Patent Application
20140138547
The present disclosure relates generally to detecting high energy photons (i.e., gamma rays and/or X-rays) with a detector built as a semiconductor detector device.
High energy photon detectors are used for various purposes such as Positron Emission Tomography (PET), back scatter imaging of high energy photons, and transmission imaging of high energy photons. For instance, an array of gamma ray detectors used in a PET scan produces a three-dimensional image of a bodily structure. Each gamma ray detector used in PET typically has a scintillator crystal coupled to a photomultiplier tube, which amplifies the light generated in the crystal by a gamma ray interaction. These gamma ray detectors are generally assembled individually and bulky. The individual detectors are then mechanically fastened together to form the array. However, image resolution may be limited due the bulkiness of each detector. That is, the minimum spacing between detectors may be limited due to the size of the detectors. In addition, fabrication costs of individual detectors can be high. Hence, it would be appreciated in various industries requiring gamma ray detector arrays, if the size and cost of the arrays could be reduced.
Disclosed is an apparatus for detecting a high energy photon. The apparatus includes a scintillator material having an array of scintillator pixels where each scintillator pixel is configured to receive a high energy photon and to scintillate upon interacting with the received high energy photon to generate a scintillation photon. A photon transducer is bonded to the scintillator material and configured to generate an electrical signal indicative of detecting the high energy photon upon the photon transducer interacting with the scintillation photon generated by a scintillator pixel in the array of scintillator pixels. An integrated circuit is coupled to the photon transducer and configured to receive the electrical signal and to provide an output signal having information related to detecting the high energy photon and identifying the scintillator pixel that interacted with the high energy photon to generate the scintillation photon.
Also disclosed is a method for detecting a high energy photon. The method includes receiving the high energy photon with a scintillator material comprising an array of scintillator pixels, each scintillator pixel being configured receive a high energy photon and to scintillate upon interacting with the high energy photon to generate a scintillation photon. The method also includes generating an electrical signal with a photon transducer that is bonded to the scintillator material and receives the scintillation photon, the electrical signal being indicative of detecting the high energy photon. The method further includes providing an output signal with an integrated circuit that is coupled to the photon transducer and receives the electrical signal, the output signal having information related to detecting the high energy photon and identifying the scintillator pixel that interacted with the high energy photon to generate the scintillation photon.
Further disclosed is a method for fabricating a detector for detecting a high energy photon. The method includes selecting a scintillator material having an array of scintillator pixels where each scintillator pixel is configured receive a high energy photon and to scintillate upon interacting with the high energy photon to generate a scintillation photon. The method also includes bonding the scintillator material to a photon transducer configured to generate an electrical signal indicative of detecting the high energy photon upon the photon transducer interacting with the scintillation photon. The method further includes coupling a readout integrated circuit to the photon transducer, the readout integrated circuit being configured to receive the electrical signal and identify a corresponding scintillator pixel from which the electrical signal is derived and to provide an output signal comprising information identifying the corresponding scintillator pixel and high energy photon detection information.
For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts:
A detailed description of one or more embodiments of the disclosed apparatus and method is presented herein by way of exemplification and not limitation with reference to the Figures.
Still referring to
The photon transducer 4 is fabricated from a semiconductor substrate or wafer. In one or more embodiments, the photon transducer 4 is a PIN diode 5 or array of PIN diodes 5 in which each PIN diode 5 includes a P-type semiconductor region, an intrinsic (I) semiconductor region, and an N-type semiconductor region. A reverse bias electric field applied across the PIN diode(s) 5 sweeps the free carriers out of the corresponding region(s) and creates the electrical signal. In one or more embodiments, the PIN diode 5 is configured to provide avalanche multiplication of the generated electrical carriers in order to provide signal gain. In one or more embodiments, the PIN diode 5 is fabricated from a silicon substrate or wafer and may be referred as a SiPIN diode.
In general, the amount of low energy photons generated by scintillation is proportional to the energy of the incoming high energy photon. Hence, the amplitude of current generated in the photon transducer 4 may be used as an indication of the energy of the incoming high energy photon. The electrical signal generated in the photon transducer 4 may include information regarding detection of a high energy photon (e.g., a signal pulse), the energy of the detected high energy photon (e.g., amplitude of a signal pulse), and/or the intensity of a detected stream of high energy photons (e.g., pulse rate of signal).
In one or more embodiments, the scintillator material 3 is a cerium-doped lutetium silicate such as LuSiO5:Ce. An advantage of cerium-doped lutetium silicate is that it has an extremely high energy photon absorption efficiency compared to other materials (including both scintillators and semiconductor absorbers), as shown in the graph in
In the embodiment of
Still referring to
During a fabrication process for fabricating the high energy photon detector 10, the scintillator material 3 is bonded to the PIN diode 5 (or photon transducer 4). In one or more embodiments, the bonding process is direct bonding that is based on chemical bonds between the scintillator material 3 and the PIN diode 5 (or photon transducer 4). The direct bonding process in general requires that the surfaces to be bonded be sufficiently clean, flat and smooth. The surfaces are generally placed in contact at room temperature in air, a special gaseous atmosphere or a vacuum where the surfaces start to bond (i.e., pre-bonding). Then, the pre-bonded surfaces are annealed at an elevated temperature that provides a certain amount of thermal energy, which forces more groups of molecules to react among each other to form new, highly stable chemical bonds. In another embodiment, the scintillator material 3 is bonded to the PIN diode 5 (or photon transducer 4) using an adhesive 20 as illustrated in
Reference may now be had to
The PIN diode 5 when used with the high energy photon detector 10 having the array 30 of scintillator pixels 31 may include a plurality of PIN diodes 5 (or photon transducers 4) or discrete regions distinguished electrically or physically (i.e., forming “unit cells”) in which each unit cell in the plurality is associated with one of the scintillator pixels 31 in the array 30. Alternatively, multiple unit cells within the PIN diode 5 (or photon transducer 4) may be associated with the same single scintillator pixel 31. Alternatively, one PIN diode 5 (or photon transducer 4) or unit cell may be used with the entire array 30 or a portion of the array 30 and electronic techniques may be used to correlate the generated electrical signal with the scintillator pixel 31 that emitted the scintillation photon used to generate the electrical signal. In one or more embodiments, these electronic techniques may include using multiple connections to the PIN diode 5 (or photon transducer 4) where each connection relates to a region in the PIN diode 5 (or photon transducer 4) that corresponds to one of the pixels 31. Thus, the connection having the highest electrical signal can be correlated to the pixel 31 that scintillates to generate that current in the diode 4. The integrated circuit 6 in the embodiment of
Reference may now be had to
The high energy photon detector 10 has several advantages over traditional gamma ray detectors such as a germanium detectors and photomultiplier tube assemblies. One advantage is that the high energy photon detector 10 lends itself to automated semiconductor or wafer fabrication and processing techniques, such as photolithography and direct bonding, which are much more easily scaled than discrete unit assembly of photomultiplier assemblies. Scaling and consequently decreased fabrication costs may mean increased applications utilizing an array of scintillator pixels. Another advantage is that wafer level direct bonding allows integration of large Lu2SiO3:Ce scintillator crystals, which have a higher absorption capability than germanium, silicon, CdZnTe, or scintillators traditionally deposited on Flat Panel Detectors (FPDs); this translates to lower detection thresholds, greater signal strengths, and low exposure dosages to objects subject to high energy photon interrogation.
Digital transmission high energy photon imaging is generally performed by FPDs. Traditional FPDs are constructed by depositing layers of semiconductor and scintillator materials onto a large glass substrate, wherein the scintillator is used to capture the energy of incoming photons and the semiconductor is patterned as thin film transistors (TFT) and used to covert light emitted by the scintillator into an electrical signal (voltage or current). However, the presence of contacts to the TFTs reduces the useful detector area (i.e., fill factor) of interface between the scintillator and the TFT, and the scintillator materials that are able to be deposited onto the substrates are not optimized for high energy photon absorption, which requires greater dosages of, for instance, X-rays to be delivered to the test subject. Further, since any logic circuitry is physically separated from the detecting region of the FPD, the complexity of the detectors operation is limited. The use of the high energy photon detector 10 in lieu of FPDs provides for a 100% fill factor (i.e., useful detector area) and incorporation of active integrated circuitry at the pixel level (for instance, per-pixel gain corrections or dynamic range adjustments.
Back-scatter imaging with high energy photons is traditionally performed by CdZnTe or Ge detectors, which must be cooled to cryogenic temperatures to operate. It is particularly advantageous that the use of the high energy photon detector 10 in these applications does not require cooling. It is especially advantageous for “field applications” such as mine or improved explosive device detection systems that the detectors not require cryogenic cooling.
Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The conjunction “or” when used with a list of at least two terms is intended to mean any term or combination of terms. The term “couple” relates to one component being coupled either directly to another component or indirectly to another component via one or more intermediate components.
While the disclosure has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
