# Patent

## Title
Potassium niobate deposited body and method for manufacturing the same, piezoelectric thin film resonator, frequency filter, oscillator, electronic circuit, and electronic apparatus

## Abstract

A method for manufacturing a potassium niobate deposited body includes: forming a buffer layer above a substrate composed of an R-plane sapphire substrate; forming above the buffer layer a potassium niobate layer or a potassium niobate solid solution layer that epitaxially grows in a (100) orientation in a pseudo cubic system expression; and forming an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer, wherein a (100) plane of the potassium niobate layer or the potassium niobate solid solution layer is formed to tilt with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.

## Background
The entire disclosure of Japanese Patent Application No. 2005-060915, filed Mar. 4, 2005 is expressly incorporated by reference herein.
BACKGROUND
1. Technical Field
The present invention relates to potassium niobate deposited bodies and methods for manufacturing the same, piezoelectric thin film resonators, frequency filters, oscillators, electronic circuits, and electronic apparatuses.
2. Related Art
Accompanying the increase in communication speed in the data communications field, the development is directed toward achieving higher frequency in communication frequency. Piezoelectric thin film resonators (film bulk acoustic resonators: FBARs) are attracting attention as devices for achieving higher frequency. Piezoelectric thin film resonators are required to achieve higher electromechanical coupling coefficient for further miniaturization and higher efficiency.
It has been found that a single crystal substrate of potassium niobate (KNbO3) (a=0.5695 nm, b=0.3973 nm, and c=0.5721 nm; hereafter this index expression is followed as “orthorhombic crystal”) exhibited a high electromechanical coupling coefficient. For example, as described in Jpn. J. Appl. Phys. Vol. 37 (1998) 2929, it was confirmed by experiments that a 0° Y-cut X propagation KNbO3 single crystal substrate would exhibit a very large value of electromechanical coupling coefficient reaching as much as about 50%. However, it may be difficult to manufacture a piezoelectric thin film resonator by forming a potassium niobate thin film over a certain substrate having a large area.
SUMMARY
In accordance with an aspect of the present invention, there are provided a potassium niobate deposited body having a potassium niobate thin film, and a method for manufacturing the same.
In accordance with another aspect of the invention, a piezoelectric thin film resonator with a high electromechanical coupling coefficient is provided.
In accordance with still another aspect of the invention, frequency filters, oscillators, electronic circuits, and electronic equipment including the piezoelectric thin film resonator are provided.
A method for manufacturing a potassium niobate deposited body in accordance with an embodiment of the invention includes: forming a buffer layer above a substrate composed of an R-plane sapphire substrate; forming above the buffer layer a potassium niobate layer or a potassium niobate solid solution layer that epitaxially grows in a (100) orientation in a pseudo cubic system expression; and forming an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer, wherein a (100) plane of the potassium niobate layer or the potassium niobate solid solution layer is formed to tilt with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.
According to the method for manufacturing a potassium niobate deposited body described above, the potassium niobate layer or the potassium niobate solid solution layer is formed to have a (100) plane that tilts with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate. According to the manufacturing method, a potassium niobate deposited body having the potassium niobate layer or the potassium niobate solid solution layer described above can be provided. By using such a potassium niobate deposited body, a piezoelectric thin film resonator having a high electromechanical coupling coefficient can be obtained.
It is noted that, in the invention, forming another specific member (hereafter referred to as “B”) above a specific member (hereafter referred to as “A”) includes a case of forming “B” directly on “A,” and a case of forming “B” over “A” through another member on “A.” Also, in the invention, “B” formed above “A” includes “B” formed directly on “A,” and “B” formed above “A” through another member on “A.”
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, an angle defined between the (100) plane of the potassium niobate layer or the potassium niobate solid solution layer and the R-plane (1-102) of the R-plane sapphire substrate may be formed to be one degree or greater but 15 degrees or smaller.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, the potassium niobate layer may be formed to include a domain that epitaxially grows in a b-axis orientation, when a lattice constant of orthorhombic potassium niobate is 21/2 b<a<c, and a c-axis is a polarization axis, and the b-axis may be formed to tilt with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, an angle defined between the b-axis and the R-plane (1-102) of the R-plane sapphire substrate may be formed to be one degree or greater but 15 degrees or smaller.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, the buffer layer may be formed to epitaxially grow in a cubic (100) orientation, and a (100) plane of the buffer layer may be formed to tilt with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate.
A method for manufacturing a potassium niobate deposited body in accordance with another embodiment of the invention includes: forming a buffer layer that epitaxially grows in a cubic (100) orientation above a substrate composed of an R-plane sapphire substrate; forming a potassium niobate layer or a potassium niobate solid solution layer above the buffer layer; and forming an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer, wherein a (100) plane of the buffer layer is formed to tilt with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of embodiment the invention, an angle defined between the (100) plane of the buffer layer and the R-plane (1-102) of the R-plane sapphire substrate is formed to be one degree or greater but 15 degrees or smaller.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, the buffer layer may be formed to consist of a metal oxide having a rock salt structure.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, magnesium oxide may be used as the metal oxide.
The method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention may include bonding another substrate above the electrode layer, and removing the buffer layer by etching to separate the substrate.
In the method for manufacturing a potassium niobate deposited body in accordance with an aspect of the invention, a solid solution that is expressed by K1-xNaxNb1-yTayO3 (0<x<1, 0<y<1) may be used as the potassium niobate solid solution layer.
A potassium niobate deposited body in accordance with an embodiment of the invention is obtained by the method for manufacturing a potassium niobate deposited body described above.
A potassium niobate deposited body in accordance with an embodiment of the invention includes: a substrate composed of an R-plane sapphire substrate; a buffer layer formed above the substrate; a potassium niobate layer or a potassium niobate solid solution layer formed above the buffer layer; and an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer, wherein the potassium niobate layer or the potassium niobate solid solution layer epitaxially grows in a (100) orientation in a pseudo cubic system expression, and a (100) plane of the potassium niobate layer or the potassium niobate solid solution layer tilts with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.
A potassium niobate deposited body in accordance with another embodiment of the invention includes: a substrate composed of an R-plane sapphire substrate; a buffer layer formed above the substrate; a potassium niobate layer or a potassium niobate solid solution layer formed above the buffer layer; and an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer, wherein the buffer layer epitaxially grows in a cubic (100) orientation, and a (100) plane of the buffer layer tilts with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.
A piezoelectric thin film resonator in accordance with an embodiment of the invention includes the potassium niobate deposited body described above.
A frequency filter in accordance with an embodiment of the invention includes the piezoelectric thin film resonator described above.
An oscillator in accordance with an embodiment of the invention includes the piezoelectric thin film resonator described above.
An electronic circuit in accordance with an embodiment of the invention includes at least one of the frequency filter and the oscillator described above.
An electronic apparatus in accordance with an embodiment of the invention includes the electronic circuit described above.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view schematically showing a potassium niobate deposited body in accordance with a first embodiment of the invention.
FIG. 2 is a cross-sectional view schematically showing the potassium niobate deposited body in accordance with the first embodiment of the invention.
FIG. 3 is a cross-sectional view schematically showing the potassium niobate deposited body in accordance with the first embodiment of the invention.
FIG. 4 is a view schematically showing a hexagonal sapphire crystal.
FIG. 5 is a view schematically showing a tilt between a buffer layer and a potassium niobate layer.
FIG. 6 is an X-ray diffraction diagram of a potassium niobate layer in accordance with a first experimental example.
FIG. 7 is a 2θ-θ scanning X-ray diffraction diagram of the buffer layer in accordance with the second experimental example.
FIG. 8 is a ω scanning X-ray diffraction diagram of the buffer layer in accordance with the second experimental example.
FIG. 9 is a ω scanning X-ray diffraction diagram of the buffer layer in accordance with the second experimental example.
FIG. 10 is a 2θ-θ scanning X-ray diffraction diagram of the KNbO3 layer in accordance with the second experimental example.
FIG. 11 is a ω scanning X-ray diffraction diagram of the KNbO3 layer in accordance with the second experimental example.
FIG. 12 is a ω scanning X-ray diffraction diagram of the KNbO3 layer in accordance with the second experimental example.
FIG. 13 is an X-ray diffraction pole figure of the sapphire substrate in accordance with the second experimental example.
FIG. 14 is an X-ray diffraction pole figure of the buffer layer in accordance with the second experimental example.
FIG. 15 is an X-ray diffraction pole figure of KNbO3 in accordance with the second experimental example.
FIG. 16 is a diagram showing Raman scattering spectra of KNbO3 in accordance with the second experimental example.
FIG. 17 is a diagram showing Raman scattering spectra of KNbO3 in accordance with the second experimental example.
FIG. 18 is a cross-sectional view of a piezoelectric thin film resonator in accordance with a second embodiment of the invention.
FIG. 19 is a cross-sectional view of a circuit structure of an oscillator in accordance with a third embodiment of the invention.
FIG. 20 is a block diagram of the basic structure of a PLL circuit.
FIG. 21 is a block diagram showing the structure of an electronic circuit in accordance with a fourth embodiment of the present invention.
FIG. 22 is a view showing a communications system that uses a reader/writer in accordance with the fourth embodiment of the present invention.
FIG. 23 is a schematic block diagram of the communications system shown in FIG. 22.



DESCRIPTION OF EXEMPLARY EMBODIMENTS
Preferred embodiments of the present invention are described below with reference to the accompanying drawings.
1. First Embodiment
1.1. FIGS. 1-3 are cross-sectional views schematically showing a potassium niobate deposited body 100 in accordance with an embodiment of the invention. As shown in FIG. 1, the potassium niobate deposited body 100 in accordance with the present embodiment includes a substrate 11, a buffer layer 12 formed on the substrate 11, a potassium niobate layer 13 formed on the buffer layer 12, and an electrode layer 14 formed on the potassium niobate layer 13.
An R-plane sapphire substrate may be used as the substrate 11. The use of an R-plane sapphire substrate is desirable because the buffer layer 12 and the potassium niobate layer 13 can be epitaxially grown thereon, a large surface area substrate can be obtained at a low price, and the R-plane sapphire substrate has a tolerance to etchant and can be used repeatedly.
As the buffer layer 12, for example, a metal oxide having a rock salt structure can be used. For example, magnesium oxide (MgO) may be used as the metal oxide having a rock salt structure. The buffer layer 12 shall be described in detail below.
The electrode layer 14 is not limited to any particular material, and for example, such electrode materials as Pt, Ir, Au, Cr, IrOx, SrRuO3, Nb—SrTiO3, La—SrTiO3, Nb—(La, Sr)CoO3 and the like can be used. It is noted that Nb—SrTiO3 is SrTiO3 doped with Nb, La—SrTiO3 is SrTiO3 doped with La, and Nb—(La, Sr)CoO3 is (La, Sr)CoO3 doped with Nb. Among those materials, metal oxides excel in electrical conductivity and chemical stability, and can be formed in a film by vapor deposition, and therefore are suitable as the material for the electrode layer 14.
The potassium niobate layer 13 has single crystal potassium niobate or polycrystal crystal potassium niobate. The thickness of the potassium niobate layer 13 can be appropriately selected according to devices to which the potassium niobate deposited body is applied without any particular limitation, but for example, may be 10 nm or greater but 10 μm or less. The potassium niobate layer 13 shall be described in detail below.
Also, the potassium niobate deposited body 100 in accordance with the present embodiment may further include another substrate (hereafter also referred to as a “second substrate”) 15 formed on the electrode layer 14. The second substrate 15 is not limited to any particular material, and a material that can be patterned by etching or the like can be used. As the second substrate 15, for example, a silicon substrate, a glass substrate composed of a photosensitive glass or the like, a metal substrate, a resin substrate or the like can be used. Also, the film thickness of the second substrate 15 is appropriately selected according to devices to which the potassium niobate deposited body 100 is applied.
Furthermore, as shown in FIG. 3, the potassium niobate deposited body 100 in accordance with the present embodiment may include a second substrate 15, an electrode layer 14 formed on the second substrate 15, and a potassium niobate layer 13 formed on the electrode layer 14.
In the present embodiment, instead of the potassium niobate layer 13 described above, it may be a layer of potassium niobate solid solution in which a part of niobium and potassium of potassium niobate is replaced with other elements. As the potassium niobate solid solution, for example, a potassium sodium niobate tantalate solid solution expressed by K1-xNaxNb1-yTayO3 (0<x<1, 0<y<1) can be enumerated. The same similarly applies to embodiments to be described below.
1.2. Next, a method for manufacturing a potassium niobate deposited body 100 is described.
(1) First, as shown in FIG. 1, a substrate composed of an R-plane sapphire substrate (hereafter also referred to as an “R-plane sapphire substrate”) 11 is prepared. The R-plane sapphire substrate 11 has been degreased and washed beforehand. Degreasing and washing can be conducted by soaking the R-plane sapphire substrate in an organic solvent with an ultrasonic washing machine. The organic solvent is not particularly limited, but may be, for example, a mixed solution of ethyl alcohol and acetone.
(2) Next, a buffer layer 12 that consists of MgO is formed on the R-plane sapphire substrate 11 by a laser ablation method, as shown in FIG. 1.
More specifically, after the R-plane sapphire substrate 11 that has been degreased and washed is loaded onto a substrate holder, it is introduced together with the substrate holder in a vacuum apparatus whose back pressure at room temperature is 1×10 −8 Torr. Next, oxygen gas is introduced such that the oxygen partial pressure becomes 5×10−5 Torr, for example, and then the substrate is heated to elevate its temperature to 400° C. at a rate of 20° C./minute with an infrared ray lamp. It is noted that the conditions such as the rate of temperature elevation, substrate temperature, pressure, etc. are not limited to the above.
Next, a plume is generated by a laser ablation method in which a laser beam is irradiated to a magnesium target for a buffer layer, thereby pounding out magnesium atoms from the target. Then, this plume is irradiated toward the R-plane sapphire substrate 11, and brought in contact with the R-plane sapphire substrate 11. As a result, a buffer layer 12 composed of MgO with a cubic (100) orientation is formed by epitaxial growth on the R-plane sapphire substrate 11. A (100) plane of the buffer layer 12 may preferably tilt with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) (hereafter also simply referred to as an “R-plane”) of the R-plane sapphire substrate 11. This is described with reference to FIG. 4 and FIG. 5.
FIG. 4 is a view schematically showing a hexagonal sapphire crystal, and FIG. 5 is a view schematically showing a tilt of the (100) plane of the buffer layer 12. The R-plane (1-102) of the R-plane sapphire substrate 11 corresponds to an N—S plane in FIG. 4. As shown in FIG. 5, with respect to the N—S plane (in other words, the R-plane) of the R-plane sapphire substrate 11, the (100) plane of the buffer layer 12 tilts with the [11-20] direction vector as a rotation axis. In other words, a linear line defined along a crossing between the (100) plane of the buffer layer 12 and the R-plane extends in parallel with the [11-20] direction vector. By forming such a buffer layer 12, a desired potassium niobate layer 13 to be described below can be obtained. An angle δ defined between the (100) plane of the buffer layer 12 and the R-plane (1-102) of the R-plane sapphire substrate 11 may preferably be one degree or greater but 15 degrees or smaller.
Also, by using MgO as the buffer layer 12, the dielectric property of the potassium niobate layer 13 may not be deteriorated even when Mg2+ substitutes Nb5+ in the potassium niobate layer 13 and K (Mg, Nb) O3 is generated.
The thickness of the buffer layer 12 is not particularly limited, but may be 5 nm or greater but 100 nm or less, in view of preventing the R-plane sapphire substrate 11 and the potassium niobate layer 13 from reacting each other, and preventing the potassium niobate layer 13 from being deteriorated due to the deliquescence of magnesium oxide itself.
As the method to pound out magnesium atoms or desired atoms from a target in a later step, besides the method of irradiating a laser beam to a target surface described above, for example, a method of irradiating (injecting) argon gas (inert gas) plasma or an electron beam to a target surface can also be used. However, the method of irradiating a laser beam to a target surface is desirable among them. According to such a method, atoms can be readily and securely pounded out from a target, with a vacuum apparatus having a simple structure equipped with an incident window of a laser beam.
The laser beam to be irradiated to a target may preferably be a pulsed beam with a wavelength of about 150-300 nm, and a pulse length of about 1-100 ns. More specifically, the laser beam may be, for example, an excimer laser such as an ArF excimer laser, a KrF excimer laser, a XeCl excimer laser, or the like, a YAG laser, a YVO4 laser, a CO2 laser or the like. Among the above, the ArF excimer laser and the KrF excimer laser are particularly preferred. The ArF excimer laser and the KrF excimer laser are easy to handle, and can effectively pound out atoms from a target.
Each of the conditions at the time of laser beam irradiation is not particularly limited as long as the plume can sufficiently reach the substrate 11, and MgO as the buffer layer 12 can be epitaxially grown. The conditions at the time of laser beam irradiation may be as follows. For example, the energy density of the laser beam may preferably be between 2 J/cm2 and 4 J/cm2. The frequency of the laser beam may preferably be between 5 Hz and 20 Hz. The distance between the target and the substrate 11 (hereafter referred to as the “target-to-substrate distance”) may preferably be between 30 mm and 100 mm. The temperature of the substrate may preferably be between 300° C. and 600° C. The partial pressure of oxygen during deposition may preferably be between 1×10−5 Torr and 1×10−3 Torr.
(3) Next, as shown in FIG. 1, a potassium niobate layer 13 is formed by a laser ablation method on the buffer layer 12.
More specifically, a plume is generated by a laser ablation method in which a laser beam is irradiated to a target for the buffer layer, for example, a K0.6Nb0.4Oy target, thereby pounding out potassium, niobium and oxygen atoms from this target. Then, the plume is irradiated toward the R-plane sapphire substrate 11, and brought in contact with the buffer layer 12. As a result, a potassium niobate layer 13 in a (100) orientation in a pseudo cubic system expression is formed by epitaxial growth on the buffer layer 12. Further, as shown in FIG. 5, the (100) plane of the potassium niobate layer 13 tilts with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate 11. It is noted that FIG. 5 is a diagram schematically showing the tilt of the (100) plane of the buffer layer 12, as described above, and is also a diagram schematically showing the tilt of the (100) plane of the potassium niobate layer 13.
More concretely, the potassium niobate layer 13 may preferably include a domain that epitaxially grows in a b-axis orientation (which is hereafter also referred to as an “orthorhombic b-axis orientation domain”), when a lattice constant of orthorhombic potassium niobate is 21/2b<a<c, and a c-axis is a polarization axis. Also, the b-axis may preferably tilt with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate 11. When such a potassium niobate layer 13 is used, a piezoelectric thin film resonator 200 (see FIG. 18) with a high electromechanical coupling coefficient can be obtained.
An angle Δ defined between the (100) plane of the potassium niobate layer 13 and the R-plane (1-102) of the R-plane sapphire substrate 11 may preferably be one degree or greater but 15 degrees or smaller. More concretely, an angle defined between the b-axis of the orthorhombic potassium niobate and the R-plane (1-102) of the R-plane sapphire substrate 11 may preferably be one degree or greater but 15 degrees or smaller. It is noted that the angle Δ defined between the (100) plane of the potassium niobate layer 13 and the R-plane can be the same as or different from the angle δ defined between the (100) plane of the buffer layer 12 and the R-plane.
The conditions of the laser ablation method are not particularly limited as long as the plume can sufficiently reach the buffer layer 12. The conditions at the time of laser beam irradiation may be as follows. For example, the energy density of the laser beam may preferably be between 2 J/cm2 and 4 J/cm2. The frequency of the laser beam may preferably be between 5 Hz and 20 Hz. The target-to-substrate distance may preferably be between 30 mm and 100 mm. The temperature of the substrate may preferably be between 600° C. and 800° C. The partial pressure of oxygen during deposition may preferably be between 1×10−2 Torr and 1 Torr.
In this embodiment, by selecting each of the conditions at the time of laser ablation, pottasium niobate can be made to have a single crystal or polycrystal (preferably polycrystal in a single phase) structure.
In the above-described example, a K0.6Nb0.4Oy target is used. However, the composition ratio of the target is not limited to the above. For example, for the formation of the potassium niobate layer 13, it is possible to use a target having a composition ratio that is suitable for conducting a Tri-Phase-Epitaxy method. Tri-Phase-Epitaxy method is a method in which a vapor phase raw material is deposited on a substrate that is maintained at temperatures in a solid-liquid coexisting region, and a solid phase is precipitated from a liquid phase.
Concretely, a plume that is a raw material in a vapor phase is supplied to a base substrate (which, in this embodiment, consists of the substrate 11 and the buffer layer 12) such that the mole composition ratio x of potassium in KxNb1-xOy in the state of a liquid phase immediately after being deposited on the base substrate is in the range of 0.5≦x≦xE. It is noted that xE is a mole composition ratio x at an eutectic point of KNbO3 and 3K2O. Nb2O5 under a predetermined oxygen partial pressure. Then, by maintaining the temperature Ts of the base substrate within the range of TE ≦Ts≦Tm, the remaining liquid of KxNb1-xOy deposited on the base substrate supplied from the plume is evaporated. By this, KNbO3 single crystal can be precipitated from KxNb1-xOy on the base substrate. It is noted that TE is a temperature at an eutectic point of KNbO3 and 3K2O·Nb2O5 under a predetermined oxygen partial pressure. Also, Tm is a complete melting temperature under a predetermined oxygen partial pressure of KxNb1-xOy in the state of a liquid phase immediately after being deposited on the base substrate.
(4) Next, as shown in FIG. 1, an electrode layer 14 composed of, for example, SrRuO3 on the potassium niobate layer 13.
More concretely, after the temperature of the R-plane sapphire substrate 11 has been lowered to about 300° C., a plume is generated by a laser ablation method in which a laser beam is irradiated to a SrRuO3 target, thereby pounding out strontium, ruthenium and oxygen atoms from this target. Then, the plume is irradiated toward the R-plane sapphire substrate 11, and comes in contact with the potassium niobate layer 13, whereby an electrode layer 14 composed of SrRuO3 is formed by epitaxial growth.
The conditions of the laser ablation method are not particularly limited as long as the plume can sufficiently reach the substrate 11. The conditions at the time of laser beam irradiation may be as follows. For example, the energy density of the laser beam may preferably be between 2 J/cm2 and 4 J/cm2. The frequency of the laser beam may preferably be between 5 Hz and 20 Hz. The target-to-substrate distance may preferably be between 30 mm and 100 mm. The temperature of the substrate may preferably be between 200° C. and 400° C. The partial pressure of oxygen during deposition may preferably be between 1×10−3 Torr and 1×10−1 Torr.
By the steps described above, the potassium niobate deposited body 100 shown in FIG. 1 can be formed.
(5) Next, as shown in FIG. 2, a second substrate 15 is bonded to the electrode layer 14. As the method of bonding the second substrate 15 to the electrode layer 14, for example, a bonding method using adhesive such as epoxy adhesive or the like, solder, gold-gold, gold-aluminum or other intermetallic solid bonding methods, or the like can be used.
By the steps described above, a potassium niobate deposited body 100 shown in FIG. 2 can be formed.
(6) Next, as shown in FIG. 3, the buffer layer 12 is etched by wet etching, thereby separating a laminated body of the potassium niobate layer 13, the electrode layer 14 and the second substrate 15 from the R-plane sapphire substrate 11.
An etching liquid that dissolves only the buffer layer 12 but does not adversely affect the other layers is used for the wet etching. In the present embodiment, an acidic solution, such as, for example, phosphoric acid, nitric acid or the like can be used as the etching liquid, because MgO is used as the buffer layer 12.
By the steps described above, a potassium niobate deposited body 100 shown in FIG. 3 can be formed.
In addition, a polishing process to planarize the surface of the potassium niobate layer 13 can be conducted if necessary. Buff polishing, CMP (Chemical Mechanical Polishing) or the like can be conducted as such a polishing process.
It is noted that, in the present embodiment, a laser ablation method is used as a film forming method for forming the buffer layer 12, the potassium niobate layer 13 and the electrode layer 14. However, the film forming method is not limited to this method, and, for example, a vapor deposition method, a MOCVD method, and a sputter method can be used.
1.3. According to the present embodiment, a buffer layer 12 composed of MgO in a cubic (100) orientation is formed on a R-plane sapphire substrate 11, and a potassium niobate layer 13 is formed on the buffer layer 12 by using a vapor phase method. By this, a single phase thin film of potassium niobate can be epitaxially grown in a b-axis orientation. By using the potassium niobate layer 13, a piezoelectric thin film resonator 200 (see FIG. 18) having a high electromechanical coupling coefficient can be obtained, as described below.
Furthermore, in accordance with the present embodiment, a (100) plane of the potassium niobate layer 13 tilts with a [11-20] direction vector as a rotation axis with respect to the R-plane (1-102) of the R-plane sapphire substrate 11. By using the potassium niobate layer 13, a piezoelectric thin film resonator 200 having a higher electromechanical coupling coefficient can be obtained, as described below.
Also, according to the present embodiment, after forming a potassium niobate layer 13, which requires the temperature of about 600-800° C., the substrate temperature is once lowered to, for example, about 300° C. or below, and then an electrode layer 14 is formed, and further a second substrate 15 can be bonded to the electrode layer 14. In this manner, after the potassium niobate layer 13 is formed, a process that exposes the potassium niobate layer 13 to a high temperature is not required. Accordingly, compositions of the electrode layer 14 would not deteriorate the potassium niobate layer through diffusion.
1.4. Experimental Examples
(1) First, a first experimental example is described. In the present experimental example, a potassium niobate deposited body 100 was formed according to a method described below. In the present experimental example, a thin film of polycrystal potassium niobate in a single phase could be obtained.
First, a substrate 11 composed of an R-plane sapphire single crystal plate was degreased and washed through soaking the substrate 11 in an organic solvent with an ultrasonic washing machine. As the organic solvent, a 1:1 mixed solution of ethyl alcohol and acetone was used. After loading the substrate 11 onto a substrate holder, it was introduced together with the substrate holder in a vacuum apparatus whose back pressure at room temperature was 1×10−8 Torr, oxygen gas was introduced such the oxygen partial pressure became 5×10−5 Torr, and then the substrate was heated to elevate its temperature to 400° C. at a rate of 20° C./minute with an infrared ray lamp.
Next, a pulsed beam of KrF excimer laser (with a wavelength of 248 nm) was injected in a surface of a magnesium target under conditions with an energy density being 2.5 J/cm2, a frequency being 10 Hz, and a pulse length being 10 ns, thereby generating a plasma plume of magnesium on the target surface. The plasma plume was irradiated to the substrate 11 under conditions with a substrate temperature being 400° C. and an oxygen partial pressure being 5×10−5 Torr, whereby a buffer layer 12 consisting of MgO was formed. The target-to-substrate distance was 70 mm, the irradiation time was 30 minutes, and the film thickness of the buffer layer 12 was 10 nm.
Next, a pulsed beam of KrF excimer laser was injected in a surface of a K0.6Nb0.4Oy target under conditions with an energy density being 3 J/cm2, a frequency being 10 Hz, and a pulse length being 10 ns, thereby generating a plasma plume of K, Nb and O on the target surface. The plasma plume was irradiated to the substrate 11 under conditions with a substrate temperature being 750° C. and an oxygen partial pressure being 1×10−1 Torr, whereby a pottasium niobate layer 13 was formed on the buffer layer 12. The target-to-substrate distance was 70 mm, the irradiation time was 240 minutes, and the film thickness of the potassium niobate layer 13 was of 1 μm.
An X-ray diffraction pattern (2θ-θ scanning) of the potassium niobate layer 13 obtained in the present experimental example is shown in FIG. 6. All peaks shown in the X-ray diffraction pattern of FIG. 6 belong to sapphire and potassium niobate, and peaks belonging to other compounds are not observed. Therefore, it was confirmed that the potassium niobate obtained in the present experimental example was polycrystalline but in a single phase.
Next, after the temperature of the substrate was lowered to 300° C., a pulsed beam of KrF excimer laser was injected in a surface of a SrRuO3 target under conditions with an energy density being 3 J/cm2, a frequency being 10 Hz, and a pulse length being 10 ns, thereby generating a plasma plume of Sr, Ru and O. The plasma plume was irradiated to the substrate 11 under conditions with a substrate temperature being 300° C., and an oxygen partial pressure being 1×10−2 Torr, whereby an electrode layer 14 consisting of a SrRuO3 layer was formed. The distance between the target and the substrate 11 was 70 mm, the irradiation time was 60 minutes, and the film thickness of the electrode layer 14 was 100 nm.
Then, a second substrate 15 composed of silicon was bonded to the electrode layer 14 by using an adhesive (epoxy adhesive), whereby a potassium niobate deposited body 100 (see FIG. 2) was obtained.
Then, the potassium niobate deposited body 100 obtained was soaked in a phosphoric acid solution to etch the buffer layer 12 consisting of MgO, whereby the substrate 11 was separated. In this manner, a potassium niobate deposited body 100 (see FIG. 3) in which the electrode layer 14 and the potassium niobate layer 13 are successively deposited on the second substrate 15 was obtained.
(2) Next, a second experimental example is described. In the present experimental example, a potassium niobate deposited body 100 is formed in the following manner. In the experimental example, a thin film of single crystal potassium niobate was obtained.
First, a substrate 11 composed of an R-plane sapphire single crystal substrate was degreased and washed, in a similar manner as the first experimental example. Next, in a manner similar to the first experimental example, after loading the substrate 11 onto a substrate holder, it was introduced together with the substrate holder in a vacuum apparatus, oxygen gas was introduced, and then the substrate was heated to elevate its temperature to 400° C. At this time, in a pattern obtained by the reflection high speed electron beam diffraction (Reflection High Energy Electron Diffraction (RHEED)) in a sapphire [11-20] direction, kikuchi lines and strong reflection points characteristic to a single crystal were observed.
Next, a pulsed beam of KrF excimer laser with a frequency being 20 Hz was injected in a surface of a magnesium target, thereby generating a plasma plume of magnesium on the target surface. In this instance, the energy density, pulse length, and wavelength were the same as those of the first experimental example, respectively. The plasma plume was irradiated to the substrate 11, whereby a buffer layer consisting of MgO was formed thereon. In this instance, the substrate temperature, oxygen partial pressure, target-to-substrate distance, irradiation time, film thickness were the same as those of the first experimental example, respectively.
A RHEED pattern in a sapphire [11-20] direction of the deposited body thus obtained was investigated. A diffraction pattern appeared in this RHEED pattern, and it was confirmed that the buffer layer 12 composed of MgO had undergone epitaxial growth.
Further, an X-ray diffraction pattern (2θ-θ scanning) of the buffer layer 12 composed of MgO in the deposited body is shown in FIG. 7. As shown in FIG. 7, no peak other than the peaks of the substrate 11 was observed. X-ray diffraction patterns (ω scanning) obtained when the value 2θ was fixed at MgO (200) (2θ=42.92° when a=0.4212 nm) are shown in FIG. 8 and FIG. 9. When the rotation axis of the ω scanning was in parallel with the sapphire [11-20], a peak shifted by 9.2° from the center was observed as shown in FIG. 8. When the rotation axis of the ω scanning was in parallel with the sapphire [−1101], no peak was observed, as shown in FIG. 9. Based on these results, it was confirmed that an MgO (100) film tilted by about 9° from the substrate 11 had undergone epitaxial growth.
Next, a pulsed beam of KrF excimer laser was injected in a surface of a K0.67Nb0.33Oy target under conditions with an energy density being 2 J/cm2, thereby generating a plasma plume of K, Nb and O on the target surface. In this instance, the frequency and pulse length were the same as those of the first experimental example. The plasma plume was irradiated to the substrate 11 under conditions with a substrate temperature being 600° C. and an oxygen partial pressure being 1×10−2 Torr, whereby a pottasium niobate layer 13 was formed on the buffer layer 12. The film thickness of the potassium niobate layer 13 was 0.5 μm. Also, the target-to-substrate distance, and irradiation time were the same as those of the first experimental example.
A RHEED pattern in a sapphire [11-20] direction of the deposited body thus obtained was investigated. A clear diffraction pattern appeared in this RHEED pattern, and it was confirmed that the potassium niobate had undergone epitaxial growth.
Further, an X-ray diffraction pattern (2θ-θ scanning) of the potassium niobate (KNbO3) layer 13 of the deposited body is shown in FIG. 10. As shown in FIG. 10, peaks of KNbO3 (100)pc, and KNbO3 (200)pc were observed, as KNbO3 is expressed by plane index of pseudo cubic. Accordingly, it was confirmed that KNbO3 was (100)pc oriented. X-ray diffraction patterns (ω scanning) of KNbO3 (200)pc (2θ=45.12°) are shown in FIG. 11 and FIG. 12. When the rotation axis of the ω scanning was in parallel with the sapphire [11-20], a peak shifted by 6.3° from the center was observed as shown in FIG. 11. When the rotation axis of the ω scanning was in parallel with the sapphire [−1101], no peak was observed, as shown in FIG. 12. Based on these results, it was confirmed that a KNbO3 (100)pc film tilted by about 6° from the substrate 11 grew.
Moreover, when X-ray diffraction pole figures were investigated, the results shown in FIG. 13-FIG. 15 were obtained. FIG. 13, FIG. 14 and FIG. 15 are X-ray diffraction pole figures of sapphire (0006) (2θ=41.7°), MgO (202) (2θ=62.3°), and KNbO3 (101)pc (2θ=31.5°), respectively. As shown in FIG. 14 and FIG. 15, spots of MgO (202) and KNbO3 (101)pc both indicate symmetry four times, and it was found that orientations of epitaxial growth were in relation of KNbO3 (100)pc/MgO (100)/sapphire (1-102) in inter-plane, and KNbO3 [010]pc//MgO [010]//sapphire [11-20] in in-plane. Also, as shown in FIG. 14 and FIG. 15, the centers of these four spots are shifted from the center of the pole figure (Psi=0 degree) in the sapphire [−1101] direction by about 9 degrees and about 6 degrees, respectively. They coincide with the shift amounts in the ω scanning described above. Accordingly, it was confirmed that the buffer layer 12 composed of MgO epitaxially grew with its (100) plane tilted with a [11-20] direction vector as a rotation axis by about 9 degrees with respect to the R-plane of the substrate 11, and the potassium niobate layer 13 epitaxially grew with its (100) plane in a pseudo cubic expression tilted with a [11-20] direction vector as a rotation axis by about 6 degrees with respect to the R-plane of the substrate 11.
Also, Raman scattering spectra were measured, and results shown in FIG. 16 and FIG. 17 were obtained. FIG. 16 and FIG. 17 correspond to the geometry of z (x, x)−z, and x (x, y)−z, respectively. The formula indicating the geometry means “the direction of momentum of incident light (polarization direction of incident light, polarization direction of scattering light)−the direction of momentum of scattering light.” In the geometry of z (x, x)−z, as shown in FIG. 16, peaks of the A1 vibration mode near 280 cm−1 and 600 cm−1 are strongly observed, but peaks of the B1 vibration mode near 250 cm−1 and 530 cm−1 are hardly observed. On the other hand, in the geometry of z (x, y)−z, as shown in FIG. 17, peaks of the B1 vibration mode near 250 cm−1 and 530 cm−1 are strongly observed, but peaks of the A1 vibration mode near 280 cm−1 and 600 cm−1 are hardly observed. In other words, the peak intensities of the A1 vibration mode and the B1 vibration mode are reversed between the case of the geometry of z (x, y)−z, and the case of the geometry of z (x, x)−z.
From these results, a consideration was made as to which one of domains that can be obtained in a pseudo cubic (100) orientation, namely, an orthorhombic (101) domain or an orthorhombic (010) domain (orthorhombic b-axis orientation domain), is predominant. Table 1 shows selection rules of phonon mode which are observed in Raman scattering spectra obtained for the respective domain structures based on the space groups. It is noted that “O” in Table 1 indicates being observable, and “N” indicates being unobservable.














TABLE 1





Domain
Geometric
B1(T0)
A1(T0)
A2
B1(T0)
A1(T0)
A1(L0)


Structure
Condition
249 cm−1
281.5 cm−1
282 cm−1
534 cm−1
606.5 Cm−1
834 cm−1







(010)
z(x, x) − z
N
O
N
N
O
N


Domain
z(x, y) − z
O
N
N
O
N
N


(101)
z(x, x) − z
O
O
O
O
O
O


Domain
z(x, y) − z
O
O
O
O
O
O









When the polarization plane of incident light and the polarization plane of scattering light are set in parallel with each other or orthogonal to each other, the polarization axis becomes to be in parallel with or orthogonal to the electric field of the incident light, respectively, in the case of the (010) domain, and therefore one of the A1 and B1 modes is selectively observed. On the other hand, in the case of the (101) domain, the polarization axis is positioned twisted with respect to the electric field of the incident light, and therefore both of the A1 and B1 modes are observed together without regard to the orientation of the polarization plane. Accordingly, the results shown in FIG. 16 and FIG. 17 coincide with the selection rules of the peaks obtained based on the assumption that the (010) domain (orthorhombic b-axis orientation domain) is predominant, and this indicates that the obtained potassium niobate layer 13 is composed of an orthorhombic b-axis orientation domain.
Furthermore, based on the results of measurement of Raman scattering spectra, and the results of measurement of X-ray diffractions described above, it was confirmed that the b-axis of orthorhombic potassium niobate tilts, with a [11-20] direction vector as a rotation axis, with respect to the R-plane of the substrate 11.
Next, the substrate temperature was reduced to 300° C., and then an electrode layer 14 composed of SrRuO3 was formed under the same conditions as those of the first experimental example.
Next, a second substrate 15 composed of silicon was bonded to the electrode layer 14 with an adhesive (epoxy adhesive), whereby a potassium niobate deposited body 100 (see FIG. 2) was obtained.
Then, the potassium niobate deposited body 100 obtained was soaked in a phosphoric acid solution to etch the buffer layer 12 consisting of MgO, whereby the substrate 11 was separated. In this manner, a potassium niobate deposited body 100 (see FIG. 3) in which the electrode layer 14 and the potassium niobate layer 13 are successively deposited on the second substrate 15 was obtained.
2. Second Embodiment
2.1. Next, an example of a piezoelectric thin film resonator in accordance with a second embodiment of the invention is described with reference to the accompanying drawings. FIG. 18 is a cross-sectional view schematically showing a piezoelectric thin film resonator 200 in accordance with the present embodiment. In FIG. 18, members that are substantially the same as the members of the potassium niobate deposited body 100 shown in FIG. 3 are appended with the same reference numbers, and their detailed description is omitted.
The piezoelectric thin film resonator 200 includes a second substrate 15 having a void section 15a, an electrode layer (hereafter also referred to as a “first electrode layer”) 14 formed on the second substrate 15, a potassium niobate layer 13 formed on the first electrode layer 14, and a second electrode layer 16 formed on the potassium niobate layer 13. Further, the first electrode layer 14 and the second electrode layer 16 are located at least above the void section 15a. The first electrode layer 14 is exposed through the void section 15a. 
The piezoelectric thin film resonator 200 of the present embodiment is formed through processing a potassium niobate deposited body in accordance with an embodiment of the present invention, for example, the potassium niobate laminated body 100 shown in FIG. 3, as described below. Accordingly, the potassium niobate layer 13 that composes the piezoelectric thin film resonator 200 has the same characteristics as those of the potassium niobate layer 13 of the potassium niobate laminated body 100. The potassium niobate layer 13 is composed of single crystal or polycrystal potassium niobate, as described above.
For the second electrode layer 16, a material similar to that of the first electrode 14 can be used. For example, Pt, Ir, Al, Au, Cu or the like may preferably be used.
2.2. The piezoelectric thin film resonator 200 in accordance with the present embodiment may be formed by using a potassium niobate deposited body in accordance with an embodiment of the invention, for example, as follows.
First, a resist layer (not shown) is formed by a lithography technique and an etching technique on the surface of the second substrate 15 of the potassium niobate deposited body 100 shown in FIG. 3. The resist layer has an opening section in an area where a void section 15a is to be formed. Then, by using the resist layer as a mask, the second substrate 15 is anisotropically etched to form a void section 15a. As the anisotropic etching, for example, a known dry etching method can be used.
Then, a second electrode layer 16 is formed on the potassium niobate layer 13 by using, for example, a sputter method and a lift-off method. At this time, the second electrode layer 16 is formed to be located above the void section 15a, and to cover the void section 15a as viewed in a plan view.
2.3. The piezoelectric thin film resonator in accordance with the present embodiment has a potassium niobate deposited body in accordance with an embodiment of the invention. Therefore, in accordance with the present embodiment, a piezoelectric thin film resonator having a high electromechanical coupling coefficient can be realized.
2.4. Next, an example of experiments conducted on the piezoelectric thin film resonator 200 in accordance with the present embodiment is described below.
(1) A piezoelectric thin film resonator 200 in accordance with a first experimental example was formed by using the potassium niobate deposited body 100 of the first experimental example in accordance with the first embodiment described above. The potassium niobate deposited body 100 had a polycrystal potassium niobate layer 13 in a single phase.
Piezoelectric vibration between the first electrode 14 and the second electrode 16 was measured with the piezoelectric thin film resonator 200 obtained. As a result, an acoustic velocity obtained based on resonance frequency was 5000 m/s. Also, an electromechanical coupling coefficient obtained from resonance frequency and antiresonant frequency was 30%.
Also, a piezoelectric thin film resonator 200 using potassium sodium niobate tantalate solid solution (K1-xNaxNb1-yTayO3(0<x<1,0<y<1)) instead of potassium niobate provided similar effects.
(2) A piezoelectric thin film resonator 200 in accordance with a second experimental example was formed by using the potassium niobate deposited body 100 of the second experimental example in accordance with the first embodiment described above. The potassium niobate deposited body 100 had a single crystal potassium niobate layer 13. The potassium niobate layer includes an orthorhombic b-axis orientation domain, and the b-axis titles, with a [11-20] direction vector as a rotation axis, with respect to the R-plane of the substrate 11.
Piezoelectric vibration between the first electrode 14 and the second electrode 16 was measured with the piezoelectric thin film resonator 200 obtained. As a result, an acoustic velocity obtained based on resonance frequency was 5000 m/s. Also, an electromechanical coupling coefficient obtained from resonance frequency and antiresonant frequency was 40%. As compared to the electromechanical coupling coefficient (30%) obtained when the polycrystal potassium niobate layer 13 was used (in the case of the first experimental example), it became clear that the electromechanical coupling coefficient improved when the single crystal potassium niobate layer 13 was epitaxially grown with its b-axis tilted.
3. Third Embodiment
Next, examples of an oscillator and a frequency filter in accordance with a third embodiment of the invention are described with reference to the accompanying drawings. FIG. 19 is a diagram of a circuit structure of an oscillator 250 in accordance with an embodiment of the invention. It is noted that “IN,” “OUT,” and “Vp” indicated in FIG. 19 mean a control input signal, an oscillation output, and a power supply voltage, respectively.
As shown in FIG. 19, the oscillator 250 has a frequency variable type piezoelectric thin film resonator 200 (see FIG. 18). The oscillator 250 may be, for example, a voltage controlled oscillator (VCO). As shown in FIG. 19, a Colpitts type oscillator 250 is formed from a transistor Tr and several passive components around the transistor. The base of the transistor Tr is connected to one of the electrode layers of the piezoelectric thin film resonator 200 through a capacitor C300. The other electrode layer of the piezoelectric thin film resonator 200 is grounded. When a DC voltage for frequency control is impressed to the piezoelectric thin film resonator 200 through a resister R1, the resonant frequency and antiresonant frequency change according to the magnitude of the voltage. The oscillation frequency of the oscillator 250 is determined according to these frequencies and the capacitances of capacitors C1, C2 and C3. Therefore, by impressing a voltage to the piezoelectric thin film resonator 200, the oscillation frequency of the oscillator 250 can be changed. In other words, the oscillation frequency of the oscillator 250 can be controlled by the voltage impressed to the piezoelectric thin film resonator 200.
The oscillator 250 can be employed, for example, as a VCO of a PLL circuit shown in FIG. 20. FIG. 20 is a block diagram showing the basic structure of a PLL circuit. The PLL circuit is formed from a phase comparator 71, a low band filter 72, an amplifier 73 and a VCO 74. The phase comparator 71 compares the phases (or frequencies) of signals inputted from an input terminal 70 and outputted from the VCO 74, and outputs an error voltage signal, the value of which is set according to the difference between these signals. The low band filter 72 transmits only the low frequency components at the position of the error voltage signal outputted from the phase comparator 71. The amplifier 73 amplifies the signal outputted from the low band filter 72. The VCO 74 is an oscillator circuit in which the oscillation frequency is continuously changed within a certain range, corresponding to the voltage value inputted.
The PLL circuit having such a structure operates so as to decrease the difference between the phases (or frequencies) inputted from the input terminal 70 and outputted from the VCO 74, and synchronizes the frequency of the signal outputted from the VCO 74 with the frequency of the signal inputted from the input terminal 70. When the frequency of the signal outputted from the VCO 74 and the frequency of the signal inputted from the input terminal 70 are synchronized with each other, the PLL circuit outputs a signal that matches with the signal inputted from the input terminal 70 after excluding a specific phase difference, and conforms to the changes in the input signal.
Furthermore, a frequency filter can be formed with the piezoelectric thin film resonator 200 (see FIG. 18). The frequency filter may include, for example, a plurality of frequency-variable type piezoelectric thin film resonators 200 and frequency control terminals. When a DC voltage is applied to the frequency control terminals, the DC voltage is impressed to each of the piezoelectric thin film resonators 200, such that the resonance frequency and antiresonant frequency of each of the piezoelectric thin film resonators 200 change accordingly. Therefore, the pass frequency band of the frequency filter can be changed by impressing a voltage to the frequency control terminals. In other words, the pass frequency band of the frequency filter can be changed by a voltage impressed to the frequency control terminals.
As described above, frequency filters and oscillators in accordance with the present embodiment have piezoelectric thin film resonators having a high electromechanical coupling coefficient in accordance with an embodiment of the invention. Therefore, in accordance with the present embodiment, miniaturization of frequency filters and oscillators can be realized.
4. Fourth Embodiment
4.1. Next, first examples of an electronic circuit and an electronic apparatus in accordance with a fourth embodiment of the invention are described with reference to the accompanying drawings. FIG. 21 is a block diagram showing an electrical structure of an electronic circuit 300 in accordance with the embodiment. It is noted that the electronic apparatus 300 may be, for example, a cellular phone.
The electronic apparatus 300 has an electronic circuit 310, a transmitter 80, a receiver 91, an input section 94, a display section 95, and an antenna section 86. The electronic circuit 310 has a transmission signal processing circuit 81, a transmission mixer 82, a transmission filter 83, a transmission power amplifier 84, a transceiver wave divider 85, a low noise amplifier 87, a reception filter 88, a reception mixer 89, a reception signal processing circuit 90, a frequency synthesizer 92, and a control circuit 93.
In the electronic circuit 310, the frequency filters described above can be used as the transmission filter 83 and the reception filter 88. The frequency that is filtered (i.e., the frequency which is permitted to pass through the filter) is set separately at the transmission filter 83 and the reception filter 88 according to the required frequency in the signal outputted from the transmission mixer 82 and the required frequency at the reception mixer 89. As the VCO 74 of the PLL circuit (see FIG. 20) that is provided within the frequency synthesizer 92, the oscillator shown in FIG. 19 can be used.
The transmitter 80 can be realized, for example, with a microphone which converts sound wave signals into electric signals. The transmission signal processing circuit 81 is a circuit for performing such processing as D/A conversion, modulation, etc. on the electric signal to be outputted from the transmitter 80. The transmission mixer 82 mixes the signal outputted from the transmission signal processing circuit 81 using the signal outputted from the frequency synthesizer 92. The transmission filter 83 permits passage of only those signals of the required frequency from among the intermediate frequencies (hereafter referred to as “IF”), and cuts unnecessary frequency signals. The signal outputted from the transmission filter 83 is converted to an RF signal by a converting circuit (not shown). The transmission power amplifier 84 amplifies the power of the RF signal outputted from the transmission filter 83 and outputs this amplified result to the transceiver wave divider 85.
The transceiver wave divider 85 transmits the RF signal that is outputted from the transmission power amplifier 84 through the antenna section 86 in the form of radio waves. Also, the transceiver wave divider 85 divides the reception signal received by the antenna 86, and outputs the result to the low noise amplifier 87. The low noise amplifier 87 amplifies the reception signal from the transceiver wave divider 85. It is noted that the signal outputted from the low noise amplifier 87 is converted to IF by a converting circuit (not shown).
The reception filter 88 permits passage of only those signals with the required frequency from among the IF that were converted by a converting circuit (not shown), and cuts unnecessary frequency signals. The reception mixer 89 uses the signal outputted from the frequency synthesizer 92 to mix the signals outputted from the reception filter 88. The reception signal processing circuit 90 performs such processing as A/D conversion, demodulation, etc., to the signal outputted from the reception mixer 89. The receiver 91 is realized with, for example, a small speaker or the like which converts electrical signals into sound waves.
The frequency synthesizer 92 is a circuit that generates the signal to be supplied to the transmission mixer 82 and the signal to be supplied to the reception mixer 89. The frequency synthesizer 92 is equipped with a PLL circuit. The frequency synthesizer 92 divides the signal outputted from this PLL circuit and can generate a different signal. The control circuit 93 controls the transmission signal processing circuit 81, the reception signal processing circuit 90, the frequency synthesizer 92, the input section 94, and the display section 95. The display section 95 displays, for example, the device status to the user of the cellular phone. The input section 94 is provided, for example, for the user of the cellular phone to input directions.
4.2. Next, second examples of an electronic circuit and an electronic apparatus in accordance with the fourth embodiment of the invention are described with reference to the accompanying drawings. In the present embodiment, a reader/writer 2000 and a communications system 3000 using the same are described as examples of an electronic apparatus. FIG. 22 is a view showing the communications system 3000 that uses the reader/writer 2000 in accordance with the present embodiment, and FIG. 23 is a schematic block diagram of the communications system 3000 shown in FIG. 22.
As shown in FIG. 22, the communications system 3000 includes the reader/writer 2000 and a contactless information medium 2200. The reader/writer 2000 transmits a radio wave W (hereafter also referred to as a “career”) having a carrier frequency fc to the contactless information medium 2200 or receives the same from the contactless information medium 2200, to thereby communicate with the contactless information medium 2200 by using radio communications. The radio wave W can use any carrier frequency fc in an arbitrary frequency band. As shown in FIG. 22 and FIG. 23, the reader/writer 2000 has a main body 2105, an antenna section 2110 located on the top surface of the main body 2105, a control interface section 2120 stored in the main body 2105, and a power supply circuit 172. The antenna section 2110 and the control interface section 2120 are electrically connected to each other by a cable 2180. Further, although not shown, the reader/writer 2000 is connected to an external host apparatus (processor apparatus, etc.) through the control interface section 2120.
The antenna section 2110 has a function to communicate information with the contactless information medium 2200. The antenna section 2110 has a prescribed communication area (area shown by a dotted line), as shown in FIG. 22. The antenna section 2110 is composed of a loop antenna 112 and a matching circuit 114.
The control interface section 2120 includes a transmission section 161, a damping oscillation cancellation section (hereafter, referred to as a “cancellation section”) 165, a reception section 168, and a controller 160.
The transmission section 161 modulates data transmitted from an external unit (not shown), and transmits the same to a loop antenna 112. The transmission section 161 has an oscillation circuit 162, a modulation circuit 163, and a driving circuit 164. The oscillation circuit 162 is a circuit for generating a carrier with a predetermined frequency. The oscillation circuit 162 is usually formed with a quartz oscillator or the like. By using the oscillator in accordance with the embodiment described above, its communication frequency can be improved to a higher frequency and its detection sensitivity can be improved. The modulation circuit 163 is a circuit that modulates the carrier according to information given. The driving circuit 164 receives the modulated career, amplifies its electric power, and drives the antenna section 2110.
The cancellation section 165 has a function to control a damped oscillation generated by the loop antenna 112 of the antenna section 2110 which occurs with ON/OFF of the career. The cancellation section 165 includes a logic circuit 166 and a cancellation circuit 167.
The reception section 168 includes a detection section 169 and a demodulator circuit 170. The reception section 168 demodulates a signal that is transmitted from the contactless information medium 2200. The detection section 169 detects a change in the current that circulates in the loop antenna 112. The detection section 169 may include, for example, an RF filter. As the RF filter, a quartz oscillator or the like may be used. By using the frequency filter in accordance with the embodiment described above, the communication frequency can be improved to a higher frequency, the detection sensitivity can be improved, and miniaturization becomes possible. The demodulator circuit 170 demodulates the changed portion detected by the detection section 169.
The controller 160 retrieves information from the demodulated signal, and transfers the same to an external device. The power supply circuit 172 receives the supply of an electric power from outside, appropriately converts the voltage, and supplies a necessary electric power to each circuit. It is noted that a built-in battery may be used as the power source.
The contactless information medium 2200 communicates with the reader/writer 2000 by using electromagnetic waves (radio waves). As the contactless information medium 2200, for example, a contactless IC tag, a contactless IC card or the like can be enumerated.
Next, operations of the communication system 3000 that uses the reader/writer 2000 in accordance with the present embodiment are described. When data is sent to the contactless information medium 2200 from the reader/writer 2000, if the data is sent from an external device (not shown), the data is processed by the controller 160 in the reader/writer 2000 and sent to the transmission section 161. In the transmission section 161, a high frequency signal of constant amplitude is supplied from the oscillation circuit 162 as a career, the career is modulated by the modulation circuit 163, and a modulated high frequency signal is outputted. The modulated high frequency signal outputted from the modulation circuit 163 is supplied to the antenna section 2110 through the driving circuit 164. At the same time, the cancellation section 165 generates a predetermined pulse signal in synchronism with an OFF timing of the modulated high frequency signal, to thereby contribute to the control of the damping oscillation in the loop antenna 112.
In the contactless information medium 2200, the modulated high frequency signal is supplied through an antenna section 186 to a reception circuit 180. Also, the modulated high frequency signal is supplied to a power supply circuit 182, and a predetermined power supply voltage necessary for each section of the contactless information medium 2200 is generated. The data outputted from the reception circuit 180 is demodulated and supplied to a logic control circuit 184. The logic control circuit 184 operates based on the output of a clock 183, processes the supplied data, and writes certain data in a memory 185.
When data is sent from the contactless information medium 2200 to the reader/writer 2000, the following operations take place. In the reader/writer 2000, a high frequency signal of constant amplitude is outputted from the modulation circuit 163 without being modulated. The high frequency signal is sent to the contactless information medium 2200 through the driving circuit 164 and the loop antenna 112 of the antenna section 2110.
In the contactless information medium 2200, data read from the memory 185 is processed by the logic control circuit 184, and supplied to a transmission circuit 181. The transmission circuit 181 may have a switch, wherein the switch turns ON and OFF according to “1” and “0” bit of the data.
In the reader/writer 2000, when the switch of the transmission circuit 181 turns ON and OFF, the load on the loop antenna 112 of the antenna section 2110 changes. Therefore, the amplitude of the high frequency current that circulates in the loop antenna 112 changes. In other words, the high frequency current is amplitude-modulated by the data supplied from the contactless information medium 2200. The high frequency current is detected by the detection section 169 of the reception section 168, and demodulated by the demodulation circuit 170 whereby data is obtained. The data is processed by the controller 160, and transmitted to an external apparatus or the like.
4.3. Electronic circuits and electronic apparatuses in accordance with the embodiment of the invention have piezoelectric thin film resonators having a high electromechanical coupling coefficient in accordance with the embodiment of the invention. Therefore, in accordance with the present embodiment, power saving of electronic circuits and electronic apparatuses can be achieved.
The embodiments of the invention are described above in detail. However, those skilled in the art should readily understand that many modifications can be made without substantially departing from the novel matter and effects of the invention. Accordingly, all of such modified examples are also included in the scope of the invention.
For example, frequency filters and oscillators in accordance with the embodiments of the invention are also applicable to wide-band filters and VCOs in UWB systems, cellular phones, and wireless LAN.
For example, in the embodiments described above, a cellular phone and a communications system using a reader/writer device are described as examples of electronic apparatuses, and electronic circuits installed in the cellular phone and the reader/writer device are described as examples of electronic circuits. However, the invention is not limited to those described above, and is applicable to various mobile telecommunications equipment and electronic circuits installed therein. For example, the invention is also applicable to floor type telecommunications equipment such as tuners that receive BS (Broadcast Satellite) broadcasting and electronic circuits installed therein, and also applicable to electronic equipment such as HUB or the like that use optical signals that propagate in optical cables and electronic circuits installed therein.

## Claims

1. A potassium niobate deposited body comprising:
a substrate composed of an R-plane sapphire substrate;
a buffer layer formed above the substrate;
a potassium niobate layer or a potassium niobate solid solution layer formed above the buffer layer; and
an electrode layer above the potassium niobate layer or the potassium niobate solid solution layer,
wherein the potassium niobate layer or the potassium niobate solid solution layer epitaxially grows in a (100) orientation in a pseudo cubic system expression, and a (100) plane of the potassium niobate layer or the potassium niobate solid solution layer tilts with a [11-20] direction vector as a rotation axis with respect to an R-plane (1-102) of the R-plane sapphire substrate.

2. A piezoelectric thin film resonator comprising the potassium niobate according to claim 1.

3. A frequency filter comprising the piezoelectric thin film resonator according to claim 2.

4. An oscillator comprising the piezoelectric thin film resonator according to claim 2.

5. An electronic circuit comprising at least one of the frequency filter recited in claim 3 or the oscillator recited in claim 4.

6. An electronic apparatus comprising the electronic circuit recited in claim 5.