A membrane, pseudo-vertical p-i-n diamond detector

We report on the membrane diamond detector, which consists of 5 μm-thick diamond p-i-n diodes and a dedicated front-end ASIC, fabricated in a 65 nm CMOS technology. The p-i-n diode has an attractive feature for low γ-ray sensitivities due to its extremely thin drift layer, which is difficult to form by etching of bulk diamond with a Metal-Insulator-Metal structure. The pseudo-vertical p-i-n diode structure was formed on the single crystal diamond {111} substrate by MWCVD and dry-etching process. The readout electronics was designed to meet specifications for real-time neutron monitoring in harsh γ-ray environments. The prototype system was evaluated in charge distribution measurements induced by α-particles from 241 Am. The charge spectra were successfully obtained from multi-channels, each of which has a diameter of 250 μm aligning in a pixel matrix. By combining with neutron converters, e.g ., 10 B or 7 Li, we expect the detector system as a good candidate for detecting spontaneous fission neutrons, emitted from submerged fuel debris at the Fukushima Daiichi Nuclear Power Plant in Japan.