JP2007288504A - Piezoelectric thin film resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric thin film resonator having a high Q value and high performance. <P>SOLUTION: The piezoelectric thin film resonator 100 includes a substrate 1, and a resonating part 10 formed above the substrate 1, the resonating part 10 having a lower electrode layer 12, a piezoelectric material layer 14 and an upper electrode layer 16 and generating acoustic vibrations in the thickness direction of the piezoelectric material layer 14 by giving an electric field to the piezoelectric material layer 14 by the lower electrode layer 12 and the upper electrode layer 16. The piezoelectric material layer 14 is included in the area of the lower electrode layer 12 in a plane view. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric thin film resonator using a longitudinal vibration of a piezoelectric film.

  In general, communication devices such as cellular phones are becoming higher in frequency and smaller in size, and for this reason, higher performance and smaller size of the RF circuit section have been demanded. Among them, as a high-frequency element such as a high-frequency filter used in a transmission / reception unit of a communication device, it is possible to realize performance equivalent to that of a conventional SAW (Surface Acoustic Wave) element. A BAW (Bulk Acoustic Wave) element that is easy to downsize is drawing attention. This BAW element has a laminated structure in which a piezoelectric layer is sandwiched between electrodes, and generates an acoustic wave in the thickness direction in the piezoelectric layer. It is easy to increase the frequency, have good withstand voltage, and easily downsize. (See, for example, Patent Documents 1 and 2 below).

  As the BAW element, the above laminated structure is formed on a substrate made of a silicon substrate or the like, and then the substrate portion under the laminated structure is removed by etching or the like, thereby enabling longitudinal vibration of the resonance part. An FBAR (Film Bulk Acoustic Resonator) type element structure (FIGS. 1 and 3 of Patent Document 1) and an acoustic reflection multilayer film in which layers having different acoustic impedances are alternately laminated are laminated structures described above There is known an SMR (Solid Mounted Resonator) type element structure (FIG. 2 of Patent Document 1) disposed between a substrate and a substrate.

By the way, in such a thin film piezoelectric resonator, good crystal growth may not be performed depending on the material of the piezoelectric layer. In that case, a sufficient Q value may not be obtained due to the morphology or leakage current of the piezoelectric layer.
JP 2001-156582 A JP 2003-158442 A

  The present invention solves the above problems, and an object thereof is to provide a high-performance piezoelectric thin film resonator having a large Q value.

The piezoelectric thin film resonator according to the present invention is
A substrate,
A resonating portion formed above the substrate, comprising a lower electrode layer, a piezoelectric layer, and an upper electrode layer, and an electric field applied to the piezoelectric layer by the lower electrode layer and the upper electrode layer. A resonance part that generates acoustic vibrations in the thickness direction of the piezoelectric layer,
Including
In plan view, the piezoelectric layer is included in the region of the lower electrode layer.

  According to this piezoelectric thin film resonator, since the piezoelectric layer can perform good crystal growth using the lower electrode layer, the morphology and leakage current of the piezoelectric layer are reduced, and a high-performance piezoelectric element with a high Q value is obtained. A thin film resonator can be obtained.

  In the present invention, when a specific B member is formed above a specific A member, when the B member is formed directly on the A member, the B member is interposed on the A member via another member. It includes the case where it is formed.

  In the present invention, “in a plan view” means to view from a direction perpendicular to the substrate.

  In the piezoelectric thin film resonator of the present invention, the piezoelectric layer and the upper electrode layer may be patterned in the same process, and the upper surface of the piezoelectric layer and the lower surface of the upper electrode layer may have the same shape. .

  The piezoelectric thin film resonator of the present invention may have a passivation layer that covers at least the piezoelectric layer and the upper electrode layer.

  In the piezoelectric thin film resonator according to the aspect of the invention, the passivation layer has an opening in a portion located on the upper electrode layer, and has a wiring layer connected to the upper electrode layer through the opening. be able to.

  In the piezoelectric thin film resonator according to the aspect of the invention, a portion where the piezoelectric layer and the upper electrode layer overlap in a plan view can be included in a free vibration region including an opening formed in the substrate.

  The piezoelectric thin film resonator of the present invention has an acoustic multilayer film formed above the substrate, and the resonance part is formed above the acoustic multilayer film, and in a plan view, A portion where the upper electrode layer overlaps may be included in a region of the acoustic multilayer film.

  In the piezoelectric thin film resonator of the present invention, the piezoelectric layer can be made of lead zirconate titanate or lead zirconate titanate solid solution.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1. First Embodiment FIG. 1 is a cross-sectional view schematically showing the structure of a piezoelectric thin film resonator 100 of this embodiment, and FIG. 2 is a plan view schematically showing the structure of the piezoelectric thin film resonator 100 shown in FIG. FIG.

  As shown in FIGS. 1 and 2, the piezoelectric thin film resonator 100 has a base layer 2 formed on a substrate 1. Furthermore, the resonance part 10 is formed on the underlayer 2.

  The substrate 1 has an opening 1a called a cavity. The opening 1a is formed by etching (wet etching or dry etching) from the back surface of the substrate 1. The opening 1a can be formed by using a base layer 2 described later as an etching stop layer. By providing the opening 1a, a mechanical restraining force to the resonance unit 10 described later is reduced, and the resonance unit 10 can freely vibrate. The illustrated example shows an FBAR type element structure.

  As the substrate 1, various substrates such as a semiconductor substrate such as a silicon substrate, a glass substrate, a sapphire substrate, a diamond substrate, and a ceramic substrate can be used. In particular, since various semiconductor circuits can be formed in the substrate 1 by using a semiconductor substrate such as a silicon substrate, the piezoelectric thin film resonator and the circuit can be integrated. Among these, using a silicon substrate is advantageous in that a general semiconductor manufacturing technique can be used.

A base layer 2 is formed on the substrate 1. The underlayer 2 is an insulating film such as a silicon oxide layer (SiO ₂ ) or a silicon nitride layer (Si ₃ N ₄ ), and may be composed of two or more composite layers. The underlayer 2 can be formed by a thermal oxidation method, a CVD method, a sputtering method, or the like.

As shown in FIG. 3, the resonance unit 10 is configured by sequentially laminating a lower electrode layer 12, a piezoelectric layer 14, and an upper electrode layer 16. The lower electrode layer 12 is formed over a wider area than the piezoelectric layer 14 and the upper electrode layer 16. In plan view, the piezoelectric layer 14 is included in the region of the lower electrode layer 12. That is, the piezoelectric layer 14 is formed so that the entire lower surface thereof is in contact with the lower electrode layer 12. By having such a laminated structure, the material of the piezoelectric layer 14 is, for example, lead zirconate titanate (PZT; Pb (Zr, Ti) O ₃ ) or lead zirconate titanate niobate (PZTN; Pb (Zr, When Ti, Nb) O ₃ ) is used, the piezoelectric layer 14 having excellent crystallinity and morphology can be formed on the lower electrode layer 12 by selecting the lower electrode layer 12. As a result, a piezoelectric thin film resonator having a high Q value and excellent long-term reliability can be obtained.

  Since perovskite oxides such as PZT and PZTN are affected by the lower electrode layer serving as a base layer when crystallized, the crystallization conditions are different between a place where there is a lower electrode layer and a place where there is no lower electrode layer. Therefore, in the region without the lower electrode layer, the Q value tends to decrease due to deterioration of the morphology of the piezoelectric layer and increase in leakage current due to a change in composition of the piezoelectric layer. Such a problem can be avoided.

  The piezoelectric layer 14 and the upper electrode layer 16 are patterned so as to have an appropriate planar shape. In order to reduce the number of steps, it is desirable that the piezoelectric layer 14 and the upper electrode layer 16 be patterned in the same step. In this case, the upper surface of the piezoelectric layer 14 and the lower surface of the upper electrode layer 16 have the same shape. For example, as shown in FIG. 3, a first conductive layer for the first electrode layer 12, a piezoelectric layer for the piezoelectric layer 14, and a second conductive for the second electrode layer 16 are formed on the base layer 2. After sequentially forming the layers, the second conductive layer and the piezoelectric layer are patterned by etching, so that the piezoelectric layer 14 and the second electrode layer 16 are within the region of the first electrode layer 12 in plan view. Formed to be included. In the present embodiment, since the piezoelectric layer 14 is formed on the region of the lower electrode layer 12, the piezoelectric layer 12 has excellent in-plane uniformity and excellent crystallinity as described above. However, the lower electrode layer 12 may be patterned in advance as long as it is larger than the region of the piezoelectric layer 12 to be patterned.

  Patterning of the piezoelectric layer 14 and the upper electrode layer 16 can be performed by a normal photolithography method. As the etching, dry etching methods such as reactive ion etching (RIE) and ion milling can be used.

  In the present embodiment, a passivation layer 20 that covers at least the piezoelectric layer 14 and the upper electrode layer 16 is provided. In the illustrated example, the passivation layer 20 is formed so as to cover the entire lower electrode layer 12, piezoelectric layer 14, and upper electrode layer 16. In the passivation layer 20, a first opening 22 for electrode extraction is formed on the lower electrode layer 12, and a second opening 24 for electrode extraction is formed on the upper electrode layer 16. A wiring layer 30 connected to the upper electrode layer 16 through the opening 24 is formed. The wiring layer 30 can use any wiring material, for example, gold or aluminum.

The passivation layer 20 is an insulating film such as a silicon oxide layer (SiO ₂ ) or a silicon nitride layer (Si ₃ N ₄ ), and may be composed of two or more composite layers. The passivation layer 20 can be formed by a thermal oxidation method, a CVD method, a sputtering method, or the like. By forming the passivation layer 20, the long-term reliability of the piezoelectric thin film resonator 100 can be improved.

  In the present embodiment, the portion where the piezoelectric layer 14 and the upper electrode layer 16 overlap in a plan view can be included in the free vibration region including the opening 1 a formed in the substrate 1. By arranging the piezoelectric layer 14 and the upper electrode layer 16 in this manner, a highly efficient piezoelectric thin film resonator 100 is obtained that does not vibrate the constrained portion such as the substrate 1 and has a small loss of vibration energy. Can do.

  The lower electrode layer 12 can use any electrode material. For example, when the piezoelectric layer 14 is made of PZ or PZTN, it is preferable to use platinum for the lower electrode layer 12. The lower electrode layer 12 can be formed on the substrate 1 (underlayer 2) by using a vapor deposition method, a sputtering method, or the like. If the above-described conditions are satisfied, the lower electrode layer 12 is patterned to have an appropriate planar shape as necessary. The thickness of the base electrode layer 11 is preferably about λ / 4 or less. In practice, if a sufficiently low electric resistance value can be obtained, it is desirable that it is 1/10 or less of λ / 4 in order not to affect the acoustic vibration. The thickness of the lower electrode layer 12 can be 10 nm or more and 5 μm or less.

  Any piezoelectric material can be used for the piezoelectric layer 14, and examples thereof include lead zirconate titanate and lead zirconate titanate niobate. The film thickness h of the piezoelectric layer 14 is preferably 0.9 × λ / 2 or more and 1.1 × λ / 2 or less when the resonance wavelength is λ, and particularly the film thickness h of the piezoelectric layer 14. Is preferably λ / 2. This is because the resonance condition at the wavelength λ when the acoustic wave in the stacking direction is confined in the piezoelectric layer 14 is established. As long as the resonance frequency is not increased, a value that is a natural number multiple can be used instead of λ / 2. The thickness of the piezoelectric layer 14 can be 100 nm or more and 10 μm or less.

  In the present embodiment, only the piezoelectric layer 14 exists between the lower electrode layer 12 and the upper electrode layer 16, but a layer other than the piezoelectric layer 14 may be formed between both electrodes. Absent. In this case, what is necessary is just to change the film thickness of the piezoelectric material layer 14 suitably according to resonance conditions.

The piezoelectric layer 14 can be formed by various methods such as vapor deposition, sputtering, laser ablation, and CVD. For example, when the piezoelectric layer 14 made of PZTN is formed using a laser ablation method, a laser beam is irradiated with a target for lead zirconate titanate, for example, Pb _1.05 Zr _0.52 Ti _0.48 NbO ₃ . The target is irradiated, lead atoms, zirconium atoms, titanium atoms, and oxygen atoms are released from the target by ablation, a plume is generated by laser energy, and the plume is irradiated toward the substrate 1. In this manner, a lead zirconate titanate thin film is formed on the lower electrode layer 12.

  The upper electrode layer 16 can be made of any electrode material, such as Pt. The upper electrode layer 16 can be formed by vapor deposition, sputtering, CVD, or the like. The thickness of the upper electrode layer 16 is preferably about λ / 4 or less. In practice, if a sufficiently low electric resistance value can be obtained, it is desirable that it is 1/10 or less of λ / 4 in order not to affect the acoustic vibration. The thickness of the lower electrode layer 12 can be 10 nm or more and 5 μm or less.

  In the piezoelectric thin film resonator 100 of the present embodiment, an acoustic field is generated in the thickness direction of the piezoelectric layer 14 by applying an electric field to the piezoelectric layer 14 by the lower electrode layer 12 and the upper electrode layer 16.

  Below, the structural example of the resonance part 10 is described.

  (A) In the first configuration example, the thickness of the lower electrode layer 12 is 0.05 μm, the thickness of the piezoelectric layer 12 is 2.0 μm, and the thickness of the upper electrode layer 13 is 0.05 μm. When the longitudinal wave velocity is 2000 m / s, the resonance frequency is 1 GHz. At this time, the Q value obtained from the frequency dependence of the impedance is 500, which is larger than the Q value 100 obtained when the lower electrode layer 12 is patterned first.

  (B) In the second configuration example, the thickness of the lower electrode layer 12 is 0.05 μm, the thickness of the piezoelectric layer 14 is 2.0 μm, and the thickness of the upper electrode layer 16 is 0.05 μm. When the longitudinal wave velocity is 2000 m / s, the resonance frequency is 1 GHz. At this time, the Q value obtained from the frequency dependence of the impedance is 500, but the Q value after one month and one year later is a large value as compared with the case without the passivation layer 20. Therefore, it is possible to obtain a piezoelectric thin film resonator having excellent long-term reliability by forming the passivation layer 20.

According to this embodiment, it has the following features. That is, the piezoelectric layer 14 is included in the region of the lower electrode layer 12 in plan view. That is, the piezoelectric layer 14 is formed so that the entire lower surface thereof is in contact with the lower electrode layer 12. By having such a laminated structure, when the material of the piezoelectric layer 14 is, for example, PZT (Pb (Zr, Ti) O ₃ ) or PZTN (Pb (Zr, Ti, Nb) O ₃ ), the lower electrode By selecting the layer 12, the piezoelectric layer 14 having excellent crystallinity and morphology can be formed on the lower electrode layer 12. As a result, the piezoelectric thin film resonator 100 having a high Q value and excellent long-term reliability can be obtained.

  In the present embodiment, by forming the passivation layer 20 that covers the lower electrode layer 12, the piezoelectric layer 14, and the upper electrode layer 16, the influence of water vapor in the atmosphere can be avoided, and the piezoelectric thin film resonator 100 can have a long term. Reliability can be increased.

2. Second Embodiment FIG. 4 is a cross-sectional view schematically showing the structure of a piezoelectric thin film resonator 200 of this embodiment. 1 and 2, substantially the same members as those of the piezoelectric thin film resonator 100 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The piezoelectric thin film resonator 200 of the second embodiment is different from the piezoelectric thin film resonator 100 of the first embodiment in the structure of the opening that forms the free vibration region.

  As shown in FIG. 4, the piezoelectric thin film resonator 200 has a base layer 2 formed on a substrate 1. Furthermore, the resonance part 10 is formed on the underlayer 2. Although not shown, this embodiment can also include a passivation layer and a wiring layer, as in the first embodiment.

  The substrate 1 has an opening 1b called an air gap. Unlike the opening 1a of the first embodiment, the opening 1b is dug to the middle of the substrate 1. Such an opening 1 b is formed by etching (wet etching or dry etching) from the surface of the substrate 1 to the middle of the substrate 1. By providing the opening 1a, the mechanical restraining force on the resonance unit 10 is reduced, and the resonance unit 10 can freely vibrate. The illustrated example shows an FBAR type element structure. As the substrate 1, the same substrate as described in the first embodiment can be used.

  The opening 1b of the air gap structure can be formed by a known method. For example, the opening 1b can be formed by the method shown in FIGS.

  First, as shown in FIG. 5A, a recess 1c is formed in the substrate 1. The recess 1c can be formed by known photolithography and etching.

  Next, as shown in FIG. 5B, an etching stopper layer 1d is formed along the surface of the recess 1c. The etching stopper layer 1d is formed using a material having a selectivity different from that of the substrate 1 in etching. For example, when the substrate 1 is a silicon substrate, a silicon oxide layer can be used as the etching stopper layer 1d. Further, a sacrificial layer 1e is formed inside the etching stopper layer 1d. The sacrificial layer 1e is formed using a material having a different selectivity from the substrate 1 and the etching stopper layer 1d in etching. When the substrate 1 is a silicon substrate and the etching stopper layer 1d is a silicon oxide layer, for example, polysilicon can be used as the sacrificial layer 1e.

  Next, as shown in FIG. 5C, the base layer 2 is formed over the substrate 1, the etching stopper layer 1d, and the sacrificial layer 1d. As the underlayer 2, the same layer as described in the first embodiment can be used. Further, as described in the first embodiment, the lower electrode layer 12, the piezoelectric layer 14, and the upper electrode layer 16 are formed on the base layer 2. Thereafter, an opening 2 a for supplying an etching solution to the base layer 2 is formed. Then, the sacrificial layer 1e is etched by supplying an etchant (etching solution or etching gas) for etching the sacrificial layer 1e through the opening 2a. Through the above steps, the opening 1b shown in FIG. 4 can be formed.

  Also in this embodiment, it has the resonance part 10 similar to 1st Embodiment. Also in the present embodiment, the portion where the piezoelectric layer 14 and the upper electrode layer 16 overlap is arranged so as to be within the free vibration region formed of the opening 1 a formed in the substrate 1 in plan view. Yes.

  According to the present embodiment, as in the first embodiment, the piezoelectric thin film resonator 100 having a high Q value and excellent long-term reliability can be obtained.

3. Third Embodiment FIG. 6 is a cross-sectional view schematically showing the structure of a piezoelectric thin film resonator 300 of this embodiment. 1 and 2, substantially the same members as those of the piezoelectric thin film resonator 100 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. The piezoelectric thin film resonator 300 of the third embodiment differs from the piezoelectric thin film resonator 100 of the first embodiment in the structure of the region constituting the free vibration region, and is an SMR type element.

  As shown in FIG. 6, the piezoelectric thin film resonator 300 has an acoustic multilayer film 3 formed on a substrate 1. Furthermore, the resonance part 10 is formed on the acoustic multilayer film 3. As the substrate 1, the same substrate as described in the first embodiment can be used. This embodiment can also have a passivation layer and a wiring layer (not shown) as in the first embodiment.

  The acoustic multilayer film 3 is configured by repeatedly laminating layers having different acoustic impedances. Specifically, layers having low acoustic impedance and layers having high acoustic impedance are alternately stacked. For example, a silicon oxide layer can be used as the layer having a low acoustic impedance, and a tungsten layer or an aluminum nitride layer can be used as the layer having a high acoustic impedance.

  The acoustic multilayer film 3 has the same function as the openings 1a and 1b of the first and second embodiments, and can reflect elastic waves. The acoustic multilayer film 3 can be formed by a known method. For example, the layer having a high acoustic impedance and the layer having a low acoustic impedance described above can be formed on the substrate 1 alternately by a known film formation method such as sputtering, vapor deposition, or CVD.

  Also in this embodiment, it has the resonance part 10 similar to 1st Embodiment. Also in the present embodiment, the portion where the piezoelectric layer 14 and the upper electrode layer 16 overlap is arranged so as to be within the free vibration region made of the acoustic multilayer film 3 formed on the substrate 1 in plan view. Yes.

  According to the present embodiment, as in the first and second embodiments, the piezoelectric thin film resonator 100 having a high Q value and excellent long-term reliability can be obtained.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same purposes and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

FIG. 3 is a cross-sectional view schematically showing the structure of the piezoelectric thin film resonator according to the first embodiment. The top view which shows typically the structure of the piezoelectric thin film resonator of 1st Embodiment. Sectional drawing which shows typically the resonance part of the piezoelectric thin film resonator of 1st Embodiment. Sectional drawing which shows typically the structure of the piezoelectric thin film resonator of 2nd Embodiment. (A) thru | or (C) is a figure which shows typically the manufacturing method of the piezoelectric thin film resonator of 2nd Embodiment. Sectional drawing which shows typically the structure of the piezoelectric thin film resonator of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 1a ... Opening part, 1b ... Opening part, 2 ... Underlayer, 3 ... Acoustic multilayer film, 10 ... Resonance part, 12 ... Lower electrode layer, 14 ... Piezoelectric body layer, 16 ... Upper electrode layer, 20 ... Passivation layer, 22, 24 ... opening, 30 ... wiring layer, 100, 200, 300 ... piezoelectric thin film resonator

Claims (7)

A substrate,
A resonating portion formed above the substrate, comprising a lower electrode layer, a piezoelectric layer, and an upper electrode layer, and an electric field applied to the piezoelectric layer by the lower electrode layer and the upper electrode layer. A resonance part that generates acoustic vibrations in the thickness direction of the piezoelectric layer,
Including
In plan view, the piezoelectric layer is a piezoelectric thin film resonator included in a region of the lower electrode layer. In claim 1,
The piezoelectric thin film resonator, wherein the piezoelectric layer and the upper electrode layer are patterned in the same process, and the upper surface of the piezoelectric layer and the lower surface of the upper electrode layer have the same shape. In claim 1 or 2,
A piezoelectric thin film resonator having a passivation layer covering at least the piezoelectric layer and the upper electrode layer. In claim 3,
A piezoelectric thin film resonator having an opening in a portion of the passivation layer located above the upper electrode layer, and a wiring layer connected to the upper electrode layer through the opening. In any of claims 1 to 4,
The piezoelectric thin film resonator in which a portion where the piezoelectric layer and the upper electrode layer overlap in a plan view is included in a free vibration region including an opening formed in the substrate. In any of claims 1 to 4,
An acoustic multilayer film formed above the substrate;
The resonance part is formed above the acoustic multilayer film, and a portion where the piezoelectric layer and the upper electrode layer overlap in a plan view is included in a region of the acoustic multilayer film. Resonator. In any one of Claims 1 thru | or 6.
The piezoelectric layer is a piezoelectric thin film resonator made of lead zirconate titanate or lead zirconate titanate solid solution.

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