Patent Application
20050211162
1. Field of the Invention
The present invention relates to a nozzle device for spraying raw material powder toward a substrate so as to form a film, and a film forming apparatus and method using the device. Furthermore, the present invention relates to an inorganic electroluminescence (EL) device, an inkjet head and an ultrasonic transducer array fabricated by using such a film forming method.
2. Description of a Related Art
Recent years, when fabricating a hard and brittle material such as ceramics, it has been under study to use film forming technologies by which thick films can be formed without mixing a binder. Among them, the aerosol deposition (AD) method by which dense and strong thick films can be formed receives attention. The AD method is a film forming method of depositing the raw material by spraying ultrafine particles of a raw material toward a substrate so that the particles impinge on the substrate or a previously formed film. The AD method is also referred to as injection deposition method or gas deposition method.
In the AD method, when a film is formed in a region having a certain area, the substrate is scanned by using a nozzle for injecting ultrafine particles of the raw material. However, as the film forming area becomes larger, scanning with the nozzle must be repeated, and it takes a lot of time to forming a film. Accordingly, in response to the request to make the film forming region larger, the nozzle size has been made larger into a slit form, or the nozzle has been made to move over a broader range regularly. However, when the nozzle size is made larger, since it is difficult to stably supply an aerosol to the nozzle or to stably inject the aerosol from the nozzle, it is inevitable that streaky defects are produced in the formed film or the film thickness becomes nonuniform.
By the way, recent years, in various technology fields, phenomena based on the chaos theory have been utilized. According to Aihara (Department of Mathematical Engineering and Information Physics, the University of Tokyo), a chaos is defined as “a phenomenon in which, although a system changes according to a firm rule, the system behaves very complexly and unstably and a state in some distant future is completely unpredictable”. Further, he also stated that, when one chaos exists, an infinite number of orders are included therein, and since the orders are inherent, the chaos can be predicted and controlled.
For example, in a film forming method in which a film forming source (e.g., target) has an area equal to or larger than a substrate like the sputtering method or the like, in order to fabricate a uniform film, sometimes the substrate is chaotically moved by giving the substrate rotation motion and revolution motion. This is because, when the substrate exhibits chaotic behavior, the substrate no longer traces the same track again because of orbit instability of chaos, and a uniform film can be formed over a broad range. However, in the AD method, unlike the sputtering method or the like, the nozzle as a film forming source can be regarded as small as a dot or line relative to the substrate. Accordingly, it is unsuitable for utilizing the above-described technique without change.
Further, Japanese Patent Application Publications JP-A-7-31575 (the first page,
The present invention has been achieved in view of the above-described problems. An object of the present invention is to provide a film forming apparatus and method by which uniform and large area films can be formed according to the AD method, and a nozzle device to be used therein. A further object of the present invention is to provide an inorganic electroluminescence device, an inkjet head to be used in an inkjet printer, and an ultrasonic transducer array to be used in an ultrasonic probe, all of which are manufactured by using such a film forming method.
In order to solve the above-described problems, a nozzle device according to the present invention is a nozzle device to be used for spraying fluid mixed with powder to a region having a predetermined area, and including: at least one nozzle for injecting the fluid mixed with the powder; displacing means for supporting and displacing the at least one nozzle; and control means for controlling at least the displacing means such that the at least one nozzle exhibit chaotic behavior.
Further, a film forming apparatus according to the present invention includes: a film forming chamber; a substrate holder located in the film forming chamber, for holding a substrate on which a structure is to be formed; exhaust means for exhausting an interior of the film forming chamber; aerosol generating means for generating an aerosol by blowing up raw material powder placed in a container with a gas; introducing means for introducing the aerosol generated by the aerosol generating means into the film forming chamber; at least one nozzle disposed oppositely to the substrate held by the substrate holder in the film forming chamber, for spraying the aerosol introduced via the introducing means toward the substrate; and displacing means for chaotically changing a relative position of the substrate held by the substrate holder and the at least one nozzle.
Furthermore, a film forming method according to the present invention includes the steps of: (a) placing a substrate, on which a structure is to be formed, in a substrate holder located in a film forming chamber; (b) exhausting an interior of the film forming chamber; (c) generating an aerosol by blowing up raw material powder placed in a container with a gas; (d) introducing the aerosol generated at step (c) into the film forming chamber; and (e) spraying the aerosol introduced at step (d) from at least one nozzle toward the substrate in the film forming chamber while chaotically changing a relative position of the substrate held by the substrate holder and the at least one nozzle disposed oppositely to the substrate so as to deposit the raw material powder on the substrate.
An inorganic electroluminescence device according to the present invention includes: a first electrode layer; a first insulating layer including a thick film deposited on the first electrode layer by spraying powder of a material having dielectricity from a nozzle toward the first electrode layer while chaotically changing a relative position of the nozzle and the first electrode layer; a luminescent layer formed on the first insulating layer and including a material that exhibits electroluminescence; a second insulating layer formed on the luminescent layer; and a second electrode layer formed on the second insulating layer.
An inkjet head according to the present invention includes: a vibrating plate; a first electrode formed on a first surface of the vibrating plate; a plurality of piezoelectric materials deposited on the first electrode by spraying piezoelectric material powder from a nozzle toward the first electrode while chaotically changing a relative position of the nozzle and the first electrode; a plurality of second electrodes formed on the plurality of piezoelectric materials, respectively; at least one partition wall for forming a plurality of pressure chambers to be filled with a liquid by partitioning space on a second surface of the vibrating plate; and a nozzle plate disposed on the at least one partition wall and formed with a plurality of openings for discharging the liquid from the plurality of pressure chambers respectively.
An ultrasonic transducer array according to the present invention is an ultrasonic transducer array to be used for transmitting and receiving ultrasonic waves in an ultrasonic probe, and including: at least one first electrode; a plurality of piezoelectric materials deposited on the at least one first electrode in a predetermined arrangement by spraying piezoelectric material powder from a nozzle toward the at least one first electrode while chaotically changing a relative position of the nozzle and the at least one first electrode; and at least one second electrode formed on the plurality of piezoelectric materials.
According to the present invention, since the respective parts are formed such that the nozzle exhibits chaotic behavior, the nozzle traces completely irregular tracks within a movable range. By applying such a nozzle chaotically moving to the film forming apparatus, the raw material powder can be sprayed evenly over the substrate. Accordingly, a large area film having a uniform thickness, in which streaky defects are suppressed, can be formed. Therefore, thick films with good quality can be sufficiently fabricated, and the yield of products employing such thick films, for example, an inorganic EL device, inkjet head and ultrasonic transducer array can be improved.
Hereinafter, embodiments of the present invention will be described in detail by referring to the drawings. The same reference numerals are assigned to the same component elements and the description thereof will be omitted.
The film forming device as shown in
The compressed gas cylinder 1 is filled with nitrogen (N2), oxygen (O2), helium (He), argon (Ar) or dry air to be used as a carrier gas. Further, a pressure regulating part 1a for regulating the supplied amount of the carrier gas is provided to the compressed gas cylinder 1.
The aerosol generating chamber 3 is a container in which micro powder of a raw material is placed. By introducing the carrier gas from the compressed gas cylinder 1 via the carrier pipe 2a into the aerosol generating chamber 3, the raw material powder placed there is blown up to generate an aerosol. The generated aerosol is supplied via the carrier pipe 2b to the nozzle part 7.
The interior of the film forming chamber 4 is exhausted by the exhaust pump 5, and thereby, maintained at predetermined degree of vacuum. Further, in the film forming chamber 4, the substrate holder 6 for holding a substrate 100 is disposed.
As shown in
The rotating tube 11 includes a rotation axis portion having a rotation axis Z1 and an arm portion extending from the rotation axis to the outside and makes rotary motion with the rotation axis Z1 as a center thereof. The position of the rotation axis Z1 is fixed relative to the film forming chamber 4 as shown in
On the other hand, the rotating tube 13 includes a rotation axis portion having a rotation axis Z2 and two arm portions extending from the rotation axis to the outside. The rotating tube 13 is provided on the end of the arm apart from the rotation axis Z1 of the rotating tube 11 by a distance r1, and makes rotary motion with the rotation axis Z2 as a center thereof. At the corners of the rotation tube 13, reflection plates 13a to 13d are disposed. The two nozzles 15 are respectively provided on the ends of the two arms apart from the rotation axis Z2 of the rotation tube 13 by a distance r2, and move within the XY plane with the rotary motions of the rotating tubes 11 and 13.
Here, it is necessary that the rotation radius r1 of the rotation axis of the rotating tube 13 and the rotation radius r2 of the two nozzles 15 satisfy the relationship of r1≦r2 in order to form a film over the entire substrate with no space. This is because, if r1>r2, the central region of the substrate can not be deposited.
When the aerosol is introduced via the carrier pipe 2a into the nozzle part 7, the aerosol is carried from the rotation axis portion of the rotating tube 11 through the arm portion to the rotating tube 13. Furthermore, the aerosol is split from the rotation axis portion of the rotating tube 13 into two arm portions, and injected from the nozzles 15 provided on the ends of the arm portions, respectively.
As shown in
The angles at which the reflection plates are set are desirably determined through the following process. That is, assuming that an angle formed by the direction in which the aerosol flows in and the direction in which the aerosol that has been turned around at the corner flows out is φT, the reflection plate is set such that the reflection surface of the reflection plate may form angles of φT/2 with each of the inflow direction and the outflow direction of the aerosol.
As a material of the reflection plate, a material with which the raw material powder contained in the aerosol easily comes into elastic collision is desirably used. For example, in the case where a film of a hard and brittle material such as ceramics or a hard material such as metals is formed, a plate coated with an elastic material such as urethane rubber and silicon rubber is suitably used as the reflection plate. Thereby, the aerosol can be allowed to smoothly flow in the carrying path without occurrence of clogging therein. By the way, it is conceivable that the raw material powder is decelerated when reflected by the reflection plate. However, even in such a case, the speed of the carrier gas is hardly reduced. Therefore, there is no problem because, even when the raw material powder is once decelerated at the corner, it will be accelerated again afterwards.
Next, the operation of the film forming apparatus according to the embodiment will be described.
First, the substrate 100 made of silicon (Si), glass, ceramics, or the like is placed on the substrate holder 6 of the film forming chamber 4 as shown in
Next, the motion of the nozzle part 7 will be described in detail. In the embodiment, the displacement body (the first and second rotating tubes) having two degrees of freedom is used to support the nozzles 15 such that the nozzles 15 may exhibit chaotic behavior. This is because, when the motion of the nozzle 15 comes into a chaotic state, the nozzle 15 never travels in the same orbit twice because of the orbit instability due to the chaotic state. However, even when the displacement body has two or more degrees of freedom, the most end of the displacement body does not necessarily exhibit the chaotic behavior, and certain conditions are required to be satisfied. Accordingly, in the embodiment, the lengths etc. of the rotating tubes 11 and 13 are designed and they are given rotary motion at angular speeds according thereto such that the nozzles 15 provided on the most ends of the displacement body may exhibit the chaotic behavior.
Here, as a characteristic amount for discriminating whether the behavior of the motion system is chaotic or not, the largest Lyapunov exponent, fractal dimension, Lyapunov dimension, etc. are known. In the embodiment, the largest Lyapunov exponent within them is used for designing the nozzle part and setting the driving conditions thereof.
One characteristic of the chaotic behavior is that two points close to each other become exponentially separated. For example, in the case where a difference between two points on an attractor is ε0 at a certain time, after a period of time “t” has elapsed, the difference expands to ε0exp(λt). Here, the motion of a dissipation system (a system that energy enters and exits from) settles in a specific point or orbit after a transient state, and such asymptotic behavior (stable state) is referred to as “attractor”. As can be clearly seen from the above relationship, if λ<0, the difference of two points contracts, and if λ=0, the difference of two points is unchanged. In these cases, the response becomes not orbit instable. Therefore, by taking an average value of the exponents (an average expanding speed) over a long period of time with respect to a certain orbit, the orbit instability as a characteristic of the chaotic behavior can be quantified. The average value of the exponents is referred to as a Lyapunov exponent. In the case where the orbit instability is evaluated in a real dynamical system, when the largest Lyapunov exponent of the system is at least positive, the dynamical system is regarded as a system having orbit instability.
Next, a method of obtaining the largest Lyapunov exponent will be described by referring to
In
Then, the minute displacement L′(t1) at time t1 is normalized to obtain minute displacement vector BB′. Subsequently, the vicinity of the minute displacement vector BB″ on the attractor is searched to obtain vector BB″′ that forms a sufficiently small angle with the vector BB″. Then, point B′″ is used in place of point B′ to obtain the minute displacement L(t1) (the magnitude of vector BB″′) and obtain the minute displacement L′ (t2) (the magnitude of vector CC′) when the point B and point B′″ move to point C and point C′ respectively after a period of time Δt2=t2−t1 has elapsed. Thereby, the rate of expansion L′(t2)/L(t1) of the orbit in the period Δt2 is obtained.
Here, the reason why the rate of expansion in the next period is obtained by using point B″′ in place of point B′ is, for example, to prevent L′(t1) from developing to the size of the attractor when the period Δt1=t1−t0 is taken longer.
Similarly, the rates of expansion L′(t3)/L(t2), L′(t4)/L(t3), . . . in the periods Δt3, Δt4, . . . are sequentially obtained. Thereby, the rate of expansion in period Δt (Δt=t0 to tM) is obtained as follows.
Further, the largest Lyapunov exponent λ1 is obtained as follows.
See “Theories and Applications of Chaotic Time Series Analysis”, edited by Kazuyuki Aihara (Sangyo Tosho Inc. in Japan, 2000), which is incorporated herein by reference. Moreover, not only the method, but also various methods can be used to obtain the largest Lyapunov exponent.
When the nozzle part 7 as shown in
As described above, in the embodiment, by providing the nozzles on the ends of the displacement body of two axes, the nozzles are allowed to move chaotically. Thereby, the orbits of the nozzles becomes completely irregular, and never travel in the same path. Therefore, by injecting the aerosol from such nozzles toward the substrate, the raw material powder can be sprayed evenly over the substrate and deposited. Since the instability at the times of supply and injection of aerosol is cancelled, a uniform thick film in which streaky defects are suppressed can be formed over a broad region.
By the way, in the embodiment, the nozzle part is formed by using the displacement body of two axes having two degrees of freedom, however, a displacement body of two or more axes may be used. That is, by overlapping two or more degrees of freedom, the most ends of the displacement body can be moved completely irregularly according to the chaotic theory.
Further, in the embodiment, the nozzles 15 as shown in
Furthermore, the nozzle motion is brought into not only the spatial chaotic state as in the embodiment, but also it may be brought into a temporal chaotic state. For example, by controlling the switching between on and off in the nozzle by using an irregular pulse, the aerosol can be chaotically injected. Alternatively, the flow rate of the aerosol injected from the nozzle may be changed along a sine curve.
In the embodiment, by providing two arms in the rotating tube 13, the two nozzles are located on the ends of the arms, respectively. However, the number of nozzles may be one, or three or more. Further, one nozzle may be located in each arm, or plural nozzles may be located on one arm. The reduction of injection speed of the aerosol can be suppressed with smaller number of nozzles, while the larger number of nozzles can shorten the time required for film formation. Therefore, the number of arms is set according to the substrate area, nozzle aperture area, or the like, and the film forming condition for aerosol injection pressure may be adjusted according thereto. In any case, since it is necessary to chaotically move all nozzles, the rotation radiuses of nozzles, angular speeds of the respective parts and so on are set by using the characteristic amount representing the chaotic state.
Next, a film forming apparatus according to the second embodiment of the present invention will be described by referring to
As shown in
The substrate holder supporting part 22 includes a first rotating rod 22a rotating with a rotation axis Z3 as the center thereof and a second rotating rod 22b rotating with a rotation axis Z4 that is an end of the rotating rod 22a as the center thereof. The substrate holder 21 is provided on an end of the rotating rod 22bFurther, the substrate driving part 23 includes a first driving part 23a for bringing the rotating rod 22a into rotary motion and a second driving part 23b for bringing the rotating rod 22b into rotary motion. The driving parts 23a and 23b are controlled by the control unit 24 to rotate the rotating rods 22a and 22b at predetermined angular speeds ω1 and ω2 respectively.
When a film is formed, the angular speeds of the rotating rod 22a and rotating rod 22b are respectively set based on the characteristic amount representing the chaotic state so that the end of the rotating rod 22b exhibits chaotic behavior. Thereby, the substrate holder 21 provided on the end of the rotating rod 22b and the substrate 100 held there chaotically move within the XY plane. By injecting the aerosol from the nozzle 20 toward the substrate 100, a uniform film can be formed evenly on the substrate 100.
In the above-described first and second embodiments of the invention, one of the nozzle and the substrate side is fixed and the other is chaotically moved, however, both of them may be moved such that the nozzle and substrate may relatively exhibit chaotic behavior.
Next, a film forming apparatus according to the third embodiment of the invention will be described by referring to
The monitor unit 31 is formed by a CCD camera, for example. The monitor unit 31 images the nozzles 15 during film formation and outputs image information representing the tracks of the nozzles 15. Further, the characteristic amount calculating unit 32 calculates a characteristic amount representing the chaotic state such as the largest Lyapunov exponent based on the image information outputted from the monitor unit 31.
The control unit 33 controls the operation of the driving parts 12 and 14 (
Thus, by monitoring the motion of the nozzles 15 and feeding back the obtained information, the nozzles 15 can be constantly placed in the chaotic state. Therefore, the state in which uniform film formation is performed can be constantly maintained.
Next, a film forming apparatus according to the fourth embodiment of the invention will be described by referring to
In the first embodiment of the invention, the carrier line for supplying the aerosol to the nozzles is provided inside of the rotating tubes that brings the nozzles into chaotic behavior, however, they are not necessarily integrated. For example, in the fourth embodiment, an aerosol carrier line for supplying an aerosol to a nozzle is provided separately from the rotation mechanism for bringing the nozzle into chaotic behavior.
As shown in
Thus, by combining the vibration of the rotary frame 42a and the rotary motion of the rotary table 42b, the nozzle 40 can be displaced under two degrees of freedom. At that time, the nozzle 40 can be moved such that it may trace the chaotic track by optimizing the vibration cycle of the rotary frame 42b and the rotation speed of the rotary table 42a based on the characteristic amount representing the chaotic state under control of the control unit 45.
According to the above-described present invention, since large area and uniform films can be formed by the AD method, the invention can be applied to, for example, the following fields.
First, an inorganic electroluminescence device according to one embodiment of the present invention will be explained.
The inorganic EL device as shown in
The first insulating layer 203 and the second insulating layer 205 are formed by dielectric materials. The first insulating layer 203 is a PZT thick film having a thickness of 40 μm, for example. Further, the second insulating layer 205 is a silicon nitride (SiNx) thin film having a thickness of 200 nm, for example.
The luminescent layer 204 is formed by a material that exhibits electroluminescence. The luminescent layer 204 is a manganese addition zinc sulfide (ZnS:Mn) phosphor thin film having a thickness of 600 nm, for example.
Such an inorganic EL device is manufactured through the following process.
First, the substrate 201 of alumina or the like is prepared, a Pt thin film having a thickness of 200 nm is formed by the sputtering method, pattern formation is performed with respect to the Pt thin film by the photolithography method and dry etching method, and thereby, the first electrodes 202 are formed.
Then, on the substrate 201 on which the first electrodes 202 are formed, a PZT thick film is formed as the first insulating layer 203. At that time, as described in the first to fourth embodiments of the present invention, film formation by the AD method is performed while chaotically varying the relative position of the nozzle that injects PZT powder and the substrate. Further, in order to improve the crystallinity of the PZT, the PZT thick film is heat treated.
Then, on the first insulating layer 203, a ZnS:Mn thin film as the luminescent layer 204 is formed by the electron beam (EB) evaporation method. Then, on the luminescent layer 204, a thin film of SiNx (e.g., Si3N4) as the second insulating layer 205 is formed. This second insulating layer may be formed according to the sputtering method or may be formed according to the AD method that has been described in the first to fourth embodiments. Furthermore, on the second insulating layer 205, a thin film of ITO is formed according to the sputtering method, pattern formation is performed with respect to the ITO thin film according to the photolithography method and dry etching method, and thereby, the second electrodes 206 are formed.
Since the dense film (AD film) formed according to the AD method can reduce leak current, the dielectric film can be made thinner, and thereby, the driving voltage of the inorganic EL device can be reduced. When such a dielectric film is formed, by using the film forming method and film forming apparatus according to the present invention, an inorganic EL panel having a large area and low power consumption can be easily manufactured.
Next, an inkjet head according to one embodiment of the present invention will be explained.
Referring to
When printing is performed, voltages are applied between the electrodes 404 and the electrodes 406 according to control signals, respectively. Thereby, the piezoelectric materials 405 expand and contract by the piezoelectric effect and the vibrating plate 403 deforms. As a result, the volumes of the pressure chambers 407 are changed and the ink filling the interior is pressurized to drop down from the discharge openings 408.
Such an inkjet head is manufactured through the following process.
First, a silicon substrate having a thickness of about 30 μm to be used as the vibrating plate 403 is prepared, and the electrode 404 is formed on the first principal surface thereof according to the sputtering method or the like. Then, on the electrode 404, the plural piezoelectric materials 405 each having a bottom surface size of about 300 μm square and a thickness of about 30 μm are arranged in a two-dimensional matrix form at intervals of about 100 μm. For this purpose, a resist is arranged in a predetermined pattern on the electrode 404, a PZT thick film is formed thereon, and then, the resist is removed. In order to form the PZT thick film, as described in the first to fourth embodiments of the present invention, film formation by the AD method is performed while chaotically varying the relative position of the nozzle that injects PZT powder and the substrate on which the electrode 400 has been formed. Furthermore, the plural electrodes 406 are formed on the plural piezoelectric materials 405, respectively.
Further, a ceramics plate of alumina (Al2O3), zirconia (ZrO2), or the like is prepared, holes as the pressure chambers 407 are formed by etching or the like, and thereby, the partition walls 402 are fabricated. Furthermore, another ceramic plate is prepared, holes as the ink discharge openings 408 are formed, and thereby, the nozzle plate 401 is fabricated.
These nozzle plate 401, partition walls 402, vibrating plate 403 on which the piezoelectric elements have been arranged are bonded by using an adhesive agent, and thereby, an inkjet head is completed.
Thus, a large number of piezoelectric materials having uniform thicknesses can be fabricated easily and efficiently by using the film forming method and film forming apparatus according to the present invention, and therefore, the invention can adequately respond to the recent requests for wider heads.
Alternatively, the partition walls and nozzle plate may be formed directly on a surface of the vibrating plate on the opposite side to the side on which the piezoelectric elements are arranged by using the film forming method and film forming apparatus according to the present invention. In this case, not only the wide head can be fabricated efficiently, but also no adhesive agent is required, and thereby, the durability and operation efficiency of the inkjet heat can be improved. Accordingly, a wide head having good characteristics can be fabricated such that high-speed printing may be performed and high viscosity ink such as pigment ink may be discharged.
Next, an ultrasonic transducer array according to one embodiment of the present invention will be explained.
This ultrasonic probe as shown in
The ultrasonic transducer array 500 includes plural ultrasonic transducers 510 for transmitting and receiving ultrasonic waves. Filling materials 511 such as epoxy resin are arranged between these ultrasonic transducers 510. The at least one acoustic matching layer 501 is formed by glass, ceramic, epoxy resin with metal powder, or the like that can transmit ultrasonic waves easily. The acoustic matching layer 501 eliminates a mismatch of the acoustic impedance between an object to be inspected as a living body and the ultrasonic transducer. Thereby, the ultrasonic wave transmitted from each ultrasonic transducer 510 propagates efficiently within the object.
The backing layer 502 is formed by a material providing large acoustic attenuation such as a material in which powder of ferrite, metal, or PZT is mixed in epoxy resin or rubber. The backing layer 502 rapidly attenuates unwanted ultrasonic wave generated by the ultrasonic transducer array 500. Further, the acoustic lens 503 is formed by silicon rubber, for example. The acoustic lens 503 focuses an ultrasonic beam, which has been transmitted from the ultrasonic transducer array 500 and passed through the acoustic matching layer 501, at a predetermined depth.
As shown in
Each ultrasonic transducer 510 includes a lower electrode 512, a piezoelectric material 513 of PZT or the like, and an upper electrode 514, and has a bottom surface size of about 300 μm square and a thickness of about 10 μm, for example. When a voltage is applied between these lower electrode 512 and upper electrode 514, the piezoelectric material 513 expands and contracts by the piezoelectric effect and ultrasonic waves are generated. At that time, the plural ultrasonic transducers 510 are driven while providing predetermined delay times, and thereby, an ultrasonic beam transmitted in a desired direction is formed.
Such an ultrasonic transducer array 500 is fabricated through the following process.
First, the plural lower electrodes 512 are formed in a two-dimensional matrix form on a substrate by the sputtering method or the like. Next, a resist is formed in regions except for the plural lower electrodes 512 on the substrate. Then, as described in the first to fourth embodiments of the present invention, film formation by the AD method is performed while chaotically varying the relative position of the nozzle that injects PZT powder and the substrate. Further, the resist is removed and filling materials 511 are arranged in the space between the plural piezoelectric materials 513. Furthermore, on the plural piezoelectric materials 513, the upper electrodes 514 are formed, respectively, according to the sputtering method or the like. The substrate may be removed or left according to need in a completed product.
By the way, in
In the manufacture of such an ultrasonic transducer array, merits of using the AD method are as follows.
Generally, the acoustic impedance Z of a living body is about 1.5 Mrayl, while the acoustic impedance Z of an ultrasonic transducer for living body is about 30 Mrayl. Here, the acoustic impedance is a value determined by a product of density of a material and a sound speed in the material. When two kinds of materials are in contact, the larger the difference between the acoustic impedances of those materials, the more easily ultrasonic wave is reflected at the boundary between them, that is, harder the ultrasonic wave is transmitted. Accordingly, in a normal ultrasonic transducer, the propagation efficiency of ultrasonic wave to the living body is not good, and therefore, one or more acoustic matching layers must be inserted between the ultrasonic transducer and the living body.
Here, by using the AD method when the piezoelectric material is formed, the density of the piezoelectric material can be controlled relatively easily. For example, by reducing the value of the acoustic impedance Z of the piezoelectric material close to the value in the living body, the propagation efficiency of ultrasonic wave to the living body can be made higher.
As a first method of controlling the density of the piezoelectric material by using the AD method, it is proposed that film formation is performed by mixing hollow silica or the like in the PZT powder as a raw material. Further, as a second method, it is proposed that the injection pressure when the PZT powder is injected from the nozzle is shifted from the optimum film formation condition. In this purpose, the injection pressure may be reduced, for example. Thereby, the packaging density of the piezoelectric material formed on the substrate or the electrodes becomes lower, and the piezoelectric material is deposited in a state of pressurized powder.
Thus, according to the AD method, the acoustic impedance value of the piezoelectric material can be manipulated, and therefore, an ultrasonic transducer array with good ultrasonic wave propagation efficiency to the living body can be fabricated. In addition, the acoustic matching layer can be omitted, the number of layers can be reduced, or the driving voltage of the ultrasonic transducer can be reduced.
Further, the merits of using the film forming method according to the present invention when the ultrasonic transducer array is manufactured by the AD method are as follows.
In the film forming apparatus according to the AD method, a nozzle having opening width of about 20 mm to 30 mm is normally used. Accordingly, it is difficult to form a film uniformly in a region having nearly the same width, and very difficult in a region having a larger width. However, in an ultrasonic probe for living body practically used in the medical fields, an ultrasonic transducer having a large area is required. For example, in an ultrasonic probe for abdomen, an ultrasonic transducer having a size of about 20 mm×100 mm is used. Further, in the case where the arrayed transducer array as shown in
Furthermore, the nozzle part to be used in the film forming apparatus according to the present invention can be applied to a sandblasting apparatus, for example. The sandblasting is a technology for grinding or cutting a target of machining by spraying abrasive grain toward the target of machining at a high speed. By applying the nozzle part according to the present invention as a nozzle for injecting such abrasive grain, uniform grinding in a large area can be performed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-093244 | Mar 2004 | JP | national |
