CMOS Sensors with high resistivity epitaxial layer

Abstract

CMOS Pixel Sensors (CPS) are foreseen to equip vertex detectors where priority is given to granularity, material budget and power consumption, potentially at the expense of read-out speed and radiation tolerance. Being initially developed for an experiment at the ILC, the sensors came out to be well suited to Heavy Ion Collision experiments (STAR at RHIC, CBM at FAIR,...), and their intrinsic potential offers attractive perspectives for the vertex detector to be operated at the SuperB factory. Another trend motivating their continuous development concerns trackers, where granularity is less an issue but material budget, power consumption and fabrication costs may be significantly reduced when using CMOS pixel sensors instead of usual semi-conducting devices. For many years, CPS were manufactured with commercial wafers featuring exclusively low resistivity (i.e. typically 10 Ω • cm) epitaxial layers. The interest of industry for high resistivity epitaxial layers is a rather recent event, with a considerable impact on the potential of the CPS (e.g. a typical signal-to-noise ratio of about 35-40). Several sensors were fabricated since early 2010 with a > 400 Ω• cm resistivity epitaxial layer, available in a 0.35 μm process, and tested on particle beams. This article illustrates the maturity and the potential of the technology, first by presenting the first vertex detector equipped with CPS (STAR-HFT upgrade), then by providing insight of the next steps of the R&D, which are based on an emerging CMOS technology using a 0.18 μm feature size, and aim at a large area beam telescope for the EU-FP7 project AIDA. Moreover, the development of a very light ladder, equipped on both faces with 50 jim thin sensors, will be overviewed.