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; and 
 a reference electrode comprising platinum (Pt). 
   
     
     
         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 determines 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 determines 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 determines 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 determines 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 poteniometric 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 reference electrode disposed on the electrolyte is sufficiently high to increase the sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         11 . The microfabricated gas sensor device of  claim 10 , wherein the exposed surface of the electrolyte layer is minimized a sufficient amount to increase the sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         12 . 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.   
     
     
         13 . 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. 
     
     
         14 . 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 of the sensing electrode is sufficiently high to increase the sensitivity of the microfabricated potentiometric gas sensor device. 
     
     
         15 . The microfabricated gas sensor device of  claim 11 , 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. 
     
     
         16 . The microfabricated sensor device of  claim 15 , 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. 
     
     
         17 . The gas sensor device of  claim 1 , wherein the surface area of the WO 3  electrode on the electrolyte is at least two times greater than the surface area of the Pt electrode on the electrolyte. 
     
     
         18 . 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. 
     
     
         19 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the layer of the WO 3  has a lateral projection on the surface of the electrolyte forming a torturous path. 
     
     
         20 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the layer of the WO 3  has a plurality of lateral projections on the surface of the electrolyte. 
     
     
         21 . The microfabricated potentiometric gas sensor device of  claim 20 , wherein the 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 that increase the triple point boundary. 
     
     
         22 . 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 ). 
     
     
         23 . 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. 
     
     
         24 . 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 combined potential difference is measurable at the first and second electrical leads. 
 
     
     
         25 . The microfabricated potentiometric gas sensor device of  claim 23 , 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. 
     
     
         26 . The microfabricated potentiometric gas sensor device of  claim 2 , wherein the combined potential difference comprises a sum of the potential differences of each of the potentiometric sensor units. 
     
     
         27 . The microfabricated potentiometric gas sensor device of  claim 1 , wherein the sensor device is made using the photolithography fabrication method. 
     
     
         28 . The microfabricated potentiometric gas sensor gas sensor device of  claim 1 , wherein the sensor device is made using the shadow mask fabrication method. 
     
     
         29 . 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. 
     
     
         30 . A method for making a microfabricated potentiometric gas sensor comprising:
 applying a photoresist mask to a surface of substrate;   depositing an electrolyte layer on the substrate;   removing the photoresist mask; and   annealing the substrate with oxygen to remove residual photo resist caused by a photoresist mask.   
     
     
         31 . The method of  claim 30 , further comprising:
 applying a second photoresist mask over the electrolyte layer;   depositing a reference electrode material over the second photoresist mask to form a reference electrode, an electrical interconnect, and an electrical contact portion of a sensing electrode;   removing the second photoresist mask; and   annealing the substrate to remove residual photo resist caused by the second photoresist mask.   
     
     
         32 . The method of  claim 31 , further comprising:
 apply a third photoresist mask over the electrolyte layer, the reference electrode layer, electrical interconnect layer, and the electrical contact for the portion of the electrode layer;   depositing material for a second portion of a sensing electrode over the third photoresist mask to form a sensing electrode;   removing the third photoresist mask; and   annealing the substrate to remove residual photo resist caused by the another photoresist mask.   
     
     
         33 . The method of  claim 32 , wherein the sensing electrode comprises a layer of tungsten oxide (WO 3 ) disposed on a platinum (Pt) contact, and the reference electrode comprising platinum (Pt). 
     
     
         34 . A method of sensing gas, the method comprising:
 receiving an original sample; and   generating a potential difference in a microfabricated potentiometric sensor in response to presence of gas in the sample, wherein the microfabricated potentiometric sensor comprises:   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; and 
 a reference electrode comprising platinum (Pt). 
   
     
     
         35 . The method of  claim 34 , comprising:
 determining a level of gas within the original sample based on the potential difference generated by the microfabricated potentiometric sensor; and   wherein the sensor device determines the gas level at a sensitivity of at least 1 ppm.   
     
     
         36 . The method of  claim 35 , wherein the gas is NOx.