Georgios Tsiligiannis

Testing a Commercial MRAM Under Neutron and Alpha Radiation in Dynamic Mode

Academic and industrial research interest in terrestrial radiation effects of electronic devices has expanded over the last years from avionics and military applications to commercial applications as well. At the same time, the need for faster and more reliable memories has given growth to new memory technologies such as Magnetic (magneto-resistive) Random Access Memories (MRAM), a promising new non-volatile memory technology that will probably replace in the future the current SRAM and FLASH based memories. In this paper, we evaluate the soft error resilience of a commercial toggle MRAM in static and dynamic test mode, under neutron radiation with energies of 25, 50 and 80 MeV as well as under a Californium (Cf-252) alpha source.

Multiple Cell Upset Classification in Commercial SRAMs

While single bit upsets on memories and storage elements are mitigated with either the use of redundancy and/or error correction codes, Multiple-Cell-Upsets (MCU) may become a significant threat to the integrity of systems when the corrupted cells belong to the same word. In this paper, we identify four types of MCUs as they were recorded during several irradiations under an atmospheric-like neutron beam (ISIS facility). An analysis is done on the underlying reasons of occurrence of each MCU type, as well as their shapes and sizes in order to classify them. The results of this work concern a commercial 90 nm SRAM that was tested under an atmospheric neutron beam in static and dynamic mode. It is shown that, when the memory is in dynamic mode, not only the typical MCUs that involve a few flipped cells may appear but also large clusters of upsets are possible to occur with hundreds or even thousands of cells being affected.

Dynamic Test Methods for COTS SRAMs

In previous works, we have demonstrated the importance of dynamic mode testing of SRAM components under ionizing radiation. Several types of failures are difficult to expose when the device is tested under static (retention) mode. With the purpose of exploring and defining the most complete testing procedures and reveal the potential hazardous behaviors of SRAM devices, we present novel methods for the dynamic mode radiation testing of SRAMs. The proposed methods are based on different word address accessing schemes and data background: Fast Row, Fast Column, Pseudorandom, Adjacent (Gray) and Inverse Adjacent (Gray). These methods are evaluated by heavy ion and atmospheric-like neutron irradiation of two COTS SRAMs of 90 nm and 65 nm technology.

Evaluation of test algorithms stress effect on SRAMs under neutron radiation

Electronic system reliability over soft errors is very critical as the transistor size shrinks. Many recent works have defined the device error rate under radiation for SRAMs in hold mode (static) and during operation (dynamic). This paper evaluates the impact of running test algorithms on SRAMs exposed to neutron radiation in order to define their stressing factor. The results that we show are based on experiments performed at the TSL facility in Uppsala, Sweden using a Quasi-Monoenergetic neutron beam. The evaluation of the test algorithms is based on the calculated device SEU cross section.

Evaluating a radiation monitor for mixed-field environments based on SRAM technology

Instruments operating in particle accelerators and colliders are exposed to radiations that are composed of particles of different types and energies. Several of these instruments often embed devices that are not hardened against radiation effects. Thus, there is a strong need for monitoring the levels of radiation inside the mixed-field radiation areas, throughout different positions. Different metrics exist for measuring the radiation damage induced to electronic devices, such as the Total Ionizing Dose (TID), the Displacement Damage (DD) and of course the fluence of particles for estimating the error rates of the electronic devices among other applications. In this paper, we propose an SRAM based monitor, that is used to define the fluence of High Energy Hadrons (HEH) by detecting Single Event Upsets in the memory array. We evaluated the device by testing it inside the H4IRRAD area of CERN, a test area that reproduces the radiation conditions inside the Large Hadron Collider (LHC) tunnel and its shielded areas. By using stability estimation methods and presenting experimental data, we prove that this device is proper to be used for such a purpose.

SRAM soft error rate evaluation under atmospheric neutron radiation and PVT variations

In current technologies, the robustness of Static Random Access Memories (SRAM) has to be investigated under any possible source of disturbance. In this paper, we evaluate the reliability of an SRAM cell exposed to atmospheric neutron radiation, affected by random threshold voltage variation and under different operation conditions (supply voltage, process corner and temperature). The SRAM cells Soft Error Rate (SER) at simulation level is estimated using accurate models of atmospheric neutron induced currents. The study shows that in extreme operation conditions and under random process variability, the SER of an SRAM can reach values up to 3X larger than the nominal value, or down to 2X smaller than the nominal value. This large SER range confirms the importance of our study and justifies the need for further evaluation of circuits under radiation at the simulation level.

Heavy-Ion Radiation Impact on a 4 Mb FRAM Under Different Test Modes and Conditions

The impact of heavy-ions on commercial Ferroelectric Memories (FRAMs) is analyzed. The influence of dynamic and static test modes as well as several stimuli on the error rate of this memory is investigated. Static test results show that the memory is prone to temporary effects occurring in the peripheral circuitry, with a possible effect due to fluence. Dynamic tests results show a high sensitivity of this memory to switching activity of this peripheral circuitry.

Methodologies for the Statistical Analysis of Memory Response to Radiation

Methodologies are proposed for in-depth statistical analysis of Single Event Upset data. The motivation for using these methodologies is to obtain precise information on the intrinsic defects and weaknesses of the tested devices, and to gain insight on their failure mechanisms, at no additional cost. The case study is a 65 nm SRAM irradiated with neutrons, protons and heavy ions. This publication is an extended version of a previous study [1].

Investigation on MCU Clustering Methodologies for Cross-Section Estimation of RAMs

During irradiation testing of RAMs, various failure scenarios may occur which may generate different characteristic Multiple Cell Upset (MCU) error patterns. This work proposes a method based on spatial and temporal criteria to identify them.

An SRAM Based Monitor for Mixed-Field Radiation Environments

CERN hosts a large number of electronic devices and equipment, functioning over its different particle accelerators. In certain areas, they operate in harsh radiation environments. In order to assure their proper functionality, the equipment or some of their sensitive components undergo several tests in experimental test areas representative of the LHC radiation fields, while specialized monitors constantly record the respective radiation levels. The purpose of this study is to evaluate the use of monitors using recent technology nodes (90 nm) in order to have a better estimation of the expected error rate of the devices. The H4IRRAD experimental test area has been specifically designed to reproduce the radiation field that is present within the LHC tunnel and shielded areas. It has been used to test our custom SRAM based monitors. The monitors have been exposed to a maximum dose and high energy hadron fluence of about 76 Gy and 1.3 × 1011 cm-2 respectively. The results show that the total ionizing dose (TID) effect does not impact the bit cross section of our devices. Moreover the Single Event occurrence is coherent to the beam intensity fluctuations, proving that these devices are appropriate for SEU monitoring under mixed particle fields.