Nonvolatile memory based on ferroelectric-graphene field-effect transistors is now a step closer to reality

February 24, 2011 By Lee Swee Heng
Schematic illustration of an improved graphene-ferroelectric FET with SiO2 basal layer. Credit: 2010 APS

A fundamental component of a field-effect transistor (FET) is the gate dielectric, which determines the number of charge carriers -- electrons or electron vacancies -- that can be injected into the active channel of the device. Graphene has recently become the focus of attention as a viable, high-performance replacement for silicon in FETs, and in recent studies on graphene-based FETs, scientists have investigated the use of thin films of a ferroelectric material for the gate dielectric.

Such films offer several interesting advantages for use in graphene-based FETs: their strong makes it possible to introduce a much higher density of carriers than can be achieved using standard dielectrics, and they have remnant electric polarization -- a property that could allow graphene–ferroelectric FETs to be used for nonvolatile memory by storing a certain level of carrier density in the absence of an electrical field.

Two collaborating teams from the A*STAR Institute of Materials Research and Engineering and the National University of Singapore, led by Kui Yao and Barbaros Özylmaz, respectively, previously demonstrated a basic graphene–ferroelectric memory device in which the polarization in the ferroelectric film was controlled by the electrical bias applied to the gate terminal. In that structure, a thin ferroelectric film was deposited on top of a graphene layer, where it injects charge carriers and thus modulates the resistance of the graphene. Unfortunately, however, the two distinct resistance states that could be read as an information bit could only be realized by polarizing and depolarizing the ferroelectric film, which presented problems due to the instability of the depolarization state.

Now, the two teams have collaborated to fabricate an improved device that includes an additional dioxide (SiO2) dielectric gate below the graphene layer (see image). The SiO2 gate, a long-standing component in traditional FETs, effectively provides a reference point from which to measure the effect of ferroelectric gating. By monitoring the resistance of the device as a function of the voltages applied to the top and bottom gates, the researchers developed a quantitative understanding of the performance and switching behavior of –ferroelectric FETs. For use as a device, the SiO2 dielectric gate also simplifies bit writing by providing an additional background source of charge carriers, allowing the ferroelectric polarization to be switched between two stable states corresponding to two opposite polarization orientations.

The new device developed by the research team achieved impressive practical results, capable of symmetrical bit writing with a resistance ratio between the two resistance states of over 500% and reproducible nonvolatile switching over 100,000 cycles.

Explore further: AMO Manufactures First Graphene Transistors

More information: Zheng, Y. et al. Graphene field effect transistors with ferroelectric gating. Physical Review Letters 105, 166602 (2010).

Related Stories

AMO Manufactures First Graphene Transistors

February 8, 2007

In the scope of his innovative project ALEGRA the AMO nanoelectronics group of Dr. Max Lemme was able to manufacture top-gated transistor-like field-effect devices from monolayer graphene.

Reverse Chemical Switching of a Ferroelectric Film

February 25, 2009

( -- Ferroelectric materials display a spontaneous electric polarization below the Curie temperature that can be reoriented, typically by applying an electric field. In this study, researchers from Argonne, Northern ...

Recommended for you

Physicists develop new technique to fathom 'smart' materials

November 26, 2015

Physicists from the FOM Foundation and Leiden University have found a way to better understand the properties of manmade 'smart' materials. Their method reveals how stacked layers in such a material work together to bring ...

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

New sensor sends electronic signal when estrogen is detected

November 24, 2015

Estrogen is a tiny molecule, but it can have big effects on humans and other animals. Estrogen is one of the main hormones that regulates the female reproductive system - it can be monitored to track human fertility and is ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Feb 25, 2011
The 2 characteristics of non volatile memory that anyone (commercially) would care about are 1. switching speed (not mentioned) and 2. density (unintelligibly mentioned in the first paragraph) "much higher density of carriers" Much higher than what exactly ?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.