Crossbar of Microelectromechanical Selectors and
Non-Volatile Memory Devices for Neuromorphic Computing

SelectX

Project financed by the European Commission through the H2020 Marie Skłodowska-Curie Actions Individual Fellowship

 

Project objective

The project proposes the use of NEMS relays as selector devices for memristor crossbars and pursues the simulation, fabrication and characterization of a proof-of-concept crossbar of monolithically integrated memristor/NEMS device.

 

Publications and reports

Paper “NEMS Relay as Integrated Selector Device for Memristor Crossbars” has been accepted for oral presentation at the 17th edition of the International Symposium on RF-MEMS and RF-MICROSYSTEMS (MEMSWAVE 2016)......................

Project description

Hybrid CMOS chips with stacked crossbars of memory devices (Figure 1a) promise to deliver the high density and connectivity required for hardware implemented artificial neural networks. However, the crossbar architecture suffers intrinsically from the sneak path problem – whereby neighbouring devices create an electrical short around the selected device (Figure 1b).

Biological systems do not suffer from sneak path problems due to the inherently nonlinear mechanism of their potentiation and spiking. A solution to reduce current leaks in hardware implemented ANNs is to have highly nonlinear memory devices, which has proven to be hard to achieve. Another option is to use a selector for each of the memory devices.

 

Figure 1. (a) The principle of a hybrid CMOS/memory chip.
The bottom layer represents the existing CMOS technology. The top layers are stacked crossbars of non-volatile memory devices interconnected with the CMOS through vias. (b) The sneak path problem in a crossbar of memory device with no selector. When a device is accessed, currents leak through adjacent devices mainly the ones in ON state (low resistance).


Two terminal MEMS relays are attractive as potential selector devices due to high nonlinearity and have been heavily researched for RF applications. This proposal outlines a specific device structure to investigate the viability of the monolithic integration of MEMS (and NEMS) switches and non-volatile memory devices (Figure 2). The proposed work is highly multi- and inter-disciplinary and will combine in all aspects knowledge from both the MEMS and the non-volatile memory device fields of study. The proposed work is not linked to a particular non-volatile memory technology (resistive switches are used as an example), being suitable for any dense crossbar system that requires selectors. The success of this project is immediately relevant to a broad field of research in hardware ANNs and non-volatile memories and to the industry players in the field.

Figure 2.(a) Integrated memristor/MEMS selector desired I-V characteristic with nonlinearity introduced by the selector.
(b) Device design highlighting the beam displacement (COMSOL simulation)

The project is a collaboration between:

National Institute for Research and Development in Microtechnologies (IMT Bucharest)
Micromachined structures, microwave circuits and devices Laboratory (RF-MEMS) (L4), 
Coordinator: Dr. Alexandru Muller

and

École Polytechnique Fédérale de Lausanne (EPFL)
Nanoelectronic Devices Laboratory (NANOLAB)
Coordinator: Dr. Mihai Adrian Ionescu

IMT-Bucharest is the beneficiary of the project and EPFL is the secondment institution. The Researcher, Dr. Adam, will pursue the main research activities of the project at IMT-Bucharest and complement them with research visits at EPFL as part of a 4-month secondment.

Dr. Muller and his L4 group have a long record of exploring challenging RF MEMS device designs. Dr. Adam contributes expertise in the field of non-volatile memory devices for neuromorphic applications. Dr. Ionescu from EPFL is an expert in non-silicon devices and MEMS devices for in- and above- CMOS.

General information   Contact

Project financed by European Commission through the H2020 Marie Skłodowska-Curie Actions,
Individual Fellowship program

Project duration:
1 April 2016 - 31 March 2018

 

National Institute for Reseach and Development in Microtechnologies- IMT Bucharest

Coordinator ("Supervisor"):  Dr. Alexandru Muller
E-mail: alexandru[dot]muller[at]imt[dot]ro;

Researcher: Dr. Gina Adam,
E-mail: gina[dot]adam[at]imt[dot]ro

Phone:  +40-21-269.07.70; +40-21-269.07.74;
Fax: +40-21-269.07.72; +40-21-269.07.76;
Website: www.imt.ro

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