No abstract

Some X-ray imaging applications demand sensitive areas exceeding the active area of a single sensor. This requires a seamless tessellation of multiple detector modules with edgeless sensors. Our research is aimed at minimising the insensitive periphery that isolates the active area from the edge. Reduction of the edge-defect induced charge injection, caused by the deleterious effects of dicing, is an important step.We report on the electrical characterisation of 300 µm thick edgeless silicon p + -ν-n + diodes, diced using deep reactive ion etching. Sensors with both n-type and p-type stop rings were fabricated in various edge topologies. Leakage currents in the active area are compared with those of sensors with a conventional design. As expected, we observe an inverse correlation between leakage-current density and both the edge distance and stop-ring width. From this correlation we determine a minimum acceptable edge distance of 50 µm. We also conclude that structures with a p-type stop ring show lower leakage currents and higher breakdown voltages than the ones with an n-type stop ring.

Driven by the demand of various applications for a detection area that is larger than the active area of a single detector module, we explore the possibility to realise a large-area detector by a seamless tessellation of multiple detectors. This requires sensors with a minimum amount of dead area at the edge. In order to be able to reduce this area, edge effects must be understood and avoided or mitigated. In this paper, we report on first tests that are performed on diamond-blade diced slim-edge pieces of cadmium telluride with a last-pixel-to-edge distance of only 65 /-tm. The results indicate that the edge-pixel response is not significantly affected with respect to the leakage current and the charge collection efficiency. First measurements towards a quantification of the detective quantum efficiency have been made on edge pixels by determining the pixel response function and the noise power spectrum.

In 2000, the requirements for a large TPC for experiments at a new linear collider were formulated. Both the GEM and Micromegas gas amplification systems had matured, such that they could be practically applied. With the Medipix chip, a pixel-segmented anode readout became possible, offering an unprecedented level of granularity and sensitivity. The single electron sensitive device is a digital detector capable to record and transfer all information of the primary ionization, provided that it can be made discharge proof.

We study the influence of active edges on the response of edge pixels by comparing simulations of the electrostatic-potential distribution to position-defined measurements on the energy deposition. A laser setup was used to measure the edge-pixel response function and shows the sensitive edge is only about 2 µm from the physical edge. 3D reconstruction of tracks from highenergy pions and muons, produced at the SPS H6 test beam facility at CERN, enabled to relate the energy deposition at edge pixels to the particle's interaction depth. A clear correlation is observed between the simulated electric-field distortion and the reconstructed interaction-depth dependent effective size.