Generic Detector development
The demands on the detectors will continue to increase in future experiments. Therefore, a continuous development of the detectors is necessary in order to cope with the future challenges. For example, the requirements for rate capability and improved time resolution will play an important role in future experiments. We are therefore trying to understand limiting properties of our current detectors and to develop improved detectors. Our main focus is on the GridPix detectors, which we will fabricate using photolithographic processes in the clean rooms of the research building Technologiezentrum Detektorbau (FTD). In addition, we are also experimenting with completely new detector concepts, new materials or readouts.
The first gaseous detectors were developed more than a hundred years ago by H. Geiger and E. Rutherford. Since then, they have made possible a large number of discoveries in particle physics and are still important components of modern experiments. Above all, the development of the multi-wire proportional chambers should be mentioned here, for which G. Charpak received the Nobel Prize in Physics in 1992. In 1988, A. Oed introduced the first microstructured gaseous detectors, which were further developed in numerous variations in the following years. Micromegas detectors, for example, consist of a fine grid stretched across the readout plane at a distance of 50 -100 µm. In this narrow area, the primary electrons can initiate a gas amplification process that ends in an electron avalanche with several thousand electrons.
GridPix Detectors
To reach the best possible spatial resolution, one must resolve the individual primary electrons from the drift region. This requires a very fine readout structure with a pixel size of several 10 µm. Due to the high density of electronic readout channels, this is only possible with a readout chip for silicon pixel sensors. Therefore we use the Timepix and Timepix3 ASIC, both developed by the Medipix collaboration at CERN. These ASICs are first covered with a 4 µm thick protective layer, which protects them in case of unwanted electrical discharges. On top of the protective layer, 50 µm high pillars and a thin grid are fabricated using photolithographic post-processing. The grid is aligned so that there is one grid hole above each readout pixel. Therefore, the entire electron avalanche triggered by a primary electron is collected on a single pixel and thus exceeds the readout threshold with high probability.
Production and further Developmenty
In this way, individual primary electrons can be detected and counted. This method offers several advantages, for example, significantly better energy resolutions can be achieved by counting the individual electrons rather than by adding up the total energy, since the statistical fluctuations of the gas amplification are not included in the measurement. In addition, the events can be recorded with high spatial resolution and reconstructed later. This makes it easier to distinguish different particles such as X-ray photons from tracks or to reconstruct the tracks of the particles.
In the future, the GridPixe will be produced in the clean rooms of the Bonn research building FTD and then characterized in our laboratories. Because of the special machine selection in the clean room and the fast characterization, much better conditions are given to improve and further develop the detectors. In particular, the protective layer is to be optimized for higher event rates and double-grid structures are to be developed for reduced ion backflow.
