Abstract
As researchers unravel the underlying mechanisms governing time-dependent electrical degradation[1], thin film piezoelectric microelectromechanical systems (piezoMEMS) display electrical lifetimes satisfactory for a wide range of technological applications. Even in the harsh ambient of space[2]. As thin film piezoMEMS devices continue to appear in commercial applications, such as Tunables’ gas detectors, Sonairs’ ultrasound for air, and PoLights’ autofocus lenses, radically new and novel applications are within reach. Be it THz-structures for 6G, metalenses for micro-cameras, or molecular detectors for space missions, factual actuator devices all demand the same: smaller structures that use less power and can electromechanically bend more. Maximizing the piezoelectric strain is key, and common strategies include minimizing the device-layer thickness, producing multilayer stacks, and increasing the active materials’ piezoelectric response. In all cases, increasing the devices’ electromechanical limit, i.e., increasing the maximum electric field that the device can withstand without electromechanically breaking down, is essential. As for lead zirconate titanate (PZT), with 𝑒31,𝑓𝑓 ~15-20 C/m2, reported breakdown strengths can reach ~1 MV/cm. In comparison, aluminum scandium nitrides with 𝑒𝑒31,𝑓𝑓 ~3-4 C/m2 can withstand up to 5 MV/cm. Their combined electrical and mechanical nature makes it challenging to understand and pinpoint the breakdown mechanisms governing thin film piezoMEMS. Depending on factors such as the electrode materials, its interface to the piezoelectric, the in-plane stress, composition and microstructure, the electrothermal breakdown events, and its ripple effects can vary significantly with field-direction (Figure 1), temperature as well as the ambient in which the measurements are carried out. What comes first? Cracks, delaminating electrodes, dielectric breakdown? Here, we present an electromechanical breakdown study of PZT-based thin film piezoMEMS. When approaching the materials’ breakdown field, the results indicate that the film initially cracks, initiating electrode delamination and an apparent dielectric breakdown through air gaps. Mitigation strategies will also be demonstrated and discussed.