Publications

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The radiation response of TaO_x-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 exhibited 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. Overall, 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.

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Color centers (defect complexes such as SiV) in diamond have shown potential in fields ranging from metrology, cybersecurity to quantum computation. Demonstrations in these fields have pushed the envelope of state-of-the-art operations – for example, single photon sources (SPS) making use of SiV centers in diamond for quantum key distribution have demonstrated all the requirements for SPS operation including: (1) stable operation with second correlation function <<1, (2) electrically driven single photon emission and (3) compatibility with frequenc y conversion to telecommunication frequencies. To-date, however, all these demonstrations have been on lab-scale one-off devices. The key question behind how to deterministically fabricate these devices, namely activation yield has been overlooked. For context, Si based semiconductor devices are hugely successful because we have a high activation yield for implanted dopants. This is not yet true for diamond color centers. As currently understood, the color center yield is dominated by a lack of vacancies in the immediate area of the implantation. We propose to optimize the activation yield of color center using a combination of (1) focused single ion implantation with in-situ detection to count the number of implanted Si ions and (2) localized point defect (vacancy) creation using a focused Li ion beam to improve the yield. These experiments build on the unique capabilities of the SNL nanoImplanter (nI) to produce focused ion beam with spatial resolution of < 10 nm of both Si and Li ions. This work will also leverage our world-leading single ion implantation and detection capabilities.

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This report documents work done at the Sandia Ion Beam Laboratory to develop a capability to produce 14 Me neutrons at levels sufficient for testing radiation effects on electronic materials and components. The work was primarily enabled by a laboratory directed research and development (LDRD) project. The main elements of the work were to optimize target lifetime, test a new thin- film target design concept to reduce tritium usage, design and construct a new target chamber and beamline optimized for high-flux tests, and conduct tests of effects on electronic devices and components. These tasks were all successfully completed. The improvements in target performance and target chamber design have increased the flux and fluence of 14 MV neutrons available at the test location by several orders of magnitude. The outcome of the project is that a new capability for testing radiation-effects on electronic components from 14 MeV neutrons is now available at Sandia National Laboratories. This capability has already been extensively used for many qualification and component evaluation and development tests.

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With the growing interest to explore Jupiter's moons, technologies with +10 Mrad(Si) tolerance are now needed, to survive the Jovian environment. Conductive-bridging random access memory (CBRAM) is a nonvolatile memory that has shown a high tolerance to total ionizing dose (TID). However, it is not well understood how CBRAM behaves in an energetic ion environment where displacement damage (DD) effects may also be an issue. In this paper, the response of CBRAM to 100-keV Li, 1-MeV Ta, and 200-keV Si ion irradiations is examined. Ion bombardment was performed with increasing fluence steps until the CBRAM devices failed to hold their programed state. The TID and DD dose (DDD) at the fluence of failure were calculated and compared against tested ion species. Results indicate that failures are more highly correlated with TID than DDD. DC cycling tests were performed during 100-keV Li irradiations and evidence was found that the mobile Ag ion supply diminished with increasing fluence. The cycling results, in addition to prior 14-MeV neutron work, suggest that DD may play a role in the eventual failure of a CBRAM device in a combined radiation environment.

The image classification accuracy of a TaO_x 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. Here, the findings in this paper are in accordance with the results of previous studies on TaO_x-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 TaO_x 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.