Comparison of the time resolution of unirradiated and irradiated LGADs and 3D sensors

Collider experiments as the upcoming Phase II-LHC or the future circular collider (FCC) will increase the demands on detectors used for tracking. In the FCC, sensors will not only face fluences of up to 1x1017 neq/cm2, but also high pile-up scenarios. Therefore, sensors that not only have a good spatial resolution and a very high radiation hardness, but also an excellent time resolution of 5 ps will be required. Currently, Low Gain Avalanche Diodes (LGADs), which have an additional gain layer to achieve fast signals through charge multiplication, are one of the main candidates when it comes to timing, reaching a resolution of below 30 ps. However, their radiation hardness is not sufficient for future colliders. A second important candidate for timing are 3D sensors, which are known to be extremely radiation hard. In 3D sensors, the electrodes are etched into the sensor from the top (junction columns) and from the back (ohmic columns), resulting in short drift distances, low depletion voltages, a high electric field and therefore, fast signals. In this study, the time resolution of both LGADs and 3D sensors was investigated with MIP-like signals generated by a beta-source, as well as measurements using a laser with an infrared wavelength. It was found that LGADs and 3D sensors have compatible time resolutions. Transient current technique (TCT) timing measurements allow a position-resolved study of the time resolution. This is especially interesting for the 3D sensors, where the more complex electric field structure influences the time resolution strongly. This can be observed in the position dependent time resolution measurements. Additionally, the timing performance of 3D sensors before and after irradiation with reactor neutrons will be discussed.