Nano-scale fatigue study of LPCVD silicon nitride thin films using a mechanical-amplifier actuator

Abstract

This paper describes a nano-scale tensile test to study the fatigue properties of LPCVD silicon nitride thin films using a novel electrostatic actuator design. Mechanical-amplifier devices made in silicon nitride thin films can apply controllable tensile stress (2.0–7.8 GPa) to test structures with relatively low actuation voltages (5.7–35.4 VRMS) at the resonant frequencies of the devices. The test devices are fabricated using a surface micromachining technique in combination with deep reactive ion etching and ion milling. With the recently developed experimental techniques inside a focused-ion-beam system, in situ fatigue measurements are performed on silicon nitride test structures with beam widths of 200 nm. The silicon nitride test structures are found to exhibit time-delayed failures with continuous increases in their compliance. By reducing the applied tensile stress to 3.8 GPa, the test structures can survive cyclic loadings up to 108 cycles.