Simone Gerardin

A New Hardware/Software Platform and a New 1/E Neutron Source for Soft Error Studies: Testing FPGAs at the ISIS Facility

We introduce a new hardware/software platform for testing SRAM-based FPGAs under heavy-ion and neutron beams, capable of tracing the bit-flips in the configuration memory back to the physical resources affected in the FPGA. The validation was performed using, for the first time, the neutron source at the RAL-ISIS facility. The ISIS beam features a 1/E spectrum, which is similar to the terrestrial one with an acceleration between 107 and 108 in the energy range 10-100 MeV. The results gathered on Xilinx SRAM-based FPGAs are discussed in terms of cross section and circuit-level modifications.

Radiation Effects in Flash Memories

We review ionizing radiation effects in Flash memories, the current dominant technology in the commercial non-volatile memory market. A comprehensive discussion of total dose and single event effects results is presented, concerning both floating gate cells and peripheral circuitry. The latest developments, including new findings on the mechanism underlying upsets due to heavy ions and destructive events, are illustrated.

Facility for fast neutron irradiation tests of electronics at the ISIS spallation neutron source

The VESUVIO beam line at the ISIS spallation neutron source was set up for neutron irradiation tests in the neutron energy range above 10MeV. The neutron flux and energy spectrum were shown, in benchmark activation measurements, to provide a neutron spectrum similar to the ambient one at sea level, but with an enhancement in intensity of a factor of 107. Such conditions are suitable for accelerated testing of electronic components, as was demonstrated here by measurements of soft error rates in recent technology field programable gate arrays.

TID Sensitivity of NAND Flash Memory Building Blocks

NAND Flash memories are the leader among high capacity non-volatile memory technologies and are becoming attractive also for radiation harsh environments, such as space. For these applications, a careful assessment of their sensitivity to radiation is needed. In this contribution, we analyze TID effects on the many different building blocks of NAND Flash memories, including the charge pumps, row-decoder, and floating gate array. Since each of these elements have dedicated circuital and technological characteristics, we identify and study the characteristic failure mode for each part.

Error Instability in Floating Gate Flash Memories Exposed to TID

We discuss new experimental results on the post-radiation annealing of Floating Gate errors in Flash memories with both NAND and NOR architecture. We investigate the dependence of annealing on the program level, linking the reduction in the number of Floating Gate errors to the evolution of the threshold voltage of each single cell. To understand the underlying physics we also discuss how temperature affects the number of Floating Gate errors.

Key Contributions to the Cross Section of NAND Flash Memories Irradiated With Heavy Ions

Heavy-ion irradiation of NAND flash memories under operating conditions leads to errors with complex, data-dependent signatures. We present upsets due to hits in the floating gate array and in the peripheral circuitry, discussing their peculiarities in terms of pattern dependence and annealing. We also illustrate single event functional interruptions, which lead to errors during erase and program operations. To account for all the phenomena we observe during and after irradiation, we propose an ldquoeffective cross section,rdquo which takes into account the array and peripheral circuitry contributions to the SEU sensitivity, as well as the operating conditions.

Drain current decrease in MOSFETs after heavy ion irradiation

In this work, we have focused our attention on MOSFETs, which are the real basic elements of all CMOS applications. We have studied the immediate and latent effects produced by heavy ion irradiation on MOSFETs with ultrathin gate oxide, even after electrical stresses subsequent to irradiation. We found that a single ion can generate a physically damaged region (PDR) localized in the Si-SiO/sub 2/ interface, which may hamper the surface channel formation. In order to generate a PDR the ion hit must be close enough to MOSFET borders, i.e., in correspondence with the STI or the LDD spacer. Consequently, if both MOSFET W and L are large enough only few ion hits may give place to a PDR, mitigating the radiation damage. Finally we have developed an original model to describe the impact of the PDR on channel conductance in the ohmic linear region. On the basis of this model, we predict a PDR size around 0.2-1 /spl mu/m.

Catastrophic Failure in Highly Scaled Commercial NAND Flash Memories

Heavy ion single-event measurements on a variety of high density commercial NAND flash memories are reported. Three single event effect (SEE) phenomena were investigated: single effect upsets (SEUs), single effect functional interrupts (SEFIs), and a new high current phenomenon which at high LETs results in catastrophic loss of ability to erase and program the device.

Heavy-Ion Induced Threshold Voltage Tails in Floating Gate Arrays

We studied heavy-ion effects on floating gate memories, focusing on the generation of tails in the threshold voltage distributions after irradiation. Using both experiments and simulations based on the Geant4 toolkit, we provide new insight, distinguishing two types of events, large events and small events, which are responsible for the secondary peak and the intermediate region in the post-rad threshold distribution, respectively. Both are well correlated with the energy deposited in the FG. Implications for error rate predictions are discussed.

Annealing of Heavy-Ion Induced Floating Gate Errors: LET and Feature Size Dependence

We discuss the room temperature annealing of Floating Gate errors in Flash memories with NAND and NOR architecture after heavy-ion irradiation. We present the evolution of raw bit errors as a function of time after the exposure, examining the annealing dependence on the particle LET, cell feature size, and, for Multi Level Cells, on the program level. The results are explained based on the statistical properties of the cell threshold voltage distributions before and after heavy-ion strikes.