In order to overcome the bottleneck between the central
processor
unit and memory as well as the issue of energy consumption, computing-in-memory
(CIM) is becoming more popular as an alternative to the traditional
von Neumann structure. However, as artificial intelligence advances,
the networks require CIM devices to store billions of parameters in
order to handle huge data traffic demands. Monolithic three-dimensional
(M3D) stacked ferroelectric thin-film transistors (FeTFTs) are one
of the promising techniques for realizing high-density CIM devices
that can store billions of parameters. In particular, oxide channel-based
FeTFTs are well suited for these applications due to low-temperature
processes, nonvolatility, and 3D integration capability. Nevertheless,
the M3D-integrated CIM devices including hafnia ferroelectric films
need the high-temperature annealing process to crystallize the ferroelectric
layer, making M3D integration difficult. When the FeTFTs are fabricated
with an M3D structure, the high-temperature process causes thermal
issues in the underlying devices. Here, we present the focused microwave
annealed (FMA) oxide FeTFTs with M3D integration at a low temperature
of 250 °C. We confirmed that the FeTFTs with metal–ferroelectric-metal–insulator–semiconductor
structure exhibited a large memory window of 3.2 V, good endurance
over 106 cycles, and a long retention time of 105 s. To understand the different electrical characteristics of FeTFTs
in the top and bottom layers, we experimentally analyzed the density
of the state of the oxide channel and ferroelectric properties of
the ferroelectric gate insulator by using multifrequency capacitance–voltage
measurement and nucleation-limited-switching model analysis, respectively.
With our approach, we demonstrate for the first time a vertical stacked
FeTFTs-based ternary-content-addressable memory (TCAM) cell for CIM
application. We believe that the proposed M3D-stacked TCAM cells composed
of FeTFTs can be used in high-density memory, energy-efficient memory,
and CIM technology.