C. A. Marin Tobon

Monolithic active pixel sensor development for the upgrade of the ALICE inner tracking system

ALICE plans an upgrade of its Inner Tracking System for 2018. The development of a monolithic active pixel sensor for this upgrade is described. The TowerJazz 180 nm CMOS imaging sensor process has been chosen as it is possible to use full CMOS in the pixel due to the offering of a deep pwell and also to use different starting materials. The ALPIDE development is an alternative to approaches based on a rolling shutter architecture, and aims to reduce power consumption and integration time by an order of magnitude below the ALICE specifications, which would be quite beneficial in terms of material budget and background. The approach is based on an in-pixel binary front-end combined with a hit-driven architecture. Several prototypes have already been designed, submitted for fabrication and some of them tested with X-ray sources and particles in a beam. Analog power consumption has been limited by optimizing the Q/C of the sensor using Explorer chips. Promising but preliminary first results have also been obtained with a prototype ALPIDE. Radiation tolerance up to the ALICE requirements has also been verified.

Radiation hardness and detector performance of new 180nm CMOS MAPS prototype test structures developed for the upgrade of the ALICE Inner Tracking System

The features of the 180nm TowerJazz1 CMOS technology allow for the first time the use of CMOS Monolithic Active Pixel Sensors (MAPS) under the harsh operational conditions of the LHC experiments. The stringent requirements of the ALICE Inner Tracking System (ITS) in terms of material budget, radiation hardness, readout speed and a low power consumption have thus lead to the choice of MAPS as baseline technology option for the recently approved upgrade of the ITS and are the key drivers for R&D efforts on basic transistor and Explorer and MIMOSA pixel sensor prototypes produced in TowerJazz technology. Though the radiation loads expected for the ITS are below those of ATLAS and CMS, it is however necessary to assess the radiation hardness for ITS MAPS prototypes. Total Ionizing Dose (TID) radiation hardness has been established for basic transistor structures using a 60keV X-ray machine. The main operational characteristics and detection properties such as noise, charge collection efficiency and signal over noise ratio of Explorer-0 and MIMOSA32 and MIMOSA34 pixel sensor prototypes have been studied using X-rays (55Fe) and test beams at CERN and DESY before and after Non Ionizing Energy Loss (NIEL) and TID irradiation. In this paper the results of these R&D activities will be presented and discussed.

MAPS development for the ALICE ITS upgrade

Monolithic Active Pixel Sensors (MAPS) offer the possibility to build pixel detectors and tracking layers with high spatial resolution and low material budget in commercial CMOS processes. Significant progress has been made in the field of MAPS in recent years, and they are now considered for the upgrades of the LHC experiments. This contribution will focus on MAPS detectors developed for the ALICE Inner Tracking System (ITS) upgrade and manufactured in the TowerJazz 180 nm CMOS imaging sensor process on wafers with a high resistivity epitaxial layer. Several sensor chip prototypes have been developed and produced to optimise both charge collection and readout circuitry. The chips have been characterised using electrical measurements, radioactive sources and particle beams. The tests indicate that the sensors satisfy the ALICE requirements and first prototypes with the final size of 1.5 × 3 cm2 have been produced in the first half of 2014. This contribution summarises the characterisation measurements and presents first results from the full-scale chips.

Front end optimization for the monolithic active pixel sensor of the ALICE Inner Tracking System upgrade

ALICE plans to replace its Inner Tracking System during the second long shut down of the LHC in 2019 with a new 10 m2 tracker constructed entirely with monolithic active pixel sensors. The TowerJazz 180 nm CMOS imaging Sensor process has been selected to produce the sensor as it offers a deep pwell allowing full CMOS in-pixel circuitry and different starting materials. First full-scale prototypes have been fabricated and tested. Radiation tolerance has also been verified. In this paper the development of the charge sensitive front end and in particular its optimization for uniformity of charge threshold and time response will be presented.

Low power, high resolution MAPS for particle tracking and imaging

We describe here the first monolithic pixel detector prototype embedding the OrthoPix architecture, specifically designed to deal with imaging applications where the relevant number of pixel hit per frame (occupancy) is small (on the order or less than 1%), like in High Energy Physics, Medical Imaging and other applications. Current state of the art employs complex circuitry into the pixel cell to discriminate relevant signals, leading to an extremely effective, non-destructive compression at the price of large power consumption and pixel area limitations. The OrthoPix architecture instead implements a passive projective compression scheme, leading to low power, small pixel cell and large area devices.

arXiv : Depleted fully monolithic CMOS pixel detectors using a column based readout architecture for the ATLAS Inner Tracker upgrade

Depleted monolithic active pixel sensors (DMAPS), which exploit high voltage and/or high resistivity add-ons of modern CMOS technologies to achieve substantial depletion in the sensing volume, have proven to have high radiation tolerance towards the requirements of ATLAS in the high-luminosity LHC era. DMAPS integrating fast readout architectures are currently being developed as promising candidates for the outer pixel layers of the future ATLAS Inner Tracker, which will be installed during the phase II upgrade of ATLAS around year 2025. In this work, two DMAPS prototype designs, named LF-Monopix and TJ-Monopix, are presented. LF-Monopix was fabricated in the LFoundry 150 nm CMOS technology, and TJ-Monopix has been designed in the TowerJazz 180 nm CMOS technology. Both chips employ the same readout architecture, i.e. the column drain architecture, whereas different sensor implementation concepts are pursued. The paper makes a joint description of the two prototypes, so that their technical differences and challenges can be addressed in direct comparison. First measurement results for LF-Monopix will also be shown, demonstrating for the first time a fully functional fast readout DMAPS prototype implemented in the LFoundry technology.

iMPACT: Innovative pCT scanner

This is a short conference record (a detailed article will be submitted for peer-reviewed publication after the project will gather the first data) about the iMPACT project, which aims to build a novel pCT scanner for protons of medical energy (200-300 MeV range) designed to improve the current state of the art in protons tracking at all levels: speed, spatial resolution and material budget. Scanning time will be limited to few seconds, the material budget reduced by a factor 4 (respect to micro-strip based detectors) and the spatial resolution pushed down to the 10 μm range mark. Such performance improvements will provide completely new opportunities to apply pCT for both diagnostic and treatment purposes. Together with the performance improvements, cost reduction would result as well, as the proposed detector is based on commercially available technology, opening the way for future commercial implementations of the system.

Explorer-0: A Monolithic Pixel Sensor in a 180 nm CMOS process with an 18 µm thick high resistivity epitaxial layer

This work presents the design and characterization of Explorer-0, a Monolithic Active Pixel Sensor (MAPS) developed in the framework of the R&D activity for the upgrade of the Inner Tracking System (ITS) of the ALICE experiment at CERN. The Explorer-0 chip has been manufactured in the TowerJazz 180 nm CMOS Imaging Sensor process, based on a high-resistivity (p > 1 k Ω · cm), 18 μm thick, epitaxial layer. It contains different pixel designs with a variation of the collection electrode shape and pixel pitch (20 μm and 30 μm). The pixel circuit offers the possibility of varying the sensor bias and to decouple the read-out time from the charge integration time. Charge collection properties of the different pixel designs have been studied with respect to the sensor bias using a 5.9 keV X-ray source (55Fe) and a 4 GeV/c electron beam. The radiation tolerance of this technology in view of the expected radiation levels foreseen in ALICE has been established as well. The sensor capacitance, which is a key parameter for a compact low-power front-end design, has been estimated. Based on these results, a second version of the Explorer chip has been designed and successfully tested. The latter has a lower contribution of the circuit to the overall input capacitance allowing for a higher sensor Signal to Noise Ratio (SNR).