  A monolithic silicon pixel prototype produced for the MONOLITH ERC Advanced
project was irradiated with 70 MeV protons up to a fluence of 1 x 10^16 1 MeV
n_eq/cm^2. The ASIC contains a matrix of hexagonal pixels with 100 {\mu}m
pitch, readout by low-noise and very fast SiGe HBT frontend electronics. Wafers
with 50 {\mu}m thick epilayer with a resistivity of 350 {\Omega}cm were used to
produce a fully depleted sensor. Laboratory tests conducted with a 90Sr source
show that the detector works satisfactorily after irradiation. The
signal-to-noise ratio is not seen to change up to fluence of 6 x 10^14 n_eq
/cm^2 . The signal time jitter was estimated as the ratio between the voltage
noise and the signal slope at threshold. At -35 {^\circ}C, sensor bias voltage
of 200 V and frontend power consumption of 0.9 W/cm^2, the time jitter of the
most-probable signal amplitude was estimated to be 21 ps for proton fluence up
to 6 x 10 n_eq/cm^2 and 57 ps at 1 x 10^16 n_eq/cm^2 . 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 x 10^16 n_eq/cm^2.
