# Patent

## Title
Micro-machine and a method of powering a micro-machine

## Abstract

A rotatable micro-machine is comprised of a solvent reservoir, a porous evaporation region and a channel connecting the solvent reservoir to the evaporation region. The evaporation region may be constructed of capillary paths that enable a capillary action which pulls solvent from the channel so as to enable a flow of solvent from the reservoir to the evaporation region through the channel. A rotatable member has portions in communication with the channel so as to be rotated by the flow. In one embodiment, the rotatable member may be a component of a micro-turbine generator. A system may be comprised of the rotatable micro-machine in combination with at least one electrical circuit. The porous region may be positioned to receive heat from the circuit. That may be accomplished in several ways; the evaporation region may be formed adjacent to the circuit, the evaporation region may be fabricated on the side of a die that is opposite of the side of the die carrying the circuit, or the reservoir, micro-turbine generator, evaporation region, and channel may be fabricated on one die and the circuit fabricated on another die. The two dies may then be connected to one another by a heat transferring adhesive with the evaporation region proximate to the circuit. Methods of operating a rotatable micro-machine are also disclosed. Because of the rules governing abstracts, this abstract should not be used in construing the claims.

## Background
BACKGROUND
The present disclosure is directed broadly to micro-electromechanical systems (MEMS) devices and, more particularly, to rotating devices built using MEMS technology.
MEMS technology borrows heavily from the field of solid state electronics manufacturing. Using the same or similar steps used by electronics manufacturers, gears with teeth measured in the tens of microns have been fabricated. The ability to fabricate gears and other moving parts on such small scales has led to the creation of micro-engines and micro-turbines.
The invention disclosed in U.S. Pat. No. 5,932,940 provides a micro-gas turbine engine and associated micro-componentry. The engine components, including, e.g., a compressor, a diffuser having diffuser vanes, a combustion chamber, turbine guide vanes, and a turbine are each manufactured by, e.g., micro-fabrication techniques, of a structural material common to all of the elements, e.g., a micro-electronic material such as silicon or silicon carbide. Vapor deposition techniques, as well as bulk wafer etching techniques, can be employed to produce the engine. The engine includes a rotor having a shaft with a substantially untapered compressor disk on a first end, defining a centrifugal compressor, and a substantially untapered turbine disk on the opposite end, defining a radial inflow turbine. The rotor is preferably formed of a material characterized by a strength-to-density ratio that enables a rotor speed of at least about 500,000 rotations per minute. An annular, axial-flow combustion chamber is provided that is located axially between the compressor and turbine disks and that has a ratio of annular height to axial length of at least about 0.5. The micro-gas turbine engine can be configured with an integral micro-generator as a source of electrical power, and can be employed for a wide range of power, propulsion, and thermodynamic cycle applications.
Problems associated with such small devices include controlling the supply of fuel and controlling parameters such as temperature and pressure needed to insure proper combustion, among others.
BRIEF SUMMARY
One aspect of the present disclosure is directed to a rotatable micro-machine comprising a solvent reservoir, a porous evaporation region and a channel connecting the solvent reservoir to the evaporation region. The evaporation region may be constructed of capillary paths that enable a capillary action which pulls solvent from the channel so as to enable a flow of solvent from the reservoir to the evaporation region through the channel. A rotatable member has portions in communication with the channel so as to be rotated by the flow. In one embodiment, the rotatable member may be a component of a micro-turbine generator.
Another aspect of the present disclosure is directed to a system comprising at least one electrical circuit, a solvent reservoir, an evaporation region and a channel connecting the solvent reservoir to the evaporation region. The evaporation region may be constructed of capillary paths that enable a capillary action which pulls solvent from the channel so as to enable a flow of solvent from the reservoir to the evaporation region through the channel. A micro-generator is in communication with the channel so as to be rotated by the flow. A controller is responsive to the generator for supplying power to the circuit. The porous region may be positioned to receive heat from the circuit. That may be accomplished in several ways; the evaporation region may be formed adjacent to the circuit, the evaporation region may be fabricated on the side of the die that is opposite of the side of the die carrying the circuit, or the reservoir, micro-turbine generator, evaporation region, and channel may be fabricated on one die and the circuit fabricated on another die. The two dies may then be connected to one another by a heat transferring adhesive with the evaporation region proximate to the circuit.
A method of operating a rotatable micro-machine is also disclosed. The method may comprise powering a micro-machine with a flow between a reservoir and an evaporation region produced by capillary forces. Additionally, heat may be applied to the evaporation region.
A method of operating a system is also disclosed. The method may comprise powering a micro-turbine generator with a flow between a reservoir and an evaporation region produced by capillary forces and supplying power produced by the micro-turbine generator to a circuit. The method may additionally comprise operating the micro-turbine generator as a pump until the circuit begins producing heat.



BRIEF DESCRIPTION OF THE DRAWINGS
For the present invention to be easily understood and readily practiced, the present invention will now be described, for purposes of illustration and not limitation, in conjunction with the following figures, wherein:
FIG. 1 is a block diagram illustrating an embodiment of the present invention; and
FIG. 2 is a block diagram illustrating another embodiment of the present invention.



DETAILED DESCRIPTION
The present disclosure is directed to a micro or nano-machine and a method of powering such a machine using capillary fluid forces. As shown in FIG. 1, the structure involves a rotatable micro-machine 10 which may range from a single rotatable micro-gear to a complicated device such as a micro-turbine generator. It should be noted that process steps for fabricating such devices are not disclosed herein as such steps are known in the art as shown by, for example, the aforementioned U.S. Pat. No. 5,932,940, the entirety of which is hereby incorporated by reference.
On one side of the micro-machine 10 is an evaporation region 12 which may be exposed to the ambient atmosphere. The evaporation region 12 may take the form of a porous region comprised of a plurality of capillary paths. On the other side of the micro-machine 10 is a solvent reservoir 14, which may have an input area (not shown) open to ambient. The surface area of the evaporation region 12 exposed to ambient is larger than the surface area of the input area of the reservoir, e.g. by a margin of two to one. The solvent is chosen to have a high vapor pressure and thus a large evaporation rate. Connecting the solvent reservoir 14 to the evaporation region 12 is a channel 16. Portions of the micro-machine 10, such as vanes, blades, or the like (shown in FIG. 2), are in communication with the channel 16. A user interface 18 may be provided for controlling a device, e.g. a valve (shown in FIG. 2), for regulating flow within channel 16.
As the solvent evaporates from a surface of the evaporation region 12 exposed to ambient, the solvent remaining within the evaporation region 12 will be drawn to those locations from which the solvent has evaporated as a result of capillary forces within the evaporation region 12. The redistribution of solvent will cause solvent to be pulled from the channel 16. The solvent pulled from channel 16 will be replaced by solvent from the reservoir 14 thus causing a flow through channel 16 which will drive or power the micro-machine 10. The micro-machine can be used to drive other parts of a structure or generate small amounts of electrical current by causing a magnetic part to move past a wire. The evaporation region 12 will cool, which cooling may be useful elsewhere in the system as will be described below in conjunction with FIG. 2.
The evaporation region 12 may take the form, as noted above, of a porous region. Such a porous region may be made by lithographically opening a pattern in a layer of resist where the substrate is to be made porous. The porous evaporation region 12 may be, for example, 100 μm on a side. The substrate may be formed of silicon, which is then implanted with another material in the area opened in the layer of resist. The resist is stripped and the substrate is anodized using known techniques to form the region 12. See, for example, U.S. 2003/0170916 A1 published Sep. 11, 2003 and entitled Methods for Fabricating Separation Apparatus, the entirety of which is hereby incorporated by reference. Alternatively, a recess of the size desired for the porous evaporation region 12 may be formed in the substrate, and the recess filled with a high surface area material like hemispherical grain silicon (HSG). The precise method used to form the porous evaporation region 12 is not an important aspect of the present invention.
Turning now to FIG. 2, another embodiment of the present invention is disclosed. In FIG. 2, like components carry the same reference numbers as in FIG. 1. FIG. 2 illustrates a system 20 fabricated on die 22. A micro-machine, in this case a micro-turbine generator 24, is provided so as to be driven by the flow within channel 16. The power generated by the micro-turbine generator 24 is input to a controller 26.
Die 20 also carries at least one electrical circuit 28. The electrical circuit may be a part of a more complicated device such as a memory device, receiver, transmitter, camera, phone, PDA, etc. The controller 26 provides power to the electrical circuit 28. The evaporation region 12 may be, but need not be depending on the solvent, positioned so as to absorb heat produced by the electrical circuit 28. Finally, a valve 30 may be provided within channel 16 with the valve ultimately responsive to user input.
Positioning the evaporation region 12 and/or positioning the circuit 28 so that the evaporation region 12 may absorb heat from circuit 28 may be accomplished in several ways. For example, the evaporation region 12 may be formed adjacent to the circuit 28, the evaporation region 12 may be fabricated on the side of the die 20 that is opposite of the side of the die carrying the circuit 28, or the reservoir 14, micro-turbine generator 24, evaporation region 12, and channel 16 may be fabricated on one die and the circuit 28 fabricated on another die. The two dies may then be connected to one another by a heat transferring adhesive with the evaporation region 12 proximate to the circuit 28.
Several methods of operating the system 20 may be implement by proper selection of a solvent. For example, if a solvent is selected which will evaporate without the addition of any heat from circuit 28, then all that need be done to begin powering micro-turbine generator 24 is to open the valve 30. Alternatively, if the solvent is chosen such that heat is needed before evaporation occurs, then a battery (not shown) or other power source will be needed to initially power circuit 28. Power from the battery or other source may also be input to the micro-turbine generator 24 through the controller 26 so that the micro-turbine generator 24 initially acts as a pump. After the circuit 28 begins to produce heat, the evaporation and resulting capillary flow will power the micro-turbine generator 24 such the battery or other power source may be disconnected from both the controller 26 and the circuit 28.
While the present invention has been described in connection with preferred embodiments thereof, those of ordinary skill in the art will recognize that many modifications and variations are possible. The present invention is intended to be limited only by the following claims and not by the foregoing description which is intended to set forth the presently preferred embodiments.

## Claims

1. A rotatable micro-machine, comprising:
a solvent reservoir having an input area exposed to ambient;
a porous evaporation region having a surface area exposed to ambient that is larger than said input area of said reservoir;
a channel connecting said solvent reservoir to said evaporation region, said evaporation region enabling a capillary action which pulls solvent from said channel so as to enable a flow of solvent from said reservoir to said evaporation region through said channel; and
a rotatable member having portions in communication with said channel so as to be rotated by said flow.

2. The micro-machine of claim 1 additionally comprising a valve positioned within said channel so as to be able to regulate flow within said channel.

3. The micro-machine of claim 1 wherein said reservoir, evaporation region, channel and rotatable member are fabricated on a die.

4. A micro-turbine generator, comprising:
a solvent reservoir having an input area exposed to ambient;
an evaporation region having a surface area exposed to ambient that is larger than said input area of said reservoir;
a channel connecting said solvent reservoir to said evaporation region, said evaporation region enabling a capillary action which pulls solvent from said channel so as to enable a flow of solvent from said reservoir to said evaporation region through said channel;
a generator in communication with said channel so as to be rotated by said flow; and
a controller responsive to said generator.

5. The micro-turbine generator of claim 4 additionally comprising a valve positioned within said channel so as to be able to regulate flow within said channel.

6. The micro-turbine generator of claim 4 wherein said controller is configured to provide power to or receive power from said generator.

7. The micro-turbine generator of claim 4 wherein said reservoir, evaporation region, channel and generator are fabricated on a die.

8. A system, comprising:
at least one electrical circuit;
a solvent reservoir having an input area exposed to ambient;
an evaporation region having a surface area exposed to ambient that is larger than said input area of said reservoir;
a channel connecting said solvent reservoir to said evaporation region, said evaporation region enabling a capillary action which pulls solvent from said channel so as to enable a flow of solvent from said reservoir to said evaporation region through said channel;
a micro-generator in communication with said channel so as to be rotated by said flow; and
a controller responsive to said generator for supplying power to said circuit.

9. The system of claim 8 wherein said porous region is positioned to receive heat from said circuit.

10. The system of claim 8 additionally comprising a valve positioned within said channel so as to be able to regulate flow within said channel.

11. The system of claim 8 wherein said controller is configured to provide power to or receive power from said generator.

12. The system of claim 8 wherein said solvent reservoir, evaporation region, channel and micro-generator are carried on a first die and said circuit is carried on a second die, said first and second dies being connected such that said evaporation region is proximate to said circuit.

13. The system of claim 8 wherein said solvent reservoir, evaporation region, channel and micro-generator are carried on a first side of a die and said circuit is carried on a second side of said die such that said evaporation region is proximate to said circuit.

14. A method of operating a rotatable micro-machine, comprising:
powering said micro-machine with a flow produced by capillary forces between a reservoir having an input area exposed to ambient and an evaporation region having a surface area exposed to ambient that is larger than said input area of said reservoir.

15. The method of claim 14 additionally comprising applying heat to said evaporation region.

16. The method of claim 14 wherein said micro-machine includes a micro-turbine generator, said method additionally comprising:
powering said micro-turbine generator with said flow; and
supplying power produced by said micro-turbine generator to a circuit.

17. The method of claim 16 additionally comprising providing heat produced by said circuit to said evaporation region.

18. The method of claim 16 additionally comprising operating said micro-turbine generator as a pump until said circuit begins producing heat.