1.3. Which factors contribute to the lifetime of a piezo?

Many TOPTICA products use stacks of piezoelectric transducers for the precise fine-adjustment of cavity lengths in order to tune a laser frequency or to scan a resonator (FPI, SHG).

They are wear-and- tear-elements that need to be replaced at times. The following FAQ will shortly describe the main factors contributing to the aging of PZT. With help of this FAQ we aim at helping you to optimize the lifetime of your piezo.


1. Mechanical strain:

In some cases the PZT operates against a mechanical force, e.g. the solid state hinge in the DL100 series. In this case the force from the hinge constitutes a shear-force on the piezo. Due to the ceramic nature of PZTs this can be a problem. TOPTICA has taken this into account by implementing PZTs with ball heads in these cases. You should keep in mind, however, that for extreme (widely opened hinges) the shearing force might lead to a failure of the PZT. Another reason for being careful with the hinge is the imminent risk of over-stretching it. As a consequence it would lose its elasticity and also the resonance frequency will change (see also the remarks below).


2. Static operation:

When operated under static (or near-static) conditions, humidity (H) and operating DC-voltage (V) are the most important factors that limit the lifetime of a PZT. Their effect can be expressed as follows:

Lifetime ≈ (1/V)3 (1/H)5

As one can see, the two parameters have a rather drastic impact. There is an interplay between DC-voltage and humidity. A high DC voltage level accelerates the diffusion of water molecules into the crystal, which leads to a subsequent deterioration and finally a breakdown. It is therefore advisable to maintain a low DC-voltage level. For instance one should try to tune the laser as close as possible to the desired wavelength without having to maintain a high DC-offset on the scan control module. 
Also a low humidity level is of course good. Most piezo failure occur during or after summer when humidity levels are usually higher than during the winter.


3. Dynamic operation

Here both mechanical and thermal factors need to be considered. Firstly the PZT should be operated well below the resonance frequency of the mechanical system the PZT is integrated into. Typically 1.5 kHz is the limit here for DL-, TA- and older DLX systems (built earlier than 2005). For the newer DLX modulation frequencies should not exceed 4 kHz.

Secondly one should be aware that driving the piezo at high frequencies AND amplitudes will result in strong internal heating which can lead to a failure as well. Here one should pay attention in cases where the piezo is part of a feedback loop (for instance for stabilizing the laser frequency against an external reference). In a worst case scenario the aforementioned scenario with high frequencies and amplitudes can occur if the regulators starts to oscillate.

Knowledge Tags
Piezo  /  PZT  /  DL 100  / 

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