Miniaturized gas sensor device and method

Abstract

Various embodiments of a gas sensor device and method of fabricating a gas sensor device are provided. In one embodiment a gas sensor device includes a base substrate, an electrolyte layer disposed on the base substrate and a plurality of potentiometric sensor units electrically coupled to the base substrate. Each potentiometric sensor unit includes an electrolyte layer disposed on the base substrate, a sensing electrode comprising tungsten oxide (WO 3 )and platinum (Pt), a reference electrode comprising Pt, and a plurality of connectors coupled to the plurality of potentiometric sensors to connect the plurality of potentiometric sensors in series.

Having described the invention, we claim: 
     
         1 . A microfabricated potentiometric gas sensor device comprising:
 a base substrate;   an electrolyte layer disposed on the base substrate;   a plurality of potentiometric sensor units connected in series and coupled to the base substrate, each potentiometric sensor unit comprising:
 an electrolyte layer disposed on the base substrate; 
 a two-part sensing electrode comprising a layer of tungsten oxide (WO 3 ) disposed on a platinum (Pt) contact; 
 a reference electrode comprising platinum (Pt); and 
   wherein the ratio of the surface area of the tungsten oxide (WO 3 ) of the sensing electrode disposed on the electrolyte to the surface area of the Pt of the reference electrode disposed on the electrolyte is at least 2 to 1.   
     
     
         2 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is a MEMS sensor device. 
     
     
         3 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is capable of determining the gas level at a sensitivity of at least 1 ppm. 
     
     
         4 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is capable of determining the gas level at a sensitivity of at least 500 ppb. 
     
     
         5 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is capable of determining the gas level at a sensitivity of at least  300  ppb. 
     
     
         6 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is capable of determining the gas level of NO x  at a sensitivity of at least 300 ppb. 
     
     
         7 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the electrolyte comprises yttria-stabilized zirconia (YSZ). 
     
     
         8 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the substrate comprises a material that is an insulator. 
     
     
         9 . The microfabriated potentiometric gas sensor device of  claim 1 , wherein a thickness of the electrolyte layer is maximized a sufficient amount to minimize the internal resistance of the corresponding potentiometric sensor unit, and such that the internal resistance of each of the plurality of potentiometric sensor units is minimized so as to minimize the overall resistance of the microfabricated potentiometric gas sensor device and increase sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         10 . The microfabricated gas sensor device of  claim 1 , wherein the exposed surface of the electrolyte layer is minimized a sufficient amount to result in increased sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         11 . The microfabricated gas sensor device of  claim 1 , wherein the electrolyte is YSZ and the surface area of the WO 3  sensing electrode on the electrolyte is fabricated using microfabrication techniques so as to maximize the ratio to that of the WO 3  to the Pt reference electrode on the electrolyte while minimizing the exposed layer of electrolyte layer. 
     
     
         12 . The microfabricated gas sensor device of  claim 1 , wherein the ratio of the surface area of the WO 3  sensing electrode to the surface area of the Pt contact is sufficiently high to increase the sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         13 . The microfabricated gas sensor device of  claim 10 , wherein the ratio of the surface area of the WO 3  sensing electrode to the surface area of the Pt contact is sufficiently high to increase the sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         14 . The microfabricated sensor device of  claim 13 , wherein a thickness of the electrolyte layer of each sensor unit is maximized a sufficient amount to minimize the internal resistance of the corresponding potentiometric sensor unit, and such that the internal resistance of each of the plurality of potentiometric sensor units is minimized so as to minimize the overall resistance of the microfabricated potentiometric gas sensor device and increase sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         15 . The gas sensor device of  claim 1 , wherein the surface area of the WO 3  electrode on the electrolyte is at least ten times greater than the surface area of the Pt electrode on the electrolyte. 
     
     
         16 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the surface area of the WO 3  electrode on the electrolyte is at least five times greater than the surface area of the Pt electrode on the electrolyte. 
     
     
         17 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the layer of the WO 3  of at least one of the plurality of potentiometric sensor units has a shape that defines a lateral projection on the surface of the electrolyte. 
     
     
         18 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the layer of the WO 3  of at least one of the plurality of potentiometric sensor units has a shape that defines a plurality of lateral projections on the surface of the electrolyte. 
     
     
         19 . The microfabricated potentiometric gas sensor device of  claim 18 , wherein at least one of the plurality of lateral projections of WO 3  has at least two edge interfaces along the surface of the electrolyte layer. 
     
     
         20 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the surface area of the platinum (Pt) contact is at least 5 times smaller than the surface area of the layer of tungsten oxide (WO 3 ). 
     
     
         21 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the surface area of the platinum (Pt) contact is at least 9 times smaller than the surface area of the sensing electrode. 
     
     
         22 . The microfabricated potentiometric gas sensor device of  claim 1  further comprising:
 a first electrical interconnect coupled to the sensing electrode of a first potentiometric sensor within the series of potentiometric sensor units; 
 a second electrical interconnect electrically coupled to the reference electrode of a last potentiometric sensor within the series of potentiometric sensors; and 
 wherein the microfabricated potentiometric gas sensor device is capable of measuring a combined potential difference at the first and second electrical leads. 
 
     
     
         23 . The microfabricated potentiometric gas sensor device of  claim 22 , further comprising a third potentiometric sensor unit electrically coupled between the first and last potentiometric sensor units within the series of potentiometric sensors, wherein the sensing electrode of the first potentiometric sensor is connected to the reference electrode of the third potentiometric sensor. 
     
     
         24 . The microfabricated potentiometric gas sensor device of  claim 23 , wherein the combined potential difference comprises a sum of the potential differences of the first, the second and the third potentiometric sensor units. 
     
     
         25 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is made using the photolithography fabrication method. 
     
     
         26 . The microfabricated potentiometric gas sensor gas sensor device of  claim 1 , wherein the sensor device is made using the shadow mask fabrication method. 
     
     
         27 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device was fabricated using photolithography method, wherein the surface of the sensor unit has been annealed with oxygen to remove a photoresist mask. 
     
     
         28 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device comprises 15 to 20 sensor units. 
     
     
         29 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the wherein the surface area of the WO 3  electrode on the electrolyte is at least five times greater than the surface area of the Pt electrode on the electrolyte, and the layer of the WO 3  has a shape that defines a plurality of lateral projections on the surface of the electrolyte. 
     
     
         30 . The microfabricated potentiometric gas sensor device of  claim 29 , wherein the surface area of the platinum (Pt) contact is at least 5 times smaller than the surface area of the layer of tungsten oxide (WO 3 ) and the electrolyte comprises yttria-stabilized zirconia (YSZ). 
     
     
         31 . A microfabricated poteniometric sensor device for detecting gas comprising:
 a base substrate;   an electrolyte layer disposed on the base substrate;   a plurality of potentiometric sensor units connected in series and coupled to the base substrate, each potentiometric sensor unit comprising:
 an electrolyte layer disposed on the base substrate; 
 a two-part sensing electrode comprising a layer of tungsten oxide (WO 3 ) disposed on a platinum (Pt) contact; 
 a reference electrode comprising platinum (Pt); and 
   wherein the ratio of the surface area of the WO 3  sensing electrode disposed on the electrolyte to the surface area of the Pt reference electrode disposed on the electrolyte is sufficiently high such that the microfabricated potentiometric gas sensor device is capable of detecting the gas level at a sensitivity of at least 1 ppm.   
     
     
         32 . The microfabricated potentiometric gas sensor device of  claim 31 , wherein the gas comprises NO x . 
     
     
         33 . The microfabricated potentiometric gas sensor device of  claim 32 , wherein the sensor device determines the gas level of NO x  at a sensitivity of at least 300 ppb. 
     
     
         34 . The microfabricated potentiometric gas sensor device of  claim 33 , wherein the layer of the WO 3  of the sensing electrode of at least one of the plurality of potentiometric sensor units has a shape defining a plurality of lateral projections on the surface of the electrolyte. 
     
     
         35 . A microfabricated poteniometric sensor device for detecting gas comprising:
 a base substrate;   an electrolyte layer disposed on the base substrate;   a plurality of potentiometric sensor units connected in series and coupled to the base substrate, each potentiometric sensor unit comprising:
 an electrolyte layer disposed on the base substrate; 
 a two-part sensing electrode comprising a layer of tungsten oxide (WO 3 ) disposed on a platinum (Pt) contact; 
 a reference electrode comprising platinum (Pt); and 
   wherein the layer of the WO 3  of the sensing electrode of at least one of the plurality of potentiometric sensor units has a shape that defines a lateral projections on the surface of the electrolyte.   
     
     
         36 . The microfabricated potentiometric gas sensor device of  claim 35 , wherein the electrolyte electrolyte comprises yttria-stabilized zirconia (YSZ) and the sensor device is capable of determining the gas level of NO x  at a sensitivity of at least 1 ppm. 
     
     
         37 . A microfabricated potentiometric gas sensor device comprising:
 a base substrate;   an electrolyte layer disposed on the base substrate;   a plurality of potentiometric sensor units connected in series and coupled to the base substrate, each potentiometric sensor unit comprising:
 an electrolyte layer disposed on the base substrate; 
 a two-part sensing electrode comprising a layer of tungsten oxide (WO 3 ) disposed on a platinum (Pt) contact; 
 a reference electrode comprising platinum (Pt); and 
   wherein a thickness of the electrolyte layer is maximized a sufficient amount to minimize the internal resistance of the corresponding potentiometric sensor unit, and such that the internal resistance of each of the plurality of potentiometric sensor units is minimized so as to minimize the overall resistance of the microfabricated potentiometric gas sensor device and increase sensitivity of the microfabricated potentiometric gas sensor device to a gas level sensitivity of at least 1 ppm.