Thick-film oxygen sensor

The model analytes, which were used to show the sensor performance of the microsystems include carbon monoxide, CO, and methane, CH4. The sensor microsystems were designed for practical applications, such as environmental monitoring, industrial safety applications or household surveillance, which implies that oxygen and water vapors are present under normal operating conditions. In the following, a brief overview of the relevant gas sensor mechanisms focused on nano crystalline tin-oxide thick-film layers will be given. 

Principles and Development of a Thick-Film Zirconium Oxide Oxygen Sensor... 

Detailed analysis of the steady-state voltage chatacter-istics of both the thick film oxygen sensor and the crucible type oxygen sensor are shown. 

Thick Film Zirconia Oxygen Sensor and Measurements... 

A cross-section schematic drawing of the newly-developed thick film oxygen sensor is shown in Figure 2. The platinum film heater is embedded in the alumina substrate. Electrical resistance of the heater is about 6 ohms at room temperature. 

Figures 5 and 6 present the experimental results obtained with the thick film oxygen sensor.

Figure 2. Schematic drawing of thick film oxygen sensor...

Figure 6. Experimental voltage curves for thick film oxygen sensor (A/F vs V curve)...

Thick film oxygen sensor with catalytic electrode (when 1-0). Substituting 1=0 into Equation 20 yields... 

Sensor voltage characteristics of the thick film oxygen sensor. Experimental data show that sensor voltage characteristics of the thick film oxygen sensor vary greatly with the value of the sensor current. 

T) A more compact thick film zirconia oxygen sensor with a built-in heater has been developed. In this sensor, the reference oxygen gas is not air the oxygen gas is generated electrolytically at the interface between the reference electrode and the porous zirconia electrolyte. 

In the case of a larger sensor current, the model for the thick film oxygen sensor used in this analysis showed favorable possibilities for a "lean oxygen sensor."... 

Lin JT. Testing of planar thick film fabricated oxygen sensor with galvanostatic techniques. PhD thesis, University of California San Diego, La Jolla, CA, 2000. 

S. H. Hahn, N. Barsan, U. Weimar, S. G. Ejakov, J. H. Visser, and R. E. Soltis, CO sensing with Sn02 thick film sensors, role of oxygen and water vapour, Thin Solid Films 436,17-24 (2003). 

Sharma, R.K. and M.C. Bhatnagar (1999). Improvement of the oxygen gas sensitivity in doped Ti02 thick films. Sensors and Actuators B-Chemical, 56(3), 215-219. 

Pollution legislation continues driving further reductions in engine emissions. The dominant exhaust-gas sensors today and in the near future are oxygen partial pressure sensors - also called lambda sensors. Due to the high temperature of exhaust gas, these sensors are made by ceramics technology in combination with thick-film processing. 

The NOx sensor has been developed to detect directly the NOx emissions in the exhaust gas of automotive engines. The basic design is derived from the thick-film based universal exhaust gas oxygen (UEGO) sensor. 

A typical example includes the yttria-stabilized-zirconia-based high-temperature potentiometric oxygen sensor which is widely used in automotive applications. Platinum thick films are applied, forming both the cathode and anode of the sensor. The thick electrode has a porous structure which provides a larger electrode surface area compared to non-porous structures. For current measurement, a porous electrode is desirable since it leads to a larger current output. If the metallic film serves as the electrocatalyst, a porous structure is also desirable, for it provides more catalytic active sites. On the other hand, electrodes formed by the thick-film technique do not have an exact, identical... 

Micromachined and microfabricated electrochemical sensors have been used either per se, or as part of a sensor system, in many practical applications. This includes various biosensors and chemical sensors reported in research literature. An example of a practical electrochemical sensor is the yttria-stabilized zirconium dioxide potentiometric oxygen sensor used for fuel-air control in the automotive industry. Thick-film metallization is used in the manufacture of this sensor. Even though the sensor is not microsize, this solid electrolyte oxygen sensor has proven to be reliable in a relatively hostile environment. It is reasonable to anticipate that a smaller sensor based on the same potentiometric or the voltammetric principle can be developed using advanced microfabrication and micromachining techniques. 

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