The ATLAS planar pixel sensor R&D project

Within the R&D project on Planar Pixel Sensor Technology for the ATLAS inner detector upgrade, the use of planar pixel sensors for highest fluences as well as large area silicon detectors is investigated. The main research goals are optimizing the signal size after irradiations, reducing the inactive sensor edges, adjusting the readout electronics to the radiation induced decrease of the signal sizes, and reducing the production costs. Planar n-in-p sensors have been irradiated with neutrons and protons up to fluences of 2 · 10¹⁶ n_eq/cm² and 1 · 10¹⁶ n_eq/cm² respectively to study the collected charge as a function of the irradiation dose received. Furthermore comparisons of irradiated standard 300 ¿m and thin 140 ¿m sensors will be presented showing an increase of signal sizes after irradiation in thin sensors. Tuning studies of the present ATLAS front end electronics show possibilities to decrease the discriminator threshold of the present FE-I3 read out chips to less than 1500 electrons which allows to reach an in-time threshold of below 3000 electrons. In the present pixel detector upgrade scenarios a flat stave design for the innermost layers requires reduced inactive areas at the sensor edges to ensure low geometric inefficiencies. Investigations towards achieving slim edges presented here show possibilities to reduce the width of the inactive area to less than 500 ¿m Furthermore, a brief overview of present simulation activities within the Planar Pixel R&D project is given.