Abnormal Thermal Instability of Al-InSnZnO Thin-Film Transistor by Hydroxyl-Induced Oxygen Vacancy at SiOx/Active Interface

We scrutinized the barrier capability of SiO
_x
, plasma Al
²
O
³
(P-Al
₂
O
₃
)/SiO
_x
, and SiN
_x
/SiO
_x
passivation layers (PLs) on the environmental stabilities of back-channel etched Al-doped InSnZnO (Al-ITZO) TFTs at 85 °C with a relative humidity of 85 % for 30 days. Turn-on voltage (V
_ON
) of SiN
_x
/SiO
_x
-passivated TFTs was dramatically shifted to the negative direction and became conductive. Compared to those of SiO
_x
and P-Al
₂
O
₃
/SiO
_x
films, more hydroxyl groups existed at the PL/active interface of SiN
_x
/SiO
_x
-passivated Al-ITZO films. Water vapor transmission rates showed that abnormal behavior was not attributed to barrier capability of PL against the water vapor. When all TFTs were kept at 85 °C for 30 days in an air-drying oven, only the V
_ON
of SiN
_x
/SiO
_x
-passivated TFTs shifted negative direction and finally became conductive. Secondary ion mass spectroscopy (SIMS) results revealed that this abnormal behavior originates from the formation of oxygen vacancy due to highly existed hydroxyl group at SiO
_x
/Active interface at an elevated temperature.