Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material
Reexamination Certificate
2001-10-16
2004-09-07
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
C585S008000, C585S459000, C585S027000, C585S008000, C585S008000, C585S464000, C585S008000, C257S528000, C257S254000, C257S532000, C257S508000, C257S415000, C257S416000, C257S417000
Reexamination Certificate
active
06787438
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to microelectromechanical devices, and more particularly, to a microelectromechanical device in which includes one or more contact structures interposed between a pair of electrodes.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Microelectromechanical devices, or devices made using microelectromechanical systems (MEMS) technology, are of interest in part because of their potential for allowing integration of high-quality devices with circuits formed using integrated circuit (IC) technology. For example, MEMS switches may exhibit lower losses and a higher ratio of off-impedance to on-impedance as compared to transistor switches formed from conventional IC technology. However, a persistent problem with implementation of MEMS switches has been the high voltage required (often about 40V or higher) to actuate the switches, as compared to typical IC operating voltages (about 5V or lower).
These relatively high actuation voltages of MEMS switches are caused at least in part by a tradeoff between the closing and opening effectiveness of a given switch design. For example, approaches to lowering the actuation voltage of switches have included reducing the stiffness of the switch beam and/or reducing the gap between the beam and the conductive pad. Unfortunately, these design changes typically result in making the switch more difficult to open. MEMS switch designs generally use an applied voltage to close the switch, and rely on the spring force in the beam to open the switch when the applied voltage is removed. In opening the switch, the spring force, or restoring force, of the beam must typically counteract what is often called “stiction.” Stiction refers to various forces tending to make two surfaces stick together such as van der Waals forces, surface tension caused by moisture between the surfaces, and/or bonding between the surfaces (e.g., through metallic diffusion). In general, modifications to a switch which act to lower the closing voltage also tend to make the switch harder to open, such that efforts to form a switch with a lowered closing voltage can result in a switch which may not open reliably (or at all).
Another limitation typically found in MEMS devices is the presence of residual stresses contained within the switch beam. In particular, the residual stresses within a beam may cause the beam to curl either away from contact structures or toward contact structures without the activation of actuation voltages. In the event that the beam curls down and closes a contact prematurely, the switch may become inoperable because significant electrostatic repulsion between the gate and the beam cannot be established. In this manner, the switch may not be opened by removing an applied voltage as described above. In other cases, MEMS devices may be designed such that the functionality of the devices is dependent on the presence of residual stresses within the beam. For example, a device may be designed to have compressive stresses within the beam in order to curl one portion of the beam in one direction as another portion of the beam curls in the opposite direction. Actuation voltages may then be used to oscillate the beam between its original state and the mirror image of the original state. Such a device, however, may be difficult to consistently fabricate since residual stresses within the beam may be dependent on the properties of the beam materials and such properties may change as variables of the fabrication process change. In addition, the range of materials used within such a MEMS device may be limited.
It would therefore be desirable to develop a MEMS device which relaxes the constraints imposed by the above-described tradeoff between opening and closing effectiveness and the presence of residual stresses within the device.
SUMMARY OF THE INVENTION
The problems outlined above may be in large part addressed by a microelectromechanical device which includes a contact structure interposed between a pair of electrodes arranged beneath a beam. In some embodiments, the device may include additional contact structures interposed between the pair of electrodes. For example, the device may include at least three contact structures between the pair of electrodes. Preferably, the additional contact structures may be spaced along and under a length of the beam adjacent to the contact structure. In some embodiments, the beam may be suspended above the pair of electrodes by a support structure affixed to a first end of the beam. Such a device may further include an additional support structure affixed to a second end of the beam. In some cases, the device may be adapted to pass a signal from the first end to the second end of the beam. In addition or alternatively, the device may be adapted to pass the signal between one and/or both ends of the beam and one or more of the contact structures.
As stated above, a microelectromechanical device is provided which includes a contact structure interposed between a pair of electrodes arranged beneath a beam. In some embodiments, the beam may be suspended by support structures affixed to first and second ends of the beam. Alternatively, the beam may be solely supported at one end of the beam. In either embodiment, the device may be adapted to pass a signal between one and/or both ends of the beam and the contact structure. In addition or alternatively, the device may be adapted to pass a signal from the first end to the second end of the beam. In particular, the device may be adapted to pass the signal through the beam upon bringing the beam in contact with the contact structure. In an alternative embodiment, the device may be adapted to pass the signal through the beam without bringing the beam in contact with the contact structure interposed between the pair of electrodes. In such an embodiment, the beam may include a contiguous layer of conductive material. Alternatively, the beam may include an insulating element interposed between the first and second ends of the beam.
In some embodiments, the device may include one or more additional contact structures interposed between the pair of electrodes. In such an embodiment, the upper surface of the contact structure may be above or below the upper surfaces of the additional contact structures. In some cases, the contact structure may include a raised section arranged upon its upper surface. Alternatively, the upper surface of the contact structure may be approximately level with upper surfaces of the additional contact structures. In such an embodiment, the beam may include a recessed portion above the contact structure. In some cases, one or more of the additional contact structures and contact structure may include multiple sections spaced apart from each other and arranged along the width of the beam.
In some cases, the device may be adapted to bring the beam in contact with one or more of the contact structures. For example, the beam may include residual forces adapted to bring the beam in contact with one or more of the contact structures. Such residual forces may be further adapted to curl the beam away from one or more of the contact structures distinct from the contact structures in contact with the beam. In an alternative embodiment, the device may be adapted to bring the beam in contact with one or more of the contact structures upon an application of one or more closing voltages to at least one of the pair of electrodes. More specifically, the beam may be brought in contact with one or more of the contact structures upon applying a closing voltage to one of the pair of electrodes. In an alternative embodiment, the beam may be brought in contact with one or more of the contact structures upon applying a closing voltage to both of the pair of electrodes. In yet another embodiment, the device may be adapted to bring the beam in contact with one or more of the contact structures by other forms of actuati
Anya Igwe U.
Conley & Rose, P.C.
Daffer Kevin L.
Everhart Caridad
Lettang Mollie E.
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