Patent Application
20070235303
Single substrate single pole double throw micro-fluidic switching devices have been designed using liquid metal actuation to provide switching. These switches can use a single switching stage for achieving the open or closed state between two outputs. In one embodiment, high frequency signals can be switched from an input to an output by applying a stimulus, for example, pressure to the liquid within the switch body. The applied pressure (which is generated by a number of methods) causes the liquid (usually liquid metal) to move to one of two bi-stable states. Currently, when more than two throws are required, a plurality of these single stage switches must be used. A four-throw switch (having four possible outputs) would require three distinct switches, where the outputs of the switch of the first stage would become the inputs for two switches of the second stage. Separate switches, in addition to taking up valuable space on a wafer substrate, require complex circuitry to operate.
In accordance with the invention, a multiple throw switching device can be achieved on a single substrate by organizing a micro-fluidic switch into spokes radiating outward from the center of a wafer such that each spoke (switch throw) controls a switched output and each switch throw, in turn, is controlled by an individual stimulus.
Device 10 comprises four single pole single throw switches sharing a single switch pole (manifold) 17 creating a multiple throw switch. The switches are comprised of throw contacts 12-1 to 12-4, contact cavities 13-1 to 13-4, heaters 14-1 to 14-4, heated gas channels 15-1 to 15-4, liquid reservoir 16, switch pole 17, vents 18-1 to 18-5, electrical (high frequency) connections 19-1 to 19-5; The shaded areas indicate conductive liquid. The conductive liquid may be any liquid that conducts electrical signals including, but not limited to liquid metals, such as mercury, gallium alloys, and indium alloys. While the present embodiment illustrates a single pole four throw switch, alternative embodiments may use any number of throws.
It is noted that while the embodiment of
Throw contacts 12-1 to 12-4, switch pole 17 are cavities formed between a flat surface of a substrate, and the etched surface of another substrate with the two substrates bonded together. The cavities store the liquid and have wetted electrically conductive surfaces attracting the liquid. Throw contacts 12-1 to 12-4 are electrically connected to connections 19-1 to 19-4, respectively, and pole 17 is electrically connected to connection 19-5. Contact cavities 13-1 to 13-4 separate pole contact 17 from throw contacts 12-1 to 12-4, respectively, and have nonwetted surfaces. These portions of the cavities are not electrically conductive, such that when a given contact cavity is empty (i.e., no metallic liquid therein) switch pole 17 is electrically isolated from the contact associated with that cavity. For example, if cavity 13-1 is empty of liquid there is electrical isolation between contact 12-1 and pole contact 17 switch pole 17 and the given contact cavity's throw contact are not electrically connected. In order to electrically connect pole 17 with a particular cavity switch of device 10, liquid must bridge the gap from pole 17 to the switch.
As illustrated in
Heat connecting channels 15-1 to 15-4 have nonwetted surfaces and serve to connect contact cavities 13-1 to 13-4 with heaters 14-1 to 14-4, respectively. These heaters could be, for example, joule heaters. As will be discussed, heaters 14-1 to 14-4 operate to control the movement of the liquid within device 10 to make connections between throw contacts 12-1 to 12-4 and contact 17. Heaters 14-1 to 14-4 operate by heating gases, which gases are passed through channels 15-1 to 15-4 thereby causing the liquid within the associated chamber of device 10 to move in a desired direction, as will be discussed.
Electrical connectors 19-1 to 19-5 allow other electrical devices to be connected to device 10. Vents 18-1 to 18-5 are cavities in substrate 11 serving to allow trapped gases to escape, which is particularly important during liquid loading of the switch, once microfabrication has been completed. These vents have nonwetted surfaces to repel and prevent the escape of liquid from throw contacts 12-1 to 12-4 (for vents 18-1 to 18-4) and pole 17 (for vent 18-5). Reservoir cavity 16 also has nonwetted surfaces which allow for the storage of excess amounts of liquid that may temporarily overflow from pole 17 during the operation of device 10. The reservoir is also used in the loading of liquid metal into the device.
Note that reservoir cavity 16 is also empty, at this time.
Assume now that it is desired to change the switch so post-electrical continuity exists between connectors 19-5 and 19-3. Referring to
Referring to
Referring to
A controlling factor in how many poles can be closed at any one time is that the switch must have enough liquid to fill all the cavities that are to be “closed.” However, if too much liquid is added, then the liquid would have no place to go and some switch throws would remain closed even when heat (pressure) is applied. Reservoir 16 is primarily used during loading, where it is filled and then expelled into the various channels. However, during switching come liquid metal could temporarily move into the reservoir. In most situations, the liquid moving between channels during switching would most likely only make it as far as the connection between the switch and the reservoir. Alternative embodiments may make electrical connections with more than one throw contact. For example, if in the previous discussion with respect to
Further, alternative embodiments may have switch throws for each electrical connection. For example, if electrical connection 19-5 were to be removed, or not used, any one or more terminals 19-1 to 19-4 could be selectively connected to any one or more other terminals 19-1 to 19-4.
Alternative embodiments may have the contact cavities of multiple poles connected to a single heater, thus creating a multi-pole switch.
It is noted that while gas pressure is used to move the liquid within device 10, alternative embodiments may use any other suitable means to move the liquid, such as electrowetting on dielectric or micro-electro-mechanical pumps and motors and combinations of the above.
As shown in
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
