. The laminated resonator includes a piezoelectric film and a pair of thin film electrodes that sandwich the piezoelectric film from above and below. A gap is formed in the substrate below the lower electrode. A piezoelectric thin film resonator called SMR is provided with an acoustic reflection film at the bottom. However, since the same concept is applied to the vibration film, only the FBAR will be described here.
When an AC voltage is applied to the upper and lower electrodes of the piezoelectric thin film resonator, the piezoelectric film sandwiched between them vibrates in the thickness direction due to the inverse piezoelectric effect, and exhibits electrical resonance characteristics. Conversely, elastic waves or vibrations generated in the piezoelectric film by the piezoelectric effect are converted into electrical signals. This elastic wave is a thickness longitudinal vibration wave having a main displacement in the thickness direction of the piezoelectric film.

  In such a piezoelectric thin film resonator, a resonance phenomenon occurs in the multilayer resonator at a frequency at which the thickness H of the multilayer resonator is an integral multiple (n times) of a half wavelength of the elastic wave. When the propagation velocity of the elastic wave determined by the type of material is V, the resonance frequency F is expressed as F = nV / 2H.

According to this equation, it is understood that the resonance frequency of the multilayer resonator can be controlled by adjusting the thickness H of the multilayer resonator.
By controlling the resonance frequency, a piezoelectric thin film resonator having a desired frequency characteristic can be manufactured. Then, by connecting such a resonator in a ladder shape, a bandpass filter having a predetermined pass frequency band can be configured.

A conventional piezoelectric thin film resonator includes a substrate having a first surface and a second surface opposite to the first surface, a first electrode film in contact with the first surface, a piezoelectric film overlapping the first electrode film, and the piezoelectric film And a second opening that opens on the first surface and a second opening that opens on the second surface at a position corresponding to the stacked resonator on the substrate. A gap that is substantially perpendicular to the first surface while having a portion is formed.
In this way, the piezoelectric thin film resonator itself is miniaturized by forming the gap portion penetrating the substrate without opening the laminated resonator excessively wide. (For example, refer to Patent Document 1).
JP 2003-204239 A (first page, FIG. 1)

However, the conventional piezoelectric thin film resonator has a predetermined temperature characteristic with respect to the frequency of the laminated resonator constituting the piezoelectric thin film resonator. Therefore, when a thick electric thin film resonator having a predetermined resonance frequency is used as a filter, for example, Since the resonance frequency changes as the temperature changes, there is a problem that the frequency selectivity as a filter is deteriorated due to the deviation of the resonance frequency.
Accordingly, in order to solve such a problem, the present invention reduces a change in temperature characteristics even if there is a temperature change so that the resonance frequency does not deviate, and a piezoelectric thin film resonator and filter with good frequency selectivity. An object of the present invention is to obtain a method for manufacturing a piezoelectric thin film resonator.

  A piezoelectric thin film resonator according to the present invention includes a substrate, a laminated resonator including a first electrode film provided on the substrate, a piezoelectric film overlapping the first electrode film, and a second electrode film overlapping the piezoelectric film. A piezoelectric thin film resonator comprising: a temperature characteristic opposite to a temperature characteristic with respect to a resonance frequency of the first electrode film or the second electrode film so as to be in contact with the first electrode film or the second electrode film. A temperature correction film is provided.

  According to the present invention, the temperature correction film having a temperature characteristic opposite to the temperature characteristic with respect to the resonance frequency of the first electrode film or the second electrode film so as to be in contact with the first electrode film or the second electrode film. Since the temperature characteristic of the temperature compensation film cancels out the temperature characteristic of the first electrode film or the second electrode film, the piezoelectric thin film resonator has a temperature characteristic that the resonance frequency does not change much even if the environmental temperature changes. The frequency selectivity is good.

In the piezoelectric thin film resonator of the present invention, the temperature correction film is provided in the middle of the substrate and the first electrode film or / and on the second electrode film.
This is a temperature correction film provided corresponding to the first electrode film and / or the second electrode film.

In the piezoelectric thin film resonator according to the aspect of the invention, the temperature correction film may be provided between the first electrode film and the piezoelectric film or / and between the piezoelectric film and the second electrode film.
In this case, a temperature correction film is provided at a position different from the above in correspondence with the first electrode film and / or the second electrode film.

In the piezoelectric thin film resonator of the present invention, the temperature correction film is a SiO2 film.
This limits the material having a temperature characteristic opposite to the temperature characteristic with respect to the resonance frequency of the first electrode film or the second electrode film by using a SiO2 film as the temperature correction film.

In the piezoelectric thin film resonator of the present invention, the first electrode film and the second electrode film may be any one of Al, Mo, Ti, Cu, W, Ta, Cr, Au, or any one or more. It is characterized by being formed as a combined laminated film or alloy film.
This indicates that the materials constituting the first electrode film and the second electrode film can be appropriately selected as long as the temperature characteristics with respect to frequency are the same.

In the piezoelectric thin film resonator of the present invention, the temperature correction film provided on the upper surface of the substrate is removed so as to have a desired frequency, or another surface is provided on the upper surface of the temperature correction film provided on the upper surface of the substrate. The temperature correction film is deposited to have a desired frequency.
Thus, the frequency can be adjusted by changing the thickness of the laminated resonator including the correction film.

In the piezoelectric thin film resonator of the present invention, a temperature correction film is provided on the opening surface of the substrate so as to have a desired frequency, or a temperature correction film provided on the opening surface of the substrate is provided with a desired frequency. It is characterized by removing.
In this way, the frequency can be adjusted by changing the thickness of the laminated resonator including the correction film.

In the piezoelectric thin film resonator of the present invention, the piezoelectric film is any one of ZnO, AlO, KNbO3, LiNbO3, LiTaO3, and quartz.
This limits the material for forming a highly oriented piezoelectric film.

A filter according to the present invention includes a plurality of the piezoelectric thin film resonators described above, and the plurality of piezoelectric thin film resonators are connected in a ladder form to be configured as a ladder type filter.
By doing so, a filter having good resonance characteristics can be obtained.

  A method for manufacturing a piezoelectric thin film resonator according to the present invention includes a substrate, a first electrode film provided on the substrate, a piezoelectric film overlying the first electrode film, and a stacked resonance comprising a second electrode film overlying the piezoelectric film. Forming the multilayer resonator in a method of manufacturing a piezoelectric thin film resonator including a step of forming a body, and a step of forming a through hole that opens at a position corresponding to the multilayer resonator on the substrate. The step includes a step of providing a temperature correction film in contact with the first electrode film or the second electrode film.

  By doing so, the piezoelectric thin film resonator according to the present invention can be manufactured. Therefore, the manufacturing method of the present invention also provides the same effects as the piezoelectric thin film resonator according to the present invention.

Embodiment 1 FIG.
1 is a cross-sectional view showing a schematic configuration of a piezoelectric thin film resonator according to Embodiment 1 of the present invention, FIG. 2 is a plan view showing a planar shape of components of the piezoelectric thin film resonator, and FIG. FIG. 4 is a graph showing a comparison of temperature characteristics of the present invention and the conventional piezoelectric thin film resonator.
The piezoelectric thin film resonator 10 includes a silicon substrate 11 and a laminated resonator 12 formed thereon. The silicon substrate 110 is a (110) cut single crystal silicon substrate, and has a first surface (upper surface) 11a and a second surface (lower surface) 11b corresponding to the (110) surface.
The laminated resonator 12 includes a lower electrode film 13 that is a first electrode film, an upper electrode film 14 that is a second electrode film, and a piezoelectric film 15 sandwiched therebetween.

A lower temperature correction film 16 is interposed between the silicon substrate 11 and the lower electrode film 13, and an upper temperature correction film 17 is provided on the upper surface of the upper electrode film 14.
In the present embodiment, the lower electrode film 13 and the upper electrode film 14 are made of, for example, Al having a uniaxially oriented structure of (111). The piezoelectric film 15 is made of, for example, ZnO having a uniaxially oriented structure of (002).

  If the piezoelectric film 15 is other than ZnO, AlN (aluminum nitride), KNbO3 (potassium niobate), LiNbO3 (lithium niobate), LiTaO3 (lithium tantalate), PZT (ceramics mainly composed of lead zirconate titanate) ), BaTiO3 (ceramics whose main component is barium titanate), quartz, or the like. The lower temperature correction film 16 and the upper temperature correction film 17 are made of SiO2.

  A through hole 18 is formed in the silicon substrate 11 below the laminated resonator 12. The through hole 18 passes through the silicon substrate 11 perpendicular to the first surface 11a and the second surface 11b, and the opening of the through hole 18 in the second surface 11b is formed in the first surface 11a. It has the same area and shape as the opening. In the present embodiment, the opening of the through hole 18 is a parallelogram.

Thus, since the opening in the first surface 11a of the through hole 18 is not wider than the opening in the second surface 11b, the silicon substrate 11 and thus the piezoelectric thin film resonator 10 can be designed to be small. It has become.
The piezoelectric thin film resonator 10 according to the first embodiment has resonance frequency characteristics as shown in the graph of FIG.

  As described above, in the piezoelectric thin film resonator 10 of the first embodiment, the lower temperature correction film 16 is interposed between the lower electrode film 13 of the multilayer resonator 12 and the silicon substrate 11, and the upper electrode film An upper temperature correction film 17 is provided on the upper surface of the substrate 14, the lower electrode film 13 and the upper electrode film 14 are formed of Al, the lower temperature correction film 16 and the upper temperature correction film 17 are formed of SiO2, and a laminated resonance. The piezoelectric film 15 of the body 12 is made of ZnO.

  The lower electrode film 13 and upper electrode film 14 made of Al and the piezoelectric film 15 made of ZnO have temperature characteristics that increase and decrease the resonance frequency as the temperature rises and falls. The lower temperature correction film 16 and the upper temperature correction film 17 formed of SiO 2 have temperature characteristics opposite to those of the lower electrode film 13, the upper electrode film 14, and the piezoelectric film 15.

  Therefore, the piezoelectric thin film resonator 10 including the lower temperature correction film 16 in contact with the lower electrode film 13 and the upper temperature correction film 17 in contact with the upper electrode film 14 corrects the temperature characteristics of the lower electrode film 13 to lower temperature. Since the film 16 cancels out and the temperature characteristic of the upper electrode film 14 is canceled out by the upper temperature correction film 17, the frequency selectivity having a temperature characteristic that does not change the resonance frequency very much even when the environmental temperature changes is good. Become.

  As can be seen from the graph of FIG. 4, the piezoelectric thin film resonator having no conventional temperature correction film has a temperature characteristic in which the resonance frequency increases and decreases as the temperature increases and decreases. It can be seen that the piezoelectric thin film resonator having the temperature correction film of the embodiment has a temperature characteristic in which the resonance frequency hardly changes even when the temperature rises and falls.

  In the first embodiment, the lower temperature correction film 16 is interposed between the lower electrode film 13 and the silicon substrate 11, and the upper temperature correction film 17 is provided on the upper surface of the upper electrode film 14. Even if the lower temperature correction film 16 is interposed between the lower electrode film 13 and the piezoelectric film 15 and is interposed between the upper temperature correction film 17 and the piezoelectric film 15, the lower temperature correction film 16 is Since it is in contact with the lower electrode film 13, the upper temperature correction film 17 is in contact with the upper electrode film 14, and has a temperature characteristic that the resonance frequency does not change much even if the environmental temperature changes in the same manner as described above. Will be good.

In the first embodiment, the lower electrode film 13 and the upper electrode film 14 are made of Al. However, depending on the piezoelectric film, the Mo, Ti, Pt, Au, W, and W are arranged so that the piezoelectric film has an optimal orientation. Of course, it may be formed of Ta or the like.
Alternatively, any two or more of Al, Mo, Ti, Pt, Au, W, and Ta may be laminated, or may be formed of two or more alloys or an alloy of laminated ones. As a combination in this case, for example, a Mo / Ti laminated film, a TiN / Al laminated film and an alloy of a Cu several percent / TiN laminated film, a Ti / Al-Cu alloy laminated film, a TiW / Cr / Au alloy There is a laminated film.

  Further, a lower temperature correction film 16 is provided between the silicon substrate 11 and the lower electrode film 13, that is, on the upper surface of the silicon substrate 11. By removing the lower temperature correction film 16, the temperature correction film is included. Since the thickness of the entire laminated resonator 12 changes, the frequency can also be adjusted by changing the resonance frequency. In this case, since the thickness of the entire laminated resonator 12 is reduced, the resonance frequency is increased.

  Further, by laminating and depositing another temperature correction film on the lower temperature correction film 16 provided on the upper surface of the silicon substrate 11, the thickness of the entire laminated resonator 12 including the temperature correction film changes. The frequency can also be adjusted by changing the resonance frequency. In this case, since the thickness of the entire laminated resonator 12 is increased, the resonance frequency is lowered.

  Furthermore, the temperature characteristic correction can be adjusted by providing a temperature correction film on the opening surface of the silicon substrate 11 on the second surface 11b side. In addition, by removing the temperature correction film provided on the opening surface on the second surface side of the silicon substrate 11, the thickness of the entire laminated resonator 12 including the temperature correction film is changed, so that the resonance frequency is also changed. The frequency can be adjusted.

  Furthermore, another temperature correction film is laminated and deposited on the temperature correction film provided on the opening surface on the second surface 11b side of the silicon substrate 11, so that the entire laminated resonator 12 including the temperature correction film is deposited. Therefore, the frequency can be adjusted by changing the resonance frequency.

Embodiment 2. FIG.
5 is a plan view showing a ladder type filter constituted by a piezoelectric thin film resonator according to Embodiment 2 of the present invention, FIG. 6 is a cross-sectional view taken along line AA in FIG. 5, and FIG. 7 is taken along line BB in FIG. FIG. 8 is a sectional view of the same ladder type filter in a package, FIG. 9 is a circuit diagram of a ladder type filter composed of the same piezoelectric thin film resonator, and FIG. 10 is a graph and diagram showing resonance characteristics of the ladder type filter. 11 is an explanatory view showing a manufacturing process of a ladder type filter constituted by the piezoelectric thin film resonator.

The ladder type filter 20 of the second embodiment is used as a band pass filter. Each piezoelectric thin film resonator constituting the ladder filter 20 includes a silicon substrate 11, a lower temperature correction film 16 formed on the silicon substrate 11, and a lower electrode film formed on the lower temperature correction film 16. 13, a piezoelectric film 15 formed on the lower electrode film 13, an upper electrode film 14 formed on the piezoelectric film 15, and an upper temperature correction film 17 formed on the upper electrode film 14. It is prepared for.
The lower electrode film 13, the piezoelectric film 15, and the upper electrode film 14 are connected in parallel to three piezoelectric thin film resonators 10 (C1 to C3 shown in FIG. 5) that are connected in series to each other. Two piezoelectric thin film resonators 10 (CA to CD shown in FIG. 5) are overlapped.

In the ladder filter 20, a total of seven piezoelectric thin film resonators 10 are integrally formed on a single silicon substrate 11. FIG. 9 is a circuit diagram of a ladder type filter 20 used as a band pass filter.
Thus, in the ladder type filter 20, the through hole 18 of each piezoelectric thin film resonator 10 opens at a position corresponding to the excitation portion of the multilayer resonator 12 in the silicon substrate 110, and the first hole of the silicon substrate 11. It is formed perpendicular to the surface 11 a or the laminated resonator 12.

Therefore, the laminated resonators 12 can be arranged close to each other, and as a result, the ladder filter 20 can be downsized.
Further, by arranging the laminated resonators 12 in close proximity, the wiring distance for electrically connecting the piezoelectric thin film resonators 10 can be shortened. As a result, the wiring resistance between the piezoelectric thin film resonators 10 can be reduced. Can be reduced.

The ladder filter 20 having such a configuration is actually used in a package as shown in FIG. 30 is a container, 31 is a container lid, 32 is a terminal, and 33 is a terminal plate. FIG. 9 is a circuit diagram of a ladder type filter 20 used as a band pass filter.
Further, the ladder filter 20 of the second embodiment has a resonance frequency characteristic as shown in the graph of FIG.

Each piezoelectric thin film resonator 10 constituting the ladder type filter 20 in the present embodiment has a lower temperature correction film 16 between the lower electrode film 13 of the laminated resonator 12 and the silicon substrate 11 as in the first embodiment. The upper temperature correction film 17 is provided on the upper surface of the upper electrode film 14, the lower electrode film 13 and the upper electrode film 14 are formed of Al, and the lower temperature correction film 16 and the upper temperature correction film are formed. 17 is formed of SiO2, and the piezoelectric film 15 of the laminated resonator 12 is formed of ZnO.
Therefore, even if the ladder filter 20 is configured, the frequency selectivity is good because the resonance frequency does not change much even when the environmental temperature changes.

  For each piezoelectric thin film resonator 10 constituting the ladder type filter 20, as in the first embodiment, the arrangement of the lower temperature correction film 16 and the upper temperature correction film 17, the lower electrode film 13 and the upper electrode film 14 are arranged. Needless to say, any material can be selected.

FIG. 11 is an explanatory view showing a manufacturing process of a ladder type filter constituted by the piezoelectric thin film resonator shown in FIG.
In manufacturing the ladder type filter, first, as shown in FIG. 11A, the first surface (upper surface) of the silicon substrate 11 is subjected to a heat treatment to form a lower temperature correction film 16 of SiO2 which is a thermal oxide film. Form a film.

  Next, as shown in FIG. 11B, a lower electrode film 13 is formed on the temperature correction film 16 by sputtering, and then dry etching or wet etching is performed through a predetermined resist pattern. By applying, the lower electrode film 13 is patterned.

In dry etching, for example, a mixed gas of BCl3 and Cl2 is used with respect to Al.
As an etchant in wet etching, for example, an aqueous solution containing phosphoric acid, acetic acid, and nitric acid is used for Al. These are also used for the subsequent etching of the electrode film.

Next, as shown in FIG. 11C, the piezoelectric film 15 is formed by a sputtering method, and thereafter, the piezoelectric film 15 is patterned by performing dry etching or wet etching through a predetermined resist pattern. To do. The piezoelectric film 15 is made of ZnO.
As an etchant in wet etching, for example, an acetic acid aqueous solution is used for ZnO, and an aqueous solution containing heated phosphoric acid is used for AlN.

  Next, as shown in FIG. 11 (d), the upper electrode film 14 is formed by sputtering, and thereafter, dry etching or wet etching is performed through a predetermined resist pattern, whereby the upper electrode film 14 is formed. Is patterned.

  Next, as shown in FIG. 11E, the upper temperature correction film 17 is formed by sputtering, and then the upper temperature correction is performed by performing dry etching or wet etching through a predetermined resist pattern. The film 17 is patterned. By patterning the upper temperature correction film 17, the laminated resonator 12 including the lower and upper temperature correction films 16 and 17 for each element is formed.

Next, as shown in FIG. 11F, wet etching is performed on the second surface (lower surface) 11b of the silicon substrate 11 through a predetermined resist pattern.
As a result, through holes 18 are formed which are perpendicular to the first surface 11a and the second surface 11b of the silicon substrate 11 and have a parallelogram shape in plan view.
For example, a KOH solution is used as an etchant in the wet etching.
In this way, a ladder type filter composed of a plurality of piezoelectric thin film resonators is completed.

  The above-described piezoelectric thin film resonator according to the present invention can be applied to a duplexer or an ink jet head.

1 is a cross-sectional view showing a schematic configuration of a piezoelectric thin film resonator according to a first embodiment of the present invention. The top view which shows the planar shape of the structural member of the same piezoelectric thin film resonator. The graph which shows the resonance characteristic of the same piezoelectric thin film resonator. The graph which shows the comparison of the temperature characteristic of the piezoelectric thin film resonator of this invention and a prior art example. The top view which shows the ladder type filter comprised with the piezoelectric thin film resonator which concerns on Embodiment 2 of this invention. AA line sectional view of Drawing 5. BB sectional drawing of FIG. Sectional drawing which put the ladder type filter in the package. The circuit diagram of the ladder type filter comprised by the same piezoelectric thin film resonator. The graph which shows the resonance characteristic of a ladder type filter. Explanatory drawing which shows the manufacturing process of a ladder type filter.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Piezoelectric thin film resonator, 11 Silicon substrate, 12 Stacked resonator, 13 Lower electrode film (first electrode film), 14 Upper electrode film (second electrode film), 15 Piezoelectric film, 16 Lower temperature correction film, 17 Upper temperature compensation film, 18 through holes

Claims (10)

In a piezoelectric thin film resonator comprising a substrate and a laminated resonator including a first electrode film provided on the substrate, a piezoelectric film overlapping the first electrode film, and a second electrode film overlapping the piezoelectric film,
A temperature correction film having a temperature characteristic opposite to the temperature characteristic with respect to the resonance frequency of the first electrode film or the second electrode film is provided so as to be in contact with the first electrode film or the second electrode film. Piezoelectric thin film resonator.   The piezoelectric thin film resonator according to claim 1, wherein the temperature correction film is provided in the middle of the substrate and the first electrode film or / and on the second electrode film.   2. The piezoelectric thin film resonator according to claim 1, wherein the temperature correction film is provided between the first electrode film and the piezoelectric film or / and between the piezoelectric film and the second electrode film.   4. The piezoelectric thin film resonator according to claim 1, wherein the temperature correction film is a SiO2 film.   The first electrode film and the second electrode film are formed as a laminated film or an alloy film in which any one or any combination of Al, Mo, Ti, Cu, W, Ta, Cr, and Au is arbitrarily combined. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is provided.   The temperature correction film provided on the upper surface of the substrate is removed so as to have a desired frequency, or another temperature correction film is provided on the upper surface of the temperature correction film provided on the upper surface of the substrate with a desired frequency. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric thin film resonator is deposited as described above.   The temperature correction film is provided on the opening surface of the substrate to have a desired frequency, or the temperature correction film provided on the opening surface of the substrate is removed to have a desired frequency. The piezoelectric thin film resonator according to any one of 1 to 5.   8. The piezoelectric thin film resonator according to claim 1, wherein the piezoelectric film is any one of ZnO, AlN, KNbO3, LiNbO3, LiTaO3, PZT, BaTiO3, and quartz.   A filter comprising a plurality of the piezoelectric thin film resonators according to claim 1, wherein the plurality of piezoelectric thin film resonators are connected in a ladder form and configured as a ladder filter. Forming a laminated resonator including a substrate, a first electrode film provided on the substrate, a piezoelectric film overlapping the first electrode film, and a second electrode film overlapping the piezoelectric film;
In the method of manufacturing a piezoelectric thin film resonator, including a step of forming a through hole that opens at a position corresponding to the laminated resonator on the substrate,
The step of forming the laminated resonator includes a step of providing a temperature correction film in contact with the first electrode film or the second electrode film.

Images