Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Utility Patent
1998-05-26
2001-01-02
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S324000, C216S039000
Utility Patent
active
06168906
ABSTRACT:
FIELD OF INVENTION
This invention relates to a micromachined membrane with locally compliant and stiff regions and a method of making them.
BACKGROUND OF INVENTION
In the fabrication of micro-transducers, acoustic transducers, and micro-pumps, one often requires a flat plate of low mass which has high stiffness in certain areas to maintain flatness (the capacitor “sense” areas) and high flexibility in other areas (the “spring” areas). Low mass is required to avoid sharp resonant peaks and to extend usable bandwidth of the transducer. Former methods created thick regions where stiffness was desired, and used thin or corrugated sections where flexibility was desired. One disadvantage of former methods is that the thick regions used to gain stiffness add considerable mass to the transducer, and thereby decrease efficiency, bandwidth and increase undesirable inertial sensitivity. Furthermore, the creation of these thick regions requires additional processing steps which increase cost and complexity.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved micromachined membrane with locally compliant and stiff regions.
It is a further object of this invention to provide an improved method of making a micromachined membrane with locally compliant and stiff regions.
It is a further object of this invention to provide such a membrane which has a light weight stiff region and consequent improved bandwidth.
It is a further object of this invention to provide such a membrane which has improved sensitivity, dynamic range and linearity.
It is a further object of this invention to provide such a membrane which simultaneously creates stiff and flexible regions.
It is therefore an object of this invention to provide such a membrane which employs corrugations to create both the stiff and the flexible regions.
The invention results from the realization that truly effective corrugated membranes with both stiff and flexible regions can be made, for use in transducers, for example, by micromachining narrow and wide grooves in a substrate, then coating the grooves with a coating that is as thick or thicker than one half the width of the narrow grooves but less than half the width of the wide grooves to produce both stiff and flexible regions, and then removing the substrate from the coated grooves.
This invention features a method of making a micromachined membrane having both stiff and flexible regions. The method includes depositing a photoresist on a substrate; exposing the photoresist to actinic radiation through a mask to define openings having a first width in the photoresist in the stiff region and openings having a second width greater than that first width in the flexible region; and developing the exposed photoresist to create the openings. The openings are etched through the developed photoresist to create grooves in the substrate and the substrate including the grooves is coated with a film of material having a thickness greater than one half of the first width and less than half of the second width to form adjacent contacting rigid corrugations in the stiff region and spaced compliant corrugations in the flexible region.
In a preferred embodiment the photoresist may be phenyl formaldehyde or rubber. The actinic radiation may be ultraviolet radiation. The etching may be reactive ion etching. The coating may be silicon nitride or silicon carbide and may be from 0.1 to 1.0 microns thick. The first width may be equal to or less than 0.2 to 2.0 microns thick, and the second width may be greater than 0.2 to 2.0 microns. The method may further include removing the substrate from under the coating. Removing the substrate may include etching away the substrate with an anisotropic etch agent. The substrate may be silicon. The etch agent may be ethylene diamine pyrocatechol. The developed photoresists may be postbaked to round the edges of the openings and the postbaking may be for two to thirty minutes at 90-100° C.
The invention also features a micromachined membrane made by the method having a first region with a plurality of spaced nonintersecting corrugations being flexible in the direction transverse to the corrugations and a second region having a plurality of adjacent contacting intersecting corrugations being stiff in the plane of the intersecting corrugations in the direction transverse to the plane.
In a preferred embodiment the intersecting corrugations may form a honeycomb of squares or of hexagons, elongated hexagons or triangles.
REFERENCES:
patent: 4241165 (1980-12-01), Hughes
patent: 4423137 (1983-12-01), Rester
patent: 5064165 (1991-11-01), Jerman
patent: 5165283 (1992-11-01), Kurtz et al.
patent: 5888412 (1999-03-01), Sooriakumar et al.
patent: 5899746 (1999-05-01), Mukai
Bernstein Jonathan J.
Cunningham Brian Thomas
Duda Kathleen
Landiorio & Teska
The Charles Stark Draper Laboratory Inc.
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