Electromechanical Analysis of Silicon Nanomembrane Based Bendable MOS Capacitors with Ultrathin Nanolaminated Encapsulation

Flexible silicon nanomembrane (Si NM) based active implants as advanced biomedical electronics are essential for futuristic applications in sensing, healthcare, and human-machine interfaces. The development of thin-film encapsulation with excellent mechanical robustness and conformability is indispensable for ensuring the long-lived operation of Si NM based functional devices in a biological environment. Here, the electrical properties have been investigated on Si NM based metal-oxide-semiconductor capacitors (MOSCAPs) encapsulated with ultrathin Al₂O₃/alucone nanolaminates under mechanical strain conditions. As illustrated in the capacitance-voltage curves under mechanical-bending stress, the variation of the accumulation capacitance (C_acc) is observed to be lower than 1 % at both inward and outward bending radii of 85 mm and 38.5 mm compared with the planar condition for the encapsulated MOSCAP with a gate area of 0.02 mm², respectively. However, the corresponding reductions of C_acc are approximately 2 % and 4 % for the bare device with the same gate area. Up to 4 % and 26 % reduction in the accumulation capacitance have been measured for the encapsulated MOSCAP with a gate area of 0.08 mm²at a bending radius of 85 mm under tensile stress and 38.5 mm under compressive stress, respectively. Furthermore, the relevant reductions of C_acc are promoted to 9 % and 36 % for the bare device with the same gate dimension. Suppression of the gate leakage current has also been observed clearly for the encapsulated Si NM based MOSCAPs with an active area of 0.08 mm²compared with bare devices during bending, while the phenomenon could not be found for the devices with smaller gate areas. These findings demonstrate the great potential of nanolaminated films of Al₂O₃/alucone as the excellent encapsulation. It is also noted that a comprehensive study of the impact of the device gate area on the electromechanical properties will be beneficial to optimizing the scalable layout for achieving high mechanical reliable and high-performance flexible Si NM based MOSFETs to create the next-generation bioelectronic implants.