JP2008211394A - Resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonator suppressing the occurrence of the crosstalk between lower electrodes and reducing manufacturing costs. <P>SOLUTION: The resonator has: a base substrate 1; and a plurality of resonators 2 composed of the lower electrode 30 formed at the main surface side of the base substrate 1, a piezoelectric thin film 40 formed at a side opposite to the side of the base substrate 1 in the lower electrode 30, and an upper electrode 50 formed at a side opposite to the side of the lower electrode 30 in the piezoelectric thin film 40. In this case, the upper electrode 50 of two adjacent resonators 2 is connected in common. The base substrate 1 has an acoustic multilayer film 12 formed by alternately laminating low and high acoustic impedance layers 13 and 14 so that the low acoustic impedance layer 13 is formed at the top while the main surface side of a support substrate 11 is covered. In this case, a cavity section 1a passing through the base substrate 1 is formed at a part overlapping with one of the two adjacent resonators 2 in a thickness direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resonance device, and more particularly to a resonance device using BAW (Bulk Acoustic Wave).

  Conventionally, in the field of mobile communication devices such as cellular phones, as a high frequency filter used in a high frequency band of 3 GHz or more, a resonance device (BAW) that employs a piezoelectric thin film formed of a piezoelectric material such as PZT, AlN, ZnO or the like. Resonators) have been proposed.

  For example, Patent Document 1 describes an SMR (Solidly Mounted Resonator) type resonator device.

  As shown in FIG. 5A, this type of resonance device includes a base substrate 1 and a plurality of resonators 2 formed on the base substrate 1.

The base substrate 1 includes a support substrate 11 and an acoustic multilayer film (acoustic mirror) 12 that is formed on the main surface side (upper surface side in FIG. 5A) of the support substrate 11 and reflects bulk acoustic waves. . Acoustic multilayer film 12, a low acoustic impedance layer 13 made of SiO ₂ on the main surface of the supporting substrate 11, the acoustic impedance than SiO ₂ is high material (e.g., tungsten, etc.) and a high acoustic impedance layer 14 made of, It is formed by alternately laminating so that the uppermost layer becomes the low acoustic impedance layer 13.

  The resonator 2 includes a lower electrode 30 formed on a side opposite to the support substrate 11 side in the acoustic multilayer film 12 (an upper surface side in FIG. 5A), and a side opposite to the acoustic multilayer film 12 side in the lower electrode 30. A plurality of resonators 2 each including a piezoelectric thin film 40 formed on the upper side and an upper electrode 50 formed on the opposite side of the piezoelectric thin film 40 from the lower electrode 30 side are provided.

  By the way, in the above resonance apparatus, since the high acoustic impedance layer 14 is formed so as to cover the entire surface of the main surface side of the support substrate 11, a conductive material such as tungsten is used as the material of the high acoustic impedance layer 14. In this case, a parasitic capacitance is generated between the high acoustic impedance layer 14 closest to the lower electrode 30 and the lower electrode 30, and crosstalk occurs between the resonators 2 having different potentials of the lower electrode 30 through the acoustic multilayer film 12. There was a problem that occurred.

Therefore, as shown in FIG. 5B, a high-acoustic impedance layer 14 of the acoustic multilayer film 12 is patterned so as to correspond to each of the plurality of resonators 2, thereby providing a resonance device that suppresses the occurrence of the crosstalk. Proposed.
JP 2001-308678 A

  However, in the acoustic multilayer film 12 of the resonance device shown in FIG. 5B, the thickness of the acoustic multilayer film 12 varies due to the patterning of the high acoustic impedance layer 14, and as shown in FIG. The flatness of the surface of the multilayer film 12 is deteriorated. As a result, when the piezoelectric thin film 40 is formed using the sol-gel method, defects such as cracks occur in the piezoelectric thin film 40.

  Therefore, in order to improve the flatness of the surface of the acoustic multilayer film 12, it has been proposed to planarize the surface of the acoustic multilayer film 12 by CMP (Chemical Mechanical Polishing).

  However, in order to obtain an acoustic multilayer film 12 with good flatness as shown in FIG. 6B by planarization processing by CMP, the low acoustic impedance layer 14 which is the uppermost layer of the acoustic multilayer film 12 is designed. It is necessary to form thicker than the thickness, and since it is necessary to remove all the thick parts by CMP, it is very time-consuming, which complicates the manufacturing process and increases the manufacturing cost. There was a problem. Further, in the planarization process by CMP, it is difficult to detect the end point, and the film thickness controllability of the uppermost low acoustic impedance layer 13 is not good, so that the acoustic multilayer film 12 having a desired acoustic reflection efficiency may not be obtained. .

  Furthermore, even in the resonance device as shown in FIG. 5B, parasitic capacitance may occur between the high acoustic impedance layer 14 and the lower electrode 30, and between the high acoustic impedances 14, respectively. The occurrence of crosstalk between them was not sufficiently suppressed.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a resonance apparatus that can suppress the occurrence of crosstalk between resonators and can reduce the manufacturing cost.

  In order to solve the above-described problem, the invention of claim 1 includes a base substrate and a plurality of resonators formed on the base substrate, and the resonator is a lower portion formed on the main surface side of the base substrate. Two adjacent resonators composed of an electrode, a piezoelectric thin film formed on the side opposite to the base substrate side in the lower electrode, and an upper electrode formed on the side opposite to the lower electrode side in the piezoelectric thin film The base substrate is composed of a low acoustic impedance layer made of a material having a relatively low acoustic impedance and a high acoustic impedance layer made of a material having a relatively high acoustic impedance. In the form of covering the main surface side of the support substrate, and having an acoustic multilayer film formed by alternately laminating so that the uppermost layer is a low acoustic impedance layer. A portion that overlaps While the thickness direction, wherein the cavity at least through the said top layer other than the low acoustic impedance layer and a high acoustic impedance layer in the acoustic multi-layer film and the supporting substrate is formed.

  According to the first aspect of the invention, since the cavity is formed in the base substrate at a portion corresponding to one of the two adjacent resonators, the parasitic capacitance between the one resonator and the acoustic multilayer film is reduced. Thus, it is possible to suppress the occurrence of crosstalk between adjacent resonators. In addition, at the time of manufacturing, there is no need for a step of patterning the high acoustic impedance layer of the acoustic multilayer film so as to correspond to each of the plurality of lower electrodes, and a step of planarizing the surface of the acoustic multilayer film by CMP, Since the parasitic capacitance can be reduced by providing the cavity portion in the base substrate, the manufacturing process can be simplified as compared with the conventional case, and the manufacturing cost can be reduced.

  In the invention of claim 2, in the invention of claim 1, the cavity is formed so as to penetrate the low acoustic impedance layer and the high acoustic impedance layer other than the uppermost layer in the acoustic multilayer film and the support substrate in the thickness direction. It is characterized by being.

  According to invention of Claim 2, the value of the resonant frequency of one resonator (resonator by the side of a cavity part) can be changed with the thickness of the low acoustic impedance of the uppermost layer of an acoustic multilayer film. In addition, since the low acoustic impedance layer at the top of the acoustic multilayer film is used as a layer for changing the resonance frequency of the resonator on the cavity side, the resonance frequency of the resonator on the cavity side is changed. There is no need to provide a separate layer, the manufacturing process can be facilitated, and the manufacturing cost can be reduced.

  The present invention can suppress the occurrence of crosstalk between the resonators and can reduce the manufacturing cost.

(Embodiment 1)
As shown in FIG. 1, the resonance device of the present embodiment includes a base substrate 1 and a plurality of resonators 2 formed on the base substrate 1.

  As shown in FIG. 1, the base substrate 1 includes, for example, a support substrate 11 such as a single crystal silicon substrate having a main surface of (100) plane, an MgO substrate, or an STO (SrTiO 3) substrate, and the main surface of the support substrate 11. 1 (upper surface side in FIG. 1) and an acoustic multilayer film 12 that reflects a bulk acoustic wave generated by the resonator 2, and the surface of the acoustic multilayer film 12 (upper surface in FIG. It becomes the main surface.

The acoustic multilayer film 12 includes a low acoustic impedance layer 13 made of a material having a relatively low acoustic impedance (for example, SiO ₂ ), and a high acoustic impedance layer 14 made of a material having a relatively high acoustic impedance (for example, tungsten). It has. The low acoustic impedance layers 13 and the high acoustic impedance layers 14 are alternately stacked so as to cover the entire surface of the support substrate 11 on the main surface side so that the uppermost layer becomes the low acoustic impedance layers 13. In the following description, the uppermost low acoustic impedance layer 13 is denoted by reference numeral 13a as necessary.

  The resonator 2 includes a lower electrode 30 formed on the main surface side (upper surface side in FIG. 1) of the base substrate 1, a piezoelectric thin film 40 formed on the opposite side of the lower electrode 30 to the base substrate 1 side, The piezoelectric thin film 40 includes an upper electrode 50 formed on the side opposite to the lower electrode 30 side. In the present embodiment, the two adjacent resonators 2 are connected to the upper electrode 50 in common by the connecting portion 51 (so that the potentials are equal).

  Meanwhile, as shown in FIG. 1, the base substrate 1 in the present embodiment is provided with a cavity 1a. The cavity 1a is formed on the base substrate 1 at a portion of the base substrate 1 that overlaps one of the two adjacent resonators 2 (right resonator 2 in the example shown in FIG. 1) in the thickness direction (vertical direction in FIG. 1). Is formed so as to penetrate through in the thickness direction.

  Below, the manufacturing method of the resonance apparatus of this embodiment is demonstrated with reference to FIG. 2 and FIG.

  First, the low acoustic impedance layer 13 and the high acoustic impedance layer 14 are formed on the main surface side of the support substrate 11 so as to cover the entire surface of the support substrate 11 on the main surface side. The acoustic multilayer film 12 is formed by alternately stacking so as to obtain the base substrate 1 having the structure shown in FIG. In addition to tungsten (W), Au, Mo, or the like may be used as a material for the high acoustic impedance layer 14.

  Next, the first conductive layer 3 serving as the basis of the lower electrode 30 is formed by covering the entire surface on the surface side of the acoustic multilayer film 12 by using a sputtering method or the like, as shown in FIG. Get the structure. In the present embodiment, the first conductive layer 3 is composed of a Pt layer. However, the first conductive layer 3 is not limited to a single layer structure, for example, a Ti layer on the acoustic multilayer film 12 and The Pt layer on the Ti layer may be used.

  After the formation of the first conductive layer 3, the piezoelectric layer 4 serving as the basis of the piezoelectric thin film 40 is formed on the entire surface of the first conductive layer 3 so that the structure shown in FIG. obtain. In this embodiment, the piezoelectric layer 4 is composed of a PZT thin film. As a method for forming (manufacturing) the PZT thin film, a method using a sol-gel method, a CVD method, a sputtering method, or the like has been proposed. A sol-gel method is used which has advantages such as reduction in manufacturing cost without being required, and formation of a PZT thin film with high in-plane uniformity of film thickness, thereby improving quality.

  In forming a PZT thin film by the sol-gel method, a PZT thin film forming composition obtained by dissolving a lead compound, a zirconium compound and a titanium compound in a solvent is applied on the surface of the first conductive layer 3 and, for example, 10 ° C. at 10 ° C. After repeating the step of temporary baking for 5 minutes until a predetermined film thickness is obtained, a step of baking at 600 ° C. for 10 minutes, for example, may be performed.

In forming the PZT thin film as described above, a seed layer (not shown) may be used. In this case, a lead compound and a titanium compound are dissolved in a solvent on the surface of the first conductive layer 3. The PbTiO ₃ thin film forming composition thus formed is applied, and the process of drying at 150 to 400 ° C. is repeated until a predetermined film thickness is obtained, and then the PZT thin film is formed by the above method.

  After the piezoelectric layer 4 is formed, the piezoelectric layer 4 is patterned into a desired planar shape using a photolithographic technique and an etching technique to form a plurality of piezoelectric thin films 40, as shown in FIG. Get the structure shown. In removing the unnecessary portion of the piezoelectric layer 4 by etching, a hydrofluoric acid etchant may be used.

  Thereafter, the first conductive layer 3 is patterned into a desired planar shape using an ion milling technique or the like to form a plurality of lower electrodes 3 to obtain the structure shown in FIG.

  Subsequently, an insulating layer 60 is formed on the entire surface of the acoustic multilayer film 12 by sputtering or the like, and then unnecessary portions of the insulating layer 60 are removed, as shown in FIG. Get the structure. Here, as a method of removing the unnecessary portion of the insulating layer 60, before forming the insulating layer 60, a resist layer is previously formed on the surface side of the acoustic multilayer film 12 where the insulating layer 60 is unnecessary. In addition, a so-called lift-off method in which unnecessary portions of the insulating layer 60 are removed together with the removal of the resist layer can be used. Further, as a method for removing unnecessary portions of the insulating layer 60, a photolithography technique, an etching technique, or the like may be used.

  In forming such an insulating layer 60, the insulating layer 60 is formed so that the surface of the insulating layer 60 and the surface of the piezoelectric thin film 40 are located on the same plane.

  After the insulating layer 60 is formed, a second conductive layer serving as the basis of the upper electrode 50 is formed on the entire surface of the acoustic multilayer film 12 using an electron beam evaporation method (EB evaporation method) or the like, Thereafter, the second conductive layer is patterned using photolithography technology and etching technology (unnecessary portions are removed), and a plurality of upper electrodes 50 each composed of a part of the second conductive layer and adjacent to each other. A connection portion 51 for electrically connecting the upper electrodes 50 of the resonator 2 is formed, and the structure shown in FIG.

  In the present embodiment, the second conductive layer is composed of an Al layer, but the second conductive layer is not limited to a single layer structure, and may be a multilayer structure. Further, a phosphoric acid-based etchant may be used to remove unnecessary portions of the second conductive layer made of the Al layer by etching.

  Thereafter, by using reactive ion etching (RIE) or the like, a portion of the base substrate 1 overlapping with one of the adjacent resonators 2 (the resonator 2 on the right side in FIG. 3C) in the thickness direction. Then, the cavity 1a is formed so as to penetrate the base substrate 1 in the thickness direction, and the structure shown in FIG. In this embodiment, the cavity 1a is formed after the upper electrode 50 is formed. However, the timing for forming the cavity 1a may be any time after the first conductive layer 3 is formed.

  By the way, in manufacturing the resonance device, a large number of resonance devices may be formed at the wafer level and then divided into individual resonance devices in a dicing process.

  As described above, according to the resonance device of the present embodiment, the base substrate 1 is formed with the cavity 1a penetrating the base substrate 1 in the thickness direction at a portion corresponding to one of the two adjacent resonators 2. As a result, the area of the high acoustic impedance layer 14 that overlaps one of the resonators 2 in the thickness direction can be reduced by the opening area of the cavity 1a, so that the parasitic between the one resonator 2 and the acoustic multilayer film 12 can be reduced. Capacitance can be reduced, and occurrence of crosstalk between adjacent resonators 2 can be suppressed. In addition, at the time of manufacture, a process of patterning the high acoustic impedance layer 14 of the acoustic multilayer film 12 so as to correspond to each of the plurality of lower electrodes 30 and a process of planarizing the surface of the acoustic multilayer film 12 by CMP at the time of manufacturing. Since the parasitic capacitance can be reduced by providing the cavity 1a in the base substrate 1, the manufacturing process can be facilitated and the manufacturing cost can be reduced.

  Further, in the present embodiment, since the piezoelectric thin film 40 is formed by PZT having a relatively large electromechanical coupling coefficient among piezoelectric materials, a resonance device having steep rise and fall characteristics in a high frequency band can be manufactured. Such a resonance device can be suitably used for a filter having a sharp cutoff characteristic and a wide bandwidth in a high-frequency band of 3 GHz or more, for example, a broadband high-frequency filter such as a UWB filter. In addition to PZT, for example, a piezoelectric material such as ZnO or AlN may be used as the material of the piezoelectric thin film 40.

In the resonance device according to the present embodiment, the resonance frequency is set to 4 GHz, the thickness of the lower electrode 30 is 100 nm, the thickness of the piezoelectric thin film 40 is 300 nm, the thickness of the upper electrode 50 is 100 nm, and SiO _{2 is} formed. The thickness of the low acoustic impedance layer 13 is set to 373 nm, and the thickness of the high acoustic impedance layer 14 formed of tungsten is set to 327 nm. However, these numerical values are merely examples and are not particularly limited. When the resonance frequency is set in the range of 3 GHz to 5 GHz, the thickness of the piezoelectric thin film 40 is in the range of 200 nm to 600 nm, and the thickness of the low acoustic impedance layer 13 is in the range of 250 nm to 550 nm. What is necessary is just to set the thickness of 14 suitably in the range of 200 nm-450 nm, respectively.

(Embodiment 2)
In the resonance apparatus of the present embodiment, the configuration of the base substrate 1 is different from that of the first embodiment, and the other configurations are the same as those of the first embodiment. To do.

  As shown in FIG. 4, the base substrate 1 in the present embodiment has a low acoustic impedance layer 13 other than the uppermost layer of the acoustic multilayer film 12 in a portion overlapping with one of the adjacent resonators 2 in the thickness direction. And the cavity 1a which penetrates the high acoustic impedance layer 14 is formed. That is, the cavity 1a in this embodiment does not penetrate the base substrate 1 in the thickness direction, but is the most part of the support substrate 11 and the acoustic multilayer film 12 that are parts of the base substrate 1 excluding the low acoustic impedance layer 13a. It is formed so as to penetrate the low acoustic impedance layer 13 and the high acoustic impedance layer 14 other than the upper layer.

  Therefore, a low acoustic impedance layer 13a, which is the uppermost layer of the acoustic multilayer film 12, is interposed between one of the resonators 2 (the resonator 2 on the right side in FIG. 4) and the cavity 1a. 13a acts as a layer for changing the resonance frequency of one resonator 2 (that is, the resonator 2 on the cavity 1a side).

  That is, according to the resonance device of the present embodiment, the value of the resonance frequency of one resonator 2 can be changed depending on the thickness of the low acoustic impedance 13a of the uppermost layer of the acoustic multilayer film 12. Moreover, since the low acoustic impedance layer 13a at the uppermost layer of the acoustic multilayer film 12 is used as a layer for changing the resonance frequency of one resonator 2, the resonance frequency of one resonator 2 is changed. There is no need to provide a separate layer, the manufacturing process can be facilitated, and the manufacturing cost can be reduced.

By the way, although the resonance frequency of the piezoelectric material such as PZT used as the material of the piezoelectric thin film 40 varies depending on the temperature, unlike the first embodiment, the resonator 2 and the cavity on the cavity 1a side are different from the first embodiment. since leaving the low acoustic impedance layers 13a between the 1a, by using the SiO ₂ as a material of the low acoustic impedance layers 13a, it can be suppressed resonance frequency of one resonator 2 is changed by temperature. That is, since a piezoelectric material such as PZT is generally negative in temperature coefficient of resonance frequency, SiO ₂ having a positive temperature coefficient of resonance frequency is used as the material of the low acoustic impedance layer 13a. As a result, the temperature coefficient of the resonance frequency can be brought close to 0 for the one resonator 2 and the low acoustic impedance layer 13a as a whole, and as a result, fluctuation of the resonance frequency due to temperature can be suppressed.

  In the present embodiment, since the low acoustic impedance layer 13a is interposed between the cavity 1a and one of the resonators 2, the resonator 2 can be formed even after the cavity 1a is formed. The timing of forming the part 1a may be any time after the base substrate 1 is formed.

  In this embodiment, since the resonator 2 on the cavity 1a side is formed on the low acoustic impedance layer 13a, the opening size of the cavity 1a is set to be equal to that of the lower electrode 30 of the resonator 2 on the cavity 1a side. The size may be larger than the size, and in this way, the lower electrode 30 and the high acoustic impedance layer 14 do not overlap in the thickness direction, so that the parasitic capacitance can be further reduced.

1 is a schematic cross-sectional view of a resonance device according to a first embodiment. 5 is an explanatory diagram of a method for manufacturing the resonance device of Embodiment 1. FIG. 5 is an explanatory diagram of a method for manufacturing the resonance device of Embodiment 1. FIG. 3 is a schematic cross-sectional view of a resonance device according to Embodiment 2. FIG. It is a schematic explanatory drawing of the conventional resonance apparatus. It is a schematic explanatory drawing of the acoustic multilayer film of the conventional resonance apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base substrate 1a Cavity part 2 Resonator 11 Support substrate 12 Acoustic multilayer film 13, 13a Low acoustic impedance layer 14 High acoustic impedance layer 30 Lower electrode 40 Piezoelectric thin film 50 Upper electrode

Claims (2)

A base substrate and a plurality of resonators formed on the base substrate, the resonator being formed on a lower electrode formed on the main surface side of the base substrate and on a side opposite to the base substrate side of the lower electrode A piezoelectric thin film, and an upper electrode formed on the opposite side of the piezoelectric thin film from the lower electrode side, wherein the upper electrodes of two adjacent resonators are connected in common,
The base substrate has a low acoustic impedance layer made of a material having a relatively low acoustic impedance and a high acoustic impedance layer made of a material having a relatively high acoustic impedance so as to cover the main surface side of the support substrate. Has an acoustic multilayer film formed by alternately laminating so as to be a low acoustic impedance layer,
A cavity that penetrates at least the low acoustic impedance layer and the high acoustic impedance layer other than the uppermost layer in the acoustic multilayer film and the support substrate is formed in a portion overlapping with one of the two adjacent resonators in the thickness direction. A resonance apparatus characterized by the above.   2. The resonance device according to claim 1, wherein the cavity is formed so as to penetrate through the low acoustic impedance layer and the high acoustic impedance layer other than the uppermost layer in the acoustic multilayer film and the support substrate.

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