Abstract
Depleted Monolithic Active Pixel Sensor (DMAPS) prototypes developed in the TowerJazz 180 nm CMOS imaging process have been designed in the context of the ATLAS upgrade Phase-II at the HL-LHC. The pixel sensors are characterized by a small collection electrode (3 μm) to minimize capacitance, a small pixel size (36.4× 36.4 μm2), and are produced on high resistivity epitaxial p-type silicon. The design targets a radiation hardness of 1×1015 1 MeV neq/cm2, compatible with the outermost layer of the ATLAS ITK Pixel detector. This paper presents the results from characterization in particle beam tests of the Mini-MALTA prototype that implements a mask change or an additional implant to address the inefficiencies on the pixel edges. Results show full efficiency after a dose of 1×1015 1 MeV neq/cm2.
Highlights
- Charge collection properties of TowerJazz 180 nm CMOS Pixel Sensors in dependence of pixel geometries and bias parameters, studied using a dedicated test-vehicle: The Investigator chip G
: Depleted Monolithic Active Pixel Sensor (DMAPS) prototypes developed in the TowerJazz 180 nm CMOS imaging process have been designed in the context of the ATLAS upgrade
Electrons first passed through 3 MALTA silicon detector planes, before entering the Device Under Test (DUT) and one extra MALTA reference plane (REF) placed close in front of the DUT
Summary
The TowerJazz process can be further modified (as shown in figure 2 bottom row) by adding a gap in the low dose n-layer through a mask change (lower right) or adding an additional production process compatible deep p-type implant (lower left). We refer to these configurations as “n− gap” and “extra deep p-well” configurations, respectively. The purpose of these modifications is to improve the charge collection at the pixel edges and corners through the creation of a stronger lateral field, which focuses the ionization charge towards the collection electrode The design of these implant structures has been optimized in TCAD simulations [8], which indicate that these modifications significantly improve the charge collection at the pixel boundaries
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