Recent advances in processing and characterization of edgeless detectors

Abstract

During past five years VTT has actively developed edgeless detector fabrication process. The straightforward and high yield process relies on ion-implantation to activate the edges of the detector. A recent fabrication process was performed at VTT to provide p-on-n edgeless detectors. The layout contained DC- and AC-coupled strip detector and pixel detectors for Medipix/Timepix readouts. The fabricated detector thicknesses were 50, 100 and 150 μm. Electrical characterization was done for 5 × 5 mm2 edgeless diodes on wafer level. All measured electrical parameters showed a dramatic dependence on the diode thickness. Leakage current was measured below 10 nA/cm2 at full depletion. Calculation using a theoretical approximation indicates the diode surface generation current of less than 300 pA. The breakdown voltages were measured to be above 140 V and increased as a function of diode thickness. Reverse bias of 10 V is enough to fully deplete designed edgeless diodes. Leakage current dependence of temperature was investigated for both p-on-n and previous n-on-n edgeless detectors and results show that the leakage current doubles for every 8.5 degree Celsius rise in temperature. TCAD device simulations reveal that breakdown occurs at the lateral p-n junction where the electric field reaches its highest value. Thick edgeless diodes have wider bulk space that allows electric potential to drop and causes smaller curvature of the equipotential lines. This releases the accumulation of electric field at the corner of anode and increases the breakdown voltage. A good match of the simulated and the measured capacitance-voltage curves enables identification of proper parameters used in the simulation.