Patent Description:
An example of a radiation detector for detecting radiation such as X-ray includes a semiconductor detector using a semiconductor. A semiconductor detector often needs to be cooled by liquid nitrogen, while a silicon drift detector (SDD) may reduce noise without being cooled to the liquid nitrogen temperature. An interface between Si and SiO<NUM> is present around the surface of the semiconductor detector using silicon (Si), and electric charges irrelevant to electric charges derived from the entrance of radiation occurs at the interface. The occurrence of electric charges causes surface current, which may be a source of noise. <CIT> discloses a technique of collecting electric charges generated around the surface of an SDD. As an example, <CIT> discloses an SDD having a river structure in which a part of a ring-shaped electrode formed on a surface is made discontinuous in order to collect electric charges.

The conventional semiconductor detector includes, on its surface, a bonding pad for flowing electric charges collected at the surface to the outside the semiconductor detector. By flowing the electric charges at the surface to the outside the semiconductor, surface current is reduced and thus noise is reduced. A problem remains, however, in that a bonding pad provided at the surface lowers the yield for production of the semiconductor detector due to a damage by bonding.

Moreover, in an SDD having the river structure disclosed in <CIT>, the state of the interface between Si and SiO<NUM> varies depending on the production state of SiO<NUM>, making it difficult to collect electric charges with high efficiency.

The present invention has been made in view of the circumstances described above and aims to provide a semiconductor detector, a radiation detector and a radiation detection apparatus that prevent the configuration for reducing surface current from being a cause of lowering the yield.

A semiconductor detector according to the present invention is defined in independent claim <NUM>.

The electric charges occurring at the surface of the semiconductor part are collected by the arc-shaped collection electrode, and thereby surface current is reduced.

In the semiconductor detector according to the present invention, the collection electrode is connected to a curved electrode located with a distance from the signal output electrode shorter than a distance between the collection electrode and the signal output electrode.

The electric charges flowing at the surface of the semiconductor part are collected by the collection electrode due to the difference in potentials between the surface of the semiconductor part and the collection electrode. Furthermore, the configuration for applying a potential to a collection electrode may be simplified.

A plurality of collection electrodes are provided between an adjacent pair of curved electrodes. The charge generated at the surface of the semiconductor part is collected by the collection electrode, and surface current is reduced.

In the semiconductor detector according to the present invention, the collection electrode is connected to a curved electrode located with a distance from the signal output electrode shorter than a distance between the pair of curved electrodes and the signal output electrode.

The potential of the curved electrode connected to the collection electrode is different from the potential of the surface of the semiconductor part at a position with which the collection electrode is located. The potential difference between the collection electrode and the surface of the semiconductor part is generated.

In the semiconductor detector according to the present invention, the plurality of curved electrodes are applied with voltage so as to monotonically change a potential from a curved electrode distant from the signal output electrode to a curved electrode close to the signal output electrode.

The potential of the curved electrode is gradually increased or decreased, and the potential gradient is generated in the semiconductor part.

The semiconductor detector according to the present invention further comprises a conductive part made of a conductive material, the conductive part having a part located on one curved electrode while being in contact with the curved electrode and another part connected to the collection electrode.

The collection electrode is connected to the curved electrodes and electric charges flow to the outside the semiconductor detector through a path used to apply the voltage to the curved electrodes.

A radiation detector according to the present invention comprises the semiconductor detector according to the present invention, a circuit board on which the semiconductor detector is mounted, and a base plate holding the semiconductor detector and the circuit board.

The structure of the semiconductor detector is simplified and the yield of the semiconductor detector is improved. Therefore, the cost for the radiation detection apparatus using the semiconductor detector is lowered.

A radiation detection apparatus according to the present invention comprises the semiconductor detector according to the present invention detecting radiation, an output part outputting a signal corresponding to energy of radiation detected by the semiconductor detector, and a spectrum generation part generating a spectrum of the radiation based on the signal output by the output part.

As the yield of the semiconductor detector is improved, the cost for the radiation detection apparatus using the semiconductor detector is lowered.

A radiation detection apparatus according to the present invention detecting radiation generated from a sample irradiated with radiation comprises an irradiation part irradiating a sample with radiation, the semiconductor detector according to the present invention detecting radiation generated from the sample, an output part outputting a signal corresponding to energy of radiation detected by the semiconductor detector, a spectrum generation part generating a spectrum of the radiation based on the signal output by the output part, and
a display part displaying the spectrum generated by the spectrum generation part.

According to the present invention, the electric charges collected by the collection electrode flow to the outside of the semiconductor detector through a path for applying voltage to the curved electrode. The configuration for reducing surface current caused at the surface of the semiconductor is simplified. Accordingly, the present invention produces a beneficial effect such as improvement in the yield of the semiconductor detector and lowering in the cost for the radiation detection apparatus.

The present invention will be described below in detail with reference to the drawings illustrating the embodiments thereof.

<FIG> is a schematic plan view of a semiconductor detector <NUM> according to Embodiment <NUM>. <FIG> is a block diagram illustrating a cross-section structure of the semiconductor detector <NUM> taken along the line II-II in <FIG> as well as a manner of electrical connection for the semiconductor detector <NUM>. <FIG> is a schematic section view of the semiconductor detector <NUM> taken along the line III-III in <FIG>. The semiconductor detector <NUM> is an SDD. The semiconductor detector <NUM> includes a circular-disc-shaped Si layer <NUM> made of silicon (Si). The Si layer <NUM> is made of, for example, an n-type Si. The Si layer <NUM> corresponds to a semiconductor part. At the middle of one surface of the Si layer <NUM>, a signal output electrode <NUM> is formed which serves as an electrode for outputting a signal at the time of detecting radiation. The constituent of the signal output electrode <NUM> is a same type Si as the Si layer <NUM>, which is doped with a specific type of impurities such as phosphorus. Moreover, one surface of the Si layer <NUM> is provided with multiple ring-shaped electrodes (curved electrodes) <NUM>. The ring-shaped electrode <NUM> is constituted by Si of a type different from that of the Si layer <NUM>. For example, the constituent of the ring-shaped electrode <NUM> is p+Si in which Si is doped with a specific type of impurities such as boron. The ring-shaped electrodes <NUM> are located in contact with the Si layer <NUM>. The multiple ring-shaped electrodes <NUM> are substantially concentric, while the signal output electrode <NUM> is located at the substantial center of the multiple ring-shaped electrodes <NUM>. Though five ring-shaped electrodes <NUM> are illustrated in the drawing, a larger number of ring-shaped electrodes <NUM> are formed in practice. It is noted that the shape of each ring-shaped electrode <NUM> may be a deformed circular ring, and the multiple ring-shaped electrodes <NUM> are not necessarily concentric. Furthermore, the signal output electrode <NUM> may be located at a position other than the center of the multiple ring-shaped electrodes <NUM>, and may be located at a position other than the middle of one surface of the Si layer <NUM>. The shape of the semiconductor detector <NUM> may be a droplet shape. The shape of the Si layer <NUM> may be a shape other than circular-disc shape, and may be square shape, rectangular shape or trapezoidal shape, etc..

At the opposite surface of the Si layer <NUM>, a rear electrode <NUM> serving as an electrode to which bias voltage is applied is formed on substantially the entire surface thereof. The rear electrode <NUM> is made of Si of a type different from that of the Si layer <NUM>. For example, the constituent of the rear electrode <NUM> is p+Si, if that of the Si layer <NUM> is n-type Si. On the surface of the Si layer <NUM> where the signal output electrode <NUM> and the ring-shaped electrodes <NUM> are not formed, as well as on a part of the ring-shaped electrodes <NUM>, the insulation film <NUM> is formed. The insulation film <NUM> is made of, for example, SiO<NUM>. The insulation film <NUM> is not illustrated in <FIG>. The rear electrode <NUM> is connected to the voltage application part <NUM>. Moreover, the ring-shaped electrode <NUM> at the innermost side and the ring-shaped electrode <NUM> at the outermost side among the multiple ring-shaped electrodes <NUM> are connected to the voltage application part <NUM>.

The voltage application part <NUM> applies voltage in such a manner that the potential at the innermost ring-shaped electrode <NUM> is highest whereas the potential at the outermost ring-shaped electrode <NUM> is lowest. Moreover, the semiconductor detector <NUM> is so configured that a predefined electric resistance occurs between adjacent ring-shaped electrodes <NUM>. For example, a constituent of one portion of the Si layer <NUM> located between adjacent ring-shaped electrodes <NUM> is adjusted to form a resistive channel for connecting the two ring-shaped electrodes <NUM>. That is, the multiple ring-shaped electrodes <NUM> are linked together through electric resistances. As voltage is applied to such ring-shaped electrodes <NUM> from the voltage application part <NUM>, the ring-shaped electrodes <NUM> have potentials monotonically increasing in sequence from the ring-shaped electrode <NUM> at the outer side to the ring-shaped electrode <NUM> at the inner side. That is, the ring-shaped electrodes <NUM> have potentials increasing in sequence from the ring-shaped electrode <NUM> distant from the signal output electrode <NUM> toward the ring-shaped electrode <NUM> close to the signal output electrode <NUM>. It is to be noted that an adjacent pair of ring-shaped electrodes <NUM> with the same potential may also be included in the multiple ring-shaped electrodes <NUM>. The potentials of the ring-shaped electrodes <NUM> generate an electric field (a potential gradient) in which the potential is increased toward the signal output electrode <NUM> and the potential is decreased toward a position distant from the signal output electrode <NUM> in a stepwise manner. Furthermore, the voltage application part <NUM> applies voltage to the rear electrode <NUM> such that the potential at the rear electrode <NUM> is intermediate between the potential of the innermost ring-shaped electrode <NUM> and the potential of the outermost ring-shaped electrode <NUM>. Accordingly, an electric field in which the potential is increased toward the signal output electrode <NUM> is generated inside the Si layer <NUM>.

The signal output electrode <NUM> is connected to a preamplifier <NUM>. A main amplifier <NUM> is connected to the preamplifier <NUM>. The semiconductor detector <NUM> is formed in the shape of a circular disc as a whole, and is used while the surface on the side where the rear electrode <NUM> is formed serves as an entrance surface for incident radiation. The shape of the semiconductor detector <NUM> may be a shape other than circular disc shape. Radiation such as X-ray, photons in general (including UV and visible light), electron beam or other charged particle beam passes through the rear electrode <NUM> and enters inside the Si layer <NUM>, which generates electric charges of an amount corresponding to the energy of radiation absorbed inside the Si layer <NUM>. The generated electric charges are electrons and holes. The generated electric charges are moved by the electric field inside the Si layer <NUM>, and one type is concentrated at the signal output electrode <NUM> while flowing therein. In the present embodiment, the electrons generated by the incident radiation move and flow into the signal output electrode <NUM>, in the case the signal output electrode <NUM> is n-type. The electric charges flowed into the signal output electrode <NUM> are output as current signals and are input into the preamplifier <NUM>. The preamplifier <NUM> converts the current signal into a voltage signal to be output to the main amplifier <NUM>. The main amplifier <NUM> amplifies the voltage signal from the preamplifier <NUM>, and outputs a signal with an amplitude corresponding to the energy of the incident radiation which entered the semiconductor detector <NUM>. The main amplifier <NUM> corresponds to an output part in the present invention.

<FIG> is a schematic perspective view of a radiation detector <NUM> including the semiconductor detector <NUM>. <FIG> is a schematic section view of the radiation detector <NUM>. The radiation detector <NUM> includes a housing <NUM> having a shape of a cylinder with one end thereof being connected to a truncated cone. At an end of the housing <NUM>, a window <NUM> is formed which allows the passage of radiation. A semiconductor detector <NUM>, a circuit board <NUM>, a shielding plate <NUM>, a cooling part <NUM> and a base plate <NUM> are arranged inside the housing <NUM>. The base plate <NUM> is also referred to as a stem. The cooling part <NUM> is a Peltier device, for example. The semiconductor detector <NUM> is mounted to a surface of the circuit board <NUM> and is located at a position facing the window <NUM>. A wiring is formed and the preamplifier <NUM> is mounted on the circuit board <NUM>. The shielding plate <NUM> is interposed between the cooling part <NUM> and the circuit board <NUM>, and is thermally in contact with a heat absorbing portion of the cooling part <NUM>. The heat dissipating portion of the cooling part <NUM> is thermally in contact with the base plate <NUM>.

The base plate <NUM> has a flat plate portion on which the cooling part <NUM> is mounted and fixed, as well as a portion penetrating the bottom part of the housing <NUM>. By the circuit board <NUM> on which the semiconductor detector <NUM> is mounted being fixed to the cooling part <NUM> via the shielding plate <NUM> and the cooling part <NUM> being fixed to the base plate <NUM>, the base plate <NUM> holds the semiconductor detector <NUM> and the circuit board <NUM>. The shielding plate <NUM> is formed with a material for shielding X-ray. The shielding plate <NUM> shields X-ray, generated from the cooling part <NUM> or the base plate <NUM> when radiation enters the cooling part <NUM> or the base plate <NUM>, so as to prevent it from entering the semiconductor detector <NUM>. The heat from the semiconductor detector <NUM> is absorbed by the cooling part <NUM> through the circuit board <NUM> and the shielding plate <NUM>, is transmitted from the cooling part <NUM> to the base plate <NUM>, and is dissipated to the outside the radiation detector <NUM> through the base plate <NUM>. The radiation detector <NUM> includes multiple lead pins <NUM> penetrating the bottom part of the housing <NUM>. The lead pins <NUM> are connected to the circuit board <NUM> by a method such as wire bonding. Application of voltage to the semiconductor detector <NUM> by the voltage application part <NUM> and output of signals from the preamplifier <NUM> to the main amplifier <NUM> may be performed through the lead pins <NUM>.

<FIG> is a block diagram illustrating a functional configuration of a radiation detection apparatus. The radiation detector <NUM> includes the semiconductor detector <NUM> and the preamplifier <NUM>. The voltage application part <NUM> and the main amplifier <NUM> are located outside the radiation detector <NUM>. The preamplifier <NUM> may partly be included in the radiation detector <NUM>, whereas the other portions thereof may be located outside the radiation detector <NUM>. The radiation detection apparatus includes a sample holding part <NUM> holding a sample <NUM>, an irradiation part <NUM> irradiating the sample <NUM> with radiation such as X-ray, electron beam or particle beam and an irradiation control part <NUM> controlling the operation of the irradiation part <NUM>. The irradiation part <NUM> irradiates the sample <NUM> with radiation, to generate radiation such as X-ray fluorescence at the sample <NUM>. The radiation detector <NUM> is located at a position where the radiation generated from the sample <NUM> may enter the semiconductor detector <NUM>. In the drawing, radiation is indicated by arrows. As described earlier, the main amplifier <NUM> outputs a signal corresponding to the energy of radiation detected by the semiconductor detector <NUM>. The main amplifier <NUM> is connected to a signal processing part <NUM> for processing the output signals. The signal processing part <NUM> performs processing of counting each value of the signals output from the main amplifier <NUM> and generating the relationship between the energy of radiation and the counted number, i.e. a spectrum of radiation. The signal processing part <NUM> corresponds to a spectrum generation part in the present invention.

The signal processing part <NUM> is connected to an analysis part <NUM>. The analysis part <NUM> is configured to include an operation part performing arithmetic operation and a memory in which data is stored. The signal processing part <NUM> outputs data indicating the generated spectrum to the analysis part <NUM>. The analysis part <NUM> receives data input from the signal processing part <NUM>, and performs processing of identifying an element contained in the sample <NUM> based on the spectrum indicated by the input data. The analysis part <NUM> may also perform processing of calculating the amount of various types of elements contained in the sample <NUM>. The analysis part <NUM> is connected to a display part <NUM> such as a liquid-crystal display. The display part <NUM> displays a result of processing performed by the analysis part <NUM>. Moreover, the display part <NUM> is connected to the signal processing part <NUM>, and displays a spectrum generated by the signal processing part <NUM>. Furthermore, the radiation detection apparatus includes a control part <NUM> controlling the operation of the entire apparatus. The control part <NUM> is connected to the voltage application part <NUM>, the main amplifier <NUM>, the irradiation control part <NUM> and the analysis part <NUM>, to control the operation of the different parts. The control part <NUM> is constituted by a personal computer, for example. The control part <NUM> may be configured to accept the operation of the user, and to control the different parts of the radiation detection apparatus in accordance with the accepted operation. Moreover, the control part <NUM> and the analysis part <NUM> may be constituted by the same computer.

As illustrated in <FIG>, in the present embodiment, an electrode <NUM> is formed in contact with a portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM>. <FIG> illustrates an example where three electrodes <NUM>, i.e. an electrode 131a, an electrode 131b and an electrode 131c, are formed. No insulation film <NUM> is provided at portions where the electrodes <NUM> are formed, while the electrodes <NUM> are in contact with the surface of the Si layer <NUM>. In the case where the Si layer <NUM> is the n-type, the electrode <NUM> includes a region doped with impurities such as phosphorus. <FIG> and <FIG> illustrate an example where electrodes <NUM> are formed respectively in three gaps among the gaps of the ring-shaped electrodes <NUM>. As illustrated in <FIG>, the shape of each electrode <NUM> is a dot, not a ring, in plan view. Moreover, a conductive part <NUM> made of a conductive material is formed on a specific ring-shaped electrode <NUM>. No insulation film <NUM> is provided at a part of a portion where the conductive part <NUM> is formed on the ring-shaped electrodes <NUM>, while the conductive part <NUM> is in contact with the ring-shaped electrode <NUM>. <FIG> illustrate an example where the conductive parts <NUM> are formed on three ring-shaped electrodes <NUM> respectively. Furthermore, a part of the conductive part <NUM> extends outward along one surface of the Si layer <NUM> and is connected to the electrode <NUM>. That is, the electrode <NUM> is connected to the ring-shaped electrode <NUM> closer to the signal output electrode <NUM> through the conductive part <NUM>. The distance between the ring-shaped electrode <NUM> connected to the electrode <NUM> and the signal output electrode <NUM> is shorter than the distance between the electrode <NUM> and the signal output electrode <NUM>. In the example illustrated in <FIG> and <FIG>, the electrode <NUM> is connected to the ring-shaped electrode <NUM> located in one inner side than the pair of ring-shaped electrodes <NUM> with a portion of the Si layer <NUM> which is in contact with the electrode <NUM> interposed in between. In this example, the distance between the ring-shaped electrode <NUM> connected to the electrode <NUM> and the signal output electrode <NUM> is shorter than the distance between the signal output electrode <NUM> and the pair of ring-shaped electrode <NUM> with the portion of the Si layer <NUM> interposed in between.

The potential at the surface of the Si layer <NUM> at a portion with which the electrode <NUM> is in contact is slightly positive with respect to the potential of the innermost ring-shaped electrodes <NUM> of the pair of ring-shaped electrodes <NUM> with the portion of the Si layer <NUM> interposed in between. As being connected to the ring-shaped electrode <NUM> closer to the signal output electrode <NUM> through the conductive part <NUM>, the electrode <NUM> has the same potential as that of the ring-shaped electrode <NUM> closer to the signal output electrode <NUM>. As such, the potential of the electrode <NUM> is made higher than the potential of the surface of the Si layer <NUM> at a position with which the electrode <NUM> is in contact. At the surface of the Si layer <NUM>, electric charges are generated that are not derived from radiation entering the semiconductor detector <NUM> at the interface between Si and SiO<NUM>. The generated electric charges are electrons and holes. The generated electric charges move along the surface of the Si layer <NUM> by the electric field inside the Si layer <NUM>, causing surface current. Actually, holes are collected immediately by the ring-shaped electrodes <NUM>, while electrons will flow to the electrodes <NUM> only if there is a conductive path to them. In the case where the electric charges that caused the surface current flows into the signal output electrode <NUM>, a signal not derived by radiation is output from the signal output electrode <NUM>, which causes noise. As the electrode <NUM> has a potential higher than that of the surface of the Si layer <NUM>, the electrons generated at the surface of the Si layer <NUM> are collected by the electrode <NUM>. This reduces surface current. The electrode <NUM> corresponds to a collection electrode in the present invention. Since the electrons collected at the electrode <NUM> will not flow into the signal output electrode <NUM>, electrons not derived from radiation are suppressed from flowing into the signal output electrode <NUM>.

An experiment was conducted to compare current output from the signal output electrode <NUM> between the semiconductor detector <NUM> according to the present embodiment and an SDD not provided with the electrode <NUM> and the conductive part <NUM>. In the experiment, voltage was applied to the ring-shaped electrode <NUM> from the voltage application part <NUM>, and current output from the signal output electrode <NUM> was measured in a state without incident radiation. <FIG> is a characteristic view illustrating measurement results of current output from the signal output electrode <NUM>. The horizontal axis represents bias voltage applied to the ring-shaped electrode <NUM> farthest from the signal output electrode <NUM>, whereas the vertical axis represents output current output from the signal output electrode <NUM>. Furthermore, the measurement results of output current obtained from the semiconductor detector <NUM> according to the present embodiment are indicated by a solid line, while the measurement results of output current obtained from the SDD not provided with the electrode <NUM> and the conductive part <NUM> are indicated by the broken line.

The output current output from the signal output electrode <NUM> in the state without incident radiation includes current by electrons of the surface current flowed into the signal output electrode <NUM>. As illustrated in <FIG>, compared to the SDD not provided with the electrode <NUM> and the conductive part <NUM>, output current is decreased in the semiconductor detector <NUM> according to the present embodiment. It is apparent that, because electrons are collected by the electrode <NUM> at the surface of the Si layer <NUM>, the surface current is reduced and thus the electrons flowing into the signal output electrode <NUM> are decreased, resulting in the decreased output current. As a reduced number of electrons causing surface current flow into the signal output electrode <NUM>, a signal not derived from radiation is suppressed from being output from the signal output electrode <NUM>, which reduces noise. The reduction in noise improves the accuracy of detecting radiation.

Furthermore, as illustrated in <FIG>, in the SDD not provided with the electrode <NUM> and the conductive part <NUM>, output current is increased in accordance with the increase in the absolute value of the bias voltage. It was found that, in the SDD not provided with the electrode <NUM> and the conductive part <NUM>, the rate of increase in the output current in accordance with the increase in the absolute value of the bias voltage is increased with the increase in the integrated value of the amount of X-ray irradiation. In view of this, it is estimated that, in the SDD not provided with the electrode <NUM> and the conductive part <NUM>, surface current is increased by X-ray irradiation and aging progresses. In the semiconductor detector <NUM> according to the present embodiment has smaller output current as well as smaller rate of increase in the output current in accordance with the increase in the absolute value of bias voltage. This suppresses the increase in the surface current by X-ray irradiation, resulting in slower aging. Accordingly, the semiconductor detector <NUM> according to the present embodiment is suppressed from aging and has a longer life by collecting surface current at the electrode <NUM>. With the semiconductor detector <NUM>, the radiation detector <NUM> having a long lifetime and small noise included in an output signal may be obtained.

According to the present embodiment, as the electrode <NUM> is connected to the ring-shaped electrode <NUM> having a distance from the signal output electrode <NUM> shorter than the distance between the signal output electrode <NUM> and the ring-shaped electrode <NUM> closest to the electrode <NUM>, the potential difference between the surface of the Si layer <NUM> and the electrode <NUM> is increased and electrons are efficiently collected. In particular, electrons, generated at a position between the pair of ring-shaped electrodes <NUM> with a portion of the Si layer <NUM> which is in contact with the electrode <NUM> interposed in between, are efficiently collected by the electrode <NUM>. Furthermore, as the electrodes <NUM> are located at several portions, electrons generated at various parts at the surface of the Si layer <NUM> are collected by the electrodes <NUM> at several different portions, which efficiently reduces noise. Moreover, in the present embodiment, even if there is variation in the state of the semiconductor detector <NUM> which is difficult to control, for example the state of the interface between Si and SiO<NUM>, electrons are efficiently collected because the distances between the generated electrons and the electrodes <NUM> are short.

Moreover, according to the present embodiment, each electrode <NUM> has a non-ring shape, which allows a portion not provided with the electrode <NUM> to be present between adjacent ring-shaped electrodes <NUM>. In the case where the collection electrode has a ring shape, it is necessary to arrange a circuit outside the semiconductor detector in order to provide potential differences between the multiple ring-shaped electrodes, which increases the technical difficulty as well as cost. According to the present embodiment, each electrode <NUM> is a non-ring-shaped electrode, which makes it possible to easily produce a structure for providing potential differences between multiple ring-shaped electrodes <NUM> by, for example, forming an electric resistance within the semiconductor detector <NUM>. For example, a resistive channel having an electric resistance is formed at a portion not provided with the electrode <NUM> which allows an electric resistance for connecting between adjacent ring-shaped electrodes <NUM> to be easily formed.

The electrons collected at the electrode <NUM> flow to the ring-shaped electrode <NUM> through the conductive part <NUM>, and further flow to the voltage application part <NUM> from the ring-shaped electrode <NUM>. This eliminates the need for a bonding pad for flowing the collected electrons to the outside the semiconductor detector <NUM>. This simplifies the configuration for reducing surface current, preventing the yield for production of the semiconductor detector <NUM> from lowering due to the configuration for reducing surface current. This improves the yield of the semiconductor detector <NUM> and reduces the cost of the semiconductor detector <NUM>. Accordingly, the cost is reduced for the radiation detector <NUM> including the semiconductor detector <NUM> as well as the radiation detection apparatus.

<FIG> is a schematic section view of the semiconductor detector <NUM> according to Embodiment <NUM>. In the present embodiment, the electrode <NUM> is embedded in a portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM>. The electrode <NUM> is connected to the conductive part <NUM>. The other configuration parts of the semiconductor detector <NUM> are similar to those in Embodiment <NUM>. Moreover, the configuration of the radiation detection apparatus including the semiconductor detector <NUM> is similar to that in Embodiment <NUM>. The potential of the electrode <NUM> is higher than the potential of the Si layer <NUM> at the position where the electrode <NUM> is formed, but without electrode <NUM>. Electrons not derived from radiation generated at the surface of the Si layer <NUM> are collected by the electrode <NUM>. In the present embodiment, as the electrode <NUM> is embedded in the Si layer <NUM>, electrons are more effectively collected at the electrode <NUM> compared to the case where the electrode <NUM> is merely in contact with the surface of the Si layer <NUM>. The electrons not derived from radiation are effectively suppressed from flowing into the signal output electrode <NUM>, thereby further reducing noise. Moreover, as in Embodiment <NUM>, the need for a bonding pad for flowing the collected electrons to the outside the semiconductor detector <NUM> is eliminated, simplifying the configuration for reducing surface current. The yield of the semiconductor detector <NUM> is improved and thus the cost for the semiconductor detector <NUM> is lowered.

While Embodiments <NUM> and <NUM> illustrated a form where multiple electrodes <NUM> are linearly arranged, the electrodes <NUM> may also be arranged non-linearly. For example, in plan view, the electrodes 131a or 131b may also be arranged at a position where the line connecting the electrode 131a or 131b and the signal output electrode <NUM> forms an angle of approximately <NUM> degrees with respect to the line connecting the electrode 131c and the signal output electrode <NUM>. Moreover, the electrodes 131a, 131b and 131c may be arranged at positions where the lines connecting the respective electrodes 131a, 131b and 131c to the signal output electrode <NUM> form an angle of approximately <NUM> degrees between each other. Moreover, the lines connecting the respective electrodes 131a, 131b and 131c to the signal output electrode <NUM> may form random angles between each other. Furthermore, while Embodiments <NUM> and <NUM> illustrated a form where one electrode <NUM> is formed at one portion of the Si layer <NUM> positioned between a pair of ring-shaped electrodes <NUM>, multiple electrodes <NUM> may alternatively be formed at one portion of the Si layer <NUM> positioned between a pair of ring-shaped electrodes <NUM>. In addition, multiple electrodes <NUM> may be connected to one ring-shaped electrode <NUM>. Moreover, while Embodiments <NUM> and <NUM> illustrated an example where the electrode <NUM> is connected to a ring-shaped electrode <NUM> which is one closer to the inner side than the inner ring-shaped electrode <NUM> closest to the electrode <NUM>, the electrode <NUM> may alternatively be connected to the ring-shaped electrode <NUM> closer to the signal output electrode <NUM>. In such a case, the potential difference between the surface of the Si layer <NUM> and the electrode <NUM> is further increased.

<FIG> is a schematic plan view of the semiconductor detector <NUM> according to Embodiment <NUM>. As in Embodiments <NUM> and <NUM>, the signal output electrode <NUM> and multiple ring-shaped electrodes <NUM> are formed at one surface of the Si layer <NUM>. An electrode <NUM> is formed in a portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM>. On a specific ring-shaped electrode <NUM>, a conductive part <NUM> is provided, the conductive part <NUM> being in contact with the ring-shaped electrode <NUM>. As a part of the conductive part <NUM> extends outward and is connected to the electrode <NUM>, the electrode <NUM> is connected to the ring-shaped electrode <NUM> located closer to the signal output electrode <NUM> via the conductive part <NUM>. The ring-shaped electrodes <NUM> located at the outer side of the electrode <NUM> has a disconnected part in the circumferential direction. Although the ring-shaped electrodes <NUM> with disconnected parts do not have the shape of rings, they are referred to as the ring-shaped electrodes <NUM> here for the sake of convenience. A disconnected portion <NUM> having no ring-shaped electrode <NUM> is formed by dividing the ring-shaped electrode <NUM>. The other configuration parts of the semiconductor detector <NUM> are similar to those of Embodiment <NUM> or <NUM>. Furthermore, the configuration of the radiation detection apparatus including the semiconductor detector <NUM> is similar to that in Embodiments <NUM> and <NUM>.

Similarly to Embodiments <NUM> and <NUM>, the potential of the electrode <NUM> is higher than the potential of the Si layer <NUM> at the position where the electrode <NUM> is formed. At the surface of the Si layer <NUM>, electrons not derived from incident radiation are generated, and the generated electrons are collected at the electrode <NUM>. In particular, the electrons generated at a position between a pair of ring-shaped electrodes <NUM> with a portion of the Si layer <NUM> provided with the electrode <NUM> interposed in between are collected at the electrode <NUM>. As in Embodiment <NUM>, electrons not derived from radiation are suppressed from flowing into the signal output electrode <NUM>, thereby reducing noise. Moreover, as in Embodiments <NUM> and <NUM>, the need for a bonding pad for flowing the collected electrons to the outside the semiconductor detector <NUM> is eliminated, which simplifies the configuration for reducing surface current. This improves the yield of the semiconductor detector <NUM> and thus lowers the cost for the semiconductor detector <NUM>.

According to the present embodiment, a part of the ring-shaped electrode <NUM> located at the outer side of the electrode <NUM> is disconnected, so that the electrons generated at the surface of the Si layer <NUM> located at the outer side of the electrode <NUM> pass through the disconnected portion <NUM>, flow to the inner side where the potential is higher, and are collected at the electrode <NUM>. Since the electrode <NUM> can collect the electrons generated at the outer side thereof, the efficiency of collecting electrons by one electrode <NUM> is improved. According to the present embodiment, therefore, the number of electrodes <NUM> may be reduced compared to Embodiments <NUM> and <NUM>.

<FIG> is a schematic plan view of a semiconductor detector <NUM> according to Embodiment <NUM>. <FIG> is a schematic section view illustrating the semiconductor detector <NUM> taken along the line XI-XI in <FIG>. <FIG> is a schematic section view illustrating the semiconductor detector <NUM> taken along the line XII-XII in <FIG>. As in Embodiments <NUM> to <NUM>, the signal output electrode <NUM> and the multiple ring-shaped electrodes <NUM> are formed on one surface of the Si layer <NUM>. Electrodes <NUM> are embeded in a portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM>. On specific ring-shaped electrodes <NUM>, conductive parts <NUM> are formed, the conductive parts <NUM> being in contact with the respective ring-shaped electrodes <NUM>. The conductive parts <NUM> are connected to extention parts <NUM> extending outward. The extention parts <NUM> are conductive. The extention parts <NUM> are connected to the electrodes <NUM>. That is, each of the electrodes <NUM> is connected to the ring-shaped electrode <NUM> that are closer to the signal output electrode <NUM> via the extension part <NUM> and the conductive part <NUM>. In <FIG>, the electrodes <NUM>, the conductive parts <NUM> and the extension parts <NUM> are hatched. As illustrated in <FIG>, each of the conductive parts <NUM> has such a shape as not to overlap the extention part <NUM> connected to another one of the conductive parts <NUM> in plan view. As illustrated in <FIG> and <FIG>, an insulation film <NUM> is located between the extention part <NUM> and the Si layer as well as ring-shape electrode <NUM>. The insulation film <NUM> is not illustrated in <FIG>.

As illustrated in <FIG>, each of the electrodes <NUM> has an arc shape in plan view. For example, the electrode <NUM> has such a shape that a part of a ring in the circumferential direction is disconnected in plan view. The portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM> includes a non-electrode part <NUM> where the electrode <NUM> is totally absent between a pair of ring-shaped electrodes <NUM>. In the non-electrode part <NUM>, for example, an electric resistance channel is provided which is connected between a pair of ring-shaped electrodes <NUM>. The electric resistance channel may not necessarily be present at the non-electrode part <NUM>. As illustrated in <FIG> and <FIG>, the electrode <NUM> is covered with the insulation film <NUM> except for the portion connected to the extension part <NUM>. The other parts of the semiconductor detector <NUM> are configured similarly to those in Embodiment <NUM> or <NUM>. Moreover, the radiation detection device provided with the semiconductor detector <NUM> is configured similarly to that in Embodiment <NUM> or <NUM>.

As in Embodiments <NUM> to <NUM>, the potential of the electrode <NUM> is higher than the potential of the Si layer <NUM> at the position where the electrode <NUM> is formed. The electrons not derived from the radiation generated at the surface of the Si layer <NUM> are collected by the electrode <NUM>. As in Embodiments <NUM> to <NUM>, the electrons not derived from the radiation are prevented from being flown into the signal output electrode <NUM>, thereby reducing the noise. Moreover, similarly to Embodiments <NUM> to <NUM>, the need for a bonding pad for flowing the collected electrons to the outside the semiconductor detector <NUM> is eliminated, thereby simplifying the configuration of reducing the surface current. This improves the yield of the semiconductor detector <NUM>, and reduces the cost thereof.

In the present embodiment, since the electrode <NUM> has an arc-like shape, a larger number of portions of the Si layer <NUM> are in contact with the electrode <NUM> compared to the case that the electrode <NUM> has a dot-like shape. Thus, the electrons not derived from the radiation generated at the surface of the Si layer <NUM> are more reliably collected by the electrode <NUM>. Furthermore, as the electrode <NUM> does not have a ring shape but an arc shape, the portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM> includes the non-electrode part <NUM>. In the case where an electric resistance channel connected to the pair of ring-shaped electrodes <NUM> is formed at the non-electrode part <NUM>, the electrode <NUM> will not overlap with the electric resistance channel. Cancellation of charges will not occur between the otherwise overlapping electrode <NUM> and the electrode resistance channel, so that the electrode <NUM> and the electric resistance channel function without affecting each other.

<FIG> is a schematic plan view of a semiconductor detector <NUM> according to Embodiment <NUM>. As in Embodiments <NUM> to <NUM>, the signal output electrode <NUM> and multiple ring-shaped electrodes <NUM> are formed on one surface of the Si layer <NUM>. A plurality of electrodes <NUM> are provided at a portion of the Si layer <NUM> located between an adjacent pair of ring-shaped electrodes <NUM>. <FIG> illustrates an example where three electrodes <NUM> are located between an adjacent pair of ring-shaped electrodes <NUM>. The number of electrodes <NUM> located between an adjacent pair of ring-shaped electrodes <NUM> may be two, or may be four or more. Each of the electrodes <NUM> has a dot-like shape in plan view. The electrode <NUM> may also have an arc-like shape in plan view.

The conductive part <NUM> is formed on and is in contact with a specific ring-shaped electrode <NUM>. The conductive part <NUM> is connected to the extension part <NUM> extending outward. The extension part <NUM> is conductive. The electrodes <NUM> located between the respective adjacent pairs of ring-shaped electrodes <NUM> are connected to the extension parts <NUM> in one-to-one correspondence. That is, each electrode is individually connected to a ring-shaped electrode <NUM> closer to the signal output electrode <NUM> via the extension part <NUM> and the conductive part <NUM>. The other configuration of the semiconductor detector <NUM> is similar to that in Embodiment <NUM> or <NUM>. The insulation film <NUM> is not illustrated in <FIG>. Furthermore, the radiation detection device comprising the semiconductor detector <NUM> is configured similarly to that in Embodiment <NUM> or <NUM>.

As in Embodiments <NUM> to <NUM>, the potential of the electrode <NUM> is higher than the potential of the Si layer <NUM> at the position where the electrode <NUM> is located. The electrons not derived from the radiation generated at the surface of the Si layer <NUM> are collected by the electrode <NUM>. As in Embodiments <NUM> to <NUM>, the electrons not derived from the radiation are prevented from being flown into the signal output electrode <NUM>, which suppresses noise. Furthermore, as in Embodiments <NUM> to <NUM>, the need for a bonding pad for flowing the collected electrons to the outside the semiconductor detector <NUM> is eliminated, thereby simplifying the configuration for reducing surface current. This improves the yield of the semiconductor detector <NUM> and reduces the cost thereof.

In the present embodiment, since a plurality of electrodes <NUM> are provided between the respective pairs of adjacent ring-shaped electrodes <NUM>, electric charges are collected by the electrodes <NUM> at a larger number of positions compared to the case where only a single electrode <NUM> is employed. Thus, the electrons not derived from the radiation generated at the surface of the Si layer <NUM> are more reliably collected by the electrodes <NUM>. In the form where each electrode <NUM> has an arc shape, a larger number of portions of Si layer <NUM> are in contact with the electrodes <NUM>, and therefore the electrons not derived from the radiation generated at the surface of the Si layer <NUM> are more reliably collected by the electrodes <NUM>.

While Embodiments <NUM> to <NUM> described above have illustrated examples in which the semiconductor part (Si layer <NUM>) is made of an n-type semiconductor whereas the ring-shaped electrode <NUM> is made of a p-type semiconductor, the semiconductor detector <NUM> may alternatively have a form in which the semiconductor part is made of a p-type semiconductor whereas the ring-shaped electrode <NUM> is made of an n-type semiconductor. In addition, Embodiments <NUM> to <NUM> have mainly illustrated a form in which electrons generated by radiation are concentrated at and flow into the signal output electrode <NUM>, the semiconductor detector <NUM> may also take a form in which holes generated by radiation are concentrated at and flow into the signal output electrode <NUM>. In such a form, the voltage application part <NUM> applies voltage such that the potential monotonically decreases in sequence from the ring-shaped electrode <NUM> distant from the signal output electrode <NUM> to the ring-shaped electrode <NUM> close to the signal output electrode <NUM> and that the potential at the rear electrode <NUM> is intermediate between the potential of the innermost ring-shaped electrode <NUM> and the potential of the outermost ring-shaped electrode <NUM>. At the surface of the Si layer <NUM>, holes generated at the interface between Si and SiO<NUM> move toward the signal output electrode <NUM>, causing surface current. The electrode <NUM> has a potential lower than that of the Si layer <NUM> at a position where the electrode <NUM> is formed, and thus collects holes.

Furthermore, while Embodiments <NUM> to <NUM> described above have illustrated that the curved electrodes are the multiple ring-shaped electrodes <NUM>, the semiconductor detector <NUM> may also take a form of including curved electrodes each having a shape other than the ring shape. The curved electrodes have distances to the signal output electrodes <NUM> that are different from each other. The curved electrodes are applied with voltage from the voltage application part <NUM>, present different potentials in sequence, and generate a potential gradient within the Si layer <NUM>. For example, the shape of each curved electrode may be an arc shape.

Claim 1:
A semiconductor detector (<NUM>), comprising: a plate-shaped semiconductor part (<NUM>), a signal output electrode (<NUM>) for outputting a signal and which is provided at one surface of the semiconductor part (<NUM>), and a plurality of curved electrodes (<NUM>) which are provided at the one surface of the semiconductor part (<NUM>) and which have distances from the signal output electrode (<NUM>) that are different from each other, wherein the plurality of curved electrodes (<NUM>) are configured to be applied with voltage so as to generate in the semiconductor part (<NUM>) a potential gradient in which a potential varies toward the signal output electrode (<NUM>),
characterized by comprising
an arc-shaped collection electrode (<NUM>) arranged in an arc shape in plan view on the plate-shaped semiconductor part (<NUM>) to collect an electric charge, generated at the semiconductor part (<NUM>),
wherein the collection electrode (<NUM>) is embedded in a part of the semiconductor part (<NUM>) located between an adjacent pair of curved electrodes (<NUM>) in the arc shape along the pair of curved electrodes (<NUM>) and arranged so as to allow said collected electric charges flow in the collection electrode (<NUM>).