Microstructuring in LiNbO₃/LiTaO₃: a route to novel MEMS devices

Ferroelectric hosts such as LiNbO3 and LiTaO3 are increasingly widely used materials for optical, nonlinear optical, electro-optic and pyroelectric devices. Domain manipulation within these hosts, at scale-lengths of order a few micron has further extended their role in applications such as quasi-phase-matching, and the supply of periodically poled materials such as PPLN and PPLT is now routine. To date, the piezoelectric properties of LiNbO3 and LiTaO3 have not yet been as fully explored in the context of micro-optical or microelectromechanical systems (MEMS), and this is the area we are currently exploring. So far however, reliable and accurate methods for machining and microstructuring LiNbO3/LiTaO3 single crystals have been lacking. We have recently been investigating several such methods, which are sensitive to ferroelectric domain orientation.[1] A sample that has been domain-engineered shows a large difference in etch characteristics: the +z face does not etch at all, whereas the -z face etches normally. Microstructured devices can be fabricated therefore, via spatially selective domain poling followed by etching. The extreme sensitivity of the etch process to domain orientation has enabled us to fabricate ridge waveguides for electro-optic modulator applications [2], alignment grooves for efficient fibre-pigtailing to LiNbO3 modulators, and micro-cantilevers using a novel technique of contact bonding of dissimilar ferroelectric hosts. Other routes exist for such microstructuring that do not depend on previous domain patterning. Light can be used to manipulate local domain inversion characteristics, and light itself can also be used to pattern the etching behaviour of LiNbO3 immersed in solutions of HF/HNO3 acids. The talk will describe our progress in microstructuring techniques, followed by our recent results in fabrication of piezoelectric cantilevers, total internal reflection electro-optic switches, and our intentions to fabricate sub-micron sized domains for tunable Bragg filters