High humidity actuators

Noliac is developing a novel piezoelectric multilayer component with high humidity resistance. Testing reveals excessive reliability at 85% humidity and 85 degrees C. Significant more testing and development is to be completed, though, before a commercial product is ready for launching.

Reliability in general

Reliability of multilayer piezoelectric actuators is naturally a very important area of focus, no matter whether it is a question of cracking/fracture or whether it is a question of increased leakage current.

The former is primarily encountered in applications where the actuator is driven at high mechanical load. Furthermore, if charging and discharging is performed too rapidly, there is a risk of rupture due to high tension forces.

Increased leakage current can be a consequence of several factors, but is most frequently a consequence of a degradation process of the dielectric material, i.e. a reduction of the insulation resistance. Another potential failure mechanism is ion migration of either the internal or external electrodes, which can result in catastrophic failure of the part.

Discs and rings more stable

Noliac has tested representative standard components for 2,000 hours at a relative humidity of 85% and 85 degree C and electrical field strength, DC, of 2kV/mm and 3kV/mm.

A factor of influence is the shape of the components. A square has a lower resistance to humidity than a ring or disc shaped actuator. Ring and disc shaped actuators survive 3kV/mm, whereas square shaped actuators mostly survive 2kV/mm.

In general, the failures of the components decrease with decreasing electrical field strength.

Prototypes available

The components are tested according to "IEC standard 60068-2-67 – Environmental testing, part 2, Damp heat, steady state accelerated test primarily intended for components", which demands a testing period of 2,000 hours.

The results so far are promising, and prototypes are available at request.