Speaker
Description
A promising approach to improve the time resolution of silicon pixel sensors into the sub-nanosecond regime is the use of BiCMOS technology. The integration of SiGe heterojunction bipolar transistors (HBTs), characterised by their high cut-off frequency and amplification, enables fast analogue front-end electronics and can additionally support high-speed data transmission. Future particle physics experiments expose detector electronics to high radiation fluences. A detailed understanding of radiation-induced degradation is therefore essential to assess the suitability of this technology for detector applications.
This talk presents results of an irradiation campaign with test structures of single HBTs, which were exposed to neutrons up to a fluence of $2 \times 10^{15}\, n_{eq}/cm^2$ and to protons in an in-situ measurement up to a fluence of $1.4 \times 10^{15}\, n_{eq}/cm^2$. Both measurements revealed a significant increase in base current, resulting in a degradation of the current gain, while the voltage gain of the transistors remains largely unaffected by radiation damage. Furthermore, the measured DC-characteristics of the HBTs are analysed and represented in an adapted compact transistor model (VBIC framework), which considers the radiation damage induced effects. For future sensors, this allows for a simulation-based verification of irradiation effects already in the design phase.
The technology is further evaluated using a prototype pixel sensor, which incorporates an HBT-based amplifier and achieves a time resolution in the order of $\mathcal{O}(300\,ps)$ for a MIP-like sginal. After irradiation with $4 \times 10^{14}\, n_{eq}/cm^2$ neutrons, a time resolution of $\sigma_t = 356 \pm 13 \, ps$ is measured at room temperature, showing no significant degradation