One-transistor ferroelectric versatile memory: Strained-gate engineering for realizing energy-efficient switching and fast negative-capacitance operation

Abstract

In this work, we report a ferroelectric versatile memory (FE-VM) with strained-gate engineering. The memory window of high strain case was improved by ∼47% at the same ferroelectric thickness, which agrees with the increase of orthorhombic crystallinity. Based on a reliable first principle calculation (FPC), we clarify that the gate strain accelerates the phase transformation from metastable monoclinic to orthorhombic and thus largely enhances the ferroelectric polarization without increasing dielectric thickness. On the other hand, the orthorhombic FE-AFE phase transition plays a key role in realizing negative capacitance (NC) effect at high gate electric field. This 1T strained-gate FE-VM with ferroelectric NC achieves a sub-60-mVdec subthreshold swing (SS) over ∼4 decade of I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</inf> to provide a 1∼10 fA/µm I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> and >108 I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf> /I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> ratio, which allows for a fast 20-ns P/E switching during 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cycling endurance.