Patent Application
20070235048
In the following, the present invention will be explained in detail by an embodiment thereof with reference to
First, the aerosol generating apparatus 2 will be explained. The aerosol generating apparatus 2 is provided with an aerosol generator 10 (container) which is formed in a circular cylinder-shaped shape. The inside of the aerosol generator 10 is partitioned into upper and lower chambers with a distribution plate 11 (partition). In other words, the aerosol generator 10 is partitioned into two chambers with the distribution plate 11.
As shown in
The gas dispersing nozzles 13 are formed in a circular-cylindrical shape and are provided with stand pipes 14, respectively. Each of the stand pipes 14 is formed in an upstanding manner on the upper surface of the plate portion 12, and is closed at its opening in its upper side. An air hole 15 which opens downwardly is formed inside each of the stand pipes 14. Further, a plurality of blow holes 16 are formed in each of the stand pipes 14 to extend obliquely outwardly in the radial direction and communicate the air hole 15 and space outside the air hole 15. The blow holes 16 are provided at a constant pitch in the circumferential direction. In such a manner, by forming the blow holes 16 such that the air-blowing side thereof is directed downwardly, the carrier gas can be ejected in an obliquely downward direction, thereby preventing the carrier gas from remaining on the upper surface of the plate portion 12. The air hole 15 and the blow holes 16 construct the hole of the present invention.
Among the chambers partitioned by the distribution plate 11, the lower chamber is a blower chamber 17, and the carrier gas is supplied to the blower chamber 17 from a gas supply section 180. The gas supply section 180 has a gas cylinder G, and a gas supply tube 18 which connects the gas cylinder G and the blower chamber 17. As the carrier gas, it is possible to use, for example, inert gas such as helium, argon or the like, or to use nitrogen, air, oxygen or the like.
The upper chamber is a powder-accommodating chamber 19, and particulate material (material particles) M is charged to the powder-accommodating chamber 19. The carrier gas supplied to the blower chamber 17 passes through the air dispersing nozzles 13 and then the carrier gas is ejected to the inside of the powder-accommodating chamber 19. With this, the particulate material M in the powder-accommodating chamber 19 is fluidized, thereby forming a fluidized bed M′ above the distribution plate 11.
A window 19B is provided on a ceiling 19A of the powder-accommodating chamber 19, and an optical sensor 30 which is an optical measuring unit is arranged on the upper side of the window 19B. A transmissive plate, through which a measuring light having a predetermined wavelength is transmissive, is fitted to the window 19B so that a light emitted from the optical sensor 30 and a reflected light from the fluidized bed M′ are transmissive through the transmissive plate. With this, it is possible to measure the position of a top layer M's of the fluidized bed M′ by operating the optical sensor 30 outside the powder-accommodating chamber 19 in a state that the powder-accommodating chamber 19 is tightly sealed.
An aerosol delivery tube 21 is connected to the powder-accommodating chamber 19. The aerosol delivery tube 21 delivers (feeds) the aerosol generated in the powder-accommodating chamber 19 to an ejection nozzle 23 which will be described later on. One end of the aerosol delivery tube 21 is inserted to the powder-accommodating chamber 19 in a state that the aerosol delivery tube 21 extends in an up and down direction (extends vertically).
An adjusting unit (vertical position adjusting mechanism) 31 is attached to the aerosol delivery tube 21. The adjusting unit 31 adjusts a vertical position of a portion, of the aerosol delivery tube 21, inserted in the powder-accommodating chamber 19 (hereinafter referred to as “inserted portion 21A”). The adjusting unit 31 includes a driving section which drives the aerosol delivery tube 21 in up and down direction; and a CPU (Central Processing Unit) which is connected to the optical sensor 30 to receive a signal from the optical sensor 30 and give a drive command to the driving section. The adjusting unit 31 receives an information about the position, of the top layer M's of the fluidized bed M′, measured by the optical sensor 30 and adjusts the vertical position of a suction port 21B formed at the tip end of the aerosol delivery 21, so that the suction port 21B is arranged at a position near to the top layer M's of the fluidized bed M′. Note that in the present application, the term “position near to” means a position at which the suction port 21B has no contact with the top layer M's of the fluidized bed M′ and the suction port 21B is positioned above the top layer M′ with a spacing distance, and at which the suction portion 21B is capable of sucking the particulate material M dispersed in the carrier gas.
The aerosol generator 10 is installed on a rotation device (horizontal driving mechanism) 40. The rotation device 40 includes a motor (not shown in the drawing) arranged on a base 41 and a rotary table 42 arranged on the upper surface of the base 41 and attached to a driving shaft of the motor. The aerosol generator 10 is placed on the rotary table 42.
Next, the film forming chamber 20 will be explained. The film forming chamber 20 is formed in a rectangular-box shape, and a stage 22 for attaching a substrate 26 thereto and an ejection nozzle 23 arranged below the stage 22 are provided inside the film forming chamber 20. The ejection nozzle 23 has a circular-cylindrical shape, has openings at both ends thereof in the up and down direction respectively, and the upper opening has a slit-shaped ejection port 23A formed therein. The lower opening of the ejection nozzle 23 is connected to the other end of the aerosol delivery tube 21 (the end opposite to the one end inserted into the powder-accommodating chamber 19), and the particulate material M and the carrier gas (aerosol) are supplied to the ejection nozzle 23 through the aerosol delivery tube 21.
The stage 22 has a rectangular-plate shape, and is capable of holding the substrate 26 on the lower surface of the stage 22. The stage 22 is suspended by a stage moving mechanism 24 in a horizontal posture from the ceiling of the film forming chamber 20. The stage moving mechanism 24 is driven in accordance with a command from a controller (not shown in the drawing), and moves the stage 22 in a plane parallel to the stage 22. This makes it possible to move the ejection nozzle 23 relative to the substrate 26. Further, a vacuum pump P is connected to the film forming chamber 20 via a powder recovery unit 25, and the inside of the film forming chamber 20 can be decompressed by the vacuum pump P.
Next, an explanation will be given about a method for forming a film with the film-forming apparatus 1 constructed as described above, with reference to
Upon forming a film of the particulate material M by using the film forming apparatus 1, first, the substrate 26 is set to the stage 22, and charge the particulate material M to the inside of the powder-accommodating chamber 19 (Charging step S1). As the particulate material M, it is possible to use, for example, lead zirconate titanate (PZT) which is a piezoelectric material.
Next, the carrier gas is supplied from the gas cylinder G to the blower chamber 17 via the gas supply tube 18 (see arrows indicated in
Here, in some case, disturbance is caused in the top surface M's of the fluidized bed M′ due to gas bubbles generated between the particles of the particulate material M and rising upwardly in the aerosol. The inventor found out the following fact, in order to suppress the disturbance in the fluidized bed M′, that it is effective to adjust the flow rate (flow velocity) of the carrier gas so that the fluidization velocity of the fluidized bed is not more than twice, preferably 1 to 2 times, of a minimum fluidization velocity UMF with respect to a central particle size of (particles of) the particulate material M. In this case, when the fluidized bed M′ is formed, the fluidization velocity of the fluidized bed M′ is equal to the flow rate of the carrier gas. Further, when the fluidized bed M′ is formed, the particulate material M forms a cluster in which a plurality of particles of the particulate material M are aggregated, and the term “central particle size of the particulate material M” means a mean particle size in the cluster of the particulate material M. Further, the term “minimum fluidization velocity UMF” means a fluidization velocity when the particles start to be fluidized (fluidization start velocity). In a case such as the embodiment of the present invention wherein a gas is flowed from a position below a solid particle layer to float the particles to thereby fluidize the particles, the minimum fluidization velocity UMF is equal to a minimum value of the gas flow velocity required for fluidizing the particles. The minimum fluidization velocity UMF is a value depending on a particle size (diameter) of the particles to be fluidized, a gas density and the like, and the minimum fluidization velocity UMF can be calculated, for example, by the following expression (1).
In the expression, Dp is particle size (μm); f is constant; φ is specific surface area (m2/g); μMF is voidage; ρp is particle density (kg/m3); p is gas density (kg/m3); μ is gas viscosity (Pa·s); and g is gravitational acceleration (m/s2).
Table 1 shows the minimum fluidization velocity in cases each using fine particles of PZT as the particles (particulate material) and helium as the carrier gas. For example, when calculation is made under the condition that the voidage (porosity) μMF is set to 10% as the upper limit for preventing the air bubbles generating between the particles, and that the constant f is 150 and the particle size Dp is 0.8 μm, then a fluidization velocity of about 0.3 mm/s is required. The flow rate of the carrier gas, supplied from the gas cylinder G, is adjusted so that the fluidization velocity of the fluidized bed is not more than twice the minimum fluidization velocity UMF as calculated above (adjusting step S3). In this case, the supply amount of the carrier gas may be adjusted by opening/closing a valve of the gas cylinder G, and a flow-rate controlling mechanism which controls the flow rate of the carrier gas, such as a valve, a mass flow controller or the like, may be provided on the gas supply tube 18.
Next, the film forming chamber 20 is decompressed by the vacuum pump P while rotating the aerosol generator 10 by the rotation device 40. Then, pressure difference is generated between the powder-accommodating chamber 19 and the film forming chamber 20, which makes the particulate material M and carrier gas in the aerosolized state in the powder-accommodating chamber 19 to be sucked into the inside of the aerosol delivery tube 21, and accelerated at high velocity and delivered to the ejection nozzle 23 (delivering step S4).
At this time, by the rotation of the aerosol generator 10, the suction port 21B of the aerosol delivery tube 21 moves horizontally relative to the top layer M's of the fluidized bed M′, along the top layer M's. By such a tracing operation, it is possible to avoid harmful effect which would be otherwise caused that the aerosol concentration is locally lowered if the suction is continued only at a specific position; it is possible to stabilize the concentration of the particulate material M sucked to the aerosol delivery tube 21; and it is further possible to stabilize the concentration of the aerosol ejected from the ejection nozzle 23.
It is enough that the suction port 21B at the tip of the aerosol delivery tube 21 is arranged close to the top layer M's of the fluidized bed M′ to the extent that the suction port 21B is capable of sucking the particulate material M from the top layer M's, and it is preferable that the suction port 21B is maintained at a position at which the suction port 21B makes no contact with the top layer M's and is distanced from the top layer M's with a slight clearance or spacing distance therebetween, for the purpose of preventing the aggregation of the particulate material M at the suction port 21B.
A mixture of the particulate material M and the carrier gas (aerosol) supplied or delivered to the ejection nozzle 23 is ejected from the ejection port 23A toward the substrate 26. The ejected particulate material M is collided against and fixed to the substrate, forming a piezoelectric film. At this time, the ejection of the aerosol is performed by moving the stage 22 with the stage moving mechanism 24 to thereby change, little by little, the position of the ejection nozzle 23 relative to the stage 22. Accordingly, the film is formed entirely on the surface of the substrate. The aerosol, after colliding against the substrate, is discharged to the side of the powder recovery unit 25 by the suction force of the vacuum pump P.
When the film forming apparatus 1 is operated for a long period of time, then the particulate material M in the powder-accommodating chamber 19 is consumed and the position of the top layer M's of the fluidized bed M′ is lowered. To address this situation, in the film forming apparatus 1, the vertical position of the aerosol delivery tube 21 is adjusted by the adjusting unit 31. The CPU of the adjusting unit 31 receives a positional information, of the top layer M's of the fluidized bed M′, detected by the optical sensor 30. When the CPU of the adjusting unit 31 judges, based on the received positional information, that the position of the top layer M's is lowered from the suction port 21B of the aerosol delivery tube 21 by not less than a predetermined distance, then the CPU gives a drive command to the driving section to make the driving section move the aerosol delivery tube 21 in the up and down direction, thereby moving the suction port 21B to a position near to the top layer M's of the fluidized bed M1. In such a manner, the aerosol concentration is prevented from fluctuating due to the change in the distance between the top layer M's of the fluidized bed M′ and the aerosol delivery tube 21 (suction height at which suction port 21B sucks the aerosol).
Further, since the non-contact type optical sensor 30 is used to measure the height of the top layer M's from outside the powder-accommodating chamber 19, there is no fear that the particulate material M adheres to the optical sensor 30 during the operation of the film forming apparatus 1. Accordingly, it is possible to prevent the measurement accuracy from lowering. In addition, the maintenance work becomes easy.
As described above, according to the embodiment, by forming the fluidized bed M′, it is possible to prevent the aggregation and solidification of the particulate material M, and thus the particulate material M having a large particle size does not settle or deposit, thereby making it possible to realize uniform particle size distribution in the height direction (bed-height direction, axial direction of the aerosol generator 10). In addition, since the adjusting unit 31 is provided to adjust the end portion, of the aerosol delivery tube 21, with respect to the top layer M's of the fluidized bed M′, the aerosol concentration is prevented from fluctuating due to the change in the distance between the top layer M's of the fluidized bed and the aerosol delivery tube 21, thereby making it possible to supply the aerosol stably.
The aerosol generator 10 is provided with the optical sensor 30 which measures the position of the top layer M's of the fluidized bed M′, and the adjusting unit 31 adjusts the up and down direction of the aerosol delivery tube 21 based on the data of the position of the top layer M's measured by the optical sensor 30. Accordingly, even when the film forming apparatus 1 is operated for a long period of time and then the particulate material M in the powder-accommodating chamber 19 is consumed and the position of the top layer M's of the fluidized bed M′ is lowered, it is possible to automatically perform an operation for detecting the position of the top layer M's to adjust the up and down direction of the aerosol delivery tube 21, and thus the suction of particles can be performed appropriately.
Furthermore, by the tracing operation for moving one end of the aerosol delivery tube 21 horizontally across (along) the top layer M's of the fluidized bed M′, it is possible to avoid harmful effect which would be otherwise caused that the particle size distribution becomes non-uniform if the suction is continued only at a specific position; and to stabilize the concentration of the supplied aerosol.
Since the optical sensor 30 is a sensor of non-contact type and is arranged outside the powder accommodating chamber 19, there is no need to open the powder-accommodating chamber 19 for the measurement. Accordingly, there is no fear that the fluidized bed M′ in the powder-accommodating chamber 19 from becoming unstable due to the influence of the measuring operation. Further, since the particulate material M does not adhere to the optical sensor 30 to pollute the optical sensor 30, the measurement accuracy is prevented from lowering and the maintenance becomes easy.
In addition, since the fluidization velocity of the fluidized bed M′ is set to be not more than twice the minimum fluidization velocity with respect to the central particle size of the particulate material M, it is possible to suppress the disturbance in the fluidized-bed surface due to gas bubbles generated between the particles and rising upwardly.
The technical scope of the present invention is not limited to the embodiment as described above, and includes, for example, the following construction as well as encompassing equivalent thereof.
In the above-described embodiment, the distribution plate 11 as the partition is a multi-nozzle plate provided with a large number of the gas dispersing nozzles 13. However, it is enough that the partition is provided with a hole (hole portion) which allows the carrier gas to pass therethrough and the partition may be, for example, a porous sintered body, a punching metal or the like.
As the driving section of the adjusting unit, any driving mechanism may be used. For example, the driving mechanism may be a driving mechanism in which a ball screw and a motor (stepping motor, servo motor, or the like) are combined, and may be a driving mechanism which uses an air cylinder or an actuator. Similarly, the rotation device is not limited to a rotation device using a rotary table attached to the rotating shaft of the motor, and may use, for example, as the rotation device, any rotating mechanism in which a driving force of the motor is transmitted to a rotary table via a predetermined gear or the like.
In the above-described embodiment, the aerosol generator 10 is rotated by the rotation device 40 to thereby move the suction port 21A of the aerosol delivery tube 21 relative to the fluidized bed M′ in the powder-accommodating chamber 19. It is allowable, however, to attach a horizontal driving unit to the aerosol delivery tube so as to directly move the aerosol delivery tube horizontally. As such a horizontal driving unit, it is allowable to use any horizontal driving mechanism such as a horizontal driving mechanism in which the above-described ball screw and motor are combined, a horizontal driving mechanism which employs an air cylinder or an (electric) actuator.
In the embodiment, although the optical sensor is used as a positional sensor of the non-contact type, the applicable non-contact type sensor is not limited to the optical sensor. It is allowable to use, for example, any positional sensor of non-contact type such as a supersonic sensor, magnetic sensor, or the like.
In the embodiment, although the suction port of the aerosol delivery tube is formed at a terminal end of the aerosol delivery tube, the position at which the suction port is formed is not limited to the terminal end. For example, the suction port may be formed in the aerosol delivery tube at an intermediate position on a side surface of the delivery tube.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006088625 | Mar 2006 | JP | national |
