High Voltage Monolithic Active Pixel Sensors

This research project of the research groups from Bochum, Heidelberg and Karlsruhe aims to jointly develop monolithic pixel detectors based on HV-CMOS sensors for particle physics experiments at large accelerator plants. The aim of the joint project is to carry out generic research and development work on high-voltage monolithic active pixel sensors (HV-MAPS), which are a promising candidate for future pixel detectors.

The aim of this research network is to continue the development of HV-MAPS by integrating additional functionality into the chip design, which was not used for the previous experiments. Its compact design makes HV-MAPS a serious alternative to other semiconductor detectors. However, for future use of HV-MAPS, e.g. For LHC upgrades, future circular collider experiments, PANDA, CLIC / ILC, Belle II or Mu3e Phase II, it is imperative to incorporate additional functionality into the design. Thus, in some experiments, a high-resolution measurement of the energy deposition is needed to distinguish on the basis of the measurement particle types, also the sensors should have a high rate tolerance and be able to separate the individual hits by a very good time resolution, it will z.T. large-area sensors needed or better spatial resolution. The implementation of these requirements into a sensor design is the aim of the research network in the coming funding period.

The previous HV-MAPS prototypes mainly provide the hit information which pixel has been hit at what time. In addition, the result of the charge collection (measured as time-over-threshold) is very variable, because the charge accumulation in the very narrow depletion zone (~ 15 μm) leads to a pronounced Landau distribution of the charge produced during the particle passage. The strong differences in the produced lag and thus in the signal height additionally influence the minimum achievable time resolution. However, the time resolution of ~ 10 ns achieved so far is not sufficient to determine the particle type on the basis of its time of flight.

To enable particle identification with HV-MAP sensors, as needed e.g. bz BelleII or PANDA, two features need to be optimized:

1. Energy resolution of the energy deposited in the sensor: The goal is to cover a dynamic range of 10 MIPs with an energy resolution sufficient to distinguish particle types based on their energy loss.
2. Time resolution of the signals generated in the sensor: In a first step, the correction of the timewalk will bring an improvement. Furthermore, the optimization of the energy resolution will improve the time resolution. The goal is to achieve a time resolution of well over 5 ns.

In experiments of hadron physics, it is not common practice to cool sensors in operation to 0 ° C or below. Due to the expected rate and radiation dose over the lifetime of the experiment, it is quite common to operate the sensors even at room temperature. It is therefore very important to clarify to what extent an increase of the sensor temperature affects the sensor performance (eg signal-to-noise ratio, energy or time resolution) (temperature tolerance).