Direct-Type Silicon Pixel Detector for a Large-Area Hybrid X-Ray Imaging Device

Abstract

We demonstrated the design and the fabrication processes of a direct-type silicon pixel detector for a digital dental radiograph made by using a high-resistivity n-type silicon substrate. The structure of the detector is based on a fully-depleted p-i-n diode. The detector is composed of 644,328 pixels with a pitch of 35 x 35 pm. The size of the detector is 2.58 x 3.47 cm and it is composed of a 4-block assembly with four read-out complementary metal-oxide semiconductor integrated circuits (CMOs ICs). We focused on experimentally evaluating the process conditions for the silicon pixel detector to reduce the leakage current and to increase the breakdown voltage. From the experimental results, we found that a high-temperature drive-in after p(+) ion implantation deteriorates the leakage current and that a p(+) passivation by thermal oxidation increases the breakdown voltage. The leakage current of the detector was 5.7 nA/cm(2) (0.07 pA/pixel) and the breakdown voltage was more than 1700 V. The read-out IC consists of a current-integrating pixel readout CMOS chip and PbSn bumps. After four read-out ICs had been bump-bonded to a pixel detector and wire-bonded to a printed circuit board (PCB), X-ray images showed a resolution of 9 lp/mm and provided a good image of human teeth.