Phase change devices, and particularly multi-terminal phase change
devices, include first and second active terminals bridged together by a
phase-change material whose conductivity can be modified in accordance
with a control signal applied to a control electrode. This structure
allows an application in which an electrical connection can be created
between the two active terminals, with the control of the connection
being effected using a separate terminal or terminals. Accordingly, the
resistance of the heater element can be increased independently from the
resistance of the path between the two active terminals. This allows the
use of smaller heater elements thus requiring less current to create the
same amount of Joule heating per unit area. The resistance of the heating
element does not impact the total resistance of the phase change device.
The programming control can be placed outside of the main signal path
through the phase change device, reducing the impact of the associated
capacitance and resistance of the device.