Fluidic MEMS device
A MEMS package comprises a substrate and a cover plate. A MEMS structure is fabricated on a surface of the substrate. The cover plate may be bonded to the substrate by a bond ring. The cover plate, the bond ring and the substrate may define an inner cavity. The cover plate, the substrate and a breach in the bond ring may define a fill port.
Certain fluidic micro-electro-mechanical systems (MEMS) applications include fluid in a hermetically sealed inner cavity of a MEMS package. Such hermetic MEMS packages may comprise rigid and/or brittle materials. The volumetric expansion rate of fluids hermetically sealed in MEMS packaging, upon increases in temperature, may be as much as 20 to 100 times greater, for example, than the expansion rate of the inner cavity of the package based on the linear expansion rate of the packaging materials. The fluid may also be incompressible or have a very low degree of compressibility. As a result, thermal excursions may result in an increase of fluid pressure in the inner cavity which may lead to fluid leakage and/or fracture of the packaging materials.
SUMMARY OF THE DISCLOSUREAn exemplary embodiment of a MEMS package comprises a substrate and a cover plate. A MEMS structure is fabricated on the substrate. The cover plate may be bonded to the substrate by a bond ring. The cover plate, the bond ring and the substrate may define an inner cavity. The cover plate, the substrate and a breach in the bond ring may define a fill port.
BRIEF DESCRIPTION OF THE DRAWINGSThese and other features and advantages of the invention will readily be appreciated by persons skilled in the art from the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawings, in which:
In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals.
The exposed portions 33 may be defined in an opening 22, for example a slot or hole in the cover plate, or may be defined in a partial slot or hole which, for example, may remain in a cover plate after singulation from a wafer-scale assembly (
In an exemplary embodiment illustrated in
Exemplary fluidic MEMS devices may be assembled using various techniques. In one exemplary process, a cover plate is attached by a bond ring to a substrate to define an inner cavity. The size of the substrate and cover plate may be chosen to permit access to bond pads in exposed areas of the substrate. For example, the cover plate may be smaller than the substrate defining exposed portions of the primary surface of the substrate after the cover plate is attached. The exemplary embodiment illustrated in
In an alternate pick-and-place embodiment illustrated in
Each cover plate 2 is attached to the wafer 300 by a bond ring 4 at a die location 35. The wafer 300, the cover plates 2 and the bond rings 4 define a plurality of inner cavities. Bond pads 34 are provided for making electrical connections to the MEMS device structures. Individual MEMS devices or dies may be singulated from the wafer after the cover plates are attached. Attaching the cover plates at the wafer level may provide some protection to the MEMS structures on the substrate during any subsequent manufacturing, assembly or handling. The individual MEMS devices could be filled with fluid at the wafer level, prior to singulation, as discussed below. The exemplary embodiments illustrated in FIGS. 2 or 3 may be assembled using this method.
In an alternate Awafer-scale@ embodiment illustrated in
The openings 22 may provide access to fill ports 111 for filling and sealing, as discussed below, and/or access to bond pads 34 for making electrical connections. When the cover plate is attached to the wafer, the access openings define exposed portions on the primary surface of the substrate or wafer. In the exemplary embodiment of
The exposed portions 33a at the fill ports may provide access to fill the inner cavity through the fill port, may provide a platform adapted to receive fluid to be provided for use in filling the inner cavity and may provide a platform for placing a seal at the fill port after filling the inner cavity. Exposed portions 33 adjacent fill ports in other exemplary embodiments may also provide a platform for providing fluid for use in filling the inner cavity and may provide a platform for placing a seal at the fill port after filling the inner cavity. The exposed portions 33b on which the bond pads 34 are arranged provide access to the bond pads to make electrical connections to the individual MEMS devices or dies after singulation from the assembly 100. Exposed portions 33 in other exemplary embodiments may also provide access to bond pads to make electrical connections to MEMS devices.
In the exemplary embodiment illustrated in
In an exemplary embodiment of a MEMS device 1, it may be desirable to fill the inner cavity 11 with fluid 6. Such fluidic MEMS device applications include without limitation micromirror arrays, micromotors, microswitches or accelerometers. Fluids used in these applications may comprise aromatic solvents, such as 1,1, Diphenylethylene, organosilianes, such as 3-chloropropyl triethoxysilane, perfluoroethers, such as Galden HT-100 (TM), silicones and silanes, such as polymethylphenylsiloxane, and polydimethylsiloxane, water, mixtures of water and water-soluble organics, ionic materials dissolved in water, pigmented fluids, colloidal suspensions.
Fluid may be introduced into an inner cavity by a method illustrated in
When the inner cavity is provided with a vacuum, an amount of fluid at least sufficient to fill the inner cavity may be provided at the feed port 111. In an exemplary embodiment illustrated in
The fluid provided at the fluid port should be arranged such that an increase in the pressure of the environment 7 surrounding the MEMS assembly or in the chamber causes fluid to enter the inner cavity through the feed port. In an exemplary embodiment illustrated in
The rate of pressure increase should be selected such that the differential pressure between the increased pressure in the environment or chamber and the low pressure or vacuum in the inner cavity causes the fluid to enter the cavity through the breach in the bond ring and completely fill the space between the silicon wafer and the cover plate. For viscous fluids, the fill time may be dominated by the time it takes the fluid to work its way in through the fill port. For fluids of lower viscosity, the fill time may be dominated by the time it takes to fully create the vacuum and evacuate air from the chamber and/or the inner cavity. A variety of factors may influence the length of the fill process, including fluid viscosity, temperature, fill port geometry, gap height, surface tension between the fluid and the cavity surfaces, and/or MEMS geometry. The duration of the fill process may be decreased by using higher than atmospheric pressure to increase the flow rate into the cavity.
The pressure of the environment or the chamber may be increased while the MEMS assembly is completely submerged in fluid or when the MEMS assembly has been removed from the liquid, leaving amounts of fluid sufficient for filling the cavities at the fill ports, or after a sufficient amount of fluid has been placed at the fill ports by other means. The amount of fluid provided at the fill port should be sufficient to fill the inner cavity and to prevent the introduction of air and/or gas into the inner cavity during the fill process. Where the MEMS assembly is submerged in fluid, the pressure due to the fluid alone may cause some fluid to enter the inner cavity before the pressure of the environment is increased. Capillary forces may also contribute to causing fluid to enter the inner cavity. The wafer is cleaned of excess fluid by an appropriate method, for example using a solvent, evaporation or wiping.
Certain alternative, optional embodiments may include several purge cycles with a gas or gasses, for example, carbon dioxide or helium, to help ensure that all of the air is removed from the inner cavity. Purge gases suitable for use in purging the inner cavity may be selected so that the gas or gases have high solubility in the fluid, the gases are inert with respect to the fluid and with respect to other materials present in the inner cavity. Suitable gases may comprise helium or carbon dioxide. In those embodiments in which a purge gas is used, the use of purge gases with high solubility in the fluid helps reduce the formation of residual gas bubbles in the fluid. The fluid used to fill the inner cavity may also be degassed prior to filling. Degassing the fluid may prevent absorbed gas from coming out of solution and nucleating a bubble in the fluid.
In exemplary embodiments, it may be desirable to remove adsorbed fluid, which may comprise water, from the surfaces of the inner cavity. The adsorbed fluid may be removed during the evacuation step. Elevated temperatures may be used to speed up the removal of adsorbed fluid.
In an alternative exemplary embodiment, capillary forces alone may be sufficient to fill the cavity without using a vacuum. The MEMS assembly may comprise a bond ring with a plurality of breaches, for example two breaches.
An amount of adhesive, which may be curable adhesive, is applied to the location of the breach or breaches and cured to complete the containment of the fluid. Suitable adhesives may comprise organic adhesives, such as epoxies, which are thermally or UV cured, solders or glass-based sealants. Suitable sealants may be chemically inert or compatible with the fluid, may have a thermal expansion coefficient compatible for use with other components, may have good adhesion to all surfaces, high reliability, hermeticity. In the exemplary embodiments illustrated in
The height 41 of the inner cavity may be selected such that the volume of the fluid contained within the inner cavity is sufficiently small so that the change in volume upon expansion is sufficiently small to be accommodated by a slight deflections of the cover plate, substrate, bond ring, adhesive seal, thereby reducing the risk of damage to the cover plate.
In an exemplary embodiment of the fluidic MEMS device and method of manufacturing a fluidic MEMS device, a plurality of inner cavities defined on a wafer may be filled with fluid simultaneously. In one exemplary embodiment, a plurality of cover plates may be individually attached to each die location on a single substrate or wafer, as illustrated in
In an exemplary embodiment, a method for filling MEMS assemblies does not require drilling holes in the substrate or silicon wafer, which may result in increased simplicity and cost savings. The fluid containment may be accomplished virtually entirely by hermetic materials, thereby increasing reliability by reducing the risks of vapor loss from and/or air ingress into the inner cavities. The fluid filling process may occur at the wafer level. Many devices are filled at once, yielding a throughput gain.
Attaching the cover plate or plates at the wafer stage may provide protection to the active silicon MEMS structures during the manufacturing process. This may be particularly advantageous for devices where particle sensitivities are high or where the silicon contains delicate structures. Assembling the MEMS device packages or assemblies at the wafer stage may also permit fully functional testing at the wafer level. This may permit faulty parts to be identified at an early stage of the manufacturing process, thereby saving further manufacturing costs. The MEMS device and methods of this disclosure may reduce or eliminate the number of fluid interconnections and/or flexible diaphragms, resulting in fewer manufacturing steps and reduced manufacturing costs.
Providing an inner cavity with sufficiently small volume will reduce the total volumetric expansion of fluid in the fluidic MEMS device, thereby reducing the risk of leakage or other structural damage to the MEMS package due to the fluid expansion. The thermal expansion of the fluid may be entirely accommodated by deflections in the cover plate, substrate and bond ring without fracturing or damaging the packaging materials.
It is understood that the above-described embodiments are merely illustrative of the possible specific embodiments which may represent principles of the present invention. Other arrangements may readily be devised in accordance with these principles by those skilled in the art without departing from the scope and spirit of the invention.
Claims
1. A MEMS package, comprising:
- a substrate with a MEMS structure fabricated on a surface of the substrate;
- a cover plate bonded to the surface of the substrate by a bond ring;
- an inner cavity defined by the substrate, the cover plate and the bond ring; and
- a fill port defined by the substrate, the cover plate and a breach in the bond ring.
2. The MEMS package of claim 1, further comprising:
- fluid sealed within the inner cavity.
3. The MEMS package of claim 2, further comprising:
- a seal disposed in the fill port.
4. The MEMS package of claim 1, wherein the bond ring comprises at least one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
5. The MEMS package of claim 3, wherein the seal comprises at least one of an adhesive, organic adhesive, epoxy, solder or glass-based sealant.
6. The MEMS package of claim 3, wherein the seal comprises a curable adhesive.
7. The MEMS package of claim 1, further comprising:
- bond pads for making electrical connections to the MEMS package arranged in an exposed portion of the substrate.
8. A MEMS package adapted for use in a range of operating temperatures comprising:
- a substrate with MEMS circuitry fabricated on a surface of the substrate;
- a cover plate bonded to the surface of the substrate by a bond ring;
- a fill port defined by the substrate, the cover plate and a breach in the bond ring;
- an inner cavity defined by the substrate, the cover plate and the bond ring; and
- fluid sealed within the inner cavity, the fluid having a coefficient of thermal expansion, wherein the inner cavity has a volume which is small enough so that expansion of the fluid throughout the range of operating temperatures is accommodated by deflections of at least the cover plate, substrate and bond ring.
9. The MEMS package of claim 8, further comprising:
- a seal disposed in the fill port.
10. The MEMS package of claim 8, wherein the bond ring comprises one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
11. The MEMS package of claim 9, wherein the seal comprises at least one of an adhesive, organic adhesive, epoxy, solder or glass-based sealant.
12. The MEMS package of claim 9, wherein the seal comprises a curable adhesive.
13. The MEMS package of claim 8, further comprising:
- bond pads arranged in an exposed portion of the surface of the substrate.
14. A MEMS assembly comprising:
- a substrate with a plurality of MEMS structures fabricated at a plurality of respective die locations on a surface of the substrate;
- a cover plate bonded to the surface of the substrate by a plurality of bond rings;
- a plurality of inner cavities associated with respective die locations, each being defined by the substrate, the cover plate and one of the plurality of bond rings; and
- a plurality of fill ports, each being defined by the substrate, the cover plate and a breach in the one of the plurality of bond rings.
15. The MEMS assembly of claim 14, wherein the cover plate comprises a plurality of openings defining a plurality of exposed portions on the substrate.
16. The MEMS assembly of claim 15, wherein:
- a first group of openings define a first group of exposed portions, each of the first group of exposed portions being adjacent a fill port; and
- a second group of openings define a second group of exposed portions on the substrate.
17. The MEMS assembly of claim 16, wherein the second group of openings comprise slots.
18. The MEMS assembly of claim 16, further comprising:
- a plurality of bond pads on the surface of the substrate arranged in the second group of exposed portions.
19. The MEMS assembly of claim 14, wherein the bond ring comprises one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
20. A MEMS assembly comprising:
- a substrate with a plurality of MEMS structures fabricated at a plurality of respective die locations on a surface of the substrate;
- a plurality of cover plates and a plurality of bond rings, each plate being bonded to the substrate by at least one of the bond rings;
- a plurality of inner cavities associated with respective die locations, each being defined by the substrate, a respective cover plate and a respective bond ring; and
- a plurality of fill ports, each being defined by the substrate, the respective cover plate and a breach in the respective bond ring.
21. The MEMS assembly of claim 20 further comprising:
- bond pads arranged in exposed portions on the substrate.
22. The MEMS assembly of claim 14, wherein the bond rings comprise one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
23. A MEMS package comprising:
- a substrate with a MEMS structure fabricated on a surface of the substrate;
- a cover plate bonded to the surface of the substrate by a bond ring;
- an inner cavity defined by the substrate, the cover plate and the bond ring; and
- a fill port defined by the substrate, the cover plate and a breach in the bond ring, wherein the MEMS assembly was singulated from an assembly comprising a plurality of inner cavities.
24. The MEMS package of claim 23, further comprising:
- fluid sealed within the inner cavity.
25. The MEMS package of claim 24, wherein the inner cavity was filled with the fluid prior to singulating the MEMS assembly from the assembly comprising a plurality of inner cavities.
26. A method of manufacturing a fluidic MEMS package comprising:
- providing a MEMS assembly with a plurality of inner cavities at a plurality of respective die locations on a substrate, each inner cavity being defined by a cover plate, the substrate and a bond ring and being associated with a fill port defined by the cover plate, the substrate and a breach in the bond ring;
- filling the inner cavities with fluid;
- sealing the fluid in the inner cavities;
- singulating a plurality of MEMS packages from the substrate.
27. The method of claim 26, wherein:
- filling the inner cavities with fluid comprises providing a vacuum in the inner cavity, providing an amount of fluid sufficient to fill the inner cavity at the fill port and providing pressure on the fluid to cause the fluid to fill the cavity.
28. The method of claim 26, wherein filling the inner cavities with fluid is performed prior to singulating a plurality of MEMS packages from the substrate.
29. The method of claim 26, wherein the bond ring comprises one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
30. A method of manufacturing a fluidic MEMS package comprising:
- attaching a cover plate with a plurality of openings to a substrate with a plurality of bond rings with breaches such that the cover plate, the substrate and the bond rings define a plurality of respective inner cavities and the cover plate, the substrate and the breaches define a plurality of respective fill ports;
- filling the inner cavities with fluid;
- sealing the fluid in the inner cavities;
- singulating a plurality of MEMS packages from the substrate.
31. The method of claim 30, wherein:
- filling the inner cavities with fluid comprises providing a vacuum in the inner cavity, providing an amount of fluid sufficient to fill the inner cavity at the fill port and providing pressure on the fluid to cause the fluid to fill the cavity.
32. The method of claim 30, wherein filling the inner cavities with fluid is performed prior to singulating a plurality of MEMS packages from the substrate.
33. The method of claim 30, wherein the bond ring comprises one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
34. A method of manufacturing a fluidic MEMS package comprising:
- attaching a plurality of cover plates to a plurality of die locations on a surface of a substrate, the attaching being done with a plurality of respective bond rings, the bond rings having breaches, the respective cover plates, bond rings and the substrate defining a plurality of respective inner cavities and the respective cover plates, breaches and the substrate defining a plurality of respective fill ports;
- filling the inner cavities with fluid;
- sealing the fluid in the inner cavities;
- singulating a plurality of MEMS packages from the substrate.
35. The method of claim 34, wherein:
- filling the inner cavities with fluid comprises providing a vacuum in the inner cavity, providing an amount of fluid sufficient to fill the inner cavity at the fill port and providing pressure on the fluid to cause the fluid to fill the cavity.
36. The method of claim 34, wherein filling the inner cavities with fluid is performed prior to singulating a plurality of MEMS packages from the substrate.
37. The method of claim 34, wherein the bond ring comprises one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
38. A method of filling a fluidic MEMS package comprising:
- providing the MEMS package with an inner cavity and a fill port;
- providing a vacuum in the inner cavity;
- at an entrance to the fill port, providing an amount of fluid at least sufficient to fill the inner cavity; and
- providing pressure on the fluid causing the fluid to fill the inner cavity.
39. The method of claim 38, further comprising:
- purging air from the inner cavity using a purge gas.
40. The method of claim 39, wherein the purge gas has high solubility.
41. The method of claim 39, wherein the purge gas is one of carbon dioxide or helium.
42. The method of claim 38, further comprising:
- providing a vacuum environment around the MEMS package.
43. The method of claim 42, wherein providing a vacuum environment comprises placing the MEMS package in a chamber and evacuating air from the chamber.
44. The method of claim 42, wherein providing a vacuum environment comprises assembling the MEMS package in a vacuum environment.
45. The method of claim 38, wherein providing an amount of fluid comprises submerging the MEMS package in fluid.
46. The method of claim 38, wherein providing an amount of fluid comprises touching a fluid carrier with fluid to the fill port.
47. A method of filling a fluidic MEMS package comprising:
- providing the MEMS package with an inner cavity defined by a cover plate, a substrate and a bond ring;
- providing the MEMS package with a fill port and an evacuate port, each being defined by the cover plate, the substrate and a respective one of a plurality of breaches in the bond ring;
- at an entrance to the fill port, providing an amount of fluid at least sufficient to fill the inner cavity; and
- selecting the fluid, substrate, bond ring and cover plate such that capillary forces draw the fluid into the inner cavity causing air within the inner cavity to evacuate through the evacuate port.
48. A spatial light modulator, comprising:
- a substrate with a MEMS mirror array fabricated on a surface of the substrate;
- a cover plate bonded to the surface of the substrate by a bond ring;
- an inner cavity defined by the substrate, the cover plate and the bond ring; and
- a fill port defined by the substrate, the cover plate and a breach in the bond ring.
49. The spatial light modulator of claim 48, further comprising:
- fluid sealed within the inner cavity.
50. The spatial light modulator of claim 49, further comprising:
- a seal disposed in the fill port.
51. The spatial light modulator of claim 48, wherein the bond ring comprises at least one of a glass frit, adhesive, eutectic solder, solder mask material, anodic bond, covalent bond, laser weld or Sol-gel material.
52. The spatial light modulator of claim 50, wherein the seal comprises at least one of an adhesive, organic adhesive, epoxy, solder or glass-based sealant.
53. A method of assembling a spatial light modulator comprising:
- providing the spatial light modulator with a MEMS mirror array fabricated on a substrate and in a package comprising an inner cavity and a fill port;
- providing a vacuum in the inner cavity;
- at an entrance to the fill port, providing an amount of fluid at least sufficient to fill the inner cavity; and
- providing pressure on the fluid causing the fluid to fill the inner cavity.
Type: Application
Filed: Jul 15, 2003
Publication Date: Jan 20, 2005
Inventors: Mark Smith (Corvallis, OR), William Boucher (Corvallis, OR), Charles Haluzak (Corvallis, OR)
Application Number: 10/620,968