Abstract
The upgrade of the ATLAS [1] tracking detector for the High-Luminosity Large Hadron Collider (LHC) at CERN requires novel radiation hard silicon sensor technologies. Significant effort has been put into the development of monolithic CMOS sensors but it has been a challenge to combine a low capacitance of the sensing node with full depletion of the sensitive layer. Low capacitance brings low analog power. Depletion of the sensitive layer causes the signal charge to be collected by drift sufficiently fast to separate hits from consecutive bunch crossings (25 ns at the LHC) and to avoid losing the charge by trapping. This paper focuses on the characterization of charge collection properties and detection efficiency of prototype sensors originally designed in the framework of the ALICE Inner Tracking System (ITS) upgrade [2]. The prototypes are fabricated both in the standard TowerJazz 180nm CMOS imager process [3] and in an innovative modification of this process developed in collaboration with the foundry, aimed to fully deplete the sensitive epitaxial layer and enhance the tolerance to non-ionizing energy loss. Sensors fabricated in standard and modified process variants were characterized using radioactive sources, focused X-ray beam and test beams before and after irradiation. Contrary to sensors manufactured in the standard process, sensors from the modified process remain fully functional even after a dose of 1015neq/cm2, which is the the expected NIEL radiation fluence for the outer pixel layers in the future ATLAS Inner Tracker (ITk) [4].
Highlights
Signal response of sensors with large pixel pitchThe change in amplitude gain is due to capacitance increase in the modified process [6]
Measurements indicate full depletion of the sensors produced in the novel modified process. This combined with pixels cells with small, low capacitance collection electrodes enables low power pixel design with high radiation tolerance
The encouraging results obtained on the Investigator chip allow us to prepare designs for more complex, full reticle-size depleted monolithic CMOS pixel sensors, meeting the challenging requirements of future tracking detectors at HL-LHC
Summary
The change in amplitude gain is due to capacitance increase in the modified process [6]. In the modified process the depleted volume is enlarged under the p-well. From the gain reduction from 26 mV to 18 mV, respectively, we estimate the capacitance increase due to process modification to be approximately 30% at a. The undepleted volumes are significantly reduced as is the contribution from slow diffusion signals These results indicate a more uniform charge collection mechanism in the modified process as the undepleted volume under the p-well is greatly diminished, the contribution of slower diffusion signals is diminished in favour of faster drift signals (cf section 4.3)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
