Charge calibration of MALTA2, a radiation hard depleted monolithic active pixel sensor

TL;DR

This paper presents a precise calibration method for the MALTA2 DMAPS sensor's charge threshold using a dedicated injection circuit and Fe-55 source, ensuring accurate charge collection understanding.

Contribution

A new calibration procedure for MALTA2 sensors is developed, utilizing a dedicated charge injection circuit and Fe-55 source for precise threshold calibration.

Findings

Average capacitance for non-irradiated samples is 257 aF.

Calibration procedure accounts for 12% divergence in capacitance.

Method improves threshold accuracy for high-rate tracking applications.

Abstract

MALTA2 is a depleted monolithic active pixel sensor (DMAPS) designed for tracking at high rates and typically low detection threshold of $\sim150\,\mathrm{e^-}$. A precise knowledge of the threshold is crucial to understanding the charge collection in the pixel and specifying the environment for sensor application. A simple procedure is developed to calibrate the threshold to unit electrons making use of a dedicated charge injection circuit and an Fe-55 source with dominant charge deposition of $1600\, \mathrm{e^-}$. The injection voltage is determined which corresponds to the injection under Fe-55 exposure and is the basis for charge calibration. The charge injection circuit incorporates a capacitance with design value of $\mathrm{C_{inj}}=$ 230 aF. Experimentally, the average capacitance value for non-irradiated samples is found to be $\mathrm{C_{inj,exp}}=$ 257 aF. The 12 % divergence motivates the need for the presented precise calibration procedure, which is proposed to be performed for each MALTA2 sensor.