Stress tensor mesostructures for freeform shaping of thin substrates

Kavli Affiliate: Youwei Yao

| First 5 Authors: Youwei Yao, Brandon Chalifoux, Ralf Heilmann, Mark Schattenburg,

| Summary:

Stress-induced shaping, which deforms thin substrates utilizing stressed
surface coatings, has enabled and enhanced a host of applications in past
decades. Owing to the touchless fabrication process compatible with modern
planar technology, the method has been applied from microscale to macroscale
applications such as self-assembled micro-structures and space mirrors.
However, the deformations created by existing stress-control schemes are
limited to certain classes of geometries (such as sphere, coma and astigmatism)
or rely on boundary constraints and hinges because the stress is unary, e.g.,
equibiaxial stress or uniaxial stress with fixed orientation. Here, we present
novel stress tensor mesostructures to spatially control the three required
stress tensor components, i.e., two normal stresses and a shear stress, over
the surface of thin substrates. Three different mesostructure types have been
created, each offering distinct advantages. For demonstration, we patterned
these mesostructures on the back sides of silicon wafers for freeform shape
generation and correction which are not achievable by conventional methods.
Stress tensor mesostructures will unleash the value of fields related to
stress-induced bending from microscale to macroscopy, such as thin freeform
substrates that will become increasingly important with the rise of wearable
and space optics.

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