  Low Gain Avalanche Detectors (LGADs) are n-on-p silicon sensors with an extra
p-layer below the collection electrode which provides signal amplification.
When the primary electrons reach the amplification region new electron-hole
pairs are created that enhance the generated signal. The moderate gain of these
sensors, together with the relatively thin active region, provide precise time
information for minimum ionizing particles. To mitigate the effect of pile-up
at the HL-LHC the ATLAS and CMS experiments have chosen the LGAD technology for
the High Granularity Timing Detector (HGTD) and for the End-Cap Timing Layer
(ETL), respectively. A full characterization of recent productions of LGAD
sensors fabricated at CNM has been carried out before and after neutron
irradiation up to 2.5 $\times$ 10$^{15}$ n$_{eq}$/cm$^{2}$ . Boron-doped
sensors produced in epitaxial and Si-on-Si wafers have been studied. The
results include their electrically characterization (IV and bias voltage
stability) and performance studies (charge and time resolution) for single pad
devices with a Sr-90 radioactive source set-up. The behaviour of the Inter-Pad
region for irradiated 2 $\times$ 2 LGAD arrays, using the Transient Current
Technique (TCT), is shown. The results indicate that the Si-on-Si devices with
higher resistivity perform better than the epitaxial ones.
