Abstract

In this thesis pre-stressed piezoelectric actuators for micro and fine mechanical applications have been developed. First, RAINBOW (Reduced And INternally Biased Oxide Wafer) and thick film actuators were manufactured and their electromechanical properties were characterised. In the second part, the novel pre-stressed piezoelectric actuator PRESTO (PRE-STressed electrOactive component by using a post-fired biasing layer) was developed and its electrical and electromechanical properties were measured.

Commercial piezoelectric PZT 5A and PZT 5H discs were used in the RAINBOW and PRESTO actuators and PLZT paste for thick film actuators. The pre-stressing of the PRESTO actuators was based on the sintering shrinkage and different thermal expansion coefficient of the piezoelectric disc and passive material. Dielectric LTCC tape and AgPd paste were utilized as pre-stressing media and passive layer by using lamination and screen-printing, respectively. Different active and passive layer thicknesses and electrode materials were realized in order to obtain high displacements and good load bearing capability for actuators.

The PRESTO actuators showed a significantly higher coercive electric field than their bulk counterparts, but a decreased remanent polarisation. The displacement as a function of load was measured under 0.3–3 N loads and electric fields up to ±0.75 MV/m. The highest displacement of 118 μm was obtained with a 250 μm thick PZT 5H actuator (Ø 25 mm) with LTCC tape (thickness ~96 μm) as the pre-stressing material. The corresponding actuator with AgPd pre-stressing material (thickness ~33 μm) produced 63 μm displacement. Additionally, PRESTO actuators were tested with a glued steel layer in a mechanical amplifier which obtained displacements up to 1.2 mm.

Effective d₃₁ coefficients of the PRESTO actuators were derived using an analysis based on unimorph model and measured displacement data. The actuators exhibited significantly enhanced effective d₃₁ coefficients (d_31eff = -690 pm/V and d_31eff = -994 pm/V for PZT 5A and 5H, respectively) comparable to the RAINBOW actuators. Mass-producible PRESTO actuators with high displacement, moderate load bearing capabilities and integration possibilities can be utilised in various micro and fine mechanical devices e.g. dosing devices, electromechanical locks, regulators, positioners vibrators, speakers, adjusters, pumps, valves, relays, dispensers, micromanipulators, etc.