Abstract:
The present invention relates to electrostatically actuated device components and methods of making the same. In an embodiment, the invention includes a method of making an electrostatically actuated device component including providing a multilayered structure comprising a first layer comprising a first polymer, a second layer comprising a conductive material, the second layer disposed over the first layer, a third layer comprising a dielectric material, the third layer disposed over the second layer, positioning the multilayered structure within an injection mold, and injecting a second polymer into the mold and bonding the first layer to the second polymer to produce an electrostatically actuated device component. In an embodiment, the invention includes a method of injection molding a stator component for an electrostatically actuated valve.

Description:
FIELD OF THE INVENTION 
     The present invention relates to electrostatically actuated device components and methods of making the same. 
     BACKGROUND OF THE INVENTION 
     Many industrial, commercial, aerospace, military and other applications depend on reliable valves for fluid (including gas) handling. For example, in a chemical plant valves are often used to control the flow of fluid throughout the facility. Likewise, in an airplane, valves are often used to control air and fuel delivery, as well as some of the hydraulic systems that drive the control surfaces of the airplane. These are just a few examples of the many applications that depend on reliable valves for fluid handling. 
     It is often desirable to minimize the power and/or voltage required to operate valves, particularly in wireless applications but also in other applications. Some low voltage/power valves are known in the art. However, many low voltage/power valves and their components have a relatively high fabrication cost. 
     SUMMARY OF THE INVENTION 
     The present invention relates to electrostatically actuated device components and methods of making the same. In an embodiment, the invention includes a method of making an electrostatically actuated device component including providing a multilayered structure comprising a first layer comprising a first polymer, a second layer comprising a conductive material, the second layer disposed over the first layer, a third layer comprising a dielectric material, the third layer disposed over the second layer, the third layer having a surface roughness of less than about 1000 angstroms, positioning the multilayered structure within an injection mold, and injecting a second polymer into the mold and bonding the first layer to the second polymer to produce an electrostatically actuated device component. 
     In an embodiment, the invention includes a method of injection molding a stator component for an electrostatically actuated valve including disposing a planar conductive assembly within an injection mold, the planar conductive assembly including a support layer comprising a first polymer, a conductive layer comprising a first side and a second side, the first side coupled to the support layer, a dielectric layer comprising a second polymer, the dielectric layer covering the entirety of the second side of the conductive layer, and injecting a third polymer into the injection mold to produce a stator component. 
     In an embodiment, the invention includes a method of forming a component of an electrostatically actuated device including extruding a first polymer to form a support layer, disposing a conductive material on the support layer to form a conductive layer extending continuously over the support layer, disposing a dielectric material on the conductive layer to form a dielectric layer having a surface roughness (Rq) of between about 100 angstroms and 1000 angstroms, placing the support layer, the conductive layer, and the dielectric layer within an injection mold defining a cavity, with the support layer facing the interior of the cavity, filling the cavity with a second polymer to form the component of the electrostatically actuated device, and removing the component of the electrostatically actuated device from the injection mold. 
     The above summary of the present invention is not intended to describe each discussed embodiment of the present invention. This is the purpose of the figures and the detailed description that follows. 
    
    
     
       DRAWINGS 
       The invention may be more completely understood in connection with the following drawings, in which: 
         FIG. 1  is a cross-sectional side view of an illustrative normally closed valve in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional side view of the valve of  FIG. 1  in an open position. 
         FIG. 3  is a cross-sectional side view of a valve stator in accordance with an embodiment of the present invention. 
         FIG. 4  is a bottom view of a valve stator in accordance with an embodiment of the invention. 
         FIG. 5  is a schematic cross-sectional view of an injection mold in accordance with an embodiment of the invention. 
         FIG. 6  is a cross-sectional side view of a multilayered structure in accordance with an embodiment of the invention. 
         FIG. 7  is a schematic illustration of an injection mold with a multilayered structure disposed therein in accordance with an embodiment of the invention. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention include methods of making electrostatically actuated device components in a manner that can reduce fabrication costs. In an embodiment, the invention includes methods for injection molding electrostatically actuated device components.  FIG. 1  is a cross-sectional side view of one type of valve  5  made in accordance with an embodiment of the present invention. In this embodiment, the valve  5  is of a type that is normally closed. The valve  5  has a body  10  with an upper body portion  13  and a lower body portion  11 . The upper body portion  13  includes a chamber wall  16 . The chamber wall  16  defines a valve chamber  12 . In the illustrative embodiment, a first port  42  (e.g. inlet port) extends through the lower body portion  11  into the valve chamber  12 . 
     A diaphragm  20  is mounted within the chamber  12 . In the embodiment of  FIG. 1 , the diaphragm  20  is spaced from the lower body portion  11  except along a valve seat  23 , which extends around the first port  42 . The lower body portion  11  defines one or more output ports  82   a  and  82   b . In the un-actuated state, the diaphragm  20  can be configured so that the diaphragm  20  covers the valve seat  23  and restricts fluid flow through the first port  42  and out the output ports  82   a  and  82   b . To actuate the valve  5 , the diaphragm  20  includes one or more electrodes, which can extend to the edges of the chamber  12 . In some embodiments, the one or more electrodes of the diaphragm  20  are surrounded or encapsulated in a dielectric material or layer. 
     In the embodiment shown in  FIG. 1 , the chamber wall  16  includes one or more stationary electrodes, such as electrode  30 . The chamber wall  16  and the diaphragm  20  can be configured so that, in the un-activated state, the separation distance between the stationary electrode  30  and the electrode of the diaphragm  20  is smaller near the edges of the chamber  12 . Referring now to  FIG. 2 , when a voltage is applied between the electrode of the diaphragm  20  and the stationary electrode  30 , the diaphragm  20  is drawn toward the chamber wall  16  in a rolling action such that the portions of the diaphragm  20  near the edges of the chamber wall  16  are drawn toward the chamber wall  16  first, followed by portions of the diaphragm farther away from the edges of the chamber wall  16 . Such a rolling action can improve efficiency and reduce the voltage requirements of the valve. When the diaphragm  20  is electrostatically actuated and pulled toward the chamber wall  16 , the diaphragm can move away from the valve seat  23  and uncover the first port  42 . This can allow fluid to flow between the first port  42  and the output ports  82   a  and  82   b.  One or more back pressure relief ports or vent openings  94  may be provided in the upper body portion  13  to relieve any back pressure that might arise because of displacement of the diaphragm  20 . 
     In some embodiments, the diaphragm  20  may become elastically deformed when electrostatically pulled toward the chamber wall  16 . When so provided, the diaphragm  20  may return to the un-activated first position under elastic restoring forces when the activation voltage is removed or reduced between the electrode of the diaphragm  20  and the electrode  30  of the chamber wall  16 . In this embodiment, the diaphragm  20  may only need to be electrostatically actuated in one direction, with the elastic restoring forces returning the diaphragm  20  to the original un-actuated state. 
     The upper body portion  13  and lower body portion  11  may be made from any suitable semi-rigid or rigid material, such as plastic, ceramic, silicon, etc. In an embodiment, upper body portion  13  and lower body portion  11  are constructed by molding a high temperature plastic such as ULTEM-1000™ (available from General Electric Company, Pittsfield, Mass.), CELAZOLE™ (available from Hoechst-Celanese Corporation, Summit, N.J.), KETRON™ (available from Polymer Corporation, Reading, Pa.), or the like. 
     It will be appreciated that the valve  5  shown in  FIGS. 1 and 2  is only one example of a valve configuration that may be made in accordance with embodiments of the invention, but that many other components and configurations are contemplated herein. By way of example, embodiments of the invention can be used to make components for valves that are normally open, valves having different shapes, electrostatically actuated pumps, and the like. 
     Referring now to  FIG. 3 , the upper body portion  13 , the chamber wall  16 , and the electrode  30  can together be considered a stator  7  in an electrostatically actuating valve structure. It will be appreciated that the stator  7  can be manufactured in various ways. In some embodiments of the invention, the stator  7  is manufactured using an injection molding process. 
     Injection molding involves injecting molten plastic into a mold at high pressure; the mold being the inverse of the desired shape. Many different types of injection molding machines can be used. One example of an injection molding machine that can be used is the Sumitomo SE7M, available from Sumitomo Plastics Machinery, Norcross, Ga. In many injection molding machines, resin pellets are poured into a feed hopper, which feeds the granules down to a screw or auger. The screw is turned by a hydraulic or electric motor that turns the screw feeding the pellets up the screw&#39;s grooves. As the screw rotates, the pellets are moved forward in the screw and they undergo extreme pressure and friction which generates most of the heat needed to melt the pellets. Heaters on either side of the screw assist in the heating and temperature control around the pellets during the melting process. The molten material is then forced into the mold under pressure and fills up a cavity inside the mold. The material is then allowed to cool and solidifies creating the part. 
       FIG. 4  is a bottom view of a valve stator in accordance with an embodiment of the invention. In this embodiment, the electrode  30  is shown with a vent opening  94  in the middle of a domed portion  32 . A plurality of post holes  34  are present and configured to receive corresponding posts that can help hold the valve structure together. 
       FIG. 5  shows an injection mold  100  that can be used in some embodiments of the invention. The injection mold  100  includes a top half  102  (core half) and a bottom half  104  (cavity half). The top half  102  and the bottom half  104  enclose a molding cavity  106 . The molding cavity  106  can have walls that are slightly angled to facilitate removal of parts from the mold  100 . The top half  102  defines an injection port  108 . The bottom half includes an interior surface  110  and a dome  112  (not to scale). Molten material which is injected into the mold  100  will take the shape of the molding cavity  106 . The top half  102  and the bottom half  104  can be separated from one another in order to facilitate removal of the resulting molded part. 
     As described previously, the stator  7  can include an electrode  30 . The electrode  30  can be covered by a layer of dielectric material. The electrode  30  may be disposed onto the chamber wall  16  in various ways. For example, the electrode  30  could be affixed onto the chamber wall  16  with an adhesive, or it could be painted, sprayed, or dip coated onto the chamber wall  16 . 
     In some embodiments, an electrode  30  is disposed onto the chamber wall  16  by first positioning a multilayered structure, including a conductive layer, within an injection mold and then injecting a molten polymer to form the stator. This type of process can be referred to as insert injection molding.  FIG. 6  shows an exemplary multilayered structure  200  that can be used in an injection molding method of the invention. The multilayered structure  200  can include a dielectric layer  202  disposed over a conductive layer  204 . The dielectric layer  202  can serve as an insulator between the conductive layer  204  and the electrode on the diaphragm. As such, in an embodiment, the dielectric layer  202  extends continuously over the conductive layer  204 . The conductive layer  204  can, in turn, be disposed over a polymeric support layer  206 . The polymeric support layer  206  can serve as a substrate for deposition of the conductive layer  204  and can facilitate sufficient attachment of the multilayered structure  200  to the chamber wall  16 . While not shown, the multilayered structure  200  can define one or more apertures to accommodate various features such as the one or more back pressure relief ports or vent openings  94  in the upper body portion  13 . 
     Referring now to  FIG. 7 , a multilayered structure  200  is shown disposed within the cavity  306  of a mold  300 . In this embodiment, the multilayered structure  200  is positioned against the interior surface  310  of the bottom half  304  of the mold  300 . Specifically, the multilayered structure  200  is positioned with the dielectric layer  202  adjacent to the interior surface  310  so that the polymeric support layer  206  is facing the cavity  306 . Molten material can then pass into the cavity  306  through an injection port  308  and then be solidified to form a molded stator. In some embodiments, the heat from the molten material can cause the polymeric support layer  206  to partially melt and form a tight bond with the molten material as it solidifies. 
     The polymeric support layer  206  of the multilayered structure  200  may be formed in various ways. In one embodiment, the polymeric support layer  206  is formed by an extrusion process. By way of example, a thermoplastic polymer, such as such as ULTEM-1000™ (polyetherimide) (available from General Electric Company, Pittsfield, Mass.) or KAPTON™ (available from DuPont Electronic Technologies, Circleville, Ohio) can be extruded to form a continuous sheet or layer that serves as the polymeric support layer  206 . The polymeric support layer  206  should be sufficiently thick so as to provide a suitable substrate for the deposition of the conductive layer  204 . The polymeric support layer  206  should be sufficiently thin so as to not reduce the flexibility of the multilayered structure  200  too much. In some embodiments, the polymeric support layer  206  is between about 10 microns to about 100 microns thick. In various embodiments, the polymeric support layer  206  is about 30, 40, 50, 60, or 70 microns thick. 
     The conductive layer  204  may be formed by printing, plating or electron beam-physical vapor deposition (EB-PVD) of metal. In some cases, the conductive layer  204  may be patterned using a dry film resist. In an embodiment, the conductive layer  204  is deposited onto the support layer  206  using thermal evaporation techniques under vacuum. In an embodiment, the conductive layer  204  extends continuously over the polymeric support layer  206 . Various techniques can be used to increase the adhesion between the conductive layer  204  and the polymeric support layer  206 . In an embodiment, the support layer  206  is plasma-treated before the conductive layer  204  is applied. 
     In some embodiments, such as where the conductive layer  204  is vapor deposited onto the support layer  206 , the conductive layer  204  will have surface roughness similar to the surface roughness of the underlying support layer  206 . In an embodiment, the support layer  206  has a surface root mean square (Rq) roughness of less than about 1000 angstroms. In an embodiment, the support layer  206  has a surface roughness (Rq) of greater than about 100 angstroms. In an embodiment, the support layer  206  has a surface roughness (Rq) of between about 100 angstroms and 1000 angstroms. 
     The conductive layer  204  can include many different materials. In an embodiment, the conductive layer  204  includes a metal. Exemplary metals can include gold, platinum, copper, aluminum, and the like. In an embodiment, the metal is of a high purity. By way of example, the metal can be about 99.99% pure. In some embodiments, the metal is about 99.999% pure, 99.9999% pure, or even 99.99999% pure. 
     The conductive layer  204  can be from about 50 to about 500 angstroms thick. In an embodiment, the conductive layer can be about 100, 200, or 300 angstroms thick. The conductive layer can have a resistivity that is appropriate for configuration as an electrode on the stator. In an embodiment, the resistivity of the conductive layer is 10, 8, 6, 4, or 2 Ohms/square or lower. 
     The roughness of the conductive layer  204  can affect the adherence of the dielectric layer  202  to the conductive layer  204 . Surface roughness can be measured using equipment such as the DekTak line profilometer (available from Veeco Instruments Inc., Woobury, N.Y.) which drags a stylus along the surface of a test substrate for a distance such as a 1 millimeter length. One standard measure of roughness that can be automatically calculated by line profilometers (such as the DekTak) is the root mean square roughness (Rq). The Rq roughness is the root mean square average of the departures of the roughness profile from the mean line. Rq roughness is also defined in ANSI B46.1. It has been found that a surface roughness (Rq) on the conductive layer  204  of less than about 100 angstroms (e.g., smoother than 100 angstroms) can lead to insufficient adhesion between the dielectric layer  202  and the conductive layer  204 . Conversely, a surface roughness (Rq) of greater than about 1000 angstroms (e.g., rougher than 1000 angstroms) can result in making the dielectric layer  202  too rough for reliable and consistent actuation of the valve. In an embodiment, the conductive layer  204  has a surface roughness (Rq) of less than about 1000 angstroms. In an embodiment, the conductive layer  204  has a surface roughness (Rq) of greater than about 100 angstroms. In an embodiment, the conductive layer  204  has a surface roughness (Rq) of between about 100 angstroms and 1000 angstroms. 
     The dielectric layer  202  is adhered to the conductive layer  204  with sufficient strength to resist separation from the conductive layer  204  during repeated actuation of an electrostatic valve. The dielectric layer  202  can be deposited onto the conductive layer  204  using a variety of techniques. In some embodiments, it can be spray coated, roller coated, dip coated, or applied using a variety of printing techniques. In some embodiments, the dielectric layer is applied using a flash evaporation technique. In some embodiments, the dielectric layer is subjected to UV light treatment after application in order to cure the dielectric layer. 
     In some embodiments, such as where the dielectric layer  202  is applied using a flash evaporation technique, the dielectric layer  202  will have surface roughness similar to the surface roughness of the underlying conductive layer  204 . In an embodiment, the dielectric layer  202  has a surface roughness (Rq) of less than about 1000 angstroms. In an embodiment, the dielectric layer  202  has a surface roughness (Rq) of greater than about 100 angstroms. In an embodiment, the dielectric layer  202  has a surface roughness (Rq) of between about 100 angstroms and 1000 angstroms. 
     After the multilayered structure  200  is used in insert molding to form a stator  7 , the dielectric layer  202  is on the surface of the stator  7  facing the valve chamber  12 . As the electrostatic valve depends on a rolling action for actuation, surface defects on the dielectric layer  202  can adversely affect the performance of the valve and in some cases cause it to cease actuating. Accordingly, in an embodiment, the dielectric layer  202  is substantially free of surface defects. 
     The dielectric layer  202  can include a variety of materials. By way of example, the dielectric layer  202  can include oxides, such as aluminum oxide. In some embodiments, the dielectric layer  202  includes one or more polymers. It will be appreciated that various polymers have dielectric properties. The dielectric layer can include polymers such as fluoropolymers (such as PTFE and fluoroacrylates), acrylate polymers, polysiloxanes (silicone), polyimides (such as polymethylglutarimide), parylene and the like. 
     The dielectric properties of a material may be gauged by its dielectric constant. The dielectric layer should have sufficient dielectric properties to be able to insulate the conductive layer from the electrode of the diaphragm. In an embodiment, the material of the dielectric layer can have a dielectric constant of between about 3.0 and about 4.0. In an embodiment, the material of the dielectric layer can have a dielectric constant of about 3.5. The dielectric properties of the dielectric layer are also influenced by the thickness of the dielectric layer. In an embodiment, the dielectric layer is between about 0.1 microns and about 5 microns. In a particular embodiment, the dielectric layer is between about 0.45 and about 0.55 microns thick. 
     The surface energy of the dielectric layer can affect how easily the diaphragm releases from the electrode on the chamber wall of the valve. In an embodiment, the surface energy of the dielectric layer is less than or equal to about 30 dynes per centimeter. 
     It will be appreciated that, although the implementation of the invention described above is directed to electrostatically actuated valve components, methods of the present device may be used with other electrostatically actuated devices such pumps and the like, and is not limited to valves or valve components. In addition, while the present invention has been described with reference to several particular implementations, those skilled in the art will recognize that many changes may be made hereto without departing from the spirit and scope of the present invention.