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تسجيل مستخدم جديدCharge collection properties of irradiated depleted CMOS pixel test structures
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Edge-TCT and charge collection measurements with passive test structures made in LFoundry 150 nm CMOS process on p-type substrate with initial resistivity of over 3 k$Omega$cm are presented. Measurements were made before and after irradiation with reactor neutrons up to 2$cdot$10$^{15}$ n$_{mathrm{eq}}$/cm$^2$. Two sets of devices were investigated: unthinned (700 $mu$m) with substrate biased through the implant on top and thinned (200 $mu$m) with processed and metallised back plane. Depleted depth was estimated with Edge-TCT and collected charge was measured with $^{90}$Sr source using an external amplifier with 25 ns shaping time. Depleted depth at given bias voltage decreased with increasing neutron fluence but it was still larger than 70 $mu$m at 250 V after the highest fluence. After irradiation much higher collected charge was measured with thinned detectors with processed back plane although the same depleted depth was observed with Edge-TCT. Most probable value of collected charge of over 5000 electrons was measured also after irradiation to 2$cdot$10$^{15}$ n$_{mathrm{eq}}$/cm$^2$. This is sufficient to ensure successful operation of these detectors at the outer layer of the pixel detector in the ATLAS experiment at the upgraded HL-LHC.
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