Patent ID: 7304308

Claim:
A digital, flat panel x-ray mammography imager exhibiting low ghosting, said imager having a top electrode directly on a selenium-based layer and having a thin-film transistor array with leakage current characteristics providing breakdown protection even when a transistor is coupled with a charge storage capacitor collecting charges from a region of the layer receiving x-rays that are not attenuated by an object being imaged in medical imaging, comprising: a substrate having an upper surface; a selenium-based charge generator layer over the upper surface of the substrate, said selenium-based layer also having an upper surface; a top electrode directly on, and in physical and electrical contact with, the upper surface of the charge generator layer; a charge collection electrode between the substrate and the charge generator layer, said charge collection electrode being patterned into a two-dimensional array of pixel electrodes; said charge generator layer generating electrical charge in response to x-ray irradiation, and said pixel electrodes collecting charge of one polarity generated at respective regions of the charge generator layer when one or more selected electric fields are established in the charge generator layer; a read-out circuit, also between the substrate and the charge generator layer, said read-out circuit comprising respective signal storage capacitors coupled with said pixel electrodes and storing electrical charge collected thereby, and further comprising a thin-film transistor array of respective gating transistors coupled with said signal storage capacitors; wherein each of said gating transistors is selectively switched between an ON state in which it passes charge from the respective storage capacitors to an outside circuit and an OFF state in which it passes leakage current; wherein the leakage current of each of said gating transistors rises at a relatively low rate with rise in potential at the respective capacitor below the range of 20-25 volts but rises at a significantly higher rate with rise in potential at the respective capacitor above said range, thereby protecting the transistors from breakdown damage even when the respective pixel electrode collects charge generated at a region of the charge generator layer receiving x-rays that are not attenuated by an object being imaged with said imager in medical imaging; and a power supply applying a voltage within the range of 500 V to 2,000 V to the top electrode.