Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/30—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from X-rays
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
  • H04N23/70—Circuitry for compensating brightness variation in the scene
  • H04N23/71—Circuitry for evaluating the brightness variation
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/10—Integrated devices
  • H10F39/12—Image sensors
  • H10F39/18—Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors
  • H10F39/189—X-ray, gamma-ray or corpuscular radiation imagers
  • H10F39/1892—Direct radiation image sensors

Definitions

• This invention relates to a self-triggering imaging device for imaging radiation, in particular, but not exclusively, to an imaging device for a self-triggerable imaging system; the imaging device comprising an array of image elements.
• Imaging devices comprising an array of image elements of various types are known.
• Charged coupled image sensors also known as charged coupled devices (CCDs) form one type of known imaging device.
• CCD type device operates in the following way:
• Charge is accumulated within a depletion region created by an applied voltage.
• the depletion region has a potential well shape and constrains electrons under an electrode gate to remain within the semiconductor substrate.
• the buffer circuits can either be on the same substrate (EP-A- 0,287,197) as the charge collection volumes, or on a separate substrate (EP-A-0,571,135) that is mechanically bonded to a substrate having the charge collection volumes in accordance with, for example, the well known bump-bonding technique.
• ASID Active-pixel Semiconductor Imaging Device
• the ASID comprises an array of pixel cells including a semiconductor substrate having an array of pixel detectors and a further array of pixel circuits.
• the pixel detectors generate charge in response to instant radiation.
• Each pixel circuit is associated with a respective pixel 2
• the pixel circuits are individually addressable and comprise circuitry which enables charge to be accumulated from a plurality of successive radiation hits on the respective pixel detectors.
• the device operates by accumulating charge on the gate, for example, of a transistor. Accordingly, analogue storage of the charge value is obtained.
• the charge from the pixel circuits can be read out and used to generate an image based on the analogue charge values stored in each of the pixel circuits.
• CCD devices suffer from disadvantages of limited dynamic range, due to the limited capacity of the potential well inside the semiconductor substrate, and also to the inactive times during which an image is read out.
• Pulse counting semiconductive pixel devices also have the disadvantage of limited dynamic range. As these devices read the pixel contact when a hit is detected, they suffer from saturation problems at high counting rates.
• the semiconductor pixel device according to WO95/33332 provides significant advantages over the earlier prior art by providing a large dyriamic range for the accumulation of images .
• a CCD is electrically connected to an X-ray source.
• a start signal is transmitted along the connecting wire to the CCD and its control circuitry to begin image acquisition and read-out.
• European Patent Application Publication No. 0 756 416 Al discloses a CCD used as an imaging device in which charge accumulated in the CCD elements is clocked from several rows into a register in order to sum the charges. The summed result is put to a threshold test. Onset of X-ray radiation is detected when the signal applied to the threshold 3
• the X-ray source and CCD have again no physical connection.
• a further sensor is arranged close to the imaging array for the CCD to detect the onset of X-ray radiation. On detection of incident X-ray energy, the sensor sends a signal to the CCD control circuitry to initiate image acquisition, as before.
• a semiconductor radiation imaging device including: an array of image elements, each image element of said array comprising an image element detector cell which generates charge in response to radiation incident on said image element and image element circuitry for accumulating said charge from said image element detector cell and for selectively outputting a signal representative of accumulated charge; and a radiation sensor element, said radiation sensor element comprising a radiation detector cell integral with said image element detector cells for generating charge in response to incident radiation on said radiation sensor element and a radiation sensor output for continuously supplying charge from said radiation detector cell.
• said radiation sensor output is adapted for continuously supplying a signal representative of charge generated in response to radiation incident on said radiation sensor element.
• said radiation detector cell is more responsive to incident radiation than an image element detector cell.
• said radiation detector cell comprises a larger area than said image element detector cell.
• said radiation detector cell comprises a guard ring for said array of image element detector cells and optionally the guard ring is substantially continuous.
• the imaging device includes a unitary substrate comprising said image element detector cell, said image element circuitry and said radiation detector cell. 4
• the imaging device includes a first and second substrate, the first substrate comprising said image element detector cell and said radiation detector cell, and the second substrate comprising said image element circuitry.
• An embodiment in accordance with a second aspect of the invention comprises a self-triggerable imaging system including an imaging device as described in the foregoing paragraphs, the imaging system further comprising control circuitry for controlling the imaging device, an image processor for processing charge values from said array of image elements to form an image on a display device, and threshold circuitry coupled to said radiation sensor output.
• the imaging device comprises threshold circuitry coupled to the radiation sensor output.
• the threshold circuitry is operable to output a trigger signal to the control circuitry for the charge or signal on the radiation sensor output exceeding a threshold value.
• the control circuitry is configurable to initiate image acquisition responsive to said trigger signal from the threshold circuitry.
• the control circuitry is configurable to periodically monitor for the trigger signal.
• the imaging system further comprises an analogue to digital converter for converting an analogue signal supplied on the radiation sensor output to a digital value, and the digital value is subjected to a threshold test.
• a method comprising providing an imaging device as described above, and including the steps of monitoring said radiation sense output, comparing signals from said radiation sense output with a threshold and outputting a control signal for initiating reading of the array for said charge or signal exceeding the threshold.
• a method for providing a trigger signal for radiation imaging comprising, providing a radiation sensor integral with an image plane including an array of radiation detectors for collecting incident radiation for forming a radiation image, the radiation sensor being more responsive to incident radiation than a one of the array of radiation detectors and generating a signal indicative of radiation incident on the radiation sensor, 5
• the method comprises further providing control circuitry for controlling reading the array responsive to said control signal.
• the step of monitoring comprises periodically monitoring the radiation sensor output or for the control signal.
• Figure 1 is a schematic block diagram of an overall imaging configuration
• Figure 2 is a cross-section of one example of an imaging device
• Figure 3 is a schematic diagram of a plan view of corner of the image device of Figure 2.
• FIG. 4 is a schematic block diagram of an imaging configuration in accordance with an embodiment of the invention.
• Figure 5 is a flow chart for operating the configuration shown in Figure 4.
• FIG. 1 is a schematic block diagram of one example of an imaging system using an imaging device in accordance with the present invention.
• This particular embodiment is directed to the imaging of high energy radiation, for example X-ray radiation.
• high energy radiation is meant radiation having an energy in excess of approximately 1 KeV.
• the invention is by no means limited to high energy radiation such as X-rays but could be applied to the detection of any particular radiation , for example ⁇ -ray, ⁇ -ray, ⁇ - ray , infra-red or optical radiation, subject to an appropriate choice of semiconductor substrate.
• the imaging system 10 of Figure 1 is shown to provide imaging of an object 12 subject to radiation 14.
• the radiation may, for example, be X-ray radiation as mentioned above, but could alternatively be ⁇ -ray, ⁇ -ray or ⁇ -ray radiation.
• the imaging device 16 comprises a plurality of image elements (here elements 18 of a two dimensional image element array).
• image elements here elements 18 of a two dimensional image element array.
• the individual image elements may have a configuration other than that of an element within a two dimensional array (eg a strip arrangement).
• the imaging device detects directly high energy incident radiation and accumulates at each image element, a count of the incident radiation hits at that image element.
• the imaging device can be configured as a single semiconductor substrate (eg, of silicon) with each image element comprising an image element detector 19 and image element circuitry 20.
• the imaging device 16 can be configured on two substrates, one with an array of image element detectors and one with an array of corresponding image element circuits 20, the substrates being mechanically connected to each other by, for example, conventional bump-bonding technology or any other appropriate technology.
• Figure 2 is a schematic cross section of part of an imaging device 16.
• the imaging device 16 comprises an image detector substrate 30 connected to an image circuit substrate 32 by means of bump-bonds 34.
• An image element detector 19 of each image element 18 is defined on the detector substrate 30 by a continuous electrode 36 which applies a biasing voltage and image element location electrodes 38 to define a detection zone for the image element 18.
• Corresponding image element circuits 20 on the image circuit substrate 32 are defined at locations corresponding to the electrodes 38 (ie to the image element detectors 19).
• the image element circuits 20 are electrically connected to the corresponding electrodes 38 by bump-bonds 34. In this manner, when charge is generated in an image element detector 19 in response to incident radiation, this charge is passed via the bump-bond 34 to the corresponding image element circuit 20.
• the actual size of the image element circuit and the image element detector will depend on the application for which the imaging device is intended. As mentioned above, the image element detectors and image element circuits could be constructed integrally on a single semiconductor substrate. Such an implementation is possible, but sets challenges unrelated to the present invention, relating to circuit manufacturing techniques. With suitable circuit manufacturing techniques, the invention as described herein is perfectly applicable to implementation on a single semiconductor substrate, as opposed to the dual-substrate technique described herein.
• any appropriate semiconductor materials can be used for the substrates.
• silicon may be used for the detector substrate and for the image circuit substrate. 7
• the material could be selected from: CdZnTe, CdTe, Hgl 2 , InSb, GaAs, Ge, TIBr, Si and Pbl.
• an electric charge is created, (or charged particle or gamma-ray is incident or absorbed for other embodiments) an electric pulse flows from image element detector 19 via the bump-bonds 34 to corresponding image element circuitry 20.
• image element circuit 20 is not relevant to the instant invention and no further description thereof shall be given, except to say that charge is accumulated within the image element circuit 20 from image element detector 19.
• Figure 2 also shows a guard ring area 48 integral with the detector substrate 30.
• the guard ring area 48 generally surrounds all the image elements 18, and may comprise several guard rings 50.
• the guard rings 50 are made from a conductive material, preferably the same material as used for image element location electrodes 38 in order for the guard rings to be fabricated at the same time as the image element electrodes 38.
• the guard ring area 48, defined by guard rings 50 reduces charge injection due to crystal defects at the edge of the detector substrate 30 by reducing the localised increase in field strength at the edge for the detector substrate 30 material.
• Continuous electrode 36 extends into the guard ring area 48 and also applies a bias voltage in the guard ring area 48. This forms a further detection zone hereinafter referred to as radiation detection cell 57, between the guard ring 48/50 and the continuous electrode 36.
• the applicant has realised that the guard ring 48/50 is exposed to radiation when the imaging device is irradiated, as well as the image element detectors 19.
• the applicant has utilised their understanding to provide a novel and inventive approach to the problems of the prior art, and to provide for self-triggering of an imaging device.
• At least one of the guard rings 50 is coupled via bump-bond 52 to output circuitry 54.
• Charge created by the absorption of X- ray photons is coupled from the guard ring 50 via bump-bond 52 to the output circuitry 54.
• Output circuitry 54 is coupled to a radiation sensor output 70.
• Figure 3 shows a corner 60 of detector substrate 30. Image element location electrodes 38 are disposed inside the guard ring area 48. As mentioned earlier, radiation 8
• guard rings 50 comprising the guard ring area 48.
• the guard ring area 48 may comprise more than one guard ring 50 for gradually reducing the field strength towards the edge of the detector substrate 30.
• the guard ring 50 is coupled to output circuitry 54 via a bump-band 52, which is directly coupled to a radiation sensor output pin on the imaging device.
• An object 66 is subject to radiation 68 from a radiation source 74.
• the radiation may be, for example, X-ray radiation, gamma-radiation, beta-ray radiation or alpha-ray radiation.
• the object 66 may be a part of the human body.
• imaging device 72 comprises a plurality of image elements in either a two or one dimensional element array or a strip arrangement, for example. Imaging device 72 is similar to imaging device 16 of Figure 1 and will be described no further, except to say that imaging device 72 comprises a guard ring 48 as described with reference to Figures 2 and 3.
• Guard ring 48 is coupled via output circuitry 54, which may be no more than a conductive path, to radiation sensor output 70.
• Radiation sensor output 70 provides a current Iguard representative of the radiation incident on the guard ring 48.
• Current Iguard is input to a current to voltage converter 78, and the resulting voltage is input to threshold circuitry 80.
• the threshold circuitry 80 has input to it a reference threshold voltage 81 Vm .
• the threshold circuitry 80 outputs a signal to control electronics 76 indicating that the threshold has been exceeded.
• Control electronics 76 initiates image acquisition electronics 83, and signals to the system controlling computer 84 that the threshold 81 has been exceeded, i.e. radiation incident an imaging device 72 and image acquisition has been initiated.
• Image acquisition comprises integrating the image, ie. charge on each image element, and continues until the threshold circuitry 80 indicates that the voltage has dropped below the threshold 81. That is to say, Iguard drops, indicating that the radiation source 74 has been switched off. 9
• the guard ring current is output, and then amplified and converted to a voltage at step 504.
• a threshold test is performed at step 506, and may be done by discrete circuitry or under program control on a digitised voltage.
• a decision is made as to whether the threshold has been exceeded. Again, such a decision may be by way of discrete circuitry included in threshold circuitry, or under the control of the suitably configured system controlling computer, for example.
• the process returns to step 502.
• the threshold is exceeded then the image acquisition mode is initiated at step 510.
• the image is integrated whilst the image acquisition mode is active, and the guard ring output is monitored against the threshold at steps 512, 514 and 516. Whilst the threshold is exceeded, image acquisition continues and the process loops round 512, 514, 516, 518, 512 . . .
• the process goes to step 520, where the image is read out. Then the process returns to step 502 begins monitoring for a new exposure.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Solid State Image Pick-Up Elements (AREA)
• Apparatus For Radiation Diagnosis (AREA)
• Measurement Of Radiation (AREA)
• Transforming Light Signals Into Electric Signals (AREA)
• Closed-Circuit Television Systems (AREA)

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• 1998
  • 1998-03-20 GB GB9806068A patent/GB2335540B/en not_active Expired - Fee Related
• 1999
  • 1999-02-24 EP EP99910298A patent/EP1064780B1/en not_active Expired - Lifetime
  • 1999-02-24 AT AT99910298T patent/ATE252804T1/de not_active IP Right Cessation
  • 1999-02-24 JP JP2000538498A patent/JP4373607B2/ja not_active Expired - Lifetime
  • 1999-02-24 AU AU29305/99A patent/AU2930599A/en not_active Abandoned
  • 1999-02-24 WO PCT/EP1999/001282 patent/WO1999049650A1/en not_active Ceased
  • 1999-02-24 DE DE69912259T patent/DE69912259T2/de not_active Expired - Lifetime
  • 1999-02-24 IL IL13797699A patent/IL137976A0/xx unknown
  • 1999-03-03 US US09/261,747 patent/US6380528B1/en not_active Expired - Lifetime
• 2002
  • 2002-04-30 US US10/134,503 patent/US20020125438A1/en not_active Abandoned

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