Thermometry of Filamentary RRAM Devices

Since thermal effects play a major role in filamentary RRAM devices, we compare the two localized thermometry methods developed for such devices. One method is based on short-pulsed measurements and the other on the measurement of minority-carrier injection from the filament into a semiconductor electrode by thermionic emission. We carried out and compared the measurements on the same functional oxide layer. Both methods indicate that the filament temperature is at least ~550 K during device operation. Furthermore, comparison between the measured thermal resistance and the thermal simulations of both techniques shows that under the conditions of low forming current compliance (~10 μA), the filament dimensions are below ~5 nm. We show that the thermionic emission method is useful for high-resistance (>100 kQ) devices operating at low-power conditions (<;10 μW), whereas the pulsed thermometry is more suitable for lower resistance devices (<;500 kQ) operated above 1 μW. The average thermal resistance measured by the pulse technique decreases with applied power. Our simulations indicate that the expansion of the heated zone surrounding the filament can explain the observed reduction in thermal resistance with applied power. The underlying physics of the two methods is discussed.