WO2020187769A1

WO2020187769A1 - Pixelation for a quantum dot porous silicon membrane-based radiation detector

Info

Publication number: WO2020187769A1
Application number: PCT/EP2020/056919
Authority: WO
Inventors: Marc Anthony CHAPPO; Ina Taylor MARTIN
Original assignee: Koninklijke Philips N.V.; Case Western Reserve University (Cwru)
Priority date: 2019-03-20
Filing date: 2020-03-13
Publication date: 2020-09-24

Abstract

A detection layer (316) of a radiation detector (312) includes a porous silicon membrane (318) having a first side (320), a second opposing side (324) having a surface (330), and a plurality of pores (326) extending entirely through the silicon from the first side to the second opposing side. The detection layer further includes a plurality of radiation sensitive quantum dots (328) in the pores. The surface of the second opposing side includes at least one 5 recess (332) into a pore of the pores filled with the quantum dots. The detection layer further includes a pixel contact (334) disposed on the second opposing and extending into the at least one recess of the second opposing side.

Description

PIXELATION FOR A QUANTUM DOT POROUS SILICON MEMBRANE-BASED

RADIATION DETECTOR

FIELD OF THE INVENTION

The following generally relates to imaging and more particular to pixelation for a quantum dot (QD) porous silicon (pSi) membrane-based radiation detector, and is described with particular application to computed tomography (CT) imaging; however, the QD-pSi membrane- based radiation detector is also amicable in other applications such as nuclear medicine, spectral radiation detectors for physics and astronomy applications, etc.

BACKGROUND OF THE INVENTION

The literature has discussed radiation detectors that include a single or multiple layers of Quantum Dot (QD) impregnated porous silicon (pSi) detection materials. FIGURE 1 shows a diagrammatic cross-sectional illustration of a sub-portion of an example of such a layer. In this example, a layer 102 includes silicon 104 with a top side 106, a bottom side 108, a plurality of pores 110 extending from the top side 106 only partially down a thickness 112 of the silicon 104, QDs 114 on the top side 106 and in the pores 110, and a pixel contact 116 on the bottom side 108. In this example, a bottom surface 118 of the pixel contact 116 is generally flat, providing a suitable surface for next level of assembly such as bonding with readout electronics.

A pSi-membrane, in contrast, has pores entirely through the Si. FIGURE 2 shows a diagrammatic cross-sectional perspective illustration of a sub-portion of an example of such a pSi-membrane. In this example, a pSi-membrane 202 includes silicon 204 with a top side 206, a bottom side 208, a plurality of pores 210 extending from the top side 206 to the bottom side 208 entirely through a thickness 212 of the silicon 204, QDs 214 on the top side 206 and in the pores 210, and a pixel contact 216 on the bottom side 208. A portion 215 of a front of the QDs 214 on the top side 206 is shown transparent to show the top side 206. The bottom side 208 is uneven, having recesses 220 at the pores 210.

As a consequence, a bottom surface 222 of the pixel contact 216 is uneven (i.e. not generally flat). Unfortunately, the uneven bottom surface 222 is not well-suited for next level of assembly such as bonding with readout electronics. For instance, reliability issues at the soldering or gluing assembly operation might be compromised. Processing technologies such as grinding and/or polishing can be added to the fabrication process to flatten the bottom surface 222 before adding the pixel contact 216. However, these additional fabrication processing steps add significant cost and/or time to the overall fabrication process and thus the product cost. SUMMARY OF THE INVENTION

Aspects described herein address the above-referenced problems and others.

The following generally relates to a porous silicon (pSi) membrane with pores extending through a thickness of the pSi membrane, filled with quantum dots (QDs) or other suitable material, and including recesses on a bottom surface. As described in greater detail below, in one non-limiting instance, a pixel contact disposed on the bottom surface extends into the recesses and has a flat outer surface, which is electrically coupled to readout electronics.

In one aspect, a detection layer of a radiation detector includes a porous silicon membrane having a first side, a second opposing side having a surface, and a plurality of pores extending entirely through the silicon from the first side to the second opposing side. The detection layer further includes a plurality of radiation sensitive quantum dots in the pores. The surface of the second opposing side includes at least one recess into a pore of the pores filled with the quantum dots. The detection layer further includes a pixel contact disposed on the second opposing and extending into the at least one recess of the second opposing side.

In another aspect, an imaging system includes a radiation source that transmits radiation, a detector array including a detector with a detection layer, where the detector detects radiation transmitted by the radiation source and generates a signal indicative thereof, and a reconstructor that reconstructs the signal to generate volumetric image data. The detection layer includes a porous silicon membrane with a first side, a second opposing side having a surface, and a plurality of pores extending entirely through the silicon from the first side to the surface of the second opposing side. The detection layer further includes a plurality of radiation sensitive quantum dots in the pores. The surface of the second opposing side includes at least one recess into a pore filled with the quantum dots. The detection layer further includes a pixel contact disposed on the second opposing side and including a generally flat outer surface.

In another aspect, a method includes transmitting, with a radiation source, radiation. The method further includes receiving, with a detection layer, transmitted radiation. The detection layer includes a porous silicon membrane with a first side, a second opposing side having a surface, and a plurality of pores extending entirely through the silicon from the first side to the surface of the second opposing side. The detection layer further includes a plurality of radiation sensitive quantum dots in the pores. The surface of the second opposing side includes at least one recess into a pore filled with the quantum dots. The detection layer further includes a pixel contact disposed on the second opposing side and including a generally flat outer surface. Those skilled in the art will recognize still other aspects of the present application upon reading and understanding the attached description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the embodiments and are not to be construed as limiting the invention.

FIGURE 1 diagrammatically illustrates a detection layer with a block of pSi with pores filled with QDs and a pixel contact, in accordance with an embodiment s) herein.

FIGURE 2 diagrammatically illustrates a pSi-membrane with pores filled with QDs and a pixel contact, in accordance with an embodiment s) herein.

FIGURE 3 diagrammatically illustrates an example imaging system with a radiation detector that includes the pSi-membrane with the QDs in the pores and the pixel contact, in accordance with an embodiment s) herein.

FIGURE 4 diagrammatically illustrates an example of the pixel contact bonded to a substrate, in accordance with an embodiment(s) herein.

FIGURE 5 shows an example of a portion of a pixel contact fabrication process, in accordance with an embodiment s) herein.

FIGURE 6 illustrates an example method in accordance with an embodiment(s) herein.

DETAILED DESCRIPTION OF EMBODIMENTS

The following generally relates to a porous silicon (pSi) membrane with pores extending through a thickness of the pSi membrane, filled with quantum dots (QDs), and including recesses on a bottom surface, wherein in one non-limiting instance a pixel contact is disposed on the bottom surface and extends into the recesses and has a flat outer surface, which is electrically coupled to readout electronics.

FIGURE 3 diagrammatically illustrates an imaging system 300 such as a computed tomography (CT) scanner. The imaging system 300 includes a stationary gantry 302 and a rotating gantry 304, which is rotatably supported by the stationary gantry 302 and rotates around an examination region 306 about a longitudinal or z-axis (“Z”).

A subject support 308, such as a couch, supports a subject or object in the examination region 306. The subject support 308 is movable in coordination with performing an imaging procedure so as to guide the subject or object with respect to the examination region 306 for loading, scanning, and/or unloading the subject or object.

A radiation source 310, such as an X-ray tube, is supported by and rotates with the rotating gantry 304 around the examination region 306. The radiation source 310 emits X- ray radiation that is collimated e.g., by a source collimator (not visible) to form a generally fan, wedge, cone or other shaped X-ray radiation beam that traverses the examination region 306.

A radiation sensitive detector array 312 subtends an angular arc opposite the radiation source 310 across the examination region 306. The radiation sensitive detector array 312 includes one or more rows of detectors 314. The detectors 314 detect radiation traversing the examination region 306 and generate electrical signals (projection data) indicative thereof.

In the illustrated example, each detector 314 includes at least one or more detection layer(s) 316. For sake of clarity, only one detection layer 316i is discussed in detail. The other detection layers 316 (if any) are structurally substantially similar to the detection layer 316i and thus will not be described in detail.

The detection layer 316i includes a p Si-membrane 318i with a top side 320i with a QD layer 322i, a bottom side 324i, pores 326i (only one shown for clarity) filled with QDs 328i (and/or any other material to convert radiation or light to electrical charge) an uneven surface 330i of the bottom side 324i with recesses 332i (only one shown for clarity) of the pores 326i, and a pixel contact 334i having a generally flat surface 336i. In this example, the QD layer 322i includes a radiation attenuating material (e.g., lead Sulfide, PbS), which attenuates the incoming radiation 338. An example of suitable QDs is described in application serial number EP

14186022.1, entitled“Encapsulated materials in porous particles,” and filed on September 23, 2014, the entirety of which is incorporated herein by reference.

As described in greater detail below, the recesses 332i are filled with contact material during fabrication of the pixel contact 334i on the uneven surface 330i of the bottom side 324i of the pSi-membrane 318i. As such, no new steps are added to the fabrication process to first flatten the uneven surface 330i before fabrication the pixel contact 334i on the uneven surface 330i. This mitigate adding additional fabrication steps to the fabrication process such as grinding and/or polishing steps to flatten the uneven surface 330i and thus the additional cost and/or time associated with such additional fabrication steps.

In one instance, the detection layer(s) 316 includes an indirect conversion (e.g., a scintillator / photosensor pair) detector. In another instance, the detection layer(s) 316 includes a direction conversion detector. Examples of p Si-based scintillator / photosensor and direction conversion detection layers are described in patent application serial number 62/202,397, filed August 7, 2015, and entitled“Quantum Dot Based Imaging Detector,” and patent application serial number 62/312,083, filed March 23, 2016, and entitled“Radiation Detector Scintillator with an Integral Through-Hole Interconnect,” the entireties of both are incorporated herein by reference.

For multi-detection layer configurations, routing signals through pixel walls described in patent application serial number 62/412,876, filed October 26, 2016, and entitled “Nano-Material Imaging Detector with an Imaging Detector with an Integral Pixel Border,” which is incorporated herein by reference in its entirety. A pixel wall with QDs in its border is further described in patent application serial number 62/312,083, filed March 23, 2016, and entitled“Nano-Material Imaging Detector with an Integral Pixel Border,” which is incorporated herein by reference in its entirety.

A reconstructor 340 reconstructs the projection data to generate volumetric image data. An operator console 342 includes a human readable output device such as a display monitor, a filmer, etc., and an input device such as a keyboard, mouse, etc. The operator console 342 is configured to control the rotating gantry 304, the subject support 308, the radiation source 310, the radiation detector 312, and/or the reconstructor 338.

FIGURE 4 diagrammatically illustrates an example showing the pixel contact 334i, the recesses 332i, contacts 402i on the pixel contact 334i, readout electronics 404i, and contacts 406i of readout electronics 404i. In this example, the pixel contact 334i incorporates the recesses 332i such that the recesses 332i are part of the pixel contact 334i and the surface 336i is flat. In this example, the contacts 402i of the pixel contact 334i are bonded (e.g., soldered, glued, covalent bond, etc.) to and in electrical communication with the contacts 402i of the readout electronics 404i. The readout electronics 404i can include an application specific integrated circuit (ASIC), a substrate, a printed circuit (pc) card (e.g., pc build up, flex, etc.), etc. Spaces 408i between pairs of the contacts 402i and contacts 406i can be filled with air, an insulative material, and/or other material.

In FIGURE 4, the recesses 332i are incorporated into the pixel contact 334i. In one instance, this allows for fabrication of the flat surface 336i. The flat surface 336i mitigates bonding reliability issues between the contacts 402i of the pixel contact 334i and contacts 402i of the readout electronics 404i such as those discussed in connection with FIGURE 1 where the recesses resulted in an uneven surface to bond with the readout electronics. Furthermore, incorporating the recesses 332i into the pixel contact 334i mitigate having to add additional processing to the fabrication process such as grinding and/or polishing to flatten the surface 336i. This mitigates the additional cost and/or time associated with such additional processing. The following describes a non-limiting example for incorporating the recesses 332i into the pixel contact 334i. Chemical vapor deposition (CVD) is used to deposit a metal into the recesses 332i and the side 324i. One approach would be to sputter metal films at pressures ranging from five (5) to thirty (30) millitorr mTorr). A higher pressure creates a more conformal coverage of the tortured surface and results in a mean free path on the order of one (1) centimeter (cm). The resulting gas phase collisions in a plasma of this density allow the depositing species to move out of the line of sight, resulting in a smoother surface coverage. FIGURE 5 shows an example of out of the line of sight trajectories 502. One approach is to use CVD to deposit thick contacts through a build-up process to achieve a desired flatness. As such, a flat interface layer is achieved with standard deposition processes without extra cost and the advantages of membranes for chemical processing and verification of QD impregnation.

Another approach is to deposit thick contacts through a sputtering build-up process. This approach uses the CVD process described above to deposit metal contacts, in conjunction with the standard line-of-sight physical vapor deposition (PVD) process. The CVD process would be used to smooth out the rough silicon surface. Then, once the surface is smoothed, PVD is used to thicken the contacts. An alternate approach would be to use a soft metal at the interface of the two layers, e.g., Indium (In), etc. Thermal evaporation of the In is used to deposit one hundred (100) to four hundred (400) nanometers (nm) of film for contacts.

In is soft at room temperature, and mild pressure or heat could be used to smooth out the rough contact area.

At 602, X-ray radiation is transmitted through an examination region and is being partially attenuated by an object thereon.

At 604, the partially attenuated X-ray radiation is detected by the detector array 312, which includes the pSi membrane 318i with the pixel contact 334i incorporating the recesses 332i, as described herein.

At 606, the detector array 312, in response to detecting the radiation, generates an electrical signal (projection data) indicative thereof.

At 608, the reconstructor 340 reconstructs the electrical signal, producing volumetric image data.

At 610, the console 342 displays volumetric image data.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

The word“comprising” does not exclude other elements or steps, and the indefinite article“a” or“an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A detection layer (316) of a radiation detector (312), comprising:

a porous silicon membrane (318), including:

a first side (320);

a second opposing side (324) having a surface (330); and

a plurality of pores (326) extending entirely through the porous silicon membrane from the first side to the second opposing side;

a plurality of radiation sensitive quantum dots (328) in the pores; wherein the surface of the second opposing side includes at least one recess (332) into a pore of the pores filled with the quantum dots; and

a pixel contact (334) disposed on the second opposing and extending into the at least one recess of the second opposing side.

2. The detection layer of claim 1, wherein the pixel contact further includes a flat outer surface (336).

3. The detection layer of claim 2, further comprising:

a plurality of contacts (402) disposed on the flat outer surface.

4. The detection layer of any of claims 1 to 3, further comprsing:

a layer of quantum dots (322) disposed on the first side.

5. The detection layer of claim 4, wherein the layer of quantum dots includes quantum dots containing lead and sulfur.

6. An imaging system (300), comprising:

a radiation source (310) that transmits radiation;

a detector array (312) including a detector (314) with a detection layer (316), the detection layer, including:

a porous silicon membrane, including:

a first side;

a second opposing side having a surface;

a plurality of pores extending entirely through the silicon from the first side to the surface of the second opposing side; a plurality of radiation sensitive quantum dots in the pores;

wherein the surface of the second opposing side includes at least one recess into a pore filled with the quantum dots; and

a pixel contact disposed on the second opposing side and including a generally flat outer surface;

wherein the detector detects radiation transmitted by the radiation source and generates a signal indicative thereof; and

a reconstructor (338) that reconstructs the signal to generate volumetric image data.

7. The detection layer of claim 6, wherein the pixel contact extends into the at least one recess of the second opposing side.

8. The detection layer of claim 7, further comprising:

a plurality of contacts disposed on the pixel contact;

readout electronics (404) including a pluraltiy of contacts (406),

wherein the plurality of contacts of the pixel contact are in electrical communication with the pluraltiy of contacts of the readout electronics.

9. The detection layer of claim 8, wherein the plurality of contacts of the pixel contact are soldered to the pluraltiy of contacts of the readout electronics.

10. The detection layer of claim 8, wherein the plurality of contacts of the pixel contact are glued to the pluraltiy of contacts of the readout electronics.

11. The detection layer of claim 8, wherein the plurality of contacts of the pixel contact are bonded to the pluraltiy of contacts of the readout electronics through a covalent bond.

12. The detection layer of claim 8, wherein the readout electronics includes an application specific integrated circuit.

13. The detection layer of claim 8, wherein the readout electronics includes a printed circuit card.

14. The detection layer of claim 8, wherein the readout electronics includes a flex circuit.

15. The detection layer of any of claims 6 to 14, further comprsing:

a layer of quantum dots disposed on the first side.

16. The detection layer of claim 15, wherein the layer of quantum dots includes quantum dots containing lead sulfide.

17. The detection layer of any of claims 15 to 16, wherein the layer of quantum dots faces the radiation source.

18. A method, comprising:

transmitting, with a radiation source, radiation; and

receiving, with a detector, transmitted radiation, wherein the detection layer includes:

a porous silicon membrane, including:

a first side;

a second opposing side having a surface; and

a plurality of pores extending entirely through the silicon from the first side to the surface of the second opposing side;

a plurality of radiation sensitive quantum dots in the pores;

a pixel contact disposed on the second opposing side and including a generally flat outer surface.

19. The method of claim 18, further comprising:

routing signal generated in the porous silicon membrane to readout electronics in electrical communication with the pixel contact.

20 The method of claim 19, comprising:

reconstructing the signal to generate volumetric image data.