Single crystal silicon as a micromechanical material

Single crystal silicon is the standard substrate for both bulk- and surface-micromachined microelectromechanical systems (MEMS). However, it can also be used as a structural material itself in microdevices. In particular, single crystal silicon micro-springs have been designed and fabricated. These springs, which are approximately 20 mu m thick and 7 mm across, incorporate a central island that can be used to apply force to an external device, such as a microvalve or micropump. Varying designs can exhibit deflections of 50 to 1500 mu m under applied loads of 5 to 50 mN. The spring behavior has been fully characterized by mechanical testing and by finite element analysis. The micromachining techniques used to fabricate these devices create distinct surfaces of varying morphology, depending on the etching methods used. The fracture behavior of these diverse silicon surfaces is examined to ensure and improve the reliability of the devices.