Description and context
CMOS image sensors are nowadays of common use for consumer and scientific applications. Their peculiarity is to have on the same substrate the radiation sensitive structures and the associated processing electronics. The use of standard, or close to standard CMOS technologies allows to tailor the sensors to each application, with dedicated functionalities, while still using standard micro-electronics CAD design software.
Since the last decade, CMOS sensors are largely being developed to detect charged particles in high energy physics detectors. The possibility to thin them and their monolithic architecture allows to obtain high-granularity, ultra-thin ((~50 µm ) and mechanically sturdy sensors. They are now sufficiently mature in terms of spatial resolution, readout speed, dissipated power and radiation resistance to be used on actual physics experiments. They are for example proposed for the vertex detector of the ILC linear collider project. They have already been used to equip a beam telescope within the EUDET project (European project, 6th PCRD). More recently, they have been chosen to equip the innermost layers of the ALICE tracker at LHC.
High energy physics sensors are purely digital, featuring an integrated zero-suppression. They are generally designed for and manufactured on epitaxied bulks routinely available from the foundries.
However, the radiation tolerance of the sensors designed up to now is still insufficient for some experiences, and notably for the upgrade and replacement of the ATLAS inner tracker by 2024 (Phase 2 upgrade of the LHC). To improve the sensor radiation tolerance, several groups propose to use High Voltage CMOS on High Resistivity bulk. This kind of sensors allows to have a fully depleted bulk, which improves considerably charge collection, and as a consequence radiation tolerance.
IRFU
Within the CEA’s physical sciences division, the Institute of Research into the Fundamental Laws of the Universe – IRFU – is a basic research institute whose activities cover the fields of astrophysics, nuclear physics, high energies physics and the associated technologies. It comprises more than 800 technicians, engineers, researchers and managers. It is located at Saclay, about 30km from Paris, FRANCE.
Team description
IRFU’s microelectronics team has long expertise in CMOS monolithic pixel sensors design and has participated to European projects such as EUDET (FP6) and AIDA (FP7) with pixel sensors. It works also presently on the development of CMOS sensors for the ALICE detector. The thesis proposed here will capitalize on this expertise and will be done in the frame of an international collaboration of several teams within the ATLAS collaboration.
Proposed work
The first part of the thesis will be devoted to the study and to the development of a small scale prototype to measure the main parameters (charge collection, noise, radiation tolerance…) of one specific HV/HR promising CMOS process. Standard micro-electronics design tools will be used.
The prototype will be tested in the laboratory. This implies setting up a dedicated test bench. Based on the experience gained with this first prototype, a more sophisticated second prototype will be developed, based on innovating architectures featuring “intelligent” pixels (with memory cells, thresholding, timing capabilities etc).
Required academic cursus and competences
Master-2 or equivalent level in electronics or physics of semi-conductor devices.
A basic knowledge of analog and digital electronics, of semi-conductor device physics is mandatory.
Having already participated to the design of a CMOS IC with commonly used CAD tools (Cadence or other) will be beneficial.
Acquired competences
The work done during the Ph D thesis will allow the successful candidate to acquire the knowledge and know-how needed for the design and characterization of a radiation tolerant CMOS sensor, with additional analog and digital functionalities. It will also allow him to widen his understanding of semiconductor sensor physics.
Collaborations/Partnerships
Within an international collaboration of several ATLAS teams, the Ph D student will have to participate to discussions and test activities that will take place in France, CERN, or abroad. There will be also discussions with sensor manufacturers. Results obtained will be presented at international conferences and published in peer-reviewed journals.
Contacts
Thesis director :
P. Schwemling (philippe.schwemling@cea.fr)
Thesis responsible :
Y. Degerli (degerli@cea.fr)