Synergistic Effect of Negative Bias Instability and Total Ionizing Dose on SiC MOSFETs

In this article, the synergistic effect of negative gate bias and radiation on SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) is investigated. Under negative gate bias (−5, −10, and −15 V), a slight decrease in the threshold voltage (
$V_{\mathrm {th}}$
) of non-irradiated SiC MOSFETs is observed. The variation of trapped-oxide charge (
$N_{\mathrm {ot}}$
) and SiC/SiO2 interface trap charge (
$N_{\mathrm {it}}$
) can be obtained through the subthreshold swing and mid-gap voltage method. Although the
$V_{\mathrm {th}}$
of non-irradiated SiC MOSFETs remains unchanged, significant increases in
$N_{\mathrm {it}}$
and
$N_{\mathrm {ot}}$
are observed due to the opposite effect of
$N_{\mathrm {ot}}$
and
$N_{\mathrm {it}}$
on
$V_{\mathrm {th}}$
. This phenomenon is attributed to holes drifting to the interface and tunneling into the oxide layer under the negative gate bias. It is found through the
$C_{\mathrm {g}}$
–
$V_{\mathrm {gs}}$
characteristic curves that holes tunneling into the oxide layer are mostly from the channel region. For irradiated SiC MOSFETs, a large number of radiation-induced holes exist in the oxide layer above the channel region and JFET region, resulting in a decrease in
$V_{\mathrm {th}}$
, which is mainly caused by an increase in
$N_{\mathrm {ot}}$
.