There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This paper reviews the basic physical mechanisms of the interactions of ionizing radiation with MOS oxides, including charge generation, transport, trapping and detrapping, and interface trap formation. Device and circuit effects are also discussed briefly.

/pdf/total-ionizing-dose-effects-in-mos-oxides-and-devices-4ndco1w6sd.pdf

Total ionizing dose effects in MOS oxides and devices

Electronic devices in space environments can contain numerous types of oxides and insulators. Ionizing radiation can induce significant charge buildup in these oxides and insulators leading to device degradation and failure. Electrons and protons in space can lead to radiation-induced total-dose effects. The two primary types of radiation-induced charge are oxide-trapped charge and interface-trap charge. These charges can cause large radiation-induced threshold voltage shifts and increases in leakage currents. Two alternate dielectrics that have been investigated for replacing silicon dioxide are hafnium oxides and reoxidized nitrided oxides (RNO). For advanced technologies, which may employ alternate dielectrics, radiation-induced voltage shifts in these insulators may be negligible. Radiation-induced charge buildup in parasitic field oxides and in SOI buried oxides can also lead to device degradation and failure. Indeed, for advanced commercial technologies, the total-dose hardness of ICs is normally dominated by radiation-induced charge buildup in either parasitic field oxides and/or SOI buried oxides. Heavy ions in space can also degrade the oxides in electronic devices through several different mechanisms including single-event gate rupture, reduction in device lifetime, and large voltage shifts in power MOSFETs.

Radiation Effects in MOS Oxides

Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. Reliability of stability data for perovskite solar cells is undermined by a lack of consistency in the test conditions and reporting. This Consensus Statement outlines practices for testing and reporting stability tailoring ISOS protocols for perovskite devices.

/pdf/consensus-statement-for-stability-assessment-and-reporting-37ng2o1dmx.pdf

Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures

This review paper discusses several key issues associated with deep submicron CMOS devices as well as advanced semiconductor materials in ionizing radiation environments. There are, as outlined in the ITRS roadmap, numerous challenges ahead for commercial industry in its effort to track Moore's Law down to the 45 nm node and beyond. While many of the classical threats posed by ionizing radiation exposure have diminished by aggressive semiconductor scaling, the question remains whether there may be unknown, potentially worse threats lurking in the deep submicron regime. This manuscript provides a basic overview of some of the materials, devices, and designs that are being explored or, in some cases, used today. An overview of radiation threats and how radiation effects can be characterized is also presented. Last, the paper provides a detailed discussion of what we know now about how modern devices and materials respond to radiation and how we may assess, through the use of advanced analysis and modeling techniques, the relative hardness of future technologies

Total-Ionizing-Dose Effects in Modern CMOS Technologies

Low-field leakage current has been measured in thin oxides after exposure to ionising radiation. This Radiation Induced Leakage Current (RILC) can be described as an inelastic tunnelling process mediated by neutral traps in the oxide, with an energy loss of about 1 eV. The neutral trap distribution is influenced by the oxide field applied during irradiation, thus indicating that the precursors of the neutral defects are charged, likely to be defects associated with trapped holes. The maximum leakage current is found under zero-field condition during irradiation, and it rapidly decreases as the field is enhanced, due to a displacement of the defect distribution across the oxide towards the cathodic interface. The RILC kinetics are linear with the cumulative dose, in contrast with the power law found on electrically stressed devices.

Radiation induced leakage current and stress induced leakage current in ultra-thin gate oxides

Slow trapping phenomenon in AlGaN/GaN HEMTs has been extensively analyzed and described in this paper. Thanks to a detailed investigation, based on a combined pulsed and transient investigation of the current/voltage characteristics (carried out over on an 8-decade time scale), we report a detailed description of the properties of trap levels located in the gate–drain surface, and in the region under the gate of AlGaN/GaN HEMTs. More specifically, the following, relevant results have been identified: (i) the presence of surface trap states may determine a significant current collapse, and reduction of the peak transconductance. During a current transient measurement, the emission of electrons trapped at surface states proceeds through hopping, as demonstrated by means of temperature-dependent measurements. The activation energy of the de-trapping process is equal to 99 meV. (ii) The presence of a high density of defects under the gate may induce a significant shift in the threshold voltage, when devices are submitted to pulsed transconductance measurements. The traps responsible for this process have an activation energy of 0.63 eV, and are detected only on samples with high gate leakage, since gate current allows for a more effective charging/de-charging of the defects.

https://iopscience.iop.org/article/10.1088/0268-1242/28/7/074021/pdf

Trapping phenomena in AlGaN/GaN HEMTs: a study based on pulsed and transient measurements

We have investigated how ultra-thin gate oxides subjected to heavy ion irradiation react to a subsequent electrical stress performed at low voltages. Even in devices exhibiting small (or even no) increase of the gate current after irradiation, the time-to-breakdown is substantially reduced in comparison with unirradiated samples due to the onset of a soft or hard breakdown, in contrast with previous results found on thicker oxides. In fact, we have demonstrated that the radiation damage acts as a seed for further oxide degradation by electrical stress during the device operating life. The accelerated oxide wear-out depends on the linear energy transfer (LET) coefficient of radiation source.

Accelerated wear-out of ultra-thin gate oxides after irradiation

Neural interfaces are a fundamental tool to interact with neurons and to study neural networks by transducing cellular signals into electronics signals and vice versa. State-of-the-art technologies allow both in vivo and in vitro recording of neural activity. However, they are mainly made of stiff inorganic materials that can limit the long-term stability of the implant due to infection and/or glial scars formation. In the last decade, organic electronics is digging its way in the field of bioelectronics and researchers started to develop neural interfaces based on organic semiconductors, creating more flexible and conformable neural interfaces that can be intrinsically biocompatible. In this manuscript, we are going to review the latest achievements in flexible and organic neural interfaces for the recording of neuronal activity.

https://www.mdpi.com/2076-3417/7/12/1292/pdf

Andrea Cester

Papers

Radiation induced leakage current and stress induced leakage current in ultra-thin gate oxides

Trapping phenomena in AlGaN/GaN HEMTs: a study based on pulsed and transient measurements

Accelerated wear-out of ultra-thin gate oxides after irradiation

Flexible and Organic Neural Interfaces: A Review

Thermal stress effects on Dye-Sensitized Solar Cells (DSSCs)