JP6581376B2 - Semiconductor device and imaging device - Google Patents

Description

  The present invention relates to a semiconductor device and an imaging device.

  Some semiconductor devices are used in high dose environments. In this case, it is necessary to consider the influence of the total dose effect. Here, the total dose effect is a phenomenon in which a large amount of radiation is irradiated on the semiconductor device, which adversely affects the operation characteristics and reliability of the semiconductor device.

Specifically, when radiation is incident on the MOSFET, electron-hole pairs are generated by the ionization action. Among the electron-hole pairs generated in the oxide film, electrons are absorbed by a nearby metal or semiconductor layer because of their high mobility, but many holes with low mobility exist at the SiO ₂ / Si interface. Since it is trapped by the hole trap and works as a fixed charge (positive charge) in the oxide film, the threshold value of the MOSFET fluctuates, causing an increase in leakage current and deterioration of switching characteristics.

  Since the generation amount of electron-hole pairs in the oxide film is proportional to the volume, the influence of the total dose effect becomes large in a thick oxide film. A field oxide film in a normal MOSFET or a BOX (Buried Oxide) layer in a MOSFET using an SOI (Silicon On Insulator) substrate is an example of the thick oxide film.

  In Patent Document 1, holes are accumulated in the BOX layer due to the total dose effect generated in the BOX layer of the SOI substrate, and a back channel is formed by the accumulated holes. It is described that it increases. In order to prevent the formation of such a back channel, in Patent Document 1, a negative voltage that decreases with time is applied to the support substrate.

JP 2003-69031 A

  On the other hand, as described above, when radiation is incident on the MOSFET, the gate oxide film produces a total dose effect in addition to the above-described BOX layer when using the thick oxide film field oxide film or SOI substrate. Normally, the influence of the total dose effect on the thick oxide film described above is dominant and does not manifest itself as a problem. However, if the influence of the total dose effect on the thick oxide film can be ignored, the gate is a thin oxide film. The total dose effect in the oxide film becomes obvious. The influence of the total dose effect generated in the gate oxide film cannot be dealt with only by changing the substrate potential as in Patent Document 1, based on the principle that the MOSFET operates with the electric field between the gate and the substrate. For example, even if a positive voltage is applied to the substrate so as to cancel the channel formed by the total dose effect, the potential difference between the substrate and each electrode is reduced, and the drive capability of the element is reduced. It is not a measure against the effect.

  As an example of the problem to be solved by the present invention, in a semiconductor device, as an example, it is possible to suppress the influence (a variation in threshold value, an increase in leakage current, a deterioration in switching characteristics, etc.) due to a total dose effect generated in a MOSFET by radiation. Can be mentioned.

The invention described in claim 1
MOSFET,
A voltage applying unit capable of applying a first voltage for generating a tunnel current in the gate insulating film of the MOSFET between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed;
It is a semiconductor device provided with.

The invention according to claim 3
MOSFET,
A voltage applying unit capable of applying a first voltage between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed at a timing when no voltage is applied between the drain electrode and the source electrode of the MOSFET;
It is a semiconductor device provided with.

The invention described in claim 5
A conversion film that converts electromagnetic waves or particle beams into electric charges;
An electron emission source facing the conversion film;
A semiconductor device for driving the electron emission source;
With
The semiconductor device includes:
A MOSFET electrically connected to the electron radiation source;
A voltage applying unit capable of applying a first voltage for generating a tunnel current in the gate insulating film of the MOSFET between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed;
It is an imaging device provided with.

The invention described in claim 6
A conversion film that converts electromagnetic waves or particle beams into electric charges;
An electron emission source facing the conversion film;
A semiconductor device for driving the electron emission source;
With
The semiconductor device includes:
A MOSFET electrically connected to the electron radiation source;
A voltage applying unit capable of applying a first voltage between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed at a timing when no voltage is applied between the drain electrode and the source electrode of the MOSFET;
It is an imaging device provided with.

1 is a diagram illustrating a configuration of a semiconductor device according to a first embodiment. 3 is a graph showing measurement results of I _DS -V _GS characteristics of the MOSFET shown in FIG. 1. It is a figure which shows the modification of FIG. 6 is a diagram illustrating a configuration of a semiconductor device according to a second embodiment. FIG. 1 is a diagram illustrating a configuration of an imaging apparatus according to a first embodiment. It is a top view which shows the structure of the electron emission layer shown in FIG. 6 is a flowchart illustrating an example of an operation performed by the imaging apparatus illustrated in FIG. 5. 6 is a diagram illustrating a configuration of an imaging apparatus according to Embodiment 2. FIG. FIG. 6 is a diagram illustrating a configuration of an imaging apparatus according to a third embodiment. FIG. 6 is a diagram illustrating a configuration of an imaging apparatus according to a fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  In the following description, the control unit 300 indicates a functional unit block, not a hardware unit configuration. The control unit 300 is realized by an arbitrary combination of hardware and software centering on an arbitrary computer CPU, memory, a program loaded in the memory, a storage medium such as a hard disk for storing the program, and a network connection interface. The There are various modifications of the implementation method and apparatus.

(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration of a semiconductor device according to the first embodiment. The semiconductor device includes a MOSFET 100, a voltage application unit 200, and a control unit 300. In the example shown in the figure, the MOSFET 100 is an N-channel MOSFET. However, MOSFET 100 may be a P-channel MOSFET. In the following description, the MOSFET 100 is an N-channel MOSFET.

  The MOSFET 100 is formed using a first conductivity type (P-type) semiconductor layer 110. The semiconductor layer 110 is, for example, a semiconductor substrate (for example, a silicon substrate). As another example, MOSFET 100 may be an epitaxial layer formed on a semiconductor substrate, for example.

  An element isolation film 120 is formed on the surface layer of the semiconductor layer 110. The element isolation film 120 is formed using, for example, LOCOS (LOCal Oxidation of Silicon) or STI (Shallow Trench Isolation). In plan view, the element isolation film 120 surrounds a region (an element formation region) where the MOSFET 100 is formed.

  In the element formation region described above, the first conductivity type region 132 is formed in the surface layer of the semiconductor layer 110. The first conductivity type region 132 has an impurity concentration higher than that of the semiconductor layer 110. Further, in the element formation region described above, a drain region 134 and a source region 136 are formed on the surface layer of the semiconductor layer 110. The drain region 134 and the source region 136 are located opposite to each other with the first conductivity type region 132 interposed therebetween. Each of the drain region 134 and the source region 136 is a second conductivity type (N-type) region.

  In the element formation region described above, a gate insulating film 142 is formed on the semiconductor layer 110. The gate insulating film 142 covers the first conductivity type region 132. In the example shown in this drawing, the gate insulating film 142 is a silicon oxide film. A gate electrode 144 is formed on the gate insulating film 142. The gate electrode 144 is formed using, for example, polysilicon. Further, a drain electrode 152 and a source electrode 154 are formed on the semiconductor layer 110 in the element formation region described above. The drain electrode 152 and the source electrode 154 are connected to the drain region 134 and the source region 136, respectively. The drain electrode 152 and the source electrode 154 are formed using, for example, polysilicon.

  The element isolation film 120, the gate electrode 144, the drain electrode 152, and the source electrode 154 are covered with an insulating layer 160. The insulating layer 160 is formed using, for example, a silicon oxide film. A contact 162 is embedded in the insulating layer 160. In the example shown in this drawing, a contact 162 connected to the drain electrode 152 and a contact 162 connected to the source electrode 154 are embedded in the insulating layer 160. The contact 162 is formed using, for example, a metal (for example, Al).

  A voltage can be applied between the drain electrode 152 and the source electrode 154 by the voltage application unit 200. As will be described in detail later, this voltage is a voltage that generates hot carriers in the semiconductor layer 110. The voltage application unit 200 is controlled by the control unit 300.

Next, the operation of the semiconductor device according to the present embodiment will be described with reference to FIG. First, when radiation (for example, γ-rays) enters the MOSFET 100, electron-hole pairs are generated in the semiconductor layer 110 due to the total dose effect. The holes generated in this case have low mobility. Accordingly, the holes are easily trapped at a level generated at the interface between the semiconductor layer 110 and the gate insulating film 142 (for example, the SiO ₂ / Si interface). The holes trapped at the above-described levels are located in the gate insulating film 142 in the vicinity of the above-described interface. Such holes function as fixed charges (positive charges). When such a fixed charge exists, the threshold voltage of the MOSFET 100 is lowered.

  In the example shown in this figure, the voltage application unit 200 has a drain electrode 152 and a source electrode 154 at a timing when a gate voltage equal to or higher than the threshold value of the MOSFET 100 is applied to the gate electrode 144 (in other words, the MOSFET 100 is in an on state). The voltage V1 is applied during the period. In this case, the source electrode 154 is grounded. When the breakdown voltage between the drain region 134 and the source region 136 is VB, 0.75 ≦ V1 / VB ≦ 0.95, preferably 0.80 ≦ V1 / VB ≦ 0.90 is satisfied. In other words, a voltage lower than the breakdown voltage between the drain region 134 and the source region 136 and close to the breakdown voltage is applied between the drain electrode 152 and the source electrode 154 by the voltage application unit 200. As a result, a high electric field is generated between the drain region 134 and the source region 136. This high electric field generates hot carriers. Some hot carriers are injected into the gate insulating film 142. In this case, when the hot carriers are combined with the fixed charges (holes) described above, the fixed charges (holes) described above can be eliminated. Thereby, the fluctuation | variation of the threshold value of MOSFET100 is negated.

  Furthermore, in the example shown in the figure, when the above gate voltage is VG, the above voltage V1 satisfies 0.95 ≦ V1 / VG. In other words, the voltage V1 described above is substantially equal to or higher than the gate voltage VG of the gate electrode 144. In this case, the channel below the gate insulating film 142 is degenerated. Accordingly, a depletion layer is formed between the drain region 134 and the gate insulating film 142 in the surface layer of the semiconductor layer 110. In this depletion layer, a high electric field is generated. And impact ionization arises by the electron accelerated by this high electric field. This impact ionization generates electrons (hot carriers) having high energy. Some hot carriers are injected into the gate insulating film 142. In this case, when the hot carriers are combined with the fixed charges (holes) described above, the fixed charges (holes) described above can be eliminated.

FIG. 2 is a graph showing measurement results of I _DS -V _GS characteristics of MOSFET 100 shown in FIG. Note that I _DS indicates a current between the drain electrode 152 and the source electrode 154, and V _GS indicates a voltage between the gate electrode 144 and the source electrode 154. In the example shown in this figure, the I _DS -V _GS characteristics of the MOSFET 100 were measured before and after irradiation of the MOSFET 100 with radiation. As shown in the figure, the threshold value of the MOSFET 100 became lower after the radiation was irradiated.

  FIG. 3 is a diagram showing a modification of FIG. As shown in the figure, the MOSFET 100 may be formed using a semiconductor layer 110 of an SOI (Silicon On Insulator) substrate 116. The SOI substrate 116 includes a substrate 112, an insulating layer 114, and a semiconductor layer 110. The substrate 112, the insulating layer 114, and the semiconductor layer 110 are stacked in this order. The substrate 112 is, for example, a silicon substrate. The insulating layer 114 is a BOX (Buried Oxide) layer, for example, a silicon oxide film. The insulating layer 114 is in contact with the first conductivity type region 132, the drain region 134, and the source region 136.

In the example shown in this figure, when radiation (for example, γ-rays) enters the MOSFET 100, electron-hole pairs are generated on the SOI substrate 116 due to the total dose effect described above. The holes generated in this case may be trapped at the level generated at the interface between the semiconductor layer 110 and the insulating layer 114 (for example, the Si / SiO ₂ interface). The holes trapped in the above levels are located in the insulating layer 114 in the vicinity of the above interface. In this case, a back channel is generated and the back channel current flows as a leakage current, thereby increasing current consumption.

  Here, as in Patent Document 1 described above, as the fixed charge due to accumulated holes increases, the negative potential on the substrate side is lowered to relatively form a potential distribution that does not form a back channel. As the holes accumulate, the necessary negative potential also increases, and the lifetime of the device is determined not only by the lifetime of the device itself but also by the ability to supply this negative potential. Further, as the negative potential increases, the potential difference between each electrode and the substrate increases, so that the withstand voltage between the substrate and each electrode also determines the lifetime of the element.

  On the other hand, in the example shown in this figure, even when holes accumulate and a back channel is formed, the voltage application unit 200 causes a gap between the drain electrode 152 and the source electrode 154 as in the example shown in FIG. By applying the voltage V 1 and applying the substrate voltage Vs to the substrate 112, hot carriers can be generated in the semiconductor layer 110. In this case, some hot carriers are combined with the above holes. Thereby, the above holes can be eliminated, and the formation of the back channel can be canceled. With such a configuration, it is possible to reduce the influence of the total dose effect without affecting the lifetime of the element.

  As described above, according to the present embodiment, the voltage application unit 200 generates a high electric field between the drain region 134 and the source region 136. Hot carriers can be generated by this high electric field. When radiation enters the MOSFET 100, the threshold value of the MOSFET 100 may fluctuate due to holes generated by the radiation. The above hot carriers are combined with the above holes. Thereby, the above-described holes can be eliminated. In this way, fluctuations in the threshold value of the MOSFET 100 can be canceled out.

(Embodiment 2)
FIG. 4 is a diagram illustrating a configuration of the semiconductor device according to the second embodiment. The semiconductor device according to the present embodiment has the same configuration as that of the semiconductor device according to the first embodiment except for the following points.

  In the example shown in this figure, the voltage application unit 200 can apply a voltage between the gate electrode 144 and the semiconductor layer 110. As will be described in detail later, this voltage is a voltage that generates a tunnel current in the gate insulating film 142. The voltage application unit 200 is controlled by the control unit 300.

  Next, the operation of the semiconductor device according to the present embodiment will be described with reference to FIG. First, when radiation (for example, γ-rays) enters the MOSFET 100, holes are located in the gate insulating film 142 in the vicinity of the interface between the semiconductor layer 110 and the gate insulating film 142, as in the first embodiment. There is. In this case, the threshold value of the MOSFET 100 is lowered.

  In the example shown in this figure, the voltage application unit 200 is configured such that the voltage is not applied between the drain electrode 152 and the source electrode 154 (in other words, no current is passed through the MOSFET 100) and the gate electrode 144 and the semiconductor layer. A voltage V 1 is applied during 110. In this case, the semiconductor layer 110, the drain electrode 152, and the source electrode 154 are grounded. When the breakdown voltage between the gate electrode 144 and the semiconductor layer 110 (that is, the gate insulating film 142) is VB, 0.65 ≦ V1 / VB ≦ 0.85, preferably 0.68 ≦ V1 / VB ≦ 0. .76 is satisfied. In other words, the voltage application unit 200 applies a voltage lower than the breakdown voltage between the gate electrode 144 and the semiconductor layer 110 and close to the breakdown voltage between the semiconductor layer 110 and the gate insulating film 142. As a result, a tunnel current is generated in the gate insulating film 142. Then, some electrons in the tunnel current are combined with the above holes. As a result, the holes described above disappear. Thereby, the fluctuation | variation of the threshold value of MOSFET100 can be negated.

Example 1
FIG. 5 is a diagram illustrating the configuration of the imaging apparatus according to the first embodiment. FIG. 6 is a plan view showing the configuration of the electron emission layer 32 shown in FIG. The imaging device includes a container 10, a transparent substrate 20, an electron source 30, and an acceleration electrode 40. Furthermore, the imaging apparatus includes a voltage application unit 200, a control unit 300, a scanning unit 400, and a current measurement unit 510. In the example shown in the figure, the voltage application unit 200, the control unit 300, the scanning unit 400, and the current measurement unit 510 are located outside the container 10. However, the voltage application unit 200, the control unit 300, the scanning unit 400, and the current measurement unit 510 may be provided inside the container 10. In this example, the voltage application unit 200 has the same configuration as the voltage application unit 200 according to the first or second embodiment.

  The container 10 has a space inside, and has an opening connected to this space. The container 10 is formed using glass, for example. This opening of the container 10 is closed by the transparent substrate 20. The transparent substrate 20 is formed using glass, for example.

  A transparent electrode 22 and a conversion film 24 are laminated in this order on the surface of the transparent substrate 20 facing the space side of the container 10. The transparent electrode 22 is formed using, for example, ITO (indium tin oxide). The conversion film 24 converts electromagnetic waves (for example, infrared rays, visible rays, ultraviolet rays, γ rays, or X rays) into electric charges. However, the conversion film 24 may convert a particle beam (for example, a neutron beam) into an electric charge. The conversion film 24 is formed using amorphous selenium, for example.

  An electron source 30 is disposed in a region facing the conversion film 24. The electron source 30 has an electron emission layer 32 on the surface facing the conversion film 24. The electron emission layer 32 has a plurality of electron emission sources 34 arranged two-dimensionally. In the example shown in this figure, each of the plurality of electron emission sources 34 is arranged at one of a plurality of lattice points of m rows and n columns (m and n are integers of 2 or more). Each of these electron emission sources 34 is a pixel of the imaging device, and each pixel of the electron emission source 34 is represented as a pixel (Xi, Yj) (1 ≦ i ≦ n, 1 ≦ j ≦ m). it can. Furthermore, in the example shown in this figure, each electron emission source 34 has a plurality of emission sites 36 arranged in 3 rows and 3 columns. Electrons are emitted from each emission site 36. The electron emission layer 32 is formed by using, for example, HEED (High-efficiency Electron Emission Device).

  Each of the plurality of electron emission sources 34 is electrically connected to different MOSFETs 100. In this example, the MOSFET 100 has the same configuration as the MOSFET 100 according to the first or second embodiment. When the MOSFET 100 is turned on, electrons are emitted from the electron emission source 34. The MOSFET 100 is driven by the scanning unit 400. Specifically, the scanning unit 400 includes an X scanning unit 410 and a Y scanning unit 420. The X scanning unit 410 selects one of the m rows. The Y scanning unit 420 selects one of the n columns. Then, the MOSFETs 100 located in the rows and columns selected by the X scanning unit 410 and the Y scanning unit 420 are driven.

  In the example shown in the figure, the scanning unit 400 sequentially selects a plurality of rows, sequentially selects the electron emission source 34 included in the selected row, and sequentially selects the MOSFETs 100 electrically connected to the selected electron emission source 34. Make it work. In this case, imaging is not performed during the period from when the scanning unit 400 ends the operation of all the MOSFETs 100 included in one row until the operation of the MOSFET 100 starts in the next row (blanking period). The voltage application unit 200 can apply a voltage to the MOSFET 100 during this blanking period in the same manner as in the first or second embodiment. Thus, the threshold value fluctuation of the MOSFET 100 can be canceled without changing the voltage applied to the MOSFET 100 while the scanning unit 400 operates the MOSFET 100 (in other words, the imaging period).

  In the example shown in this figure, for example, the voltage application is performed after the scanning unit 400 ends the operation of the MOSFET 100 in the pixel (Xn, Y2) until the operation of the MOSFET 100 in the pixel (X1, Y3) starts. The unit 200 can apply the voltage described above to the MOSFET 100. Furthermore, for example, after the scanning unit 400 ends the operation of the MOSFET 100 in the pixel (Xn, Ym) and before the operation of the MOSFET 100 in the pixel (X1, Y1) starts, the voltage application unit 200 applies the above-described voltage to the MOSFET 100. Applied voltage can be applied.

  An acceleration electrode 40 is disposed between the transparent substrate 20 and the electron source 30. The edge of the acceleration electrode 40 is held on the inner surface of the container 10. The acceleration electrode 40 is a conductive member having a plurality of openings. The acceleration electrode 40 applies a voltage for accelerating the electrons emitted from the electron emission layer 32. Thereby, the electrons radiated from the electron emission layer 32 are accelerated and then pass through the opening of the acceleration electrode 40.

  Next, an imaging method using the imaging apparatus according to the present embodiment will be described. First, electromagnetic waves (or particle beams) are irradiated from the outside of the container 10. In this case, the electromagnetic wave passes through the transparent substrate 20 and the transparent electrode 22 and then enters the conversion film 24. In this case, the electromagnetic waves form electron-hole pairs in the conversion film 24. A voltage is applied to the conversion film 24. Thereby, the holes contained in the electron-hole pair described above move to the electron source 30 side by the electric field inside the conversion film 24. Thus, in the conversion film 24, holes accumulate on the surface facing the electron source 30. The hole pattern generated in this case corresponds to the electromagnetic wave image incident on the imaging device.

  The holes accumulated on the surface of the conversion film 24 are scanned two-dimensionally by electrons emitted from the electron source 30. In this case, when electrons from the electron source 30 are combined with holes, a current flows from the conversion film 24 to the transparent electrode 22. By reading the current from the conversion film 24, the hole pattern generated on the surface of the conversion film 24 can be read.

  When the imaging apparatus according to the present embodiment is used in an environment with a high dose, or when radiation (for example, γ rays) is captured with the imaging apparatus according to the present embodiment, radiation may enter the MOSFET 100. In this case, the threshold value of the MOSFET 100 may change due to the total dose effect described above. In this example, the threshold value of the MOSFET 100 can be calibrated by applying a voltage to the MOSFET 100 by the voltage application unit 200 in the same manner as in the first or second embodiment.

  Furthermore, in the example shown in this drawing, the control unit 300 determines whether or not the integrated dose of radiation incident on the MOSFET 100 is equal to or greater than a reference value. Then, the control unit 300 controls the voltage application unit 200 based on the determination result.

  Specifically, in the example shown in this figure, the current measurement unit 510 measures the current between the drain and source of the MOSFET 100. As described above, when radiation enters the MOSFET 100, the threshold value of the MOSFET 100 decreases. In this case, even if the same gate voltage is applied to the MOSFET 100, a higher current flows between the drain and the source after the radiation is incident on the MOSFET 100 than before the radiation is incident on the MOSFET 100. For this reason, the control unit 300 determines whether or not the current measured by the current measuring unit 510 is equal to or greater than a predetermined reference value (current reference value), whereby the integrated dose is equal to or greater than the reference value. It can be determined whether or not.

  Furthermore, the control unit 300 may change the length of the voltage application time by the voltage application unit 200 according to the measurement result of the current measurement unit 510. Specifically, the control unit 300 calculates the difference between the measurement value of the current measurement unit 510 and the above-described current reference value, and controls the voltage application unit 200 based on the difference. It can be said that the larger the fluctuation of the threshold value of the MOSFET 100 (in other words, the higher the integrated dose of the MOSFET 100), the larger the current flowing between the drain and the source. For this reason, for example, the control part 300 can make the length of the above-mentioned application time long, so that above-described difference is large.

FIG. 7 is a flowchart illustrating an example of an operation performed by the imaging apparatus illustrated in FIG. First, the current measuring unit 510 measures the current _{I R} between the drain and source of MOSFET100 the first time T1 (step S102). The current _{I R} is, for example, in other words between (the image pickup device captures an image of one frame, the pixels from the start of the operation of the MOSFET 100 scanning unit 400 in the pixel (X1, Y1) (Xn, Ym) MOSFET100 This is a current that flows in the MOSFET 100 in order to scan one pixel of the conversion film 24 until the operation of (1) is completed.

  Next, the current measurement unit 510 measures the current I flowing between the drain and source of the MOSFET 100 at the second time T2 (T2> T1) (step S104). This current I is, for example, a current that flows through the MOSFET 100 in order to scan one pixel of the conversion film 24 while the imaging apparatus captures an image of the next frame after the above-described one frame.

Next, the controller 300 calculates a difference (I−I _R ) between the above-described current I _R and the above-described current I (step S200). When the difference is greater than or equal to the reference value (step S200: Yes), the voltage application unit 200 applies a voltage (step S300).

  As described above, according to the present embodiment, when the imaging apparatus is used in an environment with a high dose, or when radiation (for example, γ-rays) is captured by the imaging apparatus according to the present embodiment, the threshold value of the MOSFET 100 varies due to the radiation. Also, the fluctuation can be canceled out by the voltage application unit 200.

(Example 2)
FIG. 8 is a diagram illustrating the configuration of the imaging apparatus according to the second embodiment. The imaging apparatus according to the present embodiment has the same configuration as the imaging apparatus according to the first embodiment except for the following points.

  In the example shown in this figure, the imaging device includes an image generation unit 520. The image generation unit 520 is electrically connected to the transparent electrode 22 (in other words, the conversion film 24). As described above, the imaging device can capture an image by reading the current of the conversion film 24. In the example shown in the figure, the image generation unit 520 generates an image by reading the current flowing through the conversion film 24.

  When the image generated in the image generation unit 520 is disturbed, the threshold value of the MOSFET 100 is likely to change. Therefore, the control unit 300 can determine whether or not the integrated dose of the MOSFET 100 is greater than or equal to the reference value based on the disturbance of the image generated by the image generation unit 520. Then, the control unit 300 controls the voltage application unit 200 based on the determination result.

(Example 3)
FIG. 9 is a diagram illustrating the configuration of the imaging apparatus according to the third embodiment. The imaging apparatus according to the present embodiment has the same configuration as the imaging apparatus according to the first embodiment except for the following points.

  In the example shown in this figure, a dose measuring unit 530 is disposed outside the container 10. The dose measuring unit 530 measures the dose. The dose measurement unit 530 may be disposed inside the container 10. The controller 300 can determine whether or not the integrated dose of the MOSFET 100 is greater than or equal to a reference value based on the measurement result of the dose measurement unit 530. Then, the control unit 300 controls the voltage application unit 200 based on the determination result.

Example 4
FIG. 10 is a diagram illustrating the configuration of the imaging apparatus according to the fourth embodiment. The imaging apparatus according to the present embodiment has the same configuration as the imaging apparatus according to the first embodiment except for the following points.

  In the example shown in this drawing, the noise measuring unit 540 is electrically connected to the conversion film 24. The noise measurement unit 540 measures the current flowing through the conversion film 24 when the electrons from the electron source 30 are not irradiated on the conversion film 24. When the conversion film 24 is not irradiated with radiation, normally, no current flows through the conversion film 24 unless the conversion film 24 is irradiated with electrons. On the other hand, when the conversion film 24 is irradiated with radiation, a current flows through the conversion film 24 even if the conversion film 24 is not irradiated with electrons. For example, the control unit 300 calculates the integrated value of the current measured by the noise measurement unit 540. Thereby, the control part 300 can judge whether the integrated dose of MOSFET100 is more than a reference value. Then, the control unit 300 controls the voltage application unit 200 based on the determination result.

  As mentioned above, although embodiment and the Example were described with reference to drawings, these are illustrations of this invention and can also employ | adopt various structures other than the above.

DESCRIPTION OF SYMBOLS 10 Container 20 Transparent substrate 22 Transparent electrode 24 Conversion film 30 Electron source 32 Electron emission layer 34 Electron emission source 36 Emission site 40 Acceleration electrode 100 MOSFET
110 Semiconductor layer 112 Substrate 114 Insulating layer 116 SOI substrate 120 Element isolation film 132 First conductivity type region 134 Drain region 136 Source region 142 Gate insulating film 144 Gate electrode 152 Drain electrode 154 Source electrode 160 Insulating layer 162 Contact 200 Voltage application unit 300 Control unit 400 Scan unit 410 X scan unit 420 Y scan unit 510 Current measurement unit 520 Image generation unit 530 Dose measurement unit 540 Noise measurement unit

Claims (15)

A semiconductor device for driving an electron radiation source,
A MOSFET electrically connected to the electron radiation source ;
A voltage applying unit capable of applying a first voltage for generating a tunnel current in the gate insulating film of the MOSFET between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed;
A semiconductor device comprising: The semiconductor device according to claim 1,
The voltage application unit applies the first voltage at a timing when no voltage is applied between the drain electrode and the source electrode of the MOSFET. The semiconductor device according to claim 2 ,
When the first voltage is V1, and the breakdown voltage between the gate electrode and the semiconductor layer is VB,
A semiconductor device satisfying 0.65 ≦ V1 / VB ≦ 0.85.   The semiconductor device according to claim 1,
  The electron emission source is a semiconductor device that is a pixel of an imaging device. A conversion film that converts electromagnetic waves or particle beams into electric charges;
An electron emission source facing the conversion film;
A semiconductor device for driving the electron emission source;
With
The semiconductor device includes:
A MOSFET electrically connected to the electron radiation source;
A voltage applying unit capable of applying a first voltage for generating a tunnel current in the gate insulating film of the MOSFET between the gate electrode of the MOSFET and the semiconductor layer in which the MOSFET is formed;
An imaging apparatus comprising: The imaging apparatus according to claim 5,
The imaging apparatus, wherein the voltage application unit applies the first voltage at a timing when no voltage is applied between the drain electrode and the source electrode of the MOSFET. In the imaging device according to claim 5 or 6,
Comprising a plurality of said electron emission sources;
Each of the plurality of electron emission sources is electrically connected to the different MOSFETs, and is arranged at any of a plurality of lattice points in m rows and n columns (m and n are each an integer of 2 or more),
The semiconductor device includes a scanning unit that operates the MOSFET electrically connected to the electron emission source,
The scanning unit sequentially selects the plurality of rows, sequentially selects the electron emission sources included in the selected row, operates the MOSFETs electrically connected to the selected electron emission sources in order,
The voltage application unit may be configured such that the scanning unit finishes the operation of all the MOSFETs included in one row and starts the operation of the MOSFET included in the next row. An imaging device that applies a voltage. In the imaging device according to any one of claims 5 to 7,
An imaging apparatus comprising: a control unit that determines whether or not an integrated dose of radiation incident on the MOSFET is greater than or equal to a reference value, and that controls the voltage application unit based on the determination result. The imaging device according to claim 8,
A current measuring unit for measuring a current flowing between the drain region and the source region of the MOSFET;
The said control part is an imaging device which judges whether the said integrated dose is more than the said reference value based on the measurement result of the said electric current measurement part. The imaging device according to claim 9,
The control unit is an imaging apparatus that changes a length of application time of the first voltage by the voltage application unit according to a measurement result of the current measurement unit. The imaging device according to claim 8,
Read an electric current flowing through the conversion film, comprising an image generation unit that generates an image based on the current,
The said control part is an imaging device which judges whether the said integrated dose is more than the said reference value based on the disturbance of the said image which the said image generation part produced | generated. The imaging device according to claim 8,
A dose measuring unit for measuring a dose around the MOSFET;
The said control part is an imaging device which judges whether the said integrated dose is more than the said reference value based on the measurement result of the said dose measurement part. The imaging device according to claim 8,
A noise measuring unit for measuring a current flowing through the conversion film when the conversion film is not irradiated with electrons from the electron emission source;
The said control part is an imaging device which judges whether the said integrated dose is more than the said reference value based on the measurement result of the said noise measurement part.   A semiconductor device that drives a radiation source that radiates the electromagnetic wave or the particle beam to a conversion film that converts the electromagnetic wave or the particle beam into an electric charge,
  The semiconductor device includes:
    A semiconductor device comprising a tunnel current generating means for generating a tunnel current in a gate insulating film of a MOSFET electrically connected to the radiation source.   An imaging apparatus comprising the semiconductor device according to claim 14.

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