Fractographic Analysis of Very Small Theta Specimens

Abstract

The theta test specimen is a versatile tool for evaluating the strength of extremely small structures. Round and hexagonal rings are compressed vertically on their ends creating a uniform tension stress in the middle gauge section. The simple compression loading scheme eliminates the need for special grips. A conventional nanoindentation hardness machine with a flat indenter applied load, monitored displacement, and recorded fracture loads. Prototype miniature specimens with web sections as thin as 7.5 m were fabricated by deep reactive ion etching (DRIE) of single crystal silicon wafers. The strength limiting flaws were 200 nm to 500 nm deep surface etch pits.

Deformation and fracture of single-crystal silicon theta-like specimens

“…The SOI structure allowed for better control of sample device thickness and more robust strips for manipulation and mounting of samples for testing than previous designs. 27,59 The Si device layer and Si handle wafer layer were patterned by front-and back-side photolithographic masks and etched using deep reactive ion etching (DRIE) to define the sample and strip features, Figs. 3(b) and 3(c); the front-side mask included both Durelli and arch designs.…”

Strength and fracture analysis of silicon-based components for embedding

“…This result suggests the possible involvement of a stress concentration in the fracture process, and allows us to discard the possibility of an etch pit as the critical defect, being the fracture origin located rather in the Si layer. 26 …”

Influence of deposited metal structures on the failure mechanisms of silicon-based components

“…On the one hand, the strength in silicon depends on the crystallographic orientation and on the size and distribution of defects, which is expected to be broad. [6][7][8][9][10][11][12][13][14][15] Thus, the strength is controlled by the growth direction and surface quality. 16,17 On the other hand, on the metallised side the layered architecture produced during the deposition process can induce (thermal) residual stresses which might affect the mechanical strength and fracture response of the component.…”