**5. References**

Adamson, A. W. (1990). *Physical Chemistry of Surfaces*, 5th ed., Wiley, New York.


microstructure. Then we present the techniques to characterize the micro-scale surfaces. Finally, we introduce the adhesion models to interpret the adhesive interaction of MEMS

It is hoped that the introductions in this chapter can gain the rational understanding leading to the design of better MEMS structures in the technologically field. The interpretation of interfacial adhesion is challenging for the application of MEMS technology. It is further complicated by the inability to observe the interfacial interactions directly, resulting in conclusions from inference. The gap between theoretical research of rough surface adhesion and the real world where thousands or millions of asperities are involved remains enormous. Then it is clear that there is still a great deal of research necessary to obtain a comprehensive understanding of adhesion at the microscale. The high-resolution instrument should be developed and well calibrated, with which one can measure both the microstructure topography and adhesion, especially the biological sample and hydrophilic surface. It is essential that the proper data processing method should be presented to reflect the intrinsic characters more accurately, and helps to understand the sources of error.

Adamson, A. W. (1990). *Physical Chemistry of Surfaces*, 5th ed., Wiley, New York.

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Bhushan, B. (1999). *Handbook of Micro-Nanotribology*, Second Edition. Bharat Bhushan. CRC

Bhushan, B. (1996). *Tribology and Mechanics of Magnetic Storage Devices*, 2nd ed., Springer,

Bhushan, B. & Blackman, G.S. (1991). Atomic Force Microscopy of Magnetic Rigid Disks and Sliders and Its Applications to Tribology, *Journal of Tribology* Vol. 113: 452–458. Bhushan, B. & Dugger, M. T. (1990). Real Contact Area Measurements on Magnetic Rigid

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devices.

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Press.

New York.


**7** 

**Advanced Surfactant-Modified** 

In the area of Micro Electro Mechanical Systems (MEMS), bulk micromachining and surface micromachining are two main technologies. Bulk micromachining defines structures by selectively etching inside a substrate while surface micromachining uses a succession of thin film deposition and selective etching on top of a substrate. The two technologies are quite different, resulting in different dimensions and different mechanical properties. Although bulk micromachining is usually considered to be the older technology, the two developments run parallel. This is due to the fact that the two different approaches have trade-offs. Taking an example of MEMS capacitance accelerometers, surface micromachined structures use smaller chip area, thus leaving more space for the electronics. On the other hand, in bulk micromachining the larger mass gives greater sensitivity for accelerometers and the larger area leads to larger capacitances for easy read out, which are extremely useful

Bulk micromachining technology relies on isotropic or anisotropic liquid phase (wet) etching as well as by plasma phase (dry) etching in single crystalline silicon for the formation of functional shapes and patterns in many major applications. Although dry etching has penetrated the traditional territory of wet etchants, the high cost in dry etching and the difficulty in the etch rate uniformity on the whole wafer in wet isotropic etching still make wet anisotropic etching the most affordable method for the reliable production, if wet

The formation of crystal facets due to etching is referred to as faceting. When the primary flat of Si {100} is along the [110] direction, rectangular structures with concave corners are easily made with four (111) sidewalls and a (100) plane as the bottom. If the slow etching (111) planes meet, etching will be self-limiting to result in inverted pyramids. Etched grooves, trenches, wells and other basic structures of diaphragms (membranes), beams, and cantilevers exemplify the features of crystal plane-dependent etching. Combined with the use of mask patterns, the etch rate anisotropy becomes a most valuable property as it provides a low-cost, precise means for the production of three-dimensional shapes delimited by smooth, shiny facets, leading to complex structures with multiple

anisotropic etching can be used to deliver a similar intermediate or final structure.

**1. Introduction** 

in the inertial device fabrication.

functionalities, as shown in Fig. 1.

**1.1 Wet anisotropic etching in MEMS** 

**Wet Anisotropic Etching** 

Bin Tang and Kazuo Sato

*Nagoya University* 

*Japan* 

