Embodiments of the invention relate generally to a micro-electromechanical system (MEMS) switch.
Microelectromechanical systems (MEMS) generally refer to micron-scale structures that can integrate a multiplicity of functionally distinct elements such as mechanical elements, electromechanical elements, sensors, actuators, and electronics, on a common substrate through micro-fabrication technology. MEMS generally range in size from a micrometer to a millimeter in a miniature sealed package. A MEMS switch has a movable actuator that is moved toward a stationary electrical contact by the influence of a gate or electrode positioned on a substrate.
Power system applications of MEMS switches are beginning to emerge, such as replacements for fuses, contactors, and breakers. One of the important design considerations in constructing a power switching device with a given overall voltage and current rating is the underlying voltage and current rating of the individual switches used in the array of switches that comprise the device. In particular, the voltage that the individual switches can withstand across their power contacts is an important parameter. There are several factors and effects that determine the voltage rating of an individual MEMS switch. One such factor is the self-actuation voltage.
In a MEMS switch, the self-actuation voltage is an effect that places an upper bound on the voltage capability of the switch. Electrostatic forces between the line and load contacts (e.g. between the movable actuator and stationary contact) will cause the movable actuator to self-actuate or make contact with the stationary contact when the voltage between across the actuator and contact exceeds a certain threshold. In certain current switching applications, this self-actuation can result in catastrophic failure of the switch or downstream systems.
In one embodiment, a MEMS switch is provided including a substrate, a movable actuator coupled to the substrate and having a first side and a second side, a first fixed electrode coupled to the substrate and positioned on the first side of the movable actuator to generate a first actuation force to pull the movable actuator toward a conduction state, and a second fixed electrode coupled to the substrate and positioned on the second side of the movable actuator to generate a second actuation force to pull the movable actuator toward a non-conducting state.
In another embodiment, a method of fabricating a MEMS switch is provided. The method includes forming a first fixed control electrode and a fixed contact on an insulating layer on a substrate, forming a movable actuator on the insulating layer such that the movable actuator overhangs the first fixed control electrode and the contact and forming a second fixed control electrode on the insulating layer and overhanging the movable actuator. The method further includes releasing the movable actuator to allow the actuator to be pulled toward a first conduction state with the contact in response to a first actuation force generated between the first fixed control electrode and the movable actuator, and a second non-conducting state in response to a second actuation force generated between the second fixed control electrode and the movable actuator.
In a further embodiment, a MEMS switch array is provided. The MEMS switch array includes a substrate, a first movable actuator coupled to the substrate and having a top side and a bottom side, and a second movable actuator coupled to the substrate and having a top side and a bottom side. The MEMS array further includes a first fixed control electrode coupled to the substrate and positioned on the bottom side of the first and second movable actuators to generate a first actuation force to pull the movable actuators toward a conduction state, and a second fixed control electrode coupled to the substrate and positioned on the top side of the first and second movable actuators to generate a second actuation force to pull the movable actuators toward a non-conducting state.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the present invention. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, well known methods, procedures, and components have not been described in detail.
Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent. Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as well as their inflected forms as used in the present application, are intended to be synonymous unless otherwise indicated.
MEMS switch 20 further includes a first electrode 24 (also referred to as a gate or control electrode) and a contact 26. In one embodiment, an electrostatic force may be generated between the first electrode 24 and the movable actuator 22 upon application of a voltage differential between the two components. Thus, upon actuation, the movable actuator 22 is attracted towards the first electrode 24 and eventually makes electrical contact with contact 26. However, as was previously described, in high voltage applications, conventional MEMS switches are prone to self-actuating even when there is no signal applied to the first electrode 24. In accordance with one aspect of the present invention, a second electrode (also referred to as a counter electrode) 27 is provided to generate a second actuation force opposing the self-actuation force such that the movable actuator is pulled toward a non-conducting state away from the contact 26.
In one embodiment, the second electrode 27 is coupled to the same substrate 28 as the moveable actuator 22 and is positioned over (e.g., on the side parallel to and opposite the substrate 28) the moveable actuator 22 and at least partially over contact 26. By fabricating the counter electrode 27 on the same substrate as the movable actuator 22, variations in electrode spacing between the movable actuator 22 and the counter electrode 27 can be eliminated through tightly controlled photolithographic processes.
The electrostatic force present between the substrate contact 26 and the movable actuator 22 can be approximately computed as the force across a capacitor's plates as illustrated by Eqn. (1), where the plate area is the common area of overlap of the two electrodes:
Thus, as the voltage differential across the gap between the contact 26 and the movable actuator 22 increases, or as the overlap area (a1) increases, or as the gap (d1) decreases, the larger the resulting electrostatic force will become. Similarly, as the voltage differential across the gap between the electrode 27 and the movable actuator 22 increases, or as the overlap area (a2) increases, or as the gap (d2) decreases, the larger the resulting electrostatic force will become. Accordingly, the counter electrode 27 may be designed based upon the desired standoff voltage. In one embodiment, the distance d2 is greater than d1. In one embodiment, a2 is greater than a1.
In one embodiment, the voltage level between the first electrode 24 and the movable actuator 22 is separately controlled from the voltage level between the movable actuator 22 and the counter electrode 27. In one embodiment, when it is desirable to maintain the switch in a non-conduction (e.g., open) state, the applied voltage between the first electrode 24 and the movable actuator 22 can be set to zero or another relatively low value, while the applied voltage between the counter electrode 27 and the movable actuator 22 can be set to a relatively higher value. When it is desirable to maintain the switch in a conducting (e.g., closed) state, the applied voltage between the first electrode 24 and the movable actuator 22 can be set to a relatively high value, while the applied voltage between the counter electrode 27 and the movable actuator 22 can be set to zero or a relatively lower value.
In another embodiment, the counter electrode 27 may be electrically coupled to the contact 26 such that whatever voltage happens to exist between the contact 26 and the movable actuator 22 will also appear between the movable actuator 22 and the counter electrode 27. By appropriately selecting the size of the counter electrode 27 as well as the spacing between the counter electrode 27 and the movable actuator 22, the self-actuating force generated between the contact 26 and the movable actuator 22 can be balanced with the counter actuation force generated between the movable actuator 22 and the counter electrode 27.
As used herein, the term “above” is intended to refer to a location that is farther away from the substrate 28 than the referenced object, while the term “below” is intended to refer to a location that closer to the substrate 28 than the referenced object. For example, if an item is “above” the movable actuator 22, then the item is farther away from the substrate 28 than the referenced movable actuator 22. In one embodiment, the MEMS switch 20 may include an isolator (not illustrated) positioned above the movable actuator 22 to prevent the movable actuator from making contact with the counter electrode 27. In one embodiment, the isolator may be fabricated as part of counter electrode 27 or as a separate component. The isolator may be formed from a material having insulating, highly resistive or dielectric properties. Further, the isolator may take the form of a rigid or semi-rigid post or pillar, or the isolator may be deposited on the counter electrode as a coating. Moreover, the isolator may be fabricated on either the underside (e.g., on the same side as the substrate 28) of the counter electrode 27 or on the top side (e.g., on the side farther away from the substrate 28) of the movable actuator 22. In one embodiment, while in a non-conducting state, the movable actuator 22 may be positioned in physical contact with the counter electrode 27 while remaining electrically isolated from the counter electrode 27. In another embodiment, while in a non-conducting state the movable actuator 22 may be attracted towards the counter electrode 27 but remain mechanically and electrically isolated from the counter electrode 27. In such a non-conducting state, the movable actuator 22 may remain in a stationary position.
In
In
Once the movable actuator 132 has been formed, a counter electrode 137 as described herein may be formed. As part of the counter electrode process, a second sacrificial layer 115 may be deposited and optionally polished as illustrated in
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Number | Name | Date | Kind |
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5619061 | Goldsmith et al. | Apr 1997 | A |
Number | Date | Country | |
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20090160584 A1 | Jun 2009 | US |