Cs. Chiang et al., ELECTRICAL INSTABILITY OF HYDROGENATED AMORPHOUS-SILICON THIN-FILM TRANSISTORS FOR ACTIVE-MATRIX LIQUID-CRYSTAL DISPLAYS, JPN J A P 1, 37(9A), 1998, pp. 4704-4710
We investigated the threshold voltage shifts (Delta V-T) of inverted-s
taggered hydrogenated amorphous silicon (a-Si:H) thin-film transistors
(TFTs) induced by steady-state (dc) and pulsed (ac) gate bias-tempera
ture-stress (BTS) conditions. Our study showed that, for an equivalent
effective-stress-time, Delta V-T has an apparent pulse-width dependen
ce under negative ETS conditions-the narrower the pulse width, the sma
ller the Delta V-T. This gate-bias pulse-width dependence is explained
by an effective-carrier-concentration model, which relates Delta V-T
for negative pulsed gate-bias stress to the concentration of mobile ca
rriers accumulated in the conduction channel along the a-Si:H/gate ins
ulator interface. in addition, our investigation of the methodology of
a-Si:H TFT electrical reliability evaluation indicates that, instead
of steady-state BTS, pulsed BTS should be used to build the database n
eeded to extrapolate Delta V-T induced by a long-term display operatio
n. Using these experimental results. we have shown that a-Si:H TFTs ha
ve a satisfactory electrical reliability for a Icing-term active-matri
x liquid-crystal display (AMLCD) operation.