Mu3e

Abstract:

The MALTA2 sensor is the second prototype in the MALTA family of Depleted Monolithic Active Pixel Sensors, developed using a modified 180nm CMOS imaging process and optimized for operation in the high-radiation and high hit-rate conditions of future collider experiments. With a matrix of 224 × 512 pixels and a 36.4µm pitch, MALTA2 is designed for fast charge collection, low noise, and low power consumption. MALTA2 incorporates a low doped n − layer extending across the pixel matrix, which enhances the lateral depletion and charge collection by drift. This work evaluates a MALTA2 variant with very high n − layer doping for improved radiation hardness. The sensor has been neutron irradiated up to a fluence of 5 × 1 0 15 1 MeV n eq cm −2 and characterized in test beam campaigns at the CERN SPS using a 120 GeV/c mixed hadron beam. Hit detection efficiencies above 95% were achieved up to a fluence of 3 × 1 0 15 1 MeV n eq cm −2 . At 5 × 1 0 15 1 MeV n eq cm −2 , the hit detection efficiency measured was 64.9 ± 0.2 % at a substrate bias voltage of -60 V. To investigate this degradation, the effective active depth has been extracted as 20.3 ± 0.2 μ m from cluster size measurements as a function of the beam incident angle. The results from the very high doping will guide the development of prototypes featuring ultra-high n − layer doping, aiming to achieve greater radiation hardness in next-generation silicon tracking detectors.