Radio frequency (RF), microwave and millimeter wave circuits have been conceptualized using microelectromechanical systems (MEMS) as early as the 1990s. MEMS devices can be fabricated in large numbers on a single chip (batch production) using conventional integrated circuit (IC) and semiconductor processing technologies. The IC processing technique has been well established using surface and bulk micromachining processes since the 1980s. Advances in these processes over the last decade have accelerated the development of MEMS devices in almost all areas of engineering. The key advantages are smaller size, low cost and improved performance compared to other conventional alternatives [2]. The journey of MEMS structures started with relatively simple acceleration, pressure and temperature sensors. Since then, MEMS technology has been proven to be applicable in many areas of engineering such as microfluidics, pneumatic, RF, optical and biomedical. Figure 1.1 shows some examples of MEMS devices [3,27]. SEM images of MEMS (a) micromirror by Texas Tech University and (b) RF switch by UCSD. (From K.-J. Koh, and G. M. Rebeiz, A 6-18 GHz 5-bit active phase shifter, in <italic>IEEE MTT-S International Microwave Symposium Digest</italic>, Anaheim, CA, May 2010, pp. 792–795; and M. J. W. Rodwell et al., <italic>IEEE Trans. Microw. Theory Tech</italic>., vol. 39, pp. 1194–1204, July 1991.) https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351021340/25c374e3-6d5c-475f-93fa-a005ae1eda18/content/fig1_1_B.jpg"/>