BEOL-Compatible High-Performance Indium-Tin-Oxide Transistors Enabled by Quantum Confinement-Engineered Properties

In this work, several key contributions have been made. First, based on the observation of quantum confinement-induced properties transition in indium-tin-oxide (ITO) films with a sub-10-nm thickness, the de-doping phenomenon in ITO has been utilized to satisfy demands from different device modules, e.g., relatively thick ITO for the source/drain (S/D) and thin ITO for the channel. Second, through precise engineering of the ITO film thickness by depositing channel and S/D regions separately, a thickness-dependent hetero design has been applied to further boost the device performance by suppressing the S/D series resistance (
${R}_{\text {SD}}\text {)}$
while maintaining the integrity of the channel. Finally, a comprehensive investigation into the impact of extremely thin ITO channel thickness (
${T}_{\text {CH}}\text {)}$
at sub-4-nm regime on device characteristics has been carried out, which reveals a tradeoff between achieving high field-effect mobility (
$\mu _{\text {eff}}\text {)}$
and maintaining an appropriate threshold voltage (
${V}_{\text {th}}\text {)}$
. By integrating all the aforementioned innovations, the device with 3.5-nm
${T}_{\text {CH}}$
and 50-nm channel length (
${L}_{\text {CH}}\text {)}$
achieves one of the highest peak transconductance (
${G}_{\text {m}, \max }\text {)}$
of
$617~\mu $
S/
$\mu $
m among ITO thin-film transistors (TFTs), along with an extremely low
${R}_{\text {SD}}$
of
$140~\Omega \cdot \mu $
m. In addition, by further scaling
${T}_{\text {CH}}$
down to 2 nm, the device with 50-nm
${L}_{\text {CH}}$
demonstrates a desired enhancement-mode operation, together with a high
${G}_{\text {m, {max}}}$
of
$508~\mu $
S/
$\mu $
m, and a respectable subthreshold swing (SS) of 85 mV/decade.