Patent Application
20160346808
1. Technical Field
The present invention relates to a piezoelectric device and a probe, an electronic apparatus, and an ultrasonic imaging apparatus using the same.
2. Related Art
As disclosed in JP-A-2014-146722, a piezoelectric device includes a piezoelectric body interposed between first and second electrodes. In the piezoelectric body, (100) preferential orientation is established. According to such preferential orientation, the piezoelectric characteristics of the piezoelectric body are substantially enhanced.
As disclosed in JP-A-2002-271897, an ultrasonic transducer includes a piezoelectric device. In the piezoelectric device, first and second electrodes are disposed on the same surface of the piezoelectric body. In the piezoelectric body, (001) preferential orientation is established. In the same manner as in JP-A-2014-146722, a piezoelectric body with (100) preferential orientation is interposed between the first and second electrodes. However, in a case where the first and second electrodes are disposed on the same surface in the piezoelectric body, the (100) preferential orientation is not established in the piezoelectric body.
An advantage of some aspects of the invention is to provide a piezoelectric device that establishes (100) preferential orientation in a piezoelectric body in a case where first and second electrodes are disposed on the same surface in the piezoelectric body.
(1) An aspect of the invention relates to a piezoelectric device including: an elastic layer that forms an insulating surface region at least partially and has an amorphous structure or random orientation at least in the surface region; a piezoelectric body that is provided on the elastic layer, has a first surface in contact with the elastic layer and a second surface on an opposite side to the first surface, and is (100) preferentially oriented in an orientation region corresponding to the surface region in a plan view; a first electrode provided on the second surface of the piezoelectric body; and a second electrode that is provided on the second surface of the piezoelectric body. A gap is formed between the first and second electrodes corresponding to the orientation region in the plan view.
If the elastic layer vibrates due to the ultrasonic wave from the outside, the piezoelectric body is distorted on the elastic layer. The strain of the piezoelectric body generates an electric potential in the piezoelectric body. Since the (100) preferential orientation is established in the orientation region of the piezoelectric body, a relatively large electric potential is generated for the strain of the piezoelectric body. Such an electric potential generated by the piezoelectric response is detected as an electric potential difference between the first and second electrodes. In particular, since the bottom surface of the orientation region is in contact with the insulating surface region, the formation of a parasitic capacitance connecting the electrodes to each other is avoided. Accordingly, good receiving sensitivity can be secured. If a conductive material is present on the bottom surface of the orientation region, a parasitic capacitance connecting the electrodes to each other is formed. Therefore, the receiving sensitivity is lowered. In order to obtain high receiving sensitivity, it is preferable that electrical flux lines extend directly to the second electrode through the piezoelectric body from the first electrode.
(2) The piezoelectric body may be formed of a transition metal oxide having a perovskite structure. In this case, the piezoelectric body shows good piezoelectric characteristics.
(3) The first surface of the piezoelectric body may be formed as an orientation control layer that is formed of a transition metal oxide having a perovskite structure. In this case, the piezoelectric body shows good piezoelectric characteristics.
(4) The first surface of the piezoelectric body may be formed as an orientation control layer that is formed of a transition metal oxide having a perovskite structure that contains bismuth in an A site and iron and titanium in a B site. Such a transition metal oxide establishes the (100) preferential orientation at the time of lamination on the elastic layer with an amorphous structure or random orientation. Here, since the orientation control layer has an insulation property, the formation of a parasitic capacitance connecting the electrodes to each other can be avoided. In addition, other rare earths, such as lanthanum (La), neodymium (Nd), samarium (Sm), and praseodymium (Pr), may be included in the A site. In addition, lead (Pb) may be further included in the A site.
(5) The resistance value of the orientation control layer may be equal to or greater than 106 Ω/cm. If the resistance value satisfying this condition is used, the formation of a parasitic capacitance connecting the electrodes to each other is reliably avoided.
(6) The orientation control layer may be (100) preferentially oriented.
(7) The piezoelectric body may include a Pb(ZrTi)O3 layer laminated on the orientation control layer. The Pb(ZrTi)O3 layer establishes the (100) preferential orientation by being laminated on the orientation control layer.
(8) Pb may infiltrate into the orientation control layer. At the time of lamination of the Pb(ZrTi)O3 layer that is a piezoelectric body, the Pb(ZrTi)O3 layer may be heated to 600° C. to 750° C. In this case, Pb contained in the Pb(ZrTi)O3 layer infiltrates into the orientation control layer to be stabilized.
(9) The orientation control layer may be a continuous layer. If the orientation control layer is a continuous layer, the (100) preferential orientation can be reliably established in the Pb(ZrTi)O3 layer.
(10) The orientation control layer may be a discontinuous layer. Even if the orientation control layer is a discontinuous layer, the (100) preferential orientation can be established in the Pb(ZrTi)O3 layer.
(11) A groove may be formed on the second surface of the piezoelectric body in the gap. By forming the groove, the in-plane strain of the elastic layer due to sound pressure is concentrated on the gap. Therefore, a large voltage is generated between the first and second electrodes.
(12) The piezoelectric device may be used by being built into a probe. In this case, the probe may include the piezoelectric device and a housing that supports the piezoelectric device.
(13) The piezoelectric device may be used by being built into an electronic apparatus. In this case, an electronic apparatus may include the piezoelectric device; and a processing circuit that is connected to the piezoelectric device and processes an output of the piezoelectric device.
(14) The piezoelectric device may be used by being built into an ultrasonic imaging apparatus. In this case, the ultrasonic imaging apparatus may include: the piezoelectric device; a processing circuit that is connected to the piezoelectric device and processes an output of the piezoelectric device to generate an image; and a display device that displays the image.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, an embodiment of the invention will be described with reference to the accompanying diagrams. In addition, the present embodiment to be described below does not unduly limit the content of the invention as defined in the appended claims, and all elements described in the present embodiment are not necessarily indispensable as solving means of the invention.
The ultrasonic probe 13 includes a housing 16. The ultrasonic device unit 17 is housed in the housing 16. The ultrasonic device unit 17 includes an acoustic lens 18. A partial cylindrical surface 18a is formed as the outer surface of the acoustic lens 18. The acoustic lens 18 is formed of, for example, silicone resin. The acoustic lens 18 has an acoustic impedance close to the acoustic impedance of the living body. A window hole 16a is defined in the housing 16. The acoustic lens 18 is disposed in the window hole 16a. The outer surface of the acoustic lens 18 is exposed on the surface of the housing 16. The ultrasonic device unit 17 outputs an ultrasonic wave from the surface and receives a reflected wave of the ultrasonic wave.
As shown in
A receiving array RR and a transmission array TR are formed in the ultrasonic device unit 17. As will be described later, the receiving array RR is formed as an array of first ultrasonic transducer elements (hereinafter, referred to as “first piezoelectric devices”) that are disposed in the form of an array. As will be described later, the transmission array TR is formed as an array of second ultrasonic transducer elements (hereinafter, referred to as “second piezoelectric devices”) that are disposed in the form of an array. The receiving array RR and the transmission array TR are electrically connected to a wiring pattern (not shown) on the wiring substrate through a first flexible printed wiring board (hereinafter, referred to as a “first wiring board”) 19a and a second flexible printed wiring board (hereinafter, referred to as a “second wiring board”) 19b. The wiring pattern is connected to a connector on the back surface of the wiring board WB. The cable 14 is formed by the wiring lines connected to the connector.
Each of the second piezoelectric devices 23 includes a vibrating film 24. In
A plurality of first conductors 29 are formed on the surface of the base 21. The first conductors 29 extend in parallel in the row direction of the array. One first conductor 29 is assigned to the second piezoelectric devices 23 in one row. The first conductor 29 forms the upper electrode 26 in each second piezoelectric device 23. Both ends of the first conductor 29 are connected to a pair of lead-out wiring lines 31. The first conductor 29 can be formed of, for example, iridium (Ir). However, other conductive materials may be used for the first conductor 29.
A plurality of second conductors 32 are formed on the surface of the base 21. The second conductors 32 extend in parallel in the column direction of the array. One second conductor 32 is assigned to the second piezoelectric devices 23 in one column. The second conductor 32 forms the lower electrode 27 in each second piezoelectric device 23. For the second conductor 32, for example, a laminated film of titanium (Ti), iridium (Ir), platinum (Pt), and titanium (Ti) can be used. However, other conductive materials may be used for the second conductor 32.
The supply of power to the second piezoelectric device 23 is switched for each column. A linear scan or a sector scan is realized according to such switching of power supply. Since the second piezoelectric devices 23 in one column output ultrasonic waves at the same time, the number of devices in a column, that is, the number of rows of the array, can be determined according to the output level of the ultrasonic wave. For example, the number of rows may be set to about 10 to 15. In
The contour of the base 21 has first and second sides 21a and 21b that are a pair of parallel straight lines facing each other. A first terminal array 33a of one line is disposed between the first side 21a and the contour of the transmission array TR. A second terminal array 33b of one line is disposed between the second side 21b and the contour of the transmission array TR. The first terminal array 33a can form one line in parallel to the first side 21a. The second terminal array 33b can form one line in parallel to the second side 21b. The first terminal array 33a is formed by a pair of upper electrode terminals 34 and a plurality of lower electrode terminals 35. Similarly, the second terminal array 33b is formed by a pair of upper electrode terminals 36 and a plurality of lower electrode terminals 37. The upper electrode terminals 34 and 36 are connected to the ends of one lead-out wiring lines 31. The lead-out wiring line 31 and the upper electrode terminals 34 and 36 may be formed plane-symmetrically on a vertical plane bisecting the transmission array TR. The lower electrode terminals 35 and 37 are connected to both ends of the one second conductor 32. The second conductor 32 and the lower electrode terminals 35 and 37 may be formed plane-symmetrically on the vertical plane bisecting the transmission array TR. Here, the contour of the base 21 is formed in a rectangular shape. The contour of the base 21 may be a square, or may be a trapezoid.
The first wiring board 19a is connected to the base 21. The first wiring board 19a covers the first terminal array 33a. At one end of the first wiring board 19a, a conductive line, that is, a first signal line 39 is formed corresponding to each of the upper electrode terminal 34 and the lower electrode terminal 35. Each first signal line 39 is separately bonded to the upper electrode terminal 34 and the lower electrode terminal 35 so as to face each other. Similarly, the second wiring board 19b is connected to the base 21. The second wiring board 19b covers the second terminal array 33b. At one end of the second wiring board 19b, a conductive line, that is, a second signal line 42 is formed corresponding to each of the upper electrode terminal 36 and the lower electrode terminal 37. Each second signal line 42 is separately bonded to the upper electrode terminal 36 and the lower electrode terminal 37 so as to face each other.
As shown in
The coat layer 45 is formed by a silicon oxide (SiO2) layer 48 laminated on the surface of the substrate 44 and a zirconium oxide (ZrO2) layer 49 laminated on the surface of the silicon oxide layer 48. The coat layer 45 is in contact with the opening 46. In this manner, corresponding to the contour of the opening 46, a part of the coat layer 45 forms the vibrating film 24. Since the vibrating film 24 faces the opening 46 of the coat layer 45, the vibrating film 24 is a part that can perform film vibration in the thickness direction of the substrate 44. The thickness of the silicon oxide layer 48 can be determined based on the resonance frequency.
The lower electrode 27, the piezoelectric body 28, and the upper electrode 26 are laminated in order on the surface of the vibrating film 24. The piezoelectric body 28 can be formed of, for example, lead zirconate titanate (Pb(ZrTi)O3). Other piezoelectric materials may be used for the piezoelectric body 28.
An acoustic matching layer 51 is laminated on the surface of the base 21. The acoustic matching layer 51 covers the element array 22. The thickness of the acoustic matching layer 51 is determined according to the resonance frequency of the vibrating film 24. For example, a silicone resin film can be used as the acoustic matching layer 51. The acoustic lens 18 is disposed on the acoustic matching layer 51. The acoustic lens 18 is in close contact with the surface of the acoustic matching layer 51. The acoustic lens 18 is bonded to the base 21 by the acoustic matching layer 51. The partial cylindrical surface 18a of the acoustic lens 18 has a generatrix parallel to the first conductor 29. The curvature of the partial cylindrical surface 18a is determined according to the focal position of ultrasonic waves transmitted from the second piezoelectric devices 23 in one column that are connected to one second conductor 33. The acoustic lens 18 is formed of, for example, silicone resin. The acoustic lens 18 has an acoustic impedance close to the acoustic impedance of the living body.
A protective film 53 is fixed to the base 21. The protective film 53 is formed of, for example, a material having a water-proof property, such as an epoxy resin. However, the protective film 53 may be formed of other resin materials. The protective film 53 is in contact with the acoustic lens 18 and the acoustic matching layer 51. Here, the acoustic lens 18 and the acoustic matching layer 51 are interposed between contact surfaces 53a of the protective film 53, which are located along two virtual planes 54a and 54b that spread in parallel to the generatrix of the acoustic lens 18 and are perpendicular to the base 21.
A backing material 56 is fixed to the back surface of the base 21. The back surface of the base 21 overlaps the surface of the backing material 56. The backing material 56 closes the opening 46 on the back surface of the ultrasonic device unit 17. The backing material 56 can include a rigid base, for example. Here, the partition wall 47 is bonded to the backing material 56. The backing material 56 is bonded to each partition wall 47 in at least one bonding region. In the bonding, an adhesive can be used.
A vibrator 59 is formed on the vibrating film 58. The vibrator 59 includes a first electrode 61, a second electrode 62, and a piezoelectric body 63. The first and second electrodes 61 and 62 are disposed on the piezoelectric body 63. The second electrode 62 is disposed at a position separated from the first electrode 61 on the piezoelectric body 63. A gap 64 is formed between the first and second electrodes 61 and 62. On the surface of the vibrating film 58, a surface region 65 overlapping the gap 64 in a plan view is defined.
Here, the vibrating film 58 is formed in a rectangular shape (including a square) in a plan view. Similarly, the piezoelectric body 63 is formed in a rectangular shape in a plan view. The center of the vibrating film 58 and the center of the piezoelectric body 63 overlap each other in a plan view. The vibrator 59 is formed symmetrically with respect to a reference line 66. The reference line 66 extends in parallel to the long side of the rectangle to bisect the rectangle. At the ends of the first and second electrodes 61 and 62, a contour line is drawn in parallel to the reference line 66. Thus, the end of the first electrode 61 and the end of the second electrode 62 face each other at an equal distance with the reference line 66 interposed therebetween. The gap 64 extends along the reference line 66.
A plurality of third conductors 67 and a plurality of fourth conductor 68 are formed on the surface of the base 21. The third and fourth conductors 67 and 68 extend in parallel to each other in the column direction of the array. The third and fourth conductors 67 and 68 are alternately disposed. The first piezoelectric devices 57 of a plurality of columns are assigned for each pair of adjacent third and fourth conductors 67 and 68. Between the third and fourth conductors 67 and 68, the first piezoelectric devices 57 are connected in series to each other in each row. That is, in the first piezoelectric devices 57 adjacent to each other in a row, the first electrode 61 of one of the devices is connected to the second electrode 62 of the other device. The same materials can be used for the first electrode 61, the second electrode 62, the third conductor 67, and the fourth conductor 68. For example, a laminated film of titanium (Ti), iridium (Ir), platinum (Pt), and titanium (Ti) can be used for the first electrode 61, the second electrode 62, the third conductor 67, and the fourth conductor 68. However, other conductive materials may be used for the first electrode 61, the second electrode 62, the third conductor 67, and the fourth conductor 68.
Between the first side 21a of the base 21 and the contour of the receiving array RR, a third terminal array 69 of one line is disposed. The third terminal array 69 can form one line in parallel to the first side 21a. The third terminal array 69 includes a signal terminal 71 and a common terminal 72. The signal terminal 71 is connected to the third conductor 67. The common terminal 72 is connected to the fourth conductor 68. Here, the third terminal array 69 forms one line together with a first terminal array 38. The first wiring board 19a covers the first terminal array 33a and the third terminal array 69. At one end of the first wiring board 19a, a conductive line, that is, a third signal line 73 is formed corresponding to each of the signal terminal 71 and the common terminal 72. Each third signal line 73 is separately bonded to the signal terminal 71 and the common terminal 72 so as to face each other.
Similarly, between the second side 21b of the base 21 and the contour of the receiving array RR, a fourth terminal array (not shown) of one line may be disposed. The fourth terminal array may form one line together with a second terminal array 33b. The second wiring board 19b covers the second terminal array 33b and the fourth terminal array. At one end of the second wiring board 19b, a conductive line, that is, a fourth signal line is formed corresponding to each of the signal terminal and the common terminal. Each fourth signal line is separately bonded to the signal terminal and the common terminal so as to face each other.
As shown in
The piezoelectric body 63 is fixed to the surface of the vibrating film 58. The piezoelectric body 63 has a first surface 63a in contact with the vibrating film 58 and a second surface 63b on the opposite side (back side) to the first surface 63a. The piezoelectric body 63 is formed of a piezoelectric material containing a composite oxide having a perovskite structure, that is, an ABO3 type structure. The perovskite structure is a structure in which oxygen is 12-coordinated in the A site and is 6-coordinated in the B site to form an octahedron. The piezoelectric body 63 is formed of, for example, lead zirconate titanate (Pb(ZrTi)O3). The piezoelectric body 63 may be formed of a transition metal oxide having a perovskite structure. For the piezoelectric body 63, for example, a material obtained by adding a metal oxide, such as a niobium oxide, a nickel oxide, or a magnesium oxide, to lead zirconate titanate may be used. Specifically, lead titanate (PbTiO3), lead zirconate (PbZrO3), lead lanthanum titanate ((PbLa)TiO3), lead lanthanum zirconate titanate ((PbLa) (ZrTi)O3), magnesium niobate zirconium titanate (Pb(ZrTi) (MgNb)O3), and the like can be mentioned. In addition, as non-lead-based materials, bismuth ferrate (BiFeO3), barium titanate (BaTiO3), sodium potassium niobate ((KNa) (NbO3)), potassium sodium lithium niobate ((KNaLi) (NbO3)), potassium sodium lithium niobate tantalate ((KNaLi) (NbTa)O3), bismuth potassium titanate ((Bi1/2K1/2)TiO3), bismuth sodium titanate ((Bi1/2Na1/2) TiO3), manganese bismuth (BiMnO3), a composite oxide (x[(BixK1-x)TiO3]-(1-x) [BiFeO3]) having a perovskite structure that contains bismuth, potassium, titanium, and iron, a composite oxide ((1-x) [BiFeO3]-x[BaTiO3]) having a perovskite structure that contains bismuth, iron, barium and titanium, a material ((1-x) [Bi(Fe1-yMy)O3]-x[BaTiO3] (M is Mn, Co, or Cr)) obtained by adding a metal, such as manganese, cobalt, or chromium, to the composite oxide, and the like can be mentioned. Such a piezoelectric material having a perovskite structure is formed on an orientation control layer 75. Therefore, the piezoelectric material having aperovskite structure is preferentially oriented on the (100) plane according to the crystal orientation of the orientation control layer 75. Here, the preferential orientation refers to “(100)/[(100)+(110)] is 60% or more, preferably, 70% or more” when comparing the peak intensity derived from the (100) plane with the peak intensity derived from the (110) plane in an X-ray diffraction pattern. Having a large proportion of the peak of the (100) plane is effective in terms of displacement characteristics and durability of the piezoelectric body 63. It is preferable that (100)/[(100)+(110)] is 80% or more. More preferably, (100)/[(100)+(110)] is 90% or more. In the embodiment to be described later, it has been confirmed that (100)/[(100)+(110)] is 90% or more. From the viewpoint that the piezoelectric material has excellent displacement characteristics due to being preferentially oriented on the (100) plane, it is preferable that the piezoelectric material is rhombohedral or monoclinic. This, in the piezoelectric body 63, (100) preferential orientation is established. In the piezoelectric body 63, (100) preferential orientation is secured in at least an orientation region 74 corresponding to the surface region 65 in a plan view.
As shown in
The orientation control layer 75 has a perovskite structure, is a composite oxide containing bismuth (Bi) in the A site and iron (Fe) and titanium (Ti) in the B site, and is self-orientated on the (100) plane. Specifically, in the A site of the ABO3 type structure, oxygen is 12-coordinated. In addition, in the B site of the ABO3 type structure, oxygen is 6-coordinated. As a result, an octahedron is formed. It is preferable that a composite oxide, which forms the orientation control layer 75, is basically formed of Bi of the A site and Fe and Ti of the B site. A preferred composition ratio is in the range of 40≦x≦60 in a case where the elemental ratio is expressed as Bi:Fe:Ti=100:x: (100-x). A composite oxide having such a composition ratio is self-oriented on the (100) plane without being influenced by an underlying layer, and functions as an orientation control layer for orienting a piezoelectric material having a perovskite structure, which is formed on the composite oxide, on the (100) plane. That is, as will be described in detail later, since the orientation control layer 75 is formed after the coat layer 45 is formed, the orientation control layer 75 is formed on a zirconium oxide layer 81. However, also on a silicon oxide layer 79, the orientation control layer 75 is self-oriented on the (100) plane. Accordingly, the piezoelectric body 63 formed subsequently can also be reliably preferentially oriented on the (100) plane.
Here, being self-oriented on the (100) plane refers to being oriented on the (100) plane by itself without being influenced by an underlying layer, and includes a case in which all the crystals are oriented on the (100) plane and a case in which most of the crystals (for example, 80% or more) are oriented on the (100) plane. A composite oxide obtained by replacing some of the elements of the A site or the B site with other elements may be used to the extent that such a function is not inhibited, and this is also included in the orientation control layer according to the invention. For example, elements other than Bi, such as Ba, Sr, and La, may be further present in the A site, and elements other than Fe and Ti, such as Zr and Nb, may be further present in the B site. In addition, as long as the function described above is realized, materials having a composition deviated from the composition (ABO3) of stoichiometry due to deficiency or excess of an element (Bi, Fe, Ti, or O) are also included in the orientation control layer according to the invention. For example, as will be described later, it has been confirmed that a composite oxide, which contains Bi more than the stoichiometric ratio, is self-oriented on the (100) plane and functions as an orientation control layer.
5 Reason why the Orientation Control Layer should be an Insulator
The reason why the orientation control layer 75 should be an insulator is shown below using simulation. Simulation was performed using a finite element method (FEM) for realizing the piezoelectric effect. The vibrating film 58 and the piezoelectric body 63 were squares when viewed from above. The length of one side of a diaphragm formed by the vibrating film 58 was 40 μm, and the length of one side of the piezoelectric body 63 was 32 μm. In addition, the vibrating film 58 includes SiO2 (1000 nm), ZrO2 (400 nm), BFT (20 nm), and PZT (1350 nm) in order from below. BFT is the abbreviation of BiFeTiO3 that forms the orientation control layer 75 according to the invention. The thickness of each of the first and second electrodes 61 and 62 was 50 nm. A line that passes through the center of the gap 64 between the first and second electrodes 61 and 62 and is parallel to each of the electrodes 61 and 62 is assumed to be the reference line 66. As the piezoelectric tensor and the stiffness tensor of PZT used in the simulation, a data set of PZT-5H was adopted. In this case, the principal axis of the tensor was set to a direction perpendicular to the reference line 66 (the same as a direction in which an initialization electric field was applied). The Young's moduli of SiO2, ZrO2, and BFT were 75 GPa, 190 GPa, and 200 GPa, respectively. The Young's moduli of the first and second electrodes 61 and 62 were 200 GPa. A 1 atmosphere was applied to the vibrating film 58 from above, and an electric potential V generated between the first and second electrodes 61 and 62 at that time was examined. In order to calculate the electric potential V, the first and second electrodes 61 and 62 were in the open condition. A width W1 between the first and second electrodes 61 and 62 was set to 5 [μm].
6 Reason why the Piezoelectric Layer should have (100) Orientation Rather than (001) Orientation
Electronic state calculation based on the first principle of solid shows that piezoelectricity is increased when the piezoelectric body 63 formed of PZT has (100) orientation rather than (001) orientation. The calculation is based on the density functional theory within local density approximation. A piezoelectric constant was calculated using a linear response theory. Energy cutoff was set to 500 eV, and the mesh of k-space was set to 3×3×3. Acrystal structure for which the above calculation is to be performed is Pb(Zr0.5Ti0.5)O3 having an ABO3 perovskite structure. ABO3 type structures corresponding to 2×2×2=8 cells were prepared as a super cell, and periodic boundary conditions were used. In the following explanation, a direction perpendicular to the plane is assumed to be a c axis, and directions perpendicular to each other within the plane are assumed to be a and b axes. As a result of the calculation, in the case of (001) orientation, the crystal lattice extends in the c-axis direction. The rate of extension in the c-axis direction is about c/a=1.03. In this case, in the displacement of each atom from the central symmetry position, the <001> direction is a main displacement direction. On the other hand, in the case of (100) orientation, the crystal lattice satisfies the relationship of a=b=c. In this case, in the displacement of each atom from the central symmetry position, the <111> direction is a main displacement direction.
Next, the operation of the ultrasonic diagnostic apparatus 11 will be described briefly. In the transmission array TR, a pulse signal is supplied to the vibrator 25. The pulse signal is supplied to the second piezoelectric device 23 in each column through the lower electrode terminals 35 and 37 and the upper electrode terminals 34 and 36. In each second piezoelectric device 23, an electric field is applied to the piezoelectric body 28 between the lower electrode 27 and the upper electrode 26. The piezoelectric body 28 vibrates at a frequency of an ultrasonic wave. The vibration of the piezoelectric body 28 is transmitted to the vibrating film 24. Accordingly, the vibrating film 24 performs ultrasonic vibration. As a result, a desired ultrasonic beam is emitted toward a subject (for example, the inside of a human body).
In the receiving array RR, the supply of power to the first piezoelectric device 57 is switched for each group (a plurality of columns) interposed between the third and fourth conductors 67 and 68. The first piezoelectric device 57 receives an ultrasonic wave for each group of a plurality of columns. For each first piezoelectric device 57, the vibrating film 58 performs ultrasonic vibration. The ultrasonic vibration of the vibrating film 58 generates a strain of the piezoelectric body 63 at a desired frequency. The strain of the piezoelectric body 63 generates an electric potential. According to the piezoelectric effect of the vibrator 59, a voltage is output from the vibrator 59. Between the first and second electrodes 61 and 62, the (100) preferential orientation is established in the piezoelectric body 63. For this reason, a relatively large electric potential for the strain of the piezoelectric body 63 is generated. Such an electric potential is detected from the first and second electrodes. The electric potential is output as an electrical signal from the signal terminal 71 and the common terminal 72. In this manner, an ultrasonic wave is detected.
Transmission and reception of ultrasonic waves are repeated. As a result, a linear scan or a sector scan is realized. If the scan is completed, an image is formed based on the digital signal of the output signal. The formed image is displayed on the screen of the display panel 15.
In the first piezoelectric device 57, between the first and second electrodes 61 and 62, the bottom surface of the orientation region 74 is in contact with the insulating surface region 65. Accordingly, since the formation of a parasitic capacitance connecting the electrodes 61 and 62 to each other is avoided, good receiving sensitivity can be secured. If the bottom surface of the orientation region 74 is in contact with a conductive material, a parasitic capacitance connecting the electrodes to each other is formed. Therefore, the receiving sensitivity is lowered.
In order to obtain high receiving sensitivity, it is preferable that electrical flux lines generated when the piezoelectric body 63 is deformed by sound pressure extend directly to the second electrode 62 through the piezoelectric body 63 from the first electrode 61. For example, when viewed from above, if a region X including a conductive material is present in the vibrating film 58 below the orientation region 74, electrical flux lines extend to the second electrode 62 through the region X from the first electrode 61. In this case, the electrostatic capacitance C of a capacitor formed by the first and second electrodes 61 and 62 is effectively increased. As a result, the receiving sensitivity is lowered. As the distance between electrodes decreases, the electrostatic capacitance C increases. Since Q=CV, V is reduced when Q is fixed. This is not preferable.
In the first piezoelectric device 57a, as the distance between the first and second electrodes 61 and 62 increases, the electrostatic capacitance C of a capacitor formed by both the electrodes decreases. Accordingly, the generated voltage V of the piezoelectric body 63 is increased. In this case, as shown in
The groove 76 extends along the reference line 66 passing through the center of gravity of the vibrating film 58 in a plan view. In the vibrating film 58, bending at the time of ultrasonic vibration increases as a distance from the center-of-gravity position decreases. In this manner, if the groove 76 is disposed at a position where bending is likely to occur, the generated voltage is increased. In particular, the vibrating film 58 is formed in a rectangular shape in a plan view. The bending of the vibrating film 58 is maximized at an intermediate position equidistant from two sides extending in parallel to each other. If the groove 76 extends in parallel to the long side of the rectangle, the generated voltage is increased. Here, since the groove 76 traverses the entire one surface from one edge to the other edge of the piezoelectric body 63, the distortion of the piezoelectric body 63 is increased to the maximum extent. The generated voltage is increased to the maximum extent. The piezoelectric body 63 is formed symmetrically with respect to a straight line 65 in a plan view, and the behavior of the piezoelectric body 63 maintains the symmetry. Therefore, the behavior of the piezoelectric body 63 is stabilized at the time of vibration of the vibrating film 58.
Next, a method of manufacturing the first piezoelectric device 57a will be described briefly. As shown in
A Bi(FeTi)O3 layer 82 is formed on the surface of the coat layer 45. The Bi(FeTi)O3 layer 82 corresponds to the orientation control layer 75 according to the invention. In forming the Bi(FeTi)O3 layer 82, for example, a chemical solution method such as a metal-organic decomposition (MOD) method or a sol-gel method, a laser ablation method, a sputtering method, a pulsed laser deposition method (PLD method), a CVD method, and an aerosol deposition method can be used. In the MOD method, the Bi(FeTi)O3 layer 82 is obtained by applying a metal complex solution containing Bi, Fe, and Ti, drying the metal complex solution, and baking the metal complex solution at high temperature. The Bi(FeTi)O3 layer 82 establishes (100) preferential orientation on the randomly oriented zirconium oxide layer 81 regardless of the material of an underlying layer.
The thickness of the Bi(FeTi)O3 layer 82 may be 3 nm to 100 nm. The obtained Bi(FeTi)O3 layer 82 has an ABO3 perovskite structure. Bi is located in the A site. Fe and Ti are located in the B site. The obtained Bi(FeTi)O3 layer 82 has an insulation property. If the thickness of the Bi(FeTi)O3 layer 82 is smaller than 3 nm, it is not possible to take a manufacturing margin. If the thickness of the Bi(FeTi)O3 layer 82 exceeds 100 nm, a diaphragm is difficult to bend.
As a specific example of a formation procedure in the case of forming the orientation control layer 75 using a chemical solution method, first, an orientation control layer precursor layer is formed by applying a composite for forming an orientation control layer (precursor solution of the orientation control layer), which is a MOD solution or a sol containing a metal complex containing Bi, Fe, and Ti, using a spin coat method or the like (orientation control layer precursor solution application step). The precursor solution to be applied is obtained by mixing a metal complex capable of forming a composite oxide having a perovskite structure, in which Bi is included in the A site and Fe and Ti are included in the B site, by baking and then dissolving or dispersing the mixture in an organic solvent. As a metal complex containing Bi, Fe, or Ti, for example, alkoxides, organic acid salts, and β-diketone complexes can be used. As a metal complex containing Bi, for example, 2-ethyl hexane acid bismuth and bismuth acetate can be mentioned. As a metal complex containing Fe, for example, 2-ethyl hexane iron, iron acetate, and tris(acetylacetonate) iron can be mentioned. As a metal complex containing Ti, for example, 2-ethyl hexane acid titanium and titanium acetate can be mentioned. In addition, as solvents of the precursor solution of the orientation control layer, propanol, butanol, pentanol, hexanol, octanol, ethylene glycol, propylene glycol, octane, decane, cyclohexane, xylene, toluene, tetrahydrofuran, acetic acid, octyl acid, and the like can be mentioned. The composition ratio of Bi, Fe, and Ti is preferably Bi:Fe:Ti=100:50:50.
Then, the orientation control layer precursor layer is heated to predetermined temperature (for example, 150° C. to 200° C.), and is dried for a certain period of time (orientation control layer drying step). Then, the dried orientation control layer precursor layer is heated to predetermined temperature (for example, 350° C. to 450° C.) and is held for a certain period of time so as to be degreased (orientation control layer degreasing step). Here, “degreasing” means that organic components contained in the orientation control layer precursor layer are separated as NO2, CO2, H2O, and the like. The atmosphere of the orientation control layer drying step or the orientation control layer degreasing step is not limited, and the orientation control layer drying step or the orientation control layer degreasing step may be performed in the air, or in an oxygen atmosphere, and in an inert gas atmosphere.
Then, the orientation control layer precursor layer is heated to predetermined temperature, for example, about 600° C. to 850° C. and is held for a certain period of time, for example, 1 minute to 10 minutes, so as to be crystallized. As a result, the orientation control layer 75 formed of a composite oxide having a perovskite structure, in which Bi is included in the A site and Fe and Ti are included in the B site, is obtained (baking step).
The atmosphere of the orientation control layer baking step is not limited either, and the orientation control layer baking step may be performed in the air, or in an oxygen atmosphere, and in an inert gas atmosphere. Examples of a heating device used in the orientation control layer drying step, the orientation control layer degreasing step, and the orientation control layer baking step include a rapid thermal annealing (RTA) device that performs heating by irradiation of an infrared lamp, a hot plate, and the like.
The piezoelectric body 63 is formed on the Bi(FeTi)O3 layer 82 by the MOD method. The thickness of the piezoelectric body 63 may be 100 nm to 2000 nm. If the thickness of the piezoelectric body 63 is smaller than 100 nm, the influence of crystal defects, such as Pb or oxygen, is increased. Accordingly, since piezoelectricity is lowered, the receiving sensitivity is lowered. If the thickness of the piezoelectric body 63 is greater than 2000 nm, a crack is likely to occur in the piezoelectric body 63. This is not preferable in terms of manufacturing.
For example, first, a piezoelectric precursor layer is formed by applying a sol or a MOD solution (precursor solution), which contains an organic metal complex containing the constituent metals of a piezoelectric material for the piezoelectric body 63, on the orientation control layer 75 using a spin coat method or the like (application step). The precursor solution to be applied is obtained, for example, by mixing an organic metal complex containing the constituent metals of a piezoelectric material for the piezoelectric body 63 so that the molar ratio between the constituent metals becomes a desired molar ratio and then dissolving or dispersing the mixture using an organic solvent, such as alcohol. As an organic metal complex containing the constituent metals of a piezoelectric material, for example, metal alkoxides, organic acid salts, and β-diketone complexes can be used. Specifically, for example, the following materials can be mentioned. As an organic metal complex containing lead (Pb), for example, lead acetate can be mentioned. As an organic metal complex containing zirconium (Zr), for example, zirconium acetylacetonate, zirconium tetra acetylacetonate, zirconium mono acetylacetonate, and zirconium bisacetylacetonate can be mentioned. As an organic metal complex containing titanium (Ti), for example, titanium alkoxide and titanium isopropoxide can be mentioned. The composition ratio of Pb, Zr, and Ti, is preferably Pb:Zr:Ti=120:52:48.
Then, the piezoelectric precursor layer is heated to predetermined temperature, for example, about 130° C. to 180° C., and is dried for a certain period of time (drying step). Then, the dried piezoelectric precursor layer is heated to predetermined temperature, for example, 300° C. to 400° C. and is held for a certain period of time so as to be degreased (degreasing step). Here, “degreasing” means that organic components contained in the piezoelectric precursor layer are separated as NO2, CO2, H2O, and the like.
Then, the dried piezoelectric precursor layer is heated to predetermined temperature, for example, 650° C. to 800° C. and is held for a certain period of time so as to be crystallized. As a result, a piezoelectric layer is formed (baking step). Examples of a heating device used in the drying step, the degreasing step, and the baking step include a rapid thermal annealing (RTA) device that performs heating by irradiation of an infrared lamp, a hot plate, and the like. In addition, the piezoelectric body 63 configured to include a plurality of piezoelectric layers may be formed by repeating the application step, the drying step, and the degreasing step described above or the application step, the drying step, the degreasing step, and the baking step described above according to desired thickness or the like.
Then, the piezoelectric body 63 with a predetermined thickness that is configured to include a plurality of piezoelectric layers is formed by repeating the application step, the drying step, and the degreasing step described above or the application step, the drying step, the degreasing step, and the baking step described above according to desired thickness or the like. For example, in a case where the film thickness of the coating solution per time is about 0.1 μm, the total thickness of the piezoelectric body 63 configured to include, for example, ten piezoelectric layers is about 1.1 μm. Although the piezoelectric body 63 is provided by laminating the piezoelectric layers in the present embodiment, the piezoelectric body 63 may be formed to have only one piezoelectric layer.
As shown in
As shown in
It is preferable that a gap distance L between the first and second electrodes 61 and 62 is 2 μm or more. As the gap distance L increases, the electrostatic capacitance C of a capacitor decreases. Accordingly, the output voltage V is increased. On the other hand, if the gap distance L is too large, the initializing voltage of the piezoelectric body 63 is increased to 100 V or more. If the initializing voltage is too large, the cost of a driver IC is increased. Therefore, it is preferable that the gap distance L is 2 μm or more and 8 μm or less.
The measurement procedure of receiving sensitivity is shown below. A receiving element obtained through the above process is placed in a water tank filled with water, and an ultrasonic wave is generated from a large-diameter hydrophone located 30 cm away from the water tank. At this time, a voltage generated between the first and second electrodes 61 and 62 of the receiving element is read using a voltage amplifier. A peak-to-peak output voltage per 1 Pa is expressed as an indicator of receiving sensitivity. As an ultrasonic wave generated by the large-diameter hydrophone, a pulse wave of the 1.5 wave is generated with 3.5 MHz as a fundamental wave. Prior to reception measurement, in order to initialize the polarization of the piezoelectric body 63, a voltage of 100 V is applied between the first and second electrodes 61 and 62 of the receiving element.
One form of the embodiment is shown below. The vibrating film 58 and the piezoelectric body 63 are squares when viewed from above. The length of one side of a diaphragm formed by the vibrating film 58 is 40 μm, and the length of one side of the piezoelectric body 63 is 32 μm. In addition, the vibrating film 58 includes the silicon oxide layer 48 (1000 nm), the zirconium oxide layer 49 (400 nm), BFT (20 nm) of the orientation control layer 75, and PZT (1350 nm) of the piezoelectric body 63 in order from below. BFT is the abbreviation of BiFeTiO3 that forms the orientation control layer 75 according to the invention. The size of the gap 64 between the first and second electrodes 61 and 62 is set to 5 μm. In this case, the resonance frequency of the diaphragm in water is about 7.5 MHz.
In the case of using the orientation control layer 75 according to the invention, PZT of the piezoelectric body 63 is (100) preferentially oriented. On the other hand, as a comparative example, in a case where no orientation control layer is used, PZT of the piezoelectric body 63 is randomly oriented. The receiving sensitivity in the case of using the orientation control layer according to the invention was 3000 nV/Pa. On the other hand, in a case where no orientation control layer was used as in the comparative example, the receiving sensitivity was 2000 nV/Pa. Therefore, it can be seen that the invention using the orientation control layer has higher receiving sensitivity than in the comparative example.
While the embodiments have been described in detail above, it could be easily understood by those skilled in the art that various changes and modifications thereof could be made without departing from novel matters and effects of the invention. Accordingly, all of such modification examples are still included in the range of the invention. For example, in the specification or diagrams, a term which is described at least once together with different terms having a broader meaning or the same meaning can be replaced with the different terms in any parts of the specification or diagrams. In addition, the configurations and operations of the ultrasonic device unit 17, the device terminal 12, the second piezoelectric device 23, the coat layer 45, the vibrator 59, and the like are not limited to those described in the present embodiment, and various modifications can be made.
The entire disclosure of Japanese Patent Application No. 2015-109530 filed on May 29, 2015 is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-109530 | May 2015 | JP | national |
