Basic performance of SOI pixel detector for radiation monitor

We have developed a monolithic pixel detector with the silicon-on-insulator (SOI) pixel CMOS technology to use as radiation monitor, called RADPIX. The RADPIX intends to identify the type of radiation (α, β, γ, muon, etc.) by differences in hit pattern. The sensor is DC-coupled to the input of the pixel circuit so the leakage current I_leak of a few pA for 40 μm × 40 μm at room temperature must be sunk by the pixel circuit for long time exposure. The RADPIX has the individual leakage compensation circuit. In addition to a digital output, the analog signal also can be read by using the comparator output as a store signal to latch the analog signal for the tracking accuracy enhancement. The prototype chip consists of 32 × 32 pixels with the pixel size of 40 μm × 40 μm (~1 mm square sensitive area). We report the design and the result of the basic evaluation test.