Entwicklung von piezoelektrischen Stellantrieben mit CMOS-kompatibler Ansteuerspannung für mikrotechnische Anwendungen

Microsystems, consisting of integrated circuits (IC, CMOS), microsensors such as microactuators, can be build up monolithically as well as hybrid. These systems enable a high degree of functionality to be made with at the same time high level of integration density. While microsensors for such systems are far developed and commercially available, microactuators, which are needed for the control of energy or mass flows, are still at the beginning. The operational areas of control drives in microtechnical applications (microactuators) are various and lie within the range of micropumps, microvalves but also microswitches for the control of electric currents or voltages (microrelays) or for the specific refraction of light (micromirror). These applications require large strokes or deflections from the control drive with at the same time high switching frequencies as low CMOS-compatible applied voltages. With the piezoelectric drive principle high switching cycles are possible with low power consumption and small space requirement. To reach a high level of integration density piezoelectric materials with high piezoelectric coefficients, like lead zirconate titanate [Pb {Zr(x)Ti(1-x)} O3, PZT], have to be selected for the active layer. For this layer suitable techniques for the integration into a CMOS process have to be developed. In the context of this thesis a control drive was developed with piezoelectric energy transformation principle in a modified IC process flow on silicon substrates. The control drive was manufactured in a process consisting of procedures of microelectronics, bulk micromechanics and CSD (Chemical Solution deposition) technology. The characterisation of the microactuators took place at capacitive test-structures and at freely movable cantilever structures. Here the control drives appeared to be fully functionally with tip deflections up to 70µm at applied voltages up to 10V. For an exact evaluation of the mechanical and electrical characteristics of the piezoelectric control drive the tip deflection of the cantilever structure is needed. To determine this mechanical characteristic an experimental setup consisting of a laser interferometer was developed, with which the tip deflection as a function of the applied voltage could be measured. Additionally, the dynamic characteristics of the cantilever structures could be determined with this setup. Other important layer properties such as permittivity, electrical losses, resistivity, breakdown voltage and the ferroelectrical properties of the PZT layers were determined by CV, SE and hysteresis measurements. In addition, to the mechanical and electrical measurements XRD analyses of the crystal structure of the metallic electrodes and the piezoelectric layers were accomplished. For the achievement of good piezoelectric characteristics a specific preferred orientation in both layers is necessary. With the help of these analyses the desired textures in the material system could be proven. Important aspects in micromechanics are the tensions (stress) in complex layer systems, which can lead to unwanted deflection of cantilever structures. Therefore in the context of this work the stress influence of the different layers on each other was examined. This led to the integration of a stress compensation layer. With the help of this optimised process flow and the developed fabrication methods piezoelectric control drives were manufactured as lab samples. The full functionality of the microactuators could be shown in the context of the requirements.