We present an investigation of the dependence of low-frequency noise on device geometry in advanced npn silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). The devices examined in this work have fixed emitter width (W-E = 0.4 mu m), but varying emitter length (0.5 mu m <= L-E <= 20.0 mu m), and thus the ratio of the emitter perimeter (P-E) to the emitter area (A(E)) varies widely, making it ideal for examining geometrical effects. The SPICE noise parameter A(F) extracted from these devices decreases with increasing LE. Furthermore, the low-frequency noise measured on SiGe HBTs with significantly different P-E/A(E) ratios suggests a possibility that the fundamental noise source for the diffusion base current may be located at the emitter periphery. Transistors with different distances between the emitter edge and the shallow trench edge (XEC), and shallow trench edge to deep trench edge (XTC), are also investigated. The SiGe HBTs with a smaller value of XEC have higher low-frequency noise, but no significant difference is found in devices with varying,XTC. Explanations of the observed noise behavior are suggested. (c) 2006 Elsevier Ltd. All rights reserved.