Random telegraph signal noise mechanisms in reverse base current of hot carrier-degraded submicron bipolar transistors: Effect of carrier trapping during stress on noise characteristics

Abstract

We investigate physical mechanisms of random telegraph signal (RTS) noise in reverse base current of hot carrier-degraded polysilicon emitter bipolar junction transistors. RTS noise, analyzed in the time domain, is studied as a function of reverse base-emitter bias, temperature, and additional reverse-bias stress. Two-level RTS with a relative amplitude as high as 100% is observed at room temperature. The RTS amplitude varies exponentially with the applied reverse base-emitter voltage and depends weakly on temperature. The additional hot carrier stress is observed to induce changes in RTS amplitude and mean pulse widths (independent or correlated), and a disappearance/reappearance of the RTS fluctuations. The results are interpreted by a model where the RTS noise is caused by fluctuations of generation-recombination (g-r) parameters (i.e., capture cross sections and energy position in the gap) of a stress-induced complex bistable defect (CBD) at the Si/SiO2 interface. The complex defect is assumed to be either a two-state fast interface state or an interacting pair of a fast interface state with a slow neighboring border trap. The RTS amplitude is well explained by fluctuations in a single-defect electric-field-enhanced g-r rate between a finite value and naught. The RTS amplitude-bias characteristics and their temperature dependence are satisfactorily accounted for by an expression for a phonon-assisted tunneling current via a single deep-level state. The model parameters are the g-r parameters of the defect and its spatial position in the base-emitter p–n junction. The stress-induced changes in the RTS noise are attributed to the influence of log-time trapping of hot carriers on border states laying in the vicinity of a CBD center. The charged border traps interact with a CBD, changing both its g-r parameters and the RTS switching behavior. The variations in RTS parameters are related to the microscopic nature of the interaction and are discussed for the two types of the CBDs.