Soft, comfortable polymer dry electrodes for high quality ECG and EEG recording

Conventional gel electrodes are widely used for biopotential measurements, despite important drawbacks such as skin irritation, long set-up time and uncomfortable removal. Recently introduced dry electrodes with rigid metal pins overcome most of these problems; however, their rigidity causes discomfort and pain. This paper presents dry electrodes offering high user comfort, since they are fabricated from EPDM rubber containing various additives for optimum conductivity, flexibility and ease of fabrication. The electrode impedance is measured on phantoms and human skin. After optimization of the polymer composition, the skin-electrode impedance is only similar to 10 times larger than that of gel electrodes. Therefore, these electrodes are directly capable of recording strong biopotential signals such as ECG while for low-amplitude signals such as EEG, the electrodes need to be coupled with an active circuit. EEG recordings using active polymer electrodes connected to a clinical EEG system show very promising results: alpha waves can be clearly observed when subjects close their eyes, and correlation and coherence analyses reveal high similarity between dry and gel electrode signals. Moreover, all subjects reported that our polymer electrodes did not cause discomfort. Hence, the polymer-based dry electrodes are promising alternatives to either rigid dry electrodes or conventional gel electrodes

UV cure of oxycarbosilane low-k films

status: publishe

Mechanical integrity of nano-interconnects; the impact of metallization density

In this study the impacts of two main design parameters, namely the metal and via densities on the mechanical integrity of nano-interconnects were investigated. To this aim, analytical modelling was used in order to derive the effective mechanical properties of nano-interconnect layers which were subsequently used as material properties in a layer-specific finite element model of nano-interconnects exposed to bump level mixed mode loading. The energy release rates for nano-interconnect cracks were used to determine the impact of metal and via density variations on the mechanical integrity of nano-interconnects. Using a parametric study, the key parameters that determine the mechanical integrity of nano-interconnects under chip package interaction (CPI) loads were identified to be the via densities in the intermediate layers with ultra low-k dielectric (ULK) and the via and metal densities of the top stiff group of layers often referred to as the “Z” group. Increasing the effective stiffness of the “Z” group by maximizing its via and metal density mitigated the energy release rate at the ULK pre-cracks in the intermediate via layers by means of elastic stress shielding. In addition, increasing the via density of the via layers integrated with ULK, increases the effective critical fracture energy of the via layer (i.e. the effective via layer adhesion), thereby improving the mechanical integrity. Keywords: Nano-interconnect, Mechanical integrity, Delamination, Chip package interaction (CPI), Metal density, Via densit

Nanoindentation study of thin plasma enhanced chemical vapor deposition SiCOH low-k films modified in He/H-2 downstream plasma

The effect of He/H-2 downstream plasma (DSP) on the mechanical properties of plasma enhanced chemical vapor deposition SiCOH low-k films was studied using nanoindentation (NI) with the continuous-stiffness measurement technique. Furthermore, the main requirements for reliable NI measurements on plasma-modified low-k films are discussed. The results show that the mechanical properties of these films are intimately linked with their porosity and that exposure to He/H-2 DSP causes a change in both the porosity and the mechanical properties of the films. This change is related to the removal of porogen residue formed during the ultraviolet curing of the low-k film.status: publishe

Modeling the substrate effects on nanoindentation mechanical property measurement

Nanoindentation technique is commonly used to characterize the mechanical properties of thin films. However, the validity of the measurements is greatly affected by the indentation depth and the substrate properties. The purpose of this study is to understand the influence of the substrate properties, the thin film thickness and the mechanical properties of the thin film itself on force-displacement curves obtained by nanoindentation. The experimentally obtained force versus indentation depth curves of single and bi-layer thin film systems on silicon wafers were simulated using Finite Element Modeling (FEM). The materials properties of the thin film layers were extracted by fitting the load-displacement curves obtained by FEM and experiments. The experimental part of this study includes nanoindentation tests performed on low-k films deposited on a silicon substrate. These films were treated during different periods of time (0s, 20s, 35s, 70s, 140s, 350s and 700s) with He/H2 downstreamplasma (DSP) at a fixed temperature of 280°C, thereby resulting in a double layered structure with the same total film thickness, but with different thickness and mechanical properties of the “modified” top layer. The results of this work provide considerable insight for the determination of the mechanical properties of layered systems.status: publishe

Determining the physical properties of EpoClad negative photoresist for use in MEMS applications

In this paper, the internal stress and Young modulus of EpoClad are investigated using different methods. The swelling behavior when submerged in common processing liquids is also measured and reported. Different on-wafer micro electromechanical structures are used, together with nanoindentation measurements. The experimental results yield an internal stress that is strongly dependent on the processing conditions, the ambient and the submersion liquid. Young’s modulus is found to be 4.4 ± 0.2 GPa.status: publishe

Extraction of elastic modulus of porous ultra-thin low-k films by two-dimensional finite-element simulations of nanoindentation

Continuous scaling of integrated circuits has led to the introduction of highly porous low dielectric constant (low-k) materials, whose inferior mechanical properties raise concerns regarding the reliability of integrated circuits. Nanoindentation is proven to be a straightforward method to study mechanical properties of films. However, in the case of low-k, the measurement and analysis are complex due to the porous nature of the films and reduced film thicknesses which give rise to substrate effects. A methodology that combines nanoindentation experiments with finite-element simulations is proposed and validated in this study to extract the substrate-free elastic modulus of porous ultra-thin low-k films. Furthermore, it is shown that imperfections of the nanoindentation probe significantly affect the finite-element results. An effective analytical method that captures the actual nanoindenter behavior upon indentation is proposed by taking both tip radius and conical imperfections into account. Using this method combined with finite element modeling, the elastic modulus of sub-100 nm thick low-k films is successfully extracted. Standard indentation tests clearly overestimated the actual modulus for such thin films, which emphasizes the importance of the proposed methodology.status: publishe

Determination of elastic properties of a MnO2 coating by surface acoustic wave velocity dispersion analysis

MnO2 is a material of interest in the development of high energy-density batteries, specifically as a coating material for internal 3D structures, thus ensuring rapid energy deployment. Its electrochemical properties have been mapped extensively, but there are, to the best of the authors' knowledge, no records of the elastic properties of thin film MnO 2. Impulsive stimulated thermal scattering (ISTS), also known as the heterodyne diffraction or transient grating technique, was used to determine the Young's modulus (E) and porosity (ψ) of a 500nm thick MnO2 coating on a Si(001) substrate. ISTS is an all optical method that is able to excite and detect surface acoustic waves (SAWs) on opaque samples. From the measured SAW velocity dispersion, the Young's modulus and porosity were determined to be E=25±1GPa and ψ = 42 ± 1 %, respectively. These values were confirmed by independent techniques and determined by a most-squares analysis of the carefully fitted SAW velocity dispersion. This study demonstrates the ability of the presented technique to determine the elastic parameters of a thin, porous film on an anisotropic substrate. © 2014 AIP Publishing LLC.status: publishe