Thermoelectric hydrocarbon sensor in thick-film technology for on-board-diagnostics of a diesel oxidation catalyst

• Thermoelectric hydrocarbon sensor for automotive exhaust was manufactured in thick-film and tape technology.
• Sensors were operated at 600 °C.
• Linear output characteristics (constant sensitivity).
• LTCC-based sensors showed three times higher sensitivity than alumina-based ones.
• Very good reproducibility.

Thermoelectric hydrocarbon sensors were fully manufactured in both alumina substrate-based thick-film technique and low temperature cofired ceramics (LTCC) tape technology. Au–Pt thermocouples were screen-printed on insulating sensor substrates. Porous alumina impregnated with one weight percent platinum was used as catalytic material that covered one side of the sensor. Due to the generated thermal exothermicity, a temperature difference between the catalytically active and the catalytically inactive (reference) side occurred. Additionally, the sensor was equipped with an internal platinum heating element to operate the sensor at temperatures above the light-off temperature of the catalyst material. Owing to the lower thermal conductivity of LTCC, the sensitivity could be improved essentially. To further increase the sensor signal, the number of thermocouples per sensor was enhanced by applying thermopiles of several Au–Pt thermocouples. Therefore, the layout of the heating element was optimized. Altogether, a sensitivity of 0.57 μV/ppm propene was achieved.