  Bimorph films curl in response to temperature. The degree of curvature
typically varies linearly with temperature and in proportion to the difference
in thermal expansion of the individual layers. In many applications, such as
controlling a thermostat, this gentle linear behavior is acceptable. In other
cases, such as opening or closing a valve or latching a deployable column into
place, an abrupt motion at a fixed temperature is preferred. To achieve this
non-linear motion, we describe the fabrication and performance of a new bilayer
structure we call 'Phase Change Composite Bimorph (PCBM)'. In a PCBM, one layer
in the bimorph is a composite containing small inclusions of phase change
materials. When the inclusions melt, their large (generally positive and >1%)
expansion coefficient induces a strong, reversible step function jump in
bimorph curvature. The measured jump amplitude and thermal response is
consistent with theory.
