J. Taggart

Ionizing Radiation Effects on Nonvolatile Memory Properties of Programmable Metallization Cells

The impact of ionizing radiation on the retention and endurance of programmable metallization cells (PMC) ReRAM cells is investigated and presented for the first time, with additional work on resistance switching. This study shows that 60Co gamma-ray exposure has a minimal effect on the retention of PMC devices, up to a total ionizing dose (TID) of 2.8 Mrad (Ge30Se70), the maximum TID level tested. The retention of both high resistance states (HRS) and low resistance states (LRS) during exposure was tested. Endurance appears to be slightly reduced with gamma-ray exposure. The endurance was tested to maximum TID of 4.62 Mrad (Ge30Se70). DC response characterizations were also performed on PMC devices after cumulative dose exposures with 50 MeV protons and 100 keV electrons. The data show that PMCs are most sensitive to proton irradiation incident from the backside of the device. For the electron exposures, it is shown that the LRS is mostly unaffected, but the HRS drifts to lower resistance values with an increase in radiation exposure.

Radiation Hardening by Process of CBRAM Resistance Switching Cells

Non-volatile memory (NVM) technology highly resistant to ionizing dose and radiation effects in general continues to be a challenge for space missions. Novel NVM nano-ionic technologies known as conductive bridging random access memory (CBRAM), a resistive circuit technology, exhibits great promise for both high density memory and high total ionizing dose resilience. In this work, it is discovered that CBRAM can be sensitive to high TID levels. However, this novel technology can be radiation-hardened by process, which is demonstrated in this paper.

Total-Ionizing-Dose Effects on Resistance Stability of Programmable Metallization Cell Based Memory and Selectors

In this paper, the operation and effects of radiation on Programmable Metallization Cells (PMC) memory and selector devices are analyzed and discussed. The Ag- or Cu-Ge30Se70 devices demonstrate non-volatile memory switching characteristics while the Ag- or Cu-SiO2 devices show a volatile threshold switching property. The impact of total ionizing dose from gamma-ray irradiation on both device types is investigated experimentally. It is found that the virgin and high-resistance state of Ge30Se70 memory devices degrade after gamma-ray exposure while they are well preserved in SiO2 selector devices.

Optimization of Flexible Ag-Chalcogenide Glass Sensors for Radiation Detection

We demonstrate how the radiation response and performance of Ag-chalcogenide glass radiation sensors fabricated on a flexible substrate can be optimized by modifications of spacing between electrodes.

Ag-chalcogenide glass flexible radiation sensor: Impact of atomic ratio of Se on the TID influenced lateral diffusion of Ag

We report the results of our study on the impact of variable atomic ratio of GexSe1-x on the total ionization dose (TID) influenced lateral diffusion of Ag into chalcogenide glasses (ChG) in flexible radiation detection sensors.

Effects of 14 MeV neutron irradiation on the DC characteristics of CBRAM cells

CBRAM cells were irradiated with 14 MeV neutrons to a total fluence of 3.19×10¹³ n/cm². This is the first time that the effect of displacement damage on the DC characteristics of CBRAM has been examined. The high resistance and low resistance states of the cells are shown to converge with increasing neutron fluence. After reaching a fluence of 2.93×10¹³ n/cm², the CBRAM cells became irrecoverably locked into their final resistance state.

Flexible Ag-ChG Radiation Sensors: Limit of Detection and Dynamic Range Optimization Through Physical Design Tuning

Silver-chalcogenide glass flexible sensors were tested to study the impact of physical design parameters on the performance characteristics of the sensors in response to ionizing radiation. Results show that by changing lateral spacing between adjacent electrodes, the limit of detection and dynamic range can be regulated. Likewise, by changing the diameter of the electrodes, the sensor high and low resistance states can be adjusted to a desired range. In contrast, the influence of the electrode diameter on the sensor performance characteristics was found to have less of an impact on sensor performance. Mechanisms for ion transport and reactions are investigated using TCAD simulations in which the standard statistics and transport equations for free carriers are simultaneously solved. The simulation results are qualitatively in a good agreement with experimental data.

Ag conductive bridge RAMs for physical unclonable functions

We are presenting a method to design reliable physical unclonable functions (PUFs), with silver based conductive-bridge random access memory (CB-RAM) arrays, to protect the internet of things (loT). The arrays that we fabricated in our pilot line, and characterized, operate at extremely low power which is highly desirable for security applications, and to protect cryptographic primitives. The experimental data presented in this work supports the selection of the programming voltage, the Vset, as the parameter, to generate PUF challenge-response pairs (CRP). The median Vset voltage at 0.12V is orders of magnitude lower than other non-volatile memory technologies, which can reduce the threat of side channel analysis. The level of stability, cell to cell, of the Vset that we characterized is acceptable when combined with methods based on ternary states, and resulted in low CRP error rates. Built-in-self-test capability (BIST) is used to differentiate unstable cells of the array, that carry the state “X”, from the solid cells carrying the states “0” and “1”, which are capable of generating reliable PUF CRPs. The use of machine learning algorithms can also compensate for the temperature drifts, noise, aging, and measurement instabilities normal variations. This research work is currently used to finalize and design a prototype with a custom state machine, and FPGA. We will fabricate various CB-RAM samples to optimize the quality of the PUFs.