JP2006186831A - Piezoelectric thin film device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic multilayer film type piezoelectric thin film device with a high-performance resonance characteristic the piezoelectric layer and the acoustic reflection layer of which can be manufactured by the same materials depending on manufacturing conditions, manufacturing means or thin film properties or the like. <P>SOLUTION: The piezoelectric thin film device is characterized in that at least one of the piezoelectric layers and at least one of the acoustic reflection layers are made of the same materials and in the case of temperatures at forming each layer by the same types of materials, the temperature at forming the acoustic reflection layer is higher than the temperature at forming the piezoelectric layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric thin film device and a manufacturing method thereof, and more particularly to an acoustic multilayer film type piezoelectric thin film device using a multilayer acoustic reflection film and a manufacturing method thereof.

  In electronic devices such as computers and communication devices, various processes are performed based on regular signals (high-frequency signals) obtained from vibrators that are one of electronic components. In these electronic devices, a frequency filter using a specific vibration mode of the vibrator is also used. As described above, a vibrator (used as a piezoelectric vibrator when a piezoelectric material is used as a vibration element) is obtained by processing a piezoelectric material such as quartz into a flat plate shape. A piezoelectric element plate is used. In a crystal resonator using crystal as a piezoelectric material, the thickness of the piezoelectric element plate made of crystal can be reduced in order to increase the fundamental resonance frequency. For example, in the case of an AT-cut quartz base plate that excites the thickness-shear vibration mode in quartz, a fundamental resonance frequency of about 67 MHz can be obtained by setting the thickness of the base plate to about 25 μm.

  However, in order to obtain a higher fundamental resonance frequency (for example, several hundred MHz or more), the thickness of the piezoelectric element plate is further reduced. However, the thinner the plate thickness is, the more difficult the machining is. Moreover, practical mechanical strength cannot be obtained. A SAW device (Surface Acoustic Wave Device) that uses surface acoustic waves is used as a device that supports such high frequencies. Compared with this, a piezoelectric that can handle higher frequencies (higher frequency). Thin film devices are attracting attention, and among them, an acoustic multilayer film (SMR (Solidly Mounted Resonator)) type piezoelectric thin film device in which a piezoelectric layer is provided on a substrate via a multilayer acoustic reflection layer has been developed ( Non-patent document 1).

  In recent years, with the shift of communication systems to the ultra-high frequency band, among piezoelectric thin film devices, for example, the piezoelectric thin film vibrator is an ultra-high frequency acoustic wave element that can be stably operated in the ultra-high frequency band. Attention has been paid. The SMR type piezoelectric thin film vibrator forms a piezoelectric layer having a thickness of λ / 2 on an acoustic reflection layer in which two types of thin film layers (λ / 4) having different acoustic impedances are alternately laminated on a substrate. It is what.

  According to this configuration, the piezoelectric layer is acoustically separated from the substrate by the multilayer acoustic reflection layer, and resonance with a high Q value can be obtained. In addition, since the entire lower surface of the piezoelectric layer is fixed by the acoustic reflection layer, a stable operation is possible. Further, a technique for improving temperature characteristics by adding a thin film of SiO2 to an acoustic multilayer film type piezoelectric thin film vibrator has been proposed (Non-Patent Document 2). A technique for improving temperature characteristics without adding a new film has also been proposed.

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
KMLakin, etal.Development of Miniature Filters for Wireless Applications, IEEE Transactions on Microwave Theory and Techniques, Vol.43, No.12, p2933, December 1995. KMLakin, etal.Temperature Compensated Bulk Acoustic Thin Film Resonator, IEEE Ultrasonics Symposium paper 3H-2, October 24,2000.

  The structure of such an acoustic multilayer film type piezoelectric thin film device does not require three-dimensional processing in order to create a void structure for opening to the atmosphere, compared to the conventional diaphragm type. In addition, it is not necessary to form a thin film such as a piezoelectric film or a conductive film, and it has a strong structure against external and internal forces that destroy the device, such as external stress and internal stress. Thus, the acoustic multilayer film type piezoelectric thin film device has excellent characteristics as a device for wireless communication.

  In this way, the acoustic multilayer film type piezoelectric thin film device has very good characteristics, but in order to prevent acoustic waves from leaking to the substrate, the substrate is in contact with the vibration part (piezoelectric layer and conductive layer). It is necessary to form a plurality of acoustic reflection layers. That is, a plurality of acoustic reflection layers are required in addition to the piezoelectric layer and the conductive layer.

  When a piezoelectric thin film device is formed by using a normal thin film forming apparatus, it is impossible to form different layer materials with the same apparatus because there is a problem in the stable production of a thin film layer. Therefore, forming thin film layers of different materials increases the necessary facilities for the different layer types. Further, since the film forming conditions for different thin film layers are managed, necessary management items are increased.

  Accordingly, the inventor has developed an acoustic multilayer film type piezoelectric thin film device in which the piezoelectric layer and the acoustic reflection layer are made of the same material, and a manufacturing method thereof. However, simply using the same material for the piezoelectric layer and the acoustic reflection layer causes various problems, making it difficult to obtain excellent resonance characteristics. For example, when the same material as the piezoelectric layer such as ZnO is used for the high acoustic impedance layer constituting the acoustic reflection layer, when acoustic vibration is applied, a piezoelectric effect is generated in the high acoustic impedance layer, thereby generating a charge and loss. Become.

  Therefore, it is possible to produce an acoustic multilayer film type piezoelectric thin film device in which the piezoelectric layer and the acoustic reflection layer can be made of the same material and have high-performance resonance characteristics depending on production conditions, production means, or thin film physical properties. Is the purpose.

The piezoelectric thin film device according to the present invention includes a substrate, at least one or more piezoelectric layers formed on the substrate, and a plurality of conductive layers in the piezoelectric layer, and a plurality of conductive layers between the substrate and the piezoelectric layer. In a piezoelectric thin film device having an acoustic reflection layer group formed by laminating acoustic reflection layers,
At least one piezoelectric layer of the piezoelectric layers and at least one acoustic reflection layer of the acoustic reflection layers are formed of the same material, and the acoustic reflection film is formed of the same material as the piezoelectric layer, The piezoelectric thin film device is characterized by being formed at a temperature higher than the temperature at which the piezoelectric layer is formed.

  In the piezoelectric thin film device described above, the same material forming at least one piezoelectric layer of the piezoelectric layers and at least one acoustic reflection layer of the acoustic reflection layers is mainly composed of zinc oxide or zinc oxide. It is also a piezoelectric thin film device characterized by being a material.

  Furthermore, in the piezoelectric thin film device described in the above two paragraphs, the piezoelectric thin film device is characterized in that the temperature at the time of forming the piezoelectric layer when forming with the same material is a temperature not exceeding 200 ° C.

  Furthermore, in the piezoelectric thin film device described in the above three paragraphs, at least one of the plurality of conductive layers has a laminated structure of an Au layer and a Ti layer.

  The piezoelectric thin film device described in the above paragraph is also a piezoelectric thin film device characterized in that a conductive layer having a laminated structure of an Au layer and a Ti layer is preferentially oriented on the Au (111) plane.

  Furthermore, in the piezoelectric thin film element according to paragraph (0012), the conductive layer of the laminated structure of the Au layer and the Ti layer is preferentially oriented on the Au (111) surface, and the rocking curve is centered on the Au (111) surface. This is also a piezoelectric thin film device characterized by having a half-value width of 3 ° or less.

  Furthermore, in the piezoelectric thin film device described in the above three paragraphs, the piezoelectric thin film device is characterized in that the conductive layer having a laminated structure of an Au layer and a Ti layer is formed at a temperature not exceeding 50 ° C.

A method of manufacturing a piezoelectric thin film device according to the present invention includes a substrate, at least one or more piezoelectric layers formed on the substrate, and a plurality of conductive layers formed on the piezoelectric layer. In the method of manufacturing a piezoelectric thin film device for forming an acoustic reflection layer group formed by laminating a plurality of acoustic reflection layers on
At least one of the piezoelectric layers and at least one of the acoustic reflection layers are formed of the same material, and the temperature at which each layer is formed of the same material is piezoelectric. A method of manufacturing a piezoelectric thin film device, characterized in that a temperature at the time of forming an acoustic reflection layer is made higher than a temperature at the time of forming a layer.

  In the method for manufacturing a piezoelectric thin film device described above, the same material forming at least one piezoelectric layer of the piezoelectric layers and at least one acoustic reflection layer of the acoustic reflection layers is mainly zinc oxide or zinc oxide. It is also a method for manufacturing a piezoelectric thin film device, characterized in that it is formed of a material as a component.

  Furthermore, in the method for manufacturing a piezoelectric thin film device described in the above two paragraphs, the temperature at the time of forming the piezoelectric layer when forming with the same material is set to a temperature not exceeding 200 ° C. It is also a method.

  Furthermore, in the method for manufacturing a piezoelectric thin film device according to the three paragraphs, at least one of the plurality of conductive layers is formed by a laminated structure of an Au layer and a Ti layer. is there.

  The method for manufacturing a piezoelectric thin film device according to the paragraph, wherein a conductive layer having a laminated structure of an Au layer and a Ti layer is formed with a preferential orientation on the Au (111) surface. But there is.

  Furthermore, in the method for manufacturing a piezoelectric thin film element according to paragraph (0012), the conductive layer having a laminated structure of an Au layer and a Ti layer is formed with a preferential orientation on the Au (111) surface, and the Au (111) surface is formed. It is also a method for manufacturing a piezoelectric thin film device, characterized in that the rocking curve has a half-value width of 3 ° or less at the center.

  Furthermore, in the method for manufacturing a piezoelectric thin film device described in the above three paragraphs, the conductive layer having a laminated structure of an Au layer and a Ti layer is formed at a temperature not exceeding 50 ° C. It is also a method.

  As described above, according to the piezoelectric thin film device and the method for manufacturing the same according to the present invention, in at least one piezoelectric layer and at least one acoustic reflection layer made of the same material, the formation temperature of the layer used for the piezoelectric layer is set to By forming it at a temperature lower than the formation temperature of the layer used for the above, it becomes possible to manufacture an acoustic multilayer film type piezoelectric thin film device having high-performance resonance characteristics. Further, by using the Au / Ti layer as the conductive layer, there is an effect that it becomes possible to provide a piezoelectric thin film device with higher performance.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in order to clarify the description in each drawing, a part of the drawing is not shown. In addition, each dimension in the drawings is partially exaggerated, and the same reference numerals denote the same objects in each figure.

  FIG. 1 shows a schematic diagram of a piezoelectric thin film vibrator 1 which is one of the piezoelectric thin film devices of the present invention. The embodiment of the present invention will be described in order with reference to FIG.

  First, a substrate 2 for forming the piezoelectric thin film vibrator 1 is prepared. In this embodiment, a Si (111) substrate is used. The Si substrate 2 is a substrate having a high resistance and a specific resistance of 1000 Ω / cm or more. The surface of the Si substrate 2 has a thickness corresponding to the target resonance frequency of the Si thermal oxide film. It is formed with. The other substrate conditions are the same as those of a normal semiconductor Si substrate. However, the material of the substrate 2 is not limited to Si, and other materials such as a quartz substrate and a glass substrate can be used. Preferably, an insulating material is desired, but a conductive substrate such as low-resistance Si can be used by performing an appropriate insulating treatment.

  The substrate 2 is subjected to a cleaning process as used in a normal semiconductor process. Then, each acoustic reflection layer 3a and 3b which comprises the acoustic reflection layer group 3 is formed. The acoustic reflection layer 3a or 3b is made of a material having different acoustic impedance determined by the density and hardness of the material. FIG. 2 shows a schematic diagram of the acoustic reflection layers 3a and 3b. As shown in FIG. 2, the acoustic energy generated in the piezoelectric layer, which will be described later, is transmitted to the substrate by satisfying the acoustic wave reflection and transmission conditions by alternately and regularly forming the film layers 3a and 3b having different acoustic impedances. Without leakage, energy is confined between the acoustic reflection layer and the uppermost surface of the piezoelectric layer, and a high-performance piezoelectric thin film device can be manufactured.

  In the present invention, the structure of the acoustic reflection layer is as shown in FIG. 2, and two layers of a high acoustic impedance layer 3b and a low acoustic impedance layer 3a are used. In the configuration, the low acoustic impedance layer 3a is formed from the substrate side, and the high acoustic impedance layer 3b is formed thereon. Three to four sets of this combination were formed, and finally the low acoustic impedance layer 3a was formed to complete the acoustic reflection layer group 3.

  In this embodiment, zinc oxide is used as the high acoustic impedance layer 3b, and silicon dioxide is used as the low acoustic impedance layer 3a. Since zinc oxide has an acoustic impedance approximately 2.5 times that of silicon dioxide, these two types of materials can be used as the layer material constituting the acoustic reflection layer group 3. Zinc oxide is an excellent piezoelectric material having a large electromechanical coupling coefficient compared to a piezoelectric material such as quartz. If this zinc oxide can be used for the high acoustic impedance layer 3b of the piezoelectric layer 4 and the acoustic reflection layer, it is possible to reduce manufacturing equipment and management costs.

  A lower conductive layer 5 for applying a voltage to the piezoelectric layer 4 is formed on the acoustic reflection layer group 3. In the present invention, a conductive layer formed by laminating the Au layer 5b and the Ti layer 5a is used. The Ti layer was used to improve the adhesion between silicon dioxide and Au. The lower conductive layer 5 was formed by a lift-off method, and the conductive layer metal was formed by an evaporation method using an electron beam. In this embodiment, the lower conductive layer is formed by the above method. However, a known method such as an etching method or sputtering may be used.

  The piezoelectric layer 4 is formed so as to cover the lower conductive layer 5. In this example, zinc oxide, which is the same material as the high acoustic impedance layer 3 b constituting the acoustic reflection layer group 3, was used as the piezoelectric layer 4. The production method was the same as the method of producing the acoustic reflection layers 3a and 3b.

  On the piezoelectric layer 4, an upper conductive layer 6 that is paired with the previously formed lower conductive layer 5 is formed. In this example, it was created by the same method as the lower conductive layer. Also, the method for forming the upper conductive layer 6 is not limited to the use of a known method for forming, similarly to the lower conductive layer 5. If necessary, if the lower conductive layer 5 needs to be connected to a terminal outside the device, or if the lower conductive layer 5 and the upper conductive layer 6 need to be electrically connected, the upper conductive layer 6 Before forming, a part of the piezoelectric layer 4 may be removed.

  In addition, since zinc oxide has a negative frequency temperature coefficient, the temperature characteristic of the frequency is not zero. On the other hand, silicon dioxide has a positive frequency temperature coefficient contrary to zinc oxide. Therefore, it is possible to create a piezoelectric thin film device having a desired frequency temperature coefficient by combining zinc oxide and silicon dioxide. In this example, the frequency temperature coefficient was adjusted by forming an additional silicon dioxide layer above the upper conductive layer 6 or between the upper conductive layer 6 and the piezoelectric layer 4.

  FIG. 3 shows the electrical characteristics of an acoustic multilayer film type piezoelectric thin film vibrator produced by a conventional method. As shown in FIG. 3, although a slight resonance characteristic is obtained at a desired frequency, the performance is not sufficient and cannot be practically used as a vibrator.

  FIG. 4 shows the measurement result of the rocking curve of the (0002) plane peak of zinc oxide produced at different formation temperatures on the lower conductive layer 5 made of Au / Ti layer produced under the same conditions. 4A is formed in a state where the temperature of the substrate 2 is 200 ° C., and FIG. 4B is formed in a state where the temperature of the substrate 2 is 400 ° C. Judging from the crystallinity as shown by the results, the zinc oxide in FIG. 4B is a better thin film. Next, the electrical characteristics of the piezoelectric thin film vibrator 1 manufactured using this thin film are shown in FIGS. 5 (a) and 5 (b). As in FIG. 4, FIG. 5A uses zinc oxide formed at a substrate 2 temperature of 200 ° C. and FIG. 5B uses the substrate 2 temperature of 400 ° C. Clearly, the electrical characteristics of the piezoelectric thin film vibrator 1 using zinc oxide formed at a low temperature (200 ° C.) are better.

  Conventionally, there are many reports on zinc oxide for the piezoelectric layer 4, and there are many reports on changes in crystallinity and piezoelectricity depending on film forming conditions. Among them, it is said that the crystallinity of zinc oxide is improved when the formation temperature is raised.

  However, from the results of FIGS. 4 and 5, in the acoustic multilayer film type piezoelectric thin film vibrator 1 using at least zinc oxide as the piezoelectric layer, the crystallinity of zinc oxide is improved by increasing the formation temperature of the piezoelectric layer 4. As a result, it has been found that the electrical characteristics of the piezoelectric thin film vibrator 1 cannot be simply improved.

  According to further detailed examination, it has been found that the correlation between the electrical characteristics of the piezoelectric thin film vibrator 1 and the zinc oxide formation temperature is greatly influenced by the state of the Au / Ti lower conductive layer 5 which is the base of zinc oxide. That is, the case where the zinc oxide formed at a low temperature shown above exhibits good resonance characteristics is strongly influenced by the orientation state of the Au (111) plane in the Au / Ti lower conductive layer 5 which is the base of zinc oxide. Yes. When the orientation of the Au (111) plane is strong, zinc oxide formed at a low temperature exhibits better resonance characteristics. In particular, when the half-value width of the rocking curve centering on the Au (111) plane is less than 3 °, it has been revealed that the rocking curve has particularly good resonance characteristics.

  According to further detailed examination, the correlation between the electrical characteristics of the piezoelectric thin film vibrator 1 and the zinc oxide formation temperature is strongly influenced by the formation temperature of the Au / Ti lower conductive layer 5 serving as the base of zinc oxide, and Au / Ti When the temperature when forming the Ti lower conductive layer 5 is low, the zinc oxide of the piezoelectric layer 4 formed at a low temperature exhibits better resonance characteristics.

  In the present embodiment, zinc oxide is used as the same material commonly used for the high acoustic impedance layer 3b and the piezoelectric layer 4 constituting the acoustic reflection layer group 3, but the first material using this material is the first. The reason is that by selecting silicon dioxide as the low acoustic impedance layer 3a, the acoustic reflection layer group 3 and the piezoelectric layer 4 can all be made of an oxide-based material. That is, zinc oxide is not limited as a common material, and for example, aluminum nitride or the like can provide the same effect. Even when zinc oxide is used for the piezoelectric layer 4, there is no limitation on the combination of the low acoustic impedance layer 3 a as long as the effects of the present disclosure are exhibited, such as selecting a material such as aluminum oxide. In addition, in the present embodiment, a conductive layer in which at least the lower conductive layer 5 is made of Au and Ti is used as the metal constituting the upper and lower conductive layers, but Al, Mo, W or Pt is used for the other conductive layers. Etc. can be used, and the material is not limited. Similarly, in this example, both zinc oxide and silicon dioxide were produced using generally known film forming conditions using an RF magnetron sputtering apparatus. In addition to this RF magnetron sputtering method, an ECR sputtering method, a CVD method, or the like can be used, and the manufacturing method, film forming conditions, and the like are not limited.

FIG. 1 is a schematic perspective view schematically showing a configuration example of an embodiment of a piezoelectric thin film device (SMR type piezoelectric thin film vibrator) according to the present invention. FIG. 2 is a schematic partial cross-sectional view schematically showing a configuration example of an embodiment of a piezoelectric thin film device (SMR type piezoelectric thin film vibrator) according to the present invention. FIG. 3 shows the electrical characteristics of an acoustic multilayer film type piezoelectric thin film vibrator produced by a conventional method. FIG. 4 shows the rocking curve of the (0002) plane peak of zinc oxide produced by changing the formation temperature on the lower conductive layer 5 made of Au / Ti layer produced under the same conditions. FIG. FIG. 4B shows the rocking curve of the (0002) plane peak of zinc oxide when formed at 400 ° C. FIG. FIG. 5 shows the electrical characteristics of the piezoelectric thin film vibrator produced by changing the formation temperature on the lower conductive layer 5 made of Au / Ti layer produced under the same conditions. FIG. FIG. 4B shows the electrical characteristics when formed at 400 ° C.

Explanation of symbols

1. Piezoelectric thin film device (piezoelectric thin film vibrator)
2 ... Substrate 3 ... Acoustic reflective film group 3a ... Acoustic reflective layer (low acoustic impedance layer)
3b ... Acoustic reflection layer (high acoustic impedance layer)
4 ... Piezoelectric layer 5 ... Lower conductive layer 5a ... Ti layer 5b ... Au layer

Claims (14)

A substrate, at least one piezoelectric layer formed on the substrate, a plurality of conductive layers in the piezoelectric layer, and a plurality of acoustic reflection layers stacked between the substrate and the piezoelectric layer In a piezoelectric thin film device having a reflective layer group,
At least one piezoelectric layer of the piezoelectric layers and at least one acoustic reflection layer of the acoustic reflection layers are formed of the same material, and the acoustic reflection layer is formed of the same material as the piezoelectric layer, A piezoelectric thin film device, which is an acoustic reflection layer formed at a temperature higher than the temperature at which the piezoelectric layer is formed.   2. The piezoelectric thin film device according to claim 1, wherein the same material forming at least one piezoelectric layer of the piezoelectric layers and at least one acoustic reflecting layer of the acoustic reflecting layers is composed mainly of zinc oxide or zinc oxide. A piezoelectric thin film device characterized by comprising:   3. The piezoelectric thin film device according to claim 1, wherein a temperature at which the piezoelectric layer is formed when the same material is used does not exceed 200.degree.   4. The piezoelectric thin film device according to claim 1, wherein at least one of the plurality of conductive layers is formed of a laminated structure of an Au layer and a Ti layer. .   5. The piezoelectric thin film device according to claim 4, wherein the conductive layer having a laminated structure of an Au layer and a Ti layer is preferentially oriented on the Au (111) plane.   5. The piezoelectric thin film device according to claim 4, wherein the conductive layer having a laminated structure of an Au layer and a Ti layer is preferentially oriented on the Au (111) plane, and the half-value width of the rocking curve is centered on the Au (111) plane. A piezoelectric thin film device characterized by being 3 ° or less.   7. The piezoelectric thin film device according to claim 4, 5, or 6, wherein the conductive layer having a laminated structure of an Au layer and a Ti layer is formed at a temperature not exceeding 50 ° C. device. A substrate, at least one piezoelectric layer formed on the substrate, a plurality of conductive layers formed on the piezoelectric layer, and a plurality of acoustic reflection layers stacked between the substrate and the piezoelectric layer In the manufacturing method of the piezoelectric thin film device for forming the reflective layer group,
At least one of the piezoelectric layers and at least one of the acoustic reflection layers are formed of the same material, and the temperature at which the piezoelectric layer is formed of the same material is the same as that at the time of forming the piezoelectric layer. A method for manufacturing a piezoelectric thin film device, characterized in that a temperature at the time of forming an acoustic reflection layer is made higher than a temperature.   9. The method of manufacturing a piezoelectric thin film device according to claim 8, wherein at least one of the piezoelectric layers and the same material forming at least one of the acoustic reflection layers are zinc oxide or zinc oxide. A method for manufacturing a piezoelectric thin film device, comprising:   10. The method of manufacturing a piezoelectric thin film device according to claim 8 or 9, wherein the temperature at the time of forming the piezoelectric layer when forming with the same material is a temperature not exceeding 200 ° C. Production method.   11. The method for manufacturing a piezoelectric thin film device according to claim 8, wherein at least one of the plurality of conductive layers is formed of a laminated structure of an Au layer and a Ti layer. Manufacturing method.   12. The method of manufacturing a piezoelectric thin film device according to claim 11, wherein the conductive layer formed by stacking the Au layer and the Ti layer is formed with a preferential orientation on the Au (111) surface. .   12. The method of manufacturing a piezoelectric thin film device according to claim 11, wherein the conductive layer having a laminated structure of an Au layer and a Ti layer is preferentially oriented on the Au (111) surface, and the rocking curve is centered on the Au (111) surface. A method for manufacturing a piezoelectric thin film device, wherein the half-value width is 3 ° or less.   14. The method for manufacturing a piezoelectric thin film device according to claim 11, 12, or 13, wherein the conductive layer having a laminated structure of an Au layer and a Ti layer is formed at a temperature not exceeding 50 ° C. A method for manufacturing a piezoelectric thin film device.

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