Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2000-07-11
2003-01-14
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06507138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of microelectromechanical (MEM) systems, and in particular to a compact electrostatic actuator that can be formed by surface micromachining.
BACKGROUND OF THE INVENTION
Many different types of microelectromechanical (MEM) devices use one or more electrostatic actuators as motive sources. See, for example, U.S. Pat. No. 5,631,514 to Garcia et al which discloses a microengine that uses a pair of synchronized linear comb actuators as a power source. However, many problems exist with present electrostatic comb actuators which are generally considered to be low power, low output force devices.
Conventional comb actuators are disproportionate in size compared to other functional elements (e.g. gears, linkages, moveable assemblies, etc.) of MEM devices due to inefficient space utilization. Since a total substrate area (i.e. a die size) devoted to a particular MEM device is generally fixed by fabrication constraints, the disproportionate area required for one or more comb actuators limits the area available for use by the other functional elements of the MEM device. As a result, the complexity of a MEM device utilizing a conventional electrostatic comb actuator will ultimately be limited by the area required for each actuator.
Another problem with conventional electrostatic comb actuators is that these devices provide a relatively low drive force limited to a few tens of microNewtons (&mgr;N); and this level of drive force requires a relatively high operating voltage of up to 100 Volts or more. The relatively low drive force of conventional comb actuators limits their usefulness as power sources for many types of MEM devices.
Yet another problem with conventional electrostatic comb actuators is that a single-beam structure is commonly used; and this single-beam structure and one or more electrostatic combs supported thereon can easily be distorted due to slight asymmetries in a generated electrostatic field, or due to external loading. Such distortion can result in one or more fingers of an electrostatic comb bending or moving from a region of electrostatic stability to a region of electrostatic instability. This can result in binding of the comb actuator and limiting its range of motion. Permanent failure of the actuator can also occur as an electrical short circuit is developed between contacting fingers which are biased at different electrical potentials.
The compact electrostatic actuators of the present invention overcome many of the above limitations in the prior art.
An advantage of the present invention is that a compact design is provided for an electrostatic actuator to conserve space upon a substrate or portion thereof, thereby providing for more economical fabrication and allowing the fabrication of MEM devices of increased complexity. Embodiments of the electrostatic actuator of the present invention are provided as electrostatic comb actuators and as capacitively-coupled electrostatic plate actuators.
Another advantage of the electrostatic actuator of the present invention is that this actuator can provide an increased drive force as compared with a conventional comb actuator.
A further advantage of the present invention is that a comb actuator is provided with a more rigid structure that is less prone to distortion than a conventional electrostatic comb actuator, thereby increasing the reliability of the comb actuator even at high actuation voltages.
Still another advantage of the present invention is that an electrostatic actuator can be formed which provides a self-limiting displacement, thereby making the actuator relatively insensitive to the exact value of the applied voltage and acting to resist any further displacement due to an increase or decrease in loading.
Yet another advantage is that an electrostatic actuator according to the present invention can be provided with electrostatic shielding in critical places to minimize the effects of unwanted electrostatic fields, thereby increasing the available electrostatic drive power from the actuator and reducing any distortion of the structure of the actuator.
These and other advantages of the present invention will become evident to those skilled in the art.
SUMMARY OF THE INVENTION
The present invention relates to an electrostatic actuator formed on a substrate and comprising a plurality of capacitively-coupled electrostatic plates (also termed electrodes) including at least one row of fingerless stationary electrostatic plates formed on the substrate and oriented along a direction of movement of the electrostatic actuator, and a row of moveable electrostatic plates formed on at least one side of each row of the stationary electrostatic plates, with the moveable electrostatic plates being suspended above the substrate by a rigid frame which supports a majority of the moveable electrostatic plates at or near a midpoint thereof, the frame further surrounding and enclosing each row of the stationary electrostatic plates. In the electrostatic actuator, the frame is suspended above the substrate by a plurality of springs, with each spring being attached at one end thereof to the frame and attached at the other end thereof to the substrate. This allows the frame to be electrostatically moveable over a range of generally 0-10 microns in response to a voltage applied between the stationary electrostatic plates and the moveable electrostatic plates.
The frame can be formed from a plurality of layers (e.g. ≧3 layers) of a deposited and patterned electrically-conductive material (e.g. polycrystalline silicon when the substrate comprises silicon). Additionally, the frame comprises a plurality of links for supporting the majority of the moveable electrostatic plates at or near the midpoint thereof, with each link generally being formed from a smaller number of deposited and patterned layers than are used to form the remainder of the frame. A ground plane can be formed on the substrate below the frame at the location of each row of the moveable electrostatic plates; and an electrostatic shield can be provided between the frame and an adjacent stationary electrostatic plate.
The spacing between each moveable electrostatic plate and an adjacent stationary electrostatic plate can be made substantially the same for all of the stationary and moveable electrostatic plates. This allows the electrostatic actuator to be driven by a voltage that is simultaneously applied between all the stationary electrostatic plates and all the moveable electrostatic plates. Alternately, the stationary electrodes can be digitally addressed to provide the voltage between at least one set of the stationary electrostatic plates and the moveable electrostatic plates. In some preferred embodiments of the present invention, the spacing between adjacent moveable electrostatic plates in each row of the moveable electrostatic plates can be made substantially equal to the spacing between adjacent stationary electrostatic plates in each row of the stationary electrostatic plates.
The present invention further relates to an electrostatic actuator formed on a substrate and comprising a plurality of moveable electrodes suspended above the substrate and arranged in at least one row oriented along a direction of movement of the electrostatic actuator; a rigid frame surrounding and supporting the moveable electrodes; and a plurality of fingerless stationary electrodes formed on the substrate in a row proximate to the row of moveable electrodes, the rows of stationary and moveable electrodes acting in response to a voltage applied therebetween to urge the frame to move along the direction of movement.
The frame is suspended above the substrate by a plurality of springs, with each spring being attached at one end thereof to the frame and attached at the other end thereof to the substrate. All the electrodes of a given type (i.e. stationary or moveable) can be electrically connected together when forming a unidirectional device so that the actuator can be operated with a common voltage provided between t
Miller Samuel L.
Rodgers M. Steven
Hohimer John P.
Perez Guillermo
Ramirez Nestor
Sandia Corporation
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