Etching a substrate: processes – Etching of semiconductor material to produce an article...
Reexamination Certificate
2000-03-07
2001-12-11
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Etching of semiconductor material to produce an article...
C216S039000, C216S109000, C059S008000
Reexamination Certificate
active
06328903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to microelectromechanical (MEM) devices, and in particular to a surface-micromachined chain for use in a MEM device or structure.
BACKGROUND OF THE INVENTION
Polysilicon surface micromachining adapts planar fabrication process steps known to the integrated circuit (IC) industry to manufacture microelectromechanical or micromechanical devices. The standard building-block processes for polysilicon surface micromachining are deposition and photolithographic patterning of alternate layers of low-stress polycrystalline silicon (also termed polysilicon) and a sacrificial material (e.g. silicon dioxide or a silicate glass). Vias etched through the sacrificial layers at predetermined locations provide anchor points to a substrate and for mechanical and electrical interconnections between the polysilicon layers. Functional elements of the device are built up layer by layer using a series of deposition and patterning process steps. After the device structure is completed, it can be released for movement by removing the sacrificial material in part or entirely by exposure to a selective etchant such as hydrofluoric acid (HF) which does not substantially attack the polysilicon layers.
The result is a construction system that generally consists of a first layer of polysilicon which provides electrical interconnections and/or a voltage reference plane (e.g. a ground plane), and up to three or more additional layers of mechanical polysilicon which can be used to form functional elements ranging from simple cantilevered beams to complex systems such as a microengine connected to a gear train. Typical in-plane lateral dimensions of the functional elements can range from one micron to several hundred microns or more, while individual layer thicknesses are typically about 1-3 microns. Because the entire process is based on standard IC fabrication technology, a large number of fully-assembled devices can be batch-fabricated on a silicon substrate without any need for piece-part assembly.
For various types of microelectromechanical (MEM) devices, a precise control over movement, positioning or timing of a plurality of rotary members is needed. Such precise movement, positioning or timing control has previously been achieved using a gear train. However, gear trains require precise fabrication and are limited in their utility when the rotary members are widely spaced, or when a plurality of rotary members at different locations must be driven at the same angular speed.
An advantage of the present invention is that a surface-micromachined chain can be integrally formed on a substrate and used to simultaneously drive one or more rotary members (e.g. sprockets) that are located at a distance from a motive source (e.g. a microengine).
Another advantage is that the surface-micromachined chain of the present invention allows a single motive source (e.g. a microengine) to drive a plurality of rotary members (e.g. sprockets) in synchronism.
Yet another advantage of the present invention is that the surface-micromachined chain can be used to combine the mechanical power from a plurality of motive sources.
A further advantage of the present invention is that the surface-micromachined chain can be formed in place on a substrate without any piece-part assembly required.
These and other advantages of the method of the present invention will become evident to those skilled in the art.
SUMMARY OF THE INVENTION
The present invention relates to a surface-micromachined chain, comprising a plurality of interconnected chain links, with each chain link further comprising a plurality of deposited and patterned material layers. Each chain link can comprise a two-part link body having an inner circular member surrounded by an outer annular member, and at least one link arm extending outward from the outer annular member to connect to the inner circular member of an adjacent two-part link body. The interconnected chain links can be formed integrally on a substrate (e.g. a silicon substrate) without the need for any piece-part assembly. By integrally forming the chain links using surface micromachining, each link arm, which generally comprises polycrystalline silicon (also termed polysilicon), is permanently attached to the outer annular member of one two-part link body and to the inner circular member of an adjacent two-part link body. Additionally, the link arms can be formed coplanar with each other. Each link in the surface-micromachined chain can also be substantially identical in size and shape to all the remaining chain links. The particular size of each chain link will depend upon particular applications thereof, but will generally be in the range of 5-1000 microns in length, and about 2-20 microns in thickness. Each chain link is formed to be jointed and flexible in a plane parallel to the substrate, while being substantially inflexible in a direction perpendicular to the substrate. This allows the individual chain links to be moveable over a surface of the substrate in sliding contact with the surface of the substrate, or alternately to be supported slightly above the surface of the substrate.
The present invention also relates to a surface-micromachined chain formed integrally on a substrate (e.g. a silicon substrate) for coupling mechanical power from a motive source to a load on the substrate, with the chain comprising a plurality of link arms connected at each end thereof to flexible joints, and with the link arms and flexible joints being formed, at least in part, from polycrystalline silicon. Each flexible joint can comprise an inner circular member surrounded by an outer annular member which can also be substantially circular in shape, with the inner circular member being permanently attached to one end of one of the link arms, and with the cuter annular member being permanently attached to an opposite end of an adjacent link arm. The link arms and the flexible joints can be formed from a plurality of deposited and patterned layers of polycrystalline silicon. The spacing between the flexible joints (i.e. the pitch of the chain) can be, for example, in the range of 5-1000 microns; and the flexible joints can be adapted to drive or to be driven by a sprocket formed on the substrate using the same process steps used for forming the chain.
The present invention further relates to a surface-micromachined structure formed on a substrate (e.g. comprising silicon), with the structure comprising a drive sprocket formed on the substrate for providing motive power, a driven sprocket formed on the substrate at a distance from the drive sprocket, and a chain formed on the substrate, at least in part, from polycrystalline silicon and connected between the drive sprocket and the driven sprocket to couple the motive power from the drive sprocket to the driven sprocket thereby imparting motion to the driven sprocket. The chain can comprise a plurality of interconnected chain links each about 5-1000 microns long and 2-20 microns thick. Each chain link can further comprise a two-part link body having an outer annular member surrounding an inner circular member, with at least one link arm extending outward from the outer annular member to connect to the inner circular member of an adjacent two-part link body.
One or more electrostatic actuators can also be formed on the substrate and operatively connected to the drive sprocket to provide mechanical power to rotate the drive sprocket. Furthermore, a chain tensioner can be formed on the substrate to reduce any slack in the chain. The chain tensioner can comprise a laterally-moveable idler sprocket formed on the substrate, with the idler sprocket being mounted on a platform and moveable into a path of the chain to deflect the chain and thereby reduce the slack therein.
The present invention also relates to a surface-micromachined structure (i.e. a microelectromechanical device) formed on a substrate. The structure generally comprises one or more microengines formed on the substrate, a drive sprocket formed on the subs
Gulakowski Randy
Hohimer John P.
Olsen Allan
Sandia Corporation
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