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Description
Small pixel 3D sensors were produced by IME-CAS on 8-inch p-type wafers of 700 Ωcm. The 30 μm thick silicon detectors have trench walls (ohmic p+) and very narrow n-column columns with a diameter of only 0.5 μm. A 5 × 5 matrix of 35 ×35 μm2 was measured with Two Photon Absorption Transient Current Technique as well as with minimum ionizing electrons from 90Sr source. At higher voltages the devices show stable operation with high gain originating from impact ionization close to the n+ junction column in a similar way in gas proportional chambers without
any specially dedicated gain layer doping. The devices were fully characterized in terms of charge collection uniformity and time resolution performance across the cell at different bias voltages. The gain and time resolution measured with electrons confirmed the conclusions from TPA-TCT measurements.