3D micromachined devices based on Polyimide Joint technology

A novel and simple technology for making robust three-dimensional (3D) silicon structures with small radii of bending has been developed and investigated. The proposed self-assembling method of bending 3D structures out-of-plane, without the use of interlocking braces is based on thermal shrinkage of polyimide in V-grooves. The static bending angle for the permanent out-of-plane rotated structure can be chosen and well controlled over a wide range (from 0 to 200 degrees) by varying the curing temperature of the polyimide and the number of V-grooves in the joint. The relatively large thermal expansion of polyimide allows the structure to be used in dynamic mode for actuator applications. Local power dissipation in the joint is achieved by driving a current through integrated heaters. Displacements as large as 170 mu m have been obtained with a 500 mu m long structure. The proposed technique is compatible with both IC based surface and front bulk micromachining and batch fabrication. Therefore, the new polyimide joint may have applications where silicon structures with detailed features in all three dimensions are needed. Several different devices have been fabricated based on the polyimide joint technique taking advantage both the static and dynamic mode of the joint. Examples of applications described in this paper are 3D hot-wire flow sensors together with micro-conveyers and micro-robots based on arrays of erected legs asynchronously actuated using polyimide joint actuators.