  The classic three-terminal electronic transistors and the emerging
two-terminal ion-based memristors are complementary to each other in various
nonconventional information processing systems in a heterogeneous integration
approach, such as hybrid CMOS/memristive neuromorphic crossbar arrays. Recent
attempts to introduce transitive functions into memristors have given rise to
gate-tunable memristive functions, hetero-plasticity and mixed-plasticity
functions. However, it remains elusive under what application scenarios and in
what ways transistors can benefit from the incorporation of ion-based
memristive effects. Here, we introduce a new type of transistor named 'mempolar
transistor' to the transistor family. Its polarity can be converted reversibly,
in a nonvolatile fashion, between n-type and p-type depending on the history of
the applied electrical stimulus. This is achieved by the use of the emerging
semiconducting tellurium as the electrochemically active source/drain contact
material, in combination with monolayer two-dimensional MoS2 channel, which
results in a gated lateral Te/MoS2/Te memristor, or from a different
perspective, a transistor whose channel can be converted reversibly between
n-type MoS2 and p-type Te. With this unique mempolar function, our transistor
holds the promise for reconfigurable logic circuits and secure circuits. In
addition, we propose and demonstrate experimentally, a ternary
content-addressable memory made of only two mempolar transistors, which used to
require a dozen normal transistors, and by simulations, a device-inspired and
hardware matched regularization method 'FlipWeight' for training artificial
neural networks, which can achieve comparable performance to that achieved by
the prevalent 'Dropout' and 'DropConnect' methods. This work represents a major
advance in diversifying the functionality of transistors.
