RADIATION IMAGE DETECTOR
A radiation image detector is provided. The radiation image detector includes: a substrate, an optical image detector located on the substrate and including an array including photosensitive pixels, a radiation conversion layer, and pixelated light-collecting structures located between the photosensitive pixels and the radiation conversion layer and configured to guide visible light that would fall into a trench region or a side wall region to a central region. Each photosensitive pixel includes a first electrode including a first contact surface in direct contact with the photoelectric conversion layer, a photoelectric conversion layer including the central region and the side wall region, and a second electrode including a second contact surface in direct contact with the photoelectric conversion layer.
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The present application is based upon and claims the benefit of priority of Chinese Patent Application No. 202010072176.3, filed on Jan. 21, 2020, the entire contents of which are incorporated herein by reference.
TECHNICAL FIELDThe present disclosure pertains generally to the field of radiation detectors and, more particularly, to the field of radiation image detectors.
BACKGROUNDFlat panel X-ray image detectors have been widely used in digital radiography for medical diagnosis and radiotherapy. Compared with traditional X-ray films, the flat panel image detector has the advantages of fastness, low cost, low exposure, high image quality, etc., and is convenient for data archiving, transmission and image processing, and is readily integrated into PACS (Picture Archiving and Communication Systems).
An image detector in the related art is provided with a radiation conversion layer and a visible light image detector. First, the radiation is converted to visible light through the radiation conversion layer; then the visible light is converted to electrical signals through a photoelectric conversion device in the visible light image detector; and finally the electrical signals are readout to an external circuit to complete the detection of the radiation image. With increase of clinic adoption of the flat panel X-ray detectors, the demand for higher image quality is increasing. The image quality is characterized by detective quantum efficiency (DQE) or alternatively modulation transfer function (MTF) and signal to noise ratio (SNR). Therefore increase MTF and SNR is the primary object of this disclosure.
SUMMARYEmbodiments of the present disclosure provide a radiation image detector, which improves light utilization of the image detector and therefore increases image MTF and SNR.
In a first aspect, an embodiment of the present disclosure provides a radiation image detector, the radiation image detector includes a substrate, an optical image detector located on the substrate and including an array including a plurality of photosensitive pixels arranged periodically, a radiation conversion layer located on a side of the optical image detector facing away from the substrate and configured to convert radiation into visible light, and a plurality of light-collecting structures. Each photosensitive pixel of the plurality of photosensitive pixels includes a first electrode, a photoelectric conversion layer, and a second electrode. The first electrode includes a first contact surface in direct contact with the photoelectric conversion layer, the second electrode includes a second contact surface in direct contact with the photoelectric conversion layer, and the photoelectric conversion layer includes a central region and a side wall region. The central region includes a portion where an orthographic projection of the first contact surface onto the photoelectric conversion layer and an orthographic projection of the second contact surface onto the photoelectric conversion layer overlap with each other, and the side wall region includes a region of the photoelectric conversion layer other than the central region. The optical image detector also includes a plurality of trench regions in a certain width, insensitive to light and surrounding the plurality of photosensitive pixels of the array. Each of the plurality of light-collecting structures is pixelated and located between the plurality of photosensitive pixels and the radiation conversion layer, and is configured to guide visible light to the central region, that the visible light would otherwise fall into the side wall region or a trench region between each photosensitive pixels.
A portion of light generated in the radiation conversion layer may enter into the trench region where no light detector exists, or enter into side-wall region in a light detector where electric field is not strong enough to drive photo-generated charges to the corresponding electrodes. The light-collecting structure provided in the present disclosure deflects and guides the portion of the light that would enter into the trench region or the side wall region, into the central region of the light detector, which ensures approximately all light photons are converted into electron-hole pairs and nearly all the electron-hole pairs are separated and collected by the electrodes.
These and other features, aspects, and advantages of the present disclosure will become better understood when the following description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In order to make the features, aspects and advantages of the present disclosure better understood, the technical solutions of the present disclosure will be described in details below with reference to the accompanying drawings. It should be noted that the described embodiments are merely a part of implementations of the present disclosure, rather than all of the implementations or varieties based upon the concept disclosed in the present disclosure. All other embodiments obtained by those skilled in the art without creative efforts according to the embodiments of the present disclosure shall fall within the scope of the present disclosure.
The terms used in the embodiments of the present disclosure is for the purpose of describing particular embodiments only and are not intended to limit the present disclosure. The terms in singular forms “a” “the” and “said” used in the embodiments of the present disclosure and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.
One of the reasons that both the top electrode J1 and the bottom electrode J2 have recesses from the edge of the photoelectric conversion layer (or photodiode island after lithography patterning), is to avoid high sidewall leakage current. Manufacturing process in minimum dimension, caused mainly by accuracy of lithography process, will determine the minimum width of the recess from the edge of the photoelectric layer. Therefore the above described drawbacks, including the loss of signal and image lags, are always associated with the device structure in the prior arts unless a new structure is introduced.
Micro-lens array has been employed in CCDs and CMOS imaging sensors, which are made on tiny silicon chips with pixel dimensions less than 10 um. In the solution, one micro-lens having substantially the same size as each pixel is fabricated above each pixel to guide or focus all the light to the photodiode in the CCD or the CMOS imaging sensor. However, given the pixel size in a flat panel X-ray image detector, which can be as large as 100 um or even 200 μm, the height of each micro-lens would be in the same order of magnitude of pixel size to perform as a convex lens. This requirement leads to a great challenge in manufacturing process.
In order to overcome the drawbacks mentioned above, a radiation image detector comprising a pixelated light-collecting structure is conceived and disclosed in details in the following.
As shown in
The optical image detector 102 includes an array of photosensitive pixels P, arranged periodically. As shown in t
As shown in
The photoelectric conversion layer G can be divided into at least two portions, a central region ZQ and a side wall region BQ. The central region ZQ includes a portion where an orthographic projection of the first contact surface M1 onto the photoelectric conversion layer G and an orthographic projection of the second contact surface M2 onto the photoelectric conversion layer G overlap with each other. The side wall region BQ surrounds the central region ZQ. When a bias voltage is applied to the first electrode C1 or the second electrode C2, electron-hole pairs generated in the central region ZQ will be separated, and the electrons and holes will drift to the anode and the cathode, respectively.
The radiation image detector further includes a radiation conversion layer 103 overlaid on the entire optical image detector, and an array of light-collecting structure 104 (pixelated light-collecting structure). The radiation conversion layer 103 is positioned above the optical image detector 102 and configured to convert radiation into visible light. The radiations can be X-rays with energy ranging from 1 KeV to several hundred KeV or y (Gamma) rays which may have higher energy exceeding 1 MeV in energy distribution. The radiation conversion layer 103 comprises scintillator or phosphors, such as cesium iodide (doped with Thallium CsI(T1), or CdWO4 or GOS (Gd2O2S:Pr).
The pixelated light-collecting structure 104 is sandwiched by the photosensitive pixel P and the radiation conversion layer 103, and particularly has a curved surface near the edge of the pixel and convex toward the radiation conversion layer. As shown in the enlarged view in
Benefiting from the light-collecting structure, photoconversion efficiency is improved and so does the image lag performance.
With increase of resolution in the flat panel X-ray imaging sensor, the pixel size will be reduced accordingly, but the trench area and the side-wall region may not be downsized in the same scale, mainly due to lithography and various process limitations. Implementation of the light-collecting structure as disclosed in the embodiment into high resolution radiation image detector will have more significant improves in efficiency and image quality.
It should be noted that the radiation image detector further includes an external circuit. The external circuit is electrically connected to the photosensitive pixels. The electrical signals corresponding to the photo-generated charges in each pixel is readout by the external circuit. The external circuit is configured to perform arithmetic processing on the electric signals and then generate images according to the incident radiation on the flat panel detector.
As illustrated in
As illustrated in
A plane view of a radiation image detector as an embodiment of the present disclosure is shown in
Referring to
As shown in
In the embodiment of the present disclosure, the second portion of the light-collecting structure serves as a partial convex lens above the side wall region and the trench region, focusing or guiding those light photons, that would fall into the trench region or the side-wall region, to the central region of the photoelectric conversion layer.
With continued reference to
As shown in
Another two embodiments, which are intended to further improve the image quality of the radiation imaging detector of the present disclosure, are shown in
As shown in
Filling the void completely as shown in
In another embodiment, the filling unit is made of materials including a material opaque to visible light, aiming to improve image MTF.
The materials used to make the filling unit includes one of the following or their combinations: an organic material mixed with black particles such as black dyes, carbon powders, carbon nanotubes, or chromium oxide particles.
The above are merely exemplary embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.
Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, and the present disclosure is limit thereto. Although the present disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent replacements can be made to some or all of the technical features; and the essence of the corresponding technical solutions with these modifications or replacements do not depart from the scope of the technical solutions of the embodiments of the present disclosure.
Claims
1. A radiation image detector, comprising:
- a substrate;
- an optical image detector located on the substrate, wherein the optical image detector comprises an array comprising a plurality of photosensitive pixels arranged periodically, wherein each of the plurality of photosensitive pixels comprises a first electrode, a photoelectric conversion layer and a second electrode, wherein the first electrode comprises a first contact surface in direct contact with the photoelectric conversion layer, the second electrode comprises a second contact surface in direct contact with the photoelectric conversion layer, and the photoelectric conversion layer comprises a central region and a side wall region, wherein the central region comprises a portion where an orthographic projection of the first contact surface onto the photoelectric conversion layer and an orthographic projection of the second contact surface onto the photoelectric conversion layer overlap with each other, and the side wall region comprises a region of the photoelectric conversion layer other than the central region; and
- a plurality of trench regions in a certain width, insensitive to light and surrounding the plurality of photosensitive pixels of the array;
- a radiation conversion layer located on a side of the optical image detector facing away from the substrate and configured to convert radiation into visible light; and
- a plurality of light-collecting structures pixelated and located between the plurality of photosensitive pixels and the radiation conversion layer, wherein the plurality of light-collecting structures is configured to guide the visible light to the central region, that the visible light would otherwise fall into the side wall region or a trench region between each photosensitive pixels.
2. The radiation image detector according to claim 1, wherein each of the plurality of light-collecting structures comprises a first portion and a second portion, wherein in a direction perpendicular to the substrate, the first portion overlaps with the central region and the second portion overlaps with both the side wall region and the plurality of trench regions; and
- from the central region to the trench region, thickness of the second portion in the direction perpendicular to the substrate gradually decreases while thickness of the first portion in the direction perpendicular to the substrate remains essentially unchanged.
3. The radiation image detector according to claim 2, wherein the second portion of each of the plurality of light-collecting structures has a maximum thickness of H, the side wall region has a width of W2, and each of the plurality of trench regions has a width of W3, where H is greater than or equal to 0.5* (W2+W3), and H is smaller than or equal to (W2+W3).
4. The radiation image detector according to claim 1, wherein in each of the plurality of trench regions and the side wall region, a space is formed between two adjacent light-collecting structures of the plurality of light-collecting structures; and
- wherein the radiation image detector further comprises a filling unit, and at least a part of the space is filled with the filling unit.
5. The radiation image detector according to claim 4, wherein the filling unit is made of a material having a refractive index of n1 in the visible light, and the plurality of light-collecting structures is made of a material having a refractive index of n2 in the visible light, where n1<n2.
6. The radiation image detector according to claim 4, wherein the filling unit is made of materials which is opaque to the visible light.
7. The radiation image detector according to claim 2, wherein the second portion is a ring-shaped convex lens having a focal point inside of the central region.
Type: Application
Filed: Jun 12, 2020
Publication Date: Jul 22, 2021
Applicant: IRAY TECHNOLOGY COMPANY LIMITED (Shanghai)
Inventors: Tieer Gu (Shanghai), Zhongshou Huang (Shanghai)
Application Number: 16/899,618