Abstract
Within the ATTRACT FASTPIX project, a monolithic pixel sensor demonstrator chip has been developed in a modified 180 nm CMOS imaging process, targeting sub-nanosecond timing measurements for single ionizing particles. It features a small collection electrode design on a 25 micron thick epitaxial layer and contains 32 mini matrices of 68 hexagonal pixels each, with pixel pitches ranging from 8.66 to 20 micron. Four pixels are transmitting an analog output signal and 64 are transmitting binary hit information. Various design variations are explored, aiming at accelerating the charge collection and making the timing of the charge collection more uniform over the pixel area. Signal treatment of the analog waveforms, as well as reconstruction of time and charge information, is carried out off-chip. This contribution introduces the design of the sensor and readout system and presents the first performance results for 10 μm and 20 μm pixel pitch achieved in measurements with particle beams.
Highlights
Pixel detectors combining excellent spatial and temporal resolution with high detection efficiency and radiation tolerance are required for tracking detectors in future high-energy and high-rate particle collider experiments [1,2]
All measurements presented here were performed on a sample that was optimized for fast charge collection
The 20 μm pitch matrix has predominantly a single pixel hit per event, which is the case for 70% of events, and the fraction quickly drops off for more pixels
Summary
Pixel detectors combining excellent spatial and temporal resolution with high detection efficiency and radiation tolerance are required for tracking detectors in future high-energy and high-rate particle collider experiments [1,2] They have wide-ranging applications in other fields, such as imaging Time-of-Flight Mass Spectroscopy and Fluorescence LifeTime Imaging Microscopy, medical applications such as proton therapy and sensors used in daily life, such as LIDAR in cars. The small collection electrode design results in highly non-uniform electric fields in the sensor, causing the dependence of the charge collection time on where within the pixel the particle is incident, with typically much longer collection times if the charge is generated near the pixel edges This represents a key limitation for both precise timing and radiation tolerance as slow charge collection increases the probability of the signal charge being captured by radiation-induced traps
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