First fabrication of full 3D-detectors at SINTEF

International audienceA knowledge of the mechanical properties of bacterial biofilms is required to more fully understand the processes of biofilm formation such as initial adhesion or detachment. The main contribution of this article is to demonstrate the use of homogenization techniques to compute mechanical parameters of Pseudomonas aeruginosa PAO1 biofilms. For this purpose, homogenization techniques are used to analyze freeze substitution electron micrographs of the biofilm cross-sections. The concept of a representative volume element and the study about his representativeness allows us to determine the optimal size in order to analyze these biofilm images. Results demonstrate significant heterogeneities with respect to stiffness and these can be explained by varying cell density distribution throughout the bacterial biofilms. These stiffness variations lead to different mechanical properties along the height of the biofilm. Moreover, a numerical shear stress test shows the impact of these heterogeneities on the detachment process. Several modes of detachment are highlighted according to the local strain energy in the different parts of the biofilm. Knowing where, and how, a biofilm may detach will allow better prediction of accumulation and biomass detachment

Technologies enabling 3D stacking of MEMS

In order to realize reliable 3D stacking of micro electromechanical systems (MEMS), interconnection and through wafer via technologies have been adapted from other areas and verified for MEMS applications. True stacking of a system including MEMS requires vias through the MEMS and electrical and mechanical interconnection to other devices like signal conditioning units and communication- and power devices. MEMS will typically have specific requirements regarding mechanical issues like stiffness, robustness, volume, and mass. The mechanical issues limit the range of applicable technologies. In this work three interconnection technologies have been selected, evaluated, and compared: Au stud bump bonding, SnAg micro bumps, and the SLID (solid liquid interdiffusion) technology using Sn and Cu. One via technology has been considered, namely hollow vias, which has been improved and tested in this wor

High aspect ratio deep RIE for novel 3D radiation sensors in high energy physics applications

3D detectors with electrodes penetrating through the entire silicon substrate have many advantages over conventional planar silicon technology, for example, high radiation tolerance. High aspect ratio through-wafer holes are essential in such fabrication, and deep reactive ion etching (DRIE) is used. A series of DRIE processes were tested and optimised to achieve the required aspect ratio, and in 5-μm wide trenches, aspect ratios of 58:1 were achieve