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

The degradation of transconductance(G) of a gate-modulated generation current I GD in a 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(QL) makes the effective drain voltage diminish.Accordingly,the G peak in depletion(GMD) and that in weak inversion(GMW) decrease.It is found that △GMD and △GMW each have a linear relationship with the n-th power of stress time(tn) in a dual-log coordinate:△G MD∝tn,△GMD∝tn(n=0.25).During the alternate stress,the injected holes neutralize QL 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(QC).As a result,G MW only recovers to circa 50% of the initial value after the hole-injection-stress(HIS).Instead,G MD almost recovers.The relevant mechanisms are given in detail.