Abstract:
Integrated micro-valve is formed to control fluid flow and pressure. The valve converts supplied energy to mechanical energy through an energy conversion means resident above a flexible wall or membrane. In one embodiment a sealed cavity contains a fluid that expands and contracts as it is heated or cooled, thus causing the flexible wall to move. Movement of this wall or membrane is used to move a valve element and dynamically control the opening or closing of a valve port over a predetermined range. Additional stiffening means are added to the membrane to improve performance.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention pertains to the field of integrated, electrically operable micro-valves and, more particularly, to the field of low leak rate integrated micro-valves for industrial, corrosive and ultra-clean applications.  
       BACKGROUND OF THE INVENTION  
       [0002]     Micromachined integrated valves are known in the prior art. Examples of various embodiments of such normally open valves are given in U.S. Pat. Nos. 4,821,997 and 4,824,073 and 4,943,032 and 4,966,646; the disclosures of which are hereby incorporated by reference herein in their entirety.  
         [0003]     U.S. Pat. Nos. 5,865,417 and 6,149,123 taught how to make a normally closed, micro-machined valve with a leak rate on the order of 1×10 −9  scc-atm/sec or less of helium. U.S. Pat. No. 6,160,243 disclosed alternative methods of actuating micro-valves. U.S. Pat. Nos. 5,865,417 and 6,149,123 and 6,160,243 are included by reference herein in their entirety.  
         [0004]     An integrated micro-valve, also commonly referred to as a microminiature valve, uses a thin flexible membrane with an actuator to move a valve element. In some embodiments, the flexible membrane is coupled to a cantilever element through a solid extension located on the membrane, as described in the referenced patents and shown in  FIGS. 1 and 2 , slightly modified from as presented in U.S. Pat. No. 6,149,123. Movement of the membrane  200  causes a cantilever element  300  to move and either open or close off valve seat  410 . Port  400  is fluidically coupled to passageways serving as input  520  and output  510  channels. Element  210 , typically referred to as a pedestal, is joined to cantilever  300  by an appropriate adhesive or other bonding technique. In  FIG. 2  the membrane  200  is actuated and the cantilever  300  is now open. Element  415  is a compliant seat material meant to facilitate sealing against valve seat  410 ; typically this material is a Teflon-like material, either PTFE or derivatives thereof.  
         [0005]     As previously disclosed, membrane  200  is typically 40 to 60 microns thick and of single crystal silicon. The burst strength of the membrane is quite sensitive to design considerations such as overall area and membrane thickness. Processing conditions such as etchants and etching conditions and other variables are also factors in membrane strength. As the inlet pressure in channel  520  increases the force required to open cantilever  300  increases; in addition, as the area of channel  400  increases the opening force also increases. Depending upon the actuation mechanism employed in region  130  of  FIG. 1  membrane  200  may not expand outward uniformly; the membrane may expand in such a fashion that the cantilever remains unopened or insufficiently open to meet the design criteria.  
         [0006]     The previously disclosed valves were not able to operate reliably above an, inlet pressure of 50 psig, pounds per square inch gauge, while delivering more than 10 slm, standard liters per minute, at an acceptable pressure drop. There is a need for a valve which can flow up to 20 slm at an inlet pressure of over 100 psig with an acceptable pressure drop.  
       SUMMARY OF INVENTION  
       [0007]     In the present invention, the valve is configured as a normally closed valve with at least two pedestals, one in the position as described in U.S. Pat. No. 5,865,417 and one approximately 1 mm from the original pedestal toward the far cavity wall, as shown in  FIG. 3 . The advantages of the current invention over the previous embodiment are several. First, the membrane is stiffened and no longer can assume actuated positions which do not open the cantilever. Second, more force can now be transferred from the actuation mechanism to open the cantilever; this result further allows the line pressure to be increased to over 100 psig and the inlet ports expanded to at least 1 mm in diameter. Third, by stiffening the membrane and preventing alternate flexure modes of the membrane, greater latitude in placement of the first pedestal is gained. This latitude allows the pedestal, acting as the pivot point on the cantilever, to be moved further from the inlet port, thus moving the cantilever farther from the inlet port and decreasing the cantilever acting as a restriction in the flow path.  
         [0008]     In some embodiments of the present invention sensing devices are integrated with the valves. In some embodiments these sensing devices are pressure sensors, while in other embodiments these sensing devices are temperature sensors or both. Thus where valves in accordance with embodiments of the present invention have integrated sensing devices to provide dynamic feedback to the energy input source of the energy conversion block, these valves can provide feedback signals to facilitate the control of fluid flow or pressure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art, by referencing the accompanying drawings. For ease of understanding and simplicity, common numbering of elements within the illustrations is employed where an element is essentially the same between illustrations.  
         [0010]      FIG. 1 , slightly modified from as presented in U.S. Pat. No. 6,149,123, is the prior art.  
         [0011]      FIG. 2 , slightly modified from as presented in U.S. Pat. No. 6,149,123, is the prior art in the actuated or open position.  
         [0012]      FIGS. 3A and 3B  are alternative embodiments of the current invention as improved from the prior art.  
         [0013]      FIG. 4  is a laser profilometer scan of a single pedestal valve actuated with 100 psig air.  
         [0014]      FIG. 5  shows two laser profilometer scans of a dual pedestal valve unactuated and actuated with 100 psig air. 
     
    
     DETAILED DESCRIPTION  
       [0015]     Embodiments of the present invention will be described with reference to the aforementioned figures. These drawings are simplified for ease of understanding and description of embodiments of the present invention only. Various modifications or adaptations of the specific methods and or structures that represent embodiments of the present invention may become apparent to those skilled in the art as these embodiments are described. All such modifications, adaptations or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the present invention. For example, in some embodiments of the present invention, a valve with a single valve port is employed whereas in other embodiments multiple valve ports can be employed. Details of processes that may be used to fabricate portions of embodiments of integrated valve structures is generally known to those of ordinary skill in the art. In addition, the patents referenced, all of which have been previously incorporated by reference herein, provide processing descriptions. Thus, only some processing details, believed not readily apparent are described herein.  
         [0016]     Referring to  FIG. 3A , a simplified cross-sectional representation of a portion of an integrated, normally closed, electrically operable, valve  50  fabricated in accordance with an embodiment of the present invention is shown. Referring to  FIG. 1 , when energy is supplied to actuation means in cavity  100  it causes membrane  200  to flex or deflect outward as drawn schematically in  FIG. 3 . In addition to forming a wall of cavity  100 , flexible membrane  200  is also positioned adjacent to cantilever element  300 . Membrane  200  is mechanically coupled to cantilever element  300  through pedestal  210  at coupling point  310 . This coupling of flexible membrane  200  to cantilever element  300  advantageously provides for transfer of the movement of membrane  200  to cantilever element  300 . In the current invention, in one embodiment, additional pedestal,  240 , is added to membrane  200  as shown in  FIG. 3 . Placement of this second pedestal relative to first pedestal is shown in  FIG. 5 , being about 1 mm in the direction of the inlet port. As can be seen from the scale of  FIG. 5 , in this embodiment, second pedestal,  240 , is somewhat smaller than first pedestal,  210 . The dimensions and location of a second pedestal are not critical. What is critical is that the second pedestal be of sufficient height such that upon actuation second pedestal encounters cantilever element  300  early in the actuation cycle and lifts it slightly to start flow through valve port  400 .  
         [0017]     The other function performed by second pedestal  240  is a stiffening of membrane  200  such that it may not flex upward while pedestal  210  stays relatively motionless during the actuation cycle. This situation is known to occur when forces greater than 50 psig are placed on cantilever element  300  over the area of valve seat  410  in the direction of port  400 . This condition can be catastrophic when the burst strength of membrane  200  is less than the force required to open the valve and less than the actuation pressure applied internally.  
         [0018]     One alternative means to achieve a stiffening of membrane  200  is to form ribs of thicker cross section on the membrane in a direction parallel to first pedestal. These ribs are on the order of 20 to 80 microns wide and have thickness, including the membrane, of approximately 50 to 125 microns. Alternatively, other shapes may be used, such as small squares or circles or polygons; as the fraction of the membrane covered by these areas of increased thickness increases, so will the overall stiffness, and the actuation amount versus actuation pressure will decline.  
         [0019]     An alternative means to achieve a similar result without stiffening the membrane  200  is to form a second pedestal,  245 , as shown in  FIG. 3B , on cantilever  300 . Placing the pedestal on the cantilever simplifies the processing of the membrane while increasing the complexity of the cantilever, a somewhat straightforward task to begin with. Pedestal,  245 , hinders the membrane from expanding outward in the region apart from pedestal  210 .  
         [0020]     It should also be apparent that valves fabricated in accordance with the present invention can be either stand-alone valves, or valves that are coupled to any one of a variety of flow sensing devices known in the art. In addition, it should be apparent that the micro-valves of the present invention can be opened or closed to varying degrees. Thus valves made in accordance with the present invention can not only provide either flow or no-flow of a fluid, but can control the amount of flow of that fluid over a continuous range of flow rates; the valve may be operated in a proportional manner; the degree of openness being proportional to the degree of actuation and energy supplied to the actuation means. Control of fluid flow rate is obtained, for example, by varying the amount of energy converted to mechanical energy by the energy conversion means in portion  100 . In this manner, the position of the cantilever element is varied in proportion to the amount of deflection from the de-energized state. Thus, embodiments of the present invention can incorporate an integrated flow or pressure sensing apparatus which can provide dynamic feedback to the valve to control dynamically the flow rate or pressure provided. Where the sensing apparatus is used to sense flow rate, the micro-valve and added elements are commonly referred to as a flow controller. Where the apparatus determines pressure, the micro-valve and added elements are commonly referred to as a pressure controller. For example, a flow controller, in accordance with the present invention, can encompass a flow sensing apparatus having a first pressure sensor, a flow restrictor and a second pressure sensor where the pressure drop across the restrictor is measured. As is known, for a predetermined flow restriction the pressure drop can be accurately calibrated to the flow rate for a specific fluid. Thus the flow sensing apparatus, as described, enables dynamic control of the mass flow rate for the specific fluid selected.  
         [0021]     As one of ordinary skill in the art of micro-valves will realize, many variations, in addition to the examples herein, of valves, valve seats, valve elements, cantilevers, sensors, actuation means and restrictors are known. Thus, it would be impractical to describe each configuration. In addition, it will be realized that methods described herein, incorporated by reference from the cited patents as well as other known methods, can be employed to fabricate these configurations of valves and associated elements. Thus, it is understood that these various configurations of valves and elements used in various combinations are intended to be within the scope of the present invention.