Amorphous Silicon Based Microchannel Plates for Time-of-Flight Positron Emission Tomography

Microchannel plates fabricated from hydrogenated amorphous silicon (AMCPs) are a promising alternative to conventional lead glass microchannel plates. Their main advantages lie in their cheaper and more flexible fabrication processes, allowing for adaptable channel shapes, the possibility of vertical integration with an electronic readout, and the resistivity of the main amorphous silicon layer, which allows a charge replenishment by a current flowing directly through the bulk material. In the framework of this thesis, the design and fabrication of AMCPs were further developed to a point where they can now be considered a viable option for real applications such as time-of-flight positron emission tomography. Small channel diameter down to 1.6~\textmu m could be achieved, allowing for fast timing characteristics of the devices. By increasing the aspect ratio to 25, the multiplication gain could be enhanced to around 1500 from the previous maximum of \textasciitilde 100 of earlier generations. Characterization of the fabricated devices was done in both the continuous and transient regimes, and the time resolution of the detectors was measured for the first time. An arrival time jitter of $\sigma=4.6\pm0.1$~ps (FWHM) could be observed for the AMCP chip connected to an additional amplifier. This work on AMCP was carried out as part of the Sinergia project, "MEMS based gamma ray detectors for time-of-flight positron emission tomography". The envisioned detector in this project focuses on using Cherenkov radiation rather than scintillation to determine the annihilation site during time-of-flight PET imaging. Since Cherenkov radiation is instantaneous, this approach could significantly improve the timing resolution and, consequently, the final image's spatial resolution. Due to the low yield of Cherenkov photons per incoming gamma, detection efficiency becomes a critical factor. In an AMCP, this detection efficiency is limited by the active area of the channels. It has been increased to around 95% of the total area by fabricating funnel-shaped channel openings- demonstrating the potential of the fabrication flexibility of AMCPs.