JRA9-TIIMM: Tracking and Ions Identifications with Minimal Material budget

The JRA we propose concentrate in a technological innovation in the field of tracking detectors for experiments in the hadron physics area like the ALICE project at CERN, it is also easy to envisage possible applications in the more general area of LHC particle physics experiments and in the low energy range ion tracking and identification needed in the patient particle treatment in medical physics. Common needs to those applications is to combine at the same time a precision tracking with energy loss measurement to be used for particle identification, and very low level of crossed material to minimize multiple scattering. This should include also the easiness of the data readout produced by the sensor to cope with the specific need of all the different applications.

MAPS (Monolithic Active Pixel Sensors), the detecting technology we propose to improve, born for commercial applications like digital cameras, in the scientific realm are used for charged particle detection in particle and nuclear physics field (STAR at BNL, ALICE at CERN and Mu3e at PSI). More recently they have been used in ion fragmentation cross section measurements for hadrontherapy treatments improvement. Though most of the MAPS sensors operate in digital mode (no signal amplitude available), some particle identification capabilities have been demonstrated by some partners of the project exploiting the cluster size information. Sensors providing as output the signal amplitude of fired pixels, would allow measurement per particle and greatly increase identification capabilities. However the charge collection by diffusion due to the non depleted sensing region and its thickness limited to less than 20μm are serious limiting factors. To overcome those hindrances we propose ground-breaking technological improvements that would allow both fully depleting the sensing region and enlarging its thickness. This will be obtained by a new sensing front end that will bias the charge collecting diode, the latter with the use of high resistivity silicon layer substrates nowadays available in the standard silicon foundry processes. Those possibilities have been demonstrated by the various developments that in recent years have taken place to provide the full depletion in MAPS, like in ALICE ITS (Inner Tracking System) and Mu3e experiments. The Strasbourg partner also achieved full depletion over a few tens of micrometers, the useful thickness for the TIIMM purpose, with small prototypes implementing 22μm pixel pitch matrices in the Tower Jazz CMOS CIS 180 nm technology. A promising 298eV FWHM spectroscopic resolution at 5.9KeV energy X-ray photon per pixel has been obtained with at the same time an encouraging Radiation Hardness at the level of for NIEL (Non Ionizing Energy Loss). Those promising results are the basis on wich we found our proposal. The clear advantages of the proposed technological improvements are: faster and more efficient charge collection, improved intrinsic radiation hardness, possibility to explore the tradeoff between fluctuations of the released charge (Landau distribution) and the minimization of multiple scattering. In addition we foresee a scalable MAPS read-out architecture, allowing an easy upgrade to a large size chip targeting a specific experiment, which includes an ADC (Analog to Digital Conversion) to measure the charge collected per pixel appropriated for PID (Particle IDentification) through measurement. In the project framework, the TIIMM activity is complementary to the one in the nextDIS work package. With the approach of fully depleting a MAPS pixel sensor, using the same Tower Jazz 180 nanometers technology, we aim the energy loss measurements for particle identification while nextDIS has the goal of the particle arrival timing measurement at the nano second precision level.