Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
1998-09-01
2001-05-15
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370010
Reexamination Certificate
active
06232606
ABSTRACT:
TECHNICAL FIELD
The present invention relates to imaging systems and in particular to a flat panel detector for radiation imaging and to a pixel for use in a flat panel detector.
BACKGROUND ART
Flat panel detectors for use in x-ray radiation imaging systems are known. Examples of these pixel sensor arrays can be found in U.S. Pat. Nos. 5,184,018 and 5,381,014. One such type of flat panel detector includes a thick amorphous selenium film (a-Se) on a two-dimensional TFT switch array. The TFT switches are arranged in rows and columns to form a two-dimensional imaging system. Gate lines interconnect the TFT switches in each row while source lines interconnect the TFT switches in each column. The thick selenium film is deposited directly on top of the TFT switch array and a top electrode is deposited on the selenium film.
When x-rays are incident on the selenium film and the top electrode is biased with a high voltage, electron-hole pairs are separated by the electric field across the thickness of the selenium film. The holes which are driven by the electric field move toward the pixel electrodes (i.e. the drain electrodes of the TFT switches) and accumulate. This results in a charge being held by the pixel electrodes which can be used to develop an x-ray image. The charge held by the pixel electrodes can be read by supplying a pulse to each gate line. When a gate line receives a pulse, the TFT switches in the row turn on, allowing the signal charges on the pixel electrodes to discharge through the TFT switches on to the source lines. Charge amplifiers connected to the source lines sense the charge and provide output voltage signals proportional to the charge and hence, proportional to the radiation exposure on the selenium film.
Although this pixel design is satisfactory, alternative designs are continually being sought. It is therefore an object of the present invention to provide a novel flat panel detector for radiation imaging and a pixel for use therein.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention there is provided a pixel for a radiation imaging flat panel detector comprising:
a radiation transducer to be exposed to incident radiation;
a pixel electrode on one side of said radiation transducer to accumulate a positive charge proportional to the exposure of said radiation transducer to radiation;
a second electrode separated from said pixel electrode by a dielectric and connected to a source line, said pixel and second electrodes constituting a storage capacitor, said second electrode developing a negative charge approximately equal to the magnitude of the positive charge accumulated by said pixel electrode; and
a semiconductor switch coupled between said pixel electrode and a terminal connectable to ground, said semiconductor switch being responsive to a gating signal to connect electrically said pixel electrode to said terminal connectable to ground to discharge said pixel electrode thereon, said bottom electrode releasing said negative charge on said source line when said pixel electrode discharges to allow the charge to be detected.
According to another aspect of the present invention there is provided a flat panel detector for radiation imaging comprising:
a radiation transducer including a radiation conversion layer and an electrode on one side of said radiation conversion layer;
an array of pixels arranged in rows and columns on the other side of said radiation conversion layer;
a plurality of sources lines upon which charges accumulated by said pixels can be sensed, each of said source lines connecting the pixels in individual ones of one of said rows or columns of said array; and
a plurality of gate lines upon which gating signals are supplied to allow accumulated charges to be sensed, each of said gate lines connecting the pixels in individual ones of the other of said rows or columns of said array, each of said pixels including: a pixel electrode to accumulate positive charge as a result of hole drift in said radiation conversion layer occurring upon exposure of said radiation transducer to radiation and when said electrode is biased; a second electrode separated from said pixel electrode by a dielectric and connected to one of said source lines, said pixel and second electrodes constituting a storage capacitor, said second electrode developing a negative charge approximately equal to the magnitude of the positive charge accumulated by said pixel electrode; and a semiconductor switch coupled between said pixel electrode and a terminal connectable to ground, said semiconductor switch being responsive to a gating signal to connect electrically said pixel electrode to said terminal connectable to ground to discharge said pixel electrode thereon, said bottom electrode releasing said negative charge on said source line when said pixel electrode discharges to allow the charge to be detected.
According to yet another aspect of the present invention there is provided a flat panel detector for radiation imaging comprising:
a radiation transducer including a radiation conversion layer and an electrode on one side of said radiation conversion layer;
an array of pixels arranged in rows and columns on the other side of said radiation conversion layer and formed on a common substrate;
a plurality of sources lines formed on said substrate and upon which charges accumulated by said pixels can be sensed, each of said source lines connecting the pixels in individual ones of one of said rows or columns of said array; and
a plurality of gate lines formed on said substrate and upon which gating signals are supplied to allow accumulated charges to be sensed, each of said gate lines connecting the pixels in individual ones of the other of said rows or columns of said array, each of said pixels including: a thin film transistor switch having a drain electrode constituting a pixel electrode to accumulate positive charge as a result of hole drift in said radiation conversion layer occurring upon exposure of said radiation transducer to radiation and when said electrode is biased; a bottom electrode separated from said pixel electrode by a dielectric gate insulating layer and connected to one of said source lines, said pixel and bottom electrodes constituting a storage capacitor, said second electrode developing a negative charge approximately equal to the magnitude of the positive charge accumulated by said pixel electrode; and a source electrode coupled to a terminal connectable to ground, said thin film transistor switch being responsive to a gating signal to connect electrically said pixel electrode to said low terminal connectable to ground to discharge said pixel electrode thereon, said bottom electrode releasing said negative charge on said source line when said pixel electrode discharges to allow the charge to be detected.
According to still yet another aspect of the present invention there is provided a radiation imaging system including a radiation source and a flat panel detector, said flat panel detector comprising:
a radiation transducer including a radiation conversion layer and an electrode on one side of said radiation conversion layer;
an array of pixels arranged in rows and columns on the other side of said radiation conversion layer;
a plurality of sources lines upon which charges accumulated by said pixels can be sensed, each of said source lines connecting the pixels in individual ones of one of said rows or columns of said array;
a plurality of gate lines upon which gating signals are supplied to allow accumulated charges to be sensed, each of said gate lines connecting the pixels in individual ones of the other of said rows or columns of said array;
an array of charge amplifiers, each connected to one of said source lines to detect the charge thereon; and
a gate driver to supply gating signal to said gate lines in succession to allow the charges accumulated by said pixels to be detected on a row-by-row basis, each of said pixels including: a pixel electrode to accumulate positive charge as a result of hole drift in said radiation conve
Fay Sharpe Fagan Minnich & McKee LLP
Ham Seungsook
Hanig Richard
IFire Technology, Inc.
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