Patent Grant
7456482
This invention relates generally to electronic switching and, more particularly, relates to a nanotube-based electronic switch having small dimensions and low switching friction and switching power requirements.
The increasing miniaturization of computer digital circuitry and other components has enabled a corresponding increase in computer power and decrease in the cost of creating powerful computing devices. However, certain critical components have not progressed as rapidly with respect to miniaturization, and the effects of this lag are beginning to limit the overall miniaturization of computing devices. For example, electronic switches (as opposed to purely solid state electrical switches such as transistors) are inherently mechanical in nature, and as such rely on forming and shaping steps that are not critical with respect to purely electrical systems.
Before discussing microelectromechanical switch technology, a brief discussion of solid state switch technologies will be presented. Typically, a solid-state switch comprises a transistor element such as a FET (Field Effect Transistor), MOSFET (Metal Oxide Semiconductor Field Effect Transistor), JFET (Junction Field Effect Transistor), MESFET (Metal Semiconductor Field Effect Transistor), etc. Typically, transistor devices will operate in an essentially linear manner over only a small gate voltage region, outside of which the device is either off or saturated. The off and saturated states are useful for switching applications.
There are a number of difficulties associated with the production and use of solid-state switches such as those discussed above. Drawbacks include high insertion losses, high contact resistance, high switching capacitance, signal and gate cross-coupling, high-frequency electronic noise, reliance on semiconductor properties (with attendant requirements for heavy fabrication process control), and out diffusion difficulties. For these reasons, microelectromechanical devices may be more suitable in certain miniature switch applications.
An example of such a switch is the microelectromechanical switch described in U.S. Published Application 2003/0122640 to Deligianni et al. The device described in that application comprises a movable part, two pairs of contacts, and actuators. The movable part is laterally or pivotally deflected by the actuators to make or break connections across pairs of contacts. While the device is said to solve certain shortcomings inherent in the production and use of solid state switches and some microelectromechanical switches, many problems remain. For example, precise fabrication control with respect to pivots, brackets, etc. is required to ensure that the actuator is movable within the required bounds but that it does not stray a prohibitive amount from its intended range and path of travel. Moreover, the quality of the ohmic contact produced depends upon the precision with which the actuator moves, and hence the precision with which the various mating parts are fabricated. Moreover, the actuator experiences flexion stresses, which, while perhaps less severe than experienced in prior designs, may still cause fatigue with long-term usage.
For these reasons and others, a microelectromechanical switch is needed that eliminates the drawbacks of former solid state switches and microelectromechanical switches alike.
Embodiments of the invention provide a new microelectromechanical switch that solves the problems inherent in prior systems. The new microelectromechanical switch comprises, in an embodiment of the invention, a switch rod having switch contacts at each end of the rod. The switch rod is free to travel linearly along its primary axis between two limit positions. A hollow bearing rod having essentially the same primary axis as that of the switch rod is sized and positioned to surround the switch rod to form a bearing and to constrain the switch rod to motion along its primary axis. First and second relay contacts associated with the respective first and second switch contacts are situated near respective ends of the switch rod and are operable to move the switch rod along its primary axis. When the switch rod is at one end of its travel, the first switch contact conductively bridges a first switch terminal to a second switch terminal. When the switch rod is in at the opposite end of its travel, the first switch contact does not conductively bridge the first switch terminal to the second switch terminal and the circuit between the first and second switch terminals is thus open.
The mechanism for moving the switch rod is not critical; however in an embodiment of the invention the relay contacts are tailored to apply an electrostatic deflection field. The deflection field in turn causes the switch rod to move between the first and second limit positions. In a further embodiment of the invention, the switch element and the hollow bearing rod each comprise a nanotube comprised substantially of carbon atoms.
In yet a further embodiment of the invention, an insulator element is situated between the second relay contact and the second switch contact, so that when the switch rod is in the second limit position (i.e. the switch assembly is in an open state), the second switch contact is in contact with the insulator element and is not in conductive contact with the second relay contact. The switch described with respect to the exemplary embodiment herein preferably, although not necessarily, comprises a frame element holding each of the relay contacts and the hollow bearing rod in a fixed spatial relation with respect one another, and may also comprise an insulator portion interposed between the hollow bearing rod and the first relay contact.
In alternative embodiments of the invention, one of the relay contacts may be omitted. In addition, in a further embodiment of the invention, one or more relay contacts are situated such that insulation is not needed to shield the contact(s). In yet another embodiment of the invention, wherein the switch rod and bearing tube each comprise a nanotube, actuation of the switch rod in one direction, such as to open the switch, is by way of an intertube interaction between the switch rod and the bearing tube.
Some of the benefits attainable by the exemplary embodiment of the switch described herein are that it has low insertion loss, high immunity to electronic switching noise, and has low switching power. Due to the extremely small size of the components, especially when carbon nanotubes are employed as one or both of the bearing and the switch rod, the switch is significantly miniaturized and is useful for many applications requiring small low-loss switches.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying FIGS.
While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:
Turning to the drawings, wherein like reference numerals refer to like elements, the structure of a switch assembly according to various embodiments of the invention will be discussed, after which the fabrication of various switch components according to embodiments of the invention will be addressed.
The first and second terminals or switch contacts 107, 109 are preferably fabricated of a conductive material such as, for purposes of illustration and not limitation, heavily doped silicon or metal as will be appreciated by those of skill in the art. The substrate 111 is preferably electrically nonconductive, or insulating, such that it does not provide a conduction path between the first and second terminals 107, 109. Exemplary materials for use as the substrate 111 include silicon dioxide, silicon nitride, undoped crystalline silicon, amorphous silicon, or other inexpensive or convenient material. The substrate 111 may be comprised of multiple layers of diverse materials or a single layer. If the substrate 111 is comprised of multiple layers, at least the top layer typically should be nonconductive as discussed above. The contacts 107 and 109 may optionally be coated with a hard electrically conductive material such as doped diamond, tungsten, platinum, etc. for the area on the contact that will be subject to mechanical wear. This may be useful in enhancing the mechanical reliability of the device.
A pull-in contact 113 is positioned between the first and second terminals 107, 109 and is preferably fabricated of a conductive material such as, for example, heavily doped silicon, metal, etc. In order to electrically isolate the pull-in contact 113 from the other components of the switch 101, the pull-in contact 113 is encased on a first side by the substrate 111 and on its remaining sides by an insulation layer 115. Preferably, the top surface of the insulating layer 115 is level with or lower than the top surfaces of the first and second terminals 107, 109. This is so that an essentially planar or linear contact, to be discussed below, can bridge the first and second terminals 107, 109 without being blocked by the top surface of the insulating layer 115. In an embodiment of the invention, the layer 115 is omitted, and the contact 113 is situated so as to avoid contact with the switch element 117, to be discussed below. One such configuration is illustrated by the switch 801 shown in
In an embodiment of the invention, the switch 101 further comprises a pull-back contact 121. The pull-back contact 121 is preferably electrically conductive as with the pull-in contact 113, and may be, but is not required to be, made of the same material as the pull-in contact 113. The pull-back contact 121 is preferably electrically isolated from the movable components of the switch, discussed hereinafter, by an insulation layer 123 which may be fixed to frame 103 although such is not explicitly shown. As with the pull-in insulation layer 115, the pull-back insulation layer 123 may be fabricated of any convenient insulating material, such as among other things silicon nitride, silicon oxide, etc. Moreover, in an embodiment of the invention, the insulation layer 123 may be omitted, as illustrated by the switch 801 shown in
The switch 101 further comprises in an embodiment of the invention a movable switch element 117 and a bearing element 119. The bearing element 119 is fixed within the frame 103 to provide a guide for the switch element 117. In an embodiment of the invention to be discussed later, the frame 103 itself serves as the bearing or guide for the switch element. In overview, the switch element 117 is movable along its major axis such that at one end of its travel it bridges the first and second terminals 107, 109 and at the other end of its travel it contacts the pull-back insulation layer 123 that is situated between the element 117 and the pull-back contact 121.
Note that in an embodiment of the invention, only one of contacts 113 and 121 is used. In particular, a single contact may be used to apply both a repulsive and an attractive force for opening and closing the switch. Thus, for example, contact 113 may actuate the switch element 117 in both directions by applying voltages of opposite polarities, without the use of a contact such as contact 121.
The operation of the switch will be detailed below, but first a brief discussion of several types of switch elements and bearings will be given.
Nanotubes may be fabricated in a controlled manner via any of a number of different processes. One technique usable for the controlled fabrication of nanotubes is the technique of photolithography. Another usable technique is the technique of chemical vapor deposition, such as for example CCVD. In CCVD, catalyst nano-particles can be positioned onto a substrate lithographically to initiate nanotube growth only at desired locations. Nanotubes can be fabricated in a variety of sizes and lengths. Typically the tubes are multi-walled, meaning that a number of concentric wrapped sheets form the tube structure, however single walled tubes are also possible.
With respect to an embodiment of the invention such as shown in
Shown in
A switch rod and bearing assembly usable within yet another embodiment of the invention are illustrated in
The contacts at the ends of the switch rod are illustrated in
Any suitable material may be used, but preferred materials are metals and highly doped semiconductors. In an embodiment of the invention, the switch rod contacts 205, 207, 215, 217, 225, and 227 each comprise a metallic filament such as a copper nanowire positioned across the end of the rod. In an alternative embodiment of the invention, the contacts 205, 207, 215, 217, 225, and 227 each comprise a photolithographically defined metallic plate. Certainly the contacts do not need to be made of the same material for a given switch assembly, and in some circumstances it may be desirable to use a different material for one contact than for the other. It will be appreciated that the use of metallic contacts allows for good ohmic contact and minimal insertion loss for the switch assembly.
Given this understanding of the circuit operation of the switch, the physical operation of the switch will be described in greater detail with reference to
With respect, for example, to the embodiment of the invention illustrated in
In alternative exemplary embodiments of the invention, other mechanisms are employed for actuation of the switch element. By way of example and not limitation, two such embodiments of the invention are discussed hereinafter. Referring to
A further alternative embodiment of the invention is illustrated in
The embodiment shown in
It will be appreciated that an improved microelectromechanical switch assembly and elements have been described herein. In view of the many possible embodiments to which the principles of this invention may be applied, it should be recognized that the embodiments described herein with respect to the drawing FIGS. are meant to be illustrative only and should not be taken as limiting the scope of invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4656445 | Bagepalli et al. | Apr 1987 | A |
| 4994776 | Juncu | Feb 1991 | A |
| 5304971 | Sturman et al. | Apr 1994 | A |
| 5430597 | Bagepalli et al. | Jul 1995 | A |
| 6005459 | Hoffman | Dec 1999 | A |
| 6157043 | Miyamoto | Dec 2000 | A |
| 6366186 | Hill et al. | Apr 2002 | B1 |
| 6473351 | Tomanek et al. | Oct 2002 | B2 |
| 6515325 | Farnworth et al. | Feb 2003 | B1 |
| 6874668 | Cumings et al. | Apr 2005 | B2 |
| 7238425 | Cumings et al. | Jul 2007 | B2 |
| 7382648 | Bockrath | Jun 2008 | B2 |
| 20020001905 | Choi et al. | Jan 2002 | A1 |
| 20020070426 | Cumings et al. | Jun 2002 | A1 |
| 20020163414 | Mayer et al. | Nov 2002 | A1 |
| 20030098488 | O'Keeffe et al. | May 2003 | A1 |
| 20030122133 | Choi et al. | Jul 2003 | A1 |
| 20030122207 | Yen et al. | Jul 2003 | A1 |
| 20030122640 | Deligianni et al. | Jul 2003 | A1 |
| 20070170071 | Suh et al. | Jul 2007 | A1 |
| 20070171707 | Maslov et al. | Jul 2007 | A1 |
| 20070188268 | Naito et al. | Aug 2007 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20060273871 A1 | Dec 2006 | US |
