MRS Meetings and Events


EQ11.03.02 2022 MRS Spring Meeting

Highly Improved Resistance Controllability in the Cu-Cone Structure Inserted Conductive Bridge Random Access Memory for Synaptic Device Application

When and Where

May 10, 2022
9:00am - 9:15am

Hawai'i Convention Center, Level 3, 318A



Haejin Kim1,Cheol Seong Hwang1

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University1


Haejin Kim1,Cheol Seong Hwang1

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University1
With growing interest in the feasibility of conductive bridge random access memory (CBRAM) as a synaptic application, the ability to control the size of the nanosized conductive filament (CF) and the resistance remains a challenge. Precise control of the nanofilament is critical for the switching reliability and the multiple resistance states’ formation, which are required characteristics for being adapted as neuromorphic computing applications. To improve the switching reliability of CBRAMs for its further application, various methods were suggested for the past years, including extreme scaling down, limiting the cation injection, and integration into the 1T1R (1-transistor-1-resistor) structure.<br/>This study suggested the Cu-cone inserted CBRAM device (Pt/TiN/TiO<sub>2</sub>/Cu-cone/TiN/Pt, Cu-cone device) to improve the resistance controllability originated from the well-controlled single CF, which could serve as a feasible artificial synaptic device. The problem of random and stochastic dynamics of weak bundles of Cu CFs in Cu-based CBRAM was largely resolved by inserting the Cu cone into the memory cell. In the authors’ previous work, it was reported that including a Cu conical structure (≈300 nm in base-diameter and ≈400 nm in height) into the CBRAM as a cation source can largely enhance the reliability issue. The strong electric field concentrated on the inserted Cu cone induced a single CF near the tip of the Cu cone, making the device feature distinctive from the conventional planar structured Cu CBRAM (Pt/ TiN/TiO<sub>2</sub>/Cu/TiN/Pt, planar Cu device).<br/>The Cu-cone device exhibited improved control of the resistance states attributed to the well-controlled CF, which improved switching reliability and the stable formation of multiple resistance states. The analog resistive switching and enhanced controllability of the multiple resistance states of the Cu-cone inserted CBRAM were demonstrated in direct current – voltage sweep, closed-loop pulse switching (CLPS) test, and synaptic device characterization protocols. By exploiting the enhanced controllability of the resistance, highly improved endurance could be achieved, and the potentiation/depression performance could be emulated in the Cu-cone device. This is ascribed to the well-controlled formation/dissolution of Cu CF only near the tip region of the Cu-cone, where the strength of the Cu CF can be well manipulated as intended. Single filament formation could be induced attributed to the concentrated field on the conical structure, and the abrupt and stochastic resistive switching could be prevented. As a result, the ability to precisely control the size of the nanometer-sized CF was hugely improved, which is providing the high potential for the applicability of the Cu-cone device. The strong and single CF in the Cu-cone device offered a well-controlled formation/ dissolution depending on the potentiation and depression pulses, making them appropriate as an artificial synaptic device. The planar Cu device was also evaluated for comparison but failed to show these performances because of the stochastic and abrupt formation and rupture of bundles of weak Cu CFs.<br/>The gradually degrading linearity during the early stage of the potentiation/depression still needs to be enhanced, and other synaptic functions, such as the spike-timing-dependent-plasticity, also need to be proved for the Cu-cone device to be utilized as a synaptic device. Even though further research is still required to realize fully-functioning artificial synapses, the feasibility of the Cu-cone device based on the improved resistance controllability was suggested in this work.


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Symposium Organizers

Yoeri van de Burgt, Technische Universiteit Eindhoven
Yiyang Li, University of Michigan
Francesca Santoro, Forschungszentrum Jülich/RWTH Aachen University
Ilia Valov, Research Center Juelich

Symposium Support

Nextron Corporation

Publishing Alliance

MRS publishes with Springer Nature