Self-selective ferroelectric memory realized with semimetalic graphene channel

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.

Ferroelectrics Based on HfO2 Film

The discovery of ferroelectricity in HfO2 thin film, which is compatible with the CMOS process, has revived interest in ferroelectric memory devices. HfO2 has been found to exhibit high ferroelectricity at a few nanometers thickness, and studies have rapidly progressed in the past decade. Ferroelectricity can be induced in HfO2 by various deposition methods and heat treatment processes. By combining ferroelectric materials with field-effect transistors, devices that combine logic and memory functions can be implemented. Ferroelectric HfO2-based devices show high potential, but there are some challenges to overcome in endurance and characterization. In this paper, we discuss the fabrication and characteristics of ferroelectric HfO2 film and various applications, including negative capacitance (NC)), Ferroelectric random-access memory (FeRAM), Ferroelectric tunnel junction (FTJ), and Ferroelectric Field-effect Transistor (FeFET).

Enhancement of the Retention Characteristics in Solution-Processed Ferroelectric Memory Transistor with Dual-Gate Structure

We demonstrated the enhancement of the retention characteristics in solution-processed ferroelectric memory transistors. For enhanced retention characteristics, solution-processed Indium Gallium Zinc Oxide (InGaZnO) semiconductor is used as an active layer in a dual-gate structure to achieve high memory on-current and low memory off-current respectively. In our dual-gate oxide ferroelectric thin-film transistor (DG Ox-FeTFT), while conventional TFT characteristic is observed during bottom-gate sweeping, large hysteresis is exhibited during top-gate sweeping with high memory on-current due to the high mobility of the InGaZnO. The voltage applied to the counter bottom-gate electrode causes variations in the turn-on voltage position, which controlled the memory on- and off-current in retention characteristics. Specifically, due to the full depletion of semiconductor by the high negative counter gate bias, the memory off-current in reading operation is dramatically reduced by 104. The application of a high negative counter field to the dual-gate solution-processed ferroelectric memory gives a high memory on- and off-current ratio useful for the production of high performance multi-bit memory devices.