Charged particle detector

Abstract

A charged particle detector (1) comprises: a semiconductor detector (3) which includes an anode (3a) and a cathode (3b), and in which a first voltage is supplied to the cathode (3b) and a second voltage lower than the first voltage is supplied to the anode (3a); a conductor part (8) connected to a reference potential GND which is at a potential lower than the second voltage; and a protection part (6) which is disposed between the anode (3a) and the conductor part (8) and has applied thereto a low potential which is a potential having an absolute value lower than the absolute value of the second voltage. The protection part (6) has a resistor (62).

Description

charged particle detector

[0001] The present disclosure relates to a charged particle detector that detects ions, electrons, etc. The charged particle detector according to the present disclosure is used, for example, in mass spectrometry.

[0002] As a charged particle detector for detecting charged particles such as ions and electrons, a detector having an electron multiplier element that emits electrons in response to the incidence of a charged particle and a semiconductor detector that captures the emitted electrons and outputs them as an electrical signal is known (see, for example, Patent Document 1). The charged particle detector described in Patent Document 1 includes an avalanche diode (AD) as the semiconductor detector, and a capacitor is connected in series to the AD to reduce the combined capacitance with the capacitance of the AD, thereby achieving a high-speed response of the AD.

[0003] An input protection circuit for protecting elements of an input circuit from overvoltage caused by discharge or the like is known (see, for example, Patent Document 2). The input protection circuit described in Patent Document 2 includes an ESD protection element and a resistor. By connecting a surge-resistant resistor to the signal path, overcurrent is prevented from being input to the input circuit at a subsequent stage.

[0004] JP 2022-81982 A International Publication No. 2008 / 53555

[0005] In the above-described charged particle detector, a discharge may occur between the semiconductor detector and the reference potential, causing a large current to instantaneously flow through the semiconductor detector. Such a discharge current may adversely affect the semiconductor detector.

[0006] When the input protection circuit described in Patent Document 2 is applied to a semiconductor detector in order to prevent adverse effects on the semiconductor detector, a resistor connected on the signal path may affect the time response characteristics of the semiconductor detector.

[0007] An object of the present disclosure is to provide a charged particle detector that can suppress the influence on the time response characteristics of a semiconductor detector and prevent the semiconductor detector from being adversely affected when a discharge occurs.

[0008] A charged particle detector according to one aspect of the present disclosure comprises a semiconductor detector 3 including an anode and a cathode, in which a first voltage is supplied to the cathode and a second voltage lower than the first voltage is supplied to the anode, a conductor portion connected to a reference potential GND, which is a potential having an absolute value lower than that of the second voltage, and a protective portion arranged between the anode and the conductor portion and to which a low potential, which is a potential having an absolute value lower than that of the second voltage, is applied, and the protective portion has a resistor.

[0009] In the above-described charged particle detector, a high reverse bias voltage is supplied to the semiconductor detector, causing a current to flow from the cathode to the anode. The protective unit is disposed between the anode and the conductor and is applied with a low potential having an absolute value lower than that of the second voltage. This makes it easier for a discharge to occur between the semiconductor detector and the protective unit than between the semiconductor detector and the conductor, and the discharge current flows from the semiconductor detector, which has a higher potential, to the protective unit, which has a lower potential. Furthermore, the protective unit includes a resistor, which can reduce the discharge current. This reduces the current flowing through the semiconductor detector when a discharge occurs, preventing adverse effects on the semiconductor detector. Additionally, in the above-described charged particle detector, a resistor is not connected in the signal output path, thereby suppressing the influence of the resistor on the time response characteristics of the semiconductor detector.

[0010] The protection unit may further include a protection electrode to which a low potential is applied via a resistor. In this case, since the protection electrode is located closer to the semiconductor detector than the conductor, discharge is more likely to occur between the semiconductor detector and the protection electrode than between the semiconductor detector and the conductor, and the discharge current is more likely to flow toward the protection electrode. This makes it easier to ensure a discharge path for the discharge current via the protection electrode and the resistor.

[0011] The low potential may be a reference potential, the conductor portion may include an outer conductor connected to the reference potential and a central conductor inserted inside the outer conductor, and may have a connector connected to the semiconductor detector, and the protection portion may be connected to the outer conductor. In this case, a discharge current flows from the semiconductor detector via the protection portion and the outer conductor of the conductor portion to the reference potential. Meanwhile, an electrical signal (output signal) output from the semiconductor detector is output to the outside by the central conductor. This eliminates the need for an additional element to discharge the discharge current, thereby efficiently ensuring a discharge path for the discharge current.

[0012] The low potential may be a reference potential, the conductor portion may include an outer conductor connected to the reference potential, and the protective portion may be a resistive film covering the outer conductor. In this case, since the protective portion is a resistive film, it is not necessary to provide a resistor, for example, as a resistive element, and it is also not necessary to provide wiring connecting the protective electrode and the resistor to a low potential supply source, allowing the discharge path of the discharge current to be configured simply.

[0013] The low potential may be a potential having an absolute value higher than that of the reference potential and lower than that of the second voltage, which increases the degree of freedom in designing the low potential.

[0014] The semiconductor detector may further include a substrate on which the semiconductor detector, the protective unit, and the conductor unit are mounted, the semiconductor detector being mounted on a main surface of the substrate, and the protective unit and the conductor unit being mounted on a back surface opposite the main surface. In this case, by mounting the protective unit on the back surface opposite the semiconductor detector, it is possible to prevent the potential of the protective unit from becoming unstable when a discharge occurs, and to more safely flow the discharge current from the semiconductor detector to the protective unit.

[0015] The device may further include a substrate on which the semiconductor detector and the protection unit are mounted, and a housing that houses the substrate, and the conductor may be the housing. In this case, the discharge current can be directed toward the housing outside the substrate, preventing adverse effects on the semiconductor detector mounted on the substrate.

[0016] An analysis device according to an aspect of the present disclosure may include the above-described charged particle detector and a signal processing unit that processes an electrical signal output from the charged particle detector. In this case, in the analysis device, similar to the charged particle detector, the current flowing through the semiconductor detector when a discharge occurs is reduced, thereby preventing adverse effects on the semiconductor detector.

[0017] The charged particle detector of the present disclosure is [1] "a charged particle detector comprising: a semiconductor detector including an anode and a cathode, wherein a first voltage is supplied to the cathode and a second voltage lower than the first voltage is supplied to the anode; a conductor portion connected to a reference potential whose absolute value is lower than that of the second voltage; and a protective portion disposed between the anode and the conductor portion and to which a low potential whose absolute value is lower than that of the second voltage is applied, the protective portion having a resistor."

[0018] The charged particle detector of the present disclosure may be [2] "the charged particle detector described in [1] above, in which the protective section further has a protective electrode to which the low potential is applied via the resistor."

[0019] The charged particle detector of the present disclosure may be [3] "the charged particle detector according to [1] or [2], wherein the low potential is the reference potential, the conductor portion includes an outer conductor connected to the reference potential and a central conductor inserted inside the outer conductor, has a connector connected to the semiconductor detector, and the protective portion is connected to the outer conductor."

[0020] The charged particle detector of the present disclosure may be [4] "the charged particle detector described in [1] above, wherein the low potential is the reference potential, the conductor portion includes an outer conductor connected to the reference potential, and the protective portion is a resistive film covering the outer conductor."

[0021] The charged particle detector of the present disclosure may be [5] "the charged particle detector according to [1] or [2], wherein the low potential is a potential with an absolute value higher than the absolute value of the reference potential and a potential with an absolute value lower than the absolute value of the second voltage."

[0022] The charged particle detector of the present disclosure may be [6] "the charged particle detector according to any one of the above [1] to [5], further comprising a substrate on which the semiconductor detector, the protective part, and the conductor part are mounted, the semiconductor detector being mounted on a main surface of the substrate, and the protective part and the conductor part being mounted on a back surface opposite to the main surface."

[0023] The charged particle detector of the present disclosure may be [7] "the charged particle detector according to [1] or [2], further comprising a substrate on which the semiconductor detector and the protective part are mounted, and a housing that houses the substrate, wherein the conductor part is the housing."

[0024] The analytical device of the present disclosure may be [8] "an analytical device including a charged particle detector according to any one of [1] to [7] and a signal processing unit that processes an electrical signal output from the charged particle detector."

[0025] According to the present disclosure, it is possible to suppress the influence on the time response characteristics of the semiconductor detector and prevent the semiconductor detector from being adversely affected when a discharge occurs.

[0026] FIG. 1 is a diagram for explaining a schematic configuration of a charged particle detector according to this embodiment. FIG. 2 is a diagram showing a schematic circuit diagram of the charged particle detector. FIG. 3A is a diagram for explaining a discharge path of a discharge current in a charged particle detector according to a comparative example. FIG. 3B is a diagram for explaining a discharge path of a discharge current in the charged particle detector according to this embodiment. FIG. 4 is a cross-sectional view of a substrate in the charged particle detector. FIG. 5A is a plan view of the substrate seen from the main surface side. FIG. 5B is a plan view of the substrate seen from the back surface side. FIG. 6A is a cross-sectional view of a substrate in a charged particle detector according to a first modified example. FIG. 6B is a plan view of a substrate in a charged particle detector according to a second modified example. FIG. 7 is a cross-sectional view of a substrate in a charged particle detector according to a third modified example. FIG. 8 is a cross-sectional view of a substrate in a charged particle detector according to a fourth modified example. FIG. 9 is a diagram for explaining a schematic configuration of an analysis device 10.

[0027] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0028] 1 is a diagram illustrating a schematic configuration of a charged particle detector 1 according to this embodiment. The charged particle detector 1 is a detector that detects charged particles such as ions and electrons. The charged particle detector 1 includes an electron multiplier element 2, a semiconductor detector 3, a power supply unit 4, a signal output unit 5, and a protection unit 6.

[0029] The electron multiplier element 2 emits electrons E1 in response to the incidence of charged particles such as ions or electrons. The electron multiplier element 2 is, for example, a microchannel plate. When charged particles are incident on the input surface of the electron multiplier element 2, the electron multiplier element 2 generates electrons E1 in response to the charged particles, cascade-multiplies the electrons E1, and emits them from the output surface. The emitted electrons E1 are accelerated by an acceleration electrode (not shown), focused by a focus electrode (not shown), and then incident on the semiconductor detector 3.

[0030] The semiconductor detector 3 captures the focused electrons E1 and outputs them as an output signal S1. In this embodiment, the semiconductor detector 3 is composed of an avalanche diode (AD). The semiconductor detector 3 is mounted on the main surface of a substrate, which will be described later. The AD includes a stacked structure in which a P-type semiconductor layer and an N-type semiconductor layer are stacked. The semiconductor detector 3 includes an anode 3a and a cathode 3b. The anode 3a faces the output surface of the electron multiplier element 2. The anode 3a is an electrode on the P-type semiconductor layer side in the AD. The electrons E1 are incident on the anode 3a. The cathode 3b faces the main surface of the substrate. The cathode 3b is an electrode on the N-type semiconductor layer side in the AD. The output signal S1 is output from the cathode 3b.

[0031] The power supply unit 4 generates a first voltage V1 and a second voltage V2 for driving the semiconductor detector 3. FIG. 2 is a circuit diagram showing a schematic configuration of the charged particle detector 1. The electron multiplier element 2 is not shown in FIG. 2. The semiconductor detector 3 is also shown in FIG. 2 as an equivalent circuit consisting of a diode and a parasitic capacitance connected in parallel to the diode. As shown in FIG. 2, the power supply unit 4 includes a power supply Vcc, a power supply unit Vin, resistors R1 to R6, and a diode D1. The negative terminal of the power supply Vcc is connected to one end of the resistor R1, and the positive terminal of the power supply Vcc is connected to the other end of the resistor R4. The resistors R1 to R4 are connected in series with each other. The node between the resistors R2 and R3 is connected to the anode 3a via the resistor R5. The other end of the resistor R4 is connected to the cathode 3b via the resistor R6.

[0032] The power supply unit 4 generates a high voltage of several kV to several tens of kV from the power supply Vcc. In this embodiment, the power supply unit 4 generates a positive high voltage from the power supply Vcc. Resistors R1 to R4 divide the generated high voltage, applying a first voltage V1 to the cathode 3b via resistor R6 and a second voltage V2 to the anode 3a via resistor R5. The first voltage V1 is higher than the second voltage V2. The first voltage V1 is, for example, 10 kV, and the second voltage V2 is, for example, 9.65 kV. Therefore, a voltage (reverse bias) of, for example, 350 V is applied between the anode 3a and cathode 3b of the semiconductor detector 3, causing the semiconductor detector 3 to operate in a floating state. In the power supply unit 4, resistors R5 and R6 are current-limiting resistors that limit the current input to the semiconductor detector 3. Diode D1, connected in parallel with resistor R6, is a TVS diode that protects the cathode 3b from surge voltages and the like.

[0033] The power supply unit Vin generates a voltage to be supplied to the input surface of the electron multiplier element 2. The negative electrode of the power supply unit Vin is connected to the input surface (not shown) of the electron multiplier element 2, and the positive electrode of the power supply unit Vin is connected to the reference potential GND.

[0034] The reference potential GND described in this embodiment and the modified examples is a common reference potential and is the same potential, so that no potential difference occurs between the reference potentials, and the semiconductor detector 3 operates stably.

[0035] The signal output unit 5 outputs the output signal S1 output from the semiconductor detector 3 to the outside. The output signal S1 is an AC signal, e.g., a pulse wave that alternates between high and low levels at a predetermined cycle. As shown in FIG. 2 , the signal output unit 5 includes capacitors C1 and C2, resistors R7, R8, and Re, and a signal output terminal 51. The capacitor C1 is connected between the cathode 3b and the signal output terminal 51. The capacitor C1 is a coupling capacitor that cuts out the DC component of the output signal S1 output from the cathode 3b and extracts only the AC signal. A measuring device such as an oscilloscope is connected to the signal output terminal 51 to measure the output signal S1. The resistor Re serves as a termination resistor for impedance matching and is connected between the signal output terminal 51 and a reference potential GND.

[0036] One end of capacitor C2 is connected to the anode 3a. A resistor R7 is connected between the other end of capacitor C2 and the reference potential GND. This forms a return path between the anode 3a and the reference potential GND. As electrons continue to be incident on the semiconductor detector 3, a voltage drop occurs at the electron incident surface of the semiconductor detector 3. In this case, fluctuations in the DC component caused by this voltage drop are reflected in the output signal S1 output from the semiconductor detector 3 to the signal output terminal 51. Therefore, by placing capacitor C2 between the anode 3a and the reference potential GND, the fluctuations in the DC component reflected in the output signal S1 are canceled. Furthermore, capacitor C2 enables the output signal S1 output from the cathode 3b to the signal output terminal 51 to be returned to the anode 3a via the return path with low impedance. Resistor R7 is a damping resistor for further suppressing fluctuations in the DC component reflected in the output signal S1. Furthermore, resistor R8 is connected between the signal output terminal 51 and the reference potential GND. The resistor R8 is a current limiting resistor that prevents overcurrent from flowing into the anode 3a via the return path.

[0037] The protection unit 6 induces and suppresses a discharge current I1 flowing through the semiconductor detector 3 when a discharge occurs between the semiconductor detector 3 and a reference potential GND. In this embodiment, the reference potential GND is a potential lower than the second voltage V2. As shown in FIG. 2 , the protection unit 6 is disposed between the anode 3a and the reference potential GND. The protection unit 6 includes a protection electrode 61 and a resistor 62. The protection electrode 61 is connected to the reference potential GND via the resistor 62. The protection electrode 61 is disposed at a predetermined distance from the anode 3a. In other words, the protection electrode 61 is disposed electrically and physically separated from the semiconductor detector 3. The protection electrode 61 induces the discharge current I1 so that the discharge current I1 flows toward the protection electrode 61. The resistor 62 is a high-voltage resistor and reduces the discharge current I1. Here, if the reference potential GND is rephrased as a low potential, which is a potential with an absolute value lower than the absolute value of the second voltage, it can be considered that a low potential is applied to the protection unit 6, and that a low potential is applied to the protection electrode 61 via the resistor 62.

[0038] Next, the effect of providing the protective unit 6 will be described with reference to FIG. 3 . FIG. 3A is a diagram illustrating the discharge path of the discharge current I1 in a charged particle detector according to a comparative example that does not include the protective unit 6. When a discharge occurs between the semiconductor detector 3 and the reference potential GND, for example, a dielectric breakdown occurs between the anode 3a and the reference potential GND, resulting in a short circuit between the anode 3a and the reference potential GND. In this case, the discharge current I1 originates on the resistor Re side and flows from the cathode 3b into the semiconductor detector 3. The discharge current I1 flowing out from the anode 3a flows through the short circuit path formed between the anode 3a and the reference potential GND. For example, when a discharge voltage of 10 kV is generated, the discharge current I1 is 200 A, which is calculated by dividing the voltage value of the discharge voltage by the resistance value (e.g., 50 Ω) of the resistor Re. This causes a large current of 200 A to flow in the reverse bias direction through the semiconductor detector 3, which may adversely affect the semiconductor detector 3.

[0039] FIG. 3B is a diagram illustrating the discharge path of the discharge current I1 in the charged particle detector 1 according to this embodiment. In FIG. 3B, discharge is more likely to occur between the semiconductor detector 3 and the protective unit 6 than between the semiconductor detector 3 and the reference potential GND. In this case, for example, it is assumed that dielectric breakdown occurs between the anode 3a and the protective electrode 61, causing a short circuit between the anode 3a and the protective electrode 61. In this case, the discharge current I1 originates on the resistor Re side and flows from the cathode 3b into the semiconductor detector 3. The discharge current I1 flowing out of the anode 3a then flows through the short-circuit path formed between the anode 3a and the protective electrode 61. The discharge current I1 flows through the protective electrode 61 and the resistor 62 to the reference potential GND. For example, when a discharge voltage of 10 kV is generated, if the resistance value of the resistor 62 is 1 MΩ, the discharge current I1 is reduced to 10 mA. This significantly reduces the impact on the semiconductor detector 3 compared to when the protective electrode 61 is not provided.

[0040] Next, the arrangement of the semiconductor detector 3 and the protective part 6 will be described with reference to Figures 4 and 5. Figure 4 is a cross-sectional view of the substrate 7 in the charged particle detector 1. Figure 5(a) is a plan view of the substrate 7 as seen from the main surface 7a side. Figure 5(b) is a plan view of the substrate 7 as seen from the back surface 7b side.

[0041] As shown in FIG. 4 , the charged particle detector 1 further includes a substrate 7 and a conductor portion 8. The substrate 7 includes a main surface 7 a and a back surface 7 b opposite the main surface 7 a. The semiconductor detector 3 is mounted on the main surface 7 a. The protective portion 6 is mounted on the back surface 7 b. The substrate 7 is, for example, a printed wiring board. The substrate 7 includes multiple copper foil layers therein. The multiple copper foil layers are provided at two locations along the in-plane direction of the substrate 7, and at each location, the multiple copper foil layers are stacked along the thickness direction of the substrate 7. A predetermined space is provided between the first copper foil layer closest to the main surface 7 a and the second copper foil layer next closest to the main surface 7 a, and a stray capacitance component is formed in that space. The stray capacitance component formed in the first copper foil layer forms a capacitor C1, and the stray capacitance component formed in the second copper foil layer forms a capacitor C2. Of the multiple copper foil layers, the second and subsequent copper foil layers are electrically connected to each other, so no stray capacitance is formed.

[0042] As shown in FIG. 5( a), the capacitor C1 is connected to the cathode 3b at the conductive electrode pattern P1. The capacitor C1 is also connected to one end of the resistor R6 at the electrode pattern P2. The other end of the resistor R6 is connected to the electrode pattern P3. The electrode pattern P3 is connected to the other end of the resistor R4 shown in FIG. 2. The capacitor C2 is also connected to the anode 3a at the conductive electrode pattern P4. The capacitor C2 is also connected to one end of the resistor R5 at the electrode pattern P5. The other end of the resistor R5 is connected to the electrode pattern P6. The electrode pattern P6 is connected to a node between the resistors R2 and R3 shown in FIG. 2. Elements of the power supply unit 4 that are not shown in FIG. 5( a) other than the resistors R5, R6, and diode D1 may be disposed on or off the substrate 7.

[0043] As shown in FIG. 4 , the conductor 8 is mounted on the back surface 7b of the substrate 7. In this embodiment, the conductor 8 is composed of a connector 83. The connector 83 is, for example, an SMA jack. The connector 83 is connected to the semiconductor detector 3 via the substrate 7. The connector 83 includes a cylindrical outer conductor 81 and a center conductor 82 that passes through the interior of the outer conductor 81. The central axis of the semiconductor detector 3 and the central axis of the outer conductor 81 coincide with each other. The center conductor 82 is disposed so as to pass through the central axis of the outer conductor 81. The outer surface of the outer conductor 81 is connected to the reference potential GND. One end of the center conductor 82 is connected to a capacitor C1 via the substrate 7. The other end of the center conductor 82 is connected to a signal output terminal 51. The capacitor C1, the center conductor 82, and the signal output terminal 51 form a signal output path that outputs a signal from the semiconductor detector 3 (cathode 3b).

[0044] The protective portion 6 is disposed midway along the creeping path connecting the anode 3a on the principal surface 7a of the substrate 7 and the conductor portion 8 on the rear surface 7b. In other words, the protective portion 6 is located closer to the semiconductor detector 3 than the conductor portion 8. Specifically, as shown in FIG. 5B , the protective electrode 61 is formed on the rear surface 7b along the outer edge of the substrate 7, surrounding the conductor portion 8, resistors R7 and R8, and resistor 62. One end of the resistor 62 is connected to the protective electrode 61 via a wiring pattern P7, and the other end of the resistor 62 is connected to the peripheral conductor 81 via a wiring pattern P8. This makes it easier for a discharge to occur between the anode 3a and the protective electrode 61 than between the anode 3a and the peripheral conductor 81. In this case, when a discharge occurs, dielectric breakdown occurs between the anode 3a and the protective electrode 61, resulting in a short circuit between the anode 3a and the protective electrode 61. The discharge current I1 induced in the protective electrode 61 is suppressed by the resistor 62 when a discharge occurs, and flows to the reference potential GND via the outer conductor 81.

[0045] In the above-described charged particle detector 1, a high reverse bias voltage is supplied to the semiconductor detector 3, causing a current to flow from the cathode 3b to the anode 3a. When a discharge occurs between the semiconductor detector 3 and the conductor 8, the charge in the capacitor C1 flows as a discharge current I1 in a reverse bias direction toward the semiconductor detector 3. The protector 6 is disposed between the anode 3a and the conductor 8, and a low potential having an absolute value lower than that of the second voltage V2 is applied to the protector 6. As a result, the discharge current I1 flows from the semiconductor detector 3, which has a higher potential, to the protector 6, which has a lower potential. Furthermore, the protector 6 includes a resistor 62, which can reduce the discharge current I1. This reduces the discharge current I1 flowing through the semiconductor detector 3 when a discharge occurs, thereby preventing adverse effects such as deterioration and damage caused by a large current flowing in the reverse bias direction through the semiconductor detector 3. In addition, in the charged particle detector 1, the resistor 62 is not connected in the middle of the signal output path. Therefore, while employing a resistor with a resistance value large enough to protect the semiconductor detector 3, it is possible to suppress any impact on the characteristics of the semiconductor detector 3, such as a decrease in the time response characteristics (high-speed response) of the semiconductor detector 3.

[0046] The protection unit 6 further includes a protection electrode 61 to which a low potential (reference potential GND) is applied via a resistor 62. In this case, the protection electrode 61 is located closer to the semiconductor detector 3 than the conductor unit 8, and therefore the protection electrode 61 is more susceptible to discharge. As a result, the discharge current I1 is more likely to flow toward the protection electrode 61. This makes it easier to ensure a discharge path for the discharge current I1 via the protection electrode 61 and the resistor 62.

[0047] The low potential applied to the protector 6 is the reference potential GND. The conductor 8 includes an outer conductor 81 connected to the reference potential GND and a central conductor 82 inserted through the outer conductor 81, and has a connector 83 connected to the semiconductor detector 3. The protector 6 is connected to the outer conductor 81. In this case, a discharge current I1 flows from the semiconductor detector 3 via the protector 6 and the outer conductor 81 of the conductor 8 to the reference potential GND. Meanwhile, an output signal S1 output from the semiconductor detector 3 is output to the outside by the central conductor 82. This eliminates the need to provide an additional element as a destination for the discharge current I1, thereby efficiently ensuring a discharge path for the discharge current I1.

[0048] The charged particle detector 1 further includes a substrate 7 on which the semiconductor detector 3, the protective unit 6, and the conductor unit 8 are mounted. The semiconductor detector 3 is mounted on a main surface 7a of the substrate 7, and the protective unit 6 and the conductor unit 8 are mounted on a back surface 7b opposite to the main surface 7a. In this case, by mounting the protective unit 6 on the back surface 7b opposite to the semiconductor detector 3, it is possible to prevent the potential of the protective unit 6 from becoming unstable when a discharge occurs, and it is possible to more safely flow the discharge current I1 from the semiconductor detector 3 to the protective unit 6. [Modification]

[0049] Although the embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0050] FIG. 6A is a cross-sectional view of the substrate 7 in a charged particle detector 1A according to a first modification. FIG. 6B is a plan view of the substrate 7 in a charged particle detector 1B according to a second modification, viewed from the rear surface 7b. The protective portion 6A included in the charged particle detector 1A and the protective portion 6B included in the charged particle detector 1B differ from the protective portion 6 in that they do not include a protective electrode 61 and include a resistive film rather than a resistive element as the resistor 62. The resistive film contains, for example, powder of an inorganic material such as a metal oxide and a binder (welding agent, binding agent). As shown in FIG. 6A, in the protective portion 6A, the resistor 62 is formed to cover the outer surface of the peripheral conductor 81. As shown in FIG. 6B, in the protective portion 6B, the resistor 62 is formed around the conductor portion 8 to cover a portion of the rear surface 7b. In the protective parts 6A and 6B, the resistor 62 is also located closer to the semiconductor detector 3 than the conductor part 8, so the protective parts 6A and 6B are more susceptible to discharge, and the discharge current I1 is suppressed by the resistor 62 and flows to the reference potential GND via the outer conductor 81. Furthermore, because the protective parts 6A and 6B include a resistive film as the resistor 62, it is not necessary to provide the resistor 62 as a resistive element. In addition, wiring connecting the protective electrode 61 and the resistor 62 to a low-potential supply source (e.g., the reference potential GND) is not required, so the discharge path of the discharge current I1 can be configured simply.

[0051] The conductor connected to the resistor 62 of the protective unit 6 may be composed of something other than the connector 83. FIG. 7 is a cross-sectional view of the substrate 7 in a charged particle detector 1C according to a third modification. The charged particle detector 1C further includes a conductive housing 9 that houses the substrate 7. The housing 9 is connected to the reference potential GND. In the charged particle detector 1C, the conductor 8A is composed of the housing 9. In the example shown in FIG. 7, the protecting electrode 61 is mounted on the main surface 7a. This positions the protecting electrode 61 closer to the semiconductor detector 3 than the conductor 8A. The protecting electrode 61 may be connected to the resistor 62 via a via V that penetrates from the main surface 7a to the back surface 7b and a wiring pattern P7. The other end of the resistor 62 is connected to the housing 9 via a wiring pattern P8. In this case, the discharge current I1 flows to the reference potential GND via the housing 9. The substrate 7 may be fixed by being fitted into the inner surface of the housing 9, as shown in FIG. 7. The back surface 7b of the substrate 7 may be exposed to the outside. Alternatively, the housing 9 may include a bottom surface with an opening formed in the bottom surface. The substrate 7 may be placed on the bottom surface with the connector 83 exposed to the outside through the opening. In the charged particle detector 1C, the discharge current I1 can be made to flow toward the housing 9 outside the substrate 7, thereby reliably preventing adverse effects on the semiconductor detector 3 mounted on the substrate 7.

[0052] The conductor is not limited to the connector 83 and the housing 9. For example, the conductor may be a housing of a device separate from the charged particle detector 1. The separate device may be, for example, a vacuum chamber that puts the charged particle detector 1 into a vacuum state. Alternatively, the conductor may be a component within the charged particle detector 1 that is connected to the reference potential GND. In either case, the discharge current I1 can be made to flow out of the substrate 7.

[0053] 8 is a cross-sectional view of the substrate 7 in a charged particle detector 1D according to a fourth modification. The charged particle detector 1D differs from the charged particle detector 1 in that the protection unit 6 is connected to a low-voltage source Vcc2 rather than to the reference potential GND. The other end of the resistor 62 is connected to the low-voltage source Vcc2. A potential is applied to the protection unit 6 from the low-voltage source Vcc2, and a potential is applied to the protection electrode 61 from the low-voltage source Vcc2 via the resistor 62. The potential applied from the low-voltage source Vcc2 has an absolute value lower than that of the second voltage V2 and higher than that of the reference potential GND. Even in this case, the discharge current I1 flows from the semiconductor detector 3, which has a higher potential, to the protection unit 6, which has a lower potential. Furthermore, the charged particle detector 1D offers greater design freedom in determining the potential applied to the protection unit 6.

[0054] The power supply unit 4 may generate a negative high voltage in the power supply Vcc. In this case, when a negative high voltage is applied between the anode 3a and cathode 3b of the semiconductor detector 3, a reverse bias is applied between the anode 3a and cathode 3b, and the semiconductor detector 3 operates in a floating state. Even when a negative high voltage is applied between the anode 3a and cathode 3b of the semiconductor detector 3, a low potential whose absolute value is lower than that of the second voltage V2 is applied to the protection unit 6. As a result, the discharge current I1 flows from the protection unit 6, which has a high potential, to the semiconductor detector 3, which has a low potential.

[0055] The charged particle detectors 1 to 1D described in the embodiments and modifications may be used in an analytical device. FIG. 9 is a diagram illustrating a schematic configuration of an analytical device 10. The analytical device 10 may include the charged particle detectors 1 to 1D and a signal processing unit 20 that processes an electrical signal (output signal S1) output from the charged particle detectors 1 to 1D. The analytical device 10 is, for example, a mass spectrometer. In this case, the signal processing unit 20 may generate a mass spectrum based on the output signal S1. Furthermore, when the analytical device 10 is a mass spectrometer, the target detected by the charged particle detectors 1 to 1D is ions. The polarity of the voltage applied to the semiconductor detector 3 may be selected depending on whether the charged particle detectors 1 to 1D detect positive or negative ions. For example, when the charged particle detectors 1 to 1D detect negative ions, a positive high voltage may be applied between the anode 3a and cathode 3b of the semiconductor detector 3. Alternatively, when the charged particle detectors 1 to 1D detect positive ions, a negative high voltage may be applied between the anode 3 a and the cathode 3 b of the semiconductor detector 3. In the analysis device 10, similar to the charged particle detectors 1 to 1D, the current flowing through the semiconductor detector 3 when a discharge occurs is reduced, thereby preventing the semiconductor detector 3 from being adversely affected.

[0056] 1, 1A, 1B, 1C, 1D...charged particle detector, 10...analysis device, 20...signal processing unit, 3...semiconductor detector, 3a...anode, 3b...cathode, 6, 6A, 6B...protector, 61...protecting electrode, 62...resistor, 7...substrate, 7a...main surface, 7b...rear surface, 8, 8A...conductor portion, 9...housing, 81...peripheral conductor, 82...center conductor, 83...connector, GND...reference potential, V1...first voltage, V2...second voltage.

Claims

1. A charged particle detector comprising: a semiconductor detector including an anode and a cathode, the cathode being supplied with a first voltage and the anode being supplied with a second voltage lower than the first voltage; a conductor connected to a reference potential having an absolute value lower than that of the second voltage; and a protective unit disposed between the anode and the conductor and to which a low potential having an absolute value lower than that of the second voltage is applied, the protective unit having a resistor.

2. The charged particle detector according to claim 1, wherein the protection section further comprises a protection electrode to which the low potential is applied via the resistor.

3. A charged particle detector as described in claim 1 or 2, wherein the low potential is the reference potential, the conductor portion includes an outer conductor connected to the reference potential and a central conductor inserted inside the outer conductor, and has a connector connected to the semiconductor detector, and the protective portion is connected to the outer conductor.

4. A charged particle detector as described in claim 1, wherein the low potential is the reference potential, the conductor portion includes an outer peripheral conductor connected to the reference potential, and the protective portion is a resistive film covering the outer peripheral conductor.

5. A charged particle detector according to claim 1 or 2, wherein the low potential is a potential having an absolute value higher than that of the reference potential and lower than that of the second voltage.

6. A charged particle detector as claimed in any one of claims 1 to 5, further comprising a substrate on which the semiconductor detector, the protective section, and the conductor section are mounted, the semiconductor detector being mounted on a main surface of the substrate, and the protective section and the conductor section being mounted on a back surface opposite the main surface.

7. A charged particle detector as claimed in claim 1 or 2, further comprising: a substrate on which the semiconductor detector and the protective section are mounted; and a housing for accommodating the substrate, wherein the conductor section is the housing.

8. An analytical device comprising: a charged particle detector according to any one of claims 1 to 7; and a signal processing unit for processing an electrical signal output from the charged particle detector.

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