Speaker
Description
As next-generation high-energy physics experiments scale to unprecedented luminosity frontiers, such as the High-Luminosity LHC (HL-LHC), silicon detectors must withstand extreme radiation fluences exceeding 10^{16} neq/cm2. While conventional 3D column and trench-electrode designs mitigate radiation-induced performance degradation by reducing electrode spacing, scaling down cell size traditionally introduces severe non-homogeneous electric fields and early breakdown risks.
This contribution presents a comprehensive performance evaluation of novel 3D silicon detector geometries fabricated on 30 microns thick wafers using an 8-inch CMOS process. We investigate two distinct architectures: a 35 x 35 x 30 um3 3D Trench-column device, and cylindrical 3D multi-pixel fan-structures with cell diameters of 10 and 20 mu featuring an ultra-fine central electrode (0.5 um to1 um diameter, respectively).
Using Multi-Photon Absorption Transient Current Technique (MPA-TCT) characterization, both non-irradiated and irradiated (up to 5e15 neq/cm2) devices were evaluated. We present spatially and depth-resolved measurements of charge collection efficiency, internal gain, and timing performance.
Crucially, we report an unexpected self-stabilizing breakthrough feature: despite the sub-micron diameter of the central electrode, which conventionally exacerbates electric field peaks, the devices remain highly stable close to breakdown. This phenomenon is attributed to geometric self-suppression of gain near the electrode tip, fundamentally contradicting trends observed in ATLAS and CMS 3D designs (where larger problem was uncontrollable gain with breakdown at the electrode tip). This hypothesis is further validated by a uniform breakdown bias observed across both studied geometries (with charge uniformity variation of 20%- 25% only across the cell), offering a promising new paradigm for ultra-radiation-hard, high-precision timing detectors, with controllable (self-stabilized) gain near breakdown bias.
Moreover, study on 3D cylindrical devices enabled us to investigate the impact ionisation at high fluency in silicon.