Single-Event Effects Induced by Heavy Ions in SONOS Charge Trapping Memory Arrays

We investigate the sensitivity of silicon–oxide–nitride–silicon–oxide (SONOS) charge trapping memory technology to heavy-ion induced single-event effects. Threshold voltage (
$V_{T}$
) statistics were collected across multiple test chips that contained in total 18 Mb of 40-nm SONOS memory arrays. The arrays were irradiated with Kr and Ar ion beams, and the changes in their
$V_{T}$
distributions were analyzed as a function of linear energy transfer (LET), beam fluence, and operating temperature. We observe that heavy ion irradiation induces a tail of disturbed devices in the “program” state distribution, which has also been seen in the response of floating-gate (FG) flash cells. However, the
$V_{T}$
distribution of SONOS cells lacks a distinct secondary peak, which is generally attributed to direct ion strikes to the gate-stack of FG cells. This property, combined with the observed change in the
$V_{T}$
distribution with LET, suggests that SONOS cells are not particularly sensitive to direct ion strikes but cells in the proximity of an ion’s absorption can still experience a
$V_{T}$
shift. These results shed new light on the physical mechanisms underlying the
$V_{T}$
shift induced by a single heavy ion in scaled charge trap memory.