JP4234303B2 - Radiation detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation detector used for capturing a radiographic image, and more particularly to a small-sized radiation detector for dental use or the like used by being inserted into an oral cavity.
[0002]
[Prior art]
An X-ray image sensor using a CCD instead of an X-ray photosensitive film has been widely used as a medical X-ray diagnostic apparatus. In such a radiation imaging system, two-dimensional image data based on radiation is acquired as an electrical signal using a radiation detection element having a plurality of pixels, and this signal is processed by a processing device and displayed on a monitor. . A typical radiation detection element has a mechanism in which a scintillator is disposed on a photodetector arranged in one or two dimensions, and incident radiation is converted into light by the scintillator and detected.
[0003]
International Publication WO98 / 36291 discloses a radiation detector using CsI as a scintillator material and having a protective film made of parylene or the like for preventing the scintillator from absorbing moisture. In this radiation detector, the bonding pad is exposed from the protective film, and the image signal is read by connecting the bonding pad and external wiring.
[0004]
[Problems to be solved by the invention]
By the way, in a radiation detector that is inserted into the oral cavity for use in dentistry or the like, the entire detector must be reduced in size, while the imaging area needs to be as large as possible. When such a configuration is adopted in such a small radiation detector, if the light receiving part is enlarged, the distance from the bonding pad becomes narrow, and it becomes difficult to form a protective film and connect to external wiring. Workability deteriorates.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a radiation detector that achieves both a reduction in size and an increase in imaging area, is easy to manufacture, and can ensure durability.
[0006]
In order to solve the above problems, a radiation detector according to the present invention includes (1) a light receiving unit in which a plurality of photoelectric conversion elements are arranged, and an edge of the same surface as the light receiving surface of the light receiving unit. A solid-state imaging device including an electrode pad electrically connected to the device; (2) an external connection electrode portion disposed on one surface side; and the other surface side electrode portion, a base which have the electrode pads are electrically connected, and the solid-state image sensor with placing toward the opposite surface as the light-receiving surface of the solid-state image pickup element on the other surface side of the mounting on the surface A base on which the electrode pads of the base are placed facing each other and fixed; (3) a scintillator formed on the light receiving surface of the solid-state image sensor; and (4) a solid-state image sensor and a base. response and wiring for electrically connecting the electrode pads to each other by wire bonding to, (5) Shin With sealing the regulator, a first organic film electrically insulating is formed to cover the wiring with both of the electrode pads, (6) And a metal thin film formed on the first organic film.
[0007]
In the radiation detector according to the present invention, a solid-state image sensor is mounted and fixed in advance on a base having an electrode portion for external connection, and each electrode pad of the base and the solid-state image sensor is electrically connected by wiring. After the connection, a scintillator is formed on the surface of the light receiving unit of the solid-state imaging device, the surface of the scintillator, the wiring, and both electrode pads are covered with a first organic film, and a metal thin film is formed thereon. Therefore, it is easy to form a line for electrical connection to the outside, and workability is improved. For this reason, in a small radiation detection element, it becomes easy to form a light receiving part as large as possible. Further, since the first organic film seals the scintillator, moisture resistance can be ensured. Further, since the organic film covers and protects the electrode pads and the wiring, the disconnection of the wiring can be effectively prevented. Although the metal thin film formed on the first organic film further improves the moisture resistance, a short circuit is caused by the presence of the electrically insulating first organic film between the metal thin film and the wiring and electrode pads. Is prevented.
[0008]
A second organic film formed on the metal thin film may be further provided. The durability of the protective film is further improved by covering the metal thin film with an organic film.
[0009]
Moreover, you may further provide the protective resin which covers wiring from the 1st organic film or the 2nd organic film . Thereby, the protection from the short circuit and the disconnection of the wiring is further ensured.
[0010]
The first organic film may cover the base surface. The moisture resistance is further ensured by covering the base surface with the first organic film.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted. In addition, the dimensions and shapes in each drawing are not necessarily the same as actual ones, and some parts are exaggerated for easy understanding.
[0012]
FIG. 1 is a perspective view showing an embodiment of a radiation detector according to the present invention, FIG. 2 is an enlarged view thereof, and FIG. 3 is a sectional view thereof. In the radiation detector 100 of this embodiment, a solid-state imaging device 2 is placed on a ceramic base 1. The base 1 has a recess 10 on the surface where the solid-state imaging device 2 is placed and accommodated, and a plurality of electrode pads 11 are arranged along one side of the surface in contact with the recess 10. These electrode pads 11 are electrically connected to an external connection electrode terminal 12 disposed on the back surface of the base 1 by a wiring 13 penetrating the base 1.
[0013]
The solid-state image sensor 2 is composed of a CCD image sensor, and photoelectric conversion elements 21 are arranged to form a light receiving portion. Each photoelectric conversion element 21 is electrically connected to the corresponding electrode pad 22 among the electrode pads 22 arranged on one side of the solid-state imaging element 2 by a signal line (not shown). The solid-state imaging device 2 is placed on the base 1 so that the corresponding electrode pads 11 and 22 are close to each other, and the corresponding electrode pads 11 and 22 are electrically connected to each other by the wiring 4.
[0014]
A columnar scintillator 3 that converts incident radiation into light in a wavelength band in which the photoelectric conversion element 21 has sensitivity is formed on the light receiving portion of the solid-state imaging element 2. Various materials can be used for the scintillator 3, but Tl-doped CsI or the like having good luminous efficiency is preferable.
[0015]
Further, a protective film 5 that covers the surfaces of the solid-state imaging device 2 and the base 1 is formed. The protective film 5 is X-ray transparent and blocks water vapor, and from the base 1 side, an electrically insulating first organic film 51, a metal thin film 52, and an electrically insulating second organic film 53. Are laminated.
[0016]
For the first organic film 51 and the second organic film 53, polyparaxylylene resin (trade name Parylene, manufactured by Three Bond Co., Ltd.), particularly polyparachloroxylylene (trade name, Parylene C, manufactured by the same company) is used. preferable. The coating film made of parylene has an extremely low water vapor and gas permeation, has high water repellency and chemical resistance, has excellent electrical insulation even in a thin film, and is transparent to radiation and visible light. , 53 has excellent characteristics suitable for it. As the metal thin film 52, a metal thin film such as gold, silver, or aluminum can be used. The metal thin film 52 serves as a mirror that increases the detection sensitivity of the detector by reflecting the light emitted from the scintillator 3 toward the radiation incident surface rather than the solid-state imaging device 2 side.
[0017]
A protective resin layer 6 is formed so as to further cover and enclose the electrode pads 11 and 22 and the protective film 5 in the wiring 4 portion. As this protective resin layer 6, a resin having good adhesion to the protective film 5, for example, WORLD ROCK No.801-SET2 (70,000 cP type) manufactured by Kyoritsu Chemical Industry Co., Ltd., which is an acrylic adhesive, is used. preferable.
[0018]
Next, the manufacturing process of the radiation detector according to the present invention will be specifically described with reference to FIGS. First, a base 1 as shown in FIG. 4 is prepared. The base 1 has an electrode terminal 11 arranged on the back surface with an electrode terminal 12 for external connection on the front surface, and protrudes to the front surface on two opposite sides adjacent to one side where the electrode pad 11 is arranged. A guide portion 14 is formed, and a recess 10 is formed in a portion sandwiched between the guide portions 14.
[0019]
The solid-state imaging device 2 is placed in the recess 10 with the light receiving surface of the photoelectric conversion device 21 faced so that the electrode pad 22 faces the electrode pad 11 side of the base 1 and fixed as shown in FIG. To do. At this time, the operation is facilitated by positioning the solid-state imaging device 2 using the guide portion 14. And the electrode pad 11 and the electrode pad 22 are electrically connected by the wiring 4 by wire bonding (refer FIG. 6, FIG. 7).
[0020]
Next, as shown in FIG. 8 and FIG. 9, a scintillator 3 layer is formed by growing CsI doped with Tl as a columnar crystal having a thickness of about 200 μm on the light receiving portion of the solid-state imaging device 2 by vacuum deposition. . CsI is highly hygroscopic and will absorb and dissolve water vapor in the air if left exposed. For protection, CsI is protected by CVD (chemical vapor deposition) as shown in FIG. The entire base 1 with the solid-state imaging device 2 on which the scintillator 3 is formed is wrapped with parylene having a thickness of 10 μm to form a first organic film 51.
[0021]
Specifically, the coating is performed by vapor deposition in the same manner as metal vacuum vapor deposition. The raw material diparaxylylene monomer is thermally decomposed and the product is quenched in an organic solvent such as toluene or benzene. A process for obtaining diparaxylylene called a dimer, a process for thermally decomposing the dimer to generate a stable radical paraxylylene gas, and a gas having a molecular weight of about 500,000 by adsorbing and polymerizing the generated gas on the material. It consists of the process of polymerizing the xylylene film.
[0022]
Although there is a gap between CsI columnar crystals, since parylene enters the narrow gap to some extent, the first organic film 51 is in close contact with the scintillator 3 layer and seals the scintillator 3. In addition, the first organic film 51 is formed not only on the surfaces of the electrode pads 11 and 22 but also around the wiring 4 that connects them, and covers the wiring 4. As a result, the adhesive strength and mechanical strength of the wiring 4 are increased, so that the wiring 4 can be easily handled in the subsequent steps. By this parylene coating, a precise thin film coating having a uniform thickness can be formed on the surface of the three-layered scintillator layer. Also, parylene CVD is easier to process because it has a lower vacuum than metal deposition and can be performed at room temperature.
[0023]
Subsequently, as shown in FIG. 11, a metal thin film 52 is formed by laminating an Al film having a thickness of 0.15 μm on the incident surface side surface of the first organic film 51 by vapor deposition. When forming the metal thin film 52, an appropriate mask (not shown) is disposed in front of the scintillator 3 layer, and the metal thin film 52 is formed only on the first organic film 51 immediately above the scintillator 3 layer. It is desirable to form. However, even when a mask is disposed, metal vapor may slightly wrap around the mask during vapor deposition. For this reason, particularly when the distance between the light receiving portion and the electrode pad is narrow, it is difficult to form the metal thin film 52 only on the portion directly above the scintillator 3 layer. It may be deposited. According to the present invention, since the wiring 4 and the electrode pads 11 and 22 are covered with the first organic film 51, the metal thin film 52 is not directly formed on the wiring 4 and the electrode pads 11 and 22, A short circuit between the wiring 4 and the electrode pads 11 and 22 due to the metal thin film 52 can be effectively prevented.
[0024]
In addition, when the metal thin film 52 is deposited, the metal thin film 52 is formed up to the wiring 4 and the electrode pads 11 and 22 even when the mask is not disposed, but the wiring 4 and the electrode pads 11 and 22 are the first. Since this is covered with the organic film 51, a short circuit is prevented. Further, by forming the metal thin film 52 in a wide area covering the wiring 4 and the electrode pads 11 and 22 via the first organic film 51, the moisture resistance can be further improved.
[0025]
Then, the second organic film 53 is formed by covering the entire surface of the substrate with a thickness of 10 μm by CVD again (see FIG. 12). The second organic film 53 is for preventing contamination and peeling due to handling of the metal thin film 52 and deterioration due to oxidation. Thus, the protective film 5 formed by laminating the first organic film 51, the metal thin film 52, and the second organic film 53 is formed.
[0026]
When the metal thin film 52 is also formed on the wiring 4 and the electrode pads 11 and 22 via the first organic film 51, the metal thin film 52 and the second organic film 53 are not only the surface of the electrode pads 11 and 22, but both Is formed around the wiring 4 connecting the two, and the wiring 4 is triple-coated together with the first organic film 51, so that the mechanical strength and adhesive strength of the wiring 4 can be further increased. . Further, when the metal thin film 52 is formed using the mask as described above, a double coating of the first organic film 51 and the second organic film 53 is formed around the wiring 4 and on the electrode pads 11 and 22. Will be formed.
[0027]
Subsequently, a protective resin layer 6 is formed by applying and curing a resin so as to wrap the wiring 4 covered with the protective film 5 on the protective film 5 of the electrode pads 11 and 12. The wiring 4 protrudes on the protective film 5 covering the electrode pads 11 and 12, and when the metal thin film 52 is formed on the wiring 4 around the wiring 4, the protective film 5 including the organic films 51 and 53 and the metal thin film 52 is formed. (See FIG. 14). Further, when the metal thin film 52 is not formed on the wiring 4, it is covered with the organic films 51 and 53 (see FIG. 15). In any case, as shown in FIGS. 13 to 15, the protective resin layer 6 wraps around the covered wiring 4 and pots the wiring 4. Thereby, since the wiring 4 is further protected, it is possible to effectively prevent the wiring 4 from being damaged during use. The protective resin layer 6 is not necessarily provided, but is preferably provided for protecting the wiring 4.
[0028]
The protective film 5 on the back surface of the base 1 is removed from the protective film 5 formed after this, and the electrode terminals 12 for external connection provided on the back surface of the base 1 are exposed. The radiation detector shown is obtained.
[0029]
Next, the operation of this embodiment will be described with reference to FIGS. X-rays (radiation) incident from the incident surface side pass through all of the protective film 5, that is, the second organic film 53, the metal thin film 52, and the first organic film 51, and reach the scintillator 3. The X-rays are absorbed by the scintillator 3 and light proportional to the amount of X-rays is emitted. Of the radiated light, the light traveling in the X-ray incident direction passes through the first organic film 51 and is reflected by the metal thin film 52. For this reason, almost all the light generated in the scintillator 3 enters the photoelectric conversion element 2. For this reason, efficient and highly sensitive measurement is possible.
[0030]
In each photoelectric conversion element 2, an electrical signal corresponding to the amount of visible light is generated by photoelectric conversion and accumulated for a certain period of time. Since the amount of visible light corresponds to the amount of incident X-rays, that is, the electric signal accumulated in each photoelectric conversion element 2 corresponds to the amount of incident X-rays. An image signal corresponding to the line image is obtained. This image signal accumulated in the photoelectric conversion element 2 is finally output sequentially from the electrode terminal 12 through the electrode pad 22, the wiring 4, the electrode pad 11, and the wiring 13 from a signal line (not shown). X-ray images can be displayed by transferring the data to and processing the data with a predetermined processing circuit.
[0031]
In the above description, the protective film 5 has a structure in which the metal thin film 52 is sandwiched between the organic films 51 and 53 made of parylene, but the materials of the first organic film 51 and the second organic film 53 are as follows. When the metal thin film 52 is made of a material resistant to corrosion, such as gold, the second organic film 53 itself may not be provided.
[0032]
Here, the first organic film 51 has been described as covering the side surface portion of the base 1. However, the first organic film 51 includes at least the entire scintillator 3, the electrode pads 11 and 22, and the wiring 4. It is not necessary to cover other parts of the base 1. However, in the case where the surface of the base 1 is covered, the edge portion of the first organic film 51 is in close contact with the base 1 so that the peeling of the first organic film 51 from the edge portion can be effectively prevented. Therefore, it is preferable.
[0033]
Further, the solid-state imaging device 2 may be formed of an amorphous silicon photodiode (PD) array and a thin film transistor (TFT), or may be a MOS type image sensor.
[0034]
By adopting such a configuration, the thickness of the radiation detector can be reduced to about 2.5mm, which is about half that of the 5.0mm thickness of the conventional radiation detector with FOP (fiber optical plate). It became. In addition, by reducing the distance between the bonding pad and the light receiving part, the area around the light receiving part can be reduced while securing the same light receiving part area as the conventional product (Japanese Patent Laid-Open No. 10-282243). Since the entire area can be reduced, a compact radiation detector (about 90% of the conventional product) can be realized. This is a great advantage in a dental radiation detector used by being inserted into the oral cavity.
[0035]
【The invention's effect】
As described above, according to the present invention, the scintillator formed on the surface of the light receiving unit of the solid-state image sensor, the electrode pads of both the solid-state image sensor and the base on which the solid-state image sensor is mounted, and the two are electrically connected. The wiring to be covered is covered with an organic film, and a metal thin film is formed thereon. Therefore, it is easy to form a line for electrical connection with an external circuit, and workability is improved. In addition, in a small radiation detection element, it becomes easy to form a light receiving portion as large as possible. Furthermore, the organic film seals the scintillator to ensure the moisture resistance of the scintillator, and the organic film also covers and protects the electrode pads and the wiring, thereby effectively preventing the wiring from being disconnected. The metal thin film formed on the organic film further improves the moisture resistance of the scintillator. However, an electrical insulating organic film is interposed between the metal thin film, the wiring, and the electrode pad, so that a short circuit is effective. Is prevented.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a radiation detector according to the present invention.
FIG. 2 is a partially enlarged view of FIG.
FIG. 3 is a side view showing an embodiment of a radiation detector according to the present invention.
4 is a perspective view of a base used in the apparatus of FIG. 1. FIG.
FIG. 5 is a side view for explaining a manufacturing process of the apparatus of FIG. 1;
6 is a side view for explaining a step subsequent to the step of FIG. 5. FIG.
FIG. 7 is a perspective view illustrating the step of FIG. 6;
FIG. 8 is a side view for explaining the next step of the step of FIG. 6;
FIG. 9 is a perspective view for explaining the step of FIG. 8;
10 is a side view for explaining the next step of the step of FIG. 8. FIG.
11 is a side view for explaining the next step of the step of FIG.
12 is a side view for explaining the next step of the step of FIG. 11. FIG.
FIG. 13 is a side view for explaining the next step of the step of FIG.
14 is an enlarged cross-sectional view of a wiring portion in FIG.
FIG. 15 is an enlarged cross-sectional view of a portion corresponding to FIG. 14 in another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Solid-state image sensor, 3 ... Scintillator 4, 13 ... Wiring, 5 ... Protective film, 6 ... Protective resin layer, 10 ... Recessed part, 11, 22 ... Electrode pad, 20 ... Substrate, 21 ... Photoelectric Conversion element, 51, 53 ... organic film, 52 ... metal thin film.

Claims (5)

A solid-state imaging device comprising: a light- receiving unit in which a plurality of photoelectric conversion elements are arranged; and an electrode pad arranged along the edge of the same surface as the light-receiving surface of the light-receiving unit and electrically connected to the photoelectric conversion element; ,
And electrode portions for external connection is disposed on one surface side, it is arranged on the other surface side, a base on which to have a an electrode pad the being the electrode portion electrically connected to, the solid A base on which the element is placed with the surface opposite to the light receiving surface facing the placement surface on the other surface side, and the solid-state imaging device and each electrode pad of the base are fixed facing each other ; ,
A scintillator formed on the light receiving surface of the solid-state imaging device;
And wiring electrically connected by the solid-state imaging device and the corresponding electrode pads to each other the wire bonding of the base,
Sealing the scintillator and electrically insulating first organic film formed so as to cover both the electrode pad and the wiring;
A metal thin film formed on the first organic film;
Radiation detector.   The radiation detector according to claim 1, further comprising a second organic film formed on the metal thin film. The radiation detector of claim 1, further comprising a protective resin which covers the wiring over the first organic layer. The radiation detector according to claim 2, further comprising a protective resin that covers the wiring from above the second organic film. It said first organic film radiation detector according to any one of claims 1 to 4, which covers the base surface.

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