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 tolerance of a candidate technology for the front-end of the readout application-specific integrated circuit (ASIC) for silicon strip detectors. The devices investigated were first-generation silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). 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 10¹⁶ 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 discuss the behavior of both kinds of transistors, with a particular focus on issues of noise, power, and radiation limitations