VLSI-COMPATIBLE PROCESSING AND LOW-VOLTAGE OPERATION OF MULTIEMITTER Si/SiGe HETEROJUNCTION BIPOLAR TRANSISTORS
Previously we demonstrated a new class of VLSI-compatible multiemitter Si/SiGe/Si npn HBTs with enhanced logic functionality. These devices have two (or more) emitter contacts and no base contact. Given a potential difference between any two emitter contacts, one of the emitter-base junctions is forward biased and injects electrons into the base, while the other junction is reverse biased and small controlling current flows by interband tunneling. Because of emitter contact symmetry, the device possesses exclusive or functionality. Our first devices provided current gain of ~400 at room temperature, at an operating voltage of ~2 V. Here we present an improved version that operates at 1 V, as well as a multiemitter HBT fabrication sequence that is not only fully compatible with a VLSI BiCMOS process, but even saves several processing steps comapred to a standard HBT.