Publications

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In this paper, we provide an overview of the current knowledge of radiation effects in anion-based memristive devices. We will specifically look at the impact of high dose rate ionizing radiation, total ionizing dose (TID), and heavy ions on the electrical characteristics of tantalum oxide (TaOx), titanium dioxide (TiO2), and hafnium oxide (HfOx) memristors. The primary emphasis, however, will be placed on TaOx memristors. While there are several other anion-based memristive devices being fabricated by the semiconductor community for possible use in valence change memories, most of the present radiation work has focused on one of these types of devices. There have also been numerous studies on radiation effects in cation-based chalcogenides such as germanium sulfides and selenides. However, that will not be discussed in this paper.

In this paper, we provide an overview of the current knowledge of radiation effects in anion-based memristive devices. We will specifically look at the impact of high dose rate ionizing radiation, total ionizing dose (TID), and heavy ions on the electrical characteristics of tantalum oxide (TaOx), titanium dioxide (TiO2), and hafnium oxide (HfOx) memristors. The primary emphasis, however, will be placed on TaOx memristors. While there are several other anion-based memristive devices being fabricated by the semiconductor community for possible use in valence change memories, most of the present radiation work has focused on one of these types of devices. There have also been numerous studies on radiation effects in cation-based chalcogenides such as germanium sulfides and selenides. However, that will not be discussed in this paper.

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The locations of conductive regions in TaOx memristors are spatially mapped using a microbeam and Nanoimplanter by rastering an ion beam across each device while monitoring its resistance. Microbeam irradiation with 800 keV Si ions revealed multiple sensitive regions along the edges of the bottom electrode. The rest of the active device area was found to be insensitive to the ion beam. Nanoimplanter irradiation with 200 keV Si ions demonstrated the ability to more accurately map the size of a sensitive area with a beam spot size of 40 nm by 40 nm. Isolated single spot sensitive regions and a larger sensitive region that extends approximately 300 nm were observed.

This paper investigates the effects of high dose rate ionizing radiation and total ionizing dose (TID) on tantalum oxide (TaO_x) memristors. Transient data were obtained during the pulsed exposures for dose rates ranging from approximately 5.0 ×10⁷ rad(Si)/s to 4.7 ×10⁸ rad(Si)/s and for pulse widths ranging from 50 ns to 50 μs. The cumulative dose in these tests did not appear to impact the observed dose rate response. Static dose rate upset tests were also performed at a dose rate of ~3.0 ×10⁸ rad(Si)/s. This is the first dose rate study on any type of memristive memory technology. In addition to assessing the tolerance of TaO_x memristors to high dose rate ionizing radiation, we also evaluated their susceptibility to TID. The data indicate that it is possible for the devices to switch from a high resistance off-state to a low resistance on-state in both dose rate and TID environments. The observed radiation-induced switching is dependent on the irradiation conditions and bias configuration. Furthermore, the dose rate or ionizing dose level at which a device switches resistance states varies from device to device; the enhanced susceptibility observed in some devices is still under investigation. As a result, numerical simulations are used to qualitatively capture the observed transient radiation response and provide insight into the physics of the induced current/voltages.

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This paper evaluates the effects of ionizing radiation on tantalum oxide (TaOx) memristors. The data obtained from 60Co gamma ray and 10 keV X-ray ionizing radiation experiments indicate that it is possible for the devices to switch from a high resistance off-state to a low resistance on-state after a total ionizing dose (TID) step stress threshold has been surpassed. During irradiation, the devices were floating, grounded, or biased with a 1 Hz square wave with an amplitude of ±100 mV. While floating the terminals is not a typical bias condition within a circuit, it is speculated that this condition might be worst-case because of the lack of a discharge path. If a read measurement is performed prior to reaching the charge threshold, the devices 'reset' back to a pre-irradiation state. This suggests that the devices do not have a cumulative TID effect. However, it was observed that having a continuous bias on the device during the TID exposure did not always have the same effect. The TID threshold level at which the devices switch resistance states varies from device to device; the enhanced susceptibility observed in some devices is still under investigation. After a radiation-induced resistance change, all of the devices could be reset and still functioned properly. When the devices were set into a low resistance on-state prior to irradiation, there was not a significant variation in the resistance post-irradiation (i.e., the devices were still in the on-state). Overall, the memristor TID performance is promising and could potentially enable the discovery of a radiation-hardened nonvolatile memory technology to be used in space and aerospace applications. © 2014 IEEE.

In this report, measurements of the prompt radiation-induced conductivity (RIC) in 3 mil samples of Pyralux® are presented as a function of dose rate, pulse width, and applied bias. The experiments were conducted with the Medusa linear accelerator (LINAC) located at the Little Mountain Test Facility (LMTF) near Ogden, UT. The nominal electron energy for the LINAC is 20 MeV. Prompt conduction current data were obtained for dose rates ranging from ~2 x 10⁹ rad(Si)/s to ~1.1 x 10¹¹ rad(Si)/s and for nominal pulse widths of 50 ns and 500 ns. At a given dose rate, the applied bias across the samples was stepped between -1500 V and 1500 V. Calculated values of the prompt RIC varied between 1.39x10^-8 Ω^-1 · m^-1 and 2.67x10^-7 Ω^-1 · m^-1 and the prompt RIC coefficient varied between 1.25x10^-18 Ω^-1 · m^-1/(rad/s) and 1.93x10^-17 Ω^-1 · m^-1/(rad/s).

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