  3D silicon pixel detectors have been investigated as radiation-hard
candidates for the innermost layers of the HL-LHC upgrade of the ATLAS pixel
detector. 3D detectors are already in use today in the ATLAS IBL and AFP
experiments. These are based on 50x250 um2 large pixels connected to the FE-I4
readout chip. Detectors of this generation were irradiated to HL-LHC fluences
and demonstrated excellent radiation hardness with operational voltages as low
as 180 V and power dissipation of 12--15 mW/cm2 at a fluence of about 1e16
neq/cm2, measured at -25 degree C. Moreover, to cope with the higher
occupancies expected at the HL-LHC, a first run of a new generation of 3D
detectors designed for the HL-LHC was produced at CNM with small pixel sizes of
50x50 and 25x100 um2, matched to the FE-I4 chip. They demonstrated a good
performance in the laboratory and in beam tests with hit efficiencies of about
97% at already 1--2V before irradiation.
