Low-friction moving interfaces in micromachines and nanomachines

Abstract

A low-friction device having a moving interface comprising first and second members. Each of the members has a maximum dimension of about 100 μm or less between any two points. At least the first member is formed of diamond and the first and second members are in sliding contact or meshing contact.

Description

BACKGROUND OF THE INVENTION

This application relates generally to micromachines and nanomachines and more specifically to devices providing low-friction rotational and translational interfaces for micromachine and nanomachine contacts.

Micromachines and nanomachines are poised to solve mechanical problems at the molecular and atomic level. Such machines may solve problems in environments were other devices, such as electronic devices, fail. For example, microscale mechanical memories may be of use in environments, such as space, in which semiconductor based devices have high fault rates due to high-energy cosmic radiation. Further, microscale mechanical machines may be of surgical use, reaching areas of the body not otherwise accessible or manipulable by traditional surgical tools and techniques.

At small scale, for example in the hundreds and tens of micron range and below, mechanical elements exhibit problematic behavior that either 1) does not arise or 2) is of little consequence at relatively larger scale. For example, meshed gears in macroscale machines do not tend to exhibit problems due to stiction, which is the sticking and fusing of different elements or portions of elements into a union. However, at smaller scale, such problems can arise.

Lithographic techniques have been deployed to make relatively small mechanical devices, for example, relatively small gears etched from silicon wafers. However, such relatively small silicon gears have a tendency to stick and fuse to each other. If such gears are in mechanical motion when stiction between the gears occurs, the gears may gall each other or worse tear each other apart.

Lubricants have been applied to relatively small mechanical interfaces in an attempt to limit friction, stiction, and galling. However, like solid bits of matter of relatively small scale, liquids at relatively small scale also exhibit problematic behavior that would be of little consequence at relatively larger scale. For example, surface tension causes relatively small quantities of liquid to form small droplets that tend not to flow across a surface, thus limiting a lubricant's effectiveness.

Consequently, new microscale and nanoscale devices are sought which provide for improved performance.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention low-friction moving interfaces in micromachines and nanomachines include low-friction sliding interfaces. In one aspect of the invention, a device has first and second members in sliding contact. Each the members has a maximum dimension of about 100 μm or less between any two points and one of the first and second members is formed of diamond. In another aspect of the invention, a device has a toothed member and a tooth-engaging member in meshing contact. Both the toothed member and tooth-engaging member have dimension of about 100 μm or less between any two points and one of the toothed member and tooth-engaging member is formed of diamond.

A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the temperature of a diamond-silicon dynamic interface for a relatively small diamond according to a mathematical model of the interface;

FIG. 2 is an overall perspective view of a mechanical device having a low-friction moving interface according to an embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view of another mechanical device having a low-friction moving interface according to another embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view of another mechanical device having a low-friction moving interface according to another embodiment of the present invention;

FIG. 5 is a schematic cross-sectional view of another mechanical device having a low-friction moving interface according to another embodiment of the present invention; and

FIG. 6 is an overall perspective view of another mechanical device having low-friction moving interfaces according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Introduction

The following description sets forth embodiments of low-friction moving interfaces in micromachines and nanomachines according to the invention. Embodiments of the invention can be applied to sliding and/or meshing mechanical contacts.

Diamond is a very slippery crystal. Diamond in mechanical contact with crystals such as diamond itself or silicon exhibits relatively low-frictional heating and has a tendency not to fuse with itself or silicon. Further, the flash temperature of diamond-silicon interfaces is relatively high. The flash temperature is that at which bodies in frictional contact tend to gall each other. The flash temperature of various interfaces can be estimated by taking into account, for example, the speed at which surfaces move with respect to each other and the forces at the interface. For example, see “Tribology and Mechanics of Magnetic Storage Devices,” publisher Springer, pp. 366-411, by Bhushan in which a general formalism is developed to calculate flash temperatures.

FIG. 1 is a graph of a mathematical modeling of the temperature of a dynamic diamond-silicon interface at various interface forces and velocities. The diamond-silicon interface modeled is that of a diamond rod having a flat circular end sliding across a planar piece of silicon. The diameter of the flat circular end of the rod is about 50 nm at the interface. As indicated by the graph, the temperature of the diamond and silicon forming the interface rises from frictional heating as the force and/or velocity of the diamond and silicon increase. Pinnacle 110 at the top right of the graph represent the flash temperature of the interface. As can be seen, the flash temperature, is between 900° C. and 1000° C. The interface force of the diamond on silicon at the flash temperature is between 275 millinewtons and 300 millinewtons and the velocity of the surfaces relative to each other is about 500 millimeter/second. Forces and velocities in these ranges are relatively high indicating the general durability of the interface. While the graph represent only a single geometric interface of diamond and silicon in frictional contract, an impetus is created for the manufacture of diamond-silicon mechanical interfaces of relatively small scale.

Described below are various embodiments where two members engage each other in different ways, referred to as sliding contact and meshing contact. These types of interaction will be defined below in connection with the specific embodiments. In these embodiments, both of the members may be diamond or one of the members may be diamond with the other being, for example, silicon, quartz, a III-V material such as gallium arsenide, and the like. While substances such as silicon and gallium arsenide are of limited mechanical use at macroscale dimensions (e.g. greater than 1 millimeter) due to their fragility, such substances suffer less from fragility at relatively smaller scales, (e.g. 100 μm). At such small scales, each of the aforementioned materials in such contact with diamond provides for devices that have relatively low friction and are relatively mechanically sound. Further, each of the aforementioned materials has a relatively high flash temperature in sliding contact with diamond, for example, as high as 900° C. and above. Thus at normal operating temperature, (e.g., 300° C.) such materials tend not to gall each other.

Embodiments Having Sliding Contact

A “sliding contact” is defined herein as a first member that is in dynamic frictional contact with a second member, such that the first member and second member have surfaces that are in smooth continuous contact.

FIG. 2 is an overall perspective view of a mechanical device 200 having a low-friction moving interface 210 according to an embodiment of the present invention. The mechanical device includes a first member 215 that has a circular aperture 222. Portions of the aperture are indicated in phantom view. The aperture has a surface denoted by reference numeral 225. The mechanical device includes a second member 250 in the shape of a spindle having a rounded surface 252, portions of which are shown in phantom. As shown, the second member is fitted into the aperture. Low-friction moving interface 210 is identified as the areas at which the aperture surface and the second member are in sliding contact. The first member and second member may have a rotational degree of motion with respect to each other (as indicated by double-headed arrow 262), a translational degree of motion with respect to each other (as indicated by double-headed arrow 268), or both.

First member 215 and second member 250 may each be a single or multicrystalline structure. For example, first member 215 may be a single diamond crystal or a polycrystalline diamond.

The first and second members may be fabricated using a variety of techniques. For example, a member comprising silicon may be etched from a silicon wafer using known lithographic techniques or may be cut from a silicon wafer using cutting and sweeping techniques discussed in the above referenced U.S. patent application for “Nanomachining Method and Apparatus,” Attorney Docket No. 020921-001430US. Alternatively, a member comprising silicon may be formed by lapping techniques such as those discussed in the above referenced U.S. patent application for “Methods and Apparatus for Nanolapping,” Attorney Docket No. 020921-001450US. Each of these fabrication techniques is similarly applicable to diamond members, quartz members, and the like. Those of skill in the art will know of other useful fabrication techniques.

First member 215 may be coated into the aperture of another device such as a disk. A first member so positioned is commonly referred to as a bushing. For example, a first member comprising diamond may be coated into an aperture in a silicon disk. A first member so positioned may be formed, for example, by first forming a diamond-like carbon layer in the aperture and second growing a diamond onto the diamond-like carbon layer. Diamond-like carbon may be coated into an aperture via a vacuum arc process or via ion-beam techniques and grown using plasma-enhanced chemical vapor deposition. Those of skill in the art will know other useful coating processes for diamond-like carbon. Diamond can also subsequently be grown onto the diamond-like carbon in a diamond-anvil cell or other high-pressure device.

According to a specific embodiment of the invention, each of the first and second members has a maximum dimension of about 100 μm or less between any two points. According to another embodiment, each of the first and second members has a maximum dimension of about 5 μm or less between any two points.

FIG. 3 is a schematic cross-sectional view of a mechanical device 300 having a low-friction moving interface 310 according to another embodiment of the present invention. The mechanical device includes a first member 315 that has a round socket 322, which is defined by surface 326. Mechanical device 300 includes a second member 350 that has an arm portion 352 and a ball end 354. The ball end of the second member is in sliding contact with surface 326. Such a configuration is commonly referred to as a ball-and-socket joint.

For consistency and clarity, a particular coordinate system will be shown and referred to. FIG. 3 is considered to lie in the x-y plane, and the z-axis will be considered to extend out of the page. In accordance with standard symbology, an axis extending out of the page will be denoted by a dot in a circle while an axis extending into the page will be denoted by a + in a circle. The cross-sectional view of FIG. 3 thus shows mechanical device 300 extending laterally in the x-y plane. In most instances, references to direction and orientation that mention an axis (e.g., the x-axis) or a plane (e.g., the x-y plane) should be considered to include lines parallel to that axis, or planes parallel to that plane

First and second members 315 and 350 may have a variety of rotational degrees of motion with respect to each other, for example, member 350 may rotate relative to member 315 about the z-axis, the x-axis, or any axis laying between the z and x-axes.

FIG. 4 is an overall perspective view of a mechanical device 400 having low-friction moving interfaces 410 according to an embodiment of the present invention. The mechanical device includes a first member 415 in the shape of a plate, and a second member 420 having a slot 422. A portion of first member 415 is inserted into slot 422. The first member spins such that portions of its surfaces 423 and 425 are in sliding contact with surfaces 427 and 429, respectively.

According to a specific embodiment of the invention, each of the members has a maximum dimension of about 100 μm or less between any two points. According to another embodiment, each of the members each has a maximum dimension of about 5 μm or less between any two points. First and second members 410 and 420 may be fabricated by a variety of processes such as those described above for the fabrication of mechanical device 200 shown in FIG. 2.

Mechanical devices having components (e.g., diamond plate and silicon slotted member) providing low-friction translational contact are deployable for a variety of tasks. For example, mechanical device 400 may be of use as a fluid pump. The low-friction moving interface can drag a fluid between ends of the slot, thus providing pumping. Further, such a device, made of say diamond and silicon or diamond and diamond, provides for tremendous translational rates. For example, a diamond plate in a silicon slot of the dimension discussed above may be turned at millions or more revolutions per second prior to reaching the flash temperature.

Each of devices 200, 300, and 400 may be bearing type devices, wherein one of the members provide support, guidance, and reduces the friction of motion between the other member and moving or fixed machine parts (not pictured in FIG. 2, 3, or 4). Other moving or fixed machine parts may include, for example, a housing (e.g., a journal box) containing one of the devices, or additional members in sliding contact devices 200, 300, and 400.

Embodiments Having Meshing Contact

A “meshing contact” is defined herein as a “toothed member” being in frictional contact with a “tooth-engaging member,” such that the toothed member meshes with the tooth-engaging member to transmit motion or to change direction or speed.

FIG. 5 is a schematic cross-sectional view of a mechanical device 500 having a low-friction moving interface 510 according to another embodiment of the present invention. The mechanical device includes a gear 515 (an example of a toothed member) that has a plurality of gear teeth 520 and includes a rack 550 (an example of a tooth-engaging member) that has a plurality of gear teeth 555. As shown, gear teeth 520 and gear teeth 555 are in meshing contact. Mechanical device 500 provides for two types of motion: (a) the rack may be moved laterally along the x-axis causing the gear to rotate about the z-axis, or (b) the gear may be rotated causing the rack to be translated. Translation device 560 coupled to rack 550 may provide such translations of the rack. Translation device 560 may include a variety of devices, such as, piezoelectric transducers, thermal expansion/contraction devices, mechanical actuators, and the like. Further, such translation devices may be coupled to both ends of the rack for further control.

While rack 550 is shown to have teeth that extend beyond the region where the gear and rack mesh, the teeth may extend a lesser amount, for example, the teeth may be limited to the region where the gear and rack mesh.

According to a specific embodiment of the invention, each of the gear and rack has a maximum dimension of about 100 μm or less between any two points. According to another embodiment, each of the gear and rack has a maximum dimension of about 5 μm or less between any two points. Gears and racks made of materials such as those discussed may be fabricated by a variety of processes such as those described above for the fabrication of mechanical device 200 shown in FIG. 2.

FIG. 6 is a schematic cross-sectional view of a mechanical device 600 having a low-friction moving interface 610 according to another embodiment of the present invention. The mechanical device includes a gear 615 (an example of a toothed member) that has a plurality of gear teeth 620 and includes a worm gear 650 (an example of a tooth-engaging member) that has a thread 655. As shown, gear teeth 620 and thread 655 are in meshing contact. Mechanical device 600 provides for two types of motion: (a) worm gear 650 may be rotated about the x-axis causing gear 615 to rotate about the z-axis, or (b) gear 615 may be rotated about the z-axis causing the worm gear to rotate about the x-axis.

Both the gear and/or rack shown in FIG. 5 and the gear and/or worm gear shown in FIG. 6 may be coupled to a devices 200, 300, or 400 shown in FIGS. 2, 3, and 4. For example, the second member 252 (FIG. 2) having a spindle shape may be coupled to the center of rotation of gear 515 and/or worm gear 550. Both gear 610 and worm gear 650 have similar maximum dimension as those of gear 510 and rack 550 shown in FIG. 5 and can be fabricated by similar methods.

CONCLUSION

While the above is a complete description of specific embodiments of the invention, various modifications, alternative constructions, and equivalents by be used. For example, diamond-silicon, diamond-diamond, and the like may be variously configured while still providing low stiction, low galling, and relatively high flash temperature devices. For example, device 200 may have a first member 215 that has a trench instead of an aperture in which the second member is in sliding contact. Further, diamond-silicon, diamond-diamond, and the like meshing interfaces may include, for example, gear on gear interfaces in addition to gear on rack/worm gear interfaces. Therefore, the above description should not be taken as limiting the scope of the invention a defined by the claims

Claims

1. A low-friction device having a moving interface, the low-friction device comprising first and second members wherein: each of the members has a maximum dimension of about 100 μm or less between any two points; at least the first member is formed of diamond; and the first and second members are in sliding contact.