Abstract:
A combined wet-wet differential transducer and a gage pressure transducer located in the same housing, comprising a semiconductor chip which comprises a gage sensor chip on one section and a differential sensor chip on a second section. Each sensor chip has a Wheatstone bridge comprising piezoresistors and is responsive to an applied pressure. The gage chip and the differential chip are placed in a header having a front section and a back section adapted to receive a first and second pressure, respectively. The sensors are in communication with first and second pressure ports such that the absolute sensor provides an output indicative of a pressure applied to a first port and the differential sensor provides an output indicative of the pressure difference between the first and second pressure ports.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This Application is a continuation claiming priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/316,317 entitled “A Combined Wet-Wet Differential and Gage Transducer Employing a Common Housing,” filed Dec. 11, 2008, which is incorporated by reference in its entirety as if fully set forth herein. 
       RELATED APPLICATIONS 
       [0002]    A related application is entitled “Low Differential Pressure Transducer” filed on Feb. 14, 2008 as Ser. No. 12/070,255 hereinafter designated as the 255 application. Reference is also made to patent application Ser. No. 12/286,810 filed on Oct. 2, 2008 and entitled “Redundant Self Compensating Leadless Pressure Sensor”. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates to pressure transducers and more particularly to a combined wet-wet or wet-to-wet differential transducer as well as a gage transducer in the same housing. 
       BACKGROUND OF THE INVENTION 
       [0004]    As one can ascertain, there are many types of pressure transducers for which there are many well known uses. One type of a particularly useful transducer is conventionally characterized as being wet-to-wet which can be used to measure the differential pressure between two fluid or gaseous substances. Wet-to-wet differential transducers are used in many industries such as automotive, medical and aerospace applications. A gage transducer is also a extremely useful device and a gage or absolute transducer will measure applied pressure with respect to atmospheric pressure or applied with respect to zero pressure. Thus the term gage is employed to measure an applied pressure with respect to atmospheric pressure. As one can ascertain, the prior art is replete with a number of patents which describe various configurations and methods of fabricating pressure sensing devices. The assignee herein, namely Kulite Semiconductors Products, Inc., has many patents regarding such devices. As is true in any field, the construction and implementation of such devices and of employing such devices has improved and typically the devices should be easier to use, simpler to install and of course, simpler to construct. Thus, the prior art makes many improvements to such devices and such improvements continue to be made. In this particular application, there is disclosed a combined wet-to-wet differential transducer as well as a gage pressure transducer in the same housing. In this manner, one utilizing this transducer can obtain an output in regard to a differential pressure as well an output in regard to gage pressure. As indicated, a typical piezoresistive device is employed, which basically includes a bridge pattern as a Wheatstone bridge which are formed on a relatively thin semiconductive deflecting member or diaphragm. The deflecting member may be fabricated from silicon and deflects upon application of a pressure which causes the piezoresistors to vary their magnitudes. If a pressure P is applied to one face of the deflecting member, and a pressure P 2  is applied to the other face of the deflecting member, the result in deflection will be determined by the differences in pressure. Thus differential pressure measurements can be accomplished using a differential transducer which provides an output indicative of the difference between two pressures. The absolute pressure transducer produces a pressure which is measured with respect to zero pressure in units of force per unit of area. A gage pressure transducer measures pressure with respect to atmospheric pressure and essentially the measurement of differential pressure as well as gage pressure are very useful measurements and are made in many applications such as in the automotive, aircraft and other industries as well. Thus, as indicated, the prior art is replete with a number of patents which describe such transducers. For example, see U.S. Pat. No. 6,543,291 entitled Wet-to-Wet Pressure Sensing Assembly issued on Apr. 8, 2003 to A. D. Kurtz, et al. and assigned to Kulite Semiconductor Products, Inc., the assignee herein. That patent describes a wet-to-wet differential pressure device which is typical of a differential transducer and also contains oil filled cavities for interfacing with the wet-to-wet environment. Reference is also made to U.S. Pat. No. 6,612,179 entitled Method and Apparatus for the Determination of Absolute Pressure and Differential Pressure Therefrom issued on Sep. 2, 2003 to A. D. Kurtz and assigned to the assignee herein. That patent describes a combination absolute and differential pressure sensing device. In any event, the prior art is replete with a number of such devices and, as indicated above, it is desirable to provide improved devices to make fabrication and use simpler. Reference is also made to U.S. Pat. No. 7,057,247 issued on Jun. 6, 2006 entitled Combined Absolute Differential Transducer by A. D. Kurtz, et al., assigned to Kulite Semiconductor Products, Inc., the assignee herein. That patent discloses a combined absolute and differential pressure transducer which consists of two sensors made from the same wafer of silicon and selected to be adjacent to each other. The patent also describes the adjacent sensors, each having the same web thickness but having different size active areas, where the thermal coefficient and the thermal sensitivity are controlled by the impurity concentration of the P regions. Thereby the thermal properties of the two adjacent sensors are closely controlled and matched to each other, resulting in an improved overall combined absolute and differential transducer. The above noted patents are incorporated herein in their entirety. It is an object of the present invention to provide an improved wet-to-wet differential transducer as well as a gage pressure transducer, all employed in a common housing. Thus the present invention makes possible the construction of a low pressure differential transducer having on each end the same size large diameter isolation diaphragm while enabling one to bring out the leads from the semiconductor sensors in a simple and expeditious manner. As will be ascertained, to make a wet-to-wet differential transducer, together with a wet-to-wet absolute transducer, an additional die is installed next to the differential die which was shown previously with the wet-to-wet differential transducer. 
       SUMMARY OF THE INVENTION 
       [0005]    A combined pressure transducer, comprising: a housing having an internal hollow with a first and a second pressure port each communicating with said hollow, a header having a front and a back section, each section having an outer surface, a central section joining said front and back sections wherein said header has an “H” shaped cross section, said front section outer surface having a first depression of a given area, a first flexible isolation diaphragm covering said first depression, said back section outer surface having a second depression of said given area, a second flexible isolation diaphragm covering said second depression where first and second isolation diaphragms are relatively of the same size and area, a channel positioned within said central section and extending to and communicating with said first and second depressions, a first sensor structure on said header having a first sensor diaphragm, said sensor diaphragm having a top and a bottom surface with said top surface communicating with said channel, and said bottom surface communicating with said first flexible isolation diaphragm, a second sensor structure on said header having a second sensor diaphragm also having a top and bottom surface, with said second sensor adjacent to said first sensor structure, with the bottom surface of said second sensor diaphragm communicating with said first flexible isolation diaphragm, said header positioned in said hollow of said housing and located so that said bottom surfaces of said first and second sensor diaphragms communicates with said first pressure port of said housing, and means coupling said second sensor port of said housing to said second flexible diaphragm, whereby said first sensor provides a differential output indicative of the difference of pressure applied to said first and second ports and said second sensor provides an output indicative of the pressure applied to said first port. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]      FIG. 1  consists of  FIG. 1A  which is front view of a sensor assembly employed in this invention.  FIG. 1B  is a cross sectional view of the sensor of  FIG. 1A . 
           [0007]      FIG. 2  is a cross sectional view of a combined wet-to-wet differential and gage transducer employing a common housing according to this invention. 
           [0008]      FIG. 3  is schematic diagrams of the bridge configurations employed with the sensors. 
           [0009]      FIG. 4  is a diagram of the Wheatstone bridge assembly according to this invention. 
           [0010]      FIG. 5  is a cross sectional view of a single wafer employing a differential and gage transducer according to this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    Referring to  FIG. 1 , there is included  FIG. 1A  and  FIG. 1B .  FIG. 1  depicts a transducer assembly  10  which is also described in detail in the above noted co-pending application cited under related application as the  255  application. In the  255  application there is disclosed a wet-to-wet differential pressure transducer. The pressure transducer, as described in the above noted application and as seen in  FIG. 1B , has an H shaped cross section. The device is shown in  FIG. 1A  in a front view, as will be explained, with the isolation diaphragm removed. In any event, as indicated, the pressure transducer structure  10  as shown in  FIG. 1B  has an H shaped cross section and essentially would appear from a perspective view as a dumbbell. The device depicted in cross section in  FIG. 1B  has a front isolation diaphragm  11  which basically spans an internal cavity or front depression. There is a ceramic substrate  13  which essentially bounds the cavity or spacing between the isolation diaphragm and the substrate  13 . This spacing between the isolation diaphragm and the substrate is filled with a force transmissive oil which is placed via the oil filled tube  15  on the high side of the diaphragm. The diaphragm  11  is the same exact size or diameter as the diaphragm  21  on the low side. Both isolation diaphragms  11  and  21  are fabricated from a flexible metal, such as stainless steel. The space between the diaphragm  21  and the cavity is also filled with oil. This space is designated by reference numeral  20 . The oil filled tube  16  enables one to place oil between the diaphragm  21  and within the spacing  20 . The oil also is directed via an internal channel  23  where it is directed to the cavity in the housing enclosing a semiconductor chip  36 . The semiconductor chip  36 , as will be explained, contains a first and a second sensing device, both of which may be fabricated on the same chip. These devices, as will be explained, consist of an absolute or gage transducer chip and a delta P or differential transducer chip. Both chips may be fabricated on the same substrate and separated by an isolation groove. The chips, as will be explained, are described in the prior art and the assignee herein has pending patent applications, as well as issued patents, relating to such chip structures. In any event, it is noted that forming an absolute or gage, as well as a differential sensor arrangement on the same chip is well known. See for example the above noted patent cited as U.S. Pat. No. 7,057,247 entitled Combined Absolute Differential Transducer issued on Jun. 6, 2006. That patent discloses an absolute differential pressure transducer which consists of two sensors made from the same silicon wafer or substrate and selected to be adjacent to each other on the substrate. In any event, the patent describes in detail the fabrication of such devices as well as indicating that by choosing adjacent sensors with the same web thickness but different size active areas, one can obtain improved operation. The patent describes in detail the fabrication of such devices and how they are formed on a common substrate. The entire content of the above noted patent are included herein in its entirety. The device incorporated herein uses the sensor arrangement, as for example shown in U.S. Pat. No. 7,057,247. The structure of the low pressure differential transducer is depicted in the co-pending application Ser. No. 12/070,255 and essentially is the device depicted in  FIG. 1 , with the exception that, in this invention, there are two sensors employed on the wafer  36 , namely an absolute sensor  31  and a differential sensor  30 . As seen in  FIG. 1A , there is shown a front view of  FIG. 1B  with the isolation diaphragm  11  removed. As one can see, leads from the two sensor devices are directed to electrically glass sealed pins such as  12  of  FIG. 1  and other pins designated as  32 ,  33 ,  34  and so on in  FIG. 1A . These pins emanate from the terminals or contacts associated with each of the sensor devices. The sensor devices in  FIG. 3 , are piezoresistive devices which are typically arranged in a Wheatstone bridge configuration. As shown in  FIG. 3 , there is shown a first Wheatstone bridge  50  and a second Wheatstone bridge  51 . The bridges  50  and  51  would be associated with the differential and absolute transducer structures. It is also noted that the bridge  51  is opened at the top terminal and therefore has two output leads as  52  and  53 , while the bridge  50  is closed and has a biasing lead  55 . The outputs (volt) of both bridges are taken across the center terminals as shown. As will be subsequently explained, one bridge forms a gage transducer and the other a differential transducer. It is noted from  FIG. 1A , that the pins are arranged in a semicircular configuration about the periphery of the first housing section  25 . In this manner, the pins so arranged about the front section of the H shaped header enable leads to be easily brought out while the isolation diaphragm  21  on the low side is of the same size and diameter as the isolation diaphragm  11  on the high side. The channel  28  communicates with the back side of the differential portion  30  of the chip  36 . This channel is oil filled as indicated, and is directed to the back side of the chip to enable the differential chip portion  30  to respond to pressure P 1  applied to the backside and to pressure P 2  applied to the front side, thus providing an output proportional to the difference between pressures P 1  and P 2 . As seen again in  FIG. 1A , the device enables the leads to be simply brought out and enables the diaphragm as  11  and  21  to be of the same size and diameter. This results in a more uniform operation of the device due to the fact that both diaphragms have the same back pressure and are similarly compliant. The advantages, of such a structure are explained in the above noted  255  application. 
         [0012]    Referring to  FIG. 2 , there is shown a housing  100  which provides a common housing for the differential and absolute transducer. The housing has a front threaded section  60  which has a first inlet pressure port directed to a pressure channel  65 . The channel  65  communicates with a tube  64 , which tube goes to the isolation diaphragm  21 , and therefore the tube places pressure P 1  on the underside of the semiconductor sensor chip  36 , which underside is only directed to the differential portion of the chip  30 . The tube is shown in dashed section in  FIG. 1A . Thus the tube  64  communicates with the diaphragm  21 , on the low side, and via channel  28  impinges on the underside of the differential portion of chip  36 . Also seen is channel  66 , associated with a second inlet pressure port and which directs pressure P 2  to both the top side of the absolute transducer section  31  as well as to the differential sensor section  30 . In this manner, the chip portion  31  responds to absolute pressure, while the chip portion  30  responds to the differential pressure, namely the difference between pressures P 1  and P 2 . As seen in  FIG. 2 , the front section of the header  60  is contiguous with a rear section or shell  62 . The shell  62  essentially encloses the entire H shaped cross sectional or dumbbell header  10  as shown in  FIG. 1 . In  FIG. 2 , there is also shown an additional circuit structure  75 . Basically, there is shown a chip  70 , which again is oil filled by an oil filled tube  71  and has the space between the top surface of the semiconductor sensor chip  72  filled with oil. The semiconductor sensor chip, which is a single chip containing a piezoresistive Wheatstone bridge, has a pressure applied via aperture  77 . This pressure, as shown, is atmospheric pressure as channel  77  is vented to the outside environment, which may be for example, atmospheric pressure. In any event, this optional gage chip  70  will measure gage pressure, while chip portion  31  measures absolute pressure P 2  and differential chip portion  30  measures the difference between pressures P 1  and P 2 . 
         [0013]    In  FIG. 3 , as indicated above, there is shown a Wheatstone bridge  50  which may be the absolute Wheatstone bridge, and as well known, consists of four piezoresistors arranged as shown. Bridge  51 , as indicated, may constitute the differential bridge. It is noted now that by using the header  10  and a gage bridge, one can make or fabricate a wet-to-wet differential transducer as employing chip portion  30  one can also provide a wet-to-wet absolute transducer. To do this, an additional die  30  is installed next to the differential die or formed on the sensor chip. If one desires a wet-to-wet differential transducer together with a wet-to-wet gage pressure transducer, an additional header  75  is used to account for gage pressure. Generally speaking the gage pressure is much higher in this type of device than the differential pressure because the gage pressure is essentially the line pressure of the transducer. So a unique way of combining the two sensors in a single header is as follows. The silicon has two sensors formed on it, with two deflecting members or sensor diaphragms, each containing a Wheatstone bridge. This is indicated in  FIG. 3 . Each deflecting silicon diaphragm is of the same thickness but the differential sensor is considerably larger in area than the absolute sensor because of the lower pressure it must respond to. This, as indicated, is depicted in the prior art, as for example, explained and shown in U.S. Pat. No. 7,057,247 which, as indicated above, is incorporated herein in its entirety. Thus both diaphragms are the same thickness but one is larger in area than the other because of the lower pressure the differential sensor must respond to. In any event, both may be fabricated on the same piece of silicon as described in conjunction with  FIG. 1  and contacts are made on each Wheatstone bridge to the appropriate pins on the header as also shown in  FIG. 1A . To make an accurate gage sensor, the header  75  will be used to measure zero gage pressure and a half bridge from header  75  is connected with a half bridge from the absolute sensor portion, as for example, bridge  51 . 
         [0014]    As seen in  FIG. 4 , the piezoresistors from the sensor chip  70  are depicted and these piezoresistors can be connected as shown in a half bridge configuration to a half bridge obtained from the absolute transducer portion  31  of  FIG. 1A , as for example shown as bridge  51 . The bridge on sensor  70  is depicted by reference numeral  80  and again contains the four piezoresistors as  81 ,  82 ,  83  and  84 . As indicated above, one utilizes a single chip which chip contains an absolute sensor configuration on one portion and a differential sensor configuration on another portion. Such devices have also been described in U.S. Pat. No. 4,222,277 entitled Media Compatible Pressure Transducer issued on Sep. 16, 1980, whereby one shows a single chip having the two separate sensor structures or bridge structures, one for measuring absolute pressure and one for measuring differential pressure. 
         [0015]    Referring to  FIG. 5 , there is shown another chip configuration which can be employed. As seen in  FIG. 5 , there is a single wafer silicon  90 , which wafer of silicon contains a first chip section  91  and a second chip section  92 . The section  92  has the pressure P 2  applied via the port  93 . Section  92  has a Wheatstone bridge configured on the silicon wafer  94 , which Wheatstone bridge includes piezoresistors as  95 . There is an additional chip section  96  which also contains a Wheatstone bridge and which additional chip enables one to entirely compensate for vibration and acceleration variations, this is an extreme advantage in providing a differential operation. In any event, the chip portion  91  receives pressure P 2  via pressure input port  97  and receives pressure P 1  via the differential input port  98 . In this manner, the chip section  91  provides a differential output. It is also noted that chip section  91  has a piezoresistive array  99  on one section and has a compensating array  100  on a second section. Each of the arrays have contacts brought out, such as  101  and  102  and so on. The chip shown in  FIG. 5  is the subject matter of a co-pending application entitled Redundant Self-Compensating Leadless Pressure Sensor by A. D. Kurtz, et al. filed on Oct. 2, 2008 as Ser. No. 12/286,810. The entire disclosure of that co-pending application is incorporated herein in its entirety. The advantage of the chip depicted in  FIG. 5  is that sections  96  and  100  do not respond to pressure but respond to temperature and vibration. Hence, by using piezoresistors from these sections with piezoresistors from the pressure active sections, one forms bridge arrays which eliminate temperature and vibration effects and which provide only differential and absolute outputs. See U.S. Pat. No. 6,293,154 issued on Sep. 25, 2001 entitled Vibration Compensated Pressure Sensing Assembly to A. D. Kurtz and assigned to the assignee herein. In any event, as one can ascertain, the semiconductor chip according to this invention may be the type of chip as described in the above noted U.S. Pat. No. 4,222,277 or may be a chip as described in co-pending application Ser. No. 12/286,810. It should be apparent to one skilled in the art that numerous modifications and alternate configurations may be employed, all of which are deemed to be encompassed within the spirit and scope of the Claims appended hereto.