Femtosecond laser processing of ceria-based micro actuators

In this paper we present a novel femtosecond laser micro-processing of gadolinium doped cerium oxide (CGO) taking advantage of the unique properties of the ultra-short laser pulse. The process can be extended to other materials which are incompatible with conventional deposition/patterning/etching processes. For example, CGO electrostrictive ceramics is lead-free and non-toxic, compatible with Si-microfabrication and exhibits large electrostriction effect at low frequencies. These qualities make CGO into a promising electroactive material for MEMS applications. However, conventional CGO lithography suffers from low yield due to metal shorts and due to damage during the etch and clean processes. Wet patterning of CGO is very difficult and often results in enhanced leakage or shorts between electrodes. These process compatibility issues can be avoided by using laser patterning. As a proof of concept, a precise patterning of electro-active ceramic Ce_0.95Gd_0.05O_1.975 (CGO5) thin films (1.7 μm-thick) by femtosecond laser is demonstrated. The femtosecond laser patterning was used to fabricate double-clamped beam actuators made of CGO5 sandwiched between two metal contacts. The new process is studied and preliminary guide lines are presented. The process design rules are established; for example, a margin between the top contact edges and the CGO layer edges was defined prior to laser ablation to prevent a short-circuiting between top and bottom contacts due to metal ablation. Electro-mechanical testing of the resulting devices demonstrates the long-term mechanical and electrical endurance of 1.2 mm long beams. Using electrical excitation (voltage amplitude of 10 V with a carrier frequency of 10 MHz modulated at 10 Hz), actuation at 10 Hz induced an in-plane strain of 7×10⁻⁶ without any observable mechanical degradation for >800 k cycles. The processes presented in this work, therefore, provide a technological framework for integration of CGO into MEMS-devices.