Signal-to-noise ratio measurement and radiation damage study of silicon PIN diode with a proton beam

We designed and fabricated silicon PIN diodes having p⁺ active area of 1.0 cm × 1.0 cm on a 5-in. high resistivity (≫5 kΩ⋅cm) n-type FZ (float zone), 380 μm-thick silicon wafer. For signal-to-noise ratio (SNR) measurement of the diode, we required that the fabricated diode should be fully depleted at the operation voltage and the level of the leakage current of the sensor should be less than 10 nA/cm² at the operation voltage. The SNR of the diode was measured by using a 45 MeV proton beam from the MC-50 cyclotron at Korea Institute of Radiological and Medical Sciences (KIRAMS) in Seoul, Korea. Experiment was performed at room temperature and 46 volts was biased to fully deplete the diode. The SNR of the diode was measured to be 20.8 after corrected for the minimum ionizing particle. The different PIN diode which has relatively large leakage current was used for radiation damage test with the same proton beam. The leakage currents as a function of the reverse bias voltages were measured before and after the proton beam irradiation. The prototype was irradiated with 1.4 ×10⁷ fluence. We annealed the diode after irradiation of the proton beam and measured the leakage current dependence on times at the operation voltage. We present the understanding of radiation-induced detector deterioration and the SNR of the silicon diode in this paper.