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The Ferroelectric Tunnel Junction: a Future Synapse for the Neuromorphic Processor?

​In future neuromorphic processors, two-state transistors will be replaced by components that mimic brain synapse operation. The envisaged technologies include the ferroelectric tunnel junction studied by CEA-Leti within the scope of the European BeFerroSynaptic project.

Published on 21 July 2020
  • ​Computing units are distant from memories in a CMOS integrated circuit and data transfer from one to another is long and energy consuming. This is what is called the "von Neumann bottleneck" from the name of the inventor of this architecture in the 1940s.

  • Conversely, future neuromorphic processors will  combine computation and storage in the same assembly and the outstanding benefit will be power consumption divided by 1000!


  • The European BeFerroSynaptic project was launched at the start of 2020 and its ambition is to present a first demonstrator at the end of 2022. This project brings together eight partners including CEA-Leti, which is developing the ferroelectric tunnel junction: the basic element of the neuromorphic processor and equivalent of the synapse in the human brain.

Hafnium oxide, a material to be controlled

This element can have a multitude of states between 0 and 1, which allows it to store a "synthetic weight", explains project manager Laurent Grenouillet. "This will be possible with a new device, the ferroelectric tunnel junction, which we will assess."

                                                                                                              © CEA-Leti

  • The ferroelectric material retained for this junction is hafnium oxide (HfO2), which is well known in CMOS. However, its usage in this unprecedented context raises difficulties: for example, its crystallization in a particular phase or its thin layer deposition, whose thickness must be controlled to the nearest nanometer. Fortunately, CEA-Leti is already handling ferroelectric HfO2 in another active European project and it has produced state-of-the-art ferroelectric capacities.

It should be stated that another project partner will assess a different "synapse" technology, the ferroelectric field effect transistor, within the BeFerroSynaptic project scope.

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