A. Mahmud

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.

Single Event Susceptibility Analysis in CBRAM Resistive Memory Arrays

Ion-strike-induced single event transients in a type of nonvolatile resistive memory known as conductive bridge resistive memory (CBRAM) are investigated. Experimental data demonstrating bit upsets in 1T-1R devices under heavy ion strike are presented which show evidence of transitions from not only high to low resistance states but also from low to high resistance states. This is reported for such devices here for the first time. Device and circuit level simulations performed under various bias conditions are used to analyze possible upset modes. A crossbar CBRAM architecture without transistor selectors that offers higher density is also analyzed and shown to be susceptible to multiple bit upsets unlike 1T-1R array. Susceptibility of a 256 ×256 crossbar array to strike induced transients under two different bias schemes is simulated.

Flexible Sensors Based on Radiation-Induced Diffusion of Ag in Chalcogenide Glass

In this paper, previous work on chalcogenide-glass (ChG)-based radiation sensors is extended to include the effects of mechanical strain and temperature stress on sensors formed on a flexible polymer substrate. We demonstrate the feasibility of producing inexpensive flexible radiation sensors, which utilize radiation-induced migration of Ag+ ions in germanium selenide ( Ge20Se80) films to produce a decrease in resistance of several orders of magnitude between surface electrodes. This change in resistance can be related to total ionizing dose to give an instantaneous readout of radiation exposure. The ChG films are inherently flexible and this, along with an extremely simple device fabrication process at or near room temperature, allows inexpensive sensor structures to be fabricated on lightweight pliable polymeric substrates such as polyethylene napthalate (PEN). Test samples were irradiated with ionizing radiation (UV light and 60 Cobalt gamma rays). Irradiated samples were subjected to both tensile and compressive stress, and elevated operating temperatures. Stress and exposure to increased ambient temperature had little effect on device resistance. Analysis of the experimental data is supported by the results of COMSOL simulations that model radiation-induced lateral Ag diffusion in ChG.

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.