Microfabricated particle thin film filter and method of making it

DETAILED DESCRIPTION The present invention is directed to a filter comprising a first thin film structure having openings therethrough, and a second thin film structure positioned relative to the first thin film structure to partially block the openings to produce pores of a predetermined width.
The method of the present invention includes providing a first thin film structure having openings therethrough.
A sacrificial layer is formed on at least part of the surface of the first thin film structure.
A second thin film structure is formed over the first thin film structure and the sacrificial layer.
The sacrificial layer and the second thin film structure block the openings of the first thin film structure, and the second thin film structure leaves a portion of the sacrificial layer exposed.
The sacrificial layer is etched to provide the pores of the filter.
Fabrication is done using surface micromachining.
The locations of the pores are determined photolithographically, but the width of the pores is determined by the thickness of a sacrificial thin-film layer.
The pore width can be precisely controlled, and may be as small as about 50 angstroms.
The length and lateral extent (perpendicular to both width and length) of the pores may be determined by photolithography and may range from about 0.
3 microns to many microns.
In some embodiments, both the pore width and length may be determined by the thickness of the thin film layers, and thus, can be smaller than the limit of resolution obtainable with photolithography.
Inorganic thin film filters are suitable for use at high temperatures, and with many harsh solvents.
Applications include absolute particle filters, immunological barrier capsules, and time release diffusion barriers.
The molecular crystallization valves and liquid crystal valves described below also allow the filter properties to be changed during use.