Authors: A. Sharma, M. Kaur, D. Bansal, D. Kumar, K. Rangra
Affilation: Central Electronics Engineering Research Institute (CEERI/ CSIR), India
Pages: 344 - 348
Keywords: MEMS test structures, residual stress, stress gradient, surface micromachining
A set of microstructures for in situ stress measurement is presented. It is based on lancet principle, with dedicated design for the amplification of the dimensional variations induced by the internal stress of the structural material. Initially arrays of buckling type test structures cantilevers, fixed- fixed beams and guckel rings were used to find out critical buckling beam stress in electroplated gold. Later on single rotational type pointer and lancet structures are analyzed to find out both types of stresses compressive and tensile for plated gold. Tilted arm geometry was adopted in order to maximize the strain induced movement, keeping the design relatively simple and the lancet on the wafer plane. A set of simulations, as well as an analytical examination of the structure was performed to establish the optimal geometry: different tilt angles were simulated in a range between -200 and 200MPa internal stress. The test structures were realized by means of surface micromachining, adopting photoresist as sacrificial layer and electroplated gold as structural layer.