Parallel Tensile Testing of Single-crystal Silicon Microstructures with Integrated Piezoresistive Strain Gauges

A parallel testing method has been proposed with integrated strain gauges based on the piezoresistive effect to shorten the testing time for investigating tensile-mode fatigue characteristics of single-crystal silicon (SCS). The method allows a high loading frequency (~110 Hz) owing to the high stiffness of the testing system and reduces the testing time per specimen by parallelization. Five specimens were integrated on a testing chip and subjected to a pulling force simultaneously using a piezoelectric actuator. The parallel portion of the specimen was 2.5 µm wide, 22 µm thick, and 120 µm long. The strain gauge connected to each gauge part consisted of an array of five straight beams 100 µm in length and 2.5 µm in width. The one-active-gauge bridge was used and three reference registers of identical shape were also placed in series on the chip. The strain gauges successfully monitored the force on each specimen with sufficiently low noise for testing. The five specimens on the chip fractured at the same time, showing a tensile strength of 1.5 GPa. Because of the finite stiffness of the test system, there is coupling between the integrated specimens. However, the total displacement during parallel testing was sufficiently small (~15 µm) such that the system has the potential to operate with a loading frequency of 110 Hz for fatigue testing.