Integrated image sensors revolutionised the world of visible imaging and receive interest in many other fields. Monolithic CMOS pixel sensors have already been produced to cover a few square meters in some particle physics experiments. The ideal image sensor or camera would detect ionizing particles with an almost noise-free, large amplitude signal, tens of ps timing resolution, extreme radiation tolerance, covering even larger areas at reasonable cost with small pixels with significant inpixel functionality.
This research aims to provide a practical sensor structure to achieve the missing combination of precise timing and extreme radiation tolerance. Detailed research on the motion of signal charge and first 3D TCAD simulations indicate this is within reach in deep submicron CMOS processes. This will lay the basis for an ideal image sensor, revolutionising not only high energy physics experiments, but also other scientific measurement tools such as imaging Time-of-Flight Mass Spectroscopy, Fluorescence Life-Time Imaging Microscopy, electron microscopy, and sensors used in daily life like LIDAR in cars.
Deep submicron CMOS technologies allow tiny, sub-femtofarad collection electrodes, and large signal-to-noise ratios, essential for very precise timing. However, complex in-pixel circuits require some area, introducing timing variation depending on the location of the particle or photon hit within the pixel. We aim to provide a practical sensor structure eliminating this tradeoff between pixel size and timing variation. It will accelerate the signal charge to the collection electrode, significantly reduce timing spread and the probability to trap the signal charge, and hence increase radiation tolerance.
Simulations show significant improvement potential, but we need to study how to optimally apply the improvements, and benchmark performance for different feature sizes with Monte Carlo and 3D TCAD time-domain simulations. The principles can also be applied to optimise sensors with even better performance using new technologies, like 3D wafer stacking. The focus here is on precision timing, complementary to the SubQin4Ts ATTRACT proposal, focussing on 3D stacking and charge collection from thin layers initially without precision timing. We will benefit from the experience of Ritsumeikan University in visible imaging, and good relations of INFN and CERN with foundries to explore proof-of-principle test structures in technologies we already work with and compare simulations with measurements.
The goal is to prepare technology selection and prototype production of an ideal sensor at a later stage. R&D with several iterations over at least 5 years is expected before production of a system-ready sensor chip to cover several hundreds of m2 at reasonable cost. INFN and CERN participate in several physics experiments, all partners collaborate with many groups, and are ideally placed to disseminate results through their network and conferences.