Debayan Mahalanabis

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.

Investigation of Single Event Induced Soft Errors in Programmable Metallization Cell Memory

Programmable metallization cell (PMC) devices belong to a class of non-volatile ionic resistive memory devices that have already demonstrated tolerance to high total doses of ionizing radiation. In this work, the susceptibility of integrated 1T-1R PMC memory array to ion strike induced single event upsets is analyzed. Circuit simulations that model single event transients in 1T-1R elements are performed using a PMC compact model which captures the voltage driven resistance change mechanism experimentally observed in such devices. The relationship between incident ion LET and change in PMC resistance and its consequent susceptibility to an upset is investigated through both simulation and experiment.

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

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.

Investigation of Single-Bit and Multiple-Bit Upsets in Oxide RRAM-Based 1T1R and Crossbar Memory Arrays

In this paper, the susceptibility of oxide-based resistive switching random memory (RRAM) to heavy ion strikes is investigated. A physics-based SPICE model calibrated with HfOx RRAM is employed for circuit and array-level simulations. The RRAM state-flipping is attributed to the transient photocurrents at neighboring transistors. Single-bit-upset (SBU) caused by either single-event upset (SEU) or multiple-event upset (MEU) is modeled and simulated in the one-transistor and one-resistor (1T1R) array, which corroborates with experimental observations. In addition, circuit simulation is performed to investigate the impact of transient-induced soft errors in a 1024 ×1024 crossbar array. The sensitive locations in crossbar arrays are the driver circuits at the edge of the array. The simulations show that the crossbar array with HfOx RRAM is of high radiation tolerance thanks to the V/2 bias scheme. However, multiple-bit upset (MBU) may occur if using other oxide materials with lower operation voltage. Voltage spikes generated at the edge of the array may propagate along rows or columns as there is no isolation between cells in the crossbar array.

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.

A Nonvolatile Sense Amplifier Flip-Flop Using Programmable Metallization Cells

In this work, a zero-leakage nonvolatile flip-flop architecture based on a differential CMOS sense-amplifier flip-flop is presented. The flip-flop stores data in complimentarily programmed resistive memory devices during inactive period while power supply is turned off and then restores the data to flip-flop outputs once power supply is turned back on. The resistive memory technology considered here are known as programmable metallization cell (PMC) that switches via metal ion transport within a solid electrolyte. Simulations of the proposed circuit using a PMC compact model fitted to experimental data are performed to estimate the reliability of the read operation and energy consumption for both nominal and sub-threshold power supply regimes. Energy and reliability tradeoffs in the choice of the programmable low resistance state are also discussed. The proposed sense amplifier- based design is more compact than previously reported master-slave latch based nonvolatile designs and presents a modified data restore circuit for more robust read operation at subthreshold voltage supply levels. The wide margin between high and low resistance states of the PMC devices further improves robustness of the flip-flop. Lastly, possible extension of this architecture for low power logic computation application is briefly discussed.

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.

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.