Abstract
A new concept of read-out method for ferroelectric random-access memory (FeRAM) using a graphene layer as the channel material of bottom-gated field effect transistor structure is demonstrated experimentally. The transconductance of the graphene channel is found to change its sign depending on the direction of spontaneous polarization (SP) in the underlying ferroelectric layer. This indicates that the memory state of FeRAM, specified by the SP direction of the ferroelectric layer, can be sensed unambiguously with transconductance measurements. With the proposed read-out method, it is possible to construct an array of ferroelectric memory cells in the form of a cross-point structure where the transconductance of a crossing cell can be measured selectively without any additional selector. This type of FeRAM can be a plausible solution for fabricating high speed, ultra-low power, long lifetime, and high density 3D stackable non-volatile memory.
Highlights
There has been an enormous amount of interest in utilizing ferroelectric materials for fabricating non-volatile memory devices, so-called ferroelectric random-access memory (FeRAM), with low power consumption and high operation speed stemming from the voltage-driven fast switching of spontaneous polarization (SP) in a ferroelectric material[1,2,3,4,5,6]
We demonstrate experimentally a new type of nondestructive read-out method for FeGFET structure which does not require any additional selector for random accessing
For a typical back-gated FeGFET with its cross-sectional structure shown in Fig. 1a, the transconductance of graphene channel near-zero gate voltage (Vg) is expected to vary depending on the doping of graphene channel determined by the SP direction of ferroelectric layer thanks to the low DOS and the ambipolar carrier type of graphene[20,21]
Summary
There has been an enormous amount of interest in utilizing ferroelectric materials for fabricating non-volatile memory devices, so-called ferroelectric random-access memory (FeRAM), with low power consumption and high operation speed stemming from the voltage-driven fast switching of spontaneous polarization (SP) in a ferroelectric material[1,2,3,4,5,6]. As one way of overcoming such limitations, the FeRAM structure based on a field-effect transistor composed of graphene channel and ferroelectric gate insulator (ferroelectric GFET or FeGFET) has been studied by several research groups[11,12,13,14,15,16]. The main objective of all the previous works for FeGFET is basically for verifying this sensing mechanism. They could resolve the destructive read-out problem, the low on/off ratio of graphene channel conductance originating from the minimal conductance of graphene itself brings about the necessity of attaching a separate selector (transistor or diode) to each memory cell for realizing the random accessibility in read-out and write-in processes[15,16,18,19]
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