Black silicon—new functionalities in microsystems

Abstract

Black silicon and its application as a new assembly method for silicon wafers at room temperature is presented. Needle-like structures on the surface after deep reactive ion etching with a length of 15–25 µm and 300–500 nm in diameter interlock with each other to form a bonding interface. After compression of two wafers at room temperature they generate retention forces up to 380 N cm−2 (3.8 MPa). If low contact forces are applied with partially interlocking of the needles, it is possible to generate a reversible Velcro®-like assembly. This new bonding process can be used for applications in the area of microfluidics with catalysts, microoptical or mechanical mountings or carrier wafer bonding in microelectronics.

Wetting of Silicon Nanograss: From Superhydrophilic to Superhydrophobic Surfaces

“…[11] Over the past years, several studies have made use of the extraordinary properties of black silicon for a variety of purposes: examples are the application of nanograss for the bonding of microelectromechanical (MEMS) devices or the reduction of drag inside microfluidic channels. [12,13] In the experiments described in the following, we were interested in adjusting the wetting behavior of silicon nanograss surfaces by precisely controlling the surface chemistry. In a first step, a thin film (t ≈ 5 nm, as determined by ellipsometry measurements on flat parts of the wafer) of poly-(heptadecafluorodecylacrylate) (PFA) was photochemically attached to a nanograss surface.…”

Black poly-silicon: A nanostructured seed layer for sensor applications

“…Hoyer et al [Hoyer, 2008] reports that the black Si surface structure, in contrast to expectations for indirect semiconductors, shows an emission in the terahertz range using optical excitation [Hoyer, 2008]. Besides unique optical properties, several applications have shown its versatility in the recent past as superhydrophobic structure with self-cleaning features [Barbareglou, 2010;Zhang, 2013], as superhydrofilic layer with the help of a polymer monolayer attachment [Dorrer 2008]or as mechanical interface for promoting silicon-polymer bonding [Stubenrauch, 2006]. Utilizing the high effective surface area of silicon nanograss, impedance measurement-based biosensor was developed for label free detection of cells in cancer research [Mohammad, 2014].…”

“…With proper parameter settings the two most commonly used fluorine-based DRIE methods, the so-called Bosch-process and also the cryogenic or mixed-mode result in the formation of b-Si Jansen, 2009;Jansen, 2010]. Reactive ion etching (RIE) in CF 4 [Gharghi, 2006], in Cl 2 [Kalem, 2011] or SF 6 plasma [Stubenrauch, 2006;Yoo, 2006;Dorrer, 2008;Hoyer, 2008] have been used to realize Si nanograss. Wet chemistry based on the local catalytic action of nanometer-sized Au dots [Koynov, 2006 or laser direct writing [Serpenguzel, 2008;Barberoglou, 2010;Vorobyev, 2011] have also been reported as a reliable tool for Si nanograss formation.…”

Fabrication of Nanopillar Micropatterns by Hybrid Mask Lithography for Surface-Directed Liquid Flow

“…On the other hand, it is important to control the surface geometry when fabricating functional surfaces, because nanostructures on a surface enhance the characteristics of the surface, such as its friction force [15], wettability [16] and optical resonance [17]. The wettability of a surface can be used to control the surface tension of a liquid and restrict the flow direction in a microfluidic chip [18,19].…”