Micromachines, Volume 2, Issue 1 (March 2011) – 4 articles , Pages 1-81

Self-assembly is a promising technique to overcome fundamental limitations with integrating, packaging, and general handling of individual electronic-related components with characteristic lengths significantly smaller than 1 mm. Here we describe the use of magnetic and capillary forces to self-assemble 280 µm sized silicon building blocks into interconnected structures which approach a three-dimensional crystalline configuration. Integrated permanent magnet microstructures provided magnetic forces, while a low-melting-point solder alloy provided capillary forces. A finite element model of forces between the magnetic features demonstrated the utility of magnetic forces at this size scale. Despite a slight departure from designed dimensions in the actual fabricated parts, the combination of magnetic and capillary forces improved the assembly yield to 8%, over approximately 0.1% achieved previously with capillary forces alone. Full article

New surface mounting and packaging technologies, using self-assembly with chips having cavity structures, were investigated for three-dimensional (3D) and hetero integration of complementary metal-oxide semiconductors (CMOS) and microelectromechanical systems (MEMS). By the surface tension of small droplets of 0.5 wt% hydrogen fluoride (HF) aqueous solution, the cavity chips, with a side length of 3 mm, were precisely aligned to hydrophilic bonding regions on the surface of plateaus formed on Si substrates. The plateaus have micro-channels to readily evaporate and fully remove the liquid from the cavities. The average alignment accuracy of the chips with a 1 mm square cavity was found to be 0.4 mm. The alignment accuracy depends, not only on the area of the bonding regions on the substrates and the length of chip periphery without the widths of channels in the plateaus, but also the area wetted by the liquid on the bonding regions. The precisely aligned chips were then directly bonded to the substrates at room temperature without thermal compression, resulting in a high shear bonding strength of more than 10 MPa. Full article

Self-assembly in micro- and nanofluidic devices has been the focus of much attention in recent years. This is not only due to their advantages of self-assembling with fine temporal and spatial control in addition to continuous processing that is not easily accessible in conventional batch procedures, but they have evolved to become indispensable tools to localize and assimilate micro- and nanocomponents into numerous applications, such as bioelectronics, drug delivery, photonics, novel microelectronic architectures, building blocks for tissue engineering and metamaterials, and nanomedicine. This review aims to focus on the most recent advancements and characteristic investigations on the self-assembly of micro- and nanoscopic objects in micro- and nanofluidic devices. Emphasis is placed on the salient aspects of this technology in terms of the types of micro- and nanomaterials being assembled, the principles and methodologies, as well as their novel applications. Full article

The relative adhesion of two genetically engineered polypeptides termed as H6-(YEHK)x21-H6 and C6-(YEHK)X21-H6 has been investigated following growth and self-assembly on highly oriented pyrolytic graphite (HOPG), SiO₂, Ni, and Au substrates to study covalent surface attachment via histidine (H) and cysteine (C) groups incorporated in the polypeptides. Both polypeptides formed predominantly bilayer fibrils upon deposition, in agreement with previous studies. The relative adhesion of polypeptide fibrils to the substrate, as well as intra-fibril cohesion, was examined via a forced-scanning method employing contact mode atomic force microscopy (AFM). H6-(YEHK)x21-H6 polypeptide fibrils were observed to detach from Ni, Au, SiO₂, and HOPG substrates at normal tip forces of 106 ± 10 nN, 21 ± 3 nN, 22 ± 3 nN, and 3 ± 1 nN, respectively. C6-(YEHK)x21-H6 polypeptide fibrils were seen to detach from Au substrates at a normal spring force of 90 ± 10 nN. It is concluded that the H6-(YEHK)x21-H6 and C6-(YEHK)x21-H6 polypeptide fibrils are covalently attached to, respectively, Ni and Au substrates, which has important implications for the use of these materials for NEMS fabrication. The structural stability of deposited polypeptide fibrils was also evaluated by using normal tip forces less than those required for fibril detachment. H6-(YEHK)x21-H6 polypeptide fibrils on Ni substrates were the most structurally stable compared to C6-(YEHK)x21-H6 polypeptide fibrils on Au substrates. Controlled delayering of bilayer fibrils was also detected for sub-detachment normal forces. Full article