Development of HV-CMOS sensor technology for the next generation of particle physics experiments

Over the last 25 years, silicon sensor technology has become a critical ingredient in the success of the most challenging experiments in fundamental physics. The discovery of the Higgs boson at the Large Hadron Collider (LHC), most notably, would not have been possible without the very fine grained sensors which sit at the heart of the CERN detectors to measure (track) the trajectories of thousands of particles produced tens of millions of times per second. The next generation of experiments, being planned today, relies on a step-change in the performance of tracking sensor technologies. Scientists seek detectors that provide micron scale position accuracy and better than one nanosecond timing resolution, while being substantially thinner than a sheet of paper and requiring little cooling. To date it has not been possible to combine all of them in a single device.

In this research, I propose to develop novel Depleted Monolithic Active Pixel Sensors (DMAPS) to achieve these parameters in a single device using industry standard, and therefore cost-effective, High Voltage-Complementary Metal-Oxide-Semiconductor (HV-CMOS) processes. DMAPS have already been adopted as the chosen sensor technology for the Mu3e experiment at the Paul Scherrer Institute in Switzerland, for which I work on the construction of the first DMAPS pixel tracker that will come online in 2020. DMAPS are also developed for the planned phase-II upgrade of ATLAS at the LHC, for which the final technology decision is expected in 2019. Within the particle physics instrumentation community, there is now a wide consensus that DMAPS will replace traditional tracking sensor technologies in the next generation of particle physics experiments.

In spite of the major improvements already demonstrated by DMAPS, the enormous challenges set by future particle physics experiments demand further research to achieve yet more performant sensors. The main goal of this research is to develop highly performant DMAPS, targeting in the first place the reduction of the pixel area, the improvement of the time resolution and the increase of the radiation tolerance. I will also develop full-size DMAPS detectors with optimised performance and pursue the deployment of these devices for particle physics experiments and beyond. These new detectors can have a massive impact in experiments such as a planned upgrade of Mu3e and future upgrades at the High Luminosity-LHC (HL-LHC), but also in the medical and commercial fields as the low cost typical of HV-CMOS processes will make DMAPS tracking detectors available to many.

This research aims to push the performance limits of Depleted Monolithic Active Pixel Sensors (DMAPS) detectors to maximise the potential of the next generation of experiments in particle physics. Whilst the immediate, obvious application is in particle physics, the project has potential to go beyond the laboratory and make significant and lasting impacts in other fields of science, improve daily life for people through healthcare and train new researchers and professionals. I will split the impact of my research into: 1) technology and industry, and 2) skills development.

1) Impact through technology and industry. The goal is the advancement of society through technology developed for particle physics with engagement of UK industry to impact economy.

Ideas to deliver on the timescale of the fellowship include:

a) The department has a contract in place with Proton Partners International Ltd. (PPI), a commercial company developing a number of proton therapy centres for cancer treatment across the UK, including an on-campus facility at Liverpool. The Department of Physics will provide beam instrumentation that improves outcomes for patients particularly in paediatric cases. The DMAPS developed in this fellowship, with much improved performance, will be evaluated to establish their performance in this environment, and compare the results to traditional silicon detectors and today's state-of-the-art DMAPS.

b) Satellite applications: The Dark Matter Particle Explorer (DAMPE) is a satellite-based particle physics experiment that was launched in 2015 to study high-energy gamma-ray astronomy and search for dark matter. Motivated by the success of DAMPE, the astro-particle physics community proposed the next generation of the experiment, referred to as DAMPE-II as the priority from 2019-2030. In collaboration with the astro-particle physics research centre Purple Mountain Observatory (PMO) in China, DMAPS developed in this fellowship will be used to study the replacement of the traditional silicon detectors of DAMPE-III.

c) Precision mass spectrometry: Fast and precise mass spectrometry has a wide range of applications including the detection of explosives and narcotics, medical diagnostics and process control in industry and agriculture. DMAPS developed in this fellowship with much improved granularity will be used to study the feasibility of using this sensor technology to characterise its ability to detect low energy ions over a range of ion masses. A successful demonstration would open the door to using DMAPS as a high granularity detector in mass spectrometry, thus enhancing substantially the mass separation resolution and potentially achieving single ion sensitivity.

d) Photon, X-ray and gamma ray applications: Core R&D work in this fellowship is strongly focused on the detection of charged particles, however the exceptional timing resolution of DMAPS offers interesting applications also if sensitivity to photons across the electromagnetic spectrum can be demonstrated. DMAPS developed in this fellowship with much improved time resolution will be used to analyse the response of this sensor technology in the detection of photons, X-rays and gamma rays. Such a demonstration would open the door to applications in a multitude of new areas including fast imaging, imaging in extreme radiation environments, and gamma and x-ray cameras.

2) Impact through skills development. The goal is the recruitment and training of our young researchers and professionals.

This fellowship will offer me an excellent opportunity to attract and engage individuals from our current generation of students and train them with expertise in high-tech hardware, firmware and software skills in the environment of national and international projects. At the same time, I will engage in activities to promote this research and attract more women to Science, Technology, Engineering, Maths and Medicine (STEMM).