In the last three years we have constituted a small laboratory able to carry out mechanical tests (tension force, flexure, fracture, dynamic tests) on capacitive micro-electromechanical systems (MEMS), like e.g. accelerometers and gyroscopes.
These tests follow the on-chip approach, i.e. sensor, actuator and specimen are inserted in the same microsystem. These tests are directly carried out on silicon wafers or singled dices placed on a probe station inspected with an optical microscope (see figure 1). Micro-manipulators connect the circuit through contact pads to the microsystem (see figure 2), in order to apply voltage (i.e. mechanical load) and/or to monitor the change in capacitance, which is related to the displacement of movable MEMS parts.
[The instruments currently present in the laboratory allow us to carry out the following test:
- basic “static” tests (capacitance-voltage, i.e. load-displacement from a mechanical point of view), at imposed voltage (load) with simple wave form function up to 40 V when using a digital capacimeter, or higher voltage (up to 100 V) with the power supply (provided the MEMS includes sensor and actuator inside); a LabView interface has been carried out for the devices;
- dynamic tests with pre-assigned voltage histories (typically sinusoidal functions): the output is observed in terms of capacitance change or in terms of voltage corresponding to the device rupture for fatigue;
- dynamic tests for piezoelectric devices with measurement of voltage generated by mechanical strain;
Main measurement devices: probe station, four micro-manipulators, digital capacimeter (Agilent E4980A), power supply. (Agilent 6614DC), oscilloscope (Agilent Infiniivision 2024A), wave-form function generator (Agilent 33521A), personal computer with dedicated LabView software.
Web site: www.mems.polimi.it