JPH0534463A - X-ray image sensor - Google Patents

Abstract

PURPOSE:To obtain a high S/N by providing an array of condensing lenses between a scintilator which converts X-rays into visible rays and an array of photodiodes for detecting the visible rays, and condensing the visible rays. CONSTITUTION:A Ti film is formed on one main face of a glass base 3 by sputtering method and used as a mask to form an array of micro lenses 2 having a refractive index distribution within the base 3. CsI heavily doped with T1 is deposited on the mask to form a scintilator 1. An array 6 of photodiodes for detecting visible rays converted by the scintilator 1 are formed. Incident X-rays 25 are converted into visible rays 26 by the scintilator 1 and condensed by the micro lenses 2 and incident on a photodiode 6' and thereby the rate of signal transmission from the photodiode 6' is increased and also the size of the photodiode 6' can be reduced and so dark currents are decreased and S/N is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image sensor, and more particularly to an X-ray image sensor suitable for medical use with a large S / N ratio.

[0002]

2. Description of the Related Art A conventional X-ray image sensor comprises a scintillator which absorbs X-rays and emits visible light, and an image sensor which is composed of a large number of photodiode arrays which detect the emitted visible light. There is. As the scintillator material, C _S I heavily doped with Tl ions is used. It absorbs X-rays and is excited,
It emits visible light with a wavelength of 560 nm. Visible light from the scintillator is received by an image sensor composed of many photodiode arrays.

[0003]

However, the conventional X-ray image sensor has the following drawbacks.

(1) Since the photodiodes of the X-ray image sensor need to be insulated and separated from each other, and a signal extraction electrode and a thin film transistor as a switching element for signal reading must be provided from the photodiodes, the effective light reception of the photodiodes is required. The emission area ratio of the scintillator that the photodiode should cover with respect to the area (hereinafter,
The aperture ratio) is 0.5 or less. Therefore, since all the X-ray optical signals exchanged with visible light in the scintillator do not reach the photodiode, a large signal cannot be output.

(2) In the photodiode of the X-ray image sensor, dark current (current flowing through the photodiode when there is no input signal) increases when the light receiving area of the photodiode is increased. When used as an X-ray image sensor, a weak X-ray optical signal is detected, so that the S / N ratio cannot be increased even if the light receiving area of the photodiode is increased.

(3) The incident X-rays may not be completely absorbed in the scintillator, and reach the sensor unit where the photodiodes and thin film transistors are integrated, which deteriorates the photodiodes and thin film transistors.

[0007]

The present invention has been made to solve the above problems, and the present invention is to provide a scintillator for converting X-rays into visible light and a photodiode for detecting the converted visible light. In an X-ray image sensor provided with an array, a condensing lens array is provided between the scintillator and the photodiode array, and visible light from the scintillator is provided on the light-receiving surface of each photodiode constituting the photodiode array. It is an X-ray image sensor configured to collect light.

In the present invention, the condenser lens array has a large number of minute lenses embedded in a flat transparent plate.
Further, the scintillator can be provided on one surface of the flat plate transparent plate in which the microlenses are embedded.

Further, in the present invention, the visible light from the scintillator is condensed on the other surface of the flat transparent plate, and the light receiving surface of the photodiode is arranged at the light collecting point on the other surface of the flat transparent plate. It is possible to provide a photodiode array in which is formed.

Furthermore, in the present invention, the diameter of the microlenses embedded in the flat transparent plate varies depending on the pitch of the photodiodes, but is usually 100 μm to 400 μm.
The size of the light receiving surface of each photodiode of the photodiode array is 20 μm × 20 μm.
m to 150 μm × 150 μm, especially 50 μm × 50 μm
Before and after is preferable.

[0011]

According to the present invention, since the light emitted from the scintillator is condensed by the condenser lens array and is incident on each photodiode of the photodiode array, a substantial aperture ratio can be obtained even if the light receiving area of the photodiode is reduced. Since it can be increased and the dark current of the photodiode can be reduced, the S / N ratio is dramatically improved.

Further, according to the present invention, since the condenser lens array is provided between the scintillator and the photodiode, the X-rays transmitted through the scintillator are absorbed by the condenser lens array etc., and the X-rays of the photodiode are absorbed. The characteristic deterioration due to irradiation is small, and the reliability of the X-ray image sensor is improved.

[0013]

EXAMPLES Examples of the present invention shown in FIGS. 1 and 3 will be described below. First, the glass substrate 3 with the minute lenses 2 embedded therein is prepared.

A soda lime glass plate is used as the glass substrate 3, a Ti film having a thickness of 500 nm is formed on one main surface of the glass substrate 3 by sputtering, and a large number of circular portions having a diameter of 200 μm which are in contact with each other are removed. Pattern so that it is exposed. Then, the soda lime glass plate to which the patterned Ti film is attached is immersed in a molten salt heated to 490 ° C. for 150 hours. Molten salt molar ratio of TlNO ₃ is 30% of the mixed salt of TlNO ₃ and KNO _3, T in Na ⁺ and salt in glass Ti film as a mask
The l ⁺ and K ⁺ ions are replaced to form an array of microlenses 2 having a refractive index profile in the glass substrate 3 as schematically shown in FIG. After that, the Ti film is removed from the glass plate, and the glass substrate 3 in which the minute lenses 2 are embedded is created.

On the surface of the glass substrate 3 in which the minute lenses 2 thus prepared are embedded, the surface of the glass substrate 3 on the side of the lens 2 is vapor-deposited with C _S I heavily doped with Tl to a thickness of 100 μm to form the scintillator 1, and then the scintillator 1 is formed. X on the other side
A 100 nm-thick Al reflection film 8 is vapor-deposited so that light emitted by the lines does not leak outside.

On the other hand, a photodiode array 6 for detecting the visible light converted by the scintillator 1 is prepared. This photodiode array 6 is formed on a glass substrate 7. Explaining the photodiode array 6 shown in FIG. 3, the gate electrode 11 of the thin film transistor 23 is formed by forming a 100 nm-thick chromium film on the glass substrate 7 by sputtering and then patterning. afterwards,
Gate insulating film 12 of a-SiNx having a thickness of 300 nm
Then, a 100 nm a-Si active layer 13 and a 15 nm a-SiNx film serving as the active protection film 14 are continuously formed by plasma CVD, respectively, and then patterned to form the active protection film 14. Then, the thin film transistor 23
The N-type a-Si having a thickness of 100 nm to be the contact layers 15 and 15 'is formed by plasma CVD, and the Cr film having a thickness of 150 nm to be the source electrode 16 and the drain electrode 16' is formed to be a photodiode 6 '. 40n
m type N-type a-Si layer 17, 1000 nm thickness I-type a-
The Si layer 18 and the P-type a-Si layer 19 having a thickness of 14 nm are sequentially formed by plasma CVD, and then the ITO film to be the transparent conductive film 20 is formed by sputtering. Next, the transparent conductive film 20,
Photodiode 6 ', source / drain electrodes 16, 1
After patterning in the order of 6 ′, contact layers 15, 1
Etch to 5 '. After that, a-SiNx having a thickness of 1000 nm is formed by plasma CVD and patterned to form the protective film 21. Further, Al is sputtered to form a film, which is then patterned to form the extraction electrode 22. Although not shown in FIG. 3, a photodiode 6'having a thin film transistor for reading 23 thus formed and having a light receiving surface of 50 μm × 50 μm is not shown in FIG.
A large number of photodiode arrays 6 are formed on a glass substrate 7 at a pitch of 200 μm.

The glass substrate 3 in which the microlenses 2 prepared previously and the glass substrate 7 on which the photodiode array 6 is formed have the focal point of each lens 2 coincident with the light receiving surface of each photodiode 6 '. As shown in FIG. 1, a transparent adhesive 4 such as polyvinyl butyral is attached.

The above is one embodiment of the present invention, but the present invention can be modified as shown in FIG.

That is, in FIG. 2, the scintillator 1 deposited on the lens 2 side surface of the glass substrate 3 in which the minute lenses 2 are embedded, and the reflective film 8 deposited on the scintillator 1 are the same as those in the above embodiment. . The difference from the above embodiment is that the condensing point of the minute lens 2 is the other surface of the glass substrate 3 and the light receiving surface of the photodiode 6'of the photodiode array 6 is formed at the condensing point. Then, a protective film 24 of a-SiNx is formed to protect the photo lens array 6.

[0020]

According to the present invention, the incident X-ray 25 is converted into visible light 26 by the scintillator 1, condensed by the microlens 2 and incident on the photodiode, so that the signal intensity from the photodiode is increased. At the same time, since the size of the photodiode can be reduced, the dark current can be reduced and the S / N ratio can be dramatically improved. Further, since X-rays that pass through the scintillator are absorbed in the minute lens and the glass substrate, it is possible to suppress the deterioration of the photodiode portion due to X-ray irradiation.

[Brief description of drawings]

FIG. 1 is a schematic partial sectional view of an X-ray image sensor according to an embodiment of the present invention.

FIG. 2 is a schematic partial cross-sectional view of an X-ray image sensor according to another embodiment of the present invention.

FIG. 3 is a partially enlarged sectional view of a photodiode array 6 portion of the X-ray image sensor of the present invention.

[Explanation of symbols]

1 scintillator 2 Micro lens 3 glass substrates 6 Photodiode array 6'photodiode

Claims (3)

[Claims] 1. An X-ray image sensor provided with a scintillator for converting X-rays into visible light and a photodiode array for detecting the converted visible light, wherein a condenser lens is provided between the scintillator and the photodiode array. An X-ray image sensor, wherein an array is provided, and visible light from the scintillator is condensed on the light-receiving surface of each photodiode constituting the photodiode array. 2. The condensing lens array according to claim 1, wherein a large number of microlenses are embedded in a flat plate transparent plate, and the scintillator is provided on one surface of the flat plate transparent plate in which the microlenses are embedded. The described X-ray image sensor. 3. A photo device in which visible light from the scintillator is condensed on the other surface of the flat plate transparent plate, and a light receiving surface of a photodiode is formed at a light collecting point on the other surface of the flat plate transparent plate. The X according to claim 2, wherein a diode array is provided.
Line image sensor.