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Description
Small-pixel 3D sensors were fabricated by IME-CAS on 8-inch p-type wafers (700 Ω·cm) with a thickness of 30 μm, featuring trench walls (ohmic p⁺) and narrow n⁺ columns (0.5 μm diameter). A 5×5 matrix of 35×35 μm² pixels was characterized using Two-Photon Absorption Transient Current Technique (TPA-TCT); we varied the TPA depth, laser intensity, pulse duration, and bias. At higher bias voltages, the devices exhibit stable operation with intrinsic gain from impact ionization near the n⁺ junction (without dedicated gain-layer doping). Cross check with SPA (800 nm) was additionally performed. Both irradiated and non-irradiated samples were measured to investigate charge collection, gain and timing after radiation exposure. The effect of the amplifier on signal shape and tail was also evaluated by connecting and disconnecting it during tests. Irradiated samples were studied using both 2PA and 3PA.