Microdevice having interior cavity with high aspect ratio surface features and associated methods of manufacture and use

DETAILED DESCRIPTION The present invention relates generally to three-dimensional forms having high aspect ratio features with ultrasmooth surfaces, and to methods for fabricating such forms useful as microdevices.
More particularly, the invention relates to microdevices having an interior cavity with surface features on the order of one micrometer, yet retaining sub-micrometer surface roughness, and to a method for fabricating such microdevices using a precise contour polishing method.
To produce such a microdevice requires the preparation of a sacrificial mandrel that has the precise surface contour to be replicated in the microdevice itself.
This mandrel must have a replicating surface that is substantially free of roughness, on a scale of about one micrometer RMS or less, and has the desired surface contour.
A convenient mandrel material is a plastic, such as polymethylmethacrylate (PMMA), that can be easily polished and readily removed from the structural material that forms the microdevice.
To produce a contoured surface having precise high aspect ratio features requires a shaped bit having features of similar dimension.
A shaped bit allows for the generation of complex geometries in one operation as opposed to traditional cutting where the cutting tool must make serial cuts.
Cutting tools also require higher maintenance - a sharpened cutting edge must be whet and kept from dulling.
In one embodiment of this invention, a method for making such a shaped bit is the LIGA process, which has been demonstrated to be capable of producing precise, high aspect ratio microstructures of suitable bit materials.
LIGA bits are used because their thickness keeps them from being elastically or plastically deformed.
The sacrificial mandrel is contoured by slowly advancing the shaped bit into the rotating sacrificial mandrel that is mounted in a precision turning machine, such as a precision lathe, and whose surface has been prepared with a suitable polishing compound.
The contouring is preferably accomplished by polishing but may also be accomplished by cutting under limited circumstances