TCAD Analysis of Leakage Current and Breakdown Voltage in Small Pitch 3D Pixel Sensors

Small-pitch 3D pixel sensors have been developed to equip the innermost layers of the ATLAS and CMS tracker upgrades at the High Luminosity LHC. They feature 50 × 50 and 25 × 100 [Formula: see text] m [Formula: see text] geometries and are fabricated on p-type Si–Si Direct Wafer Bonded substrates of 150 [Formula: see text] m active thickness with a single-sided process. Due to the short inter-electrode distance, charge trapping effects are strongly mitigated, making these sensors extremely radiation hard. Results from beam test measurements of 3D pixel modules irradiated at large fluences ([Formula: see text]) indeed demonstrated high efficiency at maximum bias voltages of the order of 150 V. However, the downscaled sensor structure also lends itself to high electric fields as the bias voltage is increased, meaning that premature electrical breakdown due to impact ionization is a concern. In this study, TCAD simulations incorporating advanced surface and bulk damage models are used to investigate the leakage current and breakdown behavior of these sensors. Simulations are compared with measured characteristics of 3D diodes irradiated with neutrons at fluences up to 1.5 × 10 [Formula: see text]. The dependence of the breakdown voltage on geometrical parameters (e.g., the n [Formula: see text] column radius and the gap between the n [Formula: see text] column tip and the highly doped p [Formula: see text] handle wafer) is also discussed for optimization purposes.