Imagine a machine so small that it is imperceptible to the human eye. Imagine working machines with gears no bigger than a grain of pollen. Imagine these machines being batch fabricated tens of thousands at a time, at a cost of only a few pennies each. Imagine a realm where the world of design is turned upside down, and the seemingly impossible suddenly becomes easy. A place where gravity and inertia are no longer important, but the effects of atomic forces and surface science dominate. Welcome to the microdomain, a world now occupied by an explosive new technology known as MEMS (MicroElectroMechanical Systems) or, more simply, micromachines.

In this MEMS gear chain all gears are driven sequentially by the drive gear (top center). The fixed guide plates (mounted to the tops of the gears' shafts) are clearly visible. Gear chains such as this one have been driven at speeds up to 250,000 RPM.

Sacrificial polysilicon surface micromachining is emerging as a technology that enables the mass production of complex microelectromechanical systems by themselves, or integrated with microelectronic systems. Early versions of these micromachined systems-on-a-chip found application in the commercial world as acceleration sensors for airbag deployment - for example, ADI's ADXL50. There were two advances in manufacturing techniques for micromachined systems-on-a-chip that made possible great leaps ahead in the complexity of the systems. The first was a three-layer polysilicon micromachining process which included a fourth polysilicon electrical interconnect layer. The other was a single-layer (+ second electrical interconnect level) polysilicon surface micromachining process integrated with 1.25 micron CMOS. Samples of systems-on-a-chip built in these processes are pop-up mirrors and multi-axis accelerometers.