Flow-sensing device and method for fabrication

Abstract

A gaseous flow sensor that utilizes non-platinum resistive sensing elements and a method for fabricating such sensor are disclosed. The gaseous flow sensor is constructed by an insulating substrate; a reference resistor formed on the substrate and disposed in the gaseous flow at an ambient temperature without heating; a flow-sensing resistor formed on the substrate disposed in the gaseous flow that is heated to a temperature higher than the ambient temperature; and an electrical circuit in electrical communication with the reference resistor and the flow-sensing resistor for feeding a current into the flow-sensing resistor in order to keep the two resistors at the same temperature during the operation of the gaseous flow sensor.

1 - 21 . (canceled)  
     
     
         22 . A method for fabricating a gas flow sensor, comprising: 
 printing a reference resistor element onto a first segment of an electrically insulating substrate;    printing a flow-sensing resistor element onto a second segment of said electrically insulating substrate wherein said reference and flow-sensing resistor elements are comprised of an oxide material having a temperature coefficient of resistance in the range of about 2600 to 3800 ppm/° C.    
     
     
         23 . The method of  claim 22  wherein said reference and flow-sensing oxide-containing resistors are comprised of one or more of: Pb, Ru, Si, and Bi.  
     
     
         24 . The method of  claim 22 , further comprising: providing an electrical circuit coupled to said reference and flow-sensing resistor elements.  
     
     
         25 . The method of  claim 24  wherein said electrical circuit is capable of maintaining a target temperature differential between said reference resistor element and said flow-sensing resistor element by controlling an electrical current flow to said flow-sensing resistor element.  
     
     
         26 . A method for fabricating a gas flow sensor, comprising: printing a reference resistor element onto a first segment of an electrically insulating substrate and a flow-sensing resistor element onto a second segment of said electrically insulating substrate wherein said reference and flow-sensing resistor elements are comprised of a ruthenium-containing electrically resistive oxide in a glassy matrix having a thickness between 2 and 30 micrometers.  
     
     
         27 . The method of  claim 26  wherein said ruthenium-containing electrically resistive oxide has a temperature coefficient of resistance greater than 2500 ppm/° C.  
     
     
         28 . The method of  claim 26 , further comprising: providing an electrical circuit coupled to said reference and flow-sensing resistor elements.  
     
     
         29 . The method of  claim 28  wherein said electrical circuit is capable of maintaining a target temperature differential between said reference resistor element and said flow-sensing resistor element by controlling an electrical current flow to said flow-sensing resistor element.  
     
     
         30 . The method of  claim 26  wherein a flow rate of gases across the gas flow sensor is a function of a current flowing through said flow-sensing resistor element.  
     
     
         31 . The method of  claim 26  wherein said reference resistor element and said flow-sensing resistor element each have a thickness between 5 and 20 micrometers.  
     
     
         32 . The method of  claim 26  wherein said first and second segments are contiguous.  
     
     
         33 . The method of  claim 26  wherein said first and second segments are separated.  
     
     
         34 . A method for fabricating a gas flow sensor, comprising: 
 printing a reference resistor element onto a first segment of an electrically insulating substrate;    printing a flow-sensing resistor element onto a second segment of said electrically insulating substrate wherein said reference and flow-sensing resistor elements are comprised of an oxide electrically resistive material; and    providing an electrical circuit coupled to said reference and flow-sensing resistor elements.    
     
     
         35 . The method of  claim 34  wherein said oxide electrically resistive material comprises a ruthenium-containing oxide in a glassy matrix.  
     
     
         36 . The method of  claim 34 , further comprising: 
 providing a current source coupled to said flow-sensing resistor.    
     
     
         37 . The method of  claim 36  wherein said electrical circuit is adapted to adjust, in use, a current flow from said current source to maintain a predetermined resistance ratio between said flow-sensing resistor and said reference resistor.  
     
     
         38 . The method of  claim 37  wherein said predetermined resistance ratio is determined by calibration.