WO2011086986A1 - Elastic wave device, filter, communication module, and communication apparatus - Google Patents

Abstract

Disclosed is an elastic wave device having excellent characteristics by shifting at least one resonance frequency of a plurality of piezoelectric thin film resonators without deteriorating the characteristics. The elastic wave device has a main resonator and a sub-resonator, and each of the main resonator and the sub-resonator has a lower electrode (43), a piezoelectric film (44) provided on the lower electrode (43), and an upper electrode (45) provided on the piezoelectric film (44). The main resonator and the sub-resonator differ in weight per unit area in a resonance region (46) where the upper electrode (45) and the lower electrode (43) face each other, and a frequency control film (51) having a weight lighter than the weight difference is provided on the main resonator and/or the sub-resonator.

Description

Elastic wave device, filter, communication module, communication device

The present disclosure relates to an acoustic wave device, a filter, a communication module, and a communication apparatus.

In recent years, with the rapid spread of wireless devices typified by mobile phones, electricity in a specific frequency band can be obtained by combining a plurality of resonators using surface acoustic waves (SAW) and thickness vibration waves (BAW) using piezoelectric materials. A filter element for high-frequency communication having a characteristic of allowing only a signal to pass has been developed. Until now, mainly dielectric filters and SAW filters have been used. Recently, however, they have been constructed using piezoelectric thin film resonators, which are elements that have particularly good characteristics at high frequencies and that can be miniaturized and made monolithic. Filters are attracting attention.

Among such piezoelectric thin film resonators, there are an FBAR (Film Bulk Acoustic Resonator) type and an SMR (Solidly Mounted Resonator) type. The former has a structure of an upper electrode / piezoelectric film / lower electrode as main components on a substrate, and a gap is formed under the lower electrode at a portion where the upper electrode and the lower electrode face each other. Here, the air gap is formed by wet etching of the sacrificial layer provided on the substrate surface where the lower electrode is disposed, wet etching of the substrate from the back surface, or dry etching. The latter has a structure in which a film having a high acoustic impedance and a film having a low acoustic impedance are alternately laminated with a film thickness of λ / 4 (λ: wavelength of an elastic wave) and used as an acoustic reflection film instead of the gap. .

When a high-frequency voltage as an electric signal is applied between the upper electrode and the lower electrode of the piezoelectric thin film resonator, an elastic wave due to the inverse piezoelectric effect is excited inside the piezoelectric film sandwiched between the upper electrode and the lower electrode. Further, the distortion caused by the elastic wave is converted into an electric signal by the piezoelectric effect. Such an elastic wave is totally reflected on the surfaces where the upper electrode film and the lower electrode film are in contact with air, and thus becomes a longitudinal vibration wave having a main displacement in the thickness direction of the piezoelectric film. By utilizing such a resonance phenomenon, a resonator having a desired frequency characteristic (or a filter formed by connecting a plurality of these) can be obtained.

For example, in an FBAR type piezoelectric thin film resonator, the total film thickness H of the laminated structure portion including the upper electrode film / piezoelectric film / lower electrode film formed on the air gap as the main component is the wavelength λ of the elastic wave. Resonance occurs at a frequency (H = nλ / 2) that is an integral multiple (n times) of ½ (½ wavelength). Here, when the propagation velocity of the elastic wave determined by the material of the piezoelectric film is V, the resonance frequency F is
F = nV / 2H
Therefore, the resonance frequency F can be controlled by the total film thickness H of the laminated structure.

As a configuration of a filter using such a piezoelectric thin film resonator, there is a ladder type filter in which resonators are connected in series-parallel in a ladder shape. Ladder-type filters can be easily manipulated for insertion loss, out-of-band suppression, etc. by simply changing the number of stages built into a ladder type or the capacitance ratio of series-parallel resonators, and the design procedure is simple. Therefore, it is often used. There is a lattice type filter as a similar design method.

These filter configurations are composed of resonators having different frequencies of the series arm and the parallel arm (frequency relationship: parallel arm <series arm), and it is necessary to form resonators having different resonance frequencies in the same chip. In order to make the resonator connected to the parallel arm (hereinafter referred to as the parallel resonator) have a lower resonance frequency than the resonator connected to the series arm (hereinafter referred to as the series resonator), a mass is formed on the upper electrode of the parallel resonator. An additional film is formed, and the frequency is controlled by the mass of the mass additional film.

In Patent Document 1, in order to obtain a resonator having a plurality of resonance frequencies on the same substrate, a method of changing the film thickness of the lower electrode, the piezoelectric film, and the upper electrode, which are main constituent films of the resonator, A method of adjusting by adding is disclosed. Patent Document 2 discloses a method of adjusting by patterning a mass addition film on an electrode of a resonator.

JP 2002-335141 A US Pat. No. 6,657,363

In the acoustic wave device disclosed in Patent Document 1, in order to form mass-added films having different film thicknesses, a plurality of film forming processes, photolithography processes, and etching processes are performed. There has been a problem of increasing the cost of.

When a pattern is formed using a mass-added film of a parallel resonator as in the elastic wave device disclosed in Patent Document 2, there is a problem that the resonance characteristics are significantly deteriorated by moving the frequency of the resonator. there were.

It is an object of the present invention to provide an acoustic wave device, a filter, a communication module, and a communication apparatus that can obtain excellent characteristics by moving at least one resonance frequency of a plurality of piezoelectric thin film resonators without deterioration in characteristics. To do.

The disclosure of the present application is an acoustic wave device having a main resonator and a sub-resonator, wherein the main resonator and the sub-resonator include at least a lower electrode, a piezoelectric film provided on the lower electrode, and the piezoelectric film. The main resonator and the sub-resonator have a unit in each of the lower electrode, the piezoelectric film, and the upper electrode in a resonance region where the upper electrode and the lower electrode face each other. A frequency control film having a difference in the total weight per area, lighter than the difference in weight, and patterned in the resonance region is at least one of the main resonator and the sub-resonator. Prepare for either.

According to the disclosure of the present application, frequency characteristics can be improved in a piezoelectric thin film resonator having a plurality of resonance frequencies in the same chip. Moreover, the process for manufacturing an elastic wave device can be shortened.

Plan view of piezoelectric thin film resonator according to the embodiment Cross section of the first piezoelectric thin film resonator Cross section of the second piezoelectric thin film resonator Ladder type filter circuit diagram Sectional drawing which shows the manufacturing process of a 1st piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 1st piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 1st piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 1st piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 2nd piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 2nd piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 2nd piezoelectric thin film resonator Sectional drawing which shows the manufacturing process of a 2nd piezoelectric thin film resonator Characteristic diagram showing the relationship between frequency control film and resonance Q A characteristic diagram showing the relationship between frequency shift and resonance Q A characteristic diagram showing the relationship between frequency shift and resonance Q Characteristic diagram showing the relationship between frequency control film and resonance Q Characteristic diagram showing the relationship between frequency control film occupancy and resonance Q Plan view of piezoelectric thin film resonator according to Example 2 Sectional drawing of the 1st piezoelectric thin film resonator concerning Example 2. FIG. Sectional drawing of the 2nd piezoelectric thin film resonator concerning Example 2. FIG. Ladder type filter circuit diagram Circuit diagram of ladder filter according to embodiment 3 Frequency characteristics of Example 3 and Comparative Example Communication module block diagram Block diagram of communication device

(Embodiment)
[1. Configuration of elastic wave device)
In the acoustic wave device disclosed in Japanese Patent Laid-Open No. 2002-335141, in order to obtain a resonator having a plurality of resonance frequencies in the same chip, a mass addition film is newly added on the electrode of the resonator. Therefore, in order to obtain a resonator having a plurality of resonance frequencies in the same chip, mass-added films having different film thicknesses are required. In order to perform a plurality of film formation processes, photolithography processes, and etching processes, There has been a problem that the cost of the device is increased.

In the acoustic wave device disclosed in US Pat. No. 6,657,363, in order to obtain a resonator having a plurality of resonance frequencies in the same chip, a mass addition film formed on the electrode of the resonator is used. It shows that the resonance frequency can be adjusted by controlling the pitch in the patterning step. A single patterning process, a photolithography process, and an etching process can form different patterns for the mass-added film between the plurality of resonators, and resonators having a plurality of resonance frequencies in the same chip Can be formed. However, when a pattern is formed using a mass-added film of a parallel resonator, there is a problem that the resonance characteristics are significantly deteriorated by moving the frequency of the resonator. The specification of US Pat. No. 6,657,363 only discloses the pitch of the pattern of the mass-added film formed on the electrode of the resonator, and does not disclose requirements for other patterns.

The acoustic wave device according to the present embodiment is excellent in a filter formed by connecting a plurality of piezoelectric thin film resonators by moving at least one resonance frequency of the plurality of piezoelectric thin film resonators without deterioration in characteristics. The purpose is to obtain frequency characteristics.

Example 1
1A to 1C show an example of a piezoelectric thin film resonator which is an example of an acoustic wave device according to the present embodiment. FIG. 1A is a plan view of a piezoelectric thin film resonator. 1B is a cross-sectional view taken along a line AA in FIG. 1A, and is a cross-sectional view of the first piezoelectric thin film resonator. FIG. 1C is a cross-sectional view of the second piezoelectric thin film resonator.

FIG. 2 shows a filter circuit in which a plurality of piezoelectric thin film resonators of the present embodiment are arranged in series arms and parallel arms. Here, the resonators connected to the series arms are called first piezoelectric thin film resonators (series resonators) S1 to S4, and the resonators connected to the parallel arms are called second piezoelectric thin film resonators (parallel resonators) P1 to P3. I will do it.

1A to 1C includes a substrate 41, a gap 42, a lower electrode 43, a piezoelectric film 44, an upper electrode 45, a membrane portion 46, an etching medium introduction hole 47, an etching medium introduction path 48, and a sacrificial layer 49. The mass addition film 50 and the frequency control film 51 are provided. The substrate 41 uses silicon (Si) in this embodiment. In this embodiment, the lower electrode 43 has a two-layer structure of ruthenium (Ru) / chromium (Cr). The piezoelectric film 44 uses aluminum nitride (AlN) in this embodiment. In this embodiment, the upper electrode 45 has a two-layer structure of Cr / Ru. The lower electrode 43, the piezoelectric film 44, and the upper electrode 45 can be formed by a film forming method such as a sputtering method. For example, in the case of a piezoelectric thin film resonator having a resonance frequency of 2 GHz, the approximate thickness of each layer is as follows. 45b (Cr) is 20 nm and the first layer (Ru) is 250 nm. In addition, as an electrode film of the lower electrode 43 and the upper electrode 45, aluminum (Al), copper (Cu), chromium (Cr), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), Ruthenium (Ru), rhodium (Rh), iridium (Ir), or the like can be used. As the piezoelectric film 44, aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lead titanate (PbTiO ₃ ), or the like can be used. As the substrate 41, silicon (Si), glass, ceramics, or the like can be used.

As shown in FIG. 1C, the second piezoelectric thin film resonators P1 to P3 include a mass addition film 50. In this embodiment, the mass addition film 50 is formed of titanium (Ti) having a thickness of 125 nm. The mass addition film 50 is provided between the first layer 45 a and the second layer 45 b of the upper electrode 45. In order for the mass addition film 50 to function as a film for applying a load to the membrane portion 46 where the lower electrode 43 and the upper electrode 45 are opposed to each other, at least the membrane portion 46 where the upper electrode 45 and the lower electrode 43 are opposed to each other. As long as it is formed so as to include. Further, the mass addition film 50 is formed so as to include the membrane portion 46 where the upper electrode 45 and the lower electrode 43 are opposed to each other, and the shape matching the shape of the upper electrode 45 is defined as the maximum region. An arbitrary shape can be formed between the region and the maximum region.

As shown in FIGS. 1B and 1C, a frequency control film 51 is provided on the upper electrodes 45 of the first piezoelectric thin film resonators S1 to S4 and the second piezoelectric thin film resonators P1 to P3. In this embodiment, the frequency control film 51 is made of Ti having a thickness of 20 nm. The frequency control film 51 is provided so as to include at least a membrane portion 46 in which the upper electrode 45 and the lower electrode 43 are opposed to each other.

The frequency adjustment film 52 is provided in the uppermost layer in the membrane unit 46. The frequency adjustment film 52 is made of SiO ₂ in this embodiment. The frequency adjustment film 52 can simultaneously adjust the resonance frequencies of the first piezoelectric thin film resonators S1 to S4 shown in FIG. 1B and the second piezoelectric thin film resonators P1 to P3 shown in FIG. 1C. That is, the film configuration of the first piezoelectric thin film resonators S1 to S4 of the series arm is such that the films are in the order of SiO ₂ / Ti / Cr / Ru / AlN / Ru / Cr / Si substrate from the top layer to the bottom layer. Is formed. The film configuration of the second piezoelectric thin film resonators P1 to P3 of the parallel arm is that the films are in the order of SiO ₂ / Ti / Cr / Ti / Ru / AlN / Ru / Cr / Si substrate from the uppermost layer to the lowermost layer. Is formed. The film thickness of each layer varies depending on the required specifications of the filter, and the film of the lower electrode 43 and the upper electrode 45, the piezoelectric film 44, the mass addition film 50, and the frequency control film 51 can have other configurations. The lower electrode 43 may have a single layer structure. In addition, the mass addition film 50 is sandwiched between the first layer 45a and the second layer 45b of the upper electrode 45, so that the frequency control film 51 has the first piezoelectric thin film resonators S1 to S4 and the second piezoelectric thin film resonator. P1 to P3 can be formed on the same material. Further, the frequency adjustment film 52 may not be provided. A dome-shaped gap 42 (bulge) is formed between the substrate 41 and the lower electrode 43 in the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other. The “dome-shaped gap” is a bulge having a shape such that the inner height is low at the periphery of the gap and the inner height is higher at the center of the gap.

3A to 3D are cross-sectional views showing manufacturing steps of the first piezoelectric thin film resonators S1 to S4. 4A to 4D are cross-sectional views showing manufacturing steps of the second piezoelectric thin film resonators P1 to P3. FIGS. 3A to 3D and FIGS. 4A to 4D each show a cross section taken along a line segment (AA line in FIG. 1A) passing through the center of the membrane portion 46. FIG.

First, as shown in FIGS. 3A and 4A, a sacrificial layer 49 made of, for example, magnesium oxide (MgO) or the like is formed on the Si substrate 41 by using, for example, a sputtering method or an evaporation method. As the substrate 41, a quartz substrate, a glass substrate, a ceramic substrate, a GaAs substrate, or the like can be used in addition to the Si substrate. In particular, the substrate 41 is preferably formed of a material that is difficult to etch in order to prevent the substrate 41 from being etched during the sacrifice layer etching in the gap forming step. The sacrificial layer 49 is preferably formed of a material that can be easily dissolved by an etching solution or an etching gas, such as ZnO, Ge, Ti, or Cu. After the formation of the sacrificial layer 49, the sacrificial layer 49 is formed into a predetermined shape using an exposure technique and an etching technique.

Next, as shown in FIGS. 3B and 4B, Ru / Cr is deposited as the lower electrode 43 by a sputtering method or the like. Although the lower electrode 43 has a two-layer structure here, it may have a one-layer structure. Next, the lower electrode 43 is patterned into a desired shape so as to cover the sacrificial layer 49 by an exposure technique and an etching technique. At this time, an introduction path 48 (see FIG. 1A) for introducing an etching medium for etching the sacrificial layer 49 is formed in the lower electrode 43, and the sacrificial layer 49 is formed at the tip of the introduction path 48 when the gap is formed. An etching medium introduction hole 47 (see FIG. 1A) for etching may be formed. Subsequently, AlN is deposited as the piezoelectric film 44 by a sputtering method or the like. Next, Ru is formed as a first layer 45a of the upper electrode 45 by sputtering or the like.

Next, as shown in FIG. 4B, the second piezoelectric thin film resonator is formed by depositing Ti as the mass addition film 50 by a sputtering method or the like. Next, the mass addition film 50 is formed by the exposure technique and the etching technique so as to include at least the membrane portion 46 in which the upper electrode 45 and the lower electrode 43 are opposed to each other. Here, the lift-off method may be used for patterning the mass addition film 50. The mass addition film 50 is formed only in the manufacturing process of the second piezoelectric thin film resonator, and can be omitted in the manufacturing process of the first piezoelectric thin film resonator.

Next, as shown in FIGS. 3C and 4C, Cr is deposited as the second layer 45b of the upper electrode 45 by sputtering or the like. Here, the mass addition film 50 in the second piezoelectric thin film resonator is sandwiched between the first layer 45 a and the second layer 45 b of the upper electrode 45. Next, Ti is deposited as the frequency control film 51 on the second layer 45 b of the upper electrode 45. Next, by using an exposure technique and an etching technique, the frequency control film 51 in a region including at least the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other is patterned into a desired shape. In this step, a resonator having a plurality of resonance frequencies can be manufactured in a single step by changing the pattern on the upper electrode 45 of each resonator constituting the filter.

Here, the frequency control film 51 is patterned so that the weight per unit area does not affect the elastic wave excited by the piezoelectric film 44 (AlN). Generation of unnecessary spurious and deterioration of resonance characteristics can be suppressed. “Weight that the frequency control film 51 does not affect the elastic wave excited by the piezoelectric film 44” means that the upper electrode and the lower electrode in the first piezoelectric thin film resonator and the second piezoelectric thin film resonator. Are lighter than the difference in the total weight per unit area of the lower electrode, the piezoelectric film, the upper electrode, the mass addition film, and the frequency adjustment film in the resonance region facing each other. In this embodiment, the weight per unit area of the frequency control film is formed so as to be lighter than the weight per unit area of the mass addition film 50 formed in the second piezoelectric thin film resonator. In particular, in this embodiment, when the weight per unit area of the frequency control film 51 satisfies the condition of 0.2 g / m ² or less, generation of unnecessary spurious and resonance characteristics caused by patterning of the frequency control film 51 are achieved. Can be prevented. Here, the “weight per unit area (g / m ² )” of the upper electrode, the lower electrode, the piezoelectric film, the mass addition film, the frequency adjustment film, the frequency control film, etc. means the respective material density (g / m ³ ) is the product of the film thickness (m). In the present embodiment, the invention is disclosed with a configuration including a mass addition film and a frequency adjustment film. However, when an elastic wave device not including a mass addition film or the like is implemented, the above-described “frequency control film 51 is a piezoelectric film”. The weight that does not affect the elastic wave excited by 44 "means that in the first piezoelectric thin film resonator and the second piezoelectric thin film resonator, the lower electrode in the resonance region where the upper electrode and the lower electrode face each other, and the piezoelectric film By making the weight lighter than the difference in the total weight per unit area with the upper electrode, the same effect can be obtained.

The etching of the frequency control film 51 can use either dry etching or wet etching. However, it is preferable to use dry etching because a fine pattern shape can be easily obtained and under-etching is small.

The shape of the frequency control film 51 may be lower than the film thickness. However, in order to obtain resonators having a plurality of resonance frequencies between the resonators, it is necessary to etch patterns having different shapes on the upper electrodes 45 of the plurality of resonators. Therefore, by forming the frequency control film 51 so as to have a height corresponding to the film thickness, variations in etching during pattern formation can be reduced, and the frequency control film 51 can be precisely moved to a desired frequency. it can.

Further, if the combination of the frequency control film 51 and the upper electrode 45 is a combination of materials having etching selectivity, the other films are less damaged during etching and can be moved to a desired frequency precisely. Therefore, it is possible to stably provide an acoustic wave device having excellent characteristics.

Next, as shown in FIGS. 3D and 4D, the upper electrode 45 is patterned into a desired shape by an exposure technique and an etching technique. Next, in order to open the window of the lower electrode 43 and improve the resonance characteristics, the piezoelectric film 44 is patterned into a desired shape by an exposure technique and an etching technique. Next, a frequency adjustment film 52 (SiO ₂ ) is formed by sputtering or the like. Here, the material of the frequency adjustment film 52 is not limited to SiO ₂ , and may be another insulating film such as a metal oxide film or a metal nitride film that can be gradually reduced by excitation energy or the like.

Next, the frequency adjustment film 52 on the upper electrode 45 is removed by an exposure technique and an etching technique, and a bump pad (not shown) is formed in that part.

Finally, the frequency adjustment film 52 on the sacrificial layer etching medium introduction hole 47 (see FIG. 1A) formed in a part of the lower electrode 43 is removed by the exposure technique and the etching technique. Next, a sacrificial layer etching medium is introduced into the sacrificial layer etching medium introduction hole 47. The sacrificial layer etching medium is introduced under the lower electrode 43 through the introduction path 48 (see FIG. 1A), and the sacrificial layer 49 is removed. Thereby, the space | gap 42 which has a dome-like swelling can be formed under the membrane part 46 with which the upper electrode 45 and the lower electrode 43 oppose. As described above, the piezoelectric thin film resonator according to the present embodiment is completed.

The etching solution for the sacrificial layer 49 is preferably a material that does not easily etch the material constituting the piezoelectric thin film resonator other than the sacrificial layer 49, particularly the electrode material on the sacrificial layer 49 that contacts the etching medium.

The materials of the substrate 41, the lower electrode 43, the upper electrode 45, and the piezoelectric film 44 are not limited to the above, and other materials may be used. Further, instead of the air gap 42, an acoustic reflection film in which a film having a high acoustic impedance and a film having a low acoustic impedance are alternately laminated with a film thickness of λ / 4 (λ: wavelength of elastic wave) is used as the lower electrode 43 in the membrane portion 46. The structure arrange | positioned between the board | substrate 41 may be sufficient.

FIG. 5 is a characteristic diagram showing the relationship between the product of the material density and the film thickness of the frequency control film 51 on which the pattern is formed, that is, the weight per unit area and the resonance Q in the first piezoelectric thin film resonator. In FIG. 5, the horizontal axis represents the weight per unit area of the frequency control film 51, and the vertical axis represents the deterioration of the resonance Q. Here, the vertical axis represents a value obtained by subtracting the resonance Q value of the piezoelectric thin film resonator having the frequency control film 51 from the resonance Q value of the piezoelectric thin film resonator having no frequency control film 51. That is, on the vertical axis, a positive value indicates a deterioration amount, and a negative value indicates an improvement amount. Further, the values in FIG. 5 are values when the frequency shift amounts are all about 10 MHz. The film thickness of the frequency control film 51 was 25 nm (T1 in FIG. 5), 50 nm (T2 in FIG. 5), and 125 nm (T3 in FIG. 5). Here, when the film thickness of the frequency control film 51 is 125 nm, the case where the weight per unit area of the mass addition film | membrane formed in the 2nd piezoelectric thin film resonator is shown is shown. The frequency control film 51 is formed in the resonance region of the upper electrode 45. The frequency control film 51 has a pattern (island pattern) protruding in a convex shape, and the island pattern can give mass to the resonance part. As shown in FIG. 5, it was found that if the weight per unit area of the frequency control film 51 is 0.2 g / m ² or less, the resonance frequency can be moved without deterioration of the resonance Q.

FIG. 6A shows the rate of deterioration of resonance Q and electromechanical coupling coefficient k ² with respect to the amount of frequency movement when the weight per unit area of the frequency control film is 0.56 g / m ² . FIG. 6B shows the rate of deterioration of the resonance Q and the electromechanical coupling coefficient k ² with respect to the amount of frequency movement when the weight per unit area of the frequency control film is 0.11 g / m ² . In the case of FIG. 6A, the resonance Q and the electromechanical coupling coefficient k ² both deteriorate as the frequency shift amount increases, whereas in the case of FIG. 6B, the resonance Q and the electromechanical coupling coefficient k increase as the frequency shift amount increases. ^No deterioration of ² was observed.

Here, the mechanism of the piezoelectric thin film resonator according to the present embodiment will be described.

When a voltage is applied to the upper electrode 45 and the lower electrode 43 in the piezoelectric thin film resonator, an electric field in the thickness direction is generated in the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other, and the piezoelectric film 44 is moved in the thickness direction. Extends and contracts. In other words, the elastic wave propagates in the thickness direction of the resonance region of the piezoelectric film 44. Since the upper part of the upper electrode 45 and the lower part of the lower electrode 43 are the boundary between the vacuum (or gas), the elastic wave is reflected at the free end there. The elastic wave that repeats reflection cancels out the frequency components that are out of phase with the total film thickness where the elastic wave is generated. Eventually, only an elastic wave in which an integral multiple of half the wavelength of the elastic wave matches the total film thickness can exist, causing a resonance phenomenon.

When there is a frequency control film 51 with a pattern formed on the upper electrode 45, the total film thickness is different between the portion with the pattern and the portion without the pattern, and the resonance phenomenon is the portion with the pattern and the portion without the pattern. It occurs in two places. When a filter is manufactured using a resonator having resonance characteristics in which resonance phenomenon occurs at two locations, one resonance characteristic functions as a spurious, and therefore, it is necessary to have one resonance characteristic. In addition, since the resonance phenomenon occurs at two places, the resonance characteristics themselves deteriorate. Conventionally, it has been thought that the elastic wave cannot recognize the pattern by making the pattern pitch of the frequency control film smaller than the wavelength of the elastic wave excited by the piezoelectric film. In the resonance region, the weight per unit area of the film forming the pattern was found to affect the characteristics. When the weight per unit area of the film forming the pattern is sufficiently small, even if the film having the pattern formed on the upper electrode 45 is formed, the elastic wave excited by the piezoelectric film 44 has a portion with the pattern. He found that he couldn't recognize the part without the pattern.

FIG. 7 is a characteristic diagram in which the deterioration of the resonance Q when Ti or SiO ₂ is used as the frequency control film 51 is plotted on the vertical axis and the weight per unit area on the horizontal axis. Here, the film thickness when the frequency control film 51 is formed of SiO ₂ is 50 nm (T11 in FIG. 7). In addition, when the frequency control film 51 is formed of Ti with a thickness of 25 nm (T12), when formed with Ti with a thickness of 50 nm (T13), and when formed with Ti with a thickness of 125 nm (T14), the values are plotted. .

As shown in FIG. 7, the resonance Q when the SiO ₂ film having a thickness of 50 nm is formed (T11) and the resonance Q when the film having a thickness of 25 nm is formed (T12) are substantially the same. In other words, the frequency control film 51 has a frequency shift by making the weight per unit area the same even if there is a difference in material and a difference in thickness (SiO _{2 with} a thickness of 50 nm, Ti with a thickness of 25 nm). It can be seen that the characteristic deterioration due to can be suppressed. This is because the thickness of the frequency control film 51 is not important, and the density of the frequency control film 51 is set so that the weight per unit area does not affect the elastic wave excited by the piezoelectric film 44. It is shown that the resonance frequency of the resonator can be moved without deterioration of the resonance characteristics by setting the product of the thickness and the film thickness.

Here, the pattern of the frequency control film 51 is an island pattern (convex shape) in the present embodiment. However, if the weight per unit area can be set to an arbitrary value, the pattern is a hole pattern (concave shape). It doesn't matter.

FIG. 8 is a graph showing the relationship between the occupation ratio of the frequency control film 51 and the resonance Q. Here, the occupation ratio indicates the ratio of the area where the frequency control film 51 is formed to the area of the resonance region where the upper electrode and the lower electrode face each other. That is, when the occupation ratio is low, the area of the frequency control film 51 formed in the resonance region is small, and when the occupation ratio is high, the area of the frequency control film 51 formed in the resonance region is large. ing. As shown in FIG. 8, when the island-pattern frequency control film 51 is provided, the occupation ratio of the frequency control film 51 to the membrane portion 46 is preferably 40% or less. Further, when the hole pattern frequency control film 51 is provided, the occupation ratio of the frequency control film 51 with respect to the membrane portion 46 is preferably 60% or more.

Also, the pattern of the frequency control film 51 can be formed in a circular or elliptical shape. Further, the pattern of the frequency control film 51 can be formed in a shape including a curve. By forming the frequency control film in the above shape, it is easy to accurately form a desired pattern at the time of pattern formation, and the resonance frequency of the resonator can be accurately moved to the desired frequency.

(Example 2)
9A to 9C show an example of a piezoelectric thin film resonator which is an example of an acoustic wave device according to the present embodiment. FIG. 9A is a plan view of the piezoelectric thin film resonator. FIG. 9B is a cross-sectional view taken along the line AA in FIG. 9A, and is a cross-sectional view of the first piezoelectric thin film resonator. FIG. 9C is a cross-sectional view of the second piezoelectric thin film resonator.

FIG. 10 shows a filter circuit in which a plurality of piezoelectric thin film resonators of the present embodiment are arranged in series arms and parallel arms. Here, the resonators connected to the series arms are called first piezoelectric thin film resonators (series resonators) S1 to S4, and the resonators connected to the parallel arms are called second piezoelectric thin film resonators (parallel resonators) P1 to P3. I will do it.

The piezoelectric thin film resonator shown in FIGS. 9A to 9C includes a substrate 41, a gap 42, a lower electrode 43, a piezoelectric film 44, an upper electrode 45, a membrane portion 46, an etching medium introduction hole 47, an etching medium introduction path 48, and a frequency control film. 51 and a frequency adjustment film 52 are provided. The substrate 41 uses silicon (Si) in this embodiment. In this embodiment, the lower electrode 43 has a two-layer structure of ruthenium (Ru) / chromium (Cr). The piezoelectric film 44 uses aluminum nitride (AlN) in this embodiment. In this embodiment, the upper electrode 45 has a two-layer structure of a first layer 45a and a second layer 45b. For example, Ru can be used for the first layer 45a. For example, Cr can be used for the second layer 45b.

Here, the film thickness of the upper electrode 45 of the parallel resonator shown in FIG. 9C (second piezoelectric thin film resonators P1 to P3 in FIG. 10) is equal to the series resonator shown in FIG. 9B (first piezoelectric thin film resonator shown in FIG. 10). It is thicker than the upper electrode 45 of S1 to S4). Specifically, the film thickness of the first layer 45a of the upper electrode 45 shown in FIG. 9C is larger than the film thickness of the first layer 45a of the upper electrode 45 shown in FIG. 9B. With this configuration, the resonance frequency of the parallel resonator is made lower than the resonance frequency of the series resonator.

Each film of the lower electrode 43, the piezoelectric film 44, and the upper electrode 45 can be formed by a film forming method such as a sputtering method. For example, in the case of a piezoelectric thin film resonator having a resonance frequency of 2 GHz, the approximate thickness of each layer is as follows: Ru of the lower electrode 43 is 250 nm, Cr is 100 nm, AlN of the piezoelectric film 44 is 1150 nm, The first layer 45a (Ru) of the upper electrode 45 is 250 nm, the second layer 45b (Cr) is 20 nm, the Cr of the upper electrode 45 of the parallel resonator shown in FIG. 9C is 20 nm, and Ru is 300 nm.

The frequency adjustment film 52 is provided in the uppermost layer in the membrane unit 46. The frequency adjustment film 52 is made of SiO ₂ in this embodiment. The frequency adjustment film 52 can simultaneously adjust the resonance frequencies of the first piezoelectric thin film resonators S1 to S4 shown in FIG. 9B and the second piezoelectric thin film resonators P1 to P3 shown in FIG. 9C. That is, the film configuration of the first piezoelectric thin film resonators S1 to S4 of the series arm is such that the films are in the order of SiO ₂ / Ti / Cr / Ru / AlN / Ru / Cr / Si substrate from the top layer to the bottom layer. Is formed. The film configuration of the second piezoelectric thin film resonators P1 to P3 of the parallel arm is such that films are formed in the order of SiO ₂ / Ti / Cr / Ru / AlN / Ru / Cr / Si substrate from the top layer to the bottom layer. ing. The film thickness of each layer varies depending on the required specifications of the filter, and the lower electrode 43 and upper electrode 45 films, the piezoelectric film 44, and the frequency control film 51 may have other configurations. The lower electrode 43 may have a single layer structure. In this embodiment, the frequency difference between the resonance frequencies of the series resonator and the parallel resonator is defined by the film thickness difference between the first layer 45a and the second layer 45b of the upper electrode 45. The resonance frequency difference may be defined by the film thickness difference of the plurality of layers included in the lower electrode 43. A dome-shaped gap 42 (bulge) is formed between the substrate 41 and the lower electrode 43 in the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other. The “dome-shaped gap” is a bulge having a shape such that the inner height is low at the periphery of the gap and the inner height is higher at the center of the gap.

Here, the frequency control film 51 is patterned so that the weight per unit area does not affect the elastic wave excited by the piezoelectric film 44 (AlN). Generation of unnecessary spurious and deterioration of resonance characteristics can be suppressed. “Weight that the frequency control film 51 does not affect the elastic wave excited by the piezoelectric film 44” means that, in the second piezoelectric thin film resonator and the second piezoelectric thin film resonator, the upper electrode and the lower electrode The weight is lighter than the difference in the total weight per unit area of the lower electrode, the piezoelectric film, the upper electrode, and the frequency adjustment film in the resonance region facing each other. In this embodiment, the weight per unit area of the frequency control film is formed to be lighter than the difference in weight per unit area of the upper electrode of the first piezoelectric thin film resonator and the second piezoelectric thin film resonator. The In particular, in this embodiment, when the weight per unit area of the frequency control film satisfies the condition of 0.2 g / m ² or less, generation of unnecessary spurious and resonance characteristics caused by patterning of the frequency control film 51 are achieved. Deterioration can be suppressed. Here, the “weight per unit area (g / m ² )” of the upper electrode, the lower electrode, the piezoelectric film, the frequency adjustment film, the frequency control film, etc. means the material density (g / m ³ ) and the film thickness ( m).

(Example 3)
Next, as Example 3, a ladder filter in which the piezoelectric thin film resonator according to this embodiment is connected in a ladder shape will be described.

FIG. 11 is a circuit diagram of the ladder type filter of this embodiment. As shown in FIG. 11, the ladder filter includes first piezoelectric thin film resonators S1 to S5 connected to the series arm, and second piezoelectric thin film resonators P1 to P3 connected to the parallel arm. Yes. Here, the first piezoelectric thin film resonator and the second piezoelectric thin film resonator have the film configuration described in the first embodiment, and the second piezoelectric thin film resonator has a resonance frequency difference with the first piezoelectric thin film resonator. Therefore, a mass addition film is formed. Here, when the resonance frequency of the first piezoelectric thin film resonators S1 was f _S1, f _S1 resonant frequency of the first piezoelectric thin-film resonator S2, the resonance frequency of the first piezoelectric thin-film resonator S3, S4, S5 ( The first piezoelectric thin film resonators S1 to S5 are each provided with a frequency control film 51 in which a pattern is formed so that f _S1 -7 MHz).

FIG. 12 shows the pass characteristics of the ladder type filter when the weight per unit area of the frequency control film 51 is 0.56 g / m ² (Comparative Example) and 0.11 g / m ² (Example 3). Indicates. Here, the comparative example shows a case where the weight per unit area of the frequency control film 51 is the same as the weight per unit area of the mass-added film, and in Example 3, the weight per unit area of the frequency control film 51 is shown. Shows a case where the weight per unit area of the mass-added film is lighter. When the weight per unit area of the frequency control film 51 is 0.56 g / m ² , the resonance characteristics of each resonator deteriorate when the resonance frequency of the piezoelectric thin film resonator included in the ladder filter is moved. Resulting in. On the other hand, when the weight per unit area of the frequency control film 51 of Example 3 is 0.11 g / m ² , the resonance frequency is not degraded without degrading the resonance characteristics of the piezoelectric thin film resonator included in the ladder filter. Therefore, excellent filter characteristics can be obtained.

[2. (Configuration of communication module)
FIG. 13 shows an example of a communication module including the piezoelectric thin film resonator according to the present embodiment. As shown in FIG. 13, the duplexer 62 includes a reception filter 62a and a transmission filter 62b. The reception filter 62a is connected to reception terminals 63a and 63b corresponding to, for example, balanced output. The transmission filter 62b is connected to the transmission terminal 65 via the power amplifier 64. Here, the reception filter 62a includes the piezoelectric thin film resonator according to the present embodiment.

When performing a reception operation, the reception filter 62a passes only a signal in a predetermined frequency band among reception signals input via the antenna terminal 61, and outputs the signal from the reception terminals 63a and 63b to the outside. Further, when performing a transmission operation, the transmission filter 62b passes only a signal in a predetermined frequency band among transmission signals input from the transmission terminal 65 and amplified by the power amplifier 64, and outputs the signal from the antenna terminal 61 to the outside. To do.

By providing the communication module with the piezoelectric thin film resonator according to the present embodiment, a communication module having excellent pass characteristics can be realized. Moreover, the manufacturing process of a communication module can be shortened.

Note that the configuration of the communication module shown in FIG. 13 is an example, and the same effect can be obtained even if the filter according to the present embodiment is mounted on a communication module of another form.

[3. Configuration of communication device]
FIG. 14 shows an RF block of a cellular phone terminal as an example of a communication device including the piezoelectric thin film resonator according to the present embodiment or the communication module described above. Further, the communication apparatus shown in FIG. 14 shows a configuration of a mobile phone terminal that supports a GSM (Global System for Mobile Communications) communication system and a W-CDMA (Wideband Code Division Multiple Access) communication system. Further, the GSM communication system in the present embodiment corresponds to the 850 MHz band, 950 MHz band, 1.8 GHz band, and 1.9 GHz band. In addition to the configuration shown in FIG. 14, the mobile phone terminal includes a microphone, a speaker, a liquid crystal display, and the like. However, illustration is omitted because they are unnecessary in the description of the present embodiment. Here, the reception filters 73a and 77 to 80 include the piezoelectric thin film resonator according to the present embodiment.

First, the received signal input through the antenna 71 selects an LSI to be operated by the antenna switch circuit 72 depending on whether the communication method is W-CDMA or GSM. When the input received signal is compatible with the W-CDMA communication system, switching is performed so that the received signal is output to the duplexer 73. The reception signal input to the duplexer 73 is limited to a predetermined frequency band by the reception filter 73 a, and a balanced reception signal is output to the LNA 74. The LNA 74 amplifies the input received signal and outputs it to the LSI 76. The LSI 76 performs a demodulation process on the audio signal based on the input received signal, and controls the operation of each unit in the mobile phone terminal.

On the other hand, when transmitting a signal, the LSI 76 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 75 and input to the transmission filter 73b. The transmission filter 73b passes only a signal in a predetermined frequency band among input transmission signals. The transmission signal output from the transmission filter 73 b is output from the antenna 71 to the outside via the antenna switch circuit 72.

In addition, when the received signal to be input is a signal corresponding to the GSM communication system, the antenna switch circuit 72 selects any one of the reception filters 77 to 80 according to the frequency band and outputs the received signal. To do. A reception signal whose band is limited by any one of the reception filters 77 to 80 is input to the LSI 83. The LSI 83 performs a demodulation process on the audio signal based on the input received signal, and controls the operation of each unit in the mobile phone terminal. On the other hand, when transmitting a signal, the LSI 83 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 81 or 82 and output from the antenna 71 to the outside via the antenna switch circuit 72.

By providing the communication device with the piezoelectric thin film resonator or the communication module according to this embodiment, a communication device with excellent pass characteristics can be realized. Moreover, the manufacturing process of a communication apparatus can be shortened.

Note that the communication device shown in FIG. 14 is an example, and at least a communication device including the piezoelectric thin film resonator according to the present embodiment is the same as the present embodiment even if the communication device has other configurations. The effect of can be obtained.

[4. Effects of the embodiment, etc.]
According to the present embodiment, since the gap 42 is formed in a dome shape on the composite film side, it is not necessary to etch the substrate 41 and productivity can be improved. In addition, since the substrate 41 is not etched, it is possible to prevent the mechanical strength of the substrate 41 from being deteriorated. Further, since the area for forming the air gap 42 can be small, integration can be achieved.

Furthermore, since the shape of the membrane part 46 where the upper electrode 45 and the lower electrode 43 face each other is made elliptical or non-parallel, there is no parallel side, so that the reflected light is reflected at the outer periphery of the electrode. It can suppress that an elastic wave exists as a standing wave of a horizontal direction in a resonance part. Thereby, it can suppress that a ripple generate | occur | produces in a pass band.

Furthermore, since the projected area of the air gap onto the substrate surface includes the area where the upper electrode and the lower electrode face each other, the resonance characteristics of the piezoelectric thin film resonator can be improved and excellent performance can be obtained.

In addition, when manufacturing the piezoelectric thin film resonator shown in Example 1, and the filter shown in Example 2, it is not restricted to the said manufacturing process, Other manufacturing processes may be sufficient. For example, after obtaining the bump pad forming step without forming the sacrificial layer 49, a resist pattern is formed on the back surface of the substrate 41 so as to include the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other. Next, dry etching is performed so that the sidewall shape is substantially perpendicular to the substrate surface by performing etching with SF ₆ and formation of the sidewall protective film with C ₄ F ₈ alternately from the back surface of the substrate 41. A gap 42 is formed below the membrane portion 46 where the upper electrode 45 and the lower electrode 43 face each other. Thus, a piezoelectric thin film resonator and a filter configured by connecting a plurality of piezoelectric thin film resonators can be manufactured.

In this embodiment, a ladder type filter is given as an example. However, a lattice type filter in which a plurality of resonators are connected in a lattice type may be used.

The first piezoelectric thin film resonator (series resonator) in the present embodiment is an example of the main resonator of the present invention. The second piezoelectric thin film resonator (parallel resonator) in the present embodiment is an example of the sub-resonator of the present invention. The substrate 41 in the present embodiment is an example of the substrate of the present invention. The lower electrode 43 in the present embodiment is an example of the lower electrode of the present invention. The upper electrode 45 in the present embodiment is an example of the upper electrode of the present invention. The piezoelectric film 44 in the present embodiment is an example of the piezoelectric film of the present invention. The mass addition film | membrane 50 in this Embodiment is an example of the mass addition film | membrane of this invention. The frequency control film 51 in the present embodiment is an example of the frequency control film in the present invention. The membrane portion 46 in the present embodiment is an example of the resonance region of the present invention. The gap 42 in the present embodiment is an example of the gap of the present invention.

The following supplementary notes are disclosed regarding this embodiment.

(Appendix 1)
An acoustic wave device having a main resonator and a sub-resonator,
The main resonator and the sub resonator are
A lower electrode;
A piezoelectric film provided on the lower electrode;
An upper electrode provided on the piezoelectric film,
The main resonator and the sub-resonator have a difference in weight per unit area in a resonance region where the upper electrode and the lower electrode face each other,
An elastic wave device comprising a frequency control film lighter than the difference in weight on at least one of the main resonator and the sub-resonator.

(Appendix 2)
The elastic wave device according to appendix 1, wherein the difference in weight is a difference in thickness of an upper electrode or a lower electrode.

(Appendix 3)
The sub-resonator includes a mass addition film,
The elastic wave device according to appendix 1, wherein the difference in weight is a weight of the mass addition film.

(Appendix 4)
The elastic wave device according to appendix 1, wherein a weight per unit area of the frequency control film is 0.2 g / m ² or less.

(Appendix 5)
The elastic wave device according to any one of appendices 1 to 4, wherein the frequency control film has a convex island pattern.

(Appendix 6)
The elastic wave device according to any one of appendices 1 to 4, wherein the frequency control film has a concave hole pattern.

(Appendix 7)
5. The elasticity according to any one of appendices 1 to 4, comprising a resonator including a frequency control film having a convex island pattern and a resonator including a frequency control film having a concave hole pattern. Wave device.

(Appendix 8)
The elastic wave device according to any one of appendices 1 to 4, wherein the shape of the frequency control film is a height corresponding to a film thickness of the frequency control film.

(Appendix 9)
The elastic wave device according to any one of appendices 1 to 8, wherein the pattern formed by the frequency control film is formed dispersed in the resonance region.

(Appendix 10)
10. The acoustic wave device according to any one of appendices 1 to 9, wherein the pattern formed by the frequency control film is a circle or an ellipse.

(Appendix 11)
The elastic wave device according to any one of appendices 1 to 10, wherein the pattern formed by the frequency control film has a shape including a curve.

(Appendix 12)
The elastic wave device according to any one of appendices 1 to 11, wherein the frequency control film and the upper electrode are made of different materials.

(Appendix 13)
The elastic wave device according to any one of appendices 1 to 12, wherein the frequency control film and the upper electrode are a combination of materials having etching selectivity.

(Appendix 14)
14. The acoustic wave device according to any one of appendices 1 to 13, wherein the resonance region is elliptical.

(Appendix 15)
14. The acoustic wave device according to any one of appendices 1 to 13, wherein the resonance region is a non-parallel polygon.

(Appendix 16)
A gap having a dome-shaped bulge is provided between the substrate and the lower portion of the lower electrode that overlaps at least the resonance region,
The elastic wave device according to any one of appendices 1 to 15, wherein the outline of the gap is a closed shape made of a curve.

(Appendix 17)
The elastic wave device according to any one of appendices 1 to 16, wherein the region where the resonance region is projected onto the substrate is included in the region where the air gap is projected onto the substrate.

(Appendix 18)
The acoustic wave device according to any one of appendices 1 to 15, wherein the substrate includes a gap in a region overlapping the resonance region.

(Appendix 19)
An elastic wave device in which the main resonator and the sub resonator are connected in a ladder type or a lattice type.

(Appendix 20)
A filter comprising the acoustic wave device according to any one of appendices 1 to 19.

(Appendix 21)
A duplexer comprising the elastic wave device according to any one of appendices 1 to 19.

(Appendix 22)
A communication module comprising the acoustic wave device according to any one of appendices 1 to 19, the filter according to appendix 20, or the duplexer according to appendix 21.

(Appendix 23)
A communication apparatus comprising the acoustic wave device according to any one of appendices 1 to 19, the filter according to appendix 20, the duplexer according to appendix 21, or the communication module according to appendix 22.

This application is useful for acoustic wave devices, filters, communication modules, and communication devices.

41 Substrate 42 Gap 43 Lower electrode 44 Piezoelectric film 45 Upper electrode 46 Membrane portion 47 Etching medium introduction hole 48 Sacrificial layer etching medium introduction path 49 Sacrificial layer 50 Mass addition film 51 Frequency control film 52 Frequency adjustment film

Claims (9)

1. An acoustic wave device having a main resonator and a sub-resonator,
   The main resonator and the sub resonator are
   A lower electrode;
   A piezoelectric film provided on the lower electrode;
   An upper electrode provided on the piezoelectric film,
   The main resonator and the sub-resonator have a difference in weight per unit area in a resonance region where the upper electrode and the lower electrode face each other,
   An acoustic wave device comprising a frequency control film having a weight per unit area that is lighter than the difference in weight on at least one of the main resonator and the sub-resonator.
2. The elastic wave device according to claim 1, wherein the difference in weight is a difference due to a difference in thickness of the upper electrode or the lower electrode.
3. The sub-resonator includes a mass addition film provided on the upper electrode,
   The acoustic wave device according to claim 1, wherein the difference in weight is a difference in weight per unit area of the mass-added film.
4. 4. The acoustic wave device according to claim 1, wherein a weight per unit area of the frequency control film is 0.2 g / m ² or less.
5. 5. The acoustic wave device according to claim 1, wherein the frequency control film has a concave or convex pattern, and the pattern is dispersed in the resonance region.
6. The elastic wave device according to any one of claims 1 to 5, wherein the frequency control film is circular or elliptical.
7. A filter comprising the acoustic wave device according to any one of claims 1 to 6.
8. A communication module comprising the acoustic wave device according to any one of claims 1 to 6 or the filter according to claim 5.
9. A communication apparatus comprising the acoustic wave device according to any one of claims 1 to 6, the filter according to claim 7, or the communication module according to claim 8.

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