Charge Muliplication in Highly Irradiated Planar Sensors

Abstract

The discovery of the novel effect that amplifies the charge generated by ionising particles in heavily irradiates silicon detectors has risen hopes for further extending the lifetime of this type of sensors when exposed to heavy doses of hadron irradiation. The anomalous size (compared to expectations) of the signal generated by a minimum ionising particle (mip) in detectors irradiated to doses about one order of magnitude higher than what anticipated for the current Large Hadron Collider (LHC) at CERN has been reported for a number of years. It is now well documented that the correct interpretation for the improvement of the charge collection resides in the multiplication of the signal charge by impact ionisation. This effect is being intensively studied within the high energy physics detector community by mean of both experiments and simulations. The results of these studies are particular relevant to the silicon detectors planned for the future super LHC (sLHC) and for every silicon sensor that will be intended for very hostile environment, where the final cumulated flux will reach level of a few times 10 16 1MeV neutron equivalent (n eq ) cm -2 . A summary of the current results and the understood implications and limitations of this effect are here discussed. PoS(VERTEX 2010)020Charge multiplication in highly irradiated planar silicon sensors Gianluigi Casse

Atlas Upgrade

“…During several prototype productions, different insulation schemes and guard ring designs were tested. Besides, data taken with irradiated miniature microstrip sensors confirmed that the radiation tolerance of n + -in-p sensors well exceeds 1 · 10 15 n eq /cm 2 [13] which is the benchmark fluence for the short strip region (see fig. 3).…”

“…Atlas Upgrade Daniel Muenstermann planar silicon strip sensors that this will be the case [13] also thanks to a charge amplification effect seen at high electric field strengths [14,15]. Therefore, planar sensors are currently being manufactured and will be irradiated and tested in future test beams at CERN and DESY.…”

“…Here, on the other hand, the area to be instrumented is so small that the cost per area is of less relevance. There are four sensor candidates for the innermost pixel layer: planar silicon [13], 3D silicon [16,17], pCVD diamond [18] and the gaseous Gossip technology [19]. All technologies have shown promising results, but (also due to the lack of a sufficiently radiation hard readout chip) have not yet been able to demonstrate their performance as a pixel detector after 2 · 10 16 n eq /cm 2 .…”

R&D paths of pixel detectors for vertex tracking and radiation imaging

“…Thin planar sensors involve dealing with higher capacitance (noise) and lower signals. An interesting solution to improve the S/N ratio would be to exploit charge multiplication processes, as those observed in heavily irradiated strip sensors with n-side read-out biased at very large voltages ( 1000 V) [88]. Ideally, charge multiplication should be controlled by design and take place at lower voltages.…”

Recent Results of the ATLAS Upgrade Planar Pixel Sensor R Project

“…Recent results of the ATLAS Upgrade Planar Pixel Sensors R&D Project Giovanni Marchiori fluences of 5 × 10 15 n eq /cm 2 for bias voltages of 1 kV or higher, because of the higher electric field and possibly also due to charge multiplication inside the bulk [10]. Thinner sensors for HEP experiments have the additional advantage of the lower material budget, which improves momentum resolution and reduces energy loss in front of downstream detectors.…”