Michael Thomas Marshall

A Comparison of the Radiation Response of

The effects of radiation on memristors created using tantalum oxide and titanium oxide are compared. Both technologies show changes in resistance when exposed to 800 keV Ta ion irradiation at fluences above 1010 cm-2. TaOx memristors show a gradual reduction in resistance at high fluences whereas TiO2 memristors show gradual increases in resistance with inconsistent decreases. After irradiation TaOx devices remain fully functional and can even recover resistance with repeated switching. TiO2 devices are more variable and exhibit significant increases and decreases in resistance when switching after irradiation. Irradiation with 28 MeV Si ions causes both technologies to switch from the off-state to the on-state when ionizing doses on the order of 60 Mrad(Si) or greater (as calculated by SRIM) are reached without applying current or voltage to the part. Irradiation with 10 keV X-rays up to doses of 18 Mrad(Si) in a single step show little effect on either technology. TaOx and TiO2 memristors both show high tolerance for displacement damage and ionization damage and are promising candidates for future radiation-hardened non-volatile memory applications.

{\rm TaO}_{\rm x}

TaOx and TiO2 memristors have been irradiated with 800 keV Ta ions, 28 MeV Si ions, and 10 keV X-rays. TaOx devices were also irradiated with 70 keV electrons. Displacement damage effects are studied using 800 keV Ta ions and both technologies show changes in resistance for fluences greater than 1010 cm-2. TaOx devices show gradual resistance degradation in the off-state with increasing fluence. TiO2 devices show gradual inconsistent increases in off-state resistance with inconsistent abrupt decreases. TaOx devices show more stability and consistent off-state resistances than TiO2 devices. Ionization effects are investigated using 28 MeV Si ions, 70 keV electrons, and 10 keV X-rays. During 28 MeV Si irradiation, both technologies change from the off-state to the on-state when a critical ionizing dose is reached without applying voltage or current to the device. The critical threshold is calculated using SRIM to be on the order of 60 Mrad(Si) or higher. 10 keV X-ray irradiation of doses up to 18 Mrad(Si) per step show little effect on either technology. A single TaOx device irradiated with 70 keV electrons changed from the offstate to the on-state at a calculated dose on the order of 100 krad(Si), suggesting a difference in charge yield compared to the 28 MeV Si irradiation.

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We describe an all-optical lithography process that can make electrical contact to nanometer-precision donor devices fabricated in silicon using scanning tunneling microscopy (STM). This is accomplished by implementing a cleaning procedure in the STM that allows the integration of metal alignment marks and ion-implanted contacts at the wafer level. Low-temperature transport measurements of a patterned device establish the viability of the process.