Patent Description:
Computed tomography radiation detectors are largely comprised of crystal or garnet scintillators directly mounted to solid-state photodetectors such as photodiodes. The scintillator material produces light photons in response to bombardment with X-ray photons, which are then converted to electrical currents or pulses in the photodetector. Dual-energy spectral CT detectors include two scintillators stacked one on top of the other with photodetectors on their sides and are relatively expensive. Planar versions that have photodetectors in between scintillator layers require flex circuitry or a complex interconnect to bypass the intermediate layer(s) of scintillator(s). Spectral CT detectors made of Cadmium Zinc Telluride (CZT) or Cadmium Telluride (CdTe) have been utilized in limited applications, e.g., due to high cost, yield and/or performance issues.

Radiation detectors comprising Quantum Dot (QD) radiation absorptive materials in columns of porous silicon (pSi) membranes (i.e. QD-pSi radiation detectors) improve performance while lowering cost and decreasing thickness. QD-pSi radiation detectors require a connection to predefined areas of the Si without contacting the QD's in the pores (columns) in order to define a pixel area. In commercially available pSi membranes, the columns extend entirely through the pSi membrane and thus the QD's in the columns also extend from one side to the other side of the pSi membrane. As a consequence, while the definition of the pixel can be made by applying an electrically conductive contact having a predetermined size or by contacting an electrically conductive contact on a substrate, such an electrically conductive contact would also electrically contact the QD's in the pores of pSi membranes.

US patent <CIT> discloses direct conversion quantum dots (nano-crystals) in an active organic layer which may include electron or hole blocking of transport sub-layers.

<CIT> discloses a silicon block with columns of silicon interlaced with pores filled with quantum dots and metal contacts thereon and on an opposing side of the block.

The article "<NPL>, discloses a silicon block with columns and quantum dot-filled pores, a quantum dot layer on top and including aluminium contacts on top and bottom of the block.

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

In one aspect, an imaging module of an imaging system is provided according to claim <NUM>.

In another aspect, a computed tomography imaging system includes a radiation source configured to emit X-ray radiation, a detector array configured to detect X-ray radiation and generate an electrical signal indicative thereof, comprising a plurality of imaging modules (<NUM>) according to claim <NUM>; and a reconstructor configured to process the electrical signal and reconstruct volumetric image data.

In another aspect, a method is provided according to claim <NUM>.

Still further aspects of the present invention will be appreciated to those of ordinary skill in the art upon reading and understand the following detailed description.

The following generally describes an imaging system with a QD-pSi radiation detector that includes a pSi membrane with columnar holes that extend entirely through the Si and that are filled with QD's, which are electrically insulated (e.g., via an air gap or insulation material) from a metal pad that defines a size of a pixel. In one instance, this configuration preserves the cost reduction afforded by pSi and retains the performance of simultaneous spectral and spatial resolution inherent in a pSi/QD radiation detector.

<FIG> schematically illustrates an example imaging system <NUM> such as a computed tomography (CT) system configured for spectral and/or non-spectral imaging. The imaging system <NUM> includes a stationary gantry <NUM> and a rotating gantry <NUM>, which is rotatably supported by the stationary gantry <NUM>. The rotating gantry <NUM> rotates around an examination region <NUM> about a longitudinal or z-axis <NUM>. A radiation source <NUM>, such as an x-ray tube, is supported by the rotating gantry <NUM>, rotates therewith, and generates and emits X-ray radiation.

A radiation sensitive detector array <NUM> includes one or more rows arranged parallel to each other along the z-axis <NUM> direction, each row including a plurality of detector modules <NUM> extending transverse to the z-axis <NUM> direction. The modules <NUM> detect X-ray radiation traversing the examination region <NUM> and generate electrical signals (projection data) indicative thereof. At least one of the modules <NUM> includes a top contact <NUM>, a pSi membrane <NUM> with columnar holes filled with QD's <NUM>, a metal pad <NUM>, and a substrate <NUM> electrically coupled to the Si in the pSi membrane <NUM> via the metal pad <NUM>. A size of a pixel is defined by a size of the metal pad <NUM>, as described in greater detail below.

Also described in greater detail below, in one instance, the columnar holes extend all the way through the pSi membrane <NUM> and the QD's <NUM> in the columnar holes are electrically insulated from the metal pad <NUM>. In one instance, this is accomplished by ensuring that the QDs are recessed relative to a plane of the pSi such that a separate substrate bonded to the to the pSi plane only contacts the pSi columns within a pixel and not the QDs. As an example not forming part of the claimed invention, it is accomplished with a Si contact layer on the pSi die that only contacts the columns of pSi and not the QD's. For the former, the recess can be empty or filled with an insulating material to prohibit contact with the QDs in the column.

A reconstructor <NUM> reconstructs the electrical signals with one or more reconstruction algorithms. In one instance, the one or more reconstruction algorithms includes one or more spectral reconstruction algorithms and/or at least one non-spectral reconstruction algorithm. The one or more reconstruction algorithms reconstruct spectral volumetric image data corresponding to one or more different energy spectra, basis component, and/or material composition. The at least one non-spectral reconstruction algorithm reconstructs non-spectral volumetric image data corresponding to a mean energy spectrum of the X-ray beam.

A subject support <NUM>, such as a couch, supports an object or subject in the examination region <NUM> so as to guide the subject or object with respect to the examination region <NUM> for loading, scanning, and/or unloading the subject or object. A computing system serves as an operator console <NUM> and includes a human readable output device such as a display, an input device such as a keyboard, mouse, and/or the like, one or more processors and computer readable storage medium. Software resident on the console <NUM> allows an operator to control an operation of the imaging system <NUM>.

<FIG> and <FIG> schematically illustrate an example pixel of the module <NUM>. <FIG> includes an exploded view <NUM>. The module <NUM> includes the top contact <NUM>, the pSi membrane <NUM>, an electrically conductive connection <NUM> (e.g., an electrically conductive adhesive and/or conductive connection. ), the metal pad <NUM>, and the substrate <NUM> with one or more electrically conductive pads <NUM> and one or more electrically conductive vias <NUM>. In one instance, the substrate <NUM> includes an integrated circuit (IC), an application specific integrated circuit (ASIC), or the like.

In this example, the pSi membrane <NUM> includes a first side <NUM> and a second (contact) side <NUM>. The first side <NUM> is adjacent to the top contact <NUM> and faces the examination region <NUM> (<FIG>) and the second side <NUM> faces the electrically conductive connection <NUM>. The pSi membrane <NUM> includes a plurality of columns, including columns of Si <NUM> interlaced with columnar holes <NUM>. The pSi membrane <NUM> and hence the columns of Si <NUM> and the columnar holes <NUM> have a height <NUM> (on the order of hundreds of microns) from the first side <NUM> to the second side <NUM>. The widths of the columns of Si <NUM> and the columnar holes <NUM> are on the order of microns.

The columnar holes <NUM> of the pSi membrane <NUM> are filled with QD's <NUM> from the first side <NUM> to a depth <NUM>, which is less than the height <NUM>. A recess <NUM> of the columnar holes <NUM> of the pSi membrane <NUM> from the QD's <NUM> to the second side <NUM> and has a depth <NUM> (e.g., a smallest practical depth), which also is less than the height <NUM>. In general, a summation of the depths <NUM> and <NUM> add up to the height <NUM>. In one instance, the recess <NUM> is an empty, material free space. In another instance, the recess <NUM> is filled with an insulating material such as silicon dioxide, etc..

The QD's <NUM> in the columnar holes <NUM> and the Si in the columns of Si <NUM> interact to convert received X-ray radiation into an electrical charge (signal, pulse, etc.) via electron-hole pair generation. This is further described in application serial number <CIT>. QD's in imaging detectors are also described in application publication number <CIT>. Suitable QD's include lead sulfide (PbS) QD's and/or other QD's.

The pSi membrane <NUM> is electrically coupled to the metal pad <NUM> through the electrically conductive connection <NUM>. This coupling electrically couples the Si in the columns of Si <NUM> and not the QD's <NUM> in the columnar holes <NUM> to the metal pad <NUM>, as the QD's <NUM> in the columnar holes <NUM> are electrically insulated via the air or the insulation material in the recess <NUM> from the electrically conductive connection <NUM>. The metal pad <NUM> is disposed on the substrate <NUM>. The electrical signal is routed from the pSi membrane <NUM> through the electrically conductive connection <NUM> and the metal pad <NUM> to the substrate <NUM>, where it is readout through the one or more vias <NUM> and the one or more pads <NUM>.

A size of a pixel is determined by a surface area of the metal pad <NUM>. For example, the size of the pixel in the illustrated embodiment is determined by the number of columns of Si <NUM> in electrical contact with the metal pad <NUM>. A smaller pixel requires the metal pad <NUM> to have a smaller surface area, which electrically contacts fewer of the columns of Si <NUM>. A larger pixel requires the metal pad <NUM> to have a larger surface area, which electrically contacts more of the columns of Si <NUM>. Generally, the pitch of the columnar holes <NUM> is on the order of microns, and a typical pixel size is on the order of hundreds of microns.

The top contact <NUM>, the pSi membrane <NUM>, and the substrate <NUM> extend out past the pixel area, i.e. out past the metal pad <NUM> and the electrically conductive connection <NUM>. In this example, portions of a metal pad <NUM>' and an electrically conductive connection <NUM>' of a second pixel are shown to the left and portions of a metal pad <NUM>" and an electrically conductive connection <NUM>'' of a third pixel are shown to the right of the pixel defined by the metal pad <NUM> and the electrically conductive connection <NUM>. Gaps <NUM> electrically insulate neighboring pixels. The gaps <NUM> can be filled with air, an insulator, etc. In a variation, the pixel is an end pixel and does not have a neighboring pixel on each side.

<FIG> illustrates a variation of the module <NUM> shown in <FIG> and <FIG>. In this variation, the pSi membrane <NUM> further includes outer columns of QD's <NUM>, which extend from the first side <NUM> of the pSi membrane <NUM> to the second side <NUM> and the substrate <NUM>. Gaps <NUM> electrically insulate the metal pad <NUM> and the electrically conductive connection <NUM> from the outer columns of QD's <NUM>. The gaps <NUM> can be filled with air, an insulator, etc. In one instance, the columns <NUM> provide direct electrical connections from the first side <NUM> of the pSi membrane <NUM> to the substrate <NUM>.

An example of an electrical connection through a column of QD's is described in application serial number <CIT>, and entitled "Radiation Detector Scintillator with an Integral Through-Hole Interconnect,". Alternatively, through-silicon vias (TSVs) and/or other approaches can be used for direct electrical connections between the first side <NUM> of the pSi membrane <NUM> and the substrate <NUM>, where it is connected to the one or more pads <NUM> by the one or more vias <NUM>.

<FIG> illustrates an example method in accordance with an embodiment(s) herein.

At <NUM>, a pSi membrane with columnar holes entirely through the Si is procured.

At <NUM>, the columnar holes are entirely filled with the QD's.

At <NUM>, a contact side of the pSi membrane is placed in contact with (e.g., floated on) a viscous hydrocarbon capable of dissolving the QDs.

At <NUM>, the viscous hydrocarbon dissolves surface ligand-capped PbS QDs.

At <NUM>, the viscous hydrocarbon penetrates into the columnar holes, dissolving QDs therein and creating a recess therein. The depth of the penetration is determined based on the viscosity of the hydrocarbon and a contact time between the contact side and the viscous hydrocarbon. For example, the longer the contact time and/or the greater the viscosity, the greater the penetration depth. Generally, the contact time is a predetermined period of time t.

At <NUM>, the recesses are filled with an insulating material via standard deposition process. Alternatively, the recesses are left empty.

At <NUM>, the contact side of the pSi membrane is polished to remove material bound to the surface.

At <NUM>, the contact side of the pSi membrane is electrically coupled to the substrate via an electrically conductive adhesive and a metal pad.

In the non-limiting example method described in connection with <FIG>, any solution processed solid deposition method can be used to fill pores with active material. In a variation, a vapor/gas phase deposition (e.g., Atomic Layer Deposition, ALD) is used. Other approaches are also contemplated herein.

<FIG> illustrates an example method in accordance with an embodiment(s) herein.

At <NUM>, a contact side of the pSi membrane is chemically mechanically polished with a non-polar hydrocarbon-based polishing compound that mechanically and chemically removes surface QDs.

At <NUM>, the exposed ends of the columnar holes are chemically etched to remove QD's in the columnar holes and create recesses.

In the non-limiting example method described in connection with <FIG>, a non-polar solvent is used to mechanically and chemically remove surface QDs. In general, any solvent capable of re-solubilizing the deposited material without impacting the pSi can be used. Depending on the processing of the QDs or the chemical nature of the solid deposited in the pores, these may be polar (water, alcohol, etc.) or non-polar (hexane, toluene) or chemically reducing/oxidizing.

In another embodiment, a combination of a solvent treatment and chemical mechanical processing are employed to simultaneously abrade the back surface of the pSi membrane.

At <NUM>, at least two pSi membranes are procured.

At <NUM>, columnar holes of one of the pSi membranes are filled with the QD's.

At <NUM>, columnar holes of the other of the pSi membranes are filled with an electrical insulator or left empty.

At <NUM>, the two the pSi membranes are stacked with the pSi membrane with the QD's on top of the pSi membrane without the QD's.

At <NUM>, the stacked pSi membranes are electrically coupled to a substrate via an electrically conductive adhesive and a metal pad.

It is to be understood that the above techniques allow proper pixel sizing and operation at this level to preserve both the increased efficiency and the lower cost of the detectors. Thus, once the assembly of the detector into a standard building block of a CT detector system is accomplished, imaging performance is improved in both conventional and spectral CT at a reduced cost. This applies to medical and baggage scanning multiple energy spectral X-ray radiation detectors, such a dual energy medical CT system, as well as phase contrast and dark field imaging applications where QD pSi radiation detectors have a columnar construction that can serve as a built-in grating between pixels, and/or other applications such as spectroscopy, etc..

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.

Claim 1:
An imaging module (<NUM>) of an imaging system (<NUM>), comprising:
a porous silicon membrane (<NUM>) including:
a first side (<NUM>);
a contact side (<NUM>) opposite the first side;
columns of silicon (<NUM>) configured to extend from the first side to the contact side; and
columnar holes (<NUM>, <NUM>) interlaced with the columns of silicon and configured to extend from the first side to the contact side; and
quantum dots (<NUM>) in the columnar holes;
characterized in that
the columnar holes contain a recess (<NUM>) on the contact side, the recess is one of being an empty, material free space and being filled with an insulating material, and
the module further comprisesa metal pad (<NUM>) electrically coupled to the columns of silicon of the porous silicon membrane, wherein the quantum dots in the columnar holes are electrically insulated by means of the recess from the metal pad; and
a substrate (<NUM>) including: an electrically conductive pad (<NUM>) in electrical communication with the metal pad.