Micromechanical devices

The core components of a complete microsystem are the integrated sensing, acting or passive micromechanical devices. In most cases, a naked chip manufactured in bulk or surface micromachining is used for the detection of a physical or chemical quantity or some actuation principle, like the dosage of ink droplets in inkjet printheads. A complete microsystem can consist of a complex set of these devices. 

The majority of micromechanical devices require 3D machining of the bulk silicon material with etching depths of up to wafer thickness. Generally, three basic etching process types can be distinguished ... 

In the manufacture of micromechanical devices electrochemistry is commonly used to realize etch stop structures or to form porous layers. The first of these is discussed in Section 4.5. In the latter case, the use of PS as a preserved layer or as a sacrificial layer can be distinguished. In the first case PS is an integral part of the ready device, as discussed in Sections 10.4 to 10.6, while in the latter case the PS serves as a sacrificial layer and is removed during the manufacturing process. 

Smith J, Montague S, Sniegowski J, Murry J, McWhorter P. Embedded micromechanical devices for the monolithic integration of MEMS with CMOS. Proceedings of the IEEE International Electron Devices Meeting 1995. p 609-612. 

Angell JB, Terry SC, Barth PW. Silicon micromechanical devices. Sci Am 1983 248 44-55. 

Mastrangelo, C.H. Adhesion-related failure mechanisms in micromechanical devices. Tribology Lett. 1997, 3 (3), 223-238. 

Silicon oxides (SiOx) are the most widely used thin films in silicon microelectronic and micromechanical devices. Similar to silicon nitride (Section 5.5.4), these amorphous films exhibit dielectric properties. Silicon oxide is often utilized as part of a dielectric membrane, as a passivation or insulating layer, or as a sacrificial layer, which can be etched with hydrofluoric acid (HF)-containing etchants. Two different approaches to forming a silicon oxide thin film are... 

The intrinsic stress in silicon nitride layers is important especially in micromechanical devices the characteristic features of membranes based on silicon nitride or thin silicon structures covered with silicon nitride are very sensitive to stress variations in these layers. Similar to PECVD-oxide, the intrinsic stress of silicon nitride is influenced by several deposition parameters such as gas flow, deposition temperature, and radiofrequency (RF) power. 

For discrete micromechanical devices that do not include integrated electronics, the situation is different Platinum is an excellent choice for sensors based on a thermal measurement principle and is used in very high volumes, for example, in the air mass flow sensor chip produced at Bosch. Here, a platinum thin film serves as both a heater and a temperature sensor on a thin dielectric membrane consisting of silicon oxide and silicon nitride. The advantages of platinum as a thin film for thermal sensors compared to, for example, polysilicon are as follows ... 

Angell J B, Terry S C and Barth P W 1983 Silicon micromechanical devices Sci. 

Photoetching has also been applied to make three-dimensional processing of silicon surfaces. Porous structured silicon is of great interest for electronic and micromechanical devices (see Chapter 10). 

Cellular Mechanotransduction in Microfluidic Systems, Fig. 3 Schematics of micromechanical device cross section, (a) At rest and (b) hydraulic deflection of PDMS membrane to provide compressive stress on the adhered cells (Reprinted with permission from Kim et al. [5])... 

This interest has two reasons. First reason is that above structures can be applied in many microelectronic (like computer memory) and micromechanical devices (see, e.g. [28-31]). In such applications, the properties of a domain structure play a crucial role in the functionality of a device since it influence polarization fatigue, i.e. the gradual loss of switchable polarization after several switching cycles. 

Mayer TM, Elam JW, George SM, Kotula PG (2003) Atomic layer deposition of wear-resistant coatings for micromechanical devices. Appl Phys Lett 82 2883-2885... 

From a practical point of view one wishes to be able to control frictional forces so that the overall friction is reduced or enhanced, the chaotic regime is eliminated, and instead, smooth sliding is achieved. Such control can be of high technological importance for micromechanical devices, for instance in computer disk drives, where the early stages of motion and the stopping processes, which exhibit chaotic stick-slip, pose a real problem [56]. 

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