Patent Document

ORIGIN OF THE INVENTION 
   The invention described herein was made by an employee of the United States Government, and may be manufactured and used by the government for government purposes without the payment of any royalties therein and therefor. 

   FIELD OF THE INVENTION 
   The invention is in the field of actuator operated microvalves used primarily in combustion processes. 
   BACKGROUND OF THE INVENTION 
   My U.S. Pat. No. 6,706,549 B1 entitled MULTI-FUNCTIONAL MICRO ELECTROMECHANICAL DEVICES AND METHOD OF BULK MANUFACTURING SAME discloses and claims a method of bulk manufacturing SiC sensors, including pressure sensors and accelerometers. 
   My U.S. Pat. No. 6,845,664 B1 entitled MEMS DIRECT CHIP ATTACH PACKAGING METHODOLOGIES AND APPARATUSES FOR HARSH ENVIRONMENTS discloses methods of bulk manufacturing high temperature sensor sub-assembly packages. 
   I am a named inventor of U.S. Pat. No. 5,637,905 to Carr et al. and it discloses a high temperature pressure and displacement microsensor made from a Si substrate. A first coil structure is positioned within a recess in the Si substrate. A pressure diaphragm is glass bonded about its periphery to the rim of the recess in the semiconductor substrate. A second coil structure is positioned on the underside of the pressure diaphragm and is electrically isolated from the first coil structure. The coils are inductively coupled together and provide an output indicative of changes in the coupling between the coils. 
   My U.S. Pat. No. 6,248,646 discloses a process for making an array of SiC wafers on standard larger industry sized wafers. This patent discusses the operating conditions for SiC and SiC-On-Insulator technology and cites the need for sensors and other devices made from SiC. 
   U.S. Pat. No. 6,883,774 B2 to Nielsen et al. entitled Microelectromechanical High Pressure Microvalve discloses first and second layers of SiC or Si, a stainless steel diaphragm member and switching means. The microvalve is designed for high pressure applications and employs a thin metallic diaphragm sandwiched between first and second layers of SiC or Si. The cracking pressure at which the stainless steel diaphragm opens is approximately 800 psi and the microvalve may be modified to open at pressures from 800-1200 psi. The diaphragm is biased in the closed position and moves from the closed position to the open position when the pressure of fluid in the inlet reaches a preset value. The switching means is connected to the valve body for moving the diaphragm to the closed position against pressure of the fluid in the inlet to the valve. “A recess or cavity  50  in the valve body  26  is provided to allow the diaphragm  16 , specifically the central portion thereof, to flex upward, away from valve seat  30   a . With the preferred embodiment of microvalve  10 , a sloped “dome” is ablated in the underside of the top SiC or Si wafer in order to provide a gentle valve stop. This extends valve life by reducing stress concentrations on the valve diaphragm  16 . The smooth sloped edges of the recess provide a gentle stop and prevent rupturing the thin diaphragm of the valve.” See, col. 3, lines 54 et seq. of the &#39;774 patent. A laser is used to form the contours of the underside of the top SiC or Si wafer by ablating the SiC or Si. A shape memory alloy actuator, a piezoelectric actuator, a microsolenoid actuator, or an electromagnetic actuator may be used. The disclosure of the &#39;774 patent indicates and recites “switching means” and movement of the diaphragm from the closed position to the open position. The &#39;774 patent describes a relief valve. 
   U.S. Pat. No. 6,774,337 B2 to Claydon et al. entitled Method For Protecting The Diaphragm And Extending The Life Of SiC And/Or Si MEMS Microvalves discloses a microvalve and method of forming a diaphragm stop for a microvalve. Much of the disclosure of the &#39;337 patent is similar to the disclosure of the &#39;774 patent but the claimed subject matter differs. United States Patent Application Publication No. US 2005/0098749 A1 is a divisional of the &#39;337 patent and discloses in the proposed claims that the second layer defines a contoured, sloped recess above a central portion of the diaphragm to receive the diaphragm when the diaphragm moves from the closed position to the open position. 
   U.S. Pat. No. 6,557,820 B2 to Wetzel discloses a pre-stressed diaphragm sandwiched between the upper and lower main bodies in a two-stage valve. The valving arrangement is used to control pressure supplied to the top side of the diaphragm which in turn actuates the principal valve. 
   U.S. Pat. No. 6,592,098 B2 to Kao discloses a microvalve employing a diaphragm controlled by an electrostatic external actuator device. Both the valve seat and the valve can be comprised of Si. 
   U.S. Pat. No. 6,126,140 to Johnson et al. discloses electrically conductive polysilicon diaphragms which are corrugated on the periphery thereof. See, col. 2, lines 19-22 of the &#39;140 patent. A three wire system is employed to move the diaphragm toward the open or closed direction. 
   U.S. Pat. No. 5,452,878 to Gravesen et al. entitled Miniature Actuating Device discloses a diaphragm etched in a substrate, a carrier, and an insulator between the carrier and the diaphragm. An electrostatic field is produced between the carrier and the diaphragm to open and close the device. 
   U.S. Pat. No. 5,209,118 to Jerman entitled Semiconductor Transducer Or Actuator Utilizing Corrugated Supports discloses a semiconductor deflecting member having vertical travel which is a linear function of applied force. Capacitive plates are used to measure the movement of the deflecting member. 
   There is growing demand for improved efficient management of energy consumption in jet engines and automobiles. Global reduction of undesirable emissions of hydrocarbons and other combustion by-products such as oxides of nitrogen and carbon monoxide is being sought assiduously. Semiconductor based devices and electronics targeted for insertion in high temperature, extreme vibration, and corrosive media must satisfy a set of minimum reliability criteria before becoming acceptable for operational use. 
   Typically these devices operate in environments of 600° C. and above. This is very challenging since conventional semiconductor electronic and sensing devices are limited to operating in temperatures less than 300° C. due to the limitations imposed by material properties and packaging. Silicon carbide-based electronics and sensors have been demonstrated to operate in temperatures up to 1000° C. thereby offering promise of direct insertion into the high temperature environment. 
   SUMMARY OF THE INVENTION 
   An actuator operated microvalve and the method of making same is disclosed and claimed. The microvalve comprises a SiC housing which includes a first lower portion and a second upper portion. The lower portion of the SiC housing includes a passageway therethrough, a microvalve seat, and a moveable SiC diaphragm. The SiC diaphragm includes a centrally located boss and radially extending corrugations which may be sinusoidally shaped. The boss of the SiC diaphragm moves and modulates in a range of positions between a closed position wherein the boss interengages said microvalve seat prohibiting communication of fluid through the passageway and a fully open position when the boss is spaced apart from the seat at its maximum permitting communication of fluid through said passageway. The actuator includes a SiC top plate with an extended boss affixed to the diaphragm. A first electrode sits on top of the SiC top plate. The second upper portion of the SiC housing further includes a second electrode. 
   Each finished actuator operated microvalve is approximately 30 mm in diameter. Other sizes may be employed. The first lower portion of the housing and the second upper portion of the housing are generally circular or disk shaped. The diaphragm is generally circular or disk shaped. The SiC top plate is generally circular or disk shaped with a centrally located cylindrical protrusion which is affixed to the diaphragm. 
   All components of the actuator operated microvalve are batch fabricated in an array. An array of diaphragms is grown on a mold that is about the size of a CD (compact disk). For instance, 16 diaphragms may be manufactured using a mold which is about the size of a CD (compact disk). Alternatively, the diaphragms may be grown on molds which are 16 inches in diameter or larger. The first lower portion and second upper portion of the SiC housing components are also batch fabricated on a wafer about the size of a CD (compact disk). Alternatively, the first lower portions and the second upper portions of the SiC housing components may be batch fabricated with a wafer which is 16 inches in diameter or larger. 
   The top plate includes a first electrode upon which a first voltage is impressed. The second upper portion of the SiC housing further includes a second electrode which is typically grounded. The first electrode and hence the top plate are attracted toward the second electrode and hence the second upper portion of the housing when the first voltage is different than the second voltage urging the boss of the diaphragm toward the valve seat and the closed position. 
   The first electrode is preferably a nickel plate affixed to the top plate and the second electrode is preferably a nickel plate. The first electrode is the anode and the second electrode is the cathode. Alternatively the SiC top plate is heavily doped to be conductive and the doped top plate constitutes the first electrode. The SiC top plate includes a cylindrical portion and an insulator is affixed to the boss of the diaphragm and the cylindrical portion of the top plate to provide electrical isolation. 
   The second upper housing portion includes a second electrode which is the cathode. Typically, the second electrode is held at ground potential although other voltages may be impressed on the cathode. The second upper portion of the housing is preferably made of SiC and can be doped to be conductive. 
   The underside of the top SiC plate may also be corrugated and the top of the second upper portion of the SiC housing may also be corrugated. These corrugations are arranged such that the minima and maxima of the top plate coincide, respectively, with the minima and maxima of the second upper housing creating a large surface area between the plates. This has the advantage of allowing larger attractive to be generated by less voltage difference. This force can be approximated by the electrostatic force equation. 
   Nickel plating the corrugations surfaces has the benefit of adding stiffness to the SiC top plate and the second upper portion of the SiC housing. 
   The attraction of the SiC top plate and the second upper portion of the SiC housing is dependent on the magnitude of the voltage difference between the plates. 
   The corrugations of the diaphragm are preferably sinusoidally shaped and extend radially outwardly from the cylindrical central boss. Corrugations change the nature of the diaphragm plate to one of primarily bending. This means that deflection becomes much more linearly proportional to an applied force over a much larger deflection range than for that of a non-corrugated plate. The important feature of corrugations is that they reduce the cubic constant in proportion to the linear constant giving a more linearized force-deflection response. The SiC diaphragm comprises a cylindrical central boss portion, radially extending corrugations which extend periodically in a circumferential fashion, and a radially extending planar portion. Other shapes such as square-wave shapes may be used depending on the desired operating characteristics of the actuator operated microvalve. Generally the corrugations may be manufactured in any polygonal shape. Corrugations having sinusoidal shapes are useful in that they permit a large range of motion or stroke for the diaphragm which in turn results in high flow characteristics. The corrugated diaphragms of the instant invention can modulate at 5 kHz. The upper portion of the SiC housing includes a cylindrical central recess therein which allows the diaphragm to flex upwardly without interference. 
   The actuator operated microvalve of the present invention may be used in combination with a closed loop combustion control system wherein the voltage between the plates is modulated using a square or sinusoidal wave voltage. Alternatively, the first voltage with respect to the second voltage is continuously modulated by an analog signal. The combustion control system includes an algorithm and may be, for example, a proportional plus integral plus derivative algorithm. This algorithm can be implemented through a digital (square wave output) or analog (continuous) output to the first and second electrostatic plates. 
   An array of addressable actuator operated microvalves may be used in controlling a combustion control process in combination with a process controller. The actuator operated microvalve of the instant invention provides for distributed fuel injection into a combustion process at low pressures using low voltages across the electrostatic plates. The process controller includes inputs from an array of sensors (such as pressure and temperature sensors) which feedback processed signals for comparison to desired setpoints. The setpoints themselves may be fixed or they may be variable depending on the sophistication of the controller. The combustion control system may include an array of addressable actuator operated microvalves to distribute fuel into a flow stream along a combustion passageway in a jet engine. One application of the invention is use in turbine combustors in which ultra low NO x  emissions are achieved by burning a uniform, lean fuel-air mixture (low flame temperatures) and creating small burning zones (low residence times) due to a plurality of actuator operated microvalves arranged in arrays. These arrays can be thought of as a shower head fuel distribution system. 
   Prior art devices utilize actuators having high voltages and/or currents which tend to arc when placed in a fuel flow field. This leads to premature ignition and dangerous explosions within the flow channel. Piezoelectric actuators suffer from small displacements and are unstable at high temperatures. The production of the prior art actuators is performed on a component by component basis resulting in non-uniformity of the actuators. 
   Alternatively, the combustion may occur in a cylinder of an internal combustion engine. Performance of each cylinder can be evaluated and more or less fuel may be added to a particular cylinder or more or less fuel may be added to a particular region of a cylinder. This will result in increased fuel efficiency and less carbon monoxide and less oxides of nitrogen in the exhaust. 
   A method of making a SiC mold useful for making a SiC diaphragm is also disclosed and claimed. The steps include: applying a mask to a SiC wafer; dry etching with Sulfur Hexaflouride or Ammonium Flouride for a period of time; dissolving the mask with Hydrochloric Acid and Nitric Acid solution; repeating the previous steps as necessary to form the desired wave shape; coating the mold with a releasable material; growing or depositing the corrugation on the releasable layer of the mold; dissolving the releasable material; and, separating the mold having the desired wave shape from the diaphragm. 
   A method for making the actuator operated microvalve is also disclosed and claimed. The method comprises the steps of: forming first and second portions of a SiC housing masks, photoresist, UV light, developer and dry etching; electroplating or sputtering nickel or other metal onto the second portion of the SiC housing forming a first electrode; forming a SiC top plate and a cylinder using masks, photoresist, UV light, developer and dry etching; electroplating or sputtering nickel or other metal onto the SiC top plate forming a second electrode; forming a SiC diaphragm having a boss; attaching the SiC diaphragm to the first lower SiC housing portion; attaching an insulator to the SiC diaphragm; attaching the second portion of the SiC housing to the insulator; attaching the cylinder of the top plate to the boss of the diaphragm; attaching an insulator to the boss of the diaphragm; and, attaching the cylinder of the top plate to the insulator attached to the boss of the diaphragm. 
   The actuator operated microvalves can be mass produced using MEMS batch fabrication technology and, as such, the per unit cost of the actuator will be reduced. MEMS batch fabrication technology will also result in uniformity and reliability of the actuator operated microvalves. 
   Because of the excellent high temperature properties of the materials used for production the actuator operated microvalves can operate in environments where the temperature is in the range of 600 to 1000° C. The preferred material used in the actuator operated microvalve is SiC (Silicon Carbide). Metals such as Nickel or Titanium may be used to form the electrostatic plates. 
   Fuel pressure pushes the SiC corrugated diaphragm and the boss up which, in turn, pushes the cylinder of the SiC top plate and the anode plate up as well. This action opens the valve seat which then allows fuel to flow past the valve seat and through the passage in the first lower portion of the SiC housing. Thus, the microvalve is normally closed and is opened by the fuel pressure. To close the valve, a voltage is applied to the positive electrostatic plate while the second plate is at ground potential. The ensuing electrostatic force, when as high as the corresponding fuel force, will lead to a net zero force on the diaphragm. When the electrostatic force is higher than the corresponding fuel force, the seat is completely sealed and no flow occurs. Modulation of the fuel flow can be achieved by pulsing the applied voltage across the plates. 
   Alternatively, the second plate on the second upper portion of the SiC housing may be at a potential other than ground. Electrostatic forces due to the electric field between electrical charges can generate relatively large forces given the small electrode separations. 
   An actuator operated microvalve comprises a body having an aperture therein and a slide having an aperture therein. The microvalve comprises the slide having an aperture therein in combination with an aperture in the body. The slide is moveable in a range of positions between a first open position of the microvalve wherein the aperture of the slide is aligned with the aperture of the body and a second closed position of the microvalve wherein the aperture of the slide is not aligned with the aperture of the body. The lever arm includes a pulling portion and a pushing portion. The lever arm pivots about a fulcrum. An actuator urges the pulling portion outwardly and the pushing portion pivots about the fulcrum into engagement with the slide urging the slide toward the closed position and urging the aperture of the slide out of alignment with the aperture of the body. A bias mechanism resists movement of the slide from the first open position of the microvalve toward the second closed position of the microvalve. 
   The actuator operated microvalve is developed for insertion or embedding, partially or wholly, in the flow field of a flow channel for the purpose of controlling and modulating the flow of liquid or gas. The actuator operated microvalve provides minimum intrusion in the flow field while at the same time significantly effects the profile of the flow. The actuator operated microvalve provides reasonable valve travel that permits the control and manipulation of flow rates over a wide range. Actuation can be implemented by applying electrostatic, electromagnetic, piezoelectric or electrokinetic principles, although the preferred actuation is electrostatic. To prevent premature fuel ignition and dangerous explosions, the actuation mechanism provides electrical isolation between the fuel path and the actuating electrodes. 
   The microactuator principally slides laterally back and forth and the process closes and opens a through hole to prevent or permit the flow of gases or liquids. Because it slides laterally its movement is perpendicular to the flow path. As a result, geometrical optimization of the slide will permit only a minimal flow force to act on the slide. The result is that only a relatively small force will be required to move the slider laterally. Because it operates based on the lever-fulcrum system a small actuation displacement results in an amplified lateral displacement. Because of the excellent thermomechanical properties utilized, this sliding microactuator is predicted to operate at temperatures up to 600 degrees C. Most existing actuators cannot support high flow rates because they are limited by the force and displacement required to support such high flows. 
   The principle of operation of the sliding valve is based on the lever-fulcrum system with the flexibility to be actuated by electrostatic, piezoelectric or electromagnetic devices. The forcing arm is situated in the flow chamber and is in intimate contact with, but not attached to, the slider. The slider is a free floating flat rectangular piece of Nickel. The spring or bias mechanism is another arm similar to but thinner than the pushing arm and located opposite the pushing arm. The pushing arm extends upward and forms part of the spring system and protrudes out to form the pulling portion of the lever. The joining point between the pulling arm is the structure that is separated from the forcing arm by an air gap. This rigid structure acts as the positive plate of the actuator. The vertical face of the forcing arm is electrically grounded. The actuating arm, the pushing arm, the slider, and the return spring are all made of Nickel. Other components are made form a high performance temperature material such as silicon carbide. 
   When no voltage is applied, the inlet hole, the slider hole and the ejection hole are aligned. This allows unimpeded flow and is considered a normally open state. Except for the positively charged electrostatic plate, the other parts are grounded. When this occurs an electrostatic force is applied between the plates. Because only the forcing arm is free to move, the attraction force pulls it to the left toward the rigid positive plate. This results in the swinging of the amplifying push arm to the right, thereby pushing the slider laterally to close the through hole and prevent flow. The degree of closure is determined by the applied force on the forcing arm. When the force is removed, the spring connected to the slider restores the slider to its original position. 
   The objective of this approach is to create a force amplification that will allow a large lateral displacement of the slider when pushed by the push-arm of the lever system. Alternative embodiments may include the attachment of a piezoelectric driver directly on to the top actuating arm, such that by exciting the piezoelectric material, the pulling arm is moved sideways back and forth. The characteristically small displacement of the piezoelectric material is amplified by the long pushing arm of the actuator. Another embodiment involves the use of an electromagnetic actuator that is current intensive. Generally, any driver can be attached to the pulling arm to obtain the desired effect of amplification. 
   It is an object of the present invention to provide actuator operated microvalves in arrays for admission and control of fuel into combustion streams. 
   It is a further object of the present invention to provide modulating actuator operated microvalves having components manufactured from SiC or Si which are electrostatically operated at low voltages. 
   It is a further object of the present invention to provide modulating actuator operated microvalves with electrically isolated actuators. 
   It is a further object of the present invention to provide modulating actuator operated microvalves which are capable of operating at temperatures up to 1000° C. 
   A better understanding of these and other objects of the invention will be had when reference is made to the Brief Description Of The Drawings and the Claims which follow hereinbelow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a drawing from U.S. Pat. No. 6,774,337. 
       FIG. 2  is a schematic representation of the invention illustrating the first lower portion and the second upper portion of the SiC housing along with the SiC diaphragm and SiC top plate. 
       FIG. 2A  is another schematic representation of the invention illustrating a diaphragm having multiple corrugations and nickel plates on both the second upper housing and the top plate. 
       FIG. 2B  is another schematic representation of the invention illustrating a diaphragm having multiple corrugations in the form of the preferred sine wave. 
       FIG. 2C  is a schematic representation illustrating the microvalve off its seat permitting flow between chamber and passageway. 
       FIG. 2D  is an enlargement of a portion of  FIG. 2C . 
       FIG. 2E  is an enlargement of a portion of  FIG. 2C . 
       FIG. 2F  is another embodiment of the actuator operated microvalve wherein a sinusoidally shaped nickel plate coacts with a sinusoidally shaped nickel plate or a sinusoidally shaped lower surface of the SiC top plate. 
       FIG. 2G  is a schematic of a wafer or mold illustrating batch fabrication of components of the invention thereon or therein. 
       FIG. 3  is a three dimensional representation of the actuator operated microvalve. 
       FIG. 3A  is a three dimensional representation of the actuator operated microvalve illustrating a sinusoidally shaped corrugated diaphragm. 
       FIG. 4  is a perspective view of a diaphragm having square-wave shaped corrugations. 
       FIG. 4A  is a perspective view of a diaphragm having square-wave shaped corrugations taken along the lines  4 A- 4 A. 
       FIG. 4B  is a perspective view of a diaphragm having sinusoidally shaped corrugations. 
       FIG. 4C  is a cross-sectional view of the diaphragm of  FIG. 4C  taken along the lines  4 C- 4 C. 
       FIG. 5  is a cross-sectional schematic view of a SiC wafer from which the first housing portion is produced illustrating a mask applied to one side thereof 
       FIG. 5A  is a cross-sectional schematic view of a SiC wafer as illustrated in  FIG. 5  after etching of one side has been completed and with a mask applied to the other side thereof. 
       FIG. 5B  is a cross-sectional schematic view of a SiC wafer as illustrated in  FIG. 5A  with the other side thereof etched. 
       FIG. 6  is a cross-sectional schematic of a wafer from which a mold is manufactured. 
       FIG. 6A  is a cross-sectional schematic view similar to  FIG. 6  after the dry etching has been performed. 
       FIG. 6B  is a cross-sectional schematic of the mold/carrier with a releasable layer applied thereto. 
       FIG. 6C  is an enlargement of a portion of  FIG. 6B . 
       FIG. 6D  is a cross-sectional schematic similar to that of  FIG. 6A  with the mask as shown in  FIG. 6A  removed and a mask applied to the other side thereof. 
       FIG. 6E  is a cross-sectional schematic similar to that of  FIG. 6D  with both sides having been etched illustrating the completed two sided mold. 
       FIG. 6F  is a flow chart illustrating the process steps for making the diaphragm. 
       FIG. 7  is a cross-sectional schematic of the second upper SiC housing portion with a mask applied to one side thereof. 
       FIG. 7A  is cross-sectional schematic of the second upper SiC housing portion with the underside thereof etched 
       FIG. 7B  is a cross-sectional schematic of the second upper SiC housing portion with a portion of the yet unetched side having unimidized photoresist applied thereto and a nickel or titanium plating over the photoresist and the remaining portion of the unetched side. 
       FIG. 7C  is a cross-sectional schematic similar to  FIG. 7B  with the unimidized photoresist and nickel above the unimidized photoresist being lifted off. 
       FIG. 7D  is a cross-sectional schematic similar to  FIG. 7C  with another layer of photoresist applied over the nickel and on the exposed portion of the second upper SiC housing. 
       FIG. 7E  is a cross-sectional schematic illustrating an island of unimidized photoresist being centrally located on the second upper SiC housing. 
       FIG. 7F  is a cross-sectional schematic similar to  FIG. 7E  illustrating another layer of nickel applied to the first layer of nickel, the exposed portions of the second upper SiC housing and the island of unimidized photoresist. 
       FIG. 7G  is a cross-sectional schematic similar to  FIG. 7F  with the unimidized layer of photoresist having been lifted off of the central portion of the second upper SiC housing. 
       FIG. 7H  is a cross-sectional schematic similar to  FIG. 7F  illustrating an orifice being etched therethrough. 
       FIG. 8  is a cross-sectional schematic of a SiC top plate with a mask applied thereto. 
       FIG. 8A  is cross-sectional schematic similar to that of  FIG. 8  with the underside of the top plate having been etched. 
       FIG. 8B  is a cross-sectional schematic similar to that of  FIG. 8A  with a layer of nickel applied to the upper portion thereof. Alternatively, the top plate may be doped so that it is conductive. 
       FIG. 8C  is a cross-sectional schematic of top plate including additional nickel plating and connections between the nickel plates. 
       FIG. 9  is a cross-sectional schematic of a SiC diaphragm bonded to the first portion of the SiC housing. 
       FIG. 9A  is a cross-sectional schematic of a SiC diaphragm bonded to an insulator which is in turn secured to the second portion of the SiC housing. 
       FIG. 9B  is a cross-sectional schematic of the cylinder of the top plate secured to an insulator which in turn is secured to the diaphragm. 
       FIG. 9C  illustrates an enlarged portion of  FIG. 9B . 
       FIG. 9D  illustrates an assembled actuator employing a sinusoidally shaped diaphragm. 
       FIG. 10  is a schematic of a control system which incorporates the use of an actuator operated microvalve of this invention. 
       FIG. 11  is a schematic of a spatially oriented combustion control system employing arrays of the actuator operated microvalves of this invention. 
       FIG. 12  is a schematic representation of a piston and actuator operated microvalves of this invention shown located therein. 
       FIG. 13  is a flow diagram for manufacturing the actuator operated microvalve of this invention. 
       FIG. 14  is a schematic representation of another embodiment of an actuator operated microvalve. 
   

   A better understanding of the drawings and invention will be had when reference is made to the Description of the Invention and Claims which follow hereinbelow. 
   DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross-sectional view  100  of a drawing FIG. 3 from U.S. Pat. No. 6,774,337. Also, U.S. Pat. No. 6,883,774 B2 illustrates in FIG. 3 thereof the same drawing in a less clear fashion. U.S. Pat. No. 6,883,774 B2 to Nielsen et al. entitled Microelectromechanical High Pressure Microvalve discloses first and second layers ( 12 ,  14 ) of SiC or Si, a stainless steel diaphragm member  16 , boss  22  and switching means  20 . The microvalve is designed for high pressure applications and employs a thin metallic diaphragm sandwiched between first and second layers of SiC or Si. The cracking pressure at which the stainless steel diaphragm opens is approximately 800 psi and the microvalve may be modified to open at pressures from 800-1200 psi. The diaphragm is biased in the closed position and moves from the closed position to the open position when the pressure of fluid in the inlet reaches a preset value. The switching means is connected to the valve body for moving the diaphragm to the closed position against pressure of the fluid in the inlet to the valve. “A recess or cavity  50  in the valve body  26  is provided to allow the diaphragm  16 , specifically the central portion thereof, to flex upward, away from valve seat  30   a . With the preferred embodiment of microvalve  10 , a sloped “dome” is ablated in the underside of the top SiC or Si wafer in order to provide a gentle valve stop. This extends valve life by reducing stress concentrations on the valve diaphragm  16 . The smooth sloped edges of the recess provide a gentle stop and prevent rupturing the thin diaphragm of the valve.” See, col. 3, lines 54 et seq. of the &#39;774 patent. A laser is used to form the contours of the underside of the top SiC or Si wafer by ablating the SiC or Si. A shape memory alloy actuator, a piezoelectric actuator, a microsolenoid actuator, or an electromagnetic actuator may be used. The disclosure of the &#39;774 patent indicates and recites switching means  20  and movement of the diaphragm from the closed position to the open position. The &#39;774 patent describes a relief valve. 
     FIG. 2  is a schematic representation  200  of the actuator operated microvalve illustrating the first lower portion  201  and the second upper portion  204  of the SiC housing along with the SiC diaphragm  202  and SiC top plate  206 . The principal portions  201 ,  202 ,  204 ,  206  of the actuator operated microvalve are preferably made of SiC and can be made from other semiconductors such as Si. First lower portion  201  of the SiC housing interengages diaphragm  202  and is at equipotential therewith. The principal portions of the actuator operated microvalve are generally disk-shaped with protrusions and voids therein.  FIG. 2  illustrates the diaphragm  202  having radially extending corrugations being a portion of a sine wave  205  and  FIG. 2B  illustrates radially extending corrugation as including multiple periods of sine waves  205 B. Any number of periods of radially extending corrugations may be employed limited, of course, by the size of the MEMS device. Diaphragm  202  includes a flange portion  221  which extends radially from the discontinuation of the radially extending corrugations. A fluid under pressure is employed in the generally annular chamber  212 . Chamber  212  is interconnected with a pressure source by a passageway or channel etched into first lower portion  201 . Diaphragm  202  includes a central boss  220  which is generally cylindrically shaped. Central boss  220  is illustrated in  FIGS. 2 ,  2 A and  2 B as engaging valve seat  216 ,  217 . Valve seat  216 ,  217  is formed from the top of a generally hollow cylinder formed by the etching process. Passageway  218  resides within the generally hollow cylinder and comprises the outlet of the actuator operated microvalve. 
   SiC diaphragm  202  is bonded to the first lower portion of the SiC housing. An insulator (dielectric)  211  such as a glass bonded oxide is formed between the flange  221  of the diaphragm  202  and the second upper portion  204  of the SiC housing. A braze material such as NiCuSil or TiCuSil is used to secure the glass bonded oxide insulator to the flange  221  of the diaphragm and the second upper portion  204  of the housing. Preferably second upper portion  204  of the SiC housing includes a nickel plate  210  which is deposited thereon. Nickel plate  210  constitutes the negative plate and is at ground potential along with the second upper portion  204  of the SiC housing, the SiC diaphragm  202 , and the first lower portion  201  of the SiC housing. 
   The SiC top plate  206  includes a centrally located protruding cylinder  222 . An insulator  209  such as glass bonded oxide is interposed between the boss  220  of the diaphragm and the protruding cylinder  222 . Adhesive such as NiCuSil or TiCuSil is used to secure the insulator  209  to both the boss  220  and the cylinder  222 . The SiC top plate  206  includes a radially extending flange portion  223 . Radially extending flange portion  223  of the SiC top plate is spaced apart from the second upper portion  204  of the SiC housing. Radially extending flange portion  223  of the SiC top plate  206  may include a nickel or other metal plate deposited thereon. A nickel plate  210  or other metal is formed on the top of the second upper portion  204  of the SiC housing. A gap  208  of approximately 2 to 5 microns exists between bottom portion  230  of the SiC top plate  206  and the nickel plate  210  which is deposited on the top of the upper portion  204  of the SiC housing. Other gap spacing may be used depending on the applied voltages and the tolerances applied to the construction of the actuator operated microvalve. 
   A voltage  214  is applied to nickel plate  207  of the SiC top plate  206  and a voltage  215  that is typically at ground potential is applied to nickel plate  210  on second upper portion  204  of the SiC housing. In the event that a Nickel plate  207  is not employed in connection with the SiC top plate  206  then the entire SiC top plate may be doped to be conductive. Reference numeral  204 A represents the opening in the second SiC housing which can serve as a guide for top plate  206  and, in particular, for cylinder portion  222  of the top plate. The gap between cylinder  222  and the opening  204 A is approximately 2 microns and may be varied as desired. It will be noted from a careful review of  FIGS. 2 and 2A  that the nickel plate  210  of the second upper portion of the SiC housing does not extend coterminously with the opening  204 A. A void  213  exists above the SiC diaphragm which provides room for the diaphragm to flex upwardly when the microvalve opens and boss  220  lifts off microvalve seat  217 / 216 . Void  213  is formed by etching a circumferential space through the underside of the second upper portion  204  of the SiC housing. 
     FIG. 2A  is another schematic representation  200 A of the invention illustrating a diaphragm having multiple corrugations  205 A and nickel plates on both the second upper portion  204  of the SiC housing and the SiC top plate  206 . In this embodiment multiple square wave corrugations  205 A are illustrated. 
     FIG. 2B  is another schematic representation  200 B of the invention illustrating a diaphragm having multiple corrugations  205 B in the form of the preferred sine wave.  FIG. 2C  is a schematic representation  200 C illustrating the microvalve  220  off its seat permitting flow between chamber  212  and passageway  218 . Gap  208  is increased by upward movement of top plate  206 . Gap  208  is increased by upward movement of top plate  206 . Sinusoidally shaped corrugations  205 B are preferred as they may flex without the risk of developing a stress fracture. The actuator operated microvalve of the instant invention operates at low pressures of approximately 50 psig or less. Referring to  FIG. 2C , the pressure at which the microvalve begins to open is approximately 0.1 psig or less and the maximum pressure in chamber  212  is on the order of 50 psig or less. These electrostatically actuated valves are arranged in arrays and control the flow therethrough depending on the magnitude of the voltage difference between the plates  207 ,  210 . Since a plurality of these electrostatically actuated valves are used to supply fuel to a combustion process they may be operated at low pressure in a shower head fashion. 
     FIG. 2D  is an enlargement  200 D of a portion of  FIG. 2B  illustrating the gap  208  between the nickel plate  210  and the nickel plate of SiC top plate  206 . V 1  is the first voltage  214  and V 2  is the second voltage  215  which is typically at ground potential.  FIG. 2E  is an enlargement of a portion of  FIG. 2B  and illustrates the insulator  211  secured to the diaphragm  202  and the second upper portion  204  of the SiC housing. Reference numeral  211 A represents adhesive applied to the oxide insulator  211  to secure it to both the second upper portion of the housing and to the diaphragm. 
     FIG. 2F  is another embodiment  200 F of the actuator operated microvalve wherein sinusoidally shaped nickel plate  241  coacts with a sinusoidally shaped nickel plate or a sinusoidally shaped lower surface  240  of the SiC top plate  206 . The maxima  242  and the minima  243  of each sinusoidal wave are aligned rendering a larger surface area between the plate providing more attractive force for the same voltage difference applied across the plates. 
     FIG. 2G  is a schematic  200 G of a wafer or mold  290  illustrating batch fabrication of components  291  of the invention thereon or therein. The wafer or mold can be between the size of a CD (compact disk) and a 16 inch diameter wafer. The corrugated diaphragms can be batch fabricated with 16 diaphragms from a single mold as illustrated in  FIG. 2G . Alternatively, even more diaphragms can be made from a 16 inch diameter wafer. Similarly, the upper and lower housing portions are batch fabricated from wafers between the size of a CD and a 16 inch diameter wafer. Other wafers having larger diameters are specifically contemplated. 
     FIG. 3  is a three dimensional schematic representation  300  of the actuator operated microvalve illustrating square-wave shaped corrugated diaphragm.  FIG. 3A  is a three dimensional schematic representation  300 A of the actuator operated microvalve illustrating a sinusoidally shaped corrugated diaphragm. 
     FIG. 4  is a perspective view  400  of a diaphragm having square-wave shaped corrugations  301 .  FIG. 4A  is a cross-sectional view  400 A of the diaphragm of  FIG. 4  taken along the lines  4 A- 4 A having square-wave shaped corrugations.  FIG. 4B  is a perspective view  400 B of a diaphragm having sinusoidally shaped corrugations  402  and  FIG. 4C  is a cross-sectional view  400 C of the diaphragm of  FIG. 4C  taken along the lines  4 C- 4 C. 
     FIG. 5  is a cross-sectional schematic view  500  of a SiC wafer  501  from which the first lower portion of the SiC housing is produced illustrating a mask  502  applied to one side thereof. Nominally the wafer is approximately 750 microns thick. Reference numeral  503  is an aperture in the etch mask which enables dry etching the outlet of the actuator operated microvalve. Wafer  501  in final form is generally disk shaped and has contours thereon. Wafer  501  is manufactured using a batch process wherein it is one of a plurality of micro machine components. 
   In describing the masking and etching procedure used herein, it will be understood by those skilled in the art that the normal steps of applying photoresist, imidizing the photoresist with a UV light source, removing the imidized photoresist and then dry etching with SF 6 , NF 3 , or CF 4  are necessary to accomplish the etching as described herein and the forming of like components of the actuator operated microvalve. Sometimes herein the term “mask” is used to generically refer to the preparatory process for etching and the use of term “mask” is not being used literally. 
     FIG. 5A  is a cross-sectional schematic view  500 A of the SiC wafer as illustrated in  FIG. 5  after etching of one side has been completed and with a mask  504 ,  505 ,  506  and  507  applied to the other side thereof. Reference numeral  503 A illustrates the outlet of the microvalve which was formed by the dry etching process. Dry etching is performed to generate the contours of the first lower portion of the SiC housing as illustrated in  FIG. 5B .  FIG. 5B  is a cross-sectional schematic view  500 B of a SiC wafer as illustrated in  FIG. 5A  with the other side thereof etched. The valve seat is denoted by reference numerals  520 ,  521 . As described above in connection with  FIG. 2 , the valve seat is generally formed in the shape of an annulus. Following the etching process with SF 6 , NF 3 , CF 4 , resulting surfaces  510 ,  511  and  512  are formed and best viewed in  FIG. 5B . 
     FIG. 6  is a cross-sectional schematic  600  of a wafer  601  from which a mold is manufactured and a mask  602 ,  602 A,  604 ,  606 ,  607 ,  607 A,  609 , and  611  is applied to a portion thereof. Etched areas are represented by reference numerals  603 ,  605 ,  605 A,  608 ,  610 ,  610 A,  612 ,  613  and  614 .  FIG. 6A  is a cross-sectional schematic view similar to  FIG. 6  after the dry etching has been performed.  FIG. 6B  is a cross-sectional schematic  600 A of the mold/carrier with a releasable layer  620  applied thereto with the SiC being deposited thereon by chemical vapor deposition. Sometimes herein the process of applying the SiC by chemical vapor deposition is referred to herein as being grown.  FIG. 6C  is an enlargement of a portion of  FIG. 6B  illustrating the releasable layer  620  and the SiC  619  being deposited thereon. 
     FIG. 6D  is a cross-sectional schematic  600 D similar to that of  FIG. 6A  with the mask as shown in  FIG. 6A  removed and a mask applied to the other side thereof. Reference numerals  630 ,  632 ,  634 ,  636 ,  638 ,  640 ,  642  indicate mask sections. Apertures are indicated by reference numerals  631 ,  633 ,  635 ,  637 ,  639  and  641 .  FIG. 6E  is a cross-sectional schematic  600 D similar to that of  FIG. 6D  with both sides having been etched illustrating a completed two sided mold. The two sided mold of  FIG. 6E  is an alternative embodiment of the mold. Reference numerals  603 ,  605 ,  608 ,  610 ,  643 ,  644 ,  645 ,  646 ,  647  and  648  indicate completed reciprocal mold surfaces. A two sided mold is obviously more productive for growing the SiC diaphragms thereon after receiving a releasable layer on both sides thereof. Where a sinusoidal mold is desired, the same can be made from a repetitive process of masking as set forth in  FIG. 6C . In forming the contours of the sinusoidally shaped mold it is necessary to repeatedly apply masks so as to protect the already etched sections of the mold. 
     FIG. 6F  is a flow chart/schematic representation  600 F illustrating the process steps for manufacturing a mold/diaphragm comprising the steps: of applying or reapplying  621  a mask to a Si or SiC wafer; dry etching  622  with Sulfur Hexaflouride or Ammonium Flouride, dissolving  623  the mask with a Hydrochloric Acid and Nitric Acid solution to complete the formation of the mold; repeating  623 A steps  621 ,  622  and  623  to form a sinusoidally shaped mold; coating  624  the mold with a releasable layer; growing  625  corrugations on the mold; dissolving the releasable material; and, separating the mold from the diaphragm leaving the remaining square-wave, sinusoidal wave or other shape mold. 
     FIG. 7  is a cross-sectional schematic  700  of the second upper SiC housing portion with a mask  702 ,  703  applied to one side thereof.  FIG. 7A  is cross-sectional schematic  700 A of the second upper  701  SiC housing portion with the underside  704  thereof etched. Protected portions  702 ,  703 , sometimes referred to as masked portions, enable the etching of the underside  704 . Reference numeral  705  represents the surface following etching.  FIG. 7B  is a cross-sectional schematic  700 B of the second upper SiC housing portion with a portion of the yet unetched side having unimidized photoresist  706  applied thereto and a nickel or titanium plating  707  over the photoresist  706  and the remaining portion of the unetched side. Reference numeral  740  indicates exposed photoresist which provides a pathway for the dissolving agent to attack the photoresist.  FIG. 7C  is a cross-sectional schematic  700 C similar to  FIG. 7B  with the unimidized photoresist  706  and nickel above the unimidized photoresist being lifted off/dissolved.  FIG. 7D  is a cross-sectional schematic  700 D similar to  FIG. 7C  with another layer of photoresist  750  applied over the nickel and on the exposed portion of the second upper SiC housing.  FIG. 7E  is a cross-sectional schematic  700 E illustrating an island  760  of unimidized photoresist being centrally located on the second upper SiC housing. The remaining photoresist was removed after masking, exposing and developing.  FIG. 7F  is a cross-sectional schematic  700 F illustrating another layer of nickel  708  applied to the first layer of nickel  707 , the exposed portions of the second upper SiC housing and the island  760  of unimidized photoresist. Reference numeral  761  indicates the exposed portion of the unimidized photoresist which may be attacked by the dissolving agent. 
     FIG. 7G  is a cross-sectional schematic  700 G similar to  FIG. 7F  with the unimidized layer of photoresist  760  having been lifted off of the central portion of the second upper SiC housing. Exposed area  708 A illustrates the area left for etching.  FIG. 7H  is a cross-sectional schematic  700 H similar to  FIG. 7G  indicating an orifice  709  being etched therethrough.  FIG. 7H  also illustrates the orifice acting as a diametrical guide  709  formed in the finished second upper portion. 
     FIG. 8  is a cross-sectional schematic  800  of a SiC top plate  801  with a mask  802  applied thereto.  FIG. 8A  is cross-sectional schematic  800 A similar to that of  FIG. 8  with the underside  801 A of the top plate having been etched.  FIG. 8B  is a cross-sectional schematic  800 B similar to that of  FIG. 8A  with a layer of nickel  803  applied to the upper portion thereof. Alternatively, the top plate may be doped so that it is conductive.  FIG. 8C  is a cross-sectional schematic of the top plate  801  including additional nickel plating  806 ,  807  and connections  804 ,  805  between the nickel plates. 
     FIG. 9  is a cross-sectional schematic  900  of a SiC diaphragm  619  secured/bonded to the first portion  501  of the SiC housing.  FIG. 9A  is a cross-sectional schematic  900 A of the SiC diaphragm  619  secured to an insulator  901  by NiCuSil or TiCuSil adhesive which is in turn secured by the adhesive  902  to the second upper portion  701  of the SiC housing. Valve seat  520 ,  521  and passageway  503 A are indicated in  FIG. 9  as is the radially extending chamber  903 .  FIG. 9B  is a cross-sectional schematic  900 B of the cylinder  801  of the top plate secured to an insulator by the adhesive NiCuSil/TiCuSil which in turn is secured to the diaphragm  619 . As such,  FIG. 9B  illustrates the assembled actuator operated microvalve.  FIG. 9C  illustrates an enlarged portion  900 C of  FIG. 9B . Gap  910  is illustrated between electrostatic plates  707  and  806 .  FIG. 9D  illustrates an assembled actuator  900 D employing a sinusoidally shaped diaphragm. 
     FIG. 10  is a schematic of a control system  1000  which incorporates the use of an actuator operated microvalve of this invention. Process set point  1001  is compared to the output  1002  of the process sensor  1002 . It will be understood by those skilled in the art that a plurality of sensors may feedback a plurality of process measurements which are then compared to a plurality of setpoints. In this way combustion control can be accomplished on a distributed basis. An error signal  1003  is generated by the comparator and the error signal is then inputted into the controller  1004 . Controller  1004  then acts upon this error signal according to an algorithm(s) and then an output signal is forwarded to the actuator operated microvalves  1005  as described previously herein above. The actuators then output the correct quantity of fuel into different locations of the combustion process  1006 . The frequency response of the actuators is good enabling fast response times to add more or less fuel in the areas desired. The process is continuously generating various physical parameters such as flow, temperature, pressure etc. each of which may be sent back  1008  to the comparator to generate a plurality of error signals each of which may be acted upon by the controller. The actuator operated microvalves can receive voltage pulses or they can receive analog (continuous) signals. The algorithm used in the controller may be proportional plus integral plus derivative depending on the parameter being fed back to the comparator for the generation of the error signal. 
     FIG. 11  is a schematic  1100  of a spatially oriented combustion control system employing arrays  1101 ,  1102 ,  1103 ,  1104 ,  1105 ,  1106  of the actuator operated microvalves of this invention. The arrays may, for instance, be arranged in 4 by 4 groupings or they may be arranged in 7 by 7 groupings as desired by the combustion process designer. A combustion controller  1107  distributes control signals to the respective array and these signals may be addressable for operation of the specific microvalves of an array. 
     FIG. 12  is a schematic representation  1200  of a piston  1201  and actuator operated microvalves  1202 ,  1203 ,  1204 ,  1205  of this invention shown located therein. Reference numerals  1208 ,  1209  are views, for example, of the outputs of the individual microvalves. Reference numerals  1210  and  1211  may be sensors employing MEMS based technology to measure parameters within the cylinder. Controllers  1206 ,  1207  drive the actuator operated microvalves to admit more or less fuel in certain positions of the cylinder. Controllers  1206 ,  1207  may interact with other cylinders to add or subtract torque applied to the crankshaft to reduce vibration and/or to minimize pollutants such as Carbon Monoxide and Oxides of Nitrogen. 
     FIG. 13  is a flow diagram  1300  for manufacturing the actuator operated micro valve of this invention. The first step is forming  1301  a first lower portion of the SiC housing with a valve seat using a mask, photoresist, UV light, developer and dry etching; forming  1302  a second upper portion of the SiC housing a mask, photoresist, UV light, developer and dry etching; electroplating/sputtering  1303  nickel or other metal onto the second upper portion of the SiC housing forming an electrode or electrostatic plate; forming  1304  a top plate and cylinder using a mask, photoresist, UV light, developer and dry etching; electroplating/sputtering  1305  nickel or other metal onto the top plate forming an electrode or electrostatic plate; forming  1306  a SiC diaphragm having a boss; attaching  1307  the SiC diaphragm to the first SiC housing; attaching  1308  an insulator to the SiC diaphragm; attaching  1309  the second upper portion of the SiC housing to the insulator; attaching  1310  the cylinder of the top plate to the boss of the diaphragm; attaching  1311  an insulator to the boss of the diaphragm; and, attaching  1312  the cylinder of the top plate to the boss of the diaphragm. 
     FIG. 14  is a schematic representation  1400  of another embodiment of an actuator operated microvalve. A SiC body  1403  includes an aperture  1407  therein. A slide  1402  includes aperture  1402 A therein. Slide  1402  is preferably Nickel and sits atop the body  1403  and in the first open position the aperture  1402 A of the slide is aligned with the aperture  1407  of the body  1403 . A SiC substrate  1401  is bonded to the body  1403  at the outer peripheries thereof. Substrate  1401  also includes an inner portion  1401 A having an aperture  1415  therein. Aperture  1415  is aligned with aperture  1402 A and aperture  1407 . The inner portion  1401 A is stationary and is always aligned with aperture  1407  of the body  1403 . Adhesive  1404 A is affixed to the inner portion  1401 A of the SiC substrate. Nickel plate  1406 ,  1406 A is secured to the SiC substrate by adhesive  1404 ,  1404 A,  1405 ,  1405 A. Nickel plate  1406 ,  1406 A bridges the inner portion  1401 A and the outer portion  1401  of the SiC substrate. An insulator  1414  sits atop the outer portion of the Nickel plate  1406 ,  1406 A. Doped SiC  1412  sits atop and is secured to the insulator  1414 . 
   Still referring to  FIG. 14 , a lever  1420  includes a pulling portion  1410  and a pushing portion  1411 . It will be noted that the pulling portion  1410  is shorter in length than the pushing portion  1411 . Reference numeral  1409  denotes a fulcrum which is formed in Nickel plate  1406 . The fulcrum  1409  is an aperture in the plate  1406 . The lever  1420  is press fit into fulcrum  1409 . Reference numeral  1421  denotes contact between the lever  1420  and the sliding plate  1402 . Symbols V +  and V −  indicate the polarity of the doped SiC  1412  and the lever  1402 . As described previously hereinabove, when the electrostatic plates have a potential difference between them they are drawn together. Since the pulling portion  1410  of the lever  1420  is shorter than the pushing portion  1411  of the lever  1420 , a mechanical advantage is realized and the pushing portion  1411  moves a larger amount than the pulling portion  1410 . Therefore, for small voltage changes and lower power usage the action of the lever magnifies the movement of the pushing portion  1411 . Further, reference numeral  1421  pushes against the slide  1402  pushing the respective apertures  1402 A and  1407  out of alignment tending to close the microvalve. Slide  1402  can be thought of as the valve. 
   Still referring to  FIG. 14 , reference numerals  1413 ,  1416  illustrate a post which is press fit within the Nickel plate  1406 A. As slide  1402  is urged rightwardly the bottom  1416  of the post is urged rightwardly as well which tends to buckle Nickel plate  1406 A. Buckling of Nickel plate  1406 A stores energy and provides a resistive force on slide  1402  which tends to urge slide  1402  leftwardly which in turn tends to align the apertures. 
   Although this invention has been described by way of example and with particularity and specificity, those skilled in the art will recognize that many changes and modifications may be made without departing from the spirit and scope of the invention defined by the Claims which follow hereinbelow.

Technology Category: 2