Positive-Bias Stress Test on Amorphous In–Ga–Zn–O Thin Film Transistor: Annealing-Temperature Dependence
2014
We performed constant positive gate bias stress tests on sputter-deposited
amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs)
fabricated with various annealing conditions. We found that the time evolution
of threshold voltage shift (
$\Delta
V _{\rm th}$
) during the stress test exhibits two different
behaviors; a power function type and a logarithmic function type. Combining
with thermal desorption spectroscopy (TDS), we found that the $\Delta V _{\rm th}$
type changes from
the log-function type to the power-function type as ${{H}} _{2}$
desorption increases.
The power-function type is attributed to a H-diffusion limited process. As
for the log-function type, the magnitude of $\Delta V _{\rm th}$
has correlation with
the hysteresis width in a first transfer curve and the desorption amount of ${{H}} _{2} {{O}}$
and ${{O}}
_{2}$
species between 200 $^{\circ}{{C}}$
–300 $^{\circ}{{C}}$
. Hence, it is considered
that the traps causing the log-function type $\Delta {\rm V} _{\rm th}$
are meta-stable
states related to O- and/or OH-related weak bonds.
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