Micro charge pump actuation in SUMMiT V MEMS

Micro-Electrical-Mechanical-Systems (MEMS) may contain mechanical parts that are often actuated by an external electrical signal. Visual inspection of the mechanical parts may require a Scanning Electron Microscope (SEM) due to the extremely small dimensions involved. While imaging, electrons interact with the specimen and may generate static electric charge within features of the specimen. Recently, devices have been designed to use the forces generated as a result of interacting static electric charges within features produced during SEM imaging as means of actuating mechanical movement. This study investigates two such MEMS devices designed and fabricated using the Sandia SUMMiT V MEMS process. The first design is a test structure used to quantify the forces and charges generated through the actuation process. The test structure utilizes thin beams that bend and store energy. A theoretical beam mechanics model has been created to quantify those forces. After fabrication the test structure was cross sectioned. Actual dimensions were measured using optical and electron microscopes. These dimensions were compared with those expected from design simulations. The actual test structure dimensions were found to be suitable for micro charge pump actuation. The second design is a series of interlocking shelves intended to expand into a stepped pyramid when viewed under a SEM. This pyramid was intended to demonstrate the unique ability of the charge pump method. Unfortunately, the pyramid device was found to be too loosely designed and resulted in steps moving off track likely during final steps of fabrication. When steps were inline, SEM imaging of the pyramid expanded only partially. The design has been revised to include beams running perpendicular to and cutting into the step's top layer as well as bottom layer. These beams as well as an extra layer underneath the pyramid, should help the pyramid to survive manufacture and charge properly. A practical application of micro charge pump actuation, as well as the pyramid is discussed.