Relays are used to distribute power to selected loads. The type of relay used mostly is an electromagnetically-activated mechanical relay. The mechanical relays are reliable, can carry high current (&gt;20 A) and are inexpensive. The drawbacks of the mechanical relays are that they are bulky and require a continuous current to generate the needed force to hold the contact. The holding current consumes battery energy and produces heat in the relay undesirably.
The other popular type of switch is a power transistor. Transistors are inexpensive when they are not used to carry high current. The switching time is short, which enables the transistor to switch power to different loads at very high speeds. Because of the practice of batch fabrication, many transistors are made simultaneously and uniformly. However, a heat sink is needed to dissipate the heat generated by a transistor when it carries high current. The heat sink adds cost to power transistors in high current applications.
There are needs for reliable, small and inexpensive relays. There is a particular need for small relays in automobile applications where the relay can carry a current of, e.g., two amperes more or less continuously and a current of 10 amperes for brief periods. An electrostatically-actuated, all-metal micro-relay fits into this category. It has the advantages of transistors, small size and batch fabrication capability. Hence, it can be a low cost product. Similar to the mechanical relay, the contact resistance of an all-metal relay can be very low. There is no need to use a heat sink when the contact resistance of the relay is low--about a few milliohms. Yet, the electrostatically-actuated relay does not need conduction current to hold the contact and, consequently, no waste in battery energy.
The concept of using an electrostatic force to deflect a cantilever beam to make a contact has been tried experimentally for years. Due to the fabrication methods and the materials used, such prior devices had limited applications. The main disadvantages of these devices were high actuation voltage (much higher than 50V) and low switched current (in milliamperes).