Pore Geometry

While conventional sensors rely on hygroscopic aluminium oxide structures to attract water, HTF™ sensors rely on a pore geometry, which slows the Brownian motion of the water molecules when entering the pores. The freed energy is absorbed by the mass of the sensor and the decreased entropy of the water molecules is equalized by an increase in their total number. This results in more dielectric in the pores and consequently higher capacitance. The HTF™ pore geometry does not change over time, while conventional hygroscopic aluminum oxide structures collapse into non-hygroscopic structures. Therefore, conventional sensors are subject to drift and need to be recalibrated frequently, while HTF™ sensors need no recalibration when used in clean, non-corrosive gases.

Layer Thickness

With HTF™ technology, sensors can be produced with hyper-thin oxide layers without compromising insulation strength. The thinner oxide layer results in much higher capacitance changes because capacitance is inversely proportional to the distance of the capacitor's plates from each other.
The thinner layer also means that water molecules will travel faster in and out of the pores. HTF™ aluminum oxide sensors respond several times faster than conventional sensors.

Barrier Layer

In HTF™ sensors, the transition between the aluminum oxide and the aluminum is sharp and clearly defined. This thinner barrier layer produces a capacitor with its electrodes very close together, which in turn causes the sensor's wet-to-dry capacitance ratio to be high. The benefit of high wet-to-dry capacitance ratio is that drift in capacitance due to undesirable factors is less significant. This is clearly a benefit as can be seen in HTF™ vs. conventional sensor comparisons of temperature sensitivity and aging drift.
The sharp transition from aluminum to aluminum oxide also reduces metal migration, one of the major causes of ageing drift in conventional sensors.