It is widely accepted that the breakdown of Si02 gate dielectrics is caused by the buildup of stress-induced defects over time. Although several physical mechanisms have been proposed for the generation of these defects, very little direct experimental evidence as to the chemical and physical identity of these defects has been generated in the literature thus far. Here, we present electrically detected magnetic resonance (EDMR) measurements obtained via spin-dependent recombination currents at the interface of high-field stressed Si/Si02 metal-oxide-semiconductor field effect transistors (MOSFETs).
The radiation response of TaOx-based RRAM devices fabricated in academic (Set A) and industrial (Set B) settings was compared. Ionization damage from a 60Co gamma source did not cause any changes in device resistance for either device type, up to 45 Mrad(Si). Displacement damage from a heavy ion beam caused the Set B in the high resistance state to decrease in resistance at 1 x 1021 oxygen displacements per cm3; meanwhile, the Set A devices did not exhibit any decrease in resistance due to displacement damage. Both types of devices demonstrated an increase in resistance around 3 x 1022 oxygen displacements per cm3, possibly due to damage at the oxide/metal interfaces. These extremely high levels of damage represent near-total atomic disruption, and if this level of damage were ever reached, other circuit elements would likely fail before the RRAM devices in this study. Generally, both sets of devices were much more resistant to radiation effects than other devices reported in the literature. Displacement damage effects were only observed in the Set A devices once the displacement-induced oxygen vacancies surpassed the intrinsic vacancy concentration in the devices, suggesting that high oxygen vacancy concentration played a role in the devices’ high tolerance to displacement damage.
Analog crossbars have the potential to reduce the energy and latency required to train a neural network by three orders of magnitude when compared to an optimized digital ASIC. The crossbar simulator, CrossSim, can be used to model device nonidealities and determine what device properties are needed to create an accurate neural network accelerator. Experimentally measured device statistics are used to simulate neural network training accuracy and compare different classes of devices including TaOx ReRAM, Lir-Co-Oz devices, and conventional floating gate SONOS memories. A technique called 'Periodic Carry' can overcomes device nonidealities by using a positional number system while maintaining the benefit of parallel analog matrix operations.
The image classification accuracy of a TaOx ReRAM-based neuromorphic computing accelerator is evaluated after intentionally inducing a displacement damage up to a fluence of 1014 2.5-MeV Si ions/cm2 on the analog devices that are used to store weights. Results are consistent with a radiation-induced oxygen vacancy production mechanism. When the device is in the high-resistance state during heavy ion radiation, the device resistance, linearity, and accuracy after training are only affected by high fluence levels. The findings in this paper are in accordance with the results of previous studies on TaOx-based digital resistive random access memory. When the device is in the low-resistance state during irradiation, no resistance change was detected, but devices with a 4-kΩ inline resistor did show a reduction in accuracy after training at 1014 2.5-MeV Si ions/cm2. This indicates that changes in resistance can only be somewhat correlated with changes to devices' analog properties. This paper demonstrates that TaOx devices are radiation tolerant not only for high radiation environment digital memory applications but also when operated in an analog mode suitable for neuromorphic computation and training on new data sets.
In this study, we demonstrate creation of electroforming-free TaOx memristive devices using focused ion beam irradiations to locally define conductive filaments in TaOx films. Electrical characterization shows that these irradiations directly create fully functional memristors without the need for electroforming. Finally, ion beam forming of conductive filaments combined with state-of-the-art nano-patterning presents a CMOS compatible approach to wafer level fabrication of fully formed and operational memristors.