JP2007071757A - Vibrating body and vibration gyroscope using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibrating body and a vibration gyroscope, which are highly sensitive and can prevent destruction of environment, and whose outputs and sensitivity are excellent in temperature stability. <P>SOLUTION: The vibration body comprises: a substrate; at least two arm sections extending from the substrate; a driving-use piezo-electric vibrating element and a driving-use electrode which are disposed on the main face or the side face of the arm sections in order to bend and vibrate the arm sections; and a detection-use piezo-electric vibrating element and a detection-use electrode which detect the vibration in a direction perpendicular to the plane of above bending vibration excited by the driving-use piezo-electric vibrating element. The driving-use piezo-electric vibrating element and the detection-use piezo-electric vibrating element are made of a ferroelectric material in a bismuth layer-shaped structure having anisotropic crystal grain. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vibrating gyroscope comprising a vibrating body for detecting a rotational angular velocity for posture control or camera shake correction of a vehicle-mounted car navigation system, a robot, an aircraft, an automobile, and the like.

  Vibrating gyros are inferior in sensitivity and resolution to ring-rate gyros and fiber optic gyros that make use of optical interference, but have medium-precision performance, a simple structure, and a small number of parts, so they are small and inexpensive. is there. Piezoelectric vibration gyros are expanding the market for consumer use such as rotational angular velocity sensors for automobile navigation, hand-held camera, still camera, and camera shake detection for digital cameras.

In general, the Coriolis force Fc generated when a mass point that makes a single vibration rotates is expressed by the following equation.
Fc = -2mvΩ
Here, m is the mass of the vibrating gyroscope, v is the vibrating velocity of the vibrating gyroscope, and Ω is the angular velocity around the Z axis of the vibrating gyroscope.

  If the mass m and the vibration velocity v are known, the angular velocity Ω can be derived. In the vibrating gyroscope, the displacement of the vibrating body due to the Coriolis force is detected by the electric charge generated in the detecting piezoelectric vibrating element.

  FIG. 11 is a perspective view showing an example of a conventional tuning fork type vibration gyro. The vibrating gyroscope includes a vibrating body 101. The vibrating body 101 is formed in a tuning fork shape with a base 102 in a rectangular parallelepiped shape and two arms 103a and 103b extending from the base 102 in the same direction. The vibrating body 101 is made of, for example, a metal such as silicon and a non-piezoelectric body, and the piezoelectric vibrating element 104 is formed on the main surface or side surface of the arm portion.

Composed of two components of _PbTiO 3, PbZrO3 containing lead as the main component of the piezoelectric vibrating element 104 PZT-based material and _{PbTiO 3, PbZrO 3, Pb (} Mg 0.5 Nb 0.5) is composed of components of TiO ₃ It is made up of materials. The vibrating body 101 is formed of a piezoelectric single crystal material such as quartz or a langasite-type piezoelectric body, and electrodes are formed on the main surface and side surfaces thereof.

  When the vibrating body 101 is formed of a piezoelectric single crystal material, an electrode is formed on the side surface of the vibrating body and an electrode facing the electrode is formed. In such a vibration gyro, the piezoelectric vibration element, the electrode, and the like are formed on a part of the main surfaces and side surfaces of the arm portions 103a and 103b, or formed on the main surfaces and side surfaces of the arm portions 103a and 103b.

  In this vibration gyro, when a drive signal is input to a drive electrode formed on the drive piezoelectric vibration element, the arm portions 103a and 103b bend and vibrate in the Y-axis direction so as to open and close. In this state, when an angular velocity Ω is applied around the Z axis parallel to the arm portions 103a and 103b, the vibration direction of the arm portions 103a and 103b is changed by the Coriolis force Fc and bends and vibrates in the X axis direction.

A signal corresponding to the change in the vibration direction of the arms 103a and 103b is output from the detection electrode. Therefore, a signal corresponding to the angular velocity Ω is obtained by measuring a signal output from the electrode formed on the piezoelectric detecting element for detection in accordance with a change in the vibration of the arm portions 103a and 103b corresponding to the Coriolis force Fc. Can do.

  As a conventional tuning fork type thin-film vibration gyro, the one described in Patent Document 1 is known. This thin film vibration gyro will be described with reference to FIG. FIG. 12 is a perspective view of a thin film vibrating gyroscope.

  In FIG. 12, a vibrating body 201 of a thin film vibration gyro is made of a non-piezoelectric material having two arm portions 202a and 202b, and driving thin film piezoelectric vibration elements 203a and 203b are respectively provided on the main surfaces of the arm portions 202a and 202b. Deploy. Lower electrodes 204a and 204b and upper electrodes 205a, 205b, 205c, and 205d are disposed on the thin film piezoelectric vibration elements 203a and 203b, respectively.

  By applying an AC voltage to the upper electrodes 205a, 205b, 205c, and 205d, the vibrating body 201 resonates. And the signal output from the electrode formed in the piezoelectric vibration element for a detection arrange | positioned at the main surface or the back surface is measured.

  The thin film piezoelectric vibration elements 203a and 203b and the detection piezoelectric vibration element are composed of a PZT system containing lead having a large piezoelectric constant and a piezoelectric single crystal thin film epitaxially grown on a substrate.

JP 2003-227719 A

  Piezoelectric single crystal materials and piezoelectric ceramic materials are widely applied to the piezoelectric vibrating elements for driving and detecting the vibrating body 201 constituting the conventional vibrating gyroscope. The piezoelectric single crystal material constituting the vibrating body 201 has a production cost higher than that of the piezoelectric ceramic material, is not suitable for mass production, and is difficult to process, so there is a limit to downsizing.

Further, the main component of the piezoelectric ceramic material constituting the conventional vibration body 201 is a compound containing _lead, PbTiO 3, PbZrO ₃ of 2 components configured PZT material and _{PbTiO 3, PbZrO 3, Pb (} Mg 0 _A material composed of three components of _0.5 Nb _0.5 ) TiO ₃ is used. These materials contain lead as much as 60% or more of their own weight in terms of lead oxide as a whole raw material. Therefore, in recent years, environmental destruction due to lead has been regarded as a problem, and thus lead-free piezoelectric ceramic materials are strongly demanded.

  Most of the lead-based piezoelectric ceramic materials have a low mechanical quality factor Q, and the sensitivity decreases when used as a driving piezoelectric material. Therefore, it is desirable to increase the mechanical quality factor Q of the piezoelectric material for driving, and since the mechanical quality factor Q of the material affects the start-up time, the mechanical quality factor Q of the piezoelectric material for driving can be freely set. It is convenient to be able to adjust.

  Piezoelectric ceramics have a crystal structure phase transition point, and the piezoelectricity disappears at that temperature. Lead-based piezoelectric ceramic materials have a crystal structure phase transition point at a relatively low temperature. In the case of PZT-based materials, the temperature is about 300 ° C., and the piezoelectricity deteriorates at a high temperature. Further, the temperature stability of the resonance frequency is inferior to that of the piezoelectric single crystal material in the temperature range of −25 degrees to +125 degrees, and the temperature stability of the output and sensitivity is deteriorated due to the change in the material characteristics of the piezoelectric material.

An object of the present invention is to provide a vibrating body that can prevent environmental destruction and has high sensitivity and excellent temperature stability of output and sensitivity, and a vibrating gyroscope using the vibrating body.

  In order to solve the above problems, a vibrating body according to the present invention includes a base portion, at least two arm portions extending from the base portion, and a main surface or a side surface of the arm portion for bending vibration of these arm portions. A vibrating body having a driving piezoelectric vibration element and a driving electrode provided, and a detection piezoelectric vibration element and a detection electrode for detecting vibration orthogonal to bending vibration excited by the driving piezoelectric vibration element. Each of the piezoelectric vibrating element and the detecting piezoelectric vibrating element is a bismuth layered structure ferroelectric having crystal grains having anisotropy.

  With this configuration, a material that does not contain lead can be used for the piezoelectric vibration element for driving and detecting the vibrating body, and environmental destruction can be prevented. In addition, since crystal grains have great anisotropy, crystal grains can be easily aligned in the same direction, providing a vibrator with high sensitivity and excellent temperature stability of output and sensitivity. it can.

  In addition, the crystal grains are characterized by having a substantially aligned state so that at least one axis is oriented in the same direction.

  With this configuration, the mechanical quality factor Q, the electromechanical coupling factor k, and the temperature characteristic TC-fr of the resonance frequency can be controlled. As a result, it is possible to provide a vibrating body with high sensitivity and excellent temperature stability of output and sensitivity.

Further, in the piezoelectric vibrating element for driving, the strongest peak intensity I ₀ when the piezoelectric vibrating element in which crystal grains are present at random is measured by the X-ray diffraction method, and the same angle as I ₀ on the plane parallel to the driving electrode. The ratio I _D / I ₀ with respect to the peak intensity I _{D at} 2θ is smaller than 1.0, and in the piezoelectric vibration element for driving, the crystal particles are in a c-axis direction perpendicular to the driving electrode from a state in which they are present at random. It is characterized by being arranged in large numbers.

  With this configuration, the mechanical quality factor Q can be improved and a vibrator having high sensitivity can be provided.

Further, in the piezoelectric vibration element for detection, the strongest peak intensity I ₀ when a piezoelectric vibration element in which crystal particles are randomly present is measured by the X-ray diffraction method, and the same angle as I _{0 on} a plane parallel to the detection electrode The ratio I _S / I ₀ to the peak intensity I _{S at} 2θ is smaller than 1.0, and in the piezoelectric vibrating element for detection, a and b are perpendicular to the detection electrode in a direction perpendicular to the detection electrode in a state where the crystal particles are randomly present. It is characterized by being arranged in a large amount in the axial direction.

  With this configuration, it is possible to improve the temperature characteristic TC-fr of the electromechanical coupling coefficient k and the resonance frequency, and it is possible to provide a vibrating body with excellent temperature stability of output and sensitivity.

  In order to solve the above problems, a vibrating gyroscope according to the present invention is characterized in that an angular velocity applied from the outside is detected using the vibrating body described above. With this configuration, it is possible to improve the mechanical quality factor Q, the electromechanical coupling factor k, the temperature characteristic TC-fr of the resonance frequency, and provide a vibration gyro with high sensitivity and excellent temperature stability of output and sensitivity. Can do.

  According to the present invention, it is possible to prevent environmental destruction, improve the mechanical quality factor Q, the electromechanical coupling factor k, the temperature characteristics of the resonance frequency, vibration with high sensitivity and excellent temperature stability of output and sensitivity. A body and a vibrating gyroscope using the body can be provided.

  FIG. 1 is a perspective view showing an example of a vibrating body according to the present invention. The vibrating body 1 includes a rectangular parallelepiped base 2. Two arms 3a and 3b are formed extending from the base 2 and spaced apart from each other. Driving lower electrodes 4a, 4b, 4c, and 4d are disposed on the arm portions 3a and 3b, respectively.

  Driving piezoelectric vibration elements 5a, 5b, 5c, and 5d made of a bismuth layer structure ferroelectric material are disposed on the lower electrodes 4a, 4b, 4c, and 4d, and the driving piezoelectric vibration elements 5a, 5b, 5c, and 5d are arranged on the driving electrodes. Upper driving electrodes 6a, 6b, 6c and 6d are formed. By applying AC voltage to the driving piezoelectric vibrating elements 5a, 5b, 5c, and 5d from the driving upper electrodes 6a, 6b, 6c, and 6d, the vibrating body 1 is excited and flexurally vibrates. The direction of bending vibration that opens and closes the arm portions 3a and 3b excited at this time is the in-plane direction.

  2 is a cross-sectional view of the arm portions 3a and 3b of the vibrator 1 of the present invention shown in FIG. Driving lower electrodes 4a, 4b, 4c, 4d are arranged, and driving piezoelectric vibrating elements 5a, 5b, 5c, which are made of a bismuth layered ferroelectric on the driving lower electrodes 4a, 4b, 4c, 4d, The upper electrodes 6a, 6b, 6c, 6d for driving are formed on the piezoelectric vibrators 5a, 5b, 5c, 5d for driving.

  The lower electrodes for detection 7a, 7b are arranged opposite to the upper electrodes for driving 6a, 6b, 6c, 6d, the lower electrodes for driving 4a, 4b, 4c, 4d and the piezoelectric vibrating elements for driving 5a, 5b, 5c, 5d, Detecting piezoelectric vibrating elements 8a and 8b made of a bismuth layer-structured ferroelectric having a different orientation axis from the driving piezoelectric vibrating elements 5a, 5b, 5c and 5d are disposed on the detecting lower electrodes 7a and 7b. Then, detection upper electrodes 9a and 9b are formed on the detection piezoelectric vibration elements 8a and 8b. The arm 3b and the arm 3a of the vibrating body 1 have the same structure.

The bismuth layer structure ferroelectric is represented by the chemical formula (Bi ₂ O ₂ ) ²⁺ (A _m−1 B _m O _{3m + 1} ) ²⁻ . However, A in the chemical formula represents 1, 2, and 3 valent ions entering the A site, represents rare earth elements such as Bi, Ba, Sr, and Ca, and combinations of these ions, and B in the chemical formula represents the B site. 4, 5, and 6-valent ions are included, and metal elements such as Ti, Nb, Ta, W, Fe, and Co and combinations of these ions are indicated, and m = 1 to 8 is an integer.

  Most of these compounds are ferroelectrics and have various characteristics, and thus are widely used for piezoelectric applications. Bismuth layer structure ferroelectrics are difficult to produce single crystals except for those with m = 2 and 3. A characteristic of bismuth layered structure ferroelectrics is that they have a large crystal structure anisotropy. FIG. 3 shows the crystal structure of a bismuth layer-structure ferroelectric having m = 3.

As shown in FIG. 3, the bismuth layer structure ferroelectric has (Bi ₂ O ₂ ) ²⁺ layer 10 with relatively coarse filling and (m−1) virtual perovskite lattices (ABO ₃ ) with close filling. ) Has a crystal structure 12 in which [(A _m-1 B _m O _{3m + 1} ) ^2- ] 11 are alternately stacked, and m represents the number of stacked oxygen octahedrons, and the bismuth layer structure ferroelectricity as a whole. Represents the unit cell 13 of the field. The major features of these crystal structures are that the a-axis lattice constant and the b-axis lattice constant are substantially the same, but the ratio of the c-axis lattice constant to the a-axis and b-axis lattice constants is very large. have.

As an example of the material of the piezoelectric vibration element used in the present invention, in Bi ₄ Ti ₃ O _{12 with} m = 3, the a-axis lattice constant is 5.46Å, the b-axis lattice constant is 5.46Å, and the c-axis lattice is The constant is 32.9 mm, and the c-axis is about 6 times the a-axis and b-axis. In Sr ₂ Bi ₄ Ti ₅ O _{18 with} m = 5, the c-axis lattice constant is 48.8．, and the c-axis is about 10 times the a-axis and b-axis. As m increases, the ratio of the c-axis lattice constant to the a-axis lattice constant tends to increase.
From 2 to 5, the c-axis lattice constant / a-axis lattice constant is about 4 to 10 times.

  The bismuth layered structure ferroelectric used as the driving piezoelectric vibrating elements 5a, 5b, 5c, 5d and the detecting piezoelectric vibrating elements 8a, 8b contains at least a bismuth metal element.

For example, CaBi ₂ Nb ₂ O ₉ , SrBi ₂ Nb ₂ O ₉ , BaBi ₂ Nb ₂ O ₉ , CaBi ₂ Ta ₂ O ₉ , SrBi ₂ Ta ₂ O ₉ , BaBi ₂ Ta ₂ O ₉ , Bi ₃ TiNbO ₉ , Bi _{3 TiTaO 9, Bi 4 Ti 3 O} 12, SrBi 3 Ti 2 NbO 12, BaBi 3 Ti 2 NbO 12, CaBi 4 Ti 4 O 15, SrBi 4 Ti 4 O 15, BaBi 4 Ti 4 O 15, Na 0.5 Bi _4.5 Ti ₄ O ₁₅ , K _0.5 Bi _4.5 Ti ₄ O ₁₅ , Ca ₂ Bi ₄ Ti ₅ O ₁₈ , Sr ₂ Bi ₄ Ti ₅ O ₁₈ , Ba ₂ Bi ₄ Ti ₅ O _18, etc. .

  As m increases, the anisotropy of the crystal structure increases and a greater degree of orientation F is obtained, so m = 2 or more is preferable.

  Bismuth layer structure ferroelectrics have large crystal anisotropy and are orthorhombic and have large spontaneous polarization in the a-axis direction and exhibit large piezoelectric characteristics. On the other hand, since the spontaneous polarization in the c-axis direction has a very small property, when many crystals are aligned in the c-axis direction, the amount of spontaneous polarization is small and the piezoelectric characteristics are small.

  FIG. 4A is a diagram showing a state in which the crystal grains 14 are not oriented. FIG. 4B is an enlarged view of part A in FIG. 2 and shows a state in which the crystal grains 14 are oriented in the c-axis direction. FIG. 4C is an enlarged view of part B of FIG. 2 and shows a state in which the crystal grains 14 are oriented in the a-axis and b-axis directions.

  The crystal particle 14 is a mass formed by combining several unit cells 13 of a bismuth layered structure ferroelectric. The crystal particles 14 can be observed with an electron microscope or the like, and it can be confirmed that the crystal particles 14 have a shape having a large aspect ratio between the vertically long and the horizontally long.

  In addition, the term “orientation” refers to a polycrystal or ceramic containing crystal grains 14 having dimensional anisotropy and crystallographic anisotropy, and the crystal grains 14 have their axes in the same plane. Shows the state of being aligned as a whole.

  FIG. 4A shows a normally baked piezoelectric vibration element 15 in which each of the crystal grains 14 has a random axial direction. Ordinarily fired bismuth layered structure ferroelectrics are non-oriented. The non-oriented state indicates a state where the directions of the a-axis, b-axis, and c-axis are randomly arranged in the same plane.

  FIG. 4B shows a state in which the crystal grains 14 are oriented in a larger proportion in the c-axis direction than the non-oriented piezoelectric vibration element 15 shown in FIG. Reference numeral 5a denotes a driving piezoelectric vibration element, and reference numerals 4a and 6a denote a lower electrode and an upper electrode, respectively. Thus, by arranging the crystal particles 14 of the driving piezoelectric vibration element 5a in the c-axis direction, the mechanical quality factor Q can be improved and a highly sensitive vibration body is obtained.

  FIG. 4C shows a state in which the crystal particles 14 are oriented in a larger proportion in the a and b axis directions than the non-oriented piezoelectric vibration element 15 shown in FIG. 8a is a piezoelectric vibration element for detection, and 7a and 9a are a lower electrode and an upper electrode, respectively. Thus, by arranging the crystal particles 14 of the driving piezoelectric vibration element 5a in the a and b axis directions, the electromechanical coupling coefficient k and the temperature characteristic TC-fr of the resonance frequency can be improved. It becomes a vibrating body with excellent temperature stability of output and sensitivity.

  As a method for orienting a bulk piezoelectric material, a hot forging (HF) method, a templated grain growth (TGG) method, and the like have been established. The HF method is a method in which a compact is fired while being pressed. With this method, an oriented ceramic with a high degree of orientation F can be obtained. The TGG method is a method in which ceramic crystal grains having anisotropy are mixed in advance before forming.

  As a method of orienting a thin film piezoelectric material, there is a method of epitaxial growth using a single crystal substrate. As a report example of piezoelectric characteristics, it has been clarified that the grain-oriented bismuth layer structure ferroelectric improves the electromechanical coupling coefficient k in the 33 mode to about twice that of a normal non-oriented piezoelectric vibration element. ing. Therefore, there is a possibility that the characteristics can be controlled depending on the orientation direction and degree of crystal grains.

  The method for producing the powder of the bismuth layer structure ferroelectric ceramic used as the driving piezoelectric vibrating elements 5a, 5b, 5c, 5d and the detecting piezoelectric vibrating elements 8a, 8b was performed in the following procedure. Bismuth oxide, titanium oxide, oxide compound and carbonate compound as starting materials are weighed in a predetermined amount, wet-ground and mixed with ethanol and zirconia balls for about 10 hours in a ball mill, dried for about 4 to 5 hours, and dried in a mortar Grind and mix for 1 hour.

  The mixed raw materials were molded and calcined at 850 ° C. to 900 ° C. for about 2 hours using an electric furnace to obtain a calcined powder. The calcined powder is pulverized and mixed in a mortar for 1 hour, and then wet-pulverized and mixed for about 20 hours in a ball mill together with ethanol and zirconia balls. The mixed raw materials are dried for 4 to 6 hours, and pulverized and mixed in a mortar for 1 hour.

A non-oriented piezoelectric vibration element is produced by pressing a ceramic powder with a die at a rate of about 40 to 50 kg / mm ² , firing at 900 ° C. to 1300 ° C. for about 2 hours using an electric furnace, Make it. The method for producing the driving piezoelectric vibrating elements 5a, 5b, 5c, 5d and the detecting piezoelectric vibrating elements 8a, 8b is a hot forging method in which a uniaxial pressure is applied during firing to obtain a high degree of orientation. To do.

Slip occurs on the c-plane of the bismuth layer structure ferroelectric, and finally a grain-oriented sample with the c-axis aligned in parallel with the direction in which pressure is applied is obtained. The particle-oriented sample is produced by compressive deformation by applying a uniaxial pressure at about 5 to 10 kg / mm ² during firing. By adjusting the applied pressure, the driving piezoelectric vibration elements 5a, 5b, 5c and 5d and the detection piezoelectric vibration elements 8a and 8b having an arbitrary degree of orientation are produced. The produced piezoelectric vibration element is subjected to polarization treatment after the electrodes are formed.

  The lower electrodes for driving 4a, 4b, 4c, 4d, the lower electrodes for detection 7a, 7b, the upper electrodes for driving 6a, 6b, 6c, 6d, and the upper electrodes for detection 9a, 9b are Al, Pt, Au, Ag, Metals such as Cr, Cu, and Ti can be used. Further, from the viewpoint of improving the adhesion of the electrode material to the piezoelectric vibration element, an adhesive layer may be formed on the piezoelectric vibration element before forming each electrode.

  For example, a two-layer structure in which a chromium Cr layer is formed as an adhesive layer and then an Au layer is laminated on the entire surface may be formed. As an electrode forming method, baking of a metal paste or formation by sputtering is effective.

  X-ray diffraction was performed in order to obtain the orientation degree F of the produced driving piezoelectric vibration elements 5a, 5b, 5c, and 5d and the detection piezoelectric vibration elements 8a and 8b. X-rays were passed through a Ni filter with CuKα radiation, and the range of 2θ from 10 ° to 70 ° was measured at 1 deg / min.

The degree of orientation F is calculated using the Lottgering method as an index indicating the degree of crystal grain orientation. The degree of orientation is represented by F = (P−P ₀ ) / (1−P ₀ ) × 100 [%], where P ₀ is the peak intensity (hkl) and c-axis of all X-ray diffraction patterns when oriented. The ratio of the peak intensity (00l) of the X-ray diffraction pattern is shown, and P is the ratio of the peak intensity (hkl) of all X-ray diffraction patterns to the peak intensity (00l) of the c-axis when non-oriented produced by the ordinary firing method. .

FIG. 5 shows an example of an X-ray diffraction pattern of a bismuth layered structure ferroelectric in a non-oriented state in which crystal grains necessary for calculating the degree of orientation F are present at random. The strongest peak intensity I ₀ 16 has 2θ around 31 °.

FIG. 6 shows an example of an X-ray diffraction pattern of a bismuth layered structure ferroelectric material preferentially oriented with respect to the c-axis used in the driving piezoelectric vibration elements 5a, 5b, 5c, and 5d. The highest intensity peak intensity I ₀ 16 when the piezoelectric vibration element in which crystal grains of the same composition exist randomly is measured by the X-ray diffraction method, and the peak intensity at the same angle 2θ as I ₀ on the plane parallel to the driving electrode. The ratio I _D / I ₀ with I _D 17 is less than 1.0. From the obtained X-ray diffraction pattern, the degree of orientation F can be calculated by the Lottgering method to confirm the degree of orientation.

FIG. 7 shows an example of an X-ray diffraction pattern of a bismuth layer-structured ferroelectric material oriented in the a- and b-axis directions used in the detection piezoelectric vibrating elements 8a, 8b. The peak intensity I ₀ 16 having the strongest intensity when measured by the piezoelectric vibration element X-ray diffraction method in which crystal grains of the same composition are present at random, and the peak intensity I at the same angle 2θ as I ₀ on the plane parallel to the detection electrode The ratio I _S / I ₀ with _S 18 is less than 1.0

FIG. 8 is an illustrative view showing the relationship between the orientation degree F and the mechanical quality factor Q. When the planes parallel to the driving electrodes 6a, 6b, 6c, 6d in the driving piezoelectric vibration elements 5a, 5b, 5c, 5d are measured by the X-ray diffraction method, the strongest peak intensity I _D 17 is obtained. The ratio I _D / I between the crystal plane where the strongest peak intensity is obtained and the peak intensity I ₀ 16 in the same crystal plane in the piezoelectric vibrator in which crystals having the same composition as the piezoelectric vibrators 5a, 5b, 5c, 5d are present at random. _{When 0} becomes smaller, the orientation degree F becomes larger.

In the center of FIG. 8, I _D / I ₀ = 1.0 is a non-oriented state and shows an orientation degree F = 0%. From the non-oriented state, the right side has a larger orientation to the c-axis and the mechanical quality factor. Q increases, and the orientation F in the a and b axis directions increases from the non-oriented side to the left side, and the mechanical quality factor Q decreases. When a bismuth layered structure ferroelectric is used, a mechanical quality factor Q higher than that of a lead-based material conventionally used can be obtained.

Thus, by making I _D / I ₀ smaller than 1.0, there is an effect of improving the mechanical quality factor Q, and a vibrating body having high sensitivity is obtained.

  The relationship between the degree of orientation F and the electromechanical coupling coefficient k is that, from the non-oriented state, the orientation axis is c-axis and the orientation degree F is large and the electromechanical coupling coefficient k is small. The degree of orientation F increases and the electromechanical coupling coefficient k increases. A piezoelectric vibration element having an orientation degree of about 90% and oriented along the a and b axes exhibits an electromechanical coupling coefficient k that is about twice that of a piezoelectric vibration element in an unoriented state.

FIG. 9 is an illustrative view showing the relationship between the degree of orientation F with the orientation axes a and b and the temperature characteristic TC-fr of the resonance frequency. The temperature characteristic of the resonance frequency is calculated as TC−fr = Δfr / (fr [20 ° C.] × Δt) [ppm / ° C.], where Δfr indicates the amount of change in resonance frequency in the temperature range from −25 ° C. to 125 ° C., fr [20 ° C.] represents a resonance frequency at 20 ° C., and Δt represents a temperature change. When the orientation direction is a and b axes from the non-oriented state and the orientation degree F increases, the temperature characteristic TC-f of the resonance frequency
r indicates a tendency to improve.

Thus, by making I _S / I ₀ smaller than 1.0, there is an effect of improving the temperature characteristic TC-fr of the electromechanical coupling coefficient k and the resonance frequency, and vibration with excellent temperature stability of output and sensitivity. Become a body.

  From the relationship between the degree of orientation F, mechanical quality factor Q, electromechanical coupling factor k, and temperature characteristic TC-fr of the resonance frequency, the orientation of the driving piezoelectric vibrating elements 5a, 5b, 5c, 5d and the detecting piezoelectric elements 8a, 8b. Degree F and orientation direction are set.

It is desirable that the piezoelectric vibration elements 5a, 5b, 5c, and 5d for driving have as high a mechanical quality factor Q as possible in order to make them highly sensitive, so that I _D / I ₀ is as small as possible and the degree of orientation F is large. When the orientation degree F of the material increases, the polarization process becomes difficult and good piezoelectricity is not exhibited, and conversely the mechanical quality factor Q deteriorates. Therefore, the orientation degree F in the c-axis direction with an orientation degree F of about 60% is appropriate. .

The piezoelectric vibration elements for detection 8a and 8b have a large electromechanical coupling coefficient k and an orientation in which the temperature characteristic TC-fr of the resonance frequency is good. In the a and b axis directions, I _S / I ₀ is as small as possible and the degree of orientation F is large. preferable. However, if the orientation degree F is too high, slipping at the crystal grain interface occurs and the mechanical strength deteriorates, so an orientation degree F of about 80% is appropriate.

An example of the characteristics of the driving piezoelectric vibrating elements 5a, 5b, 5c, 5d and the detecting piezoelectric vibrating elements 8a, 8b of the vibrating body 1 of the present invention will be shown. The mechanical quality factor Q of the piezoelectric vibration element in the non-oriented state is 3800, whereas I _D / I ₀ is smaller than 1.0, and the piezoelectric vibration element for driving whose c-axis orientation degree F is about 60% The mechanical quality factor Q of 5a, 5b, 5c and 5d is approximately 8000. By controlling the crystal anisotropy, the mechanical quality factor Q is improved about twice.

The temperature characteristic TC-fr of the resonance frequency of the piezoelectric vibration element in the non-oriented state is about 70 ppm / ° C., whereas I _S / I ₀ is smaller than 1.0, and the degree of orientation F of the a and b axes is about 80. The temperature characteristic TC-fr of the resonant frequency of the% detecting piezoelectric vibrating elements 8a and 8b is approximately 40 ppm / ° C. By controlling the crystal anisotropy, the temperature characteristic TC-fr of the resonance frequency is improved by about 40%.

  The vibrating gyroscope of the present invention has a vibrating body 1 as shown in FIG. The outer driving upper electrodes 6a and 6d are connected to the midpoint of the power supply voltage, and the oscillation circuit 20 is connected between the outer driving upper electrodes 6a and 6d and the inner electrodes 6b and 6c. The oscillation circuit 20 includes, for example, an amplifier circuit and a phase correction circuit, amplifies the signals output from the outer driving upper electrodes 6a and 6d, corrects the phase, and supplies the amplified signals to the inner electrodes 6b and 6c. As a result, the two tuning-fork-shaped arms 3a and 3b are flexibly vibrated in the in-plane direction so as to open and close.

  The detection electrodes 9 a and 9 b are connected to the differential circuit 21. The differential circuit 21 is configured by, for example, an operational amplifier or a resistor. Further, the output terminal of the differential circuit 21 is connected to the synchronous detection circuit 22. In the synchronous detection circuit 22, for example, the output signal of the differential circuit 21 is detected in synchronization with the signal of the oscillation circuit 20. The output signal of the synchronous detection circuit 22 is converted into a DC signal by the integration circuit 23. Further, the output signal of the integration circuit 23 is amplified by the DC amplification circuit 24.

In the vibrating gyroscope according to the present invention, drive signals having mutually opposite phases are given between the outer driving upper electrodes 6a and 6d and the inner electrodes 6b and 6c so that the arms 3a and 3b open and close in the in-plane direction. Vibrate. The drive signal given here is a signal corresponding to the resonance frequency of the vibrating body 1. By this drive signal, bending vibration is generated in the driving piezoelectric vibration elements 5a, 5b, 5c, and 5d.

  At this time, a reverse displacement occurs between the outer driving piezoelectric vibrating elements 5a and 5d and the inner driving piezoelectric vibrating elements 5b and 5c. That is, when one of the outer or inner driving piezoelectric vibrating elements extends in the thickness direction, the other driving piezoelectric vibrating element contracts in the thickness direction. Conversely, when one driving piezoelectric vibration element contracts in the thickness direction, the other driving piezoelectric vibration element extends in the thickness direction.

  Therefore, the arms 3a and 3b vibrate and vibrate so as to open and close. At this time, since the two arm portions 3a and 3b of the vibrating body 1 vibrate in the same state with respect to the polarization direction, the signals output from the detection electrodes 9a and 9b are the same. Therefore, no signal is output from the differential circuit 21.

  When a rotational angular velocity Ω is applied about the z axis in the direction in which the arms 3a and 3b extend from the base 2 in a state where the arms 3a and 3b of the vibrating body 1 are bent and vibrated so as to open and close, Coriolis force Fc acts in a direction orthogonal to the direction. Therefore, the arms 3a and 3b vibrate in the direction in which the driving force applied in the opening / closing direction and the Coriolis force Fc are combined by the Coriolis force Fc.

  By the Coriolis force Fc, the arm portions 3a and 3b are displaced in the direction in which the detecting piezoelectric vibrating elements 8a and 8b are arranged. Due to the displacement of the arm portions 3a and 3b, when one of the detection piezoelectric vibration elements 8a extends in the thickness direction, the other detection piezoelectric vibration element 8b contracts in the thickness direction. Conversely, when one of the detection piezoelectric vibration elements 8a is contracted, the other detection piezoelectric element 8b is extended.

  Therefore, when the output of one detection piezoelectric vibration element 8a is increased as compared with the non-rotation state, the output of the other detection piezoelectric vibration element 8b is decreased. Further, when the output of one of the detection piezoelectric vibration elements 8a is decreased as compared with the non-rotation state, the output of the other detection piezoelectric vibration element 8b is increased. Therefore, if the difference between the output signals of the detection electrodes 9a and 9b is obtained by the differential circuit 21, a large signal corresponding to the Coriolis force can be obtained.

  The output signal of the differential circuit 21 is detected by the synchronous detection circuit 22 in synchronization with the signal of the oscillation circuit 20. Thereby, only the positive part or only the negative part of the output signal of the differential circuit 21 is detected. The output signal of the synchronous detection circuit 22 is converted into a DC signal by the integration circuit 23 and further amplified by the DC amplification circuit 24.

  Since the level of the output signal from the detection electrodes 9a and 9b is determined by the magnitude of the displacement of the arm portions 3a and 3b of the vibrating body 1, when the large Coriolis force Fc works, the level of the main signal increases. Therefore, the magnitude of the rotational angular velocity Ω can be detected from the level of the output signal of the DC amplifier circuit 24.

  Further, the direction of the Coriolis force Fc applied to the two arm portions 3a and 3b of the vibrating body 1 varies depending on the direction in which the rotational angular velocity Ω is applied. Therefore, the phases of the signals output from the two detection electrodes 9a and 9b also change, and the differential circuit 21 outputs a signal having an opposite phase depending on the direction of the rotational angular velocity Ω.

  Therefore, in the synchronous detection circuit 22, if the positive portion of the signal is detected when the rotational angular velocity Ω is applied in one direction, the negative portion of the signal is detected when the rotational angular velocity Ω is applied in the other direction. Therefore, the polarity of the output signal of the DC amplifier circuit 24 changes depending on the direction in which the rotational angular velocity Ω is applied. That is, the direction in which the rotational angular velocity is applied can be known from the polarity of the output signal of the DC amplifier circuit 24.

The drive piezoelectric vibrator having an I _D / I ₀ smaller than 1.0 and an orientation degree F in the c-axis direction of about 60% has a mechanical quality factor Q improved about twice as much as that in the non-oriented state. The sensitivity of the vibration gyro obtained by the circuit is improved.

I _S / I ₀ is smaller than 1.0, and the piezoelectric vibrator for detection having an orientation degree F in the a- and b-axis directions of about 80% has a temperature characteristic TC-fr of the resonance frequency that is smaller than that in the non-oriented state. The output obtained by the circuit of FIG. 10 is improved by about 40% and has excellent temperature stability. The driving piezoelectric element and the detecting piezoelectric element have been shown to be effective in improving characteristics due to the different crystal orientation planes.

  The driving piezoelectric vibration elements 5a, 5b, 5c, and 5d and the detection piezoelectric vibration elements 8a and 8b of the vibrating body 1 of the present invention may be formed of a thin film formed by a sputtering method, a CVD method, a sol-gel method, or the like.

It is a perspective view which shows an example of the vibrating body of this invention. It is sectional drawing in an example of the vibrating body shown in FIG. It is an illustration figure which shows the crystal structure of a bismuth layer structure structure ferroelectric substance. It is an illustrative view showing the distribution of crystal grains (a) non-oriented, (b) oriented in the c-axis direction, (c) oriented in the a- and b-axis directions. It is an example of the X-ray diffraction pattern of a non-oriented bismuth layer structure ferroelectric substance. It is an example of the X-ray diffraction diagram of the drive piezoelectric vibrating body used for this invention. It is an example of the X-ray-diffraction figure of the piezoelectric material for a detection used for this invention. FIG. 4 is a relationship diagram between an orientation degree F and a mechanical quality factor Q. It is a relationship figure of orientation degree F and temperature characteristic TC-fr of resonance frequency. It is a block diagram which shows the circuit for using the vibrating body shown in FIG. 1 as a vibration gyro. It is a perspective view of the vibrating body of the conventional vibration gyro. It is a perspective view of the vibrating body of the conventional thin film vibration gyro.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 101, 201 ... Vibrating body 2, 102 ... Base part 3a, 3b, 103a, 103b, 202a, 202b ... Arm part 4a, 4b, 4c, 4d ... Lower electrode 5a, 5b, 5c, 5d ... Drive piezoelectric Vibration element 6a, 6b, 6c, 6d ... Driving upper electrode 7a, 7b ... Detection lower electrode 8a, 8b ... Detection piezoelectric vibration element 9a, 9b ... Detection upper electrode 10 ... Bismuth layered structure ferroelectric bismuth oxide Layer (Bi ₂ O ₂ ) ²⁺
11. Pseudo-perovskite layer [(A _m-1 B _m O _{3m + 1} ) ²⁻ ] of bismuth layer structure ferroelectric
12. Pseudo-perovskite layer alternately stacked crystal structure 13. Bismuth layered structure ferroelectric unit cell 14 Bismuth layered structure ferroelectric crystal particle 15 Non-oriented piezoelectric vibration element 16 Non-oriented piezoelectric vibration The strongest peak intensity I ₀ of the X-ray diffraction pattern of the device
17: Peak intensity I _D of the X-ray diffraction pattern on the same crystal plane as I ₀ of the driving piezoelectric vibration element
18: Peak intensity I _S of the X-ray diffraction pattern on the same crystal plane as I _{0 of the} piezoelectric vibration element for detection
DESCRIPTION OF SYMBOLS 20 ... Oscillation circuit 21 ... Differential circuit 22 ... Synchronous detection circuit 23 ... Integration circuit 24 ... DC amplification circuit 104 ... Piezoelectric vibration element
203a, 203b ... thin film piezoelectric vibration elements 204a, 204b ... lower electrodes 205a, 205b, 205c, 205d ... upper electrodes

Claims (7)

The base,
At least two arms extending from the base;
A driving piezoelectric vibration element and a driving electrode provided on a main surface or a side surface of the arm portion to bend and vibrate these arm portions;
A detection piezoelectric vibration element and a detection electrode for detecting vibration orthogonal to the bending vibration excited by the driving piezoelectric vibration element;
In a vibrating body having
The drive piezoelectric vibration element and the detection piezoelectric vibration element are each a bismuth layer-structure ferroelectric substance in which crystal grains have anisotropy.   The vibrating body according to claim 1, wherein the crystal particles have a substantially aligned state so that at least one axis is oriented in the same direction. In the driving piezoelectric vibrating element, a piezoelectric vibration element in which the crystal grains are present randomly strongest peak intensity I ₀ as measured by X-ray diffraction method, and the I ₀ in a plane parallel to the driving electrodes 3. The vibrating body according to claim 1, wherein a ratio I _D / I ₀ to a peak intensity I _D at the same angle 2θ is smaller than 1.0. In the detecting piezoelectric vibrating element, said piezoelectric vibrating element crystal particles are present in a random strongest peak intensity I ₀ as measured by X-ray diffractometry, and the I ₀ in the plane perpendicular to the detection electrode 3. The vibrating body according to claim 1, wherein a ratio I _S / I ₀ to a peak intensity I _S at the same angle 2θ is smaller than 1.0.   5. The drive piezoelectric vibration element according to claim 1, wherein the crystal grains are arranged in a larger amount in the c-axis direction in a direction perpendicular to the drive electrode than in a state of being present at random. The vibrating body according to one item.   5. The piezoelectric vibration element for detection according to claim 1, wherein the crystal particles are arranged more in the a- and b-axis directions in a direction perpendicular to the detection electrode than in a randomly existing state. The vibrating body according to any one of the above.   A vibrating gyroscope that detects an angular velocity applied from the outside using the vibrating body according to claim 1.

Images