The present invention relates to a CEM assembly including a channel electron multiplier (described as “a CEM” below) and an electron multiplier device including the CEM assembly.
A CEM having an electron multiplication function includes a multiplication channel in which a secondary electron emission layer is provided, via a resistive layer, on an inner wall surface of a through-hole formed in a structural body or on a surface of defining a groove provided in the surface of the structural body. An input electrode is provided at an input end of the multiplication channel, and an output electrode set to have a potential higher than a set potential of the input electrode is provided at an output end of the multiplication channel. If charged particles taken from the input end reach a secondary electron emission surface, secondary electrons are emitted from the secondary electron emission surface. The emitted secondary electrons are multiplied in a cascade manner while propagating from the input electrode toward the output electrode.
The above-described CEM constitutes a CEM assembly along with a voltage supply circuit for applying a predetermined voltage between the input electrode and the output electrode, and the CEM assembly is applied to various sensing devices. As an example, the CEM assembly is combined with a structure (for example, electrode such as an anode) of collecting electrons emitted from the CEM, and thus may be applied to an electron multiplier device or the like which is widely used in the technical field of ion detection or the like.
The inventors have examined a channel electron multiplier (CEM) in the related art and a CEM assembly including a voltage supply circuit applied thereto, and have found problems as follows.
That is, the CEM in the related art in which a secondary electron emission layer and the like are formed in a structural body comprised of lead glass has required a resistance value (resistance value from the input end of the multiplication channel to the output end) of 10 MΩ or larger in order to ensure a stable operation. In the CEM in the related art in which lead glass is applied for the structural body, a lead layer deposited by the reduction treatment of PbO is used as the resistance layer. In recent years, a low-resistance CEM in which a resistive film and a secondary electron emission film are thrilled by atomic layer deposition (described as “ALD” below) on the surface of a structural body comprised of an insulating material or ceramic is manufactured.
In particular, in the above-described single low-resistance CEM, the resistance value of the CEM is decreased by heat generated in operation, or voltage drop occurs at an output end by an increase of an output current. Such a decrease of the output potential of the CEM causes an increase in the gain of the CEM, such that there is a problem in that the linearity (described as “DC linearity” below) of the CEM by DC voltage control is lost. There are individual differences in resistance value between a plurality of manufactured CEMs. Therefore, “an individual difference in resistance value between CEMs” is also required to be considered for fixing the output potential of the CEM.
In this specification, “DC linearity” means operation characteristics of a CEM, which are calculated by a ratio (described as “an input-and-output current ratio) of an input amount (in terms of a current value) of charged particles to the CEM and an output current of the CEM. When the input amount of the charged particles to the CEM is small, the input-and-output current ratio shows a constant value (linearity). However, in a case where charged particles of an excessive amount are inputted to the CEM, the input-and-output current ratio deviates (±10%) from a reference value. The reference value (a.u.) is an input-and-output current ratio in a range in which DC linearity can be sufficiently ensured (range where the output current is as low as about 1 to 100 nA), and is given by the following Expression (1).
Output current (A)/input amount (A) of charged particles (1)
DC linearity (%) is given by the following Expression (2). Thus, in a case of a range in which the output current is relatively low, the input-and-output current ratio is necessarily substantially equal to the reference value (DC linearity is 100%). However, as the output current increases beyond the above range, the voltage drop at the output end of the CEM increases, and thus a difference between the input-and-output current ratio and the reference value becomes significant (DC linearity is broken).
Output current (A)/input amount (A) of charged particles/reference value (a.u.)×100 (2)
Here, “the input amount of charged particles” is given as a current value based on charged particles reaching the input end of the CEM. “The output current” is given as a current value based on electrons reaching an anode from the CEM.
As means for solving deterioration of DC linearity by fluctuation of the output potential in the above-described CEM, for example, a method of providing a power source unit configured to set an input potential of the CEM and a power source unit configured to set an output potential of the CEM is considered. However, a voltage supply circuit including such two power source units has a problem in that manufacturing cost of a CEM assembly including the CEM increases, and it is difficult to reduce a size of the CEM assembly.
The present invention has been made to solve the above-described problems, and an object thereof is to provide a CEM assembly having a structure for avoiding an increase in size of the CEM assembly including a CEM and substantially fixing an output potential of the CEM, and an electron multiplier device including the CEM assembly as an example of an application technology.
According to an embodiment, a CEM assembly comprised a channel electron multiplier, and a voltage supply circuit including a power source unit (this power source unit generates the entirety of an electromotive force in a circuit) configured to apply a predetermined voltage to the channel electron multiplier. The channel electron multiplier includes at least a multiplication channel, an input electrode, and an output electrode. The multiplication channel includes an input end for taking charged particles in, an output end for emitting secondary electrons, and a secondary electron emission layer continuously provided from the input end toward the output end. The input electrode is provided at the input end of the multiplication channel in a state of being in contact with the secondary electron emission layer. The output electrode is provided at the output end of the multiplication channel in a state of being in contact with the secondary electron emission layer. The voltage supply circuit includes one power source unit in the entirety of the circuit. A predetermined voltage is applied between the input electrode and the output electrode by the power source unit. In particular, the voltage supply circuit includes a first terminal set to a first reference potential, a second terminal connected to the input electrode, a third terminal connected to the output electrode, a fourth terminal set to a second reference potential, and a constant voltage generation unit, in addition to the power source unit. Here, the power source unit generates an electromotive force for ensuring a potential difference between the first terminal and an input-side reference node. The constant voltage generation unit is disposed between the third terminal and the fourth terminal to hold a target potential for adjusting a potential of the output electrode. The constant voltage generation unit includes a constant voltage supply unit provided to cause voltage drop for ensuring a potential difference between the fourth terminal and an output-side reference node.
Further, according to an embodiment, as an example of an application technology to which the CEM assembly having the above-described structure is applied, an electron multiplier device includes the CEM assembly having the above-described structure, and an anode disposed so as to face the output end of the CEM to collect electrons outputted from the output end of the CEM.
The embodiments according to the present invention can be more sufficiently understood from the following detailed descriptions and the accompanying drawings. The examples are given just for the purpose of illustration and should not be considered as limiting the present invention.
Further application range of the present invention will be apparent from the following detailed descriptions. However, the detailed description and specific examples show the preferred embodiment of the invention, but this is just an example. Various modifications and improvements in the scope of the present invention will be apparent to those skilled in the art from the detailed descriptions.
Firstly, details of embodiments of the present application invention will be individually described in order.
(1) According to an aspect of an embodiment, a CEM assembly comprises a channel electron multiplier (CEM), and a voltage supply circuit including a power source unit (this power source unit generates the entirety of an electromotive force in a circuit) configured to apply a predetermined voltage to the CEM. The CEM includes, at least, a multiplication channel, an input electrode, and an output electrode. The multiplication channel has an input end for taking charged particles in, an output end for emitting a secondary electron, and a secondary electron emission layer continuously provided from the input end toward the output end. The input electrode is provided at the input end of the multiplication channel in a state of being in contact with the secondary electron emission layer. The output electrode is provided at the output end of the multiplication channel in a state of being in contact with the secondary electron emission layer. The voltage supply circuit includes one power source unit in the entirety of the circuit. A predetermined voltage is applied between the input electrode and the output electrode by the power source unit.
In particular, the voltage supply circuit includes a first terminal set to a first reference potential, a second terminal connected to the input electrode, a third terminal connected to the output electrode, a fourth terminal set to a second reference potential, and a constant voltage generation unit, in addition to the power source unit. Each of the first reference potential and the second reference potential may be connected to a common terminal set to a ground potential, for example (the first reference potential and the second reference potential may be equal to each other). The power source unit is disposed between the first terminal and the second terminal. The power source unit generates an electromotive force for ensuring a potential difference between the first terminal and an input-side reference node. The input-side reference node is a node which is set to the same potential as the potential of the input electrode via the second terminal and is located between the first terminal and the second terminal. The constant voltage generation unit is disposed between the third terminal and the fourth terminal and holds a target potential for adjusting a potential of the output electrode. The constant voltage generation unit includes an output-side reference node and a constant voltage supply unit provided to cause voltage drop for ensuring a potential difference between the fourth terminal and the output-side reference node. That is, in the constant voltage supply unit, the power source unit generating an electromotive force is not disposed between the third terminal and the fourth terminal. The output-side reference node is a node set to the target potential for adjusting the potential of the output electrode and is a node located between the third terminal and the fourth terminal.
(2) According to another aspect of the embodiment, preferably, the constant voltage generation unit further includes a first resistor and a potential fixing element. The first resistor is disposed between the input-side reference node and the output-side reference node. The potential fixing element has a function to eliminate a potential difference between the output electrode and the output-side reference node via the third terminal.
(3) According to still another aspect of the embodiment, preferably, the constant voltage supply unit includes a second resistor disposed between the output-side reference node and the fourth terminal. According to still another aspect of the embodiment, preferably, the resistance value of the first resistor is higher than the resistance value of the second resistor. Further, according to still another aspect of the embodiment, preferably, the resistance ratio between the first resistor and the second resistor is set to be within a range of 100:1 to 2:1.
(4) According to still another aspect of the embodiment, preferably, the constant voltage supply unit includes a Zener diode disposed between the output-side reference node and the fourth terminal.
(5) According to still another aspect of the embodiment, preferably, the potential fixing element includes any of a MOS transistor, a FET, and a bipolar transistor. In a case where such a three-terminal element is applied as the potential fixing element, the potential fixing element has a first element end connected to the output-side reference node, a second element end connected to the third terminal, and a third element end connected to the fourth terminal.
(6) According to still another aspect of the embodiment, preferably, the constant voltage supply unit may include one or more IC units connected in series between the output-side reference node and the fourth terminal. In this case, the output-side reference node is electrically connected to the output electrode via the third terminal. Each of the IC units includes a shunt regulator IC, a third resistor, and a fourth resistor. The third resistor and the fourth resistor are connected in series between an input end and an output end of the shunt regulator IC at a predetermined resistance ratio.
(7) According to still another aspect of the embodiment, preferably, the multiplication channel further includes a structural body provided to support a secondary electron emission layer and being comprised of an insulating material, and a resistive film provided between the secondary electron emission layer and the structural body. According to still another aspect of the embodiment, preferably, the insulating material includes ceramic or glass excluding lead glass or ceramic.
(8) According to still another aspect of the embodiment, preferably, the resistance value of the multiplication channel located between the input electrode and the output electrode is less than 10 MΩ.
(9) According to an aspect of an embodiment, as an example of an application technology to which the CEM assembly having the above-described structure, an electron multiplier device includes the CEM assembly having the above-described structure and an anode. The anode is an electrode disposed to face the output end of the CEM and has a function to collect electrons outputted from the output end of the CEM.
As described above, each of the aspects listed in this section [Description of Embodiments of Invention] is applicable to each of all the remaining aspects or to all combinations of the remaining aspects.
A specific example of the CEM assembly and the electron multiplier device including the CEM assembly according to the invention will be described below in detail with reference to the accompanying drawings. Regarding the embodiment disclosed below, it is assumed that an example of an electron multiplier device among various sensing devices to which the CEM assembly according to the present invention is applied will be described. The present invention is not limited to the descriptions. The present invention is defined by the claims, and is intended to include any change within the meaning and the scope equivalent to those of the claims. In the descriptions of the drawings, the same components are denoted by the same reference signs, and repetitive descriptions will be omitted.
According to the embodiment, the electron multiplier device illustrated in
Firstly, in the example in
The voltage supply circuit 200 configured to apply a predetermined voltage between the input electrode 130A and the output electrode 130B includes a single power source unit 300 (only the power source unit 300 generates an electromotive force in the entirety of the circuit) generating the entirety of the electromotive force in the circuit, first to fourth terminals 210A to 210D, and a constant voltage generation unit 400. In particular, the first terminal 210A is set to a first reference potential (set to a ground potential via the common terminal in the example in
In the voltage supply circuit 200, an input-side reference node 310 is located between the power source unit 300 and the second terminal 210B. The input-side reference node 310 is a node set to the same potential as the potential of the input electrode 130A via the second terminal 210B. The power source unit 300 generates an electromotive force for ensuring a potential difference between the first terminal 210A and the input-side reference node 310.
In the voltage supply circuit 200, the constant voltage generation unit 400 is disposed between the third terminal 210C and the fourth terminal 210D and holds a target potential for fixing the potential of the output electrode 130B. The target potential is set for an output-side reference node 410 which is not influenced by potential fluctuation of the output electrode 130B. Specifically, the potential difference between the fourth terminal 210D and the output-side reference node 410 is ensured by voltage drop by a constant voltage supply unit 500. The output-side reference node 410 is a node set to the target potential for adjusting the potential of the output electrode 130B and is a node which is directly or indirectly connected to the third terminal 210C.
As illustrated in
In the electron multiplier device according to the first comparative example, the configurations of the CEM (low-resistance CEM having a resistance value of 2 MΩ) 100 constituting a portion of the CEM assembly, the anode 150, and the current measurement circuit 180 (or signal output circuit including the amplifier 160) are the same as those in the configuration example in
As illustrated in
The configuration of the electron multiplier device according to the first embodiment is similar to the configuration in the first comparative example, which is illustrated in
The voltage supply circuit 200B configured to apply a predetermined voltage between the input electrode 130A and the output electrode 130B includes the power source unit 300 configured to generate the entirety of the electromotive force in the circuit, the first to fourth terminals 210A to 210D, and a constant voltage generation unit 400B. The first terminal 210A is set to the ground potential (first and second reference potentials) via the common terminal. The second terminal 210B is connected to the input electrode 130A. The third terminal 2100 is connected to the output electrode 130B. Similar to the first terminal 210A, the fourth terminal 210D is set to the ground potential via the common terminal.
In the voltage supply circuit 200B, the input-side reference node 310 is located between the power source unit 300 and the second terminal 210B. The power source unit 300 generates an electromotive force for ensuring a potential difference between the first terminal 210A and the input-side reference node 310. With this configuration, the input-side reference node 310 is set to −1000 to −4000 V.
In the voltage supply circuit 200B, the constant voltage generation unit 400B includes the first resistor 420, a potential fixing element 430A, and the constant voltage supply unit 500A. The first resistor 420 is disposed between the input-side reference node 310 and the output-side reference node 410. The constant voltage generation unit 400B is disposed between the third terminal 210C and the fourth terminal 210D and holds the target potential for fixing the potential of the output electrode 130B. The target potential is set for an output-side reference node 410 which is not influenced by potential fluctuation of the output electrode 130B. Specifically, the potential difference between the fourth terminal 210D and the output-side reference node 410 is ensured by voltage drop by the constant voltage supply unit 500A configured by a resistor (second resistor). The potential fixing element 430A configured by an N-type MOS transistor (described as “an NMOS” below) is disposed between the output-side reference node 410 and the third terminal 210C.
A gate G (first element end) of the NMOS is connected to the output-side reference node 410. A source S (second element end) of the NMOS is connected to the third terminal 210C. A drain D (third element end) of the NMOS is connected to the fourth terminal 210D. As the potential fixing element, any of a MOS transistor, a FET, and a bipolar transistor can be applied, as in this embodiment. Preferably, the resistance value of the first resistor 420 is preferably higher than the resistance value of the second resistor constituting the constant voltage supply unit 500A. The resistance ratio between the first resistor 420 and the second resistor is preferably set to be within a range of 100:1 to 2:1.
In the embodiment, if the output current increases (electrons emitted from the CEM 100 toward the anode 150 increase) in an operation of electron multiplication, voltage drop occurs on the output side (output electrode 130B) of the CEM 100. At this time, a voltage VGS between the gate G and the source S of the potential fixing element (NMOS) 430A increases, and the NMOS turns into an ON state at a time point at which VGS exceeds a threshold voltage. When the NMOS is in the ON state, instantaneously, electrons flow from the output electrode 130B toward the fourth terminal 210D via the third terminal 210C, and thus voltage drop of the output electrode 130B in the CEM 100 is eliminated. If the voltage drop is eliminated, VGS also decreases, and thus the NMOS turns into an OFF state. That is, the potential of the output electrode 130B is fixed to the target potential of the output-side reference node 410. As described above, according to this embodiment, it is possible to completely fix the resistance ratio between the first resistor 420 and the second resistor (constant voltage supply unit 500A) (the set potential of the output-side reference node 410 is not influenced by voltage fluctuation of the output electrode 130B).
In the first embodiment, the resistance value of the first resistor 420 is set to 20 MΩ, and the resistance value of the second resistor (constant voltage supply unit 500A) is set to 2 MΩ. The input-side reference node 310 is set to −1100 V, and the output-side reference node 410 is set to −100 V. The first comparative example in
As understood from
The electron multiplier device according to the second embodiment is different from the electron multiplier device according to the first embodiment illustrated in
With the CEM assembly having the above-described configuration according to the second embodiment, it is also possible to fix the potential of the output electrode 130B to the output-side reference node 410 in the CEM 100. The output potential (potential of the output electrode 130B) of the CEM 100 is required to about −100 V. As an example, in a case where the resistance ratio between the first resistor 420 and the second resistor (constant voltage supply unit 500A) is set to 10:1, when the set potential (potential of the input-side reference node 310) of the input electrode 130A is −1100 V, the set potential of the output electrode 130B becomes −100 V, and this is ideal. If the set potential of the input electrode 130A is changed to −2200 V, the set potential of the output electrode 130B becomes −200 V, and voltage loss of 100 V occurs. Thus, as in the second embodiment, if a Zener diode (constant voltage supply unit 500B) having VZ=100 V is applied instead of the second resistor (constant voltage supply unit 500A), an operation with no voltage loss is possible.
In
In a measurement result of
The configuration of the electron multiplier device according to the third embodiment is similar to the configuration in the first embodiment illustrated in
The voltage supply circuit 200D configured to apply a predetermined voltage between the input electrode 130A and the output electrode 130B includes the power source unit 300 configured to generate the entirety of the electromotive force in the circuit, the first to fourth terminals 210A to 210D, and a constant voltage generation unit 400D. The first terminal 210A is set to the ground potential (first and second reference potentials) via the common terminal. The second terminal 210B is connected to the input electrode 130A. The third terminal 210C is connected to the output electrode 130B. Similar to the first terminal 210A, the fourth terminal 210D is set to the ground potential via the common terminal.
In the voltage supply circuit 200D, the input-side reference node 310 is located between the power source unit 300 and the second terminal 210B. The power source unit 300 generates an electromotive force for ensuring a potential difference between the first terminal 210A and the input-side reference node 310. With this configuration, the input-side reference node 310 is set to −1000 to −4000 V.
In the voltage supply circuit 200D, the constant voltage generation unit 400D includes the first resistor 420, a potential fixing element 430B, and the constant voltage supply unit 500A. The first resistor 420 is disposed between the input-side reference node 310 and the output-side reference node 410. The constant voltage generation unit 400D is disposed between the third terminal 210C and the fourth terminal 210D and holds the target potential for fixing the potential of the output electrode 130B. The target potential is set for an output-side reference node 410 which is not influenced by potential fluctuation of the output electrode 130B. Specifically, the potential difference between the fourth terminal 210D and the output-side reference node 410 is ensured by voltage drop by the constant voltage supply unit 500A configured by a resistor (second resistor). The potential fixing element 430B configured by a P-type MOS transistor (described as “a PMOS” below) is disposed between the output-side reference node 410 and the third terminal 210C.
Preferably, the resistance value of the first resistor 420 is higher than the resistance value of the second resistor constituting the constant voltage supply unit 500A. The resistance ratio between the first resistor 420 and the second resistor is set to be within a range of 100:1 to 2:1. A gate G (first element end) of the PMOS is connected to the output-side reference node 410. A drain D (second element end) of the PMOS is connected to the third terminal 210C. A source S (third element end) of the PMOS is connected to the fourth terminal 210D. If VDS of the PMOS is set to be substantially equal to the potential difference between the output-side reference node 410 and the fourth terminal 210D, it is possible to stabilize the potential of the output electrode 130B in a high output of the CEM 100.
In this embodiment, in the potential fixing element 430B, the source S is connected to the fourth terminal 210D, and the gate G is connected to the output-side reference node 410. Generally, in this configuration, VGS exceeds the threshold voltage by voltage drop of the constant voltage supply unit 500A. Thus, the potential fixing element (PMOS) 430B turns into the ON state. In the ON state, electrons flow from the output electrode 130B toward the fourth terminal 210D via the third terminal 210C, but electrons not less than a predetermined amount do not flow. Therefore, even in a case where voltage drop occurs on the output end of the CEM 100, a state where a bias is applied in a direction in which voltage drop is eliminated is normally maintained (at least, the potential difference VDS between the output electrode 130B and the fourth terminal 210D is ensured).
The configuration of the electron multiplier device according to the fourth embodiment is similar to the configuration in the first comparative example illustrated in
The voltage supply circuit 200E configured to apply a predetermined voltage between the input electrode 130A and the output electrode 130B includes the power source unit 300 configured to generate the entirety of the electromotive force in the circuit, the first to fourth terminals 210A to 210D, and a constant voltage generation unit 400E. The first terminal 210A is set to the ground potential (first and second reference potentials) via the common terminal. The second terminal 210B is connected to the input electrode 130A. The third terminal 210C is connected to the output electrode 130B. Similar to the first terminal 210A, the fourth terminal 210D is set to the ground potential via the common terminal
In the voltage supply circuit 200E, the input-side reference node 310 is located between the power source unit 300 and the second terminal 210B. The power source unit 300 generates an electromotive force for ensuring a potential difference between the first terminal 210A and the input-side reference node 310. With this configuration, the input-side reference node 310 is set to −1000 to −4000 V.
In the voltage supply circuit 200E, the constant voltage generation unit 400E includes the output-side reference node 410 and a plurality of IC units 500C1 to 500C3 corresponding to the constant voltage supply unit 500 illustrated in
For example, a case where voltage drop on the output side of the CEM 100 (the potential of the output electrode 130B is decreased) is considered. In this case, in the IC unit 500C1, since the potential difference between the fourth terminal 210D and the output-side reference node 410 increases, the shunt regulator IC 510 causes electrons from the output electrode 130B to pass (short-circuited state) at a time point at which the above potential difference exceeds a reference voltage of the shunt regulator IC 510 set at a resistance ratio between the third resistor 520 and the fourth resistor 530. The target potential of the output-side reference node 410 rises in a period in which the electrons pass through the shunt regulator IC 510. Thus, the potential of the output electrode 130B connected to the output-side reference node 410 also rises (elimination of voltage drop at the output end of the CEM 100). In a case where voltage drop occurs largely, the above-described operation is performed in order of the IC unit 500C2 and the IC unit 500C3. If the voltage drop on the output side of the CEM 100 is eliminated, the potential of the output-side reference node 410 is restored to the target potential before the operation of each of the IC units 500C1 to 500C3, by voltage drop of the third resistor 520 and the fourth resistor 530 which are connected in series in each of the IC units 500C1 to 500C3.
In
As understood from
According to this embodiment, since the target potential as an adjustment target of the output potential is set in the output-side reference node which is not influenced by fluctuation of the output potential of the CEM, it is possible to fix the output potential to the target potential even in the voltage supply circuit including only a single power source unit. In particular, regarding the fixation of the target potential, considering individual differences in resistance values between a plurality of manufactured CEMs is not required.
From the above descriptions of the present invention, it is apparent that the present invention can be modified in various ways. Such modifications cannot be construed as departing from the spirit and scope of the present invention, and improvements which are obvious to one skilled in the art are intended to be included within the scope of the following claims.
Number | Date | Country | Kind |
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2018-204147 | Oct 2018 | JP | national |