Radiation tolerance of ultra-thin PIN silicon detectors evaluated with a MeV proton microbeam

Highlights: • We investigated the radiation hardness of ultra-thin silicon detectors using a 2.55 MeV focused proton beam. The detectors had thicknesses ranging between 6.5 and 22 μm, and four different regions of each detector were irradiated with fluences up to 2 × 10¹⁵ protons/cm². • The fluence limit with almost no observable damage was at Ø = 2 × 10¹³ cm⁻² for detectors of 6.5 and 10 μm thickness and Ø = 2 × 10¹² cm⁻² for detectors of 15 and 22 μm thickness. • As a comparison, the detectors can be used under constant fluence of 10⁵ protons/cm² for a few months up to years with little risk of being damaged. - Abstract: A focused MeV proton beam at the Lund Ion Beam Analysis Facility has been used to induce radiation damage in transmission semiconductor detectors. The damage alters the response of detectors and degrades their charge transport properties. In this work, the radiation tolerance of ultra-thin silicon PIN detectors was studied as a function of proton fluences and detector thickness using a scanning proton microprobe. The investigated detectors had thicknesses ranging between 6.5 and 22 μm, and different selected regions of each detector were irradiated with fluence up to 2 × 10¹⁵ protons/cm². The results show that the charge collection efficiency (CCE) decreases as a function of the proton fluence. Compared with non-irradiated regions, the CCE was above 94% at the lowest fluence of 2 × 10¹² protons/cm² for all the detectors studied. Degradation of the devices caused spectral peak shifting toward lower energies. The highest possible fluence of 2.55 MeV protons that could be used, causing only minor radiation damage, was 2 × 10¹³ cm⁻² for the thinnest detectors (6.5 and 10 μm) and 2 × 10¹² cm⁻² for the thickest detectors (15 and 22 μm)