Farokh Irom

Single Event Effect Characterization of High Density Commercial NAND and NOR Nonvolatile Flash Memories

Heavy ion single-event measurements on a variety of high density commercial NAND and NOR flash memories were reported. Three SEE phenomena were investigated: SEUs, SEFIs, and catastrophic loss of ability to erase and write to the device. Although for all devices under test SEUs and SEFIs were observed, these commercial high densities devices appear to be much less susceptible than typical flash devices that have been tested lately. A new high current phenomenon in the high density NAND flash memories and charge pump failure in the NOR flash memory are discussed.

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.

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.

Frequency dependence of single-event upset in advanced commercial PowerPC microprocessors

Single-event upset (SEU) from heavy ions is measured for advanced commercial microprocessors in a dynamic mode with clock frequencies up to 1 GHz. Frequency and core voltage dependence of SEUs in registers and D-Cache are discussed. The results of our studies suggest the SEU in registers and D-Cache tend to increase with frequency. This might have important implications for the overall SEU trend as technology moves toward higher frequencies.

Evaluation of Mechanisms in TID Degradation and SEE Susceptibility of Single- and Multi-Level High Density NAND Flash Memories

Heavy ion single-event measurements and total ionizing dose (TID) response for 8 Gb commercial NAND flash memories are reported. Radiation results of multi-level flash technology are compared with results from single-level flash technology. The single-level devices are less sensitive to single event upsets (SEUs) than multi-level devices. In general, these commercial high density memories exhibit less TID degradation compared to older generations of flash memories.

Single-event upset in evolving commercial silicon-on-insulator microprocessor technologies

Single-event upset effects from heavy ions are measured for Motorola and IBM silicon-on-insulator (SOI) microprocessors with different feature sizes and core voltages. Multiple-bit upsets in registers and D-cache were measured and compared with single-bit upsets. Also, the scaling of the cross section with reduction of feature size for SOI microprocessors is discussed.

Single-Event Transients in Voltage Regulators

Single-event transients are investigated for two voltage regulator circuits that are widely used in space. A circuit-level model is developed that can be used to determine how transients are affected by different circuit application conditions. Internal protection circuits-which are affected by load as well as internal thermal effects-can also be triggered from heavy ions, causing dropouts or shutdown ranging from milliseconds to seconds. Although conventional output transients can be reduced by adding load capacitance, that approach is ineffective for dropouts from protection circuitry

Single-event transients in high-speed comparators

Single-event transients are investigated in comparators with switching speed below 80 ns, including one BiCMOS device. Modeling results show that the collapse of internal junctions after an ion strike delays the onset of collector current because of transient currents in the substrate that are not shielded by the buried layer. Transients in high-speed comparators are strongly affected by differential input voltage, but are suppressed in the bipolar comparators when the differential input voltage exceeds 200 mV. The BiCMOS device behaves differently because of the CMOS circuitry in latter stages.

Effects of Scaling in SEE and TID Response of High Density NAND Flash Memories

Heavy ion single-event effect (SEE) measurements and total ionizing dose (TID) response for Micron Technology single-level cell 1, 2, 4, 8 Gb commercial NAND flash memory and multi-level cell 8, 16, 32 Gb are reported. The heavy ion measurements were extended down to LET 0.1 MeV-cm2/mg. Scaling effects in SEE and TID response are discussed. Floating gate bit error upset cross section does not scale with feature size at high LETs, except for single-level cell 8 Gb device which is built with 51 nm processes. The threshold LET does not change with scaling. Charge pump TID degradation and standby current improves with scaling. In general, the effect of radiation is either unchanged or is less severe for highly scaled NAND flash memories.

Investigation of Current Spike Phenomena during Heavy Ion Irradiation of NAND Flash Memories

A series of heavy ion and laser irradiations was performed to investigate previously reported current spikes in flash memories. High current events were observed, however, none matches the previously reported spikes. Plausible mechanisms are discussed.