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3D integration of a logic/memory CUBE for In-Memory-Computing

Periodic Reporting for period 1 - MY-CUBE (3D integration of a logic/memory CUBE for In-Memory-Computing)

Reporting period: 2019-04-01 to 2020-09-30

For integrated circuits to be able to leverage the future “data deluge” coming from the cloud and cyber-physical systems, the historical scaling of Complementary-Metal-Oxide-Semiconductor (CMOS) devices is no longer the corner stone. At system-level, computing performance is now strongly power-limited and the main part of this power budget is consumed by data transfers between logic and memory circuit blocks in widespread Von-Neumann design architectures. An emerging computing paradigm solution overcoming this “memory wall” consists in processing the information in-situ, owing to In-Memory-Computing (IMC).
However, today’s existing memory technologies are ineffective to In-Memory compute billions of data items, as it is the case in the brain. Things may change with the emergence of three key enabling technologies: non-volatile resistive memory, new energy-efficient nanowire transistors and 3D-monolithic. My-CUBE will leverage them towards a functionality-enhanced system with a tight entangling of logic and memory. Only such a technology can support the scalability of the IMC concept.
Following a holistic approach from the system to the material, My-CUBE unique solution relies on a new class of nano-technology, mixing at the fine-grain level a high capacity of non-volatile resistive memory coupled with new junctionless nanowire transistors 3D-interconnected at low-temperature, to perform data-centric computations. A 3D IMC accelerator circuit will be designed, manufactured and measured, targeting a 20x reduction in (Energy x Delay) Product vs. Von-Neumann systems. This technology that adds smartness to memory/storage will not only be a game changer for artificial intelligence, machine learning, data analytics or any data-abundant computing systems but it will also be, more broadly, a key computational kernel for next low-power, energy-efficient European integrated circuits.
The Von-Neumann bottleneck is a clear limitation for data-intensive applications, bringing In-Memory Computing (IMC) solutions to the fore. Since large data set are usually stored in Non-Volatile Memory (NVM), various solutions have been proposed based on emerging memories, such as OxRAM, that rely mainly on area hungry, one transistor (1T) one OxRAM (1R) bit-cell. To tackle this area issue, whereas keeping the programming control provided by 1T1R bit-cell, we propose to combine Gate-All-Around stacked junctionless nanowires, and OxRAM technology to create a 3D memory pillar with ultra-high-density. Nanowire junctionless transistors have been fabricated, characterized, and simulated to define current conditions for the whole pillar. Finally, based on SPICE simulations, we demonstrated IMC scouting logic operations up to three pillar’s layers, with one operand per layer.
We have explored a novel 3D one transistor / one RRAM (1T1R) memory cube. The proposed architecture integrates HfO2-based OxRAM with select junctionless transistors based on low-voltage Gate-All-Around (GAA) stacked NanoSheet (NS) technology. Extensive characterization of junctionless transistors and OxRAMs was perfomed to show their ability to be co-integrated inside a same 1T1R memory cell. Electrical characterization of OxRAM arrays showed a large memory window (HRS/LRS=20) up to 1E4 cycles with a current compliance of 150 microA, compatible with the performances of junctionless transistors. Then, we experimentally demonstrated scouting logic operations capability with 2 operands, which should be extended to 4 operands thanks to an original two cells/bit “double coding” scheme assessed by SPICE simulation. Finally, we evidenced that this computing scheme is 2 times more energy efficient than a write-verify approach. In the future, the scalability of this novel high-density 3D memory technology will be assessed and its potential applications investigated.