Y. Gonzalez-Velo

Total-Ionizing-Dose Effects on the Resistance Switching Characteristics of Chalcogenide Programmable Metallization Cells

Programmable metallization cells (PMCs) are emerging ReRAM devices exhibiting resistance switching due to cation transport in a solid-state electrolyte and redox reactions at the electrodes. Their non-volatility and low power requirements have led to increased interest in their development for non-volatile memory applications. Investigation of the total dose response of PMCs will contribute to our understanding of radiation induced effects in these novel memory devices as well as assess their suitability for use in ionizing radiation environments. This work investigates the impact of total ionizing dose on the switching characteristic of silver doped Ge30Se70 PMC memory devices. The results obtained show that the resistance switching characteristic of these cells which use a solid state electrolyte based on Ge30Se70 is not affected by a total dose exposure of up to 10 Mrad( Ge30Se70).

Total Ionizing Dose Retention Capability of Conductive Bridging Random Access Memory

Resistance switching memory devices based on cation transport through an electrolyte and redox reactions at the electrodes have been implemented in a commercial memory technology known as conductive bridging random access memory (CBRAM). In this letter, the number of bit errors and variations in the supply current of CBRAM circuits exposed to ionizing radiation is investigated and compared with common memory technologies. The results indicate that even after exposure to high levels of ionizing radiation, CBRAM devices show no degradation in memory retention, which suggests that the technology has high reliability capability when compared with existing nonvolatile memory solutions.

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.

Effects of Cobalt-60 Gamma-Rays on Ge-Se Chalcogenide Glasses and Ag/Ge-Se Test Structures

Solid state electrolytes fabricated with chalcogenide glass (ChG) are considered viable candidates for the next generation of non-volatile memory technologies. These glasses, which are composed of group IV and/or group V elements with those of group VI chalcogens (S, Se, and Te), are excellent metal ion conductors. Because of this property, the resistance across structures composed of ChG films sandwiched between active metal (e.g., Ag) and inert metal (e.g., Ni) electrodes can be switched upon the application of sufficient bias, thereby enabling memristive action. In this paper, the effects of 60Co gamma-ray irradiations on Ag/Ge30Se70 test structures are investigated. The results show that exposure to high-energy photons can trigger the transport of Ag+ & ions from an active Ag top layer into an underlying Ge30Se70 ChG film. Post-irradiation annealing experiments also indicate that this “photo-doping” process is reversible once the radiation stress is removed. Numerical simulations which model the mechanisms of radiation-induced photo-doping and recovery are shown to agree well with the data. The results and analysis presented in this paper suggest the ChG-based memristors may be more susceptible to transient radiation effects than cumulative radiation damage.

Total Ionizing Dose Tolerance of

Programmable Metallization Cells (PMC) are two-terminal elements that exhibit resistance switching based on the combination of bias dependent ion conduction through a solid-state electrolyte and reduction/oxidation (redox) reactions occurring at the electrode terminals. PMC based resistive random access memory (ReRAM) is currently used in emerging nonvolatile memory technologies and has the potential to be the successor of current flash memory. In this study we demonstrate the radiation tolerance of Ag-doped Ge40S60 based PMC elements that were irradiated up to a total ionizing dose (TID) of 10 Mrad(Ge40S60) using 60Co gamma rays. The irradiation tests on the PMC devices, with two different Ag anode thicknesses (35 nm and 100 nm), show no significant degradation in the resistance switching characteristics.

{\rm Ag} - {\rm Ge}_{40}{\rm S}_{60}

Chalcogenide glass-based programmable metallization cell (PMC) devices undergo Ag+-ion transport and controlled resistance change under the application of electrical bias. In this paper, photo-doped PMC devices are characterized with impedance spectroscopy. Photo doping is an important step in PMC fabrication as it introduces the mobile Ag into the electrolyte and, therefore, has a significant effect on device characteristics. Data obtained from measurements on devices with different areas in both their high resistance state (HRS) and low resistance state (LRS) are used to parameterize equivalent circuit models. The models elucidate the differences in the HRS and LRS electrical properties.

based Programmable Metallization 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.

Impedance measurement and characterization of Ag-Ge30Se70-based programmable metallization cells

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.

Radiation Hardening by Process of CBRAM Resistance Switching Cells

The Cu-SiO2 based programmable metallization cell (PMC) is a promising alternative to the Ag-chalcogenide glass PMC because of its low power consumption and CMOS-compatibility. Understanding its total ionizing dose (TID) response helps in assessing the reliability of this technology in ionizing radiation environments and benefits its expansion in the space electronics market. In this paper, the impacts of TID on the switching characteristics of Cu-SiO2 PMC are investigated for the first time. The devices were step irradiated with 60Co gamma-rays to a maximum dose of 7.1 Mrad ( SiO2). The results show that gamma-ray irradiation has a negligible impact on the virgin-state and on-state resistance of Cu-SiO2 PMCs. The off-state resistance slightly decreases after the first 1.5 Mrad( SiO2) of exposure, but this reduction saturates after higher levels of TID. Other switching characteristics such as the set voltage, multilevel switching capability and endurance were also studied, all of which did not show observable changes after gamma-ray radiation. The immunity to ionizing radiation is attributed to the suppression of the photo-doping process.

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

The switched dose rate technique has been proposed as an accelerated test technique for enhanced low-dose-rate sensitivity. The physical mechanisms at play when this technique is applied are investigated in this paper. The variation of Not and Nit is characterized using gated lateral pnp transistors to understand the kinetics of device degradation related to differences in mechanisms between high dose rate and low dose rate irradiations.