Patent Application
20150279639
The present invention relates to a micro-channel plate, a method for manufacturing a micro-channel plate, and an image intensifier.
In the image intensifiers with the micro-channel plate used for multiplication of electrons, feedback of ions of Cs and/or residual gas from the inside of the micro-channel plate to a photoelectron surface has been hitherto known as a factor to degrade life characteristics. For dealing with this problem, for example, in the case of the device described in Patent Literature 1, a film of metal such as Al (ion barrier film) is formed so as to cover the front surface of the micro-channel plate.
Patent Literature 1: U.S. Pat. No. 3,742,224
In the above-described conventional technique, prior to forming the ion barrier film on the surface of channels, an organic film is formed over the entire front surface of the micro-channel plate. Thereafter, the ion barrier film is formed on the organic film as underlying layer and, after completion of the formation of the ion barrier film, the organic film is removed by firing or the like. In this technique, however, since the organic film was situated in between the metal film and the channel surface, the organic film could remain on the front surface of the micro-channel plate. For this reason, the residual organic film could degrade the performance of the ion barrier film, raising a possibility of failure in achieving a sufficient improvement in life characteristics of the micro-channel plate. Furthermore, the ion barrier film is preferably as thin as possible, in order to secure secondary electron permeability, but if the conventional ion barrier film was simply made thinner, it would pose a problem in terms of mechanical strength.
The present invention has been accomplished in order to solve the above problem and it is an object of the present invention to provide a micro-channel plate, a method for manufacturing a micro-channel plate, and an image intensifier capable of achieving a sufficient improvement in life characteristics while suppressing the ion feedback.
In order to solve the above problem, a micro-channel plate according to the present invention comprises: a substrate having a front surface and a back surface; a plurality of channels penetrating from the front surface to the back surface of the substrate; an electron emission film formed on inner wall faces of the channels; and an ion barrier film formed so as to cover openings on the front surface side of the substrate in the channels, wherein the electron emission film and the ion barrier film are integrally formed by the same film formation step.
In this micro-channel plate, the electron emission film and the ion barrier film are integrally formed by the same film formation step. In this structure, the electron emission film and the ion barrier film are made as continuous and firm films and thus the ion barrier film can be made thinner than in the conventional structure. Since the ion barrier film is formed on the back side of the organic film (or on the opening side of the channels), the organic film can be kept exposed during removal of the organic film. This prevents the organic film from remaining on the front surface of the substrate of the micro-channel plate, which can suppress the performance degradation of the ion barrier film due to the residual organic film. Therefore, the ion feedback from the micro-channel plate can be suppressed well.
Preferably, the electron emission film and the ion barrier film are formed containing a metal oxide. Since the metal oxide has excellent chemical stability, use of the metal oxide leads to suppression of temporal change of the electron emission film and the ion barrier film.
Preferably, the electron emission film and the ion barrier film are deposited by an atomic layer deposition method. When the atomic layer deposition method is adopted, the electron emission film and the ion barrier film can be made more definitely as firm and fine films.
Preferably, a metal film formed so as to cover the front surface of the substrate is formed on the ion barrier film. In this case, the metal film can also serve as an electrode on the channel IN side (input electrode). The metal film can supply electrons, which can prevent the ion barrier film from becoming electrically charged.
Preferably, a resistive film is formed inside with respect to the electron emission film on the inner wall faces of the channels. In this case, when a voltage is applied between the channel IN side and OUT side, a potential gradient is established by the resistive film, enabling electron multiplication.
Preferably, the resistive film is integrally formed by the same film formation step as the electron emission film and the ion barrier film are. This facilitates the formation of the resistive film.
Preferably, an input electrode is formed at an end on the front surface side of the substrate in the channels and an output electrode is formed at an end on the back surface side of the substrate in the channels. In this case, a sufficient region is secured as a region functioning as the electron emission film.
Preferably, the output electrode is formed outside with respect to the electron emission film. In this case, emission angles of secondary electrons from the electron emission film are limited, which can enhance the resolution.
A method for manufacturing a micro-channel plate according to the present invention, comprises: a substrate preparation step of preparing a substrate in which a plurality of channels are formed so as to penetrate from a front surface to a back surface; an organic film formation step of forming an organic film so as to cover the front surface of the substrate; a functional film formation step of, by use of an atomic layer deposition method, forming an electron emission film on inner wall faces of, the channels and, at the same time, forming an ion barrier film covering openings on the front surface side of the substrate in the channels so as to overlap the organic film, integrally with the electron emission film; and an organic film removal step of removing the organic film from the front surface of the substrate, after formation of the electron emission film and the ion barrier film.
In this method for manufacturing the micro-channel plate, the electron emission film and the ion barrier film are integrally formed by the atomic layer deposition method. By this, the electron emission film and the ion barrier film are made as continuous and firm films and thus the ion barrier film can be made thinner than by the conventional method. Since the ion barrier film is formed inside with respect to the organic film (or on the opening side of the channels), the organic film can be kept exposed during removal of the organic film. This prevents the organic film from remaining on the front surface of the substrate of the micro-channel plate, which can suppress the performance degradation of the ion barrier film due to the residual organic film. Therefore, the ion feedback from the micro-channel plate can be suppressed well.
Preferably, the method further comprises a metal film formation step of forming a metal film so as to cover a face of the ion barrier film on the far side from the substrate, after the organic film removal step. In this case, the metal film can also serve as an electrode on the channel IN side (input electrode). The metal film can supply electrons, which can prevent the ion barrier film from becoming electrically charged.
Another method for manufacturing a micro-channel plate according to the present invention, comprises: a substrate preparation step of preparing a substrate in which a plurality of channels are formed so as to penetrate from a front surface to a back surface; an organic film formation step of forming an organic film so as to cover the front surface of the substrate; a metal film formation step of forming a metal film so as to cover a face of the organic film on the far side from the substrate; an organic film removal step of removing the organic film from the front surface of the substrate, after formation of the metal film; and a functional film formation step of, by use of an atomic layer deposition method, forming an electron emission film on inner wall faces of the channels and, at the same time, forming an ion barrier film covering openings on the front surface side of the substrate in the channels so as to overlap the metal film, integrally with the electron emission film, after the organic film removal step.
In this method for manufacturing the micro-channel plate, the electron emission film and the ion barrier film are integrally formed by the atomic layer deposition method. By this, the electron emission film and the ion barrier film are made as continuous and firm films and thus the ion barrier film can be made thinner than by the conventional method. Since the organic film is removed from the front surface of the substrate after the formation of the metal film, the organic film is prevented from remaining on the front surface of the substrate of the micro-channel plate, which can suppress the performance degradation of the ion barrier film due to the residual organic film. Therefore, the ion feedback from the micro-channel plate can be suppressed well.
Preferably, the method further comprises a resistive film formation step of forming a resistive film on the inner wall faces of the channels, prior to the organic film formation step. With this resistive film, when a voltage is applied between the channel IN side and OUT side, a potential gradient is established by the resistive film, enabling electron multiplication.
Preferably, in the functional film formation step, a resistive film is formed integrally with the electron emission film and the ion barrier film, between the inner wall faces of the channels and the electron emission film. In this case, this facilitates formation of the resistive film
Preferably, the method further comprises an output electrode formation step of forming an output electrode at an end on the back surface side of the substrate in the channels, after the functional film formation step. In this case, emission angles of secondary electrons from the electron emission film are limited, which can enhance the resolution.
An image intensifier according to the present invention comprises: a photocathode for converting incident light into photoelectrons; the aforementioned micro-channel plate for multiplying the photoelectrons emitted from the photocathode; and an electron incidence surface for receiving electrons multiplied by the micro-channel plate.
This image intensifier uses the foregoing micro-channel plate to suppress the degradation of the photocathode due to the ion feedback, which can achieve a sufficient improvement in life characteristics.
According to the present invention, the ion feedback from the micro-channel plate is suppressed well, so as to achieve the sufficient improvement in life characteristics of the image intensifier.
Preferred embodiments of the micro-channel plate, the method for manufacturing the micro-channel plate, and the image intensifier according to the present invention will be described below in detail with reference to the drawings.
The interior of the image intensifier 1 is held in a high vacuum state while the two ends of the housing 2 of a substantially hollow columnar shape are hermetically sealed by an entrance window 11 and an exit window 12 of a substantially circular disk shape. The housing 2 is composed, for example, of a ceramic side tube 13 of a substantially hollow cylindrical shape, a silicone rubber molded member 14 of a substantially hollow columnar shape covering the side of the side tube 13, and a ceramic case member 15 of a substantially hollow cylindrical shape covering the side and bottom of the molded member 14.
For example, two through holes are formed at the two ends of the molded member 14. One end of the case member 15 is open, while a through hole with the same periphery as one through hole of the molded member 14 is formed at the other end of the case member 15. On the one end side of the molded member 14, the entrance window 11 of glass is joined to the surface of the surrounding region around the one through hole of the molded member 14. The photoelectron surface 3 of a thin film shape is provided in a substantially central region of the vacuum-side surface of the entrance window 11. The entrance window 11 is, for example, a platelike member comprised of silica glass and the photoelectron surface 3 is formed by evaporating an alkali metal such as K or Na on the platelike member.
On the other hand, on the other end side of the molded member 14, the exit window 12 is fit in the other through hole of the molded member 14. The phosphor screen (electron incidence surface) 5 of a thin film shape is provided in a substantially central region of the vacuum-side surface of the exit window 12. The exit window 12 is, for example, a fiber plate composed of a large number of optical fibers bundled in a plate shape. The optical fibers of the fiber plate are held in a state in which their optical axes are perpendicular to the photoelectron surface 3 and in which their vacuum-side end faces are aligned so as to be flush with each other. The phosphor screen 5 is formed by applying a fluorescent material such as (ZnCd)S:Ag onto the vacuum-side surface of this fiber plate. A light image emitted from the phosphor screen 5 passes through the fiber plate and then is taken generally by an imaging device such as a CCD camera. In this example, electrons multiplied by the micro-channel plate are converted into a light image by the fluorescent material of electron incidence surface and the light image is taken finally by the CCD camera; however, it is also possible to implement the imaging by making use of an electron bombardment type solid-state image sensor (e.g., EBCCD) as electron incidence surface.
A metal back layer and a low-electron-reflectance layer are successively stacked on the vacuum-side surface of the phosphor screen 5. The metal back layer is formed, for example, by evaporation of Al and has a relatively high reflectance for light having passed through the micro-channel plate 4 and a relatively high transmittance for photoelectrons from the micro-channel plate 4. The low-electron-reflectance layer is formed, for example, by evaporation of C, Be, or the like and has a relatively low reflectance for photoelectrons from the micro-channel plate 4.
The micro-channel plate 4 of a substantially circular disk shape is located between the photoelectron surface 3 and the phosphor screen 5. The micro-channel plate 4 is supported by inner edges of mount members 21, 22 fixed to the inner wall of the side tube 13 and is kept opposed with a predetermined space to the photoelectron surface 3 and to the phosphor screen 5. The micro-channel plate 4 functions as a multiplication portion to multiply electrons, which multiplies photoelectrons generated in the photoelectron surface 3 and thereafter outputs resultant electrons toward the phosphor screen 5.
In a peripheral region of the vacuum-side surface of the entrance window 11, a metal wiring layer (not shown) is electrically connected to the photoelectron surface 3. For the connection between this wiring layer and the photoelectron surface 3, a mount member 23 sandwiched between the side tube 13 and the entrance window 11 is fixed so as to extend into the molded member 14. In a peripheral region of the vacuum-side surface of the exit window 12, another wiring layer of metal (not shown) is electrically connected to the phosphor screen 5. For the connection between this wiring layer and the phosphor screen 5, a mount member 24 sandwiched between the side tube 13 and the molded member 14 is fixed so as to extend into the molded member 14.
Connected to ends of the mount members 21 to 24 are one ends of lead wires 25 to 28 comprised, for example, of Kovar metal. The other ends of the lead wires 25 to 28 project hermetically through the molded member 14 and the case member 15 to the outside to be electrically connected to an external voltage source (not shown). This allows a predetermined voltage from the external voltage source to be applied to the photoelectron surface 3, the micro-channel plate 4, and the phosphor screen 5. A potential difference, e.g., approximately 200 V is set between the photoelectron surface 3 and an input surface 4a (cf.
Next, the above-described micro-channel plate 4 will be described in further detail.
As shown in
The resistive film 33 is provided over the entire inner wall faces of the channels 32 and inside with respect to the electron emission film 36. The thickness of the resistive film 33 is, for example, approximately from 100 Å to 10000 Å. This resistive film 33 is formed as follows, for example, when the substrate 31 is made of lead glass: the substrate 31 is set in a vacuum furnace, and hot hydrogen gas is made to flow into the furnace to reduce the surface of lead glass. The resistance of the resistive film 33 can be adjusted to a desired value by controlling an ambient temperature in the vacuum furnace, a concentration of hydrogen gas, a reduction time, and so on. The resistive film 33 can be formed by a below-described atomic layer deposition method. When the atomic layer deposition method is adopted, the resistive film 33 can be formed, for example, by depositing a plurality of Al2O3 layers and ZnO layers. The preferred thickness of the resistive layer 33 in this case is from 20 Å to 400 Å.
The input electrode 34 and the output electrode 35 are provided at the end on the input surface 4a side and at the end on the output surface 4b side, respectively, in the channels 32. The input electrode 34 and the output electrode 35 are formed, for example, by evaporation of ITO films comprised of In2O3 and SnO2, NESA films, Nichrome films, Inconel (registered trademark) films, or the like. By use of the evaporation, the input electrode 34 is formed over a region except openings 32a of the channels 32 in the input surface 4a and over the ends on the input surface 4a side in the inner wall faces of the channels 32, and the output electrode 35 is formed over a region except openings 32b of the channels 32 in the output surface 4b and over the ends on the output surface 4b side in the inner wall faces of the channels 32. The thicknesses of the input electrode 34 and the output electrode 35 are, for example, approximately 1000 Å.
The electron emission film 36 is provided over the entire inner wall faces of the channels 32 so as to cover the resistive film 33, the input electrode 34, and the output electrode 35. The ion barrier film 37 is formed so as to cover the openings 32a on the input surface 4a side in the channels 32. The thicknesses of the electron emission film 36 and the ion barrier film 37 are, for example, approximately from 10 Å to 200 Å. These electron emission film 36 and ion barrier film 37 are integrally formed by the same step, for example, by use of the atomic method deposition method (ALD: Atomic Layer Deposition).
The atomic layer deposition method is a technique of repetitively carrying out an adsorption step of molecules of a compound, a film formation step by reaction, and a purge step of removing excess molecules, thereby to stack atomic layers one by one, so as to obtain a thin film. From the viewpoint of achieving chemical stability, a metal oxide is used as a material for making up the electron emission film 36 and the ion barrier film 37. Examples of such metal oxide include Al2O3, MgO, BeO, CaO, SrO, BaO, SiO2, TiO2, RuO, ZrO, NiO, CuO, GaO, ZnO, and so on.
Next, a method for manufacturing the micro-channel plate 4 will be described.
For manufacturing the micro-channel plate 4 having the configuration as described above, the resistive film 33, input electrode 34, and output electrode 35 each are first formed on the substrate 31. Then, as shown in
After formation of the organic film 38, as shown in
For example, when the electron emission film 36 and the ion barrier film 37 are formed using Al2O3, a reactant gas to be used can be, for example, trimethyl aluminum. In this case, the film formation process includes an adsorption step of H2O, a purge step of H2O, an adsorption step of trimethyl aluminum, and a purge step of trimethyl aluminum. These steps are repeated until achievement of the desired thickness (e.g., 10 Å to 100 Å) of the electron emission film 36 and the ion barrier film 37, thereby forming the electron emission film 36 and ion barrier film 37.
After formation of the electron emission film 36 and ion barrier film 37, heating is carried out for a predetermined duration to remove the organic film 38 from the input surface 4a. This process results in obtaining the micro-channel plate 4.
In the image intensifier 1, as described above, the electron emission film 36 and the ion barrier film 37 formed on the substrate 31 of the micro-channel plate 4 are integrally formed by the same film formation step by means of the atomic layer deposition method. In this structure, the electron emission film 36 and ion barrier film 37 are made as continuous and firm films and, therefore, the ion barrier film 37 can be made thinner than in the conventional structure. Since the ion barrier film 37 is formed on the back side of the organic film (or on the opening 32a side of the channels 32), the organic film 38 can be kept exposed during removal of the organic film 38. This prevents the organic film 38 from remaining on the input surface 4a of the micro-channel plate 4, which can suppress the degradation of performance of the ion barrier film 37 due to the residual organic film serving as a gas source. Therefore, the ion feedback from the micro-channel plate 4 is prevented well, whereby a sufficient improvement can be achieved in life characteristics of the image intensifier 1.
In the micro-channel plate 4, the electron emission film 36 and the ion barrier film 37 are formed containing the metal oxide. Since the metal oxide has excellent chemical stability, use of the metal oxide leads to suppression of temporal change of the electron emission film 36 and the ion barrier film 37.
The input electrode 34 and the output electrode 35 are formed inside with respect to the electron emission film 36 at the end on the input surface 4a side and at the end on the output surface 4b side, respectively, in the channels 32. When the input electrode 34 and the output electrode 35 are formed inside with respect to the electron emission film 36 in this manner, a sufficient region can be secured as a region where the electron emission film 36 is exposed in the channels 32.
The present invention does not have to be limited to the above embodiment, but the present invention can be modified in many ways.
For manufacturing the micro-channel plate 41 having this configuration, the resistive film 33, input electrode 34, and output electrode 35 each are first formed on the substrate 31. Next, as shown in
After removal of the organic film 38, as shown in
This form also achieves the same effect as the above embodiment. In addition, the metal film 39 on the ion barrier film 37 can supply electrons, which can prevent the ion barrier film 37 from becoming electrically charged. Furthermore, since the metal film 39 on the ion barrier film 37 can serve as an electrode on the channel IN side (input electrode), it also becomes possible to omit formation of the input electrode 34 in
Furthermore, the above embodiment described the case where the electron emission film 36 and the ion barrier film 37 were integrally formed by the same film formation step, but another available method may be configured to further integrally form the resistive film 33 as well by the same film formation step. In this case, as shown in
Furthermore, the above embodiment is configured to form the electron emission film 36 and the ion barrier film 37 after the output electrode 35 is preliminarily formed on the substrate 31, but the formation of the output electrode 35 may be carried out after formation of the resistive film 33, the electron emission film 36, and the ion barrier film 37. In this case, the output electrode 35 is formed on the electron emission film 36 at the end on the output surface 4b side in the channels 32, as in a micro-channel plate 62 shown in
The below will describe an effect verification test of the present invention.
This effect verification test is to prepare a plurality of samples of the image intensifier equipped with the micro-channel plate wherein the electron resistive film and the ion barrier film are integrally provided for the channels by the same step (Example) and a plurality of samples of the image intensifier equipped with the micro-channel plate without the ion barrier film (Comparative Example) and to measure a relative change of output from each sample with incidence of light by electric current values of a silicon monitor.
A light source used in the test was one with the color temperature of 2856K. Then the relative output was measured with respect to the output of 1 at the point of time 0 while one cycle was defined as a total of twelve minutes including five seconds under the illuminance of 5400 μlx, five minutes under the illuminance of 540 μlx, three seconds under the illuminance of 54 lx, five minutes and fifty two seconds under the illuminance of 540 μlx, and one minute in a power-off state, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-211194 | Sep 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/069001 | 7/11/2013 | WO | 00 |
