JPS6030059B2 - Electron impact multiplier using solid-state image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an electron impact intensifier tube using a collective image sensor.

[Prior art and its problems] Solid-state image sensors are being used one after another in the application fields of image pickup tubes.

Another special use of ordinary imaging cameras is their application to electron impact multiplier tubes. As shown in FIG. 1, the photoelectrons 2 emitted by the optical image incident on the photocathode 1 are accelerated by the electric field formed by the electrode 3, concentrated, and incident on the solid-state image sensor 4, resulting in a large number of photoelectrons due to the electron enhancement effect. Converts into an electron-hole pair.
In a solid-state image sensor, this corresponds to the incident of photoelectrons from an electron beam instead of normal incident light, and the converted signal charges (usually electrons) are collected in a potential well and read out after a certain period of time. In this type of electron impact multiplier tube 5, a frame transfer type CCD is usually used as the solid-state image sensor 4. By changing the photocathode to one for X-rays or radiation, it can be used not only for optical images but also for X-ray or radiation images.
FIG. 2 shows a vertical sectional view of a conventional example of a frame transfer type CCD used in an electron impact intensifier tube.

The electron beam 6 is made incident on the back surface of the frame transfer type CCD. Here, the back surface refers to the transfer electrodes 7, 2, and 3 of the CCD.
, 4 is not formed on the Si substrate 8 side. The incident electrons form electron-hole pairs in the Si substrate due to electron impact, and signal charges are accumulated in the potential well 9 indicated by the dotted line and read out after a certain period of time. Since it is a back-illuminated type, if the Si substrate is thick, the probability that generated electrons will recombine with holes within the substrate before reaching the potential well increases, resulting in poor sensitivity. Furthermore, since the generated electrons diffuse in various directions, they also reach adjacent potential wells or potential wells slightly distant, resulting in a disadvantage that the resolution deteriorates. In order to eliminate these drawbacks, a method has been adopted in which the back surface of the Si substrate is etched like the etched surface of a Si vidicon to make it thin as shown in FIG. The surrounding area is left unetched for reinforcement purposes. Although this method can improve the drawbacks in terms of sensitivity and resolution, it cannot be said to be perfect. Furthermore, new drawbacks arise, such as the need for advanced technology to remain thin, and the fact that the substrate is easily bent due to the effects of distortion on the transfer electrode side. The potential wells are normally formed under two of the four transfer electrodes 7-1, 2, 3, and 4.

In FIG. 2, they are formed under two electrodes 7-1 and 7-2. In the case of jump scanning, potential wells are formed under two electrodes 7-3 and 7-4 in the next field. In standard television systems, the number of pixels corresponding to 256 scanning lines in each field in the vertical direction is formed by potential wells. FIG. 3 shows an overall configuration diagram of a frame transfer type CCD.

Each pixel in FIG. 2 is horizontally separated by a channel stopper 11 and vertically separated by a potential well of a transfer electrode. In the first A field, a potential well is formed in the portions A-1 to A-256 of the image section 12, and the signal charge is vertically transferred to the storage section 13 at high speed during the vertical blanking period, and then is transferred to the storage section 13 corresponding to one horizontal scanning line. The signal is transferred to the horizontal transfer register 14. The signal is read out to the outside through the output section 15 by horizontal transfer.
On the other hand, in order to accumulate the B field signal after the vertical transfer of the A field signal, the B-1 of the image section 12 is
A potential well is formed in ~B-256, and the same operation as in the A field is repeated.

In such a frame transfer type CCD, since the same number of pixels are formed in the image section and the storage section, the chip area becomes large, and when applied to an electron impact multiplier, the space occupancy rate becomes high. Current frame transfer type CCDs that are compatible with standard imaging methods are 500V x 340 day pixels and 500V narrow channel frame transfer type CCDs.
Although it has 570 pixels, its resolution is still nowhere near that of an image pickup tube. To achieve this, it is necessary to increase the number of pixels, but
This cannot be achieved without advances in manufacturing technology such as BI. [Objective of the Invention] The present invention improves the drawbacks of the above-mentioned conventional electron impact multiplier tube using an image pickup device, and provides an electron impact multiplier tube capable of reproducing high-resolution images. The purpose is to

[Summary of the invention]

The present invention uses a solid-state imaging device having discrete effective areas for incident electron beams, and captures electron beams emitted from a photocathode at appropriate times in accordance with optical images, X-ray images, or radiation images. This is an electron impact intensifier tube that has the function of deflecting the beam in a desired direction.

That is, in the first signal reading period, signals corresponding to discrete effective areas are read, and in the next signal reading period, the electron beam is deflected to enable the electron beam that was incident on the invalid area in the previous signal reading. By guiding the signal to the area and converting the signal, the number of pixels is increased in a pseudo manner, and the resolution is increased. [Effects of the Invention] Conventional solid-state imaging devices usually have a pixel count of 500V x 400 days, which has a lower resolution limit than that of an image pickup tube, but according to the present invention, the resolution is equivalent to imaging with at least twice the number of pixels. A marginal resolution equivalent to or better than that of an image pickup tube can be obtained.

Therefore, high-resolution reproduced images required especially in medical X-ray imaging can be obtained by the present invention. Furthermore, since a solid-state image sensor is used, it is possible to reproduce high-quality images without image retention or burn-in.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows an example of an interline transfer type CCD which is a solid-state image sensing device which is an important component of the present invention and has been improved for the purpose of the present invention. The figure shows a horizontal cross-section. Each pixel is composed of photodiodes 22a, b, c consisting of n-type regions formed on a p-type Si substrate 21 by diffusion or ion implantation, and vertical transfer CCDs 23a, b, c.

Transfer electrodes 24 made of poly-Si or the like are arranged on the vertical transfer CCDs 23a, b, and c. The figure shows an example of a two-layer poly-Si electrode. The poly-Si electrode 24 is electrically isolated from the substrate 21 by an insulating film 25 such as Si02. In a conventional solid-state image sensor for photoelectric conversion, photodiodes 22a, b, and c, which are transparent to light and serve as photosensitive parts, are formed in an insulating film.
It is also formed on top. However, in the present invention, the insulating film on the photodiode is removed over a desired area for each pixel by etching, and the n-type region is exposed and opened.
Department. In the figure, the opening □ is etched as vertically as possible, and then a thin mountain film is deposited over the entire surface. On the photodiode, the exposed n-type Si surface protection AI film 26
, a, b, and c, and on the insulating film 25 becomes an antistatic mountain film 27 as described later. The electron beam emitted from the photocathode is accelerated and reaches the interbody image sensor, but the electrons 28-1 that enter the closed part pass through the thin AI films 26a, b, and c and directly enter the photodiode part. The electron bombardment generates a large number of electron-hole pairs.

Electrons generated as signal charges are effectively stored in the photodiode section. On the other hand, the electrons 28-2 of the electron beam that reach areas other than the opening do not enter the Si substrate and become invalid signals. The AI film in the ineffective area prevents the effect of electrons accumulating in this area and becoming electrically charged, which obstructs the subsequent arrival of the incident beam. The accumulated signal charges are transferred to the vertical transfer CCD 23a after a certain period of time.
,b,c.

FIG. 5 shows the overall structure of an interline transfer type CCD. In the figure, over slow drain is omitted. P, . ~ PMN' photodiodes and field shift from those photodiodes.
Vertical transfer CCDs C to CM for reading signal charges transferred by the gate 31 mainly constitute an image section. The signal charges of the vertical CCD are transferred to the horizontal CCD register 32 for each stage corresponding to a horizontal scanning line, transferred into the register during the horizontal valid period, and sequentially read out from the output section 33. In addition, field shift gate 3
1 uses a part of the poly-Si electrode 24 shown in FIG. FIG. 6 is an explanatory diagram of the configuration of one pixel in the improved interline transfer type CCD of FIGS. 4 and 5. FIG.

A CD 42 is provided by vertical transfer adjacent to the entrance part 41 which is an effective area for the electron beam. The hatched portion other than the open circle portion becomes an invalid portion 43 for signal conversion. FIG. 7 shows an electron impact multiplier according to the present invention. Photoelectrons 52 emitted by the optical image incident on the photocathode 51 are accelerated by the electric field formed by the electrode 53, focused, and incident on the solid-state image sensor 54, where they are converted into a large number of electron-hole pairs by the electron multiplication effect. do. The Kameko impact multiplier tube of the present invention differs from the conventional tube shown in FIG. 1 in that it is provided with a deflection electrode 55 and is controlled by a deflection pulse 56, as shown in FIG. The operation of this deflection electrode will be explained in conjunction with the operation of the solid-state image sensor with reference to FIG. FIG. 8a shows a unit pixel of the improved interline transfer type CCD, in which the hatched area shows the area ineffective against the electron impact effect, and the white area shows the open area which is the effective area.

In the first field, A field, a deflection voltage is applied to the deflection electrode as shown in Figure b. EF is not applied, and at this time, the electron beam image shown in c in the figure is irradiated onto the pixel in a in the figure. After the accumulation between fields A, the signal obtained from the pixel by applying VH to the field shift gate voltage (FsG) and transferring it as shown in d of the same figure is the white of the monochrome image, as shown in e of the same figure. will be the corresponding value. When entering the next B field, a voltage VM' is applied to the deflection voltage HoEF of the deflection electrode to deflect the electron beam in the horizontal direction. This operation causes the electron beam image from the light masking surface to move in the horizontal direction. If the voltage value of VM' is set appropriately and the signal is accumulated by shifting it to the right by half a pixel as shown in the figure f, the signal obtained after being transferred by the field shift gate of the B field is As shown in g in the figure, is a value corresponding to black and white, which was not obtained in the previous A field. In the reproduced image, the positional shift of the B field signal is adjusted as shown by the dotted arrow, and a black and white image is obtained as shown in h' in the figure. Note that the movement is between 0 and VM' in HoEF, but 1
It is clear that it can be considered that the center is at /2VM' and moved left and right. Further, when moving the electron beam image, an electronic shield may be used to prevent the electron beam from reaching the solid-state image sensor. Although the number of pixels in the horizontal direction has been pseudo-doubled, in order to comply with the normal standard television system, the signal readout method for pixels in the vertical direction has been changed to a field accumulation type interline transfer type CCD.
It is necessary to make it a movement. That is, in FIG. 5, reading of the A field is performed by P, . and P′, . ,P,
2 and P', 2, . . . , the signals of the two pixels shown by the solid line at the right end are read out. In the B field, P', . and P, 2, P', 2 and P, 3...
・Read out the signals of the two pixels indicated by the dotted line at the right end.
With the electron impact multiplier tube of the present invention, the limit resolution determined by the number of horizontal pixels of a conventional solid-state image sensor can be doubled at once.

High-resolution changes when twice as many pixels are forcibly incorporated in the horizontal direction using VLSI technology will result in closed area and vertical transfer CC.
While the area of D is halved and the sensitivity and dynamic range are halved, the present invention eliminates these drawbacks and can easily achieve high resolution. Another advantage is that the external circuit for the solid-state image sensor can be almost the same as the conventional one. A major feature of the present invention is that information in a portion conventionally discarded as an invalid area is effectively utilized. [Other Embodiments of the Invention] In FIG. 8, the electron beam image is moved in the horizontal direction in a pulsed manner with a rectangular wave, but the method of movement may also be the method shown in FIGS. 9 to 11 below. .

That is, Fig. 9 shows an example of movement using a triangular wave, and Fig. 9a shows Fsc, Fig. 9b shows HoEF, and Fig. 10a and b.
11A and 11B are examples of moving in a trapezoidal manner, and FIGS. 11a and 11b are examples of moving in a sine wave. In either case, we will show an example of swinging left and right, taking into account the center of movement.
This is an example in which the timing of transfer by the gate is the center of movement. Furthermore, FIGS. 12a and 12b are examples in which a triangular wave is used as in FIG. 9, but the timing of transferring the accumulated signal charges is shifted from the center of movement.

Due to the timing shift, the sensitivities of the left and right pseudo pixels increase, and there is an advantage that an image with fewer pseudo signals can be obtained.
Shifting the timing of transfer is not only applicable to triangular waves, but can also be applied to trapezoidal and sine wave vibrations, although there are differences in degree.
It is important to set the movement distance of the electron beam image in FIG. 8 and subsequent figures so that the pseudo pixels are arranged at an equidistant distance from each other in order to make the reproduced image easier to see.

The same can be said for movement not only horizontally but also in various directions described below. FIG. 13a shows an example in which the electron beam image is moved in an oblique direction.

Horizontal deflection HoEF in figure b and vertical deflection V Cape F in figure c.
synchronize and move diagonally to read out signals from each location. Four pixels are arranged in a checkered pattern, which has the advantage of doubling the number of pixels both horizontally and vertically. Signals can be read out using the method described in FIG. 8, or by modifying the vertical transfer CCD so that signals can be read out from each pixel in each field, an extremely high-resolution image can be obtained. FIGS. 14a to 14d are examples in which the effective gateway portions are pseudo-sensitized at four locations in the pixel, and the electron beam images are deflected horizontally and vertically. In the A field, the horizontal is VM and the vertical is -VN so that the bottom right of the pixel is the effective part.
Apply a polarized voltage of
At the same time as the data is transferred by the shift gate, the vertical deflection voltage is switched to VN to move the effective part to the upper right of the pixel, making it a B field. Repeat the same operation until the top left of the pixel,
Scan the bottom right and return. By this operation, the effective closing part only in the lower right shown in figure a is increased to 4 in total as shown in figure e.
It becomes a pixel and enables high-resolution imaging. Figure e shows how pseudo pixels are equally distributed horizontally and vertically, taking into account adjacent pixels. In this method, one frame is made up of four fields A to D, unlike the standard television system. If there is no large movement in the captured image, one field may be set to 1/6 of the usual inkstone sand, but in the case of an image with far movement, it is necessary to adjust the field time appropriately. FIG. 15 shows an example of the operation of the electron impact type image pickup tube of the present invention using an intermittent exposure method, apart from the standard television method.

At the time of the horizontal deflection of the electron beam. EF to VM
, move the pixel to the right. From time t2 to t3
Exposure (Exp) is performed at . This exposure may be performed, for example, by instantaneous exposure to light, X-rays, or a radiation image, or by continuous exposure, and the converted electron beam is constantly
It is also possible to set it as FF and turn it ON only at this time. A signal is accumulated in each pixel in FIG. 5 through this one exposure, and the transfer of the field shift gate at different times is performed by P, . ~Performed at every other pixel in the vertical direction of PMN. After reading all the signals from these pixels, the remaining P', . -PMN' pixel signals are transferred and read out. That is, signal reading is performed twice for one exposure. Furthermore, time t7
In this step, the deflection voltage of the electron beam is set to -VM, and the pixel is moved to the left. Next, exposure is performed at times Ut8 to Ut9, and the time ratios, . and t,2
The signal is read out twice. One frame consists of two exposures and four signal readouts (4 fields), resulting in a high-resolution image.

This method has the effect of preventing deterioration of resolution in the vertical direction due to obtaining signals from two pixels in the vertical direction as described in FIG. Note that the timing of deflection of the electron beam is not limited to the example shown by the solid line, but also the timing t4 and Lo shown by the dashed line.
and t, 6 may also be used. In other words, it is sufficient that the position of the effective pixel is moved during exposure. In FIG. 16, only horizontal positional movement has been explained, but it is clear that the invention can be applied to movement in various directions, including the diagonal movement described in FIG. 13.

In the above embodiments, the solid-state image sensor is explained using the example shown in FIG. 4, but the solid-state image sensor is not limited to this. If so, it can be used for the purposes of the present invention.

Examples of these will be explained with reference to FIGS. 16 to 20.
Fig. 16 is almost the same as the embodiment shown in Fig. 4, but the ineffective signal in the part of the antistatic AI film 27 in Fig. 4 is actively used and guided to the outside to image the incident image. This is an example of an element having a structure that is used as a signal to monitor the brightness of the entire background.

Although the thickness of the antistatic AI film may be used as is, in the example shown in the figure, a thick AI film 61 is used to guide the captured electrons to the outside and feed them back to an accelerating voltage, etc., so that a signal with a constant brightness is always generated. Control what you get. FIG. 17 shows an example in which a thin AI film on a photodiode is extended onto an insulating film to form an AI electrode 62 that defines a pixel.

While the photodiode section exhibits the primary sensitivity due to the electron multiplication effect, the mountain film on the insulating film has no multiplication effect but serves to guide incident electrons to the photodiode section and exhibits secondary sensitivity. At the same time, it also plays a role in preventing static electricity on the insulating film. N
It is clear that the cut in the membrane becomes an ineffective area. 18th
The figure shows a structure known as a so-called two-story solid-state image sensor, in which a photoconductive film 64 such as a-Sj is formed on top of a mountain electrode 63 similar to that in FIG. 17, and a thin transparent electrode 65 is further formed on the top. Form.

The electron beam passes through the transparent electrode 65 and performs electron enrichment in the a-Si photoconductive film 64, and the generated electrons pass through the A1 electrode 63 and are collected in the photodiode. is discharged to. A pixel is defined by a mountain electrode 63, and a-S corresponding to the part without this electrode
j A sufficient electric field is not formed in the photoconductive film 63, and separation of electrons and holes is insufficient, resulting in an ineffective portion as a signal. Note that a thin AI electrode or the like may be used as the transparent electrode 65. FIG. 19 has almost the same structure as FIG. 18, but thick AI electrodes 66 are arranged in a striped or cross-shaped pattern on the a-Si photoconductive film 64 in order to make the ineffective portions more prominent.

Although this is an example in which a low resistance a-Si film 67 formed by glow discharge is used as the electrode for the entire surface, it is clear that the same effect can be obtained even if a cross-shaped electrode is formed on FIG. . FIG. 20 is an example applied to the conventional frame transfer type shown in FIG. 2, in which an ineffective portion is formed by an AI electrode 68 or the like on the electron beam incident side.

The above embodiments mainly use a head of a format such as an interline transfer type CCD or a frame transfer type CCD, in which accumulated signals are vertically transferred from all pixels or half of the pixels at the same time to a CD or a storage section. The body image sensor has been explained.

On the other hand, X-Y
In the case of an address or line address type, the timing of transfer is different for each pixel, and it cannot be used for the purpose of the present invention as easily as the above-mentioned field address or frame address CCD. However, for example, in the intermittent exposure described in FIG. 15, the purpose of the present invention can be achieved by adopting a method of reading out signals at a specific location before the next exposure. Both are hot
Inter transfer type C in that it has separate diode sections.
This is because, in the same device as a CD, there is an effective part and an ineffective part for the video signal with respect to the electron beam. In the embodiment, an example of movement of substantially two pixels in the horizontal, vertical, or diagonal direction was shown, but depending on the television system, movement of three or more pixels may be possible.

In the above embodiment, an example was described in which the deflection of the electron beam was manipulated by an electric field, but the deflection may be performed by a magnetic field from an external coil or the like, or both may be used in combination.

The present invention makes it possible to increase the resolution of images, making it possible to make a significant contribution to medical diagnosis.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an electron impact multiplier tube using a solid-state image sensor, Figure 2 is a cross-sectional view of a conventional solid-state image sensor for an electron impact multiplier tube, and Figure 3 is the element shown in Figure 2. Frame transfer type C
FIG. 4 is a cross-sectional view of one embodiment of the improved interline transfer type CCD solid-state image sensor used in the present invention, FIG. 5 is an overall configuration diagram of FIG. 4, and FIG. 6 is a pixel diagram. 7 is a diagram showing an embodiment of the present invention,
Figures 8a to 8h are explanatory diagrams of the operation of the present invention; Figures 9a and b; Figures 10a and b; Figures 11a and b; Figures 12a and b;
3 a to d, 14 a to e, and 15 are explanatory diagrams of other operation examples of the present invention, and FIGS. 16, 17, 18, 19, and 20 are illustrations of other operation examples of the present invention. FIG. 3 is a cross-sectional view of another embodiment of a solid-state image sensor used for. 21...Si substrate, 22a, b, c...
・Photodiode, 23a, b, c... Vertical transfer CCD, 24... Poly-Si transfer electrode, 25...
Insulating film, 26a'b, c, 27... Mountain film, 28-1, 2
...Electron beam, 31...Field shift gate, 32...Horizontal CCD register, 33...
...Output part, 4 1...Closing part, 42...
...CD for vertical transfer, 43... Invalid part, 51.
...Photocathode, 52...Photoelectron, 53...
...Electrode, 54...Solid-state imaging device, 55...
- Deflection electrode, 56... Deflection pulse, 61...
... Mountain membrane, 62, 63 ... AI electrode, 64 ... a-S
i photoconductive film, 65...transparent electrode, 66...AI electrode, 6
7...Low resistance a-Sj film, 68...AI
electrode. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 16 Figure 13 Figure 14 Figure 15 Figure 17 Figure 18 Figure 19 Figure 20

Claims (1)

[Claims] 1 Electron impact multiplication device having as an output section a solid-state image sensor consisting of an input section that converts an optical image, an X-ray image, or a radiation image into an electron beam image, and a pixel that has a limited section that effectively converts the incident electron beam into a signal. The tube includes means for deflecting the electron beam image in an arbitrary direction at a predetermined time, and the deflection causes the effective component of the pixel to be relative to a portion of the incident electron beam image that has not undergone signal conversion before the deflection. An electron impact multiplier tube using a solid-state image sensor, which is characterized by moving the tube and performing new signal conversion.