Reliability Characteristics of a 150GHZ fT/fmax Si/SiGeC Heterojunction Bipolar Transistor Under Reverse, Forward and Mixed-Mode Stress

Major reliability characteristics of studied HBT infer dual conclusions. On a first level, similar electrical response to any type of stress is measured as HC are responsible for the creation of mid-gap defects, giving rise to a G-R leakage current component. A common basis for base current degradation model is thus provided. On a second level, acceleration factors, defects location, impact on LF noise and recovery behavior are different. Defect types are thus distinct. Degradation model, in turn, must be adapted to each type of stress

SiGe:C Heterojunction Bipolar Transistors (HBTs) are particularly relevant today for power amplifiers [1] as well as analog/mixed-signal applications for wireless communication systems [2]. Performance improvement was mostly achieved through the vertical scaling of the device, which is accompanied by an increased electric fields and operation current density. Consequently, device robustness and reliability studies are mandatory. In this work, reliability characteristics of a 150 GHz fT/fmax, 1.7V BVCE0 SiGe:C HBT [3] (Fig. 1) are studied under the three main types of degradation modes presently reported for bipolar transistors : reverse mode [7], high current forward mode (ON) [8]-[13] and Mixed-Mode (MM) [14]-[17]. An original comparative study of these three degradation modes is proposed, based on the fact that they all lead to a base current increase as a function of stress time. A typical Gummel plot aging after any type of reliability stress is shown in Fig. 2. Fig. 1. Schematic cross-section of studied NPN HBT Fig. 2. Typical Gummel plot aging after any type of reliability stress (VCB=0V)