Radiation tolerance of SiGe BiCMOS monolithic silicon pixel detectors without internal gain layer

A monolithic silicon pixel prototype produced for the MONOLITH ERC Advanced project was irradiated with 70 MeV protons up to a fluence of 1 × 10¹⁶1 MeV n_eq/cm². The ASIC contains a matrix of hexagonal pixels with 100 μm pitch, readout by low-noise and very fast SiGe HBT frontend electronics. Wafers with 50 μm thick epilayer with a resistivity of 350 Ωcm were used to produce a fully depleted sensor. Laboratory tests conducted with a⁹⁰Sr source show that the detector works satisfactorily after irradiation. The signal-to-noise ratio is not seen to change up to fluence of 6 × 10¹⁴n_eq/cm². The signal time jitter was estimated as the ratio between the voltage noise and the signal slope at threshold. At -35°C, sensor bias voltage of 200 V and frontend power consumption of 0.9 W/cm², the time jitter of the most-probable signal amplitude was estimated to be σ_t⁹⁰Sr = 21 ps for proton fluence up to 6 × 10¹⁴n_eq/cm² and 57 ps at 1 × 10¹⁶n_eq/cm². Increasing the sensor bias to 250 V and the analog voltage of the preamplifier from 1.8 to 2.0 V provides a time jitter of 40 ps at 1 × 10¹⁶n_eq/cm².