ABSTRACT
One of the great promises of MEMS and surface micromachining is the small size of the devices that can be fabricated. From Jonathan Swift’s stories about the Lilliputians in 1726, to the dollhouses and model trains that fascinate both children and adults in the present, humans are fascinated by small things. The advantages of smaller machines are sometimes very important: in aviation and space applications, a decrease in size and weight corresponds to an increased range or a reduction in the amount of fuel required for a given mission. The advantages of the different physical effects at the microscale level are less obvious. Smaller scales mean that surface micromachined devices are more resistant to shock and vibration than macrosized machines, because the component strength decreases as the square of the dimensions while the mass and inertia decrease as the cube of the dimensions. Another difference is that surface forces, such as van der Waals forces and electrostatic attraction, are much more important at the microscale than at the macroscale, while volume forces such as gravity are much less important. Reduced assembly costs are another advantage of surface micromachined devices. Surface micromachining allows
the creation of machines that are assembled at the same time as their constituent components. Instead of using skilled workers to assemble intricate mechanisms by hand or investing in complicated machinery, the assembly is done as a batch process during the integrated-circuit-derived fabrication process. Preassembly imposes certain limitations on the designer, such as the inability to build devices with as-fabricated stored mechanical energy or preload. Instead, structures such as springs must have energy added to them. Preassembly also requires structures that operate out of the plane of the substrate to be erected prior to use.
