JP2009290374A - Method for manufacturing baw resonator - Google Patents

Abstract

An object of the present invention is to provide a method of manufacturing a BAW resonator capable of improving the bonding strength between a piezoelectric material portion and a lower electrode and improving the Q value.
A method of manufacturing a BAW resonator includes a bonding metal layer forming step of forming a bonding metal layer on one surface in a thickness direction of a KNN element, and then a bonding metal layer and a surface of a base substrate. A bonding step of bonding the lower electrode 2 stacked on the substrate, and an upper electrode forming step of forming the upper electrode 4 on the other surface side in the thickness direction of the KNN element 30 thereafter. When laminating on one surface, the lower metal layer 22 which is the lower layer in the lower electrode 2 is laminated on one surface of the base substrate 1 and then the upper layer which is the upper layer in the lower electrode 2 on the lower metal layer 22. The metal layer 21 is laminated, a metal having a lower density than the upper metal layer 21 is used as the material of the lower metal layer 22, and the bonding metal layer 31 is used as the material of the upper metal layer 21 than the lower metal layer 22. Metal with high bondability with There.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a BAW (Bulk Acoustic Wave) resonator, and more particularly to a method for manufacturing a BAW resonator using KNN.

In recent years, research and development for improving the performance of high-frequency communication devices such as mobile phones and UWB (Ultra Wide Band) devices have been actively conducted in various places. Here, in improving the performance of a high-frequency communication device, it is required to reduce the loss of the high-frequency bandpass filter used in the high-frequency communication device (to reduce the insertion loss of the filter). Therefore, a filter using a BAW resonator that can increase the Q value in a high frequency band as compared with a conventionally provided LC filter has attracted attention (for example, see Patent Document 1).

The BAW resonator disclosed in Patent Document 1 is a so-called SMR (Solidly Mounted Resonator) type BAW resonator, and includes a base substrate provided with an acoustic multilayer film, and one surface of the base substrate (on the acoustic multilayer film layer). A lower electrode, a piezoelectric material part formed using a piezoelectric thin film laminated on the lower electrode, and an upper electrode laminated on the piezoelectric material part. The acoustic multilayer film is for reducing the loss of resonance energy by reflecting the bulk acoustic wave generated in the piezoelectric material part and suppressing the bulk acoustic wave from propagating to the base substrate side. Te, on one side in the thickness direction of the semiconductor substrate, and a low acoustic impedance layer made of SiO _2, acoustic impedance than SiO ₂ is high material (e.g., tungsten, etc.) and a high acoustic impedance layer made of, outermost layer low It is formed by alternately laminating so as to be an acoustic impedance layer.

  Since the filter using the BAW resonator as described above has a high Q value in a high frequency band, it has the characteristics that it has excellent pass characteristics and cutoff characteristics and can achieve low loss. In addition, this type of filter has a feature that a high-frequency bandpass filter having a different bandwidth can be obtained depending on a difference in piezoelectric materials (for example, AlN, ZnO, PZT, KNN, etc.) to be used.

  For example, UWB filters are required to have steep rising and falling characteristics in a high frequency band of about 300 to 400 MHz. In order to satisfy such characteristics, an electromechanical coupling coefficient (electromechanical coupling coefficient) is used as a piezoelectric material. It is preferable to use PZT or KNN (potassium sodium niobate) having a relatively large coefficient), and it is particularly preferable to use KNN, which is a lead-free piezoelectric material, considering the environmental load.

  Here, as a method of forming (manufacturing) a piezoelectric thin film made of KNN, a method using a sol-gel method has been proposed (for example, see Patent Document 2). In forming the piezoelectric thin film, a silicon substrate is often used as the semiconductor substrate of the base substrate, and Pt or Pt / Ti (formed by forming a Pt layer on the Ti layer) is used as the lower electrode. There are many cases.

  In forming a piezoelectric thin film made of KNN by the sol-gel method, an organic metal compound containing Na (for example, sodium ethoxide), an organic metal compound containing K (for example, potassium ethoxide), and an organic material containing Nb are formed on the lower electrode. Apply a solution prepared by dissolving a metal compound (eg, niobium ethoxide) in an organic solvent or the like so that each metal has a desired molar ratio, dry on a hot plate, pre-fire, and then anneal at 700 ° C. What is necessary is just to repeat the process to perform until a desired film thickness is obtained.

In Patent Document 2, as a method of forming a piezoelectric thin film made of KNN, a method using a sputtering method or a chemical vapor deposition (CVD) method is proposed in addition to the sol-gel method described above. Yes. Even when the sputtering method or the CVD method is used, a silicon substrate is often used as the semiconductor substrate, and Pt or Pt / Ti is often used as the lower electrode.
JP 2006-229282 A JP 2007-184513 A (refer to paragraph [0066] in particular)

  However, in the BAW resonator having the piezoelectric material portion formed by the sol-gel method, the sputtering method, or the CVD method as described above, the actual Q value is lower than the designed Q value, and a desired Q value is obtained. There was a problem that it could not be obtained.

  Here, the reason why the desired Q value cannot be obtained is thought to be due to the film quality of the piezoelectric material portion. For example, when the sol-gel method is used, K or Na (particularly K) in KNN diffuses or evaporates in the lower electrode during annealing, and the vicinity of the interface between the lower electrode and the upper electrode in the piezoelectric material portion. It is thought that this is caused by a lack of K and Na in KNN.

  On the other hand, when the sputtering method or the CVD method is used, the surface of the piezoelectric thin film obtained by the sputtering method or the CVD method is rough, so that resonance energy escapes at the time of resonance and it is difficult for a standing wave to be generated. It is thought that it is from. In addition, when forming a piezoelectric thin film, a silicon substrate is used as a semiconductor substrate as described above. When such a silicon substrate is used as a growth substrate for a KNN thin film, a single crystal MgO substrate or the like is used. Compared to the case where it is used as a growth substrate, KNN is likely to be polycrystalline, and deterioration of the crystallinity of the piezoelectric thin film is considered to be one of the causes for the Q value to decrease.

  Therefore, instead of forming a piezoelectric thin film on the lower electrode using a sol-gel method or the like, a KNN element (not shown) prepared in advance as a basis of the piezoelectric material portion is used, and this KNN element is used as a base substrate. A method of bonding to the lower electrode laminated on top has been proposed. Here, as the KNN element, one cut out from the bulk of KNN or one obtained by removing the single crystal substrate from the KNN thin film grown on the single crystal substrate is used.

  According to this method, the Q value resulting from the shortage of the main constituent elements in the KNN in the vicinity of the interface between the lower electrode and the upper electrode in the piezoelectric material portion or the surface roughness of the piezoelectric material portion becoming rough. Therefore, it is possible to obtain a BAW resonator having a high Q value as compared with the case where a sol-gel method or the like is used.

  However, if the smoothness (flatness) of the upper surface of the lower electrode to which the KNN element is bonded is poor, the adhesion between the piezoelectric material part and the lower electrode is deteriorated, resulting in a decrease in bonding strength. Another problem was that cracks would occur.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method of manufacturing a BAW resonator capable of improving the bonding strength between the piezoelectric material portion and the lower electrode and improving the Q value. is there.

  In order to solve the above-described problem, in the invention of claim 1, a base substrate, a lower electrode laminated on one surface of the base substrate, and a KNN element are used and laminated on the lower electrode. A method of manufacturing a BAW resonator comprising a piezoelectric material portion and an upper electrode laminated on the piezoelectric material portion, wherein a bonding metal layer for bonding to the lower electrode is formed on one surface in the thickness direction of the KNN element. A bonding metal layer forming step to be formed, a bonding step of bonding the bonding metal layer formed by the bonding metal layer forming step and the lower electrode laminated on the one surface of the base substrate, and the bonding step An upper electrode forming step of forming the upper electrode on the other surface side in the thickness direction of the KNN element, and in stacking the lower electrode on the one surface of the base substrate, the base substrate Said one of As a material of the lower metal layer, a lower metal layer serving as a lower layer in the lower electrode is laminated on a surface, and then an upper metal layer serving as an upper layer in the lower electrode is laminated on the lower metal layer. A metal having a density lower than that of the upper metal layer is used, and a metal having a higher bonding property to the bonding metal layer than the lower metal layer is used as a material of the upper metal layer.

  According to the first aspect of the present invention, the bonding metal layer formed on one surface in the thickness direction of the KNN element and the upper metal layer made of a metal having a higher bonding property to the bonding metal layer than the lower metal layer of the lower electrode are provided. Since the KNN piece is bonded to the lower electrode by bonding, the adhesion between the piezoelectric material portion and the lower electrode is improved, so that the bonding strength between the piezoelectric material portion and the lower electrode can be improved. In addition, since the lower metal layer is formed of a metal having a lower density than the upper metal layer, the lower electrode can be reduced in weight, so that the piezoelectric material portion is likely to resonate, and as a result, the Q value is improved. Can be planned. In addition, since the sol-gel method, the sputtering method, and the CVD method do not have to be performed when forming the piezoelectric material portion, the Q value can be improved as compared with the case where these methods are performed.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the lower metal layer is a porous metal layer.

  According to the invention of claim 2, since the lower metal layer is a porous metal layer, the lower metal layer is crushed when the KNN element and the lower electrode are joined, and the smoothness of one surface of the base substrate is reduced. Even if it is bad, since the adhesion between the lower electrode and the base substrate is improved, the bonding strength between the lower electrode and the base substrate can be improved. In addition, even when excessive stress is applied to the KNN element when the KNN element and the lower electrode are joined, such stress can be reduced by the lower metal layer. It can suppress that a crack arises.

  The invention of claim 3 is characterized in that, in the invention of claim 1, Au is used as a material of the bonding metal layer and the upper metal layer, and Al is used as a material of the lower metal layer.

  According to the invention of claim 3, since the material of the bonding metal layer and the upper metal layer are both Au, the thermal expansion coefficients of the upper metal layer and the bonding metal layer are equal and the adhesion is improved. The bonding strength between the part and the lower electrode can be improved. In addition, since Al having a lower density than Au is used as the material of the lower metal layer, the weight of the lower electrode can be reduced, so that the piezoelectric material portion is likely to resonate, and as a result, the Q value can be improved. . In addition, since Al is a relatively soft metal among the metals, the lower metal layer is liable to be crushed when the KNN element and the lower electrode are joined, thereby improving the adhesion between the lower electrode and the base substrate. The bonding strength between the lower electrode and the base substrate can be improved, and furthermore, the occurrence of cracks in the KNN element can be suppressed. Further, Al is a metal having a relatively low electrical resistivity among metals (as in the past, Pt or Pt used as a material for the lower electrode when forming a piezoelectric material portion by a sol-gel method, a sputtering method, or a CVD method) Since the electrical resistivity is lower than that of Ti), the resistance value of the lower electrode can be reduced, so that the Q value can be improved.

  The invention of claim 4 is characterized in that, in the invention of claim 2, Au is used as a material of the bonding metal layer and the upper metal layer, and the lower metal layer is a porous Al layer. .

  According to the invention of claim 4, since the materials of the bonding metal layer and the upper metal layer are both Au, the thermal expansion coefficients of the upper metal layer and the bonding metal layer are equal and the adhesion is improved. The bonding strength between the part and the lower electrode can be improved. In addition, since Al having a lower density than Au is used as the material of the lower metal layer, the weight of the lower electrode can be reduced, so that the piezoelectric material portion is likely to resonate, and as a result, the Q value can be improved. . In addition, since Al is a relatively soft metal among the metals, the lower metal layer is liable to be crushed when the KNN element and the lower electrode are joined, thereby improving the adhesion between the lower electrode and the base substrate. The bonding strength between the lower electrode and the base substrate can be improved, and furthermore, the occurrence of cracks in the KNN element can be suppressed. Further, Al is a metal having a relatively low electrical resistivity among metals (as in the past, Pt or Pt used as a material for the lower electrode when forming a piezoelectric material portion by a sol-gel method, a sputtering method, or a CVD method) Since the electrical resistivity is lower than that of Ti), the resistance value of the lower electrode can be reduced, so that the Q value can be improved. In addition, since the porous Al layer can be formed by a simple method such as vacuum deposition of Al under a rare gas atmosphere, the manufacturing becomes easy.

  The invention of claim 5 is characterized in that, in the invention of any one of claims 1 to 4, the KNN segment is cut out from a bulk of KNN.

  According to the fifth aspect of the present invention, it is possible to select and use a KNN element for forming the piezoelectric material portion having a high Q value from a previously prepared bulk. Q value can be easily obtained, and the Q value can be reliably improved.

  The invention according to claim 6 is the invention according to any one of claims 1 to 4, wherein the KNN element is a KNN thin film grown as a single crystal on one surface side of a single crystal substrate. The crystal substrate is used after being removed.

  According to the sixth aspect of the present invention, it is possible to use a KNN thin film having a thickness of about 100 nm to 1 μm as the KNN piece for forming the piezoelectric material portion, so that it corresponds to a high frequency of about 1 G to 10 GHz. Can do. Moreover, since the KNN thin film is a single crystal grown on the single crystal substrate, it is possible to reduce the presence of polycrystalline KNN in the KNN thin film, and to obtain a KNN thin film having a high Q value. , Q value can be improved.

  The present invention has an effect that the bonding strength between the piezoelectric material portion and the lower electrode can be improved, and the Q value can be improved.

(Embodiment 1)
As shown in FIG. 1 (j), the BAW resonator in this embodiment includes a base substrate 1, a lower electrode 2 stacked on one surface of the base substrate 1 (upper surface in FIG. 1 (j)), and a KNN. And a piezoelectric material part 3 formed on the lower electrode 2 and an opening 5a that exposes a part of one surface in the thickness direction of the piezoelectric material part 3 (upper surface in FIG. 1 (j)). An insulating layer 5 made of an insulating material such as SiO ₂ provided on the one surface side of the base substrate 1 so as to cover the material portion 3 and the lower electrode 2, and a piezoelectric exposed from the aperture 5 a of the insulating layer 5. This is an SMR-type BAW resonator including an upper electrode 4 made of a metal material such as Al formed on the one surface side in the thickness direction of the material portion 3.

The piezoelectric material portion 3 is formed using a KNN element 30 (see FIG. 1C). Here, as the KNN element 30, a piece cut from the bulk 300 of KNN formed by sintering as shown in FIG. 2A so as to have a desired size is used. Here, the composition formula of KNN is K _x Na _1-x NbO ₃ , and x is preferably 0.5.

  The piezoelectric material portion 3 is formed by bonding the KNN piece 30 to the lower electrode 2 and then patterning the KNN piece 30 into a desired planar shape. In joining the KNN piece 30 to the lower electrode 2, A bonding metal layer 31 for bonding to the lower electrode 2 is formed on one surface in the thickness direction of the KNN element 30 (the lower surface in FIG. 1C). Here, Au is used as the material of the bonding metal layer 31.

  The lower electrode 2 includes a lower metal layer 22 laminated on the one surface of the base substrate 1 and an upper metal layer 21 laminated on the lower metal layer 22 and joined to the KNN element 30. The lower metal layer 22 is made of a metal having a lower density (lower mass density) than that of the upper metal layer 21, and the upper metal layer 21 is made of a bonding metal described later than the lower metal layer 22. A metal having high bondability with the layer 31 is used. In the present embodiment, since the bonding metal layer 31 is formed of Au, the same Au as the bonding metal layer 31 is used as the material of the upper metal layer 21. On the other hand, as the material of the lower metal layer 22, Al which is a metal having a lower density than Au is used.

  The lower metal layer 22 may be made of a material having a lower density than that of the upper metal layer 21, but a metal having an electrical resistivity of 10 μΩ · cm or less, such as Al (the electrical resistivity of Al is 2.6548 μΩ · cm) is preferably used. Here, the electrical resistivity is set to 10 μΩ · cm or less for the following reason. That is, in the above-described high-frequency communication device, a BAW resonator having a Q value of about 300 to 400 is actually used. Therefore, in the BAW resonator of this embodiment, the Q value is 300 to 400. However, when a metal having an electrical resistivity of more than 10 μΩ · cm is used as the metal used for the lower metal layer 22 of the lower electrode 2, the result is that the Q value is less than 300. It is.

The base substrate 1 is formed using a semiconductor substrate (for example, a silicon substrate) 10, and is formed on one surface in the thickness direction of the semiconductor substrate 10 (upper surface in FIG. 1 (j)) from the piezoelectric material portion 3 to the base substrate 1 side. An acoustic multilayer film (acoustic mirror layer) 11 is provided for reducing the loss of resonance energy by reflecting the traveling BAW. As shown in FIG. 1J, the acoustic multilayer film 11 includes a low acoustic impedance layer 12 made of a material having a relatively low acoustic impedance (for example, SiO ₂ ) and a material having a relatively high acoustic impedance (for example, , ZnO, Mo, W, etc.) and the high acoustic impedance layer 13 are alternately laminated so that the low acoustic impedance layer 12 is the outermost layer. In addition, what is necessary is just to set each film thickness of the low acoustic impedance layer 12 and the high acoustic impedance layer 13 to 1/4 of the wavelength of the elastic wave (bulk elastic wave) of the resonant frequency of the piezoelectric material part 3. FIG.

  Below, the manufacturing method of the BAW resonator of this embodiment is demonstrated with reference to FIG. 1 and FIG. First, after the low acoustic impedance layer 12 is formed on the one surface side in the thickness direction of the semiconductor substrate 10 serving as the base of the base substrate 1, the high acoustic impedance layer 13 and the low acoustic impedance layer are formed on the low acoustic impedance layer 12. 12 are alternately laminated so that the low acoustic impedance layer 12 is the outermost layer, and the surface of the outermost low acoustic impedance layer 12 is flattened by CMP (Chemical Mechanical Polishing) to obtain an acoustic multilayer. The base substrate 1 is obtained by forming the film 11.

When the semiconductor substrate 10 is a silicon substrate as in the present embodiment, when the low acoustic impedance layer 12 is first formed on the one surface side of the semiconductor substrate 10, the one surface side of the semiconductor substrate 10 is subjected to a thermal oxidation method. The low acoustic impedance layer 12 made of SiO ₂ may be formed by oxidation by, for example.

  Thereafter, the lower electrode 2 is laminated on the one surface of the base substrate 1. Here, in laminating the lower electrode 2 on the one surface of the base substrate 1, as shown in FIG. 1A, the lower metal serving as a lower layer in the lower electrode 2 on the one surface of the base substrate 1. After the layer 22 is laminated, an upper metal layer 21 that is an upper layer in the lower electrode 2 is laminated on the lower metal layer 22 as shown in FIG. In addition, as a method of laminating the upper metal layer 21 and the lower metal layer 22, a sputtering method, a CVD method, an EB vapor deposition method, a vacuum vapor deposition method, or the like can be used.

  Next, the KNN element 30 which is the basis of the piezoelectric material portion 3 is bonded to the lower electrode 2. Before the KNN element 30 is bonded, as shown in FIG. A bonding metal layer 31 is formed on one surface in the thickness direction (the lower surface in FIG. 1C) by sputtering, CVD, electron beam (EB) evaporation, vacuum evaporation, or the like (bonding metal). Layer forming step). In addition, since the joining metal layer formation process should just be performed before the joining process mentioned later at the latest, the order of the process of forming the base substrate 1 and the process of forming the lower electrode 2 is not ask | required. .

  Thereafter, the bonding metal layer 31 formed on the one surface of the KNN element 30 is bonded to the upper metal layer 21 serving as an upper layer in the lower electrode 2 (bonding step). Here, the bonding between the bonding metal layer 31 and the upper metal layer 21 is performed, for example, after the KNN element 30 is placed on the lower electrode 2 so that the bonding metal layer 31 and the upper metal layer 21 are in contact with each other. By pressing the KNN element 30 toward the base substrate 1 in a state where the metal layer 21 and the bonding metal layer 31 are heated to, for example, about 200 ° C. to 300 ° C. (pressing the bonding metal layer 31 and the upper metal layer 21). Just do it. Further, the upper metal layer 21 and the bonding metal layer 31 press the KNN element 30 toward the base substrate 1 side after performing surface activation treatment on the bonding metal layer 31 and the upper metal layer 21 that face each other. Bonding may be performed by pressurizing the bonding metal layer 31 and the upper metal layer 21. In this case, since it is not necessary to heat, bonding at room temperature is possible. In joining the joining metal layer 31 and the upper metal layer 21, in addition to the above example, the joining metal layer 31 and the upper metal layer 21 are appropriately heated by appropriately heating the joining metal layer 31 and the upper metal layer 21. And eutectic bonding.

  As shown in FIG. 1D, the upper metal layer 21 and the bonding metal layer 31 are bonded and integrated by the bonding process described above, so that the adhesion between the KNN element 30 and the lower electrode 2 is improved. As a result, the bonding strength between the KNN element 30 and the lower electrode 2 is improved.

  After the bonding process, the piezoelectric material portion 3 is formed by patterning the KNN element 30 into a desired planar shape using a photolithographic technique and an etching technique to obtain the structure shown in FIG. .

  Thereafter, the structure shown in FIG. 1F is obtained by patterning the lower electrode 2 into a desired planar shape using a photolithographic technique and an etching technique. At this time, unnecessary portions of the bonding metal layer 31 (portions that do not overlap with the piezoelectric material portion 3 in the thickness direction) are removed together with unnecessary portions of the upper metal layer 21 of the lower electrode 2.

  Subsequently, as shown in FIG. 1G, an insulating layer 5 is formed on the entire surface of the one surface side of the base substrate 1 by using a sputtering method, a CVD method, or the like, and thereafter, a photolithography technique, an etching technique, or the like. Then, unnecessary portions of the insulating layer 5 are removed and an opening 5a is formed to obtain the structure shown in FIG. Note that a lift-off method may be used as a method of obtaining the patterned insulating layer 5.

  Next, as shown in FIG. 1I, an upper electrode 4 is formed on the entire surface of the one surface side of the base substrate 1 by using a sputtering method, an EB vapor deposition method, or the like, and thereafter, a photolithography technique and an etching technique. By patterning the upper electrode 4 into a desired shape using the above, a BAW resonator as shown in FIG. 1J is obtained. In the manufacture of BAW resonators, a large number of BAW resonators may be formed at the wafer level and then divided into individual BAW resonators in a dicing process.

  According to the method for manufacturing the BAW resonator of the present embodiment described above, the bonding metal layer 31 made of Au formed on one surface in the thickness direction of the KNN piece 30 and the lower metal layer 22 made of Al of the lower electrode 2. Since the KNN element 30 is bonded to the lower electrode 2 by bonding the upper metal layer 21 made of Au, which has higher bonding properties to the bonding metal layer 31, the adhesion between the piezoelectric material portion 3 and the lower electrode 2 is improved. As a result, the bonding strength between the piezoelectric material portion 3 and the lower electrode 2 can be improved. In particular, since the materials of the bonding metal layer 31 and the upper metal layer 21 are both Au, the thermal expansion coefficients of the upper metal layer 21 and the bonding metal layer 31 are equal, and the adhesion is further improved. The bonding strength between the part 3 and the lower electrode 2 can be further improved.

  In addition, since the lower metal layer 22 is made of Al, which is a metal having a lower density than the upper metal layer 21, the lower electrode 2 can be reduced in weight, so that the piezoelectric material portion 3 is likely to resonate. Thus, the Q value can be improved. In addition, since Al is a relatively soft metal among the metals, the lower metal layer 22 is easily crushed when the KNN piece 30 and the lower electrode 2 are joined. Therefore, the bonding strength between the lower electrode 2 and the base substrate 1 can be improved, and furthermore, the occurrence of cracks in the KNN element 30 can be suppressed.

  Furthermore, Al is a metal having a relatively low electric resistivity among metals, and its electric resistivity is 10 μΩ · cm or less. Therefore, the piezoelectric material portion is formed by a sol-gel method, a sputtering method, or a CVD method as in the past. The electrical resistivity is lower than that of Pt (electric resistivity is 10.6 μΩ · cm) and Ti (electric resistivity is 47.8 μΩ · cm) used as the material of the lower electrode when forming the film, and the resistance value of the lower electrode 2 Therefore, the Q value can be improved as compared with the case where Pt and Ti are used as the material of the lower electrode 2.

By the way, in the conventional method for manufacturing a BAW resonator described above, when forming a piezoelectric thin film using a sol-gel method, a sputtering method, or a CVD method, the base substrate is heated to 600 ° C. to 700 ° C. while flowing an O ₂ gas. In this case, the high acoustic impedance layer made of a metal material such as tungsten of the base substrate is violently oxidized, and the surface shape of the base substrate becomes rough.

In contrast, according to the manufacturing method of the BAW resonator of this embodiment, and sol-gel method as described above, the sputtering method, it is not necessary to perform the CVD method, the base substrate 1 while introducing O ₂ gas 600 Since it is not necessary to go through a process of heating to a high temperature of from ℃ to 700 ℃, the high acoustic impedance layer 13 of the base substrate 1 is not violently oxidized and the surface shape of the base substrate 1 is not roughened.

  In the method for manufacturing a BAW resonator according to this embodiment, as shown in FIG. 2A, a KNN element 30 cut out from a bulk 300 of KNN is used as the KNN element 30 serving as the basis of the piezoelectric material portion 3. Therefore, it is possible to select and use a high-Q value from the bulk 300 prepared in advance as the KNN element 30 used for the BAW resonator. The Q value can be easily obtained, and the Q value can be reliably improved.

  By the way, in this embodiment, although the KNN piece 30 cut out from the bulk 300 is used as the basis of the piezoelectric material part 3, as the KNN piece 30, as shown in FIG. A KNN thin film 410 grown on a main surface side of a single crystal substrate 400 made of an MgO substrate through a Pt thin film 500 and a buffer layer 600 made of PTO, PLT, or SRO, such as epitaxial growth, A substrate obtained by removing the crystal substrate 400, the Pt thin film 500, and the buffer layer 600 may be used.

  When such a single crystal substrate 400 is used, a KNN thin film 410 having a thickness of about 100 nm to 1 μm can be formed. Therefore, by forming the piezoelectric material portion 3 using such a KNN thin film 410, a BAW resonator is formed. Can be adapted to high frequencies of about 1 G to 10 GHz. In addition, since the KNN thin film 410 is a single crystal grown on the single crystal substrate 400, the KNN thin film 410 can be reduced from containing polycrystalline KNN, and the KNN thin film 410 having a high Q value can be obtained. Therefore, the Q value can be improved.

  The BAW resonator of the present embodiment is an SMR type BAW resonator, but a base configured to freely vibrate the piezoelectric material portion 3 by providing a cavity under the lower electrode 2. It may be a BAW resonator of FBAR type (Film Bulk Acoustic Resonator) using a substrate (not shown). This also applies to Embodiment 2 described later.

(Embodiment 2)
The manufacturing method of the BAW resonator of this embodiment is different from that of Embodiment 1 in that the lower metal layer 22 of the lower electrode 2 is not an Al layer but a porous Al layer, and other steps are performed. Since it is the same as that of form 1, description is abbreviate | omitted.

  Therefore, according to the method of manufacturing the BAW resonator of the present embodiment, the same effects as those of the first embodiment can be obtained, and the lower metal layer 22 is a porous Al layer. Since the lower metal layer 22 is more liable to be crushed when joining the lower electrode 2 and the lower electrode 2, the adhesion between the lower electrode 2 and the base substrate 1 is improved even if the smoothness of the one surface of the base substrate 1 is poor. As a result, the bonding strength between the lower electrode 2 and the base substrate 1 can be improved, and the occurrence of cracks in the KNN element 30 when the KNN element 30 and the lower electrode 2 are bonded can be further suppressed. . In addition, since the porous Al layer can be formed by a simple technique such as vacuum deposition of Al on the one surface of the base substrate 1 in a rare gas atmosphere, the manufacture becomes easy.

In addition, as KNN used as a material of the piezoelectric material part 3, what added predetermined impurities (for example, Li, Nb, Ta, Sb, Cu, etc.) may be used. The material of the piezoelectric material portion 3 is not limited to KNN, and for example, a niobium oxide-based lead-free piezoelectric material (lead-free piezoelectric ceramic) such as KN (KNbO ₃ ) or NN (NaNbO ₃ ) is adopted. be able to.

It is explanatory drawing of the manufacturing method of the BAW resonator of Embodiment 1 of this invention. It is explanatory drawing of the formation method of a piezoelectric material part in the same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base substrate 2 Lower electrode 3 Piezoelectric material part 4 Upper electrode 21 Upper metal layer 22 Lower metal layer 30 KNN fragment 31 Bonding metal layer 300 Bulk 400 Single crystal substrate 410 KNN thin film

Claims (6)

A base substrate, a lower electrode laminated on one surface of the base substrate, a piezoelectric material portion formed using a KNN element and laminated on the lower electrode, and an upper electrode laminated on the piezoelectric material portion; A method of manufacturing a BAW resonator comprising:
A bonding metal layer forming step of forming a bonding metal layer for bonding to the lower electrode on one surface in the thickness direction of the KNN element; the bonding metal layer formed by the bonding metal layer forming step; and the base substrate A bonding step of bonding the lower electrode stacked on the one surface; and an upper electrode forming step of forming the upper electrode on the other side in the thickness direction of the KNN element after the bonding step. ,
In laminating the lower electrode on the one surface of the base substrate, a lower metal layer serving as a lower layer in the lower electrode is laminated on the one surface of the base substrate, and then the lower metal layer is formed on the lower metal layer. The upper metal layer that is the upper layer in the lower electrode is laminated,
As a material for the lower metal layer, a metal having a lower density than the upper metal layer is used.
A method of manufacturing a BAW resonator, wherein a metal having a higher bonding property to the bonding metal layer than the lower metal layer is used as a material of the upper metal layer.   2. The method of manufacturing a BAW resonator according to claim 1, wherein the lower metal layer is a porous metal layer. As the material of the bonding metal layer and the upper metal layer, Au is used,
2. The method of manufacturing a BAW resonator according to claim 1, wherein Al is used as a material of the lower metal layer. As the material of the bonding metal layer and the upper metal layer, Au is used,
3. The method of manufacturing a BAW resonator according to claim 2, wherein the lower metal layer is a porous Al layer.   The method for manufacturing a BAW resonator according to any one of claims 1 to 4, wherein a piece cut from a bulk of KNN is used as the KNN element.   5. The KNN element according to claim 1, wherein the KNN thin film is a KNN thin film grown on a single surface of a single crystal substrate, from which the single crystal substrate is removed. A method for producing the BAW resonator according to the item.

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