Fabrication of a direct-type silicon pixel detector for a large area hybrid x-ray imaging device

We demonstrated the design and the fabrication processes of a direct-type silicon pixel detector for a digital dental radiography made using a high-resistive 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 mum. The size of the detector is 2.58 cm x 3.47 cm and it is composed of a 4-block assembly with four read-out CMOS ICs. We focused on experimentally evaluating the process conditions for the silicon pixel detector to reduce the leakage current and improve the breakdown voltage. From the experimental results, we found that the high temperature drive-in after p⁺ ion implantation deteriorates the leakage current and p⁺ passivation by thermal oxidation improves the breakdown voltage. The leakage current of a pixel was 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 bump-bonding four read-out ICs to a pixel detector and wire-bonding to a PCB, X-ray image tests showed a resolution of 11 lp/mm and provided a good image of human teeth.