Impact of X-ray induced radiation damage on FD-MAPS of the ARCADIA project

Abstract

Recent advancements in Monolithic Active Pixel Sensors (MAPS) demonstrated the ability to operate in high radiation environments of up to multiple kGy’s, which increased their appeal as sensors for high-energy physics detectors. The most recent example in such application is the new ALICE inner tracking system, entirely instrumented with CMOS MAPS, that covers an area of about 10 m2. However, the full potential of such devices has not yet been fully exploited, especially in respect of the size of the active area, power consumption, and timing capabilities. The ARCADIA project is developing Fully Depleted (FD) MAPS with an innovative sensor design, that uses a proprietary processing of the backside to improve the charge collection efficiency and timing over a wide range of operational and environmental conditions. The innovative sensor design targets very low power consumption, of the order of 20 mW cm−2 at 100 MHz cm−2 hit flux, to enable air-cooled operations of the sensors. Another key design parameter is the ability to further reduce the power regime of the sensor, down to 5 mW cm−2 or better, for low hit rates like e.g. expected in space experiments. In this contribution, we present a comparison between the detector characteristics predicted with Technology Computer Aided Design (TCAD) simulations and the ones measured experimentally. The comparison focuses on the current-voltage (IV) and capacitance-voltage (CV) characteristics, as well as noise estimated from in-pixel capacitances of passive/active pixel matrices. In view of the targeted applications of this technology, an emphasis is set on the modeling of X-ray induced radiation damage at the Si-SiO2 interface and the impact on the in-pixel sensor capacitance. The so-called new Perugia model has been used in the simulations to predict the sensor performance after total ionizing doses of up to 10 Mrad.

First characterization results of ARCADIA FD-MAPS after X-ray irradiation

“…However, the simulations show overall lower capacitances, which could originate from an underestimated concentration of positive oxide charges N ox in the SiO 2 layer. As described in previous works, we found that the single-pixel capacitance is impacted by an electron accumulation layer below the Si-SiO 2 interface [3,11]. The simulations include an oxide charge concentration of 6.5 × 10 10 cm −3 , based on the Hamamatsu parametrisation of the new Perugia model [7].…”

Charge Collection Dynamics of the ARCADIA Passive Pixel Arrays: Laser Characterization and TCAD Modeling

“…CV measurements were performed as well to estimate the pixel capacitance and compare them with simulation results. The preliminary results of the electrical characterization of the passive pixel arrays are reported in [15]. Table 1 contains the measured full depletion and punch-through voltages and the pixel capacitance in full depletion condition extracted from TCAD simulations for an applied nwell voltage of 0.8 V.…”

“…In order to investigate the effect of the applied reverse bias voltage (V bias ) on the signal evolution, we performed measurements on the pixel matrices varying V bias in a voltage range that starts below V depl and ends above V PT . The punch through voltage does not represent an absolute limit to the applicable bias voltage since the punch through current is still in the nA range with a V bias exceeding V PT by several volts [15]. For this reason, we can apply a voltage higher than V PT while still granting a low power consumption for the detector.…”