Patent Publication Number: US-2013233085-A1

Title: Differential pressure sensor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2012-049491, filed on Mar. 6, 2012, the entire content of which being hereby incorporated herein by reference. 
     FIELD OF TECHNOLOGY 
     The present invention relates to a differential pressure sensor that uses a sensor diaphragm for detecting a signal in response to a pressure differential. 
     BACKGROUND ART 
     Conventionally, commercial differential pressure transmitters have used a differential pressure transmitter that includes a differential pressure sensor that uses a sensor diaphragm that outputs a signal in response to a differential pressure. This differential pressure transmitter is configured so that the pressures that are applied to a high-pressure side and a low-pressure side of a pressure bearing diaphragm are transmitted to the respective sides of the sensor diaphragm through a sealed liquid, as a pressure transmitting medium, where strain on the sensor diaphragm is detected as, for example, a change in a resistance value of a strain resistance gauge, where this change in resistance value is converted into an electric signal that is read out. 
     Such differential pressure transmitters are used, for example, to measure the height of a fluid surface in, for example, a high temperature reaction tower in an oil refinery by detecting the differential pressure between two locations at different has in a closed tank that stores the fluid that is being measured. 
       FIG. 4  illustrates schematically a conventional differential pressure transmitter. The differential pressure transmitter  100  is structured with a sensor chip  1  having a sensor diaphragm (not shown) incorporated in a meter body  2 . The sensor diaphragm in the sensor chip  1  is made from silicon, glass, or the like, and the strain resistance gauge is formed on the surface of the diaphragm, which is formed as a thin plate. The meter body  2  is made from a main unit portion  3 , made out of metal, and a sensor portion  4 , where barrier diaphragms (pressure-bearing diaphragms)  5   a  and  5   b,  which form a pair of pressure-bearing portions, are provided on the side faces of the main unit portion  3 , and the sensor chip  1  is incorporated in the sensor portion  4 . 
     In the meter body  2 , between the sensor chip  1  that is incorporated into the sensor portion  4  and the barrier diaphragms  5   a  and  5   b  that are provided in the main unit portion  3 , pressure transmitting mediums  9   a  and  9   b,  such as silicone oil, are sealed into connecting ducts  8   a  and  8   b  that connect the sensor chip  1  and the barrier diaphragms  5   a  and  5   b  through connecting, respectively, through pressure buffering chambers  7   a  and  7   b  that are separated by a large-diameter center diaphragm  6 . 
     Note that the reason why the pressure medium, such as silicone oil, is necessary is because it is necessary to separate the sensor diaphragm, which has the sensitivity to the stress (pressure), from the pressure-bearing diaphragm, which is resistant to corrosion, in order to prevent foreign material within the measurement medium from adhering to the sensor diaphragm and to prevent corrosion of the sensor diaphragm. 
     In this differential pressure transmitter  100 , a first measurement pressure Pa from a process is applied to the barrier diaphragm  5   a  and a second measurement pressure Pb, from the process, is applied to the barrier diaphragms  5   b,  as illustrated schematically for the proper operating state in  FIG. 5(   a ). As a result, the barrier diaphragms  5   a  and  5   b  dislocate and the pressures Pa and Pb that are applied thereto are conveyed through the pressure transmitting mediums  9   a  and  9   b  through the pressure buffering chambers  7   a  and  7   b  that are separated by the center diaphragm  6 , to the respective sides of the sensor diaphragm of the sensor chip  1 . As a result, the sensor diaphragm of the sensor chip  1  undergoes dislocation corresponding to the differential pressure ΔP between these two transmitted pressures Pa and Pb. 
     In contrast, when, for example, an excessively large pressure Pover is applied to the barrier diaphragm  5   a,  the barrier diaphragm  5   a  undergoes a large dislocation, as illustrated in  FIG. 5(   b ), and thus the center diaphragm  6  undergoes deformation so as to absorb the excessively large pressure Pover. Moreover, when the barrier diaphragm  5   a  tightly contacts the bottom face (an excessive pressure protecting face) of a recessed portion  10   a  of the meter body  2  so that that dislocation is constrained, this prevents the transmission of any differential pressure ΔP in excess of that to the sensor diaphragm through the barrier diaphragm  5   a.  Similarly, when an excessively large pressure Pover is applied to the barrier diaphragm  5   b,  then, in the same manner as when an excessively large pressure Pover was applied to the barrier diaphragm  5   a,  then when the barrier diaphragm  5   b  tightly contacts the bottom face (the excessive pressure protecting face) of the recessed portion  10   b  of the meter body  2  so that that dislocation is constrained, this prevents the transmission of any differential pressure ΔP in excess of that to the sensor diaphragm through the barrier diaphragm  5   b.  The result is that this prevents breakage of the sensor chip  1  by the application of the excessively large pressure Pover, that is, this prevents in advance breakage of the sensor diaphragm in the sensor chip  1 . 
     In this differential pressure transmitter  100 , the sensor chip  1  is enclosed within the meter body  2 , thus making it possible to protect the sensor chip  1  from the external corrosive environment, such as the process fluids. However, because the recessed portions  10   a  and  10   b  are provided in order to constrain the dislocation of the center diaphragm  6  and the barrier diaphragms  5   a  and  5   b,  in a structure to protect the sensor chip  1  from the excessive pressure Pover thereby, the dimensions thereof are unavoidably larger. 
     Given this, a first stopper member and a second stopper member are provided in the sensor chip, where recessed portions of the first stopper member and the second stopper member face the respective surfaces of the sensor diaphragm to thereby prevent excessive dislocation of the sensor diaphragm when an excessively large pressure is applied, in a structure that has been proposed for preventing breakage/destruction of the sensor diaphragm thereby. See, for example, Japanese Unexamined Patent Application Publication 2005-69736 (“the JP &#39;736”). 
       FIG. 6  illustrates schematically a sensor chip that uses the structure shown in the JP &#39;736. In this figure,  11 - 1  is a sensor diaphragm,  11 - 2  and  11 - 3  are first and second stopper members that are bonded with the sensor diaphragm  11 - 1  interposed therebetween, and  11 - 4  and  11 - 5  are pedestals to which the stopper members  11 - 2  and  11 - 3  are bonded. The stopper members  11 - 2  and  11 - 3  and the pedestals  11 - 4  and  11 - 5  are formed from silicon, glass, or the like. 
     In the sensor chip  11 , recessed portions  11 - 2   a  and  11 - 3   a  are formed in the stopper members  11 - 2  and  11 - 3 , where the recessed portion  11 - 2   a  of the stopper member  11 - 2  faces one face of the sensor diaphragm  11 - 1 , and the recessed portion  11 - 3   a  of the stopper member  11 - 3  faces the other face of the sensor diaphragm  11 - 1 . The recessed portions  11 - 2   a  and  11 - 3   a  have curved surfaces (spherical surfaces), following the dislocation of the sensor diaphragm  11 - 1 , and, at the apexes thereof, pressure guiding holes  11 - 2   b  and  11 - 3   b  are formed. In the pedestals  11 - 4  and  11 - 5  as well, pressure guiding holes  11 - 4   a  and  11 - 5   a  are formed at positions corresponding to the pressure guiding holes  11 - 2   b  and  11 - 3   b  of the stopper members  11 - 2  and  11 - 3 . 
     When this type of sensor chip  11  is used, when an excessively large pressure is applied to one face of the sensor diaphragm  11 - 1 , causing the sensor diaphragm  11 - 1  to undergo dislocation, the entirety of the dislocated face is supported and stopped by the curved surface of the recessed portion  11 - 3   a  of the stopper member  11 - 3 . Moreover, if an excessively large pressure is applied to the other face of the sensor diaphragm  11 - 1 , causing the sensor diaphragm  11 - 1  to undergo dislocation, the entirety of the dislocation face is supported and stopped by the curved surface of the recessed portion  11 - 2   a  of the stopper member  11 - 2 . 
     As a result, when an excessively large pressure is applied to the sensor diaphragm  11 - 1  excessive dislocation is prevented, making it possible to increase the excessive pressure-protected operating pressure (durability) by effectively preventing accidental damage to the sensor diaphragm  11 - 1  through the application of an excessively large pressure, through making it so that there are no concentrated stresses at the peripheral edge portions of the sensor diaphragm  11 - 1 . Moreover, in the structure illustrated in  FIG. 4 , it is possible to achieve miniaturization of the meter body  2  through eliminating the center diaphragm  6  and the pressure buffering chambers  7   a  and  7   b  and guiding the measurement pressures Pa and Pb directly from the barrier diaphragms  5   a  and  5   b  to the sensor diaphragm  11 - 1 . 
     In the structure of such a sensor chip  11 , the static pressure that acts on the interior thereof depends on the diameter of the sensor diaphragm  11 - 1 . In order to increase the rangeability, it is necessary to increase the diameter of the sensor diaphragm  11 - 1  and to decrease the film thickness of the sensor diaphragm  11 - 1 . However, satisfying such demands enlarges the pressure bearing surface internally, causing the application of pressures that are large enough to break the bonded portions within the sensor chip  11 . 
     In the case of the sensor chip  11  that is illustrated in  FIG. 6 , there is a five-layer structure of the sensor diaphragm  11 - 1 , the stopper members  11 - 2  and  11 - 3 , and the pedestals  11 - 4  and  11 - 5 . In this case, when there is a high pressure there is the risk that large pressure forces will act on the bonded portions in this five-layer structure, causing the bonded portions to delaminate. Moreover, when there is a change in the ambient temperature, thermal stresses caused by differences in coefficients of thermal expansion between the sensor chip  11  and the package  2  will also have an effect, which may cause the bonded portions within the sensor chip  11  to delaminate. 
     The present invention was created in order to solve such problems, and an aspect of the present invention is to provide a differential pressure sensor able to prevent delamination of the bonded portions within the sensor chip. 
     SUMMARY 
     In order to achieve such an aspect, the differential pressure sensor according to the present invention includes a sensor chip that has a sensor diaphragm that outputs a signal in accordance with a differential pressure, a first stopper member that is bonded to the sensor diaphragm with a recessed portion of the first stopper member facing one face of the sensor diaphragm, and stops excessive dislocation when an excessively large pressure is applied to the other face of the sensor diaphragm, and a second stopper member that is bonded to the sensor diaphragm with a recessed portion of the second stopper member facing the other face of the sensor diaphragm, and stops excessive dislocation when an excessively large pressure is applied to the one face of the sensor diaphragm. The differential sensor also includes a first duct member, bonded to one face of the sensor chip, having, therein, a pressure guiding duct that guides a measurement pressure to the one face of the sensor diaphragm, a second duct member, bonded to the other face of the sensor chip, having, therein, a pressure guiding duct that guides a measurement pressure to the other face of the sensor diaphragm, and an elastic holding member that applies an elastic force to the first duct member in the direction of the one face of the sensor chip, applies an elastic force to the second duct member in the direction of the other face of the sensor chip, and holds the sensor chip under pressure between the first duct member and the second duct member. 
     In the present invention, the sensor chip is held under pressure, by an elastic holding member, between a first duct member and a second duct member. That is, an elastic force is applied to the first duct member by the elastic holding member in the direction of one face of the sensor chip, and an elastic force is applied to the second duct member in the direction of the other face of the sensor chip, to hold the sensor chip under pressure between the first duct member and the second duct member. This buffers the pressure forces and thermal stresses that act on the bonded portions of the sensor chip when there is a high-pressure or a change in the ambient temperature, preventing the bonded portions within the sensor chip from delaminating. 
     In the present invention, the elastic holding member is structured, for example, from an elastic first connecting duct that connects to the pressure guiding duct of the first duct member, and an elastic second connecting duct that connects to the pressure guiding duct of the second duct member, or may be leaf springs that are lain on the outsides of the first duct member and the second duct member. When the elastic holding member is structured from the elastic first connecting duct and second connecting duct, it can also act as a connecting duct that guides the measurement pressure to the sensor chip (a duct in which is sealed a pressure transmitting medium), thus making it possible to reduce part counts, reduce size, and reduce costs. 
     The present invention, includes a first duct member, bonded to one face of the sensor chip, having, therein, a pressure guiding duct that guides a measurement pressure to the one face of the sensor diaphragm and a second duct member, bonded to the other face of the sensor chip, having, therein, a pressure guiding duct that guides a measurement pressure to the other face of the sensor diaphragm, and the sensor chip is held under pressure by the elastic holding member between the first duct member and the second duct member, and thus the pressure forces and thermal stresses that act on the bonded portions within the sensor chip are buffered when there is a high pressure or a change in the ambient temperature, thus making it possible to prevent delamination of the bonded portions within the sensor chip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating the critical portions (the supporting structure for the sensor chip that is incorporated in the meter body) of an example of a differential pressure sensor according to the present invention. 
         FIG. 2  is a diagram illustrating an example wherein ring-shaped leaf springs are provided lying on the outside of the first duct member and the second duct member, which are sandwiched therebetween. 
         FIG. 3  is a diagram illustrating an example wherein a U-shaped leaf spring is provided lying on either side of the first duct member and the second duct member, which are sandwiched therein. 
         FIG. 4  is a diagram illustrating a schematic structure for a conventional differential pressure transmitter. 
         FIG. 5  is a diagram illustrating schematically the operating state of this differential pressure transmitter. 
         FIG. 6  is a diagram illustrating schematically a sensor chip that uses the structure illustrated in the JP &#39;736. 
     
    
    
     DETAILED DESCRIPTION 
     A form of example according to the present invention will be explained below in detail, based on the drawings.  FIG. 1  is a diagram illustrating the critical portions in an example of a differential pressure sensor according to the present invention. In this figure, a supporting structure for the sensor chip  11  ( FIG. 6 ) that is incorporated in a meter body is illustrated as the structure for the differential pressure sensor that is incorporated in the differential pressure transmitter. 
     In this supporting structure, a first duct member  12  is bonded to one face of the sensor chip  11 , and a second duct member  13  is bonded to the other face of the sensor chip  11 . The first duct member  12  has, therein, a pressure guiding duct  12   a  that guides the measurement pressure Pa to the one face of the sensor diaphragm  11 - 1  and the second duct member  13  has, therein, a pressure guiding duct  13   a  for guiding the measurement pressure Pb to the other face of the sensor diaphragm  11 - 1 . 
     Moreover, in this supporting structure, elastic first connecting duct  14  and second connecting duct  15  protrude from the top face of a pedestal  16 , separated by a specific distance L, where the first connecting duct  14  is connected to the pressure guiding duct  12   a  of the first duct member  12 , and the second connecting duct  15  is connected to the pressure guiding duct  13   a  of the second duct member  13 . 
     At this time, the elasticity of the connecting ducts  14  and  15  apply an elastic force PA onto the first duct member  12  in the direction of the one face of the sensor chip  11 , and apply an elastic force PB to the second duct member  13  in the direction of the other face of the sensor chip  11 , so as to hold the sensor chip  11  under pressure between the first duct member  12  and the second duct member  13 . 
     That is, in the present form of example, the first connecting duct  14  is caused to have two functions, the function of a duct wherein the pressure transmitting medium  9   a  is sealed, and a function for producing an elastic force PA in the compressing direction, pressing on the sensor chip  11 , and the second connecting duct  15  is caused to have two functions, the function of a duct wherein the pressure transmitting medium  9   b  is sealed, and a function for producing an elastic force PB in the compressing direction, pressing on the sensor chip  11 . In this case, the first connecting duct  14  and the second connecting duct  15  function as the “elastic holding member” in the present invention. As a result, it is possible to prevent the delamination of the bonded portions within the sensor chip  11  through buffering the pressure forces and thermal stresses that act on the bonded portions within the sensor chip  11  when there is a high pressure or a change in the ambient temperature. 
     Note that in this supporting structure, the materials of the first duct member  12  and the second duct member  13  may be, for example, Kovar, and the materials for the first connecting duct  14  and the second connecting duct  15  may be, for example, SUS316. 
     While in the example described above the sensor chip  11  was held under pressure between the duct members  12  and  13  through the use of elastic connecting ducts  14  and  15 , instead, as illustrated in  FIG. 2 , ring-shaped leaf springs  17  may be provided lying on the outsides of the first duct member  12  and the second duct member  13 , which are sandwiched therebetween. Moreover, as illustrated in  FIG. 3 , a U-shaped leaf spring  18  may be provided lying on the outsides of the first duct member  12  and the second duct member  13 , which are sandwiched therein. In these cases there is no need for the connecting ducts  14  and  15  to be elastic, but rather it is the leaf springs  17  and  18  that function as the elastic holding member in the present invention. 
     As illustrated in  FIG. 1 , when the elastic holding member is structured from the elastic connecting ducts  14  and  15 , they can also serve as the guiding ducts (ducts wherein a pressure transmitting medium is sealed) for guiding the measurement pressure to the sensor chip  11 , making it possible to reduce parts counts, reduce size, and achieve cost reductions. Moreover, the outer diameter within the ducts can be adjusted for the connecting ducts  14  and  15 , enabling a design with any arbitrary elastic force PA or PB, making it possible to handle easily the high-pressure and high-differential-pressure applications for which there has been growing demand over recent years. 
     Furthermore, while in the example set forth above the structure of the sensor chip  11  is a five-layer structure wherein the sensor diaphragm  11 - 1  and stopper members  11 - 2  and  11 - 3  are bonded to pedestals  11 - 4  and  11 - 5 , the structure need not necessarily be one with bonded pedestals  11 - 4  and  11 - 5 , but rather may be a three-layer structure of the sensor diaphragm  11 - 1  and the stopper members  11 - 2  and  11 - 3 . 
     Note that while in the example set forth above the sensor diaphragm  11 - 1  was of a type wherein a strain resistance gauge was formed wherein the resistance value changes in response to a change in pressure, the sensor chip may instead be of an electrostatic capacitance type. A sensor chip of an electrostatic capacitance type is provided with a substrate that is provided with a specific space (a capacitance chamber), a diaphragm that is provided over the space in the substrate, a stationary electrode that is formed on the substrate, and a movable electrode that is formed on the diaphragm. When the diaphragm bears pressure and is deformed, the spacing between the movable electrode and the stationary electrode changes, changing the electrostatic capacitance therebetween. 
     Extended Forms of Example   
     While the present invention has been explained above in reference to the form of example, the present invention is not limited to the form of example set forth above. The structures and details in the present invention may be varied in a variety of ways, as can be understood by one skilled in the art, within the scope of technology in the present invention.