This technology can be used to produce 3D MEMS structures using conventional planar microfabrication techniques. These 3D MEMS structures have diverse applications in the development of novel MEMS sensors.
Traditional microfabrication techniques such as surface and bulk micromachining are limited in their ability to produce highly out-of-plane elements. A number of methods are available to extend their 3D fabrication capabilities, including polyimide joint technology (PJT), polymeric microstereolithography, and deep reactive ion etching (DRIE). However, these methods suffer from limitations such as the inability to accurately lock out-of-plane elements in position and the relatively low strength and thermal stability of polymers compared to traditional MEMS materials like silicon or metals. This invention describes a method of 3D MEMS fabrication that addresses these issues.
Buckling refers to the sudden lateral deformation of a structural member compressed past its limits of mechanical stability. Typically, slender structural members buckle long before loads exceed material strength limits, allowing buckled members to retain their integrity and continue supporting loads in the laterally deformed configuration. By exploiting this phenomenon, highly out-of-plane MEMS elements can be created from planar elements made using conventional 2D techniques such as surface micromachining and complementary metal oxide semiconductor (CMOS) processes.
This invention describes a set of four different 3D MEMS architectures that allow the buckling behavior of a planar element to be controlled independently of its residual state of stress, thereby enabling the use of CMOS techniques, which provide limited control over cross-sectional shape and residual stress states within individual layers. For example, the “patch” architecture places thin film patches with large gradient residual stresses near the ends of a microbridge where they exert control moments on the microbridge. Given knowledge of, but not necessarily control over, the state of stress in a microbridge, patches can designed to make it buckle in the direction opposite to that dictated by its intrinsic stress state.
- Enables construction of highly out-of-plane MEMS elements capable of accurately locking in position using 2D microfabrication techniques
- Enables buckling behavior to be controlled independently of residual states of stress, lowering flexibility requirements on 2D fabrication process