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

Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

Local mechanical stress is currently an important topic of concern in microelectronics processing. A technique that has become increasingly popular for local mechanical stress measurements is micro-Raman spectroscopy. In this paper, the theoretical background of Raman spectroscopy, with special attention to its sensitivity for mechanical stress, is discussed, and practical information is given for the application of this technique to stress measurements in silicon integrated circuits. An overview is given of some important applications of the technique, illustrated with examples from the literature: the first studies of the influence of external stress on the Si Raman modes are reviewed; the application of this technique to measure stress in silicon-on-insulator films is discussed; results of measurements of local stress in isolation structures and trenches are reviewed; and the use of micro-Raman spectroscopy to obtain more information on stress in metals, by measuring the stress in the surrounding Si substrate is explained.

https://iopscience.iop.org/article/10.1088/0268-1242/11/2/001/pdf

Micro-Raman spectroscopy to study local mechanical stress in silicon integrated circuits

https://hal.archives-ouvertes.fr/hal-00120432/document

Raman Spectroscopy of Nanomaterials: How Spectra Relate to Disorder, Particle Size and Mechanical Properties

The different steps that have to be taken in order to derive information about local mechanical stress in silicon using micro‐Raman spectroscopy experiments, including theoretical and experimental aspects, are discussed. It is shown that the calculations are in general less complicated when they are done in the axes system of the sample. For that purpose, the secular equation is calculated in the axes system [110], [−110], [001], which is important for microelectronics structures. The theory relating Raman mode shift with stress tensor components is applied using two analytical stress models: uniaxial stress and planar stress. The results of these models are fitted to data from micro‐Raman spectroscopy experiments on Si3N4/poly‐Si lines on silicon substrate. In this fit procedure, the dimensions of the laser spot and its penetration depth in the substrate are also taken into account.

Stress measurements in silicon devices through Raman spectroscopy: Bridging the gap between theory and experiment

Reliability issues currently hamper the commercialization of capacitive RF MEMS switches. The most important failure mode is parasitic charging of the dielectric of such devices. In this paper we present an improved analytical model that enables us to calculate and understand the effect of insulator charging on the behavior of capacitive RF MEMS switches, and to describe the way they fail, and their reliability. Emphasis is placed on a shift of the pull-out voltage to predict failures. Tests with capacitive RF MEMS switches have been performed that validate the most important features of the model.

https://iopscience.iop.org/article/10.1088/0960-1317/14/4/011/pdf

A comprehensive model to predict the charging and reliability of capacitive RF MEMS switches

The application of micro-Raman spectroscopy for the measurement of local stress in silicon microelectronics samples is discussed. Practical issues of concern for local stress measurements using micro-Raman spectroscopy are dealt with. Copyright © 1999 John Wiley & Sons, Ltd.

Stress measurements in Si microelectronics devices using Raman spectroscopy

We present a new material for highly resistive heaters: thin Ti/TiN layers. Their resistivity is indeed comparable to the resistivity of NiCr, i.e. 50-100 micro-Ohn-cm. However, as opposed to the latter material, Ti/TiN is CMOS compatible and thus easier to incorporate in CMOS integrated MEMS processing. To test the reliability of thin Ti/TiN resistive heaters, both 5 nm Ti/30 nm TiN and 5 nm Ti/60 nm TiN heaters were fabricated. A thermal analysis shows a small temperature coefficient of resistivity. To test the reliability of such heaters at temperatures up to 300 degrees C, 1 micron wide Ti/TiN lines were biased using high currents. Both DC and pulsed DC current stressing resulted in very small deviations from the initial resistance for sintered and passivated heaters. The temperature uniformity over the heater line is investigated using Emission Microscopy.

Ingrid De Wolf

Papers

Micro-Raman spectroscopy to study local mechanical stress in silicon integrated circuits

Stress measurements in silicon devices through Raman spectroscopy: Bridging the gap between theory and experiment

A comprehensive model to predict the charging and reliability of capacitive RF MEMS switches

Stress measurements in Si microelectronics devices using Raman spectroscopy

Fabrication and reliability testing of Ti/TiN heaters