  Flexible and biocompatible memristive devices are particularly attractive for
bioelectronic systems due to the interest in improving computing capabilities
and the motivation to interface electronics with biological systems including
drug delivery, neural interfaces and biosensors. Structures made of more
unorthodox, organic material can address different issues due to their
characteristics: flexibility, conformability, biocompatibility and simple and
low-cost fabrication. It has been observed that gating graphene/ionic liquid
(IL) devices leads to the formation of an electrical double layer (a thin layer
of ions with a thickness of a few nanometers) at the graphene/IL interface due
to the local potential difference which also controls the local conductivity.
This structure provides a memristive mechanism based on a dynamic p-n junction
formation along the channel. Motivated by this memristive behavior, graphene/IL
devices were assembled with the aim of demonstrating memristive behavior and
associative learning. This work investigates memristive properties of flexible
graphene/ IL devices on polymer substrates. The I-V characteristics of these
novel devices and switching mechanism are investigated. Two distinct topologies
(single input, single output and double input, single output) of devices are
manufactured and tested to mimic conditioning. It is observed that the
application of voltage pulse trains of both positive and negative polarities
increases the device conductance and allows larger currents to pass after
repetitive excitation. This characteristic was exploited to condition devices
and emulate associative learning.
