Investigation of the in-pixel response of the Mupix11 monolithic pixel sensor using a microfocus X-ray beam at Diamond Light Source

TL;DR

This study characterizes the in-pixel response of the MuPix11 monolithic pixel sensor using a microfocus X-ray beam, revealing uniform response at nominal bias and location-dependent response without bias.

Contribution

It provides detailed measurements of MuPix11's in-pixel response with a microfocus X-ray beam, highlighting effects of bias voltage on detector uniformity.

Findings

Uniform response across pixels at nominal voltage and threshold.

Reduced detection rate at pixel boundaries without reverse bias.

Response depends on bias voltage and pixel location.

Abstract

MuPix11 is a High-Voltage Monolithic Active Pixel Sensor (HV-MAPS) developed for the tracking system of the Mu3e experiment. The in-pixel photon response of a MuPix11 sensor thinned to 70 {\mu}m was measured using an 8 keV X-ray beam with a 3 {\mu}m spot size at the B16 beamline at Diamond Light Source, emulating the passage of a minimum ionising particle (MIP). At nominal operating voltage and threshold, high-resolution scans across the pixel matrix show the detector response to be uniform. In the absence of reverse bias (0 V), the relative sub-pixel response is location-dependent as a reduced detection rate is observed at pixel boundaries.