By: Eldy Zuniga, MEMS Engineer
My first exposure to microelectromechanical systems, MEMS, came during my time at the University of Michigan. A friend got me in contact with a professor at the Lurie Nanofabrication Facility for a part-time job. There I learned how to design and fabricate these devices, and to love their simplicity and the gratification of their systematic fabrication.
MEMS encompass any device with components under 0.1 millimeters and down to 100 nanometers. The only other accepted criteria to define a MEMS device is that at least one of its parts has some mechanical functionality. However, they do not have to technically move.
MEMS components have four significant functions: microstructures, microelectronics, microsensors, and microactuators. The first two are typically present in most designs and function as the device’s foundations. A microstructure is any structure in a MEMS device that is itself inert or provides structural support for other components. One example is the free mass in many accelerometers. Microelectronics are instead electric built in the device typically made to interact with the device’s supporting electronics. Due to MEMS fabrication using similar CMOS techniques, most electronics components can be built into a MEMS device, such as capacitors, transistors, and resistors.
The final two functions are transducers due to their nature in changing their input energy to different output energy. The main difference between the two categories is where the electrical power is located. They take whatever force or event microsensors are designed to interact with and generate some electrical output calibrated to create a definable reading. A simple example is a classic pressure sensor. As the sensor deforms, it causes a pathway for the electrical current, which increases proportionally as the path’s resistance lowers due to the sensor’s deformation. This is an example of a mechanical input converting to an electrical output.
Microactuators are the complete opposite consuming electrical energy to generate some reaction. The ones I most commonly use are called thermal actuators. These actuators are designed using silicon’s natural heat expansion to allow controlled displacements. A current running through the actuator heats the structure, displaces it, and provides a mechanical push to another or simply acts as an obstacle.
These are simple examples of MEMS functions. Still, over the years, the variety of options and complexity the MEMS community has generated is impressive. This variety of components allows MEMS to be present in most modern devices. They are typically very modular and use similar fabrication methods to be easily updated for other improved designs.
Overall, with these four functions, MEMS can be as flexible as they can be versatile. This trend will continue as our fabrication technology improves. More designs, which for now are closed off, will become available to us. I am most interested in the inclusion of additive manufacturing, which will allow new materials and structures to be included in designing and fabrication, but that is a topic for another day.