Self-supported Gd-doped ceria films for electromechanical actuation: Fabrication and testing

- Membranes, bridges and cantilevers were built from 1.4-2 μm Gd-doped ceria films.
- Only Si-compatible processes and materials were used.
- Only membranes with Ti contacts produce electrostrictive response.
- Tethered 2 mm diameter membranes show ∼0.4 μm deflection under 10 Vp-p/1.6 μm field.
- The estimated electrostriction strain coefficient is >2.1 × 10−18 m2/V2.

In this study, we explored the feasibility of employing Gd-doped ceria (GDC) thin films (1-2 μm) as functional, mechanically reliable material for microelectromechanical systems (MEMS). Self-supported structures, based on microscopic-scale GDC membranes, bridges, and cantilevers, were fabricated using Si-compatible processes and materials. With voltages of different amplitudes and frequencies and a variety of metal electrodes, we monitored structural stability and device response. The membrane-based structures displayed much higher stability under voltage and better mechanical robustness than those based on bridges or cantilevers. At low frequencies (a few Hz), the use of Ti contacts resulted in observable displacement of the membranes in the presence of moderately low voltage (≤10 V/1.6 μm), while Al, Cr, and Ni contacts did not provide such functionality. Although for all contact metals tested, formation of a blocking layer at room temperature is evident, for the case of Ti, the barrier height is much lower. In view of the fact that the crystallographic space group of weakly doped GDC is Fm-3 m, the electromechanical response of the microfabricated GDC membranes is most likely electrostrictive, but a strict proof is not yet available. At high frequencies (>100 kHz), the membranes produce lateral displacement as large as several microns due to Joule heating, i.e., a thermo-electromechanical response.