JP2009290369A - Baw resonance device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a BAW resonance device capable of improving crystallinity and piezoelectric characteristics in a piezoelectric layer made of a lead-based piezoelectric material. <P>SOLUTION: The BAW resonance device has: an acoustic mirror layer 2 formed at one surface side of a support substrate 1 made of MgO or SrTiO<SB>3</SB>; and a resonator 3 formed on the acoustic mirror layer 2. The resonator 3 has: a lower electrode 31 formed on the acoustic mirror layer 2 and made of SrRuO<SB>3</SB>; a piezoelectric layer 32 formed on the lower electrode 31 and made of a lead-based piezoelectric material (for example, PMN-PZT); and an upper electrode 33 formed at a side opposite to the side of the lower electrode 31 in the piezoelectric layer 32. In the acoustic mirror layer 2, a high acoustic impedance layer 21 formed from the same material as the lower electrode 31 and a low acoustic impedance layer 22 formed from the same material as the piezoelectric layer 32 are laminated alternately, and an uppermost layer at the side of the lower electrode 31 is composed of the low acoustic impedance layer 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a BAW (Bulk Acoustic Wave) resonance device including a resonator using a longitudinal vibration mode in a thickness direction of a piezoelectric layer.

Conventionally, as shown in FIG. 4, as a resonance device applicable to a high frequency filter used in a high frequency band of 2 GHz or more in the field of mobile communication devices such as mobile phones, a support substrate 1 ′ and a support substrate 1 ′ are provided. There is proposed a BAW resonator including an acoustic mirror layer 2 ′ formed on one surface side and a resonator 3 ′ formed on the acoustic mirror layer 2 ′ (see, for example, Patent Document 1). Here, the acoustic mirror layer 2 ′ includes a high acoustic impedance layer 21 ′ made of a metal material (eg, W, Mo, etc.) and a low acoustic impedance layer made of a dielectric material (eg, SiO ₂ , Si ₃ N ₄ etc.). The resonator 3 ′ has a stacked structure of a lower electrode 31 ′, a piezoelectric layer 32 ′, and an upper electrode 33 ′, and is used as a piezoelectric material of the piezoelectric layer 32 ′. AlN or the like is used. In the BAW resonator described in Patent Document 1, a plurality of resonators 3 ′ are formed on the acoustic mirror layer 2 ′ and connected appropriately to form a filter.

By the way, in the above-mentioned BAW resonance apparatus, AlN is adopted as the piezoelectric material of the piezoelectric layer 32 ′, and Si, GaAs or glass is adopted as the material of the support substrate 1 ′. However, as a UWB (Ultra Wide Band) filter. When applied, as a piezoelectric material of the piezoelectric layer 32 ', it is possible to obtain a bandwidth of about 10% with respect to the center frequency as compared with AlN whose bandwidth is only 4 to 5% with respect to the center frequency. It is conceivable to employ a lead-based piezoelectric material (for example, PZT, PMN-PZT, etc.) and employ MgO or SrTiO ₃ as the material of the support substrate 1 ′ in order to improve the crystallinity of the piezoelectric layer 32 ′. The BAW resonator described in Patent Document 1 is an SMR (Solidly Mounted Resonator) provided with an acoustic mirror layer 2 ′, and a cavity is formed in the support substrate 1 ′ without providing the acoustic mirror layer 2 ′. Compared with FBAR (Film Bulk Acoustic Resonator), there is an advantage that it can be made robust.
JP 2002-251190 A

However, in the BAW resonator having the configuration shown in FIG. 4, even if a lead-based piezoelectric material is used as the piezoelectric material of the piezoelectric layer 32 ′ and MgO or SrTiO ₃ is used as the material of the support substrate 1 ′, the acoustic mirror layer Since the high acoustic impedance layer 21 ′ constituting 2 ′ is formed of a metal material such as W or Mo, and the low acoustic impedance layer 22 ′ is formed of a dielectric material such as SiO ₂ or Si ₃ N ₄ , piezoelectric The crystallinity of the layer 32 ′ cannot be sufficiently improved, and improvement in piezoelectric characteristics (electromechanical coupling coefficient, etc.) has been desired.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide a BAW resonance device capable of improving the crystallinity and piezoelectric characteristics of a piezoelectric layer made of a lead-based piezoelectric material.

The invention of claim 1 includes an acoustic mirror layer formed on one surface side of a support substrate made of MgO or SrTiO _3, and a resonator formed on the opposite side of the support substrate side in the acoustic mirror layer. The child includes a lower electrode made of SrRuO ₃ formed on the opposite side of the acoustic mirror layer to the support substrate side, and a piezoelectric layer made of a lead-based piezoelectric material formed on the opposite side of the lower electrode to the acoustic mirror layer side. The upper electrode formed on the opposite side of the piezoelectric layer from the lower electrode side, and the acoustic mirror layer is formed of the same material as the piezoelectric layer and the high acoustic impedance layer formed of the same material as the lower electrode The low acoustic impedance layers are alternately laminated, and the uppermost layer on the lower electrode side is constituted by a low acoustic impedance layer.

According to the present invention, a lead-based piezoelectric material is used as the material of the piezoelectric layer, the support substrate is formed of MgO or SrTiO ₃ , the lower electrode is formed of SrRuO ₃ , and the acoustic mirror layer is the same as the lower electrode Since the high acoustic impedance layer made of material and the low acoustic impedance layer made of the same material as the piezoelectric layer are alternately laminated and the uppermost layer on the lower electrode side is composed of the low acoustic impedance layer, lead-based piezoelectric It becomes possible to improve the crystallinity and piezoelectric characteristics of the piezoelectric layer made of the material.

  The invention of claim 2 is characterized in that, in the invention of claim 1, a Pt layer is formed between the acoustic mirror layer and the lower electrode as a buffer layer for relaxing the lattice mismatch between the two.

  According to this invention, the crystallinity of the lower electrode can be improved, and the crystallinity of the piezoelectric layer can be further improved.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a Pt layer is formed between the support substrate and the acoustic mirror layer as a buffer layer that relaxes the lattice mismatch between the two. And

  According to this invention, the crystallinity of each of the high acoustic impedance layer and the low acoustic impedance layer of the acoustic mirror layer can be improved, the crystallinity of the lower electrode can be improved, and the crystallinity of the piezoelectric layer can be further improved. Become.

  The invention of claim 4 is the invention of claims 1 to 3, wherein the material of the upper electrode is at least one selected from the group of Mo, W, Ir, Cr, Ru, and Pt. To do.

  According to the present invention, the mechanical quality factor of the upper electrode can be increased and the mechanical quality factor of the entire resonator can be increased compared to the case where the material of the upper electrode is Al or Au, which are typical electrode materials. It becomes possible.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, a plurality of resonators are formed on the acoustic mirror layer to form a UWB filter, and the acoustic mirror layer includes adjacent resonators. The high acoustic impedance layer is patterned so as not to be capacitively coupled through the high acoustic impedance layer.

  According to the present invention, capacitive coupling between the resonators via the high acoustic impedance layer of the acoustic mirror layer can be prevented, and the filter characteristics can be improved.

  According to the first aspect of the invention, there is an effect that it is possible to improve crystallinity and piezoelectric characteristics of a piezoelectric layer made of a lead-based piezoelectric material.

(Embodiment 1)
As shown in FIG. 1, the BAW resonator of the present embodiment is formed on a support substrate 1, an acoustic mirror layer (acoustic multilayer film) 2 formed on one surface side of the support substrate 1, and the acoustic mirror layer 2. And a piezoelectric film formed on the opposite side of the lower electrode 31 from the support substrate 1 side. The lower electrode 31 has a resonator 3 formed on the acoustic mirror layer 2. It has a laminated structure of a layer 32 and an upper electrode 33 formed on the opposite side of the piezoelectric layer 32 to the lower electrode 31 side. The piezoelectric layer 32 is made of a lead-based piezoelectric material (for example, PMN-PZT, PZT). Etc.).

  Further, in the BAW resonance device of the present embodiment, the insulating layer 4 having the opening 4a that defines the contact area between the upper electrode 33 and the piezoelectric layer 32 is formed on the opposite side of the piezoelectric layer 32 from the lower electrode 31 side. In the piezoelectric layer 32, a region in contact with both the lower electrode 31 and the upper electrode 33 constitutes a resonance region.

The BAW resonator of the present embodiment employs PMN-PZT as the piezoelectric material of the piezoelectric layer 32, and supports the piezoelectric layer 32 so as to obtain a piezoelectric thin film composed of a (001) -oriented PMN-PZT thin film. As the substrate 1, a single crystal MgO substrate having a (001) plane as its main surface is used as the substrate 1. However, as the support substrate 1, a single crystal STO (with a (001) plane as its main surface is used as the support substrate 1. : SrTiO ₃ ) substrate may be used. The PMN-PZT thin film may be a single crystal film or a single orientation film, and the orientation is not limited to (001) orientation, and may be, for example, (111) orientation. In the BAW resonator of this embodiment, a kind of conductive oxide material is used as a material of the lower electrode 31 in order to control the crystal orientation of the piezoelectric layer 32 to a single orientation and to suppress lattice distortion of the piezoelectric layer 32. SRO (: SrRuO ₃ ) is employed.

In this embodiment, Al is adopted as the material of the upper electrode 33, but the material of the upper electrode 33 is not limited to Al, and is selected from, for example, a group of Mo, W, Ir, Cr, Ru, and Pt. If at least one of the above is employed, the mechanical quality factor of the upper electrode 33 can be increased compared to the case where the material of the upper electrode 33 is Al or Au, which is a typical electrode material, and the entire resonator 3 It is possible to increase the mechanical quality factor. Also adopts the SiO ₂ as the material of the insulating layer 4 is not limited to SiO _2, for example, may be adopted _Si 3 _{N 4.}

The piezoelectric layer 32 is formed of a piezoelectric thin film made of a (001) -oriented PMN-PZT thin film. Here, the composition of PMN-PZT is represented by the chemical formula x (Pb (Mn _1/3 Nb _2/3 ) O _3- (1-x) (PbZr _y Ti _1-y O ₃ ), and this embodiment In this embodiment, x = 0.10 and y = 0.52, but these values are only examples and are not particularly limited, and in this embodiment, the piezoelectric material of the piezoelectric layer 32 is a lead-based piezoelectric material. Since the material is employed, the electromechanical coupling coefficient can be increased as compared with the case where the piezoelectric material is AlN or ZnO.

  The acoustic mirror layer 2 is formed by alternately laminating a high acoustic impedance layer 21 made of a material having a relatively high acoustic impedance and a low acoustic impedance layer 22 made of a material having a relatively low acoustic impedance. Is formed of a low acoustic impedance layer 22.

  In the BAW resonator of this embodiment, the resonance frequency of the resonator 3 is set to 4 GHz, the thickness of the lower electrode 31 is 100 nm, the thickness of the piezoelectric layer 32 is 300 nm, the thickness of the upper electrode 33 is 100 nm, Although the thickness of the acoustic impedance layer 21 is set to 350 nm and the thickness of the low acoustic impedance layer 22 is set to 400 nm, these numerical values are merely examples and are not particularly limited. When the resonance frequency is designed in the range of 3 GHz to 5 GHz, the piezoelectric layer 32 has a thickness of 200 nm to 600 nm, the high acoustic impedance layer 21 has a thickness of 200 nm to 450 nm, and the low acoustic impedance layer 22. The thickness of each may be set appropriately in the range of 250 nm to 550 nm.

By the way, in this embodiment, SrRuO ₃ which is the same material as the lower electrode 31 is adopted as the material of the high acoustic impedance layer 21, and PMN-PZT which is the same material as the piezoelectric layer 32 as the material of the low acoustic impedance layer 22. However, the material of the low acoustic impedance layer 22 may be the same material as that of the piezoelectric layer 32. For example, when the material of the piezoelectric layer 32 is PZT, PZT may be employed.

  Hereinafter, a method for manufacturing the BAW resonator according to the present embodiment will be briefly described.

First, a step of forming a high acoustic impedance layer 21 made of (110) -oriented SrRuO ₃ on the entire surface on the one surface side of the support substrate 1 made of a single-crystal MgO substrate having a (001) plane on the one surface (001) The acoustic mirror layer forming step of forming the acoustic mirror layer 2 is performed by alternately repeating the step of forming the low acoustic impedance layer 21 made of oriented PMN-PZT. Here, the high acoustic impedance layer 21 may be formed by, for example, a sputtering method or a CVD method, and the low acoustic impedance layer 22 may be formed by, for example, a sputtering method, a CVD method, or a sol-gel method.

After the acoustic mirror layer forming step described above, a lower electrode forming step is performed in which a lower electrode 31 made of SrRuO ₃ with (110) orientation is formed on the surface side of the acoustic mirror 2 by sputtering or CVD.

  After the lower electrode formation step described above, a piezoelectric layer formation step is performed in which the piezoelectric layer 32 made of PMN-PZT with (001) orientation is formed on the entire surface of the lower electrode by sputtering, CVD, sol-gel method, or the like.

  After this piezoelectric layer forming step, a piezoelectric layer patterning step for patterning the piezoelectric layer 32 into a desired planar shape is performed using a photolithographic technique and an etching technique, followed by a lower portion using a photolithographic technique and an etching technique. A lower electrode patterning step for patterning the electrode 31 into a desired planar shape is performed.

Thereafter, an insulating layer forming step for forming the insulating layer 4 having the above-described aperture 4a on the one surface of the support substrate 1 is performed, and then an upper electrode forming step for forming the upper electrode 33 is performed, thereby performing the BAW. A resonant device is obtained. Here, in the insulating layer forming step, the insulating layer 4 made of, for example, SiO ₂ is formed on the entire surface of the support substrate 1 by the sputtering method, the CVD method, or the like, and then the photolithography technique and the etching technique are used. To form the opening 4a. In the upper electrode forming step, the upper electrode 33 is formed on the entire surface of the one surface side of the support substrate 1 by a sputtering method, a vapor deposition method, or the like, and then the upper electrode 33 is utilized using a photolithography technique and an etching technique. Is patterned into a desired planar shape.

  In manufacturing the BAW resonance device described above, a large number of BAW resonance devices may be formed at the wafer level using a wafer as the support substrate 1 described above, and then divided into individual BAW resonance devices in a dicing process.

Since the BAW resonator of the present embodiment described above is an SMR having the acoustic mirror layer 2, it can be made more robust than the FBAR, and of course, a lead-based piezoelectric material is used as the material of the piezoelectric layer 32, and the support substrate 1. Is made of MgO or SrTiO ₃ , the lower electrode 31 is made of SrRuO ₃ , and the acoustic mirror layer 2 is made of the same material as the high acoustic impedance layer 21 and the piezoelectric layer 32 made of the same material as the lower electrode 31. The formed low acoustic impedance layers 22 are alternately laminated, and the uppermost layer on the lower electrode 31 side is constituted by the low acoustic impedance layer 22, and the support substrate 1, the acoustic mirror layer 2, and the lower electrode 31 are all piezoelectric. Since it is made of a material having a lattice constant close to that of the layer 32, the crystallinity and piezoelectric characteristics of the piezoelectric layer 32 made of a lead-based piezoelectric material are improved. Rukoto is possible.

  By the way, in the above-described BAW resonator, a (001) -oriented Pt layer (hereinafter referred to as a first Pt layer) is used as a buffer layer for relaxing the lattice mismatch between the acoustic mirror layer 2 and the lower electrode 31. ), The crystallinity of the lower electrode 31 can be improved, the crystallinity of the piezoelectric layer 32 can be further improved, and between the support substrate 1 and the acoustic mirror layer 2, If a (001) -oriented Pt layer (hereinafter referred to as a second Pt layer) is formed as a buffer layer that alleviates lattice mismatch, the high acoustic impedance layer 21 and the low acoustic impedance of the acoustic mirror layer 2 are formed. The crystallinity of each layer 22 can be improved, the crystallinity of the lower electrode 31 can be improved, and the crystallinity of the piezoelectric layer 32 can be further improved. Note that the first Pt layer and the second Pt layer described above may be formed by sputtering, vapor deposition, or the like, and both the first Pt layer and the second Pt layer may be provided. Only one of them may be provided.

  In the BAW resonance device of the present embodiment, the piezoelectric material of the piezoelectric layer 32 is PMN-PZT, and as the electrode material of the upper electrode 33, for example, Al or another metal material may be adopted. If at least one selected from the group of Mo, W, Ir, Cr, Ru, and Pt is adopted, the mechanical quality factor of the upper electrode 33 can be increased as compared with the case of Au as a typical electrode material. Thus, the mechanical quality factor of the entire resonator 3 can be increased. In this embodiment, PMN-PZT is adopted as the piezoelectric material of the piezoelectric layer 32. However, the piezoelectric material may be a lead-based piezoelectric material, such as PZT or PZT to which an appropriate impurity is added. The PZT material may be used.

(Embodiment 2)
In the BAW resonator according to the present embodiment, a plurality of the resonators 3 described in the first embodiment are formed on the acoustic mirror layer 2 on the one surface side of the support substrate 1 as shown in FIGS. (BAW filter) is different. Here, in the BAW resonator of this embodiment, the plurality of resonators 3 are connected so as to form a ladder filter, and have a sharp cutoff characteristic and a wide bandwidth in a high frequency band of 2 GHz or more. It can be used as a filter, for example, a UWB filter. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  By the way, the acoustic mirror layer 2 in the BAW resonator of this embodiment has the high acoustic impedance layer 21 patterned so that the adjacent resonators 3 are not capacitively coupled via the high acoustic impedance layer 21. Here, the BAW resonance apparatus of the present embodiment includes a plurality of sets (9 sets in the illustrated example) of two resonators 3 in which the lower electrodes 31 are electrically connected to each other. In the two resonators 3, the lower electrode 31 and the piezoelectric layer 32 are continuously formed, and the upper electrodes 33 are patterned so as to be insulated from each other. Since they are connected and have the same potential, the high acoustic impedance layer 21 is patterned so as to be an island-like pattern that straddles the two resonators 3 of each set and is independent for each set of two resonators 3. is there. Here, between adjacent pairs, the upper electrodes 33 of the two adjacent resonators 3 are electrically connected to each other through a metal wiring 34 formed continuously with the upper electrode 33. Moreover, the area | region which contact | connects both the lower electrode 31 and the upper electrode 33 among the piezoelectric layers 32 formed ranging over the two resonators 3 of each group comprises each resonance area | region, It is located in the projection area of the high acoustic impedance layer 21.

  In the BAW resonator of the present embodiment, the plane size of the high acoustic impedance layer 21 that overlaps in the thickness direction of the support substrate 1 is set so as to gradually decrease as the distance from the support substrate 1 increases. The flatness of the surface of the uppermost low acoustic impedance layer 22 can be improved (the level difference of the surface irregularities can be reduced), and the crystallinity of the piezoelectric layer 32 can be improved.

  In the BAW resonance device of the present embodiment described above, capacitive coupling between the resonators 3 via the high acoustic impedance layer 21 of the acoustic mirror layer 2 can be prevented, and the filter characteristics can be improved.

It is a schematic sectional drawing of the BAW resonance apparatus of Embodiment 1. FIG. 6 is a schematic plan view of a BAW resonance device according to a second embodiment. The BAW resonance apparatus same as the above is shown, (a) is a schematic plan view of the main part, and (b) is a schematic cross-sectional view of (a). It is a schematic sectional drawing of the BAW resonance apparatus which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support substrate 2 Acoustic mirror layer 3 Resonator 4 Insulating layer 4a Opening part 21 High acoustic impedance layer 22 Low acoustic impedance layer 31 Lower electrode 32 Piezoelectric layer 33 Upper electrode

Claims (5)

An acoustic mirror layer formed on one surface side of a support substrate made of MgO or SrTiO ₃ and a resonator formed on the opposite side of the acoustic mirror layer from the support substrate side, the resonator in the acoustic mirror layer A lower electrode made of SrRuO ₃ formed on the side opposite to the support substrate side, a piezoelectric layer made of a lead-based piezoelectric material formed on the side opposite to the acoustic mirror layer side in the lower electrode, and a lower electrode side in the piezoelectric layer The acoustic mirror layer is composed of alternating high-impedance impedance layers made of the same material as the lower electrodes and low-acoustic impedance layers made of the same material as the piezoelectric layer. A BAW resonance device characterized in that the uppermost layer on the lower electrode side is formed of a low acoustic impedance layer.   2. The BAW resonator according to claim 1, wherein a Pt layer is formed between the acoustic mirror layer and the lower electrode as a buffer layer for relaxing the lattice mismatch between the acoustic mirror layer and the lower electrode.   3. The BAW resonator according to claim 1, wherein a Pt layer is formed between the support substrate and the acoustic mirror layer as a buffer layer that relaxes the lattice mismatch between the support substrate and the acoustic mirror layer.   4. The BAW resonance according to claim 1, wherein the material of the upper electrode is at least one selected from the group consisting of Mo, W, Ir, Cr, Ru, and Pt. 5. apparatus.   A plurality of resonators are formed on the acoustic mirror layer to form a UWB filter. The acoustic mirror layer is patterned with a high acoustic impedance layer so that adjacent resonators are not capacitively coupled via the high acoustic impedance layer. The BAW resonance device according to any one of claims 1 to 4, wherein the BAW resonance device is formed.

Images