Evaluation of the radiation tolerance of SiGe heterojunction bipolar transistors under 24 GeV proton exposure

For the potential use in future high luminosity applications in high energy physics (HEP) (e.g. the Large Hadron Collider (LHC) upgrade), we evaluated the radiation hardness of a candidate technology for the front-end of the readout application-specific integrated circuit (ASIC) for silicon strip detectors. The devices were a variety of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) manufactured by IBM in a modified 5HP process. The current gain as a function of collector current has been measured at several stages: before and after irradiation with 24 GeV protons up to fluences of 10 ¹⁶ p/cm², and after annealing at elevated temperature. The analog section of an amplifier for silicon strip detectors typically has a special front transistor, chosen carefully to minimize noise and usually requiring a larger current than the other transistors, and a large number of additional transistors used in shaping sections and for signal-level discrimination. We will discuss the behavior of both kinds of transistors, with a particular focus on issues of noise, power and radiation limitations