Patent Description:
An X-ray detector that is a planar radiation detector using an active matrix or a solid-state imaging element such as CCD, CMOS, etc., is drawing attention as a new-generation X-ray diagnostic image detector. By irradiating X-rays onto the X-ray detector, an X-ray image or a real time X-ray image is output as a digital signal.

The X-ray detector includes a photoelectric conversion substrate that converts light into an electrical signal, and a scintillator layer that contacts the photoelectric conversion substrate and converts the X-rays incident from the outside into light. Then, the light of the incident X-rays converted by the scintillator layer reaches the photoelectric conversion substrate and is converted into charge; and the charge is read as an output signal and converted into a digital image signal by a prescribed signal processing circuit, etc..

In the case where the scintillator layer includes CsI which is a halide, simple CsI cannot convert the incident X-rays into visible light; therefore, similarly to a general fluorescer, an activator is included to activate the excitation of the light due to the incident X-rays.

In the X-ray detector, because the peak wavelength of the light reception sensitivity of the photoelectric conversion substrate exists at the vicinity of <NUM> to <NUM> in the visible light region, in the case where CsI is used in the scintillator layer, Tl is used as the activator because the wavelength of the light excited by the incident X-rays in Tl is at the vicinity of <NUM>.

In the case where the scintillator layer is a fluorescer of CsI containing Tl as an activator and the CsI is a halide, similarly to a fluorescer containing a general activator, the characteristics of the scintillator layer are greatly affected by the concentration and concentration distribution of Tl which is the activator.

In an X-ray detector or a scintillator panel including the scintillator layer containing the activator, in the case where the concentration and concentration distribution of the activator are not corrected, this causes characteristic degradation of the scintillator layer, affects the afterimage (the phenomenon in which the subject image of the X-ray image of the (n-<NUM>)th time or earlier remains in the X-ray image of the nth time), and affects the sensitivity (the luminous efficiency) relating to the light emission characteristics of the scintillator layer.

For example, because the imaging conditions are greatly different between the subjects in the diagnosis using the X-ray image (the ray amount of the incident X-rays being about <NUM> mGy to <NUM> mGy (because the X-ray transmittance is different between sections)), a large difference may occur in the ray amount of the incident X-rays between the X-ray image of the (n-<NUM>)th time and the X-ray image of the nth time. Here, in the case where the ray amount difference of the incident X-rays of the X-ray images of the (n-<NUM>)th time and the nth time is (n-<NUM>) > n, the afterimage occurs because the light emission characteristics of the scintillator layer of the non-subject portion of the X-ray image of the (n-<NUM>)th time change due to the large energy of the incident X-rays; and the effects remain through the X-ray image of the nth time.

For the diagnosis using the X-ray image, the afterimage characteristics are important characteristics even when compared to other characteristics of the scintillator layer such as the sensitivity (the luminous efficiency) and the resolution (the MTF).

In the diagnosis using the X-ray image, normally, there are many cases where the diagnosis is performed in the state in which the subject is disposed at the central portion of the X-ray image; therefore, the characteristics in the central region of the formation region of the scintillator layer are important.

Conventionally, there have been proposals to regulate the concentration and concentration distribution of the activator of the scintillator layer to improve the sensitivity (the luminous efficiency) and the resolution (the MTF).

<CIT> discloses a radiation detection apparatus provided with a fluorescent material layer for converting radiation into light and an optical detector comprising a plurality of photoelectric conversion elements for converting the light into an electrical signal.

<CIT> discloses a radiation detecting element including needle crystal scintillators and a protruding pattern in which one end of the needle crystal scintillators is in contact with upper surfaces of the multiple protrusions, and a gap corresponding to a gap between the multiple protrusions is provided between portions of the needle crystal scintillators in contact with the uppers surfaces of the multiple protrusions.

<CIT> discloses a scintillator panel and a radiation detector which give a radiation image reduced in sensitivity unevenness and sharpness unevenness. The scintillator panel comprises a support and, deposited thereon, a phosphor layer comprising columnar crystals of a phosphor which have been formed by the vapor deposition method. The columnar crystals of a phosphor comprise cesium iodide (CsI) as a base ingredient and thallium (Tl) as an activator ingredient and have, in a root part thereof, a layer containing no thallium.

Conventionally, many improvements of the characteristics of the scintillator layer relate to the sensitivity (the luminous efficiency) and the resolution (the MTF); but few relate to overall characteristic improvement including the afterimage characteristics.

The problem to be solved by the invention is to provide a radiation detector and a method for manufacturing the radiation detector in which the overall characteristics including the afterimage characteristics of the scintillator layer can be improved.

Accordingly, there is provided a radiation detector as set out in independent claim <NUM>, and a method for manufacturing a radiation detector as set out in independent claim <NUM>. Advantageous developments are defined in the dependent claims.

Embodiments according to the invention will now be described with reference to <FIG>.

The basic configuration of a radiation detector <NUM> is described with reference to <FIG> show first to fourth structure examples. <FIG> is an equivalent circuit diagram of the basic configuration.

First, the first structure example of the X-ray detector <NUM> will be described as the radiation detector with reference to <FIG> and <FIG>. As shown in <FIG>, the X-ray detector <NUM> is an indirect X-ray planar image detector. The X-ray detector <NUM> includes a photoelectric conversion substrate <NUM> which is an active matrix photoelectric conversion substrate that converts visible light into an electrical signal.

The photoelectric conversion substrate <NUM> includes a support substrate <NUM> as an insulating substrate formed in transparent glass or the like having a rectangular flat plate configuration. Multiple pixels <NUM> are arranged two-dimensionally in a matrix configuration in the surface of the support substrate <NUM> with spacing between the pixels <NUM>; and a thin film transistor (TFT) <NUM> as a switching element, a charge storage capacitor <NUM>, a pixel electrode <NUM>, and a photoelectric conversion element <NUM> such as a photodiode or the like are formed in each of the pixels <NUM>.

As shown in <FIG>, control electrodes <NUM> as multiple control lines along a row direction of the support substrate <NUM> are provided on the support substrate <NUM>. The multiple control electrodes <NUM> are positioned between the pixels <NUM> on the support substrate <NUM> and are provided to be separated from each other in a column direction of the support substrate <NUM>. The gate electrodes <NUM> of the thin film transistors <NUM> are electrically connected to the control electrodes <NUM>.

Multiple read-out electrodes <NUM> along the column direction of the support substrate <NUM> are provided on the support substrate <NUM>. The multiple read-out electrodes <NUM> are positioned between the pixels <NUM> on the support substrate <NUM> and are provided to be separated from each other in the row direction of the support substrate <NUM>. The source electrodes <NUM> of the thin film transistors <NUM> are electrically connected to the multiple read-out electrodes <NUM>. A drain electrode <NUM> of the thin film transistor <NUM> is electrically connected to both the charge storage capacitor <NUM> and the pixel electrode <NUM>.

As shown in <FIG>, the gate electrodes <NUM> of the thin film transistors <NUM> are formed in island configurations on the support substrate <NUM>. An insulating film <NUM> is formed to be stacked on the support substrate <NUM> including the gate electrodes <NUM>. The insulating film <NUM> covers each of the gate electrodes <NUM>. The multiple semi-insulating films <NUM> that have island configurations are formed to be stacked on the insulating film <NUM>. The semi-insulating film <NUM> includes a semiconductor and functions as a channel region of the thin film transistor <NUM>. The semi-insulating films <NUM> are disposed to respectively oppose the gate electrodes <NUM> and respectively cover the gate electrodes <NUM>. In other words, the semi-insulating films <NUM> are provided, with the insulating film <NUM> interposed, respectively on the gate electrodes <NUM>.

The source electrode <NUM> and the drain electrode <NUM> that have island configurations are formed on the insulating film <NUM> including the semi-insulating film <NUM>. The source electrode <NUM> and the drain electrode <NUM> are insulated from each other and are not electrically connected to each other. The source electrode <NUM> and the drain electrode <NUM> are provided on two sides on the gate electrode <NUM>; and one end portion of the source electrode <NUM> and one end portion of the drain electrode <NUM> are stacked on the semi-insulating film <NUM>.

As shown in <FIG>, the gate electrode <NUM> of each thin film transistor <NUM> and the gate electrodes <NUM> of the other thin film transistors <NUM> positioned in the same row are electrically connected to a common control electrode <NUM>. The source electrode <NUM> of each thin film transistor <NUM> and the source electrodes <NUM> of the other thin film transistors <NUM> positioned in the same column are electrically connected to a common read-out electrode <NUM>.

As shown in <FIG>, the charge storage capacitor <NUM> includes a lower electrode <NUM> having an island configuration formed on the support substrate <NUM>. The insulating film <NUM> is formed to be stacked on the support substrate <NUM> including the lower electrodes <NUM>. The insulating film <NUM> that is on the gate electrode <NUM> of each thin film transistor <NUM> extends onto each lower electrode <NUM>. Upper electrodes <NUM> having island configurations are formed to be stacked on the insulating film <NUM>. The upper electrodes <NUM> are disposed to oppose the lower electrodes <NUM> and cover each of the lower electrodes <NUM>. In other words, the upper electrodes <NUM> are provided, with the insulating film <NUM> interposed, respectively on the lower electrodes <NUM>. The drain electrodes <NUM> are formed to be stacked on the insulating film <NUM> including the upper electrodes <NUM>. One other end portion of the drain electrode <NUM> is stacked on the upper electrode <NUM> and electrically connected to the upper electrode <NUM>.

An insulating layer <NUM> is formed to be stacked on the insulating film <NUM> including the semi-insulating film <NUM>, the source electrode <NUM>, and the drain electrode <NUM> of each of the thin film transistors <NUM> and the upper electrode <NUM> of each of the charge storage capacitors <NUM>. The insulating layer <NUM> is formed of silicon oxide (SiO<NUM>), etc., and is formed to surround each of the pixel electrodes <NUM>.

A through-hole <NUM> is made in a portion of the insulating layer <NUM> as a contact hole communicating with the drain electrode <NUM> of the thin film transistor <NUM>. The pixel electrode <NUM> having the island configuration is formed to be stacked on the insulating layer <NUM> including the through-hole <NUM>. The pixel electrode <NUM> is electrically connected to the drain electrode <NUM> of the thin film transistor <NUM> via the through-hole <NUM>.

The photoelectric conversion element <NUM> such as a photodiode or the like that converts visible light into an electrical signal is formed to be stacked on each of the pixel electrodes <NUM>.

A scintillator layer <NUM> that converts X-rays as the radiation into visible light is formed in the surface of the photoelectric conversion substrate <NUM> where the photoelectric conversion element <NUM> is formed. By vapor deposition such as vacuum vapor deposition, sputtering, CVD, etc., the scintillator layer <NUM> is formed by depositing, in columnar configurations on the photoelectric conversion substrate <NUM>, a fluorescer such as a halogen compound such as cesium iodide (CsI), an oxide compound such as gadolinium oxide sulfur (GOS) (not forming part of the claimed invention), etc., which are high-luminance fluorescent substances. The scintillator layer <NUM> is formed to have a columnar crystal structure in which columnar crystals <NUM> having multiple rectangular configurations are formed in the planar direction of the photoelectric conversion substrate <NUM>.

A reflective layer <NUM> for increasing the utilization efficiency of the visible light converted by the scintillator layer <NUM> is formed to be stacked on the scintillator layer <NUM>. A protective layer <NUM> that protects the scintillator layer <NUM> from the moisture inside ambient air is formed to be stacked on the reflective layer <NUM>. An insulating layer <NUM> is formed to be stacked on the protective layer <NUM>. An X-ray grid <NUM> that has a lattice configuration and shields between the pixels <NUM> is formed on the insulating layer <NUM>.

Then, in the X-ray detector <NUM> thus configured, X-rays <NUM> that are incident on the scintillator layer <NUM> as the radiation are converted into visible light <NUM> by the columnar crystals <NUM> of the scintillator layer <NUM>.

The visible light <NUM> reaches the photoelectric conversion element <NUM> of the photoelectric conversion substrate <NUM> via the columnar crystals <NUM> and is converted into an electrical signal. The electrical signal that is converted by the photoelectric conversion element <NUM> flows in the pixel electrode <NUM>; and until the gate electrode <NUM> of the thin film transistor <NUM> connected to the pixel electrode <NUM> is switched to a driving state, the electrical signal moves into the charge storage capacitor <NUM> connected to the pixel electrode <NUM> and is maintained and stored by the charge storage capacitor <NUM>.

At this time, when one of the control electrodes <NUM> is switched to the driving state, the one row of thin film transistors <NUM> that is connected to the control electrode <NUM> switched to the driving state is switched to the driving state.

The electrical signals that are stored in the charge storage capacitors <NUM> connected to the thin film transistors <NUM> switched to the driving state are output to the read-out electrodes <NUM>.

As a result, because the signals corresponding to the pixels <NUM> of a designated row of the X-ray image are output, the signals corresponding to all of the pixels <NUM> of the X-ray image can be output by the drive control of the control electrodes <NUM>; and the output signals are converted into digital image signals and output.

The second structure example of the X-ray detector <NUM> will now be described with reference to <FIG>. The same reference numerals as the first structure example of the X-ray detector <NUM> are used; and a description of similar configurations and effects is omitted.

The structure and effects of the photoelectric conversion substrate <NUM> are the same as those of the first structure example.

A scintillator panel <NUM> is bonded onto the photoelectric conversion substrate <NUM> with a bonding layer <NUM> interposed. The scintillator panel <NUM> includes a support substrate <NUM> that transmits the X-rays <NUM>. The reflective layer <NUM> that reflects light is formed on the support substrate <NUM>; the scintillator layer <NUM> that includes the multiple columnar crystals <NUM> having rectangular configurations is formed on the reflective layer <NUM>; and the protective layer <NUM> that seals the scintillator layer <NUM> is formed to be stacked on the scintillator layer <NUM>. Further, the X-ray grid <NUM> that has a lattice configuration and shields between the pixels <NUM> is formed on the support substrate <NUM>.

Then, in the X-ray detector <NUM> thus configured, the X-rays <NUM> that are incident on the scintillator layer <NUM> of the scintillator panel <NUM> are converted into the visible light <NUM> by the columnar crystals <NUM> of the scintillator layer <NUM>.

The visible light <NUM> reaches the photoelectric conversion elements <NUM> of the photoelectric conversion substrate <NUM> via the columnar crystals <NUM>, is converted into electrical signals, and is converted into digital image signals and output as described above.

The third structure example of the X-ray detector <NUM> will now be described with reference to <FIG>. Compared to the first structure example of the X-ray detector <NUM> shown in <FIG>, the scintillator layer <NUM> of the third structure example of the X-ray detector <NUM> does not include the columnar crystals <NUM>; but the other configurations are similar.

The fourth structure example of the X-ray detector <NUM> will now be described with reference to <FIG>. Compared to the second structure example of the X-ray detector <NUM> shown in <FIG>, the scintillator layer <NUM> of the fourth structure example of the X-ray detector <NUM> does not include the columnar crystals <NUM>; but the other configurations are similar.

In the X-ray detector <NUM> having the structures shown in <FIG>, the scintillator layer <NUM> is a fluorescer of CsI containing Tl as an activator; the CsI is a halide; and the scintillator layer <NUM> has the following features (<NUM>), (<NUM>), (<NUM>), and (<NUM>).

Here, the results of a test of the correlation between the characteristics and the Tl concentration in the scintillator layer <NUM> for the X-ray detector <NUM> of the first structure example shown in <FIG> having a film thickness of the scintillator layer <NUM> of <NUM> and an activator of Tl are shown in <FIG>. The results of a test of the correlation between the characteristics and the stacking period (the formation period of the unit film thickness (the film thickness formed each rotation of the substrate)) of the scintillator layer <NUM> in the case where the Tl concentration in the scintillator layer <NUM> is set to be constant are shown in <FIG>.

<FIG> shows the correlation between the sensitivity ratio and the Tl concentration in the scintillator layer <NUM>. The test conditions include incident X-rays of <NUM> kV/<NUM> mGy. The sensitivity ratio is a ratio in which the sensitivity when the Tl concentration in the scintillator layer <NUM> is <NUM> mass% is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples. As shown in <FIG>, the sensitivity is improved most when the Tl concentration in the scintillator layer <NUM> is at the vicinity of <NUM> mass% to <NUM> mass%.

<FIG> shows the correlation between the MTF ratio which is the resolution and the Tl concentration in the scintillator layer <NUM>. The test conditions include incident X-rays of <NUM> kV/<NUM> mGy. The MTF ratio is a ratio in which the MTF (at <NUM> Lp/mm) when the TI concentration in the scintillator layer <NUM> is <NUM> mass% is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples. As shown in <FIG>, the Tl concentration in the scintillator layer <NUM> is substantially constant until the vicinity of <NUM> mass%.

<FIG> shows the correlation between the afterimage ratio and the Tl concentration in the scintillator layer <NUM>. The test conditions include: a ray amount difference of the incident X-rays of the X-ray images of the (n-<NUM>)th time and the nth time of (n-<NUM>) > n; incident X-rays of <NUM> kV/<NUM> mGy, a subject of a lead plate (having a plate thickness of <NUM>), and an X-ray imaging interval of <NUM> sec for the X-ray image of the (n-<NUM>)th time; and incident X-rays of <NUM> kV/<NUM> mGy, no subject, and an X-ray imaging interval of <NUM> sec for the X-ray image of the nth time. The afterimage ratio is a ratio in which the afterimage when the Tl concentration in the scintillator layer <NUM> is <NUM> mass% is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples. As shown in <FIG>, the afterimage has a minimum level when the Tl concentration in the scintillator layer <NUM> is at the vicinity of <NUM> mass%. The afterimage is not confirmed in the region where the afterimage ratio is <NUM> (favorably <NUM>) or less and where the Tl concentration is <NUM> mass% ±<NUM> mass%.

<FIG> shows the correlation between the sensitivity ratio and the stacking period of the scintillator layer <NUM>. The test conditions include incident X-rays of <NUM> kV/<NUM> mGy and a Tl concentration in the scintillator layer <NUM> of <NUM> mass%. The sensitivity ratio is a ratio in which the sensitivity when the stacking period of the scintillator layer <NUM> is <NUM> is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples.

<FIG> shows the correlation between the MTF ratio and the stacking period of the scintillator layer <NUM>. The test conditions include incident X-rays of <NUM> kV/<NUM> mGy and a Tl concentration in the scintillator layer <NUM> of <NUM> mass%. The MTF ratio is a ratio in which the MTF (at <NUM> Lp/mm) when the stacking period of the scintillator layer <NUM> is <NUM> is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples.

<FIG> shows the correlation between the afterimage ratio and the stacking period of the scintillator layer <NUM>. The test conditions include: a ray amount difference of the incident X-rays of the X-ray images of the (n-<NUM>)th time and the nth time of (n-<NUM>) > n; incident X-rays of <NUM> kV/<NUM> mGy, a subject of a lead plate (having a plate thickness of <NUM>), and an X-ray imaging interval of <NUM> sec for the X-ray image of the (n-<NUM>)th time; and incident X-rays of <NUM> kV/<NUM> mGy, no subject, and an X-ray imaging interval of <NUM> sec for the X-ray image of the nth time. The Tl concentration in the scintillator layer <NUM> is set to <NUM> mass%. The afterimage ratio is a ratio in which the afterimage when the stacking period of the scintillator layer <NUM> is <NUM> is used as a reference. The scintillator layer formation conditions (other than the Tl concentration in the scintillator layer <NUM>) are the same for each of the test samples.

As shown in <FIG>, there is a tendency for each of the characteristics to degrade in the region where the stacking period of the scintillator layer <NUM> is <NUM> or more.

Because the refractive index of CsI which is the main material of the scintillator layer <NUM> is <NUM> while the peak wavelength of the light emission wavelength of the scintillator layer <NUM> is at the vicinity of <NUM>, it can be considered that λ1 = <NUM>/<NUM> = <NUM> from the relationship between the refractive index and the wavelength, where λ1 is the peak wavelength of the light emission wavelength propagating through the scintillator layer <NUM>. Accordingly, it is considered that the results of <FIG> are caused by the high likelihood of being affected by the degradation of the optical characteristics (scattering, attenuation, etc.) due to the fluctuation of the crystallinity of the scintillator layer <NUM>, the fluctuation of the Tl concentration in the scintillator layer <NUM>, etc., in the case where the stacking period of the scintillator layer <NUM> is larger than λ1.

As shown in <FIG>, the afterimage has a minimum level when the concentration of the activator inside the fluorescer which is the scintillator layer <NUM> is at the vicinity of <NUM> mass%; and the afterimage is not confirmed in the region of <NUM> mass% ±<NUM> mass% where the afterimage ratio is <NUM> (favorably <NUM>) or less. As shown in <FIG>, because the characteristics of the sensitivity and the MTF are good in the region of <NUM> mass% ±<NUM> mass%, the region of <NUM> mass% ±<NUM> mass% is favorable for the concentration of the activator.

As shown in <FIG>, because each of the characteristics is near the stable state in the region where the Tl concentration in the scintillator layer <NUM> is <NUM> mass% ±<NUM> mass%, the fluctuation of each of the characteristics is small even when the Tl concentration in the scintillator layer <NUM> fluctuates (about ±<NUM>%).

From the correlation diagrams shown in <FIG>, the characteristic (particularly, the afterimage characteristic) improvement effects of the scintillator layer <NUM> are largest in the region where the Tl concentration in the scintillator layer <NUM> is <NUM> mass% ±<NUM> mass%; and there is an optimal value at the vicinity of <NUM> mass%. Since the scintillator layer <NUM> is a fluorescent substance of CsI containing Tl as an activator and the CsI is a halide, the following characteristics (a), (b), and (c) are obtained.

Thus, the effects of (a) to (c) recited above are obtained more as the Tl concentration in the scintillator layer <NUM> increases.

In a diagnosis or the like using an X-ray image, normally, there are many cases where the diagnosis is performed in the state in which the subject is disposed at the central portion of the X-ray image. Therefore, it is possible to improve the overall characteristics including the afterimage characteristics of the scintillator layer <NUM> and increase of the reliability of the X-ray detector <NUM> if the Tl concentration in the fluorescer is set to <NUM> mass% ±<NUM> mass% and the Tl concentration in the fluorescer in the in-plane direction of the scintillator layer <NUM> has the relationship of central portion > peripheral portion, where the central portion 31a is the central region of the formation region of the scintillator layer <NUM>, and the peripheral portion 31b is the outer circumferential region of the formation region of the scintillator layer <NUM> as in the feature of (<NUM>) recited above.

The X-ray detector <NUM> suited to the diagnosis or the like using the X-ray image can be provided by setting the central portion 31a of the scintillator layer <NUM> to occupy <NUM>% or more of the formation region of the scintillator layer <NUM> as in the feature of (<NUM>) recited above.

Even in the region where the concentration of the activator inside the fluorescer is <NUM> mass% ±<NUM> mass%, each of the characteristics easily fluctuates greatly if there is a large bias in the concentration distribution of the activator inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>. Therefore, it is favorable for the concentration distribution of the activator to be within ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>. If the concentration distribution of the activator inside the fluorescer is within the fluctuation range of about ±<NUM>%, the fluctuation of each of the characteristics is small and the effect is small.

Each of the characteristics easily fluctuates greatly if there is a large bias in the concentration distribution of the activator inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM> in at least of the region of the scintillator layer <NUM> having the unit film thickness of <NUM> or less. Therefore, even in the region having the unit film thickness of <NUM> or less, it is favorable for the concentration distribution of the activator to be within ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>.

Accordingly, it is favorable for the concentration distribution of the activator to be ±<NUM>% or less inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>, and for the concentration distribution of the activator to be within ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM> in a region having a unit film thickness of <NUM> or less as in the feature of (<NUM>) recited above.

Here, <FIG> is a schematic view of a general method for forming the scintillator layer <NUM>. <FIG> and <FIG> are schematic views of formation methods that change the concentration of the activator inside the fluorescer between the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM>.

In <FIG>, the film of the scintillator layer <NUM> is formed by stacking by disposing a substrate <NUM> (corresponding to the photoelectric conversion substrate <NUM> or the support substrate <NUM>) inside a vacuum chamber <NUM> and by performing vacuum vapor deposition that vapor-deposits, onto the stacked surface of the substrate <NUM>, evaporated particles from an evaporation source <NUM> of CsI and evaporated particles from an evaporation source <NUM> of TlI mounted inside the vacuum chamber <NUM> while rotating the substrate <NUM>.

At this time, the TI concentration distribution in the in-plane direction and the film thickness direction per stacking period of the scintillator layer <NUM> can be controlled arbitrarily by controlling the rotation period of the substrate <NUM> and the evaporation of CsI and TII. Therefore, when forming the scintillator layer <NUM>, if the uniformity of the Tl concentration distribution in the in-plane direction and the film thickness direction per stacking period of the scintillator layer <NUM> is ensured, the uniformity of the TI concentration distribution in the in-plane direction and the film thickness direction of the entire scintillator layer <NUM> also is ensured.

It is possible to change the Tl concentration distribution in the in-plane direction of the scintillator layer <NUM> by disposing one evaporation source <NUM> of TII to oppose the substrate <NUM> on the central axis (on the center of rotation) of the substrate <NUM> as shown in <FIG>, or by using two evaporation sources <NUM> of TII and disposing one of the two evaporation sources <NUM> to oppose the substrate <NUM> on the central axis (on the center of rotation) of the substrate <NUM> as shown in <FIG>. By the formation method, it is possible to form the concentration of the activator inside the fluorescer in the in-plane direction of the scintillator layer <NUM> to have the relationship of central portion > peripheral portion, where the central portion 31a is the central region of the formation region of the scintillator layer <NUM>, and the peripheral portion 31b is the outer circumferential region of the formation region of the scintillator layer <NUM>.

Thereby, if the scintillator layer <NUM> made of a fluorescer of CsI containing Tl as an activator in which the CsI is a halide is provided with the features of (<NUM>) to (<NUM>) recited above by considering the characteristics of (a) to (c) recited above, it is possible to improve the overall characteristics including the afterimage characteristics of the scintillator layer <NUM> and increase the reliability of the X-ray detector <NUM>.

An example of the X-ray detector <NUM> of the first structure example shown in <FIG> will now be described. In the example, the film thickness of the scintillator layer <NUM> was <NUM>; the stacking period of the scintillator layer <NUM> was <NUM>; Tl was used as the activator; and the formation region of the scintillator layer <NUM> was <NUM> by <NUM>. The central portion 31a of the scintillator layer <NUM> was set to be a concentric circular region occupying <NUM>% with the center of the formation region of the scintillator layer <NUM> as a reference; the peripheral portion 31b of the scintillator layer <NUM> was set to be the region other than the central portion 31a of the formation region of the scintillator layer <NUM>; and the concentration distribution of the activator was set to ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM> in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM>. Using such conditions, sample A, B, C, D, and E of the X-ray detector <NUM> were made in which the concentration of the activator in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM> was changed as shown in <FIG>.

The X-ray images (the nth time) for sample A, B, C, D, and E of the X-ray detector <NUM> in which the subject is imaged using the prescribed imaging conditions and the image that is imaged is processed using the prescribed image processing conditions are shown in <FIG>. The results of the characteristics at this time are shown in the table of <FIG>. In <FIG>, the sensitivity ratio, the MTF ratio, and the afterimage ratio are values for which a Tl concentration in the scintillator layer <NUM> of <NUM> mass% is used as a reference.

The imaging conditions are set so that the ray amount difference of the incident X-rays of the X-ray images of the (n-<NUM>)th time and the nth time is (n-<NUM>) > n; incident X-rays of <NUM> kV/<NUM> mGy, a subject of a lead plate (having a plate thickness of <NUM>), and an X-ray imaging interval of <NUM> sec are used for the X-ray image of the (n-<NUM>)th time; and incident X-rays of <NUM> kV/<NUM> mGy, no subject, and an X-ray imaging interval of <NUM> sec are used for the X-ray image of the nth time.

The image processing conditions are set so that the flat field correction is ON and the windowing is ON (the histogram average value of the image is ±<NUM>%).

As shown in <FIG>, afterimages are confirmed in the area surrounded with the quadrilateral broken line in <FIG> for sample A in which the concentration of the activator inside the fluorescer in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM> is <NUM> mass% and for sample B in which the concentration is <NUM> mass%. On the other hand, as shown in <FIG>, afterimages are not confirmed in the area surrounded with the quadrilateral broken line in <FIG> for sample C in which the concentration of the activator inside the fluorescer in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM> is <NUM> mass%, for sample D in which the concentration of the activator inside the fluorescer in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer <NUM> is <NUM> mass%, and for sample E in which the concentration of the activator inside the fluorescer at the central portion 31a of the scintillator layer <NUM> is <NUM> mass% and the concentration of the activator inside the fluorescer at the peripheral portion 31b of the scintillator layer <NUM> is <NUM> mass%. In <FIG>, the inner side of the circular imaginary line illustrated by the double dot-dash line corresponds to the imaging region at the central portion 31a of the scintillator layer <NUM>; and the outer side of the circular imaginary line corresponds to the imaging region at the peripheral portion 31b of the scintillator layer <NUM>.

Accordingly, by providing the scintillator layer <NUM> with the features of (<NUM>) to (<NUM>) recited above specified in the embodiment, it is possible to increase the performance and reliability of the X-ray detector <NUM> because the afterimage characteristics can be improved with the sensitivity and the MTF in good states.

An embodiment in which the scintillator layer according to the invention is used in a scintillator panel will now be described.

<FIG> show the first to fourth structure examples (not forming part of the claimed invention) and describe the basic configuration of a scintillator panel <NUM>.

First, the first structure example of the scintillator panel <NUM> will be described with reference to <FIG>. The scintillator panel <NUM> includes a support substrate <NUM> that transmits X-rays as radiation. A reflective layer <NUM> that reflects light is formed on the support substrate <NUM>; a scintillator layer <NUM> that converts radiation into visible light is formed on the reflective layer <NUM>; and a protective layer <NUM> that seals the scintillator layer <NUM> is formed to be stacked on the scintillator layer <NUM>.

The support substrate <NUM> includes a substance that includes an element lighter than a transition metal element as a major component and has a high transmittance of X-rays.

The reflective layer <NUM> includes a metal material having a high reflectance such as Al, Ni, Cu, Pd, Ag, etc., and increases the light utilization efficiency by reflecting the light produced by the scintillator layer <NUM> in the opposite direction of the support substrate <NUM>.

The scintillator layer <NUM> is formed by depositing, in columnar configurations on the support substrate <NUM>, a fluorescer such as a halogen compound of cesium iodide (CsI) or the like, an oxide compound such as gadolinium oxide sulfur (GOS) (not forming part of the claimed invention) or the like, etc., which are high-luminance fluorescent substances by, for example, a vapor deposition such as vacuum vapor deposition, sputtering, CVD, etc. Then, the scintillator layer <NUM> is formed to have a columnar crystal structure in which columnar crystals 93a having multiple rectangular configurations are formed in the planar direction of the support substrate <NUM>.

Then, in the scintillator panel <NUM> thus configured, X-rays <NUM> that are incident on the scintillator layer <NUM> as the radiation from the support substrate <NUM> side are converted into visible light <NUM> by the columnar crystals 93a of the scintillator layer <NUM>; and the visible light <NUM> is emitted from the surface of the scintillator layer <NUM> (the surface of the protective layer <NUM>) on the side opposite to the support substrate <NUM>.

<FIG> shows the second structure example of the scintillator panel <NUM>. Compared to the first structure example of the scintillator panel <NUM> shown in <FIG>, the second structure example of the scintillator panel <NUM> does not include the reflective layer <NUM>; but the other configurations are similar.

<FIG> shows the third structure example of the scintillator panel <NUM>. Compared to the first structure example of the scintillator panel <NUM> shown in <FIG>, the scintillator layer <NUM> does not include the columnar crystals 93a in the third structure example of the scintillator panel <NUM>; but the other configurations are similar.

<FIG> shows the fourth structure example of the scintillator panel <NUM>. Compared to the second structure example of the scintillator panel <NUM> shown in <FIG>, the scintillator layer <NUM> does not include the columnar crystals 93a in the fourth structure example of the scintillator panel <NUM>; but the other configurations are similar.

<FIG> shows an imaging device <NUM> which is, for example, a CCD-DR type and includes the scintillator panel <NUM>. The imaging device <NUM> includes a housing <NUM>; the scintillator panel <NUM> is mounted at one end of the housing <NUM>; an optical lens <NUM> and a reflection plate <NUM> having a mirror surface are mounted in the interior of the housing <NUM>; and a light receiving element <NUM> such as, for example, a CCD or the like is mounted at the other end of the housing <NUM>. The X-rays <NUM> are radiated from an X-ray generation source (an X-ray tube) <NUM> and are incident on the scintillator panel <NUM>; and the visible light <NUM> converted by the scintillator layer <NUM> is emitted from the surface of the scintillator layer <NUM>. The X-ray image is projected onto the surface of the scintillator layer <NUM>; the X-ray image is reflected by the reflection plate <NUM>, condensed by the optical lens <NUM>, and irradiated on the light receiving element <NUM>; and the X-ray image is converted into an electrical signal by the light receiving element <NUM> and output.

In the scintillator panel <NUM> having the structure shown in <FIG>, the scintillator layer <NUM> is a fluorescer of CsI containing Tl as an activator in which the CsI is a halide, and has the following features (<NUM>), (<NUM>), (<NUM>), and (<NUM>) similarly to the scintillator layer <NUM>.

As described in the description in reference to <FIG>, by using the scintillator layer <NUM> having the features of (<NUM>) to (<NUM>) recited above in the scintillator panel <NUM>, it is possible to improve the afterimage characteristics with the sensitivity of the scintillator panel <NUM> in a good state.

It is also similar in that the effects of (a) to (c) described above are obtained more as the Tl concentration in the scintillator layer <NUM> increases.

In a diagnosis or the like using an X-ray image, normally, there are many cases where the diagnosis is performed in the state in which the subject is disposed at the central portion of the X-ray image. Therefore, it is possible to improve the overall characteristics including the afterimage characteristics of the scintillator layer <NUM> and increase the reliability of the scintillator panel <NUM> if the Tl concentration in the fluorescer is set to <NUM> mass% ±<NUM> mass% and the Tl concentration in the fluorescer in the in-plane direction of the scintillator layer <NUM> has the relationship of central portion > peripheral portion, where the central portion 93b is the central region of the formation region of the scintillator layer <NUM> and the peripheral portion 93c is the outer circumferential region of the formation region of the scintillator layer <NUM> as in the feature of (<NUM>) recited above.

The scintillator panel <NUM> suited to the diagnosis or the like using the X-ray image can be provided by setting the central portion 93b of the scintillator layer <NUM> to occupy <NUM>% or more of the formation region of the scintillator layer <NUM> as in the feature of (<NUM>) recited above.

Even in the region where the concentration of the activator inside the fluorescer is <NUM> mass% ±<NUM> mass%, each of the characteristics easily fluctuates greatly if there is a large bias in the concentration distribution of the activator inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>; therefore, it is favorable for the concentration distribution of the activator to be within ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>. If the concentration distribution of the activator inside the fluorescer is within the fluctuation range of about ±<NUM>%, the fluctuation of each of the characteristics is small and the effect is small.

Each of the characteristics easily fluctuates greatly if there is a large bias in the concentration distribution of the activator inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM> in at least the region of the scintillator layer <NUM> having the unit film thickness of <NUM> or less; therefore, even in a region having a unit film thickness of <NUM> or less, it is favorable for the concentration distribution of the activator to be within ±<NUM>% inside the fluorescer in the in-plane direction and the film thickness direction of the scintillator layer <NUM>.

Thus, by providing the scintillator layer <NUM> with the features of (<NUM>) to (<NUM>) recited above specified in the embodiment, it is possible to increase the performance and reliability of the scintillator panel <NUM> because the afterimage characteristics can be improved with the sensitivity and the MTF in good states.

It is possible to use a method similar to the method for forming the scintillator layer <NUM> described using <FIG> as the method for forming the scintillator layer <NUM>.

Claim 1:
A radiation detector (<NUM>), comprising:
a photoelectric conversion substrate (<NUM>) converting light into an electrical signal; and
a scintillator layer (<NUM>) contacting the photoelectric conversion substrate (<NUM>) and converting radiation incident from the outside into light,
wherein
the scintillator layer is a fluorescent substance of CsI containing Tl as an activator, the CsI is a halide, the scintillator layer (<NUM>) includes a central portion (31a) and a peripheral portion (31b), the central portion (31a) is a central region of a formation region of the scintillator layer (<NUM>), the peripheral portion (31b) is an outer circumferential region of the formation region of the scintillator layer (<NUM>), a
concentration of the activator inside the fluorescent substance in an in-plane direction of the scintillator layer (<NUM>) in the central portion (31a) is higher than a concentration of the activator inside the fluorescent substance in an in-plane direction of the scintillator layer (<NUM>) in the peripheral portion (31b),
characterized in that
the concentration of the activator inside the fluorescent substance is <NUM> mass% ± <NUM> mass%.