MEMS ACTUATION DEVICES BASED ON GADOLINIUM-DOPED CERIUM-OXIDE FILMS

Eran Mishuk ¹ Evgeniy Makagon ¹ Andrei Ushakov ³ Sidney Cohen ² Ellen Wachtel ¹ Ronit Popovitz-Biro ² Vladimir Shur ³ Andrei Kholkin ⁴ Igor Lubomirsky ¹

¹Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
²Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel
³School of Natural Sciences and Mathematics, Ural Federal University, Yekaterinburg, Russia
⁴Physics and CICECO - Aveiro Institute of Materials, University of Aveiro, Aveiro, Portugal

Gadolinium-doped cerium-oxide (GDC) is the first low dielectric constant / low elastic compliance material to demonstrate a large electrostriction response (so-called non-classical electrostriction) that is comparable with those of commercial electrostrictive lead-based materials. To this end, we fabricated thin GDC self-supported structures in the form of millimeter-sized membranes, bridges, and cantilevers, using only Si-compatible processes and materials [1]. The films were prepared with thickness 1-2 µm to avoid pinholes and electrical breakdown upon application of voltage.

For circular membranes the contacts are separated by a continuous GDC film, and they exhibited the highest mechanical and electrical integrity. The nature of the electrical contacts plays a critical role in the functionality of the films. Titanium electrodes were the most suitable for active MEMS based on GDC membranes, since they present a lower contact resistance than the other metals tested (Cr, Ni and Al). Quantitative measurements of the displacement with atomic force microscope (AFM) revealed a predominantly quadratic dependence on voltage, which is characteristic of electrostriction. At a frequency of 10m Hz, a displacement of 2 µm is readily detected at 10V, corresponding to strain electrostriction-coefficient of ~10^-17m²V^-2. The displacement is rapidly decreasing with increasing frequency with a characteristic response time of ~30s, which may be an inherent property of GDC, related to the electric field-dependent kinetics of the point defects.

Our experimental results confirm our expectation that, with the proper microfabrication protocol and electrode material, GDC may be viewed as a robust and ecologically friendly material for MEMS applications.

Self-Supported Structures of GDC: Cantilever, Bridges and Circular Membrane (From Left to Right)

[1] E. Mishuk et.al., “Self-supported Gd-doped ceria films for electromechanical actuation: fabrication and testing”, Sensors & Actuators: A. Physical. Volume 264, 333-340, 2017.