Patent Application
20090045741
The present invention relates to a photomultiplier which has an electron-multiplier section cascade-multiplying photoelectrons generated by a photocathode.
Conventionally, photomultipliers (PMT: Photo-Multiplier Tube) have been known as optical sensors. A photomultiplier comprises a photocathode that converts light into electrons, a focusing electrode, an electron-multiplier section, and an anode, and is constituted so as to accommodate those in a vacuum case. In a photomultiplier, when s incident into a photocathode, photoelectrons are emitted from the photocathode into a vacuum case. The photoelectrons are guided to an electron-multiplier section by a focusing electrode, and are cascade-multiplied by the electron-multiplier section. An anode outputs, as signals, electrons having reached among multiplied electrons (for example, see the following Patent Document 1 and Patent Document 2).
The inventors have studied the conventional photomultiplier in detail, and as a result, have found problems as follows.
That is, as optical sensors expand in application, smaller photomultipliers are desired. On the other hand, accompanying such downsizing of photomultipliers, a high-precision processing technology has been required for components constituting the photomultipliers. In particular, when the miniaturization of components themselves is advanced, it is increasingly hard to realize an accurate layout among the components, which makes it impossible to obtain high detection accuracy, and leads to a great variation in detection accuracy of each of the manufactured photomultipliers.
For example, when a multi-anode photomultiplier having a plurality of anodes so as to correspond to a plurality of electron-multiplier configurations respectively constituting electron-multiplier channels is manufactured by microfabrication, spacing between the anodes as well are markedly made narrow, which increases the possibility of bringing about a reduction in detection accuracy or a variation in detection accuracy of each manufactured photomultiplier due to cross talk among the respective channels.
The present invention is made to solve the aforementioned problem, and it is an object to provide a photomultiplier having a fine structure capable of obtaining higher detection accuracy.
A photomultiplier according to the present invention is an optical sensor having an electron-multiplier section cascade-multiplying photoelectrons generated by a photocathode, and depending on a layout position of the photocathode, there is a photomultiplier having a transmission type photocathode emitting photoelectrons in a direction which is the same as a direction of incident light, or a photomultiplier having a reflection type photocathode emitting photoelectrons in a direction different from the incident direction of light. In particular, the electron-multiplier section has a plurality of groove portions which will be respectively electron-multiplier channels, and the aforementioned photomultiplier is a multi-anode photomultiplier having a plurality of anodes so as to correspond to the plurality of groove portions (electron-multiplier channels).
In concrete terms, the photomultiplier comprises a housing whose inside is maintained in a vacuum state, a photocathode accommodated in the housing, an electron-multiplier section accommodated in the housing, and anodes whose at least parts are accommodated in the housing. The housing is constituted by a lower frame comprised of a glass material, a sidewall frame in which the electron-multiplier section and the anodes are integrally etched, and an upper frame comprised of a glass material or a silicon material.
The electron-multiplier section has a plurality of groove portions or a plurality of through-holes extending along an electron traveling direction. Each of groove portions is defined by a pair of wall parts onto which microfabrication has been performed with an etching technology, and secondary electron emission surfaces, for cascade-multiplying photoelectrons from the photocathode, are formed on the respective surfaces of the pair of wall parts defining the groove portion, which functions as one electron-multiplier channel. In the same way, each through-hole is defined by wall parts onto which microfabrication has been performed with an etching technology, and secondary electron emission surfaces, for cascade-multiplying photoelectrons from the photocathode, are formed on the surfaces of the wall parts defining the through-hole, which functions as one electron-multiplier channel.
In particular, in the photomultiplier according to the present invention, the above-described anodes are disposed so as to respectively correspond to the plurality of groove portions provided in the electron-multiplier section, and are constituted by a plurality of channel electrodes which are disposed at least partially in spaces sandwiched between pairs of wall parts defining corresponding groove portions. Furthermore, in a case of a configuration in which a plurality of through-holes are provided as electron-multiplier channels in the electron-multiplier section, the anodes are provided so as to respectively correspond to the plurality of through-holes provided in the electron-multiplier section, and are constituted by a plurality of channel electrodes which are disposed at least partially in spaces sandwiched between pairs of wall parts defining corresponding through-holes. In either configuration, each channel electrode functions as an anode allocated to one of the electron-multiplier channels.
As described above, as a multi-anode photomultiplier, due to the anodes being constituted by a plurality of channel electrodes, and the respective channel electrodes being disposed so as to be partially inserted in groove portions or through-holes, secondary electrons multiplied in the respective groove portions or secondary electrons multiplied in the respective through-holes exactly reach corresponding channel electrodes (a reduction in cross talk among the electron-multiplier channels), and higher detection accuracy can be obtained.
Here, in a case in which the electron-multiplier section has a plurality of groove portions as electron-multiplier channels, the respective channel electrodes constituting the above-described anodes preferably have protruding portions whose tips are inserted in spaces sandwiched between pairs of wall parts defining corresponding groove portions. Also, in a case in which the electron-multiplier section has a plurality of through-holes as electron-multiplier channels, the respective channel electrodes constituting the above-described anodes preferably have protruding potions whose tips are inserted in spaces sandwiched between wall parts defining corresponding through-holes.
At this time, the respective channel electrodes constituting the above-described anodes preferably have a configuration in which a main body portion thereof is fixed to a part of the housing, and a protruding portion thereof is supported by the main body portion so as to be spaced by a predetermined distance from the housing.
In the photomultiplier according to the present invention, the respective channel electrodes constituting the above-described anodes are preferably comprised of silicon as a material easy to perform microfabrication.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.
As described above, in accordance with the present invention, a plurality of the respective channel electrodes constituting the anodes, which are provided so as to correspond to a plurality of groove portions or through-holes respectively corresponding to electron-multiplier channels, are disposed so as to be partially inserted in corresponding groove portions or through-holes, and therefore cross talk among the channels is effectively reduced, as a result, it is possible to obtain high detection accuracy.
1
a: photomultiplier; 2: upper frame; 3: sidewall frame; 4: lower frame (glass substrate); 22: photocathode; 31: electron-multiplier section; 32: anode; 42: anode terminal; and 320 channel electrode.
In the following, respective embodiments of a photomultiplier according to the present invention will be explained in detail by using
The sidewall frame 3 is constituted by a rectangular flat plate shaped silicon substrate 30 serving as a base material. A depressed portion 301 and a penetration portion 302 are formed from a main surface 30a of the silicon substrate 30 toward a surface 30b facing it. The both openings of the depressed portion 301 and the penetration portion 302 are rectangular, and the depressed portion 301 and the penetration portion 302 are coupled with one another, and the peripheries thereof are formed along the periphery of the silicon substrate 30.
An electron-multiplier section 31 is formed in the depressed portion 301. The electron-multiplier section 31 has a plurality of wall parts 311 installed upright so as to be along one another from a bottom 301a of the depressed portion 301. Groove portions are formed as electron-multiplier channels among the respective wall parts 311 in this way. Secondary electron emission surfaces comprised of secondary electron emission materials are formed at the sidewalls of the wall parts 311 (sidewalls defining the respective groove portions) and the bottom 301a. The wall parts 311 are provided along a longitudinal direction of the depressed portion 301, and one ends thereof are disposed to be spaced by a predetermined distance from one end of the depressed portion 301, and the other ends are disposed at positions facing the penetration portion 302. Anodes 32 are disposed in the penetration portion 302. Note that, as electron-multiplier channels, not only the groove portions among the respective wall parts 311, but also the region of the inner wall of the sidewall frame 2 (inner side of the housing) corresponding to the electron-multiplier section 31 and the groove portions between the wall parts 311 adjacent to the regions as well can be utilized.
Note that the anodes 32 are constituted by a plurality of channel electrodes 320 (which are electrically isolated respectively) provided to respectively correspond to the groove portions, and these channel electrodes 320 are disposed to provide a void part from the inner wall of the penetration portion 302, and main body portions thereof are fixed to the lower frame 4 by anode joining, diffusion joining, and still further joining using a sealing material such as low melting metal (for example, indium, etc.), or the like (hereinafter, a case merely described as joining denotes any one of these joining methods). On the other hand, the respective channel electrodes 320 have protruding portions partially inserted in the spaces defined by the wall parts 311 defining the groove portions, and the protruding portions are supported with the main body portions so as to be spaced by a predetermined distance from the lower frame 4.
The lower frame 4 is comprised of a rectangular flat plate shaped glass substrate 40 serving as a base material. A hole 401, holes 402, and a hole 403 are respectively provided from a main surface 40a of the glass substrate 40 toward a surface 40b facing it. A photocathode side terminal 41, anode terminals 42, and an anode side terminal 43 are respectively inserted into the hole 401, the holes 402, and the hole 403 to be fixed. Further, the anode terminals 42 are made to electrically contact the anodes 32 of the sidewall frame 3.
The depressed portion 301 and the penetration portion 302 of the sidewall frame 3 are disposed at the position corresponding to the depressed portion 201 of the upper frame 2. The electron-multiplier section 31 is disposed in the depressed portion 301 of the sidewall frame 3, and a void part 301b is formed between the wall at one end of the depressed portion 301 and the electron-multiplier section 31. In this case, one end of the electron-multiplier section 31 of the sidewall frame 3 is to be positioned directly beneath the photocathode 22 of the upper frame 2. The channel electrodes 320 constituting the anodes 32 are respectively disposed in the penetration portion 302 of the sidewall frame 3. Because the protruding portions of the respective channel electrodes 320 are disposed not to contact the inner wall of the penetration portion 302, a void part 302a is formed between the protruding portions of the respective channel electrodes 320 and the penetration portion 302. Further, the protruding portions of the respective channel electrodes 320 and corresponding groove portions are disposed so as to be partially overlapped in
By joining of the surface 30b of the sidewall frame 3 (see
The photocathode side terminal 401 and the anode side terminal 403 of the lower frame 4 are respectively made to electrically contact the silicon substrate 30 of the sidewall frame 3, and therefore it is possible to generate an electric potential difference in a longitudinal direction of the silicon substrate 30 (a direction crossing a direction in which photoelectrons are emitted from the photocathode 22, and a direction in which secondary electrons travel in the electron-multiplier section 31) by applying predetermined voltages respectively to the photocathode side terminal 401 and the anode side terminal 403. Furthermore, the anode terminals 402 of the lower frame 4 are prepared for each of the channel electrodes 320 of the sidewall frame 3 (made to electrically contact the anodes 32), and it is possible to take out electrons reaching each of the channel electrodes 320 as signals.
In
The photomultiplier 1a operates as follows. That is, −2000V is applied to the photocathode side terminal 401 of the lower frame 4, and 0V is applied to the anode side terminal 403, respectively. Note that a resistance of the silicon substrate 30 is about 10 MΩ. Furthermore, a value of resistance of the silicon substrate 30 can be adjusted by changing a volume, for example, a thickness of the silicon substrate 30. For example, a value of resistance can be increased by making a thickness of the silicon substrate thinner. Here, when light is incident into the photocathode 22 via the upper frame 2 comprised of a glass material, photoelectrons are emitted from the photocathode 22 toward the sidewall frame 3. The emitted photoelectrons reach the electron-multiplier section 31 positioned directly beneath the photocathode 22. Since an electric potential difference is generated in the longitudinal direction of the silicon substrate 30, the photoelectrons reaching the electron-multiplier section 31 head for the side of the anodes 32. The groove portions defined by the plurality of wall parts 311 are formed as electron-multiplier channels in the electron-multiplier section 31. That is, the photoelectrons reaching the electron-multiplier section 31 from the photocathode 22 collide against the sidewalls of the wall parts 311 and the bottom 301a among the wall parts 311 facing one another, and a plurality of secondary electrons are emitted. In the electron-multiplier section 31, cascade-multiplication of secondary electrons is carried out one after another at every electron-multiplier channel, and 105 to 107 secondary electrons are generated per photoelectron reaching the electron-multiplier section from the photocathode. The generated secondary electrons reach a corresponding channel electrode 320 to be taken out as signals from the anode terminals 402.
Next, an effective layout relationship between the channel electrodes 320 constituting the anodes 32 and the groove portions will be explained by using
First, in the area (a) of
On the other hand, as shown in the area (b) of
That is, in a configuration in which a tip of one corresponding channel electrode 320 is inserted in a space sandwiched between a pair of wall parts defining one groove portion (one electron-multiplier channel), because secondary electrons cascade-multiplied at the wall parts 311 defining a groove portion and the bottom 301 are not emitted from the end of the groove portion, but directly reach the channel electrode 320 corresponding thereto, cross talk among the electron-multiplier channels does not occur structurally. Therefore, after the electrons from the photocathode 22 are cascade-multiplied in a groove portion, these exactly reach the channel electrode 320 corresponding to the groove portion, and higher detection accuracy can be obtained.
Note that the area (c) of
In the above-described embodiment, the photomultiplier having a transmission type photocathode has been described. However, the photomultiplier according to the present invention may have a reflection type photocathode. For example, by forming a photocathode on the end opposite the anode side terminal in the electron-multiplier section 31, a photomultiplier having a reflection type photocathode can be obtained. Furthermore, by forming an inclined surface facing the anode side at an end side opposite the anode side of the electron-multiplier section 31, and by forming a photocathode on the inclined surface, a photomultiplier having a reflection type photocathode can be obtained. In either configuration, it is possible to obtain a photomultiplier having a reflection type photocathode in a state of having other configurations which are the same as those of the above-described photomultiplier 1a.
Also, in the above-described embodiment, the electron-multiplier section 31 disposed in the housing is formed integrally so as to contact the silicon substrate 30 constituting the sidewall frame 3. However, in a state in which the sidewall frame 3 and the electron-multiplier section 31 contact one another in this way, there is a possibility that the electron-multiplier section 31 is under the influence of external noise via the sidewall frame 3, which deteriorates detection accuracy. Then, the electron-multiplier section 31 and the anodes 32 (channel electrodes 320) formed integrally with the sidewall frame 3 may be respectively disposed in the glass substrate 40 (the lower frame 4) so as to be spaced by a predetermined distance from the sidewall frame 3. To describe concretely, the void part 301b is made to be a penetration portion, and the photocathode side terminal 401 is disposed to electrically contact the photocathode side end of the electron-multiplier section 31, and the anode side terminal 403 is disposed to electrically contact the anode side end of the electron-multiplier section 31.
Furthermore, in the above-described embodiment, the upper frame 2 constituting a part of the housing is comprised of the glass substrate 20, and the glass substrate 20 itself functions as a transmission window. However, the upper frame 2 may be comprised of a silicon substrate. In this case, a transmission window is formed at any one of the upper frame 2 or the sidewall frame 3. As a method for forming a transmission window, for example, etching is carried out onto the both surfaces of an SOI (Silicon On Insulator) substrate in which a spatter glass substrate is sandwiched from the both sides by silicon substrates, and an exposed part of the spatter glass substrate can be utilized as a transmission window. Further, a columnar or mesh pattern may be formed in several μm on a silicon substrate, and this portion may be thermally oxidized to be glass. In addition, etching may be carried out such that a silicon substrate of an area to be formed as a transmission window is made to have a thickness of about several μm, and this may be thermally oxidized to be glass. In this case, etching may be carried out from the both surfaces of the silicon substrate, or etching may be carried out only from one side.
Next, one example of a method for manufacturing the photomultiplier 1a shown in
First, as shown in the area (a) of
After the photoresist film 70 is removed from the state shown in the area (b) of
After the silicon thermally-oxidized film 61 is removed from the state shown in the area (d) of
Subsequently, as shown in the area (b) of
The silicon substrate 50 and the glass substrate 80 which have been made to progress up to the process of the area (a) of
In the sidewall frame 12, a large number of holes are provided in parallel with a direction of a tube axis in a silicon substrate 12a. The protruding portions 121a against which electrons are made to collide are provided to the inner surfaces of the holes 121, and secondary electron emission surfaces are formed on the inner surfaces of the holes 121 including the protruding portions 121a (each hole 121 serves as an electron-multiplier channel). Note that an inner wall of the sidewall frame 12 (the inside of the housing) can be utilized as a part of the walls of the electron-multiplier channels. In addition, a surface electrode 122 and a back surface electrode 123 are disposed in the vicinity of the openings at the both ends of each hole 121. A positional relationship between the holes 121 and the surface electrode 122 is shown in the area (b) of
The first lower frame 13 is a member for coupling the sidewall frame 12 and the second lower frame 14, and is joined to both of the sidewall frame 12 and the second lower frame 14.
The second lower frame 14 is comprised of a silicon substrate 14a to which a large number of holes 141 are provided. A plurality of channel electrodes 142 constituting anodes are inserted into the respective holes 141 to be fixed. Furthermore, a protruding portion 142a is provided to each of these channel electrodes 142, and the protruding portion 142a is fixed so as to be partially inserted in the hole 121.
In the photomultiplier 10 shown in
Next, an optical module to which the photomultiplier 1a having a configuration as described above is applied will be described. The area (a) of
The solvent which has passed through the extraction path 853a is introduced into the reagent mixing-reaction paths 854 so as to include the extract material of interest. There are a plurality of the reagent mixing-reaction paths 854, and due to corresponding reagents being introduced into the respective paths from the reagent paths 857, the reagents are mixed into the solvent. The solvent into which the reagents have been mixed travels toward the detecting element 855 through the reagent mixing-reaction paths 854 while carrying out reactions. The solvent in which detection of the material of interest has been completed in the detecting element 855 is discarded to the waste liquid pool 856.
A configuration of the detecting element 855 will be described with reference to the area (b) of
As described above, since the electron-multiplier section having a plurality of grooves (for example, in number corresponding to twenty channels) is provided to the photomultiplier 1a, it is possible to detect from which position (from which reagent mixing-reaction path 854) fluorescence or transmitted light has changed. This detected result is outputted from the output circuit 855b. Also, the power supply 855c is a power supply for driving the photomultiplier 1a. Note that, a glass substrate (not shown) is disposed on the glass plate 850, and covers the extraction path 853a, the reagent mixing-reaction paths 854, the reagent paths 857 (except for the sample injecting portions) except for the contact portions between the gas inlet pipe 851, the gas exhaust pipe 852, and the solvent inlet pipe 853, and the glass plate 850, the waste liquid pool 856, and sample injecting portions of the reagent paths 857.
As described above, in accordance with the present invention, as a multi-anode photomultiplier, due to the anodes being constituted by a plurality of channel electrodes, and the respective channel electrodes being disposed so as to be partially inserted in the groove portions or the through-holes, secondary electrons multiplied in the respective groove portions or secondary electrons multiplied in the respective through-holes exactly reach corresponding channel electrodes (a reduction in cross talk among the electron-multiplier channels), and higher detection accuracy can be obtained.
In addition, by providing the protruding portions 311a having a desired height on the surfaces of the wall parts 311 defining the groove portions of the electron-multiplier section 31, it is possible to dramatically improve the electron-multiplication efficiency.
Furthermore, since the grooves are formed in the electron-multiplier section 31 by performing microfabrication onto the silicon substrate 30a, and the silicon substrate 30a is joined to the glass substrate 40a, there is no vibratory portion. That is, the photomultiplier according to the respective embodiments is excellent in vibration resistance and impact resistance.
Since the plurality of channel electrodes 320 constituting the anodes 32 are joined to the glass substrate 40a, there is no metal droplet at the time of welding. Therefore, the photomultiplier according to the respective embodiments is improved in electrical stability, vibration resistance, and impact resistance. Since the channel electrodes 320 are joined to the glass substrate 40a at the entire bottom face thereof, the anodes 32 do not vibrate due to impact or vibration. Therefore, the photomultiplier is improved in vibration resistance and impact resistance.
Furthermore, in the manufacture of the photomultiplier, because there is no need to assemble the internal structure, and handling thereof is simple and work hours are shortened. Since the housing (vacuum case) constituted of the upper frame 2, the sidewall frame 3, and the lower frame 4, and the internal structure are integrally built, it is possible to easily downsize the photomultiplier. There are no separate components internally, and therefore electrical and mechanical joining is not required.
In the electron-multiplier section 31, cascade-multiplication of electrons is carried out while electrons collide against the sidewalls of the plurality of grooves formed by the wall parts 311. Therefore, since the configuration is simple and a large number of components are not required, it is possible to easily downsize the photomultiplier.
From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.
The electron-multiplier tube according to the present invention can be applied to various fields of detection requiring detection of low light.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2005-232535 | Aug 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/311009 | 6/1/2006 | WO | 00 | 12/11/2007 |
