ALUMINUM OXIDE
MOISTURE AND DEW POINT ANALYSIS
Aluminum Oxide ( Al 2 O 3 ) sensors work by measuring the capacitance between the aluminum core and a gold film deposited on the oxide layer .
The capacitance varies according to the water vapor content in the pores of the oxide layer .
The ultra-thin Al 2 O 3 sensors have three innovative structural improvements that offer better performance than traditional Al 2 O 3 sensors , with advantages for sensitivity and stability .
1 . A MUCH THINNER OXIDE LAYER
This results in higher capacitance , since this is inversely proportional to the distance of the capacitor ’ s plates from each other . Higher capacitance results in a more sensitive measurement . The thinner layer also allows water molecules to travel in and out of the pores more quickly , ensuring a faster response .
2 . A BETTER-DEFINED BARRIER LAYER
The sharply defined barrier means that the sensor ’ s wet to dry capacitance ratio is very high , reducing the effects of any drift due to undesirable factors . It also reduces metal migration , one of the major causes of drift in conventional Al 2 O 3 sensors .
3 . UNIQUE PORE GEOMETRY
Holding more water than conventional sensors , the ordered pore geometry increases the change in capacitance for a given change in dew point . This means greater accuracy and a quicker response . It is also more stable , so only annual calibration checks are needed when the sensor is used in clean , non-corrosive gases .
ALUMINUM OXIDE SENSOR STRUCTURE
Hyper-Thin Film Other Al2O3
Pore geometry Barrier layer Layer thickness
Aluminum Oxide Aluminum
Gold Water Molecule
Drawing not to scale
P68