Radiation detector

Abstract

The radiation detector includes a GaN detector array including a plurality of GaN detectors tiled to form a desired array structure, a leadout element electrically connected to the GaN detectors, and a base circuit substrate electrically connected to the leadout element.

Description

[Technical Field]

[0001] The present invention relates to a radiation detector that can be used in a radiation imaging device. [Background technology]

[0002] Existing radiation detectors contain single crystals, such as CdTe or CZT:CdZnTe, as a radiation-sensitive conversion layer. However, these single crystals contain cadmium, a toxic heavy metal, so alternative single crystals are needed.

[0003] Gallium nitride (GaN) single crystals are known as a replacement for cadmium-based single crystals. GaN has a large energy band gap like CdTe, making it suitable for implementing image acquisition methods such as photon counting, and is therefore attracting attention as a radiation detector material.

[0004] On the other hand, GaN single crystals are known to have many advantages over CdTe single crystals as a radiation detector material, such as high resolution and high contrast due to the direct conversion method, lower energy than CdTe, high sensitivity at approximately 10 to 30 keV, excellent radiation resistance, stable electrical properties at high temperatures compared to CdTe, a highly flexible manufacturing process, and ease of handling due to its harder material properties compared to CdTe.

[0005] There is a need for a technology to realize a radiation detector using GaN with such excellent characteristics. In particular, when tiling individual GaN detectors to form a detector with a larger area, there is a need for a method that can reduce the size of the dummy region between the active regions. There is also a need for a GaN detector that has reduced noise and easy impedance matching. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent No. 2764552 [Patent Document 2] U.S. Patent No. 8,405,037 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a radiation detector that can reduce the size of the dummy area between multiple tiled GaN detectors and prevent leakage current in the edge area. [Means for solving the problem]

[0008] A radiation detector according to an embodiment of the present invention includes a GaN detector array including a plurality of GaN detectors tiled to form a desired array structure, a leadout element electrically connected to the GaN detectors, and a base circuit substrate electrically connected to the leadout element.

[0009] The GaN detector may include an active region including a plurality of pixels for radiation detection, and a barrier region surrounding the active region, and the barrier region may have a size corresponding to one pixel of the GaN detector.

[0010] The GaN detector may include a GaN substrate, a nitride semiconductor layer formed on the GaN substrate, a lower electrode formed on the GaN substrate, and an upper electrode formed on the nitride semiconductor layer. A side surface of the nitride semiconductor layer may include an inclined surface formed at a predetermined angle with respect to a vertical direction.

[0011] The predetermined angle may be a value between 8 degrees and 10 degrees.

[0012] The GaN detector may include a plurality of pixels for sensing radiation, each of which may include a capacitor for storing charge generated in response to incident radiation, and a transistor coupled to the capacitor and functioning as a charge-sensitive amplifier. [Effects of the Invention]

[0013] According to the present invention, the size of the dummy area between the tiled GaN detectors can be reduced, and leakage current caused by sparks at the edge area can be effectively prevented. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a plan view of a radiation detector according to an embodiment of the present invention; [Figure 2] 1 is a diagram schematically illustrating a cross-sectional structure of a radiation detector according to an embodiment of the present invention. [Figure 3] FIG. 1 is a cross-sectional view of a GaN detector of a radiation detector according to an embodiment of the present invention. [Figure 4] 1 is a diagram showing an example of an internal circuit structure of a pixel of a GaN detector according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in various different forms and is not limited to the described embodiments.

[0016] In this specification, when a component is referred to as being above or below another component, this means that the component may be directly above or below the other component, or that other components may be interposed therebetween. Also, in the drawings, the thickness of components or layers may be exaggerated for ease of explanation and to facilitate understanding. It should be understood that parts designated with the same reference numerals throughout the specification refer to the same components.

[0017] Referring to Figure 1, a radiation detector 10 according to an embodiment of the present invention includes an array 12 of a plurality of rectangular GaN detectors 11 arranged in a rectangular structure. For example, four GaN detectors 11 may be arranged to form a 2*2 array. While Figure 1 illustrates an example in which an array of four GaN detectors 11 is tiled in a 2*2 configuration to form a rectangular structure, the number and arrangement of the GaN detectors may be varied in various ways.

[0018] An insulating region, i.e., a barrier region 13, is provided in the edge region to prevent leakage current due to sparks generated at the edge when power is applied to operate the GaN detector 11. As shown in the dotted circle in FIG. 1 , the GaN detector 11 includes an active region 13, which is a radiation-sensing region, and a barrier region 15 formed around the active region 13. The active region 13 may include multiple pixels that sense radiation and generate charges, and the barrier region 15 may be formed in the edge region of the GaN detector 11 to surround the active region 13. The barrier region 15 of each GaN detector 11 is formed to have a size corresponding to one pixel, so that between adjacent GaN detectors 11, there is a barrier region 15 corresponding to two pixels.

[0019] In conventional CdTe detectors, each detector has a barrier region corresponding to 2 to 3 pixels, and there is a barrier region corresponding to 4 to 6 pixels between adjacent detectors. In contrast, in embodiments of the present invention, a GaN detector 11 is used as the radiation detector, and therefore there is a narrower barrier region corresponding to 2 pixels than in conventional CdTe detectors. Because images are not acquired in the barrier region during radiation imaging, if there is a wide barrier region, an accurate image cannot be generated by interpolation calculations to generate an image corresponding to the barrier region. As a result, when using a radiation imaging device using a conventional CdTe detector, the radiation detector must be slightly moved and then another image taken. In contrast, in a radiation imaging device using a GaN detector according to embodiments of the present invention, there is a relatively narrow barrier region corresponding to 2 pixels, and therefore an image of the barrier region can be calculated with high accuracy by interpolation calculations.

[0020] FIG. 2 shows a schematic cross-sectional structure of a radiation detector according to an embodiment of the present invention. A readout element 21, such as an ASIC or other type of readout chip, is disposed below the GaN detector array 12 and is electrically connected to the GaN detector array 12 via an electrically conductive element 23. The electrically conductive element 23 may be a solder bump made of an electrically conductive material such as silver. The readout element 21 is also electrically connected to a base circuit board 27 via an electrically conductive element 25, such as a solder bump. The base circuit board 27 may be embodied as a printed circuit board. The GaN detector 11 generates an electrical signal corresponding to each pixel when radiation such as X-rays is incident on it, and the generated electrical signal is transmitted to the base circuit board 27 via the readout element 21.

[0021] 3 shows a cross-sectional view of a GaN detector 11 according to an embodiment of the present invention. Referring to FIG. 3, a nitride semiconductor layer 31 may be formed on a GaN substrate 33. For example, the nitride semiconductor layer 31 may include a first nitride semiconductor layer 311, a second nitride semiconductor layer 312, and a third nitride semiconductor layer 313 that are sequentially stacked on the GaN substrate 33. For example, the nitride semiconductor layer 31 may be formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like.

[0022] The first nitride semiconductor layer 311, the second nitride semiconductor layer 312, and the third nitride semiconductor layer 313 may contain gallium nitride (GaN). For example, the first nitride semiconductor layer 311 may contain n-type gallium nitride, the second nitride semiconductor layer 312 may contain p-type gallium nitride, and the third nitride semiconductor layer 313 may contain p+-type gallium nitride.

[0023] A bottom electrode 35 may be formed on the bottom of the GaN substrate 33, and a top electrode 37 may be formed on the top of the nitride semiconductor layer 31. The bottom electrode 35 is a cathode and may be formed by sputtering or evaporation of a titanium or aluminum-based metal, for example. The top electrode 37 is an anode and may be formed by a lift-off process using a metal such as nickel or platinum.

[0024] In order to prevent avalanche breakdown due to electric field concentration that may occur at the edge region of the GaN detector 11, an inclined surface 39 is formed on the side surface of the nitride semiconductor layer 31. As shown in FIG. 3, the inclined surface 39 may be formed over the entire nitride semiconductor layers 311, 312, and 313 that constitute the nitride semiconductor layer 31, or may be formed only on a portion of the nitride semiconductor layers. For example, the inclined surface 39 may be formed by a mesa etching process. The inclined surface 39 may be formed to form an angle of 8 to 10 degrees with the vertical direction, which is suitable for use as a radiation detector using a bias voltage of approximately 100 to 500 V.

[0025] 4 is a diagram showing the circuit structure of a pixel 40 of a GaN detector 11 according to an embodiment of the present invention. Referring to FIG. 4, each pixel includes a capacitor 41 that stores charge generated by incident radiation and a transistor 43 that is connected to the capacitor 41 and functions as a charge sensitive amplifier, thereby improving the signal-to-noise performance of the detector. The capacitor 41 and the transistor 43 may be formed using the same manufacturing process.

[0026] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and includes all changes and modifications that can be easily modified from the embodiments of the present invention by a person having ordinary knowledge in the technical field to which the present invention belongs and are recognized as equivalent. [Industrial Applicability]

[0027] The present invention relates to a radiation detector and has industrial applicability.

Claims

1. a GaN detector array including a plurality of GaN detectors tiled to form a desired array structure; a readout element electrically coupled to the GaN detector; a base circuit board electrically coupled to the readout element.

2. the GaN detector includes an active region including a plurality of pixels for radiation sensing, and a barrier region surrounding the active region; 2. The radiation detector of claim 1, wherein the barrier region has a size corresponding to one pixel of the GaN detector.

3. the GaN detector includes a GaN substrate, a nitride semiconductor layer formed on the GaN substrate, a lower electrode formed on a lower portion of the GaN substrate, and an upper electrode formed on an upper portion of the nitride semiconductor layer; 2. The radiation detector according to claim 1, wherein the side surface of the nitride semiconductor layer includes an inclined surface formed at a predetermined angle with respect to the vertical direction.

4. 4. The radiation detector according to claim 3, wherein the predetermined angle is a value between 8 degrees and 10 degrees.

5. the GaN detector includes a plurality of pixels for sensing radiation; 2. The radiation detector of claim 1, wherein each of the plurality of pixels includes a capacitor for storing a charge generated in response to incident radiation, and a transistor connected to the capacitor and functioning as a charge-sensitive amplifier.

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