Degradation of the transconductance of gate-modulated generation current in nMOSFET

The degradation of transconductance (G) of gate-modulated generation current I_GD in LDD nMOSFET is investigated. The G curve shifts rightward under the single electron-injection-stress (EIS). The trapped electrons located in the gate oxide over the LDD region (Q_L) makes the effective drain voltage minish. Accordingly, the G peak in depletion (G_MD) and that in weak inversion (G_MW) decrease. It is found that Δ G_MD and Δ G_MW each have a linear relationship with the n-th power of stress time (tⁿ) in dual-log coordinate: Δ G_MD ∝ tⁿ, Δ G_MD ∝ tⁿ (n=0.25). During the alternate stress, the injected holes neutralize Q_L induced by the previous EIS. This neutralization makes the effective V_D restore to the initial value and then the I_GD peak recovers completely. Yet the threshold voltage recovery is incomplete due to the trapped electron located over the channel (Q_C). As a result, G_MW only recovers to the circa 50% of the initial value after the hole-injection-stress (HIS). Instead, G_MD is almost recovered. The relevant mechanisms are given in detail.