JP4895323B2 - Thin film piezoelectric resonator - Google Patents

Description

  The present invention relates to a thin film piezoelectric resonator. Thin film piezoelectric resonators are used, for example, to construct filters or duplexers that are components of electronic circuits of communication equipment.

  The RF circuit part of a cellular telephone is always required to be downsized. Recently, it has been demanded to give various functions to a cellular telephone, and it is preferable to incorporate as many circuit components as possible in order to realize the functions. On the other hand, the size of cellular telephones is limited, so in the end, the requirements for reducing the area occupied by each component in the equipment (mounting area) and height have become stricter, so the components that make up the RF circuit section are also exclusively used. What has a small area and a low height is required.

  Under such circumstances, a thin film piezoelectric filter using a thin film piezoelectric resonator that can be reduced in size and weight can be used as a band pass filter used for an RF circuit component. Such a thin film piezoelectric filter forms a piezoelectric layer made of aluminum nitride (AlN), zinc oxide (ZnO) or the like so as to be sandwiched between upper and lower electrodes on a semiconductor substrate, and elastic wave energy leaks into the semiconductor substrate. Therefore, the RF filter uses a thin film piezoelectric resonator in which a vibration space or an acoustic reflection layer is provided immediately below. As described above, there are two types of thin film piezoelectric resonators. The first is a Film Bulk Acoustic Resonator (FBAR) in which a void (vibration space) is provided immediately below a piezoelectric resonance stack composed of an upper electrode, a lower electrode, and a piezoelectric layer, and the second is on a substrate. A surface mounted resonator (SMR) in which a piezoelectric resonance stack is formed on an acoustic reflection layer in which two types of layers having different acoustic impedances are alternately laminated.

  In these thin film piezoelectric resonators, as described in Japanese Patent Application Laid-Open No. 2006-128993 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2006-109472 (Patent Document 2), elastic energy leaks outside the vibration region. As a result, the resonator characteristics, particularly the impedance at the anti-resonance frequency, may be lowered.

As a method for suppressing the dissipation of elastic energy and suppressing the decrease in resonance characteristics, particularly the impedance at the anti-resonance frequency, Patent Document 1 discloses that the piezoelectric layer outside the upper electrode is removed by etching in the same shape as the upper electrode. The technique to do is described. Furthermore, “AIR-BACKED Al / ZnO / Al FILM BULK ACOUSTIC RESONATOR WITHOUT ANY SUPPORT LAYER”, 2002 IEEE International Frequency Symposium, 2002, pp. 20-26 (Non-Patent Document 1) describes a method of removing the piezoelectric layer outside the vibration region and the upper and lower electrode layers. Further, in Patent Document 2, by disposing an annular band on the outer peripheral portion of the upper electrode, the acoustic impedance between the inner part surrounded by the annular band and the annular band is made different, thereby dissipating the elastic wave outside the vibration region. It has been shown to obtain a thin film piezoelectric resonator that is suppressed and has a high Q value. Furthermore, Japanese Patent Laid-Open No. 2005-33775 (Patent Document 3) adjusts the resonance frequency of a thin film piezoelectric resonator by making the thickness of the piezoelectric layer outside the vibration region thinner than the thickness of the piezoelectric layer inside the vibration region. Is described as being easy.
JP 2006-128993 A JP 2006-109472 A JP 2005-33775 A “AIR-BACKED Al / ZnO / Al FILM BULK ACOUSTIC RESONATOR WITHOUT ANY SUPPORT LAYER”, 2002 IEEE International Frequency Symposium, 2002, pp. 20-26

  As described above, the thin film piezoelectric filter is required to reduce the insertion loss in the pass band and increase the attenuation outside the pass band. Therefore, thin film piezoelectric resonators are required to reduce the impedance at the resonance frequency and increase the Q value, and increase the impedance at the antiresonance frequency and increase the Q value.

  In order to improve the resonance characteristics of the thin film piezoelectric resonator, particularly the impedance characteristics at the antiresonance frequency, it is necessary to suppress the dissipation of elastic energy outside the vibration region. However, for a material having a Poisson's ratio of 1/3 or less, such as an AlN thin film, it is difficult to confine energy, and resonance characteristics are likely to deteriorate.

  The technique described in Patent Document 2 can increase the Q value of the thin film piezoelectric resonator, but has a drawback of increasing spurious near the resonance frequency. In addition, the methods described in Patent Document 1 and Non-Patent Document 1 have a problem that the thin film piezoelectric resonator is easily damaged, resulting in a decrease in yield. Furthermore, Patent Document 3 does not describe suppression of impedance reduction at an anti-resonance frequency, and it is difficult to realize good resonator characteristics based on this description.

  The present invention has been made in view of the above circumstances, and provides a thin film piezoelectric resonator having a high Q value that is structurally resistant to damage and that suppresses a decrease in impedance at an anti-resonance frequency. The main purpose.

  Still another object of the present invention is to provide a thin film piezoelectric resonator in which generation of spurious modes is suppressed.

According to the present invention, the object as described above is achieved.
A piezoelectric resonance stack having a piezoelectric layer and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, a void or an acoustic reflection layer formed under the piezoelectric resonance stack, and the piezoelectric resonance stack A thin film piezoelectric resonator comprising a substrate supporting
The piezoelectric resonance stack includes a vibration region in which the upper electrode and the lower electrode face each other through the piezoelectric layer and are positioned corresponding to the gap or the acoustic reflection layer, a support region in contact with the substrate, and the vibration A buffer region located between the region and the support region,
The thickness t of the piezoelectric layer in the buffer region and the thickness T of the piezoelectric layer in the vibration region satisfy the relationship of T / 8 ≦ t ≦ T / 2, and the standing wave existing in the direction parallel to the substrate A thin film piezoelectric resonator, wherein the wavelength λ and the size x of the buffer region with respect to the direction of the standing wave satisfy a relationship of λ / 200 ≦ x ≦ λ / 20,
Is provided.

  In one aspect of the present invention, the size x of the buffer region is in the range of 0.5 μm to 40 μm. In one aspect of the present invention, the piezoelectric layer is made of a material mainly composed of AlN. In one aspect of the present invention, the shape of the vibration region in a plane parallel to the substrate is an ellipse.

  According to the thin film piezoelectric resonator of the present invention, the piezoelectric resonance stack has a buffer region located between the vibration region and the support region, and the thickness t of the piezoelectric layer in the buffer region and the thickness of the piezoelectric layer in the vibration region. T satisfies the relationship of T / 8 ≦ t ≦ T / 2, and the wavelength λ of the standing wave existing in the direction parallel to the substrate and the size x of the buffer region in the direction of the standing wave are λ / 200 ≦ x Since the relationship of ≦ λ / 20 is satisfied, a high Q value can be realized without causing a decrease in impedance at the antiresonance frequency.

  Further, in the thin film piezoelectric resonator of the present invention, by setting the width x of the buffer region within the range of 0.5 μm or more and 40 μm or less, the thin film piezoelectric resonator having a large impedance at the antiresonance frequency and having a high Q value can be stabilized. Can be provided.

  In the thin film piezoelectric resonator of the present invention, a higher Q value can be realized by configuring the piezoelectric layer with a material mainly composed of AlN.

  Further, in the thin film piezoelectric resonator of the present invention, it is possible to suppress the generation of spurious modes by making the shape of the vibration region in a plane parallel to the substrate an ellipse.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings described below, the same or corresponding reference numerals are given to members or portions having the same function.

  FIG. 1 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator of the present invention, and FIGS. 2 and 3 are a schematic sectional view taken along line XX and a schematic sectional view taken along line YY, respectively. .

  The thin film piezoelectric resonator of the present embodiment includes a substrate 8 made of a semiconductor such as silicon, and a piezoelectric resonance stack 14 formed on the substrate. A recess 9 is formed on the upper surface of the substrate 8. The shape of the recess 9 in a plane parallel to the upper surface of the substrate 8 is a square. The depth of the recess 9 is, for example, 0.5 μm to 10 μm. The recess 9 forms a vibration space (gap) 4 on one side (lower side) of the piezoelectric resonance stack. The other side (upper side) of the piezoelectric resonance stack 14 is entirely in contact with the atmosphere. Therefore, the region of the piezoelectric resonance stack 14 corresponding to the vibration space 4 is allowed to vibrate.

  The piezoelectric resonance stack 14 is a laminate including the piezoelectric layer 2 and the lower electrode 10 and the upper electrode 12 formed so as to sandwich the piezoelectric layer. The lower electrode 10 and the upper electrode 12 are manufactured as thin films such as aluminum (Al), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), and gold (Au). It can be made of a layer made of a metal material that can be patterned and patterned, or a laminate thereof. The piezoelectric layer can be made of aluminum nitride (AlN), zinc oxide (ZnO), or the like, but is preferably made of a material mainly composed of AlN in order to achieve a higher Q value. Here, “main component” means that the content in the layer is 50 mol% or more.

  The lower electrode 10 is formed in a pattern and includes a main body portion 10A and a connection terminal portion 10B. Similarly, the upper electrode 12 is formed in a pattern and includes a main body portion 12A and a connection terminal portion 12B. An in-plane region in which the lower electrode main body portion 10A and the upper electrode main body portion 12A overlap with each other via the piezoelectric layer 2 (herein, the in-plane region indicates an area when viewed in the vertical direction) is a piezoelectric resonance stack. 14 vibration regions 20. The dimension “a” of the vibration region 20 in a plane parallel to the upper surface of the substrate 8 is, for example, 50 μm to 400 μm. The in-plane region that is in contact with the upper surface of the substrate 8 and is supported by the substrate is a support region 24 of the piezoelectric resonance stack 14. Then, the in-plane region located between the vibration region 20 and the support region 24 is defined as a buffer region 22 of the piezoelectric resonance stack 14.

  As described above, the piezoelectric resonance stack 14 has a laminated structure of the lower electrode 10, the piezoelectric layer 2, and the upper electrode 12 in the entire vibration region 20, but at least part of the support region 24 and the buffer region 22. The piezoelectric layer 2 has a single structure, a laminated structure of the piezoelectric layer 2 and the lower electrode 10, or a laminated structure of the piezoelectric layer 2 and the upper electrode 12. The lower electrode main body 10 </ b> A closes the vibration space 4. The vibration space 4 communicates with the outside air through a small through-hole 18 formed so as to penetrate the laminated structure of the piezoelectric layer 2 and the lower electrode 10 in the buffer region 22 in the vertical direction.

  The buffer region 22 has a width x. That is, the YY direction dimension of the portion extending in the XX direction of the buffer region 22 and the XX direction dimension of the portion extending in the YY direction of the buffer region 22 are both x. In the present embodiment, the thickness t of the piezoelectric layer 2 in the buffer region 22 is made thinner than the thickness T of the piezoelectric layer 2 in the vibration region 20. In particular, the relationship between the thickness t of the piezoelectric layer 2 in the buffer region 22 and the thickness T of the piezoelectric layer 2 in the vibration region 20 satisfies T / 8 ≦ t ≦ T / 2, more preferably T / 6 ≦ t ≦ T / 2. To meet the relationship. When the wavelength of the standing wave propagating in the direction parallel to the upper surface of the substrate 8 is λ, the wavelength λ of the standing wave and the width x of the buffer region 22 are λ / 200 ≦ x ≦ λ / 20. And more preferably λ / 100 ≦ x ≦ λ / 25. As a result, the Q value of the resonator can be increased.

  When t is larger than T / 2, the effect of increasing the impedance at the antiresonance frequency tends to be reduced, and it becomes difficult to obtain a thin film piezoelectric resonator having a high Q value. On the other hand, when t is less than T / 8, the piezoelectric resonance stack is easily damaged during the manufacturing process of the resonator, and it is difficult to stably manufacture the thin film piezoelectric resonator. Therefore, by satisfying the relationship of T / 8 ≦ t ≦ T / 2, preferably T / 6 ≦ t ≦ T / 2, it has a robust structure that is not easily damaged and has an impedance at an anti-resonance frequency. Is large (for example, 1300Ω or more), and a thin film piezoelectric resonator having a large Q value can be easily obtained.

  The thin film piezoelectric resonator has a plurality of vibration modes. In the present invention, piezoelectric vibration in which a standing wave is generated in the thickness direction is used. The thickness of the piezoelectric resonance stack 14 is an elastic wave in the vibration region 20. Is half the wavelength. However, on the other hand, standing waves also exist in the in-plane direction parallel to the upper surface of the substrate 8, and in the thin film piezoelectric resonator of the embodiment of FIGS. A standing wave having a wavelength λ is generated such that a distance a between two sides in the XX direction or two sides in the YY direction) is λ / 2. When the width x of the buffer region 22 is less than λ / 200, the effect of increasing the impedance at the anti-resonance frequency tends to decrease. When x exceeds λ / 20, spurious is likely to occur in the resonance band, and the effect of increasing the impedance at the anti-resonance frequency tends to decrease. Therefore, the dissipation of elastic energy from the vibration region 20 is suppressed by setting the width x of the buffer region 22 so that λ / 200 ≦ x ≦ λ / 20, preferably λ / 100 ≦ x ≦ λ / 25. Therefore, it is possible to obtain a thin film piezoelectric resonator having a high Q value and a large impedance at the antiresonance frequency.

  The thin film piezoelectric resonator of the present invention is intended to be used in a high frequency region of GHz or higher. In this case, the thickness of the piezoelectric resonance stack 14 is 3 μm or less in the vibration region 20, and when the gap 4 is formed by the substrate recess 9 below the vibration region 20 as in the embodiment of FIGS. In order to stably manufacture the resonant stack 14, the resonator size (the dimension a of the vibration region 20) is preferably set to 400 μm or less. Furthermore, in consideration of conductor loss in the high frequency region, it is preferable to use a line width of 50 μm or more (the width of the lower electrode connection terminal portion 10B and the upper electrode connection terminal portion 10B). For this reason, resonance is performed to reduce the conductor loss. The vessel size is preferably 50 μm or more. That is, a preferable resonator size is 50 μm or more and 400 μm or less. In this case, the wavelength λ of the standing wave in the in-plane direction parallel to the upper surface of the substrate 8 is 50 μm ≦ λ / 2 ≦ 400 μm. Therefore, the relational expression λ / 200 ≦ x ≦ λ / 20 related to the width x of the buffer region 22 is 0.5 μm ≦ x ≦ 40 μm, and the relational expression λ / 100 ≦ x ≦ λ / 25 is 1 μm ≦ x ≦ 32 μm. It becomes.

  The thin film piezoelectric resonator of the embodiment of FIGS. 1 to 3 can be manufactured as follows. First, after forming the recess 9 on the upper surface of the substrate 8 by a technique such as wet etching, a sacrificial layer is formed by a film forming technique such as sputtering, vapor deposition, or CVD. As the sacrificial layer, a material that is easily etched, such as PSG (phospho-silicate glass), is suitable. Thereafter, the upper surface of the substrate 8 with the sacrificial layer is planarized by a planarization technique such as CMP, so that the sacrificial layer remains only inside the recess 9. On top of that, the lower electrode 10, the piezoelectric layer 2 and the upper electrode 12 are formed by the above-described film forming method, and the lower electrode 10, the piezoelectric layer 2 and the upper electrode 12 are formed by using a patterning technique such as wet etching, RIE, and lift-off method. Each layer of the electrode 12 is patterned. Further, by using the patterning technique, the thickness of the piezoelectric layer 2 in the buffer region 22 and the support region 24 shown by hatching in FIG. 1 is preferably from T to t (T / 8 ≦ t ≦ T / 2). Is etched so that T / 6 ≦ t ≦ T / 2). In this etching, the patterned upper electrode 12 can be used as an etching mask. Thereafter, through holes 18 reaching the sacrificial layer from the upper surface of the piezoelectric resonant stack 14 are formed in the buffer region 22, and the sacrificial layer is removed by supplying an etching solution through the through holes 18. Thereby, a vibration space 4 is formed between the recess 9 and the piezoelectric resonance stack 14.

  FIG. 4 is a schematic plan view showing still another embodiment of the thin film piezoelectric resonator of the present invention. In the embodiment of FIGS. 1 to 3, the shape of the vibration region 20 of the piezoelectric resonance stack 14 is a square. In the embodiment of FIG. 4, the shape of the vibration region 20 of the piezoelectric resonance stack 14 is an ellipse. In this embodiment, the in-plane shape of the substrate recess 9 is an ellipse. Correspondingly, the shape of the vibration region 20 is an ellipse having a major axis a and a minor axis b, and the shape of the buffer region 22 is a substantially elliptical ring. Only the embodiment of FIGS.

  As in the present embodiment, when the in-plane shape of the vibration region 20 of the piezoelectric resonance stack 14 is an ellipse, spurious due to standing waves in the in-plane direction can be further reduced.

  FIG. 5 is a schematic cross-sectional view showing still another embodiment of the thin film piezoelectric resonator of the present invention. In the embodiment of FIGS. 1 to 3 and the embodiment of FIG. 4, the vibration space 4 is formed by the recess 9 formed on the surface of the substrate 8. In the embodiment of FIG. The insulating layer 6 is formed on the insulating layer 6, and the vibration space 4 is formed by the opening 7 formed in the insulating layer 6. This embodiment is different from the embodiment of FIGS. 1 to 3 or the embodiment of FIG. 4 only in that the insulating layer 6 is formed on the upper surface of the substrate 8 and the recess 9 is formed in the insulating layer.

The thin film piezoelectric resonator of the embodiment of FIG. 5 can be manufactured as follows. First, the insulating layer 6 is formed on a semiconductor substrate 8 such as a silicon substrate by a film formation technique such as sputtering or CVD. When the insulating layer 6 is made of SiO _2, the insulating layer 6 can be formed by thermal oxidation of the silicon substrate 8. Thereafter, a sacrificial layer that is easily dissolved by an etching solution is formed by a film formation method such as sputtering or vapor deposition, and patterning is performed using a patterning technique such as wet etching, RIE, or lift-off. As the sacrificial layer, a metal such as germanium (Ge), aluminum (Al), titanium (Ti), magnesium (Mg), or a metal oxide thereof is suitable. Thereafter, the lower electrode 10, the piezoelectric layer 2, and the upper electrode 12 are formed by a film forming method such as sputtering or vapor deposition, and each layer is patterned using a patterning technique such as wet etching, RIE, or lift-off. Further, by using the patterning technique, the buffer layer 22 and the piezoelectric layer 2 in a part of the support region 24 shown by the hatched portion in FIG. 1 or FIG. 4 are transferred to T / 8 ≦ t ≦ T / 2, preferably T / 6 ≦. Etching is performed so that t ≦ T / 2. Thereafter, using the patterning technique, through holes 18 reaching the sacrificial layer from the upper surface of the piezoelectric resonant stack 14 are formed in the buffer region 22, and an etching solution is supplied through the through holes 18 to remove the sacrificial layer. To do. Furthermore, by selecting an etchant that can etch the insulating layer 6 and etching the insulating layer 6, the insulating layer 6 can be etched in the same pattern as the sacrificial layer. Thereby, the opening 7 can be formed in the insulating layer 6 and the vibration space 4 can be formed.

  FIG. 6 is a schematic cross-sectional view showing still another embodiment of the thin film piezoelectric resonator of the present invention. The embodiment of FIG. 6 differs from the embodiment of FIGS. 1 to 3 or the embodiment of FIG. 4 only in that the vibration space 4 is formed by a through-opening 9 ′ reaching from the upper surface to the lower surface of the substrate 8. .

  The thin film piezoelectric resonator according to the embodiment of FIG. 6 can be manufactured as follows. First, the lower electrode 10, the piezoelectric layer 2, and the upper electrode 12 are formed by the above-described film formation method, and each layer is patterned by using a patterning technique such as wet etching, RIE, or lift-off method. Thereafter, by using the patterning technique, the buffer region 22 and the piezoelectric layer 2 which is a part of the support region 24 shown by hatching in FIG. 1 or FIG. 4 are applied to T / 8 ≦ t ≦ T / 2, preferably T / 6 ≦. Etching is performed so that t ≦ T / 2. Furthermore, a through-opening 9 ′ is formed in the substrate 8 by etching the substrate 8 from the lower surface side of the semiconductor substrate 8 by a deep etching technique such as anisotropic wet etching or Deep-RIE, and vibration is generated by the through-opening. A space 4 can be formed.

FIG. 7 is a schematic plan view showing still another embodiment of the thin film piezoelectric resonator of the present invention, and FIGS. 8 and 9 are a schematic XX partial sectional view and a schematic YY partial sectional view, respectively. It is. In the embodiment shown in FIGS. 1 to 3, the embodiment shown in FIG. 4, the embodiment shown in FIG. 5, and the embodiment shown in FIG. 6, the vibration space 4 is formed below the piezoelectric resonance stack 14. In the embodiment of FIGS. 7 to 9, the acoustic reflection layer 30 is formed on the lower side of the piezoelectric resonance stack 14. The acoustic reflection layer 30 is composed of an alternating laminate of low impedance layers and high impedance layers. The low impedance layer is made of a material having a small acoustic impedance such as SiO ₂ or AlN, and the high impedance layer is made of a material having a large acoustic impedance such as Mo, W, Ta ₂ O ₅ , The thicknesses of these low impedance layer and high impedance layer are set so as to correspond to a quarter wavelength of the elastic wave.

  The thin film piezoelectric resonator of the embodiment of FIGS. 7 to 9 can be manufactured as follows. First, a pit portion is formed on the semiconductor substrate 8 such as a silicon substrate by a technique such as wet etching, and the acoustic reflection layer 30 is formed by a film forming technique such as sputtering, vapor deposition, or CVD. Thereafter, the upper surface of the substrate 8 with the acoustic reflection layer is planarized by a planarization technique such as a CMP method to obtain a substrate on which the acoustic reflection layer 30 is deposited only inside the pits. The lower electrode 10, the piezoelectric layer 2, and the upper electrode 12 are formed by a film forming method such as sputtering or vapor deposition, and each layer is patterned using a patterning technique such as wet etching, RIE, or lift-off. Further, by using the patterning technique, the buffer layer 22 and the part of the piezoelectric layer 2 in the support region 24 indicated by the hatched portion in FIG. 7 are subjected to T / 8 ≦ t ≦ T / 2, preferably T / 6 ≦ t ≦ T. Etch to be / 2.

  FIG. 10 is a schematic cross-sectional view showing still another embodiment of the thin film piezoelectric resonator of the present invention, and shows a portion corresponding to FIG.

The thin film piezoelectric resonator according to the present embodiment has the lower dielectric layer 26 attached to the lower surface of the piezoelectric resonant stack 14 and the upper dielectric layer 28 attached to the upper surface of the piezoelectric resonant stack 14 as shown in FIG. -3 or the embodiment of FIG. As the lower dielectric layer 26 and the upper dielectric layer 28, relatively elastic modulus such as aluminum nitride (AlN), aluminum oxynitride (AlO _x N _y ), silicon nitride (Si ₃ N _x ), and sialon (SiAlON) is used. A large material is preferred. The thickness of the lower dielectric layer 26 and the upper dielectric layer 28 is, for example, 0.05 μm to 0.5 μm.

  According to the present embodiment, as in the above-described embodiments of FIGS. 1 to 3, it is possible to obtain a thin film piezoelectric resonator having a high Q value in which a decrease in impedance at the antiresonance frequency is suppressed. Furthermore, according to this embodiment, since the lower dielectric layer 26 and the upper dielectric layer 28 are provided, the lower electrode 10 and the upper electrode 12 can be protected, respectively.

  Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.

(Example 1 to Example 3, Comparative Example 1 to Comparative Example 3)
A thin film piezoelectric resonator having the form shown in FIGS. 2 to 4 in which the in-plane shape of the vibration region 20 is an ellipse having a major axis of 210 μm and a minor axis of 122 μm was produced. The lower electrode 10 is made of Mo and has a thickness of 300 nm, the piezoelectric layer 2 is made of AlN, the thickness T in the vibration region 20 is 1200 nm, and the thickness t in the buffer region 22 is 200 nm (Example 1: t = T / 6). The upper electrode 12 was composed of a laminated film of a Mo layer and an Al layer and had a thickness of 300 nm (each layer was 150 nm). Further, the width x of the buffer region 22 was set to x = λ / 40 = 8.0 μm. Here, since the in-plane shape of the vibration region 20 is an ellipse, the wavelength λ of the standing wave in the in-plane direction is set to λ = 2 (a × b) ^1/2 = 320 μm.

  FIG. 11 shows the frequency (Frequency) -impedance (Z) relationship of the fabricated thin film piezoelectric resonator. The impedance at the anti-resonance frequency is 2500Ω, and the Q value is 980, indicating good resonator characteristics.

  Subsequently, the thickness t of the piezoelectric layer 2 in the buffer region 22 was changed to T (Comparative Example 1: t = T) to produce a similar thin film piezoelectric resonator.

  FIG. 12 shows the frequency (Frequency) -impedance (Z) relationship of the fabricated thin film piezoelectric resonator. The impedance at the antiresonance frequency is 1100Ω, the impedance is considerably smaller than the result of Example 1, and the resonator characteristics are considerably inferior to those of Example 1.

  Subsequently, the thickness t of the piezoelectric layer 2 in the buffer region 22 is further changed (Example 2: t = T / 3, Example 3: t = T / 2, Comparative Example 2: t = 2T / 3), and the like. A thin film piezoelectric resonator was fabricated.

  FIG. 13 shows Example 1 [Ex. 1] to Example 3 [Ex. 1], Comparative Example 1 [Com. Ex. 1] and Comparative Example 2 [Com. Ex. 2] shows the relationship between t / T and the impedance (Zmax) at the antiresonance frequency in the thin film piezoelectric resonator obtained in [2]. The thin film piezoelectric resonators obtained in Examples 1 to 3 have a large impedance at the antiresonance frequency and exhibit good resonator characteristics. On the other hand, the thin film piezoelectric resonators obtained in Comparative Examples 1 and 2 have low impedance at the antiresonance frequency and inferior resonator characteristics.

  When t / T = 0, that is, when the piezoelectric layer 2 is completely removed in the buffer region 22 (Comparative Example 3), the piezoelectric resonance stack is damaged in the manufacturing process, and the resonator characteristics cannot be measured. It was.

(Examples 4 to 8 and Comparative Examples 4 to 5)
The width x of the buffer region 22 was changed (Example 4: x = λ / 53.3 = 6.0 μm, Example 5: x = λ / 80 = 4.0 μm, Example 6: x = λ / 26. 7 = 12.0 μm, Example 7: x = λ / 160 = 2.0 μm, Example 8: x = λ / 20 = 16.0 μm, Comparative Example 4: x = 0 μm, Comparative Example 5: x = λ / 16 = 20.0 μm) A thin film piezoelectric resonator was manufactured in the same manner as in Example 1.

  FIG. 14 shows Example 1 [Ex. 1], Example 4 [Ex. 4] to Example 8 [Ex. 8], Comparative Example 4 [Com. Ex. 4] and Comparative Example 5 [Com. Ex. 5] shows the relationship between x / λ and the impedance (Zmax) at the antiresonance frequency in the thin film piezoelectric resonator obtained in [5]. The thin film piezoelectric resonators obtained in Example 1 and Examples 4 to 8 have a large impedance at the antiresonance frequency and exhibit good resonator characteristics. In particular, the thin film piezoelectric resonators obtained in Example 1 and Examples 4 to 6 have a particularly large resonator characteristic with an impedance of 200Ω or more at the antiresonance frequency, which is extremely good. On the other hand, the thin film piezoelectric resonators obtained in Comparative Example 4 and Comparative Example 5 have low impedance at the antiresonance frequency and inferior resonator characteristics. In the thin film piezoelectric resonator obtained in Comparative Example 5, spurious was generated in the resonance band.

1 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator of the present invention. It is typical XX partial sectional drawing of FIG. FIG. 2 is a schematic YY partial cross-sectional view of FIG. 1. 1 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator of the present invention. It is a typical sectional view showing an embodiment of a thin film piezoelectric resonator of the present invention. It is a typical sectional view showing an embodiment of a thin film piezoelectric resonator of the present invention. 1 is a schematic plan view showing an embodiment of a thin film piezoelectric resonator of the present invention. It is typical XX partial sectional drawing of FIG. FIG. 8 is a schematic YY partial cross-sectional view of FIG. 7. It is a typical sectional view showing an embodiment of a thin film piezoelectric resonator of the present invention. It is a figure which shows the frequency-impedance relationship of the thin film piezoelectric resonator produced in the Example. It is a figure which shows the frequency-impedance relationship of the thin film piezoelectric resonator produced by the comparative example. It is a figure which shows the relationship between t / T in the thin film piezoelectric resonator obtained by the Example and the comparative example, and the impedance in an antiresonance frequency. It is a figure which shows the relationship between x / (lambda) in the thin film piezoelectric resonator obtained by the Example and the comparative example, and the impedance in an antiresonance frequency.

Explanation of symbols

2 Piezoelectric layer 4 Vibration space 6 Insulating layer 7 Opening 8 Semiconductor substrate 9 Recess 9 'Through opening 10 Lower electrode 10A Lower electrode main part 10B Lower electrode connecting terminal part 12 Upper electrode 12A Upper electrode main part 12B Upper electrode connecting terminal part 14 Piezoelectric Resonant stack 16 Connecting conductor 18 Small through hole 20 Vibration region 22 Buffer region 24 Support region 26 Lower dielectric layer 28 Upper dielectric layer 30 Acoustic reflection layer

Claims (4)

A piezoelectric resonance stack having a piezoelectric layer and an upper electrode and a lower electrode formed so as to face each other with the piezoelectric layer interposed therebetween, a void or an acoustic reflection layer formed under the piezoelectric resonance stack, and the piezoelectric resonance stack A thin film piezoelectric resonator comprising a substrate supporting
The piezoelectric resonance stack includes a vibration region in which the upper electrode and the lower electrode face each other through the piezoelectric layer and are positioned corresponding to the gap or the acoustic reflection layer, a support region in contact with the substrate, and the vibration A buffer region located between the region and the support region,
The thickness t of the piezoelectric layer in the buffer region and the thickness T of the piezoelectric layer in the vibration region satisfy the relationship of T / 8 ≦ t ≦ T / 2, and the standing wave existing in the direction parallel to the substrate A thin film piezoelectric resonator, wherein the wavelength λ and the size x of the buffer region with respect to the direction of the standing wave satisfy a relationship of λ / 200 ≦ x ≦ λ / 20.   2. The thin film piezoelectric resonator according to claim 1, wherein a dimension x of the buffer region is in a range of 0.5 μm to 40 μm.   The thin film piezoelectric resonator according to claim 1, wherein the piezoelectric layer is made of a material mainly composed of AlN.   The thin film piezoelectric resonator according to claim 1, wherein a shape of the vibration region in a plane parallel to the substrate is an ellipse.

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