JP2017005661A - Ultrasonic vibrator and ultrasonic diagnostic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic vibrator and ultrasonic diagnostic apparatus having high-sensitive vibration elements without increasing a production cost.SOLUTION: An ultrasonic vibrator includes multiple lamination bodies where a diaphragm, a bottom electrode, a piezoelectric body film, and an upper electrode are laminated in each lamination body in this order. The multiple lamination bodies are divided for each predetermined number so as to constitute multiple vibration elements. Each of ones of the lamination bodies includes the bottom electrode different in material or material composition ratio from that of the bottom electrode of each of the other lamination bodies concerning at least the one vibration elements among the multiple vibration elements.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an ultrasonic transducer and an ultrasonic diagnostic apparatus.

  The ultrasonic diagnostic apparatus transmits an ultrasonic pulse from the ultrasonic probe into the subject, receives an echo signal from the subject with the ultrasonic probe, and converts it into an electrical signal. The ultrasonic probe has an ultrasonic transducer that converts an electrical signal into mechanical vibration and vice versa. For the ultrasonic vibrator, for example, a vibration element (bulk type vibration element) obtained by dividing a bulk piezoelectric body in which a piezoelectric material and an electrode material are stacked is used. A large number of vibration elements are arranged in the longitudinal direction of the ultrasonic probe.

  In the electronic scanning method, an ultrasonic beam is scanned by sequentially driving the arranged vibration elements one by one in the long axis direction of the ultrasonic probe. An ultrasonic tomographic image of the subject is obtained based on the echo signal obtained by scanning the ultrasonic beam.

  The resolution of the ultrasonic tomographic image depends on the pitch in the scanning direction of the ultrasonic beam. This pitch is determined by the width of the vibration element. Therefore, in order to increase the resolution of the ultrasonic tomographic image, it is required to reduce the size and density of the vibration element.

  In general, when a mechanical stress is generated by applying a compressive stress or a tensile stress to the vibration element, polarization occurs in the vibration element, and a voltage proportional to the strain is generated. Therefore, it is also required to increase the sensitivity of the vibration element by ensuring the ease of distortion of the vibration element so that the voltage when the ultrasonic pulse is received changes greatly.

  In recent years, an ultrasonic probe using a semiconductor microfabrication technology (MEMS technology) has been proposed in response to the demand for downsizing and high density of vibration elements. For example, a vibration element manufactured by MEMS technology described in Patent Document 1 is configured by sequentially forming a piezoelectric film and an upper electrode on a vibration plate that also serves as a lower electrode.

  Further, for example, in Patent Document 2, in order to make the vibration element highly sensitive, the vibration plate is removed and the piezoelectric film is easily deformed into a non-flat shape (for example, a dome shape) and added to the bending mode. Obtaining high electrical opportunity coupling is described.

JP2013-93760A U.S. Pat. No. 8,767,512

  However, in the vibration element described in Patent Document 1, the piezoelectric film has a shape formed on a flat vibration plate. Since this is a shape that is not easily distorted, the vibration element provided with such a piezoelectric film has a problem in that the sensitivity is lower than that of the bulk-type vibration element.

  Further, the diaphragm dome shape of the vibration element described in Patent Document 2 has a complicated structure and is difficult to manufacture by the MEMS technology. For this reason, there was a problem that the yield was lowered and a high-level manufacturing process was required to produce the dome shape.

  The present invention solves the above-described conventional problems, and an object thereof is to provide an ultrasonic transducer and an ultrasonic diagnostic apparatus having a highly sensitive vibration element without using a complicated structure such as a dome shape. .

In order to achieve the above object, the ultrasonic transducer of the present invention has a plurality of laminates in which a diaphragm, a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order,
A plurality of laminated bodies are divided into a predetermined number to constitute a plurality of vibration elements,
In each of at least one vibration element among the plurality of vibration elements, one of the stacked bodies has a lower electrode having a material or a material composition ratio different from that of the lower electrode of any of the other stacked bodies.

  According to the present invention, the lower electrodes having different materials or material composition ratios are mixed in a predetermined number of laminated bodies constituting individual vibrating elements without complicating the structure of the laminated bodies constituting the vibrating elements. By adjusting the mixing ratio, the physical properties of the piezoelectric film, especially the dielectric constant of the piezoelectric film, can be controlled appropriately, so the stack can be made smaller and more dense without a complicated structure. That is, the vibration element can be easily reduced in size and density, and an ultrasonic transducer and an ultrasonic diagnostic apparatus having a highly sensitive vibration element can be provided.

1 is a block diagram showing an overall configuration of an ultrasonic diagnostic apparatus in an embodiment of the present invention. It is a circuit diagram of the signal detection by MOSFET. It is a figure which shows the arrangement | sequence of a vibration element. It is sectional drawing which shows an example of a laminated body group roughly. It is a figure which shows the mixture ratio of the several laminated body in the same channel. FIG. 6A is a diagram showing a transducer arrangement, FIG. 6A is a diagram when a combination of two laminates is arranged as a laminate group, and FIG. 6B is a diagram when a combination of three laminates is arranged as a laminate group. FIG. 6C is a diagram when a combination of four stacked bodies is arranged as a stacked body group. FIG. 4 is a diagram illustrating stacked body aggregate portions arranged in a distributed manner in a vibration element. FIG. 8A is a view when the areas of the lower electrode and the upper electrode included in the same laminate are made different, FIG. 8A is a view when the upper electrode is made into a small circle shape, and FIG. 8B is a view where the upper electrode is made into a ring shape. It is a figure of time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of the ultrasound diagnostic apparatus S in the present embodiment.

  The ultrasonic diagnostic apparatus S includes an ultrasonic diagnostic apparatus main body 1 and an ultrasonic probe 2. The ultrasonic diagnostic apparatus body 1 includes a control unit 3, a signal processing unit 14, an image generation unit 15, a display control unit 16, and a user interface UI. The user interface UI includes a display unit 17 and an operation unit 18.

  The ultrasonic probe 2 includes a probe control unit 2A, a transmission / reception unit 11, and an ultrasonic transducer 10. The ultrasonic transducer 10 has a transducer array 20A (described later) in which a plurality of transducer elements 20 (described later) are arranged. The ultrasonic probe 2 is provided with a transmission / reception switching unit (switch) 4 connected to the transmission unit 12 and the reception unit 13 of the transmission / reception unit 11.

  The transmission / reception switching unit 4 switches the connection between each vibration element 20 and the transmission unit 12 or the reception unit 13 in accordance with a transmission / reception switching signal from the probe control unit 2A. By switching the transmission / reception switching unit 4, each vibration element 20 is connected to the transmission unit 12 or the reception unit 13. The vibration element 20 connected to the transmission unit 12 functions as a transmission vibration element 20 and generates an ultrasonic pulse by a voltage pulse supplied from the transmission unit 12. The vibration element 20 connected to the reception unit 13 functions as a reception vibration element 20, receives a reflection (echo) signal from the subject, and outputs the signal to the reception unit 13. The transmission / reception unit 11 may be configured in the ultrasonic diagnostic apparatus main body 1 as a configuration provided in the ultrasonic probe 2.

The receiving unit 13 converts the charge induced by the vibration element 20 with the reception of the reflected (echo) signal into a voltage signal corresponding to the amount of charge. The receiving unit 13 includes a detection system 130 provided in one-to-one correspondence with each vibration element 20, and the detection system 130 includes one or more detection elements. As the detection element, for example, a MOSFET (metal oxide semiconductor field effect transistor) is used. FIG. 2 is a circuit diagram of MOSFET detection in which the vibration element 20 and the detection system 130 are connected. As shown in FIG. 2, the voltage signal (V) generated by piezoelectric conversion of the reflected signal received by the vibration element 20 is detected as a detection signal (Vin) by the detection system 130. In order to maximize the sensitivity of the vibration element 20, the first capacitance C _f on the vibration element 20 side and the second capacitance C _in (gate capacitance) on the detection system 130 side must be matched. Will be described later.

  The probe control unit 2A switches the connection in the transmission / reception switching unit 4 at a predetermined switching timing according to a preset arrangement pattern indicating the positions of the transmission vibration element 20 and the reception vibration element 20, whereby each vibration element 20. Is connected to the transmission unit 12 or the reception unit 13, and the vibration element 20 is switched between transmission and reception.

  The signal processing unit 14 performs various processes such as a process of applying a BPF (Band Pass Filter) to the voltage signal from the receiving unit 13, nonlinear compression, depth correction, and a detection process. The image generation unit 15 generates image data representing the tissue shape of the subject based on the data after the signal processing. The display control unit 16 receives an input operation from the operation unit 18 (keyboard, mouse, touch panel, etc.), and displays a tomographic image on the display unit 17 (liquid crystal screen, etc.) based on the image data.

  FIG. 3 is a diagram schematically illustrating an example of the ultrasonic transducer 10.

  As shown in FIG. 3, the transducer array 20 </ b> A has 128 vibration elements 20 arranged in the major axis direction of the ultrasonic probe 2 (scanning direction indicated by X in FIG. 3). The vibration element 20 constitutes one unit (one channel) as a target for giving a delay time during electronic scanning. In other words, the plurality of vibration elements 20 constitutes an array of a plurality (here, 128) channels.

  Each vibration element 20 has a predetermined number (26 in this case) of laminates having the same structure in the major axis direction and the minor axis direction perpendicular to the major axis direction (the elevation direction indicated by Y in FIG. 3) 2 ×. It is arranged in 13 matrix forms. In other words, a plurality of laminated bodies are divided into a predetermined number to constitute a plurality of vibration elements 20. Each laminated body includes a piezoelectric body, and when manufactured by MEMS technology, this may be referred to as a “pMUT cell” (pMUT: piezoelectric Micromachined Ultrasound Transducer). May be referred to as a “pMUT cell group”.

  In the present embodiment, in each vibration element 20, two types of laminated bodies are mixed to increase sensitivity. Hereinafter, the first type laminate is referred to as a laminate 30A, and the second type laminate is referred to as a laminate 30B. In the following description, a set of two or more laminates (laminates 30A and 30B) is referred to as a laminate group 300. The generic name of the stacked bodies 30A and 30B is referred to as a stacked body 30.

  FIG. 4 is a cross-sectional view schematically illustrating an example of the stacked body group 300. In this example, the stacked body group 300 includes one stacked body 30A and a stacked body 30B.

Each of the stacked bodies 30 </ b> A and 30 </ b> B includes a diaphragm (diaphragm) 32, a lower electrode 33, a piezoelectric film 34, and an upper electrode 35. The diaphragm 32, the lower electrode 33, the piezoelectric film 34, and the upper electrode 35 are laminated in this order. Although not shown, a film for protection and insulation is formed on the upper electrode 35. For this film, for example, an oxide film such as SiO ₂ (silicon oxide) or an organic film such as epoxy resin or parylene is used.

  Both ends of the diaphragm 32 are supported by the substrate 31. The diaphragm 32 is formed integrally with the substrate 31. For example, the diaphragm 32 is formed in a thin plate shape by partially thinning a silicon substrate as a material of the substrate 31 by etching.

  The lower electrode 33 is formed on the flat diaphragm 32. Further, the piezoelectric film 34 is formed on the lower electrode 33. Further, the upper electrode 35 is formed on the piezoelectric film 34. In the present embodiment, since these stacks are flat and not complicated, they can be easily and finely manufactured by a normal film formation technique and a MEMS technique. As a result, the vibration element 20 can be reduced in size and density.

  The material of the upper electrode 35 may be the same material as the material of the lower electrode 33 described later for ease of manufacture, but may be a material different from that of the lower electrode 33.

  The material of the piezoelectric film 34 may be a conventionally known material such as lead zirconate titanate.

  As shown in FIG. 4, the stacked bodies 30A and 30B have the same structure. The same structure means that the substrate 31, the vibration plate 32, the lower electrode 33, the piezoelectric film 34, the upper electrode 35, etc. have the same thickness and cross-sectional shape. In addition, although the board | substrate 31 contains the location shared between the laminated body 30A and the laminated body 30B, it is the same by the structure when it divides in half. The same range includes manufacturing errors. For example, the piezoelectric film 34 is made of the same material and has the same thickness. Further, as described above, the diaphragm 32 has a flat plate shape. Furthermore, the piezoelectric film 34 and the upper electrode 35 can be easily manufactured in the same manufacturing process. For this reason, it becomes easy to produce the laminated bodies 30A and 30B, and, in turn, the production of the vibration element 20 is facilitated.

  Here, by making the structure of the laminated body 30 non-planar, or by making the material of the piezoelectric film 34 different between the laminated body 30A and the laminated body 30B so as to have different dielectric constants. Although it is conceivable to obtain the vibration element 20 with high sensitivity, this may increase the production cost of the vibration element 20.

In the present embodiment, the individual vibration elements 20 can be manufactured without complicating the structure of the multilayer body 30 in a non-planar shape and without making the materials of the piezoelectric films 34 in the multilayer bodies 30A and 30B different from each other. In the predetermined number of laminated bodies 30 to be configured, lower electrodes 33 having different materials or material composition ratios are mixed, and the mixing ratio is adjusted, whereby the physical properties of the piezoelectric film 34, particularly the dielectric constant ( The relative dielectric constant ε _γ ) can be appropriately controlled. Thereby, the highly sensitive vibration element 20 can be obtained without increasing the production cost.

  The material of the lower electrode 33 can produce the piezoelectric effect of the piezoelectric material deposited on the upper layer, does not generate a reaction compound with the component elements in the piezoelectric material, has good surface smoothness, and does not form a piezoelectric material. Those that do not precipitate an alloy phase due to changes in the film process temperature are desirable. As a result, the piezoelectric film 34 and the lower electrode 33 are hardly adhered and peeled off, and an effect of suppressing deterioration over time of the piezoelectric characteristics can be obtained.

  For example, as the material of the piezoelectric film 34, when the material having the lattice constant representing the unit cell size of the crystal of 3.9 to 4.1 [Å] is used, the material of the lower electrode 33 that can obtain the above-described effect. In this case, those having a lattice constant in the range of 3.9 to 4.1 [Å] are used.

As a material of the lower electrode 33 having such a lattice constant, for example, a perovskite type compound such as platinum (Pt) or LNO (LaNiO ₃ ), a silver alloy (Ag) containing palladium (Pd) containing silver (Ag) as a main component. -Pd).

  Other examples of materials that can be used in the lower electrode 33 include copper (Cu), silicon (Si), chromium (Cr), titanium (Ti), nickel (Ni), gold (Au), platinum (Pt ), Aluminum (Al), tantalum (Ta), and cobalt (Co).

The material of the lower electrode 33 may be (Ba, La) TiO ₃ or (Ba, La) SnO ₃ having a lattice constant of 4.0 to 4.1 [Å]. Furthermore, SrRuO ₃ may be used. These materials have a piezoelectric effect of a piezoelectric material, like platinum (Pt), LNO, and silver alloy (Ag—Pd).

  As a method of forming the lower electrode 33 on the diaphragm 32, PVD methods such as sputtering, ion plating, molecular beam epitaxy, laser ablation, ionized cluster beam evaporation, and ion beam evaporation are used. It is done. Note that a sputtering method using the above-described material as a target material is preferably used as the film formation method.

  If the lower electrode 33 is formed on the vibration plate 32 by, for example, a multi-source sputtering method, and when silver (Ag) and palladium (Pd) are used as the target material, depending on the positional relationship between the sample and the target material, In addition, a region in which the contents of silver (Ag) and palladium (Pd) are slightly different from each other can be produced at a time, fine adjustment of the lattice constant can be facilitated, the lattice constant of the piezoelectric film 34 and the lattice constant of the lower electrode 33 Can be adjusted appropriately, and the dielectric constant can be controlled.

  When the material of the lower electrode 33 is a silver alloy (Ag—Pd), the lower electrode 33 of any of the stacked bodies 30A and 30B is different from the lower electrode 33 of any of the other stacked bodies 30A and 30B. It has a composition ratio of silver (Ag) and palladium (PD). Thereby, the electrostatic capacity of the stacked body 30A is different from the electrostatic capacity of the stacked body 30B.

The relative dielectric constant ε _γ of the piezoelectric film 34 can be confirmed by a known measurement method.

An example of a method of measuring the relative dielectric constant epsilon _gamma is described. For the measurement of the relative dielectric constant ε _γ of the piezoelectric film 34, for example, as a measurement target of the relative dielectric constant ε _γ , PZT (Pb (Zr, Ti) O ₃ ) / PLT (Pb, La) TiO ₃ ) is used. This measurement object is set in, for example, a Soya tower circuit, and an AC power supply 1 [MHz] is applied to both electrodes of the piezoelectric film 34. A voltage applied to both electrodes of the piezoelectric film 34, based on the charge induced on both poles of the piezoelectric film 34, the dielectric constant of the piezoelectric film 34 epsilon _gamma is measured.

The relationship between the relative dielectric constant epsilon _gamma of materials and the piezoelectric film 34 of the lower electrode 33 is, for example, as follows. When the material is platinum (Pt), the relative dielectric constant ε _γ is 480. When the material is LNO (LaNiO ₃ ), the relative dielectric constant ε _γ is 550. Furthermore, if the material composition ratio of silver-silver alloy Ag-Pd containing 45% palladium as the main component (Pd) (Ag) (45 %), relative dielectric constant epsilon _gamma is 260. Furthermore, if the material composition ratio of silver of 25% palladium (Ag) as the main component silver alloy Ag-Pd containing (Pd) (25%), relative dielectric constant epsilon _gamma is 230.

From this, even if the stacked bodies 30A and 30B have the same structure, the capacitances of the stacked bodies 30A and 30B differ due to different materials and the like of the lower electrodes 33. Therefore, by adjusting the combination of the stacked bodies 30A and 30B in the stacked body group 300 connected to the MOSFET (detecting element), the capacitance on the stacked body group 300 (laminated body 30A and 30B) side is changed to the detection system 130. Thus, it is possible to match the capacitance on the input side of the MOSFET (detection element) electrically connected to the stacked body group 300, and the highly sensitive vibration element 20 is obtained. Further, by adopting a technique for matching the first capacitance C _f on the vibration element 20 side with the second capacitance C _in on the detection system 130 side in this way, MOSFET manufacturing tolerance (individual difference), etc. Even if the second electrostatic capacity C _in on the detection system 130 side is not always the same due to the above, the first electrostatic capacity C _f on the vibrating element 20 side is always matched with the second electrostatic capacity C _in . Can be made.

FIG. 5 shows an example of adjusting the mixing ratio of the stacked bodies 30A and 30B. The laminated body 30A is indicated by a white circle, and the laminated body 30B is indicated by a hatched circle. In this example, the total number of the stacked bodies 30A and 30B in the same channel is 26, and the mixing ratio of the stacked bodies 30A and 30B is adjusted from “13:13” to “24: 2”. In this way, it is possible to adjust the first capacitance C _f of the entire vibration element 20 by changing the mixture ratio of the stacked bodies 30A and 30B.

Next, see Table 1 for matching the first capacitance C _f on the side of the stack group connected to the MOSFET (detection element) with the second capacitance C _in on the input side of the MOSFET (detection element). To explain. In addition, in order to make the explanation easy to understand, a case where the number of stacked bodies in the stacked body group 300 connected to the MOSFET (detecting element) is 2 to 4 will be described as an example.

Table 1 shows the first capacitance C _f on the side of the stacked body group 300 produced by different materials or material composition ratios of the lower electrode 33. In order to facilitate the fabrication of the vibration element 20, since the stacked bodies in the same channel (vibration element 20) have the same structure, the thickness d of the piezoelectric film 34 is the same and the dimensions (for example, the length of the side) ) It is a precondition that L is the same.

In Table 1, d is the thickness of the piezoelectric film 34, ε _γ is the relative dielectric constant of the piezoelectric film 34, and C _f is the capacitance of the piezoelectric film 34 (for each stacked body in the stacked body group 300). L is the length of the side of the square piezoelectric film 34. Note that when a laminated body for 5 [MHz] is manufactured, a piezoelectric film 34 having a length L of 53 [μm] is used. Further, when a laminated body for 1 [MHz] is manufactured, a piezoelectric film 34 having a length L of 106 [μm] is used. By substituting these into equation (1), the first capacitance C _{f of} each laminate is calculated. The vacuum dielectric constant ε _o is 8.85 [pF / m].
_{C f = ε o ε γ L} 2 / d (1)

From Table 1, for example, when the piezoelectric film 34 has d = 1 [μm], ε _γ = 200, and L = 53 [μm], the first capacitance C _f of the stacked body is 5 [pF]. For example, when the piezoelectric film 34 has d = 1 [μm], ε _γ = 400, and L = 53 [μm], the first capacitance Cf of the stacked body is 10 [pF]. Note that the thickness d of the piezoelectric film 34 is the same and the length L of the sides is the same under the above preconditions.

In contrast, when the second capacitance C _in on the input side of the MOSFET (detection element) is 15 [pF], two types of piezoelectric films 34 having the two types of first capacitances C _f are used. When the stacked bodies 30A and 30B are manufactured, the total of the first capacitances C _f is 15 (= 5 + 10) [pF]. A stacked body group 300 is configured by a combination of the stacked bodies 30A and 30B, and one MOSFET (detecting element) is connected to the stacked body group 300, whereby the first electrostatic bodies on the combined stacked bodies 30A and 30B side are arranged. it can be aligned with the second capacitance _{C in} the input side of the total MOSFET (detection element) of the capacitor _{C f.} Incidentally, when performing matching of above, the sum of the first capacitance C _f fitted to the second capacitance C _in, it is not necessary to always coincide. Since the total of the first capacitance C _f indicates a discontinuous numerical value, when it is difficult to match, the total of the first capacitance C _f is the second static value so that the vibration element 20 has high sensitivity. so as to approach the capacitance C _in, by combining the laminate may be the sum of the first capacitance C _f is aligned so as to substantially coincide with the second capacitance C _in. Incidentally, the difference between the total and the second capacitance _{C in} the first capacitance _{C f} is desirably about -20% to +20%.

  As described above, when the stacked body group 300 is configured by the combination of the stacked bodies 30A and 30B, the stacked bodies 30A and 30B (indicated by A and B in FIG. 6) are staggered as shown in FIG. 6A. In this way, the stacked body groups 300 are arranged in the elevation direction (Y direction). The reason is that the laminated bodies 30A and 30B having different first electrostatic capacities are mixed as much as possible to achieve uniform acoustic characteristics. In addition, the laminated body group 300 is shown with a broken line in FIG. 6A. In the stacked bodies 30A and 30B in the stacked body group 300, the lower electrodes 33 are connected to each other.

Further, from Table 1, for example, when the piezoelectric film 34 has d = 1 [μm], ε _γ = 100, and L = 53 [μm], the first capacitance C _f of the stacked body is 2.5 [pF. ]. For example, when the piezoelectric film 34 has d = 1 [μm], ε _γ = 400, and L = 53 [μm], the first capacitance C _f of the stacked body is 10 [pF]. Note that the thickness d of the piezoelectric film 34 is the same and the length L of the sides is the same under the above preconditions.

On the other hand, when the second capacitance C _in on the input side of the MOSFET (detection element) is 22.5 [pF], the piezoelectric film 34 having the two types of first capacitances C _f is used. be manufactured two types of laminates, the sum of their first capacitance _{C f} becomes 22.5 (= 2.5 + 10 + 10 ) [pF]. A laminated body group 300 is configured by a combination of two laminated bodies 30A and one laminated body 30B, and a single MOSFET (detecting element) is connected to the laminated body group 300, thereby combining the laminated bodies. The sum of the first capacitances C _f on the 30A and 30B sides can be matched with the second capacitance C _in on the input side of the MOSFET (detection element).

  As described above, when the stacked body group 300 is configured by combining two stacked bodies 30A and one stacked body 30B, as shown in FIG. The overall shape of the stacked body group 300 that combines the single stacked body 30A and the single stacked body 30B is, for example, an L-shape, and is configured such that one stacked body 30B is arranged at the corner. Each stacked body group 300 is arranged in the elevation direction (Y direction) so that the L shapes are combined with each other. In addition, the laminated body group 300 is shown with a broken line in FIG. 6B. In the stacked bodies 30A and 30B in the stacked body group 300, the lower electrodes 33 are connected to each other.

Although not shown in Table 1, a laminate group 300 is configured by a combination of four types of laminates 30A, 30B, 30C, and 30D, and one MOSFET (detection element) is connected to the laminate group 300. Thus, the first capacitance C _f on the stacked body group 300 (stacked bodies 30A and 30B) side can be matched with the second electrostatic capacitance C _in on the input side of the MOSFET (detection element). When the laminate group 300 is configured by combining the four types of laminates 30A, 30B, 30C, and 30D, in order to achieve uniform acoustic characteristics, the overall shape of the laminate group 300 is as shown in FIG. The laminated bodies 30A, 30B, 30C, and 30D have a quadrangular shape arranged at the four corners. This quadrangular laminate group 300 is arranged in the elevation direction (Y direction). The laminated body group 300 is shown with a broken line in FIG. 6C. In the stacked bodies 30A and 30B in the stacked body group 300, the lower electrodes 33 are connected to each other.

As described above, the first capacitance C _f of the stacked body group 300 electrically connected to the MOSFET in accordance with the MOSFET (detection element) _in which the second capacitance C _in changes according to the area. Can be adjusted. Needless to say, when the laminated bodies 30 are electrically connected to individual MOSFETs one by one and their capacitances coincide with each other, they may be electrically connected one-on-one.

  As shown in FIGS. 6A to 6C, different types of stacked bodies 30 </ b> A and 30 </ b> B can be dispersed and arranged in the vibration element 20, but the same type of stacked bodies 30 </ b> A or 30 </ b> B are used for capacitance adjustment. It can also be placed adjacent. An example is shown in FIG. In this example, a stacked body assembly 301 composed of eight adjacently disposed stacked bodies 30A and a stacked body assembly 301 composed of eight adjacently disposed stacked bodies 30B are alternately disposed in the vibration element 20. Has been.

  In the vibration element 20 in which the stacked body aggregate 301 is arranged in this way, the size of each stacked body aggregate 301 is equal to or less than the half wavelength of the ultrasonic wave to be received. As shown in FIG. 7, for example, L is the dimension in the elevation direction (Y direction) of the laminated body assembly 301 (the aggregate of the laminated bodies 30A or the aggregate of the laminated bodies 30B), and λ is the wavelength of the ultrasonic wave to be received. In this case, the arrangement condition of the laminated body assembly portion 301 that is allowed for achieving uniform acoustic characteristics is L ≦ λ / 2.

  In the above embodiment, the lower electrode 33 and the upper electrode 35 included in the same stacked body 30A, 30B have the same area. On the other hand, the sensitivity may increase because the areas of the lower electrode 33 and the upper electrode 35 included in the same stacked body 30A, 30B are different. In order to increase sensitivity, the area of the other electrode may be made smaller than the area of one electrode, but here, the area of the upper electrode 35 is made smaller than the area of the lower electrode 33. This is because the lower electrode 33 needs to ensure a certain area because the piezoelectric film 34 is formed thereon.

  For example, as shown in FIG. 8A, the area of the upper electrode 35 is made smaller than the area of the lower electrode 33 by making the diameter R1 of the circle of the upper electrode 35 smaller than the diameter R of the circle of the lower electrode 33.

  Further, for example, as shown in FIG. 8B, the lower electrode 33 has a circular shape, the upper electrode 35 has a ring shape, the lower electrode 33 has a circular diameter R2 and the ring-shaped outer diameter R3 of the upper electrode 35. When the upper electrode 35 is formed into a ring shape (indicated by a ring-shaped inner diameter R4), the area of the upper electrode 35 is made smaller than the area of the lower electrode 33.

  In the ultrasonic vibrator 10 described above, the laminated body includes a laminated body 30A (corresponding to the “first laminated body” of the present invention) and a laminated body 30B (corresponding to the “second laminated body” of the present invention), When a plurality of vibration elements form an array of a plurality of channels, the stacked bodies 30A are preferably arranged so as not to be adjacent to each other in one channel. Accordingly, the laminated body 30A is mixed with a different kind of laminated body (for example, the laminated body 30B) and the like, so that the acoustic characteristics can be made uniform.

  In the ultrasonic transducer 10 described above, the vibration element 20 constitutes one channel, but a predetermined number of laminated bodies 30A and 30B constituting the vibration element 20 of the same channel are divided into a plurality of subchannels. May be. At this time, the lower electrodes 33 included in the same subchannel among the plurality of subchannels are electrically connected to each other. Although the number of stacked bodies in the subchannel used for electronic scanning is smaller than the number of stacked bodies in one channel, it is possible to scan a shallow portion in the subject.

  In addition, each of the above-described embodiments is merely an example of a specific example for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

  The present invention can be applied to an ultrasonic diagnostic apparatus including an ultrasonic transducer. By using a small and high density vibration element, the ultrasonic probe becomes small and lightweight, and the operability of the ultrasonic probe can be improved.

S ultrasonic diagnostic apparatus 1 ultrasonic diagnostic apparatus main body 2 ultrasonic probe 10 ultrasonic transducer 20A transducer array 20 vibrating element 30 laminated body 30A laminated body 30B laminated body 31 substrate 32 diaphragm 33 lower electrode 34 piezoelectric film 35 upper part Electrode 130 Detection system 300 Laminate group

Claims (14)

An ultrasonic vibrator having a plurality of laminates in which a diaphragm, a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order,
The plurality of laminated bodies are divided into a predetermined number to constitute a plurality of vibration elements,
In each of at least one vibration element among the plurality of vibration elements, one of the stacked bodies has a lower electrode having a material or a material composition ratio different from that of the lower electrode of any of the other stacked bodies. .   The ultrasonic transducer according to claim 1, wherein the piezoelectric films are made of the same material and have the same thickness among the plurality of stacked bodies.   The ultrasonic transducer according to claim 1, wherein the plurality of stacked bodies have the same structure.   The ultrasonic transducer according to any one of claims 1 to 3, wherein the lower electrode and the upper electrode included in the same laminate have different areas.   The predetermined number of laminated bodies constituting each of the at least one vibration element is electrically connected to one detection element for each laminated body group of one or a combination of two or more laminated bodies. The electrostatic capacity of each body or the electrostatic capacity of each stacked body group is matched with the electrostatic capacity of the one detection element that is electrically connected. Ultrasonic transducer.   The ultrasonic transducer according to claim 5, wherein a capacitance of each stacked body or a capacitance of each stacked body group matches a capacitance of the one detection element that is electrically connected. The laminate includes a first laminate and a second laminate having a lower electrode having a different material or material composition ratio from the lower electrode of the first laminate,
The plurality of vibration elements constitute an array of a plurality of channels,
The ultrasonic transducer according to claim 1, wherein the first stacked bodies are arranged so as not to be adjacent to each other in one channel. In each of the at least one vibration element, the stacked body aggregate portions in which two or more stacked bodies having the lower electrode of the same material or material composition ratio are adjacently disposed are disposed in a dispersed manner.
The ultrasonic transducer according to any one of claims 1 to 7, wherein the dimension of each stacked body aggregate is equal to or less than a half wavelength of an ultrasonic wave to be received.   The ultrasonic transducer according to any one of claims 1 to 5, wherein a material having a lattice constant of 3.9 to 4.1 [Å] is used for all or a part of the material of the lower electrode.   The ultrasonic vibrator according to claim 9, wherein a silver alloy containing Pd in Ag is used as a material of the lower electrode.   The ultrasonic transducer according to claim 1, wherein the plurality of vibration elements constitute an array of a plurality of channels.   The ultrasonic transducer according to claim 11, wherein the lower electrodes included in a vibration element of the same channel among the plurality of vibration elements are electrically connected to each other. The predetermined number of laminated bodies constituting the vibration element of the same channel among the plurality of vibration elements are divided into a plurality of subchannels,
The ultrasonic transducer according to claim 11, wherein the lower electrodes included in the same subchannel among the plurality of subchannels are electrically connected to each other.   An ultrasonic diagnostic apparatus comprising the ultrasonic transducer according to claim 1.

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