Wet etching, anisotropic

Tanaka et al. [73] developed another MEMS system for the catalytic combustion of butane. It is composed of a combustion chamber 8 mm wide, 14 mm long and 150 pm deep which was prepared by anisotropic wet etching of a silicon substrate. The substrate was then covered with Pyrex glass applying anodic bonding. Combustion was performed on a platinum/titania catalyst... 

HF-HNOj Unspecified etch rate Anisotropic Wet Etch i... 

What are the differences between isotropic and anisotropic wet etch of silicon (2 marks)... 

Micro-reaction chambers for the thermal cycling of DNA amphfication by the polymerase chain reaction (PCR) in silicon by bulk machining using anisotropic wet etching have been fabricated by Moore and co-workers [40]. The rapid temperature cycling and the small size of the chambers may be combined with an appropriate transducer in a miniaturized analytical system. 

Kudelka, S., Michaelis, A. and Tobben, D. (2002) Bottle Shaped Trench Formation by Anisotropic Wet Etch, US Patent 98-0324. 

D lithography was performed by using the contact mask aligner (Karl Suss, MA6/BA6). The channel formed by anisotropic wet etching was chosen for the channel fabrication of the pDMFC because UV light can be irradiated to the sidewall. The photograph of the fabricated pDMFC is shown in Fig. 5.5. The performance of... 

Different etchants used in anisotropic wet etching have specific etch rates for each crystallographic plane in the material being removed. It is the difference in etch rates between planes that produce shapes within the material being etched that appear to follow the planes within the crystalline structure as seen in Fig. 1. For more information on the crystalline structure of silicon and how miller indices are used in designating crystal planes, see The MEMS Handbook [1]. It is commonly accepted that the (111) plane etches the slowest regardless of the etchant used. However, the crystal plane that etches the fastest depends on the etchant composition [2]. Ammonium hydroxide etchants (NH4OH and TMAH) are frequently used to... 

The anisotropic wet etching of silicon is a unique fabrication process in the MEMS field. The need to develop new processes to fabricate functional 3D microstructures in various materials is urgent for progress in microfluidic systems, microsensors, micro-actuators, and microinstrumentation. At present, to integrate surface micromachined devices and standard IC devices with bulk micromachined structures to demonstrate a new functional MEMS application is still a challenge for researchers who work in this field. The cooperation of multidisciplinary researchers will be required to develop miniature systems with the most appropriate building philosophy and the best operation performance. 

Since the etch rate in isotropic etching is the same in all directions, its undercut rate is 1. For orientation-dependent anisotropic wet etching, the undercut rate is basically < 1. If the undercut rate can be controlled in the etching process, the lateral contours along the z direction will be changed, and a special 3D structure can be created with a 2D mask pattern. 

Combining DRIE and anisotropic wet etching can produce unique structures. For example, (111) silicon cannot be etched by the standard KOH, TMAH, and EDP etchants, but if an initial trench has been etched by DRIE, fast-etching crystal planes are exposed, and wet etching can proceed. If this is combined with spacer structures to protect sidewalls and another DRIE step, (111) free-standing silicon structures can be made. 

DRIE in combination with electrochemical etching of silicon enhances shape freedom in electrochemical etching. If anisotropic wet etching is used to create the initial pits for electrochemical etching, the usual limitations of crystal... 

Anisotropic wet etching of single crystal Si using KOH. The surface of the wafer is a 100 plane. 

A microfabricated device that works in a manner similar to that shown in Fig. 4 bas been developed by Peterson et al. [7]. Three inlet and three outlet channels feed a single parallel sided channel anisotropically wet etched into a silicon substrate. This channel is excited at its half-wave resonance by a transducer mounted in the plane of the silicon, perpendicular to the axis of the standing wave. Similar devices have been used by the same group for a number of applications, including the separation of lipids from blood (in which the lipids move to the pressure antinode and the red cells to the pressure node) and fractionation of different size beads. 

Hsieh et al. (1997) employed microelectromechanical system (MEMS) technologies to develop a miniature ECM using polymer electret as show in Fig. 7. The diaphragm is 0.91 pm LPCVD silicon nitride fabricated through backside anisotropic wet etching of <100> silicon substrate. Teflon AF is spun on with the thickness of 1.2 pm over the nitride membrane and is used as the electret layer. After charging, the silicon chip with the diaphragm is bonded to the other silicon chip with a photoresist spacer. 

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