Study of neutron irradiation effects in Depleted CMOS detector structures

Abstract

In this paper the results of Edge-TCT and I-V measurements with passive test structures made in LFoundry 150 nm HV-CMOS process on p-type substrates with different initial resistivities ranging from 0.5 to 3 kΩcm are presented. Samples were irradiated with reactor neutrons up to a fluence of 2·1015 neq/cm2. The depletion depth was measured with Edge-TCT. The effective space charge concentration Neff was estimated from the dependence of the depletion depth on bias voltage and studied as a function of neutron fluence. The dependence of Neff on fluence changes with initial acceptor concentration in agreement with other measurements with p-type silicon. A long term accelerated annealing study of Neff and detector current up to 1280 minutes at 60°C was made. It was found that Neff and current in reverse biased detector behave as expected for irradiated silicon.

Edge-TCT evaluation of high voltage-CMOS test structures with unprecedented breakdown voltage for high radiation tolerance

“…At the highest fluence of 1 × 10 16 1 MeV n eq cm −2 a depletion depth of ≈50 μm is achieved at −400 V. The effective doping profile extracted from the fit was also used to find the resistivity of the chip [18]. The nominal resistivity of the substrate is 1.9 kΩ cm, however the actual resistivity was found to be 1.19 ± 0.14 kΩ cm which is in agreement with measurements of similar sensors crafted in the same technology, process, and nominal resistivity [19,20]. The effective doping concentration is plotted against the fluence and fitted using:…”

“…have large uncertainties, however the data was sufficient to establish the stable damage introduction rate (g c ) as 0.011 ± 0.002 cm −1 , which was lower than other measurements of chips produced with the same and different technologies, but was in agreement with the literature, as were the other variables of the fit, table 1 [17,19,21,22].…”

Measurements of time resolution of the RD50-MPW2 DMAPS prototype using TCT and 90Sr

“…The width of the measured profiles is consistent with the 60 µm size of the pixels with some charge sharing beyond the pixel boundary present, as was seen in the Backside-TCT measurement. The depletion depth decreases with irradiation due to the increase of the effective space charge concentration [19]. At the highest laser intensities, the time resolution reaches a value of around 300 ps, while at low intensities, it degrades to a value above 1 ns.…”

“…For the studies presented -2 - here, a comparator baseline of 900 mV was used at two threshold voltages of 950 mV and 1000 mV, corresponding to a threshold in electrons of 1.2 ke − and 2 ke − respectively for trim-DACs set to 0 [18]. Considering a breakdown voltage of passive structures at around 120 V [19], the bias voltage was set to 100 V for all measurements.…”