Speaker
Description
This study investigates a novel, ultra-thin 3D silicon detector featuring submicron columnar electrodes fabricated via an advanced 8-inch CMOS process at the IME-CAS. With an active thickness of 30 μm and a column diameter of only 0.5 μm, the architecture generates high localized electric fields that enable intrinsic charge multiplication without the requirement for dedicated gain layers (e.g., as in LGADs). The sensors were characterized using Two-Photon and Three-Photon Absorption Transient Current Techniques (2PA-TCT and 3PA), allowing for high-resolution, position-resolved mapping of charge collection, gain, and timing across the device volume. In non-irradiated devices, clear evidence of impact-ionization-driven gain was observed at bias voltages above full depletion, reaching values of 7.5 at 60 V (near breakdown) with a relatively uniform lateral distribution.
Key Findings:
• Spatial Gain Profile: Charge multiplication exhibits a pronounced depth dependence, peaking at the tip of the central electrode where the electric field is most intense.
• Radiation Tolerance: Following irradiation to a fluence of 5e15 neq/cm2, a gain of 5 was still achievable at room temperature. Further testing at -20C demonstrated increased maxima. bias and enhanced gain performance.
• Self-Stabilization Mechanism: Notably, the electrode tip, traditionally the primary site for premature breakdown for 3D column devices, exhibits a "self-quenching" behavior. This stabilization is driven by field-focusing and subsequent screening of the external field, a phenomenon absent in the thicker columnar geometries used in current ATLAS and CMS 3D pixel upgrades.
These results suggest that geometry-driven gain in submicron 3D detectors offers a robust path toward radiation-hard, fast-timing sensors with inherent breakdown protection.