A new ATLAS pixel chip FE-I4 is being developed for use in upgraded LHC luminosity environments, including the near-term Insertable B-Layer (IBL) upgrade. FE-I4 is designed in a 130 nm CMOS technology, presenting advantages in terms of radiation tolerance and digital logic density compared to the 0.25 µm CMOS technology used for the current ATLAS pixel IC, FE-I3. The FE-I4 architecture is based on an array of 80×336 pixels, each 50×250 µm 2 , consisting of analog and digital sections.In the summer 2010, a first full scale prototype FE-I4A was submitted for an engineering run. This IC features the full scale pixel array as well as the complex periphery of the future full-size FE-I4. The FE-I4A contains also various extra test features which should prove very useful for the chip characterization, but deviate from the needs for standard operation of the final FE-I4 for IBL. In this paper, focus will be brought to the various features implemented in the FE-I4A submission, while also underlining the main differences between the FE-I4A IC and the final FE-I4 as envisioned for IBL.Keywords: Pixel detector, ATLAS, upgrade, IBL, FE-I4
Scope of the project and introduction to FE-I4In these first years of operational experience with the LHC, the road to higher LHC luminosity is clearing up, allowing the detector communities to devise plans for detector upgrades.The ATLAS pixel detector will see two major phases of upgrade, phase I during the year 2016 shutdown, and phase II for the High Luminosity upgrade (HL-LHC) in 2020. For the phase I upgrade, the addition of a fourth layer to the pixel system with a smaller beam pipe is foreseen: This project is called the Insertable B-layer (IBL). For the HL-LHC upgrade, a new Inner Tracker will replace the existing one.The design of the FE-I4 has started when it was realized that the FE-I3 IC [2] presently used in the ATLAS 1 Corresponding author: barbero@physik.uni-bonn.de 2 Visitor from Laboratoire de l'Accélérateur Linéaire, Orsay, FR pixel detector [3] features an architecture which scales badly with hit rates higher than the ones expected for LHC full design luminosity. The FE-I3 is based on an architecture which requires transfer of every pixel hit down to data buffers belonging to the periphery of the IC. The pixel hit data fill these buffers until expiration of the trigger latency -typically of order 3 µs-before being transmitted for readout if triggered or, with much higher probability, erased if not triggered. The data transfer mechanism from the pixel to the periphery is time consuming and becomes highly inefficient at higher hit rates (for more information about hit recording inefficiencies at high hit rate in the current pixel FE and in FE-I4, see [4]).One of the first test chips submitted in the framework of the FE-I4 collaboration at the end of 2006 was an exploratory prototype analog array [5]. This test chip was tested in 2007 and is the basis of the present analog