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Summary 500 words
The tracking performances of CMOS Pixel Sensor (CPS) are now well established and the sensors are foreseen to equip several vertex detectors. The STAR HFT (Heavy Flavor Tracker) upgrade has generated the first vertex detector based on CPS. The pixel detector (PXL), composed of two layers of high resolution CPS, is presently being fabricated.
This development began more than eight years ago in collaboration with LBNL. Three generations of sensors have been designed at IPHC. The first generation sensor featured analogue outputs (MimoSTAR-1, -2 and -3) and did not integrate signal processing circuitry. A 3 sensors telescope has been constructed with MimoSTAR-2 and operated inside the STAR apparatus near the RHIC beam in 2007. It was the first test of the CPS technology in a collider environment. The second generation sensors have reticle dimensions (Phase-1 and Phase-2) and binary outputs but no integrated zero suppression logic. In 2012, an engineering prototype detector with limited coverage (1/3) will be installed with Phase-1 or Phase-2 sensors. The third generation is represented by the ULTIMATE sensor, which was designed to fulfil all STAR HFT PXL specifications, in particular those concerning hit density (2 x 105 hits/cm2/s), spatial resolution (~ 6-8 µm), power consumption (~ 100 mW/cm²), radiation tolerance (~ 100 kRad and few 1012 MeV neq/cm2 per year) and operation at room temperature (~ 30 – 35 °C). The final detector, composed of two complete layers of 400 ULTIMATE sensors, will be installed in 2013.
ULTIMATE is a full reticle size (~2x2 cm2) sensor with binary output and integrated zero suppression logic. Its main characteristics are similar to those of MIMOSA26 sensor, fabricated in 2009 for the EUDET beam telescope [1]. The design has incorporated the test results of MIMOSA26 [1]. The architecture of ULTIMATE is based on a column parallel readout with amplification and correlated double sampling (CDS) inside each pixel. Each column is ended with a high precision discriminator and is read out in rolling shutter mode at 5 MHz (200 ns / row). The discriminator outputs are processed through an integrated zero suppression micro circuit, which results are stored in two memories according to a ping-pong arrangement allowing for a continuous readout. The data are multiplexed onto two LVDS outputs at 160 MHz.
This contribution will discuss in details the design of the ULTIMATE sensor with its optimisation approaches, and show its test results, including charged particle detection performances measured at the CERN-SPS.
[1] Ch. Hu-Guo et al. "First reticule size MAPS with digital output and integrated zero suppression for the EUDET-JRA1 beam telescope", Nuclear Instruments and Methods in Physics Research A, 623(2010) 480-482
