A directly converting high-resolution intra-oral X-ray imaging sensor

A digital intra-oral X-ray imaging sensor with an active area of 3.6×2.9 cm2 and consisting of six charge-integrating CMOS signal readout circuits bump bonded to one high-resistivity silicon pixel detector has been developed and tested. The pixel size is 35 μm. The X-rays entering the sensor window are converted directly to electrical charge in the depleted detector material yielding minimum lateral signal spread and maximum image sharpness. The signal charge is collected on the gates of the input field effect transistors of the CMOS signal readout circuits. The analog signal readout is performed by multiplexing in the current mode independent of the signal charge collection enabling multiple readout cycles with negligible dead time and thus imaging with wide dynamic range. Since no intermediate conversion material of X-rays to visible light is needed, the sensor structure is very compact. The analog image signals are guided from the sensor output through a thin cable to signal processing, AD conversion and memory circuitry, which is realized as an intermediate electronic unit between the sensor and the computer. This unit controls the sensor, collects the data and transfers it via one of the standard computer buses for image processing, display and storage. The overall sensor design and operation are described and experimental MTF, SNR and DQE data are presented together with X-ray images.