Nav: Home

Operation mechanism of ferroelectric HfO2-based transistor and memory has been elucidated

December 13, 2018

As a part of JST PRESTO program, Associate professor Masaharu Kobayashi, Institute of industrial Science, The University of Tokyo, has experimentally clarified the operation mechanism of low voltage operation of a transistor with ferroelectric-HfO2 gate insulator. In addition, he has theoretically elucidated scalability of ferroelectric tunnel junction (FTJ) memory with ferroelectric-HfO2 down to 20nm diameter.

Negative capacitance FET (NCFET) with ferroelectric-HfO2 gate insulator is attracting interests as a steep subthreshold slope transistor for ultralow voltage operation, which can break the physical limit of 60mV/dec in the conventional MOSFET. However, its operation mechanism has not been fully clarified yet in terms of polarization switching dynamics. FTJ memory with ferroelectric-HfO2 is a promising high-capacity nonvolatile memory. However, its scalability considering resistance ratio between read current for access speed, resistance ratio between on-state and off-state for sensing margin, depolarization field for retention characteristics has not been fully elucidated yet.

In this study, he has experimentally demonstrated sub-60mV/dec subthreshold slope in a transistor with ferroelectric-HfO2 and clarified that the physical mechanism is attributed to charge injection assisted by polarization switching in ferroelectric-HfO2 gate insulator improves subthreshold characteristics as shown in Fig. 1. Furthermore, he has systematically investigated the relationship between subthreshold characteristics and polarization switching by monitoring gate current with high resolution and clarified that polarization switching dynamics causes transient negative capacitance by depolarization effect due to small depletion layer capacitance, as shown in Fig. 2.

As for FTJ, he has established non-equilibrium Green function method with self-consistent potential involving polarization charge and semiconductor surface potential to calculate current through FTJ memory. This simulation framework is calibrated by experimental results of ferroelectric-HfO2 FTJ memory in the form of metal-ferroelectric-semiconductor structure, which was previously developed and demonstrated in the same JST PRESTO program. By utilizing this simulation framework, he has theoretically predicted that ferroelectric-HfO2 FTJ can be scaled down to 20nm diameter size by systematically investigating the impacts of material properties and considering the trade-off among read current for access speed, resistance ratio between on-state and off-state for sensing margin, and depolarization field for data retention characteristics, as shown in Fig. 3.

The achievements in this study will largely contribute to guiding device design of ultralow power operating NCFET and high-capacity FTJ memory, which leads to enabling ultralow power IoT edge devices, deploying highly sophisticated network system, and thus providing more strategic social services utilizing big data.
This work was presented in IEEE International Conference on Electron Device Meeting on December 4th and 5th in 2018, which was held in San Francisco.

Japan Science and Technology Agency

Related Memory Articles:

Memory boost with just one look
HRL Laboratories, LLC, researchers have published results showing that targeted transcranial electrical stimulation during slow-wave sleep can improve metamemories of specific episodes by 20% after only one viewing of the episode, compared to controls.
VR is not suited to visual memory?!
Toyohashi university of technology researcher and a research team at Tokyo Denki University have found that virtual reality (VR) may interfere with visual memory.
The genetic signature of memory
Despite their importance in memory, the human cortex and subcortex display a distinct collection of 'gene signatures.' The work recently published in eNeuro increases our understanding of how the brain creates memories and identifies potential genes for further investigation.
How long does memory last? For shape memory alloys, the longer the better
Scientists captured live action details of the phase transitions of shape memory alloys, giving them a better idea how to improve their properties for applications.
A NEAT discovery about memory
UAB researchers say over expression of NEAT1, an noncoding RNA, appears to diminish the ability of older brains to form memories.
Molecular memory can be used to increase the memory capacity of hard disks
Researchers at the University of Jyväskylä have taken part in an international British-Finnish-Chinese collaboration where the first molecule capable of remembering the direction of a magnetic above liquid nitrogen temperatures has been prepared and characterized.
Memory transferred between snails
Memories can be transferred between organisms by extracting ribonucleic acid (RNA) from a trained animal and injecting it into an untrained animal, as demonstrated in a study of sea snails published in eNeuro.
An immunological memory in the brain
Inflammatory reactions can change the brain's immune cells in the long term -- meaning that these cells have an 'immunological memory.' This memory may influence the progression of neurological disorders that occur later in life, and is therefore a previously unknown factor that could influence the severity of these diseases.
Anxiety can help your memory
Anxiety can help people to remember things, a study from the University of Waterloo has found.
Pores with a memory
Whether for separation processes, photovoltaics, catalysis, or electronics, porous polymer membranes are needed in many fields.
More Memory News and Memory Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at