  HfO2-based Ferroelectric field-effect transistor (FeFET) has become a center
of attraction for non-volatile memory applications because of their low power,
fast switching speed, high scalability, and CMOS compatibility. In this work,
we show an n-channel FeFET-based Multibit memory, termed MirrorBit, which
effectively doubles the chip density via programming the gradient ferroelectric
polarizations in the gate using an appropriate biasing scheme. We have
experimentally demonstrated MirrorBit on GlobalFoundries HfO2-based FeFET
devices fabricated at 28 nm bulk HKMG CMOS technology. Retention of MirrorBit
states has been shown up to $10^5$ s at different temperatures. Also, the
endurance is found to be more than $10^3$ cycles. A TCAD simulation is also
presented to explain the origin and working of MirrorBit states based on the
FeFET model calibrated using the GlobalFoundries FeFET device. We have also
proposed the array-level implementation and sensing methodology of the
MirrorBit memory. Thus, we have converted 1-bit FeFET into 2-bit FeFET using a
particular programming scheme in existing FeFET, without needing any notable
fabrication process alteration, to double the chip density for high-density
non-volatile memory storage.
