Electrical Properties of CuTCNQ Based Organic Memories Targeting Integration in the CMOS Back End-of-Line
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Electrical Properties of CuTCNQ Based Organic Memories Targeting Integration in the CMOS Back End-of-Line Robert Mueller1, Joris Billen1,2, Rik Naulaerts1,2, Olivier Rouault1,3, Ludovic Goux1, Dirk J Wouters1, Jan Genoe1, and Paul Heremans1,2 1 IMEC vzw., Kapeldreef 75, Leuven, 3001, Belgium 2 ESAT, KULeuven, Kasteelpark Arenberg 10, Leuven, 3001, Belgium 3 INSA Toulouse, 135 avenue de Rangueil, Toulouse, 31077, France
ABSTRACT CuTCNQ (TCNQ=7,7,8,8-tetracyanoquinodimethane) is a resistive switching chargetransfer complex which can be used for organic nonvolatile memories. In this contribution we report on a thorough investigation of the electrical switching of CuTCNQ memories. Our memories currently achieve an endurance of up to 10000 write/erase cycles with a clear distinction between ON and OFF reading currents. ON and OFF threshold voltages follow a Gaussian distribution. Temperature dependent measurements of CuTCNQ based organic memories show a semiconductor like behavior for the ON state. The retention time of the ON state exceeded 60 hours at room temperature. Electrical switching of CuTCNQ memories in air was virtually not affected by temperatures up to 80∞C, but becomes erratic at 120∞C. The CuTCNQ material itself already starts to decompose around 200∞C in presence of oxygen as shown by thermogravimetric analysis.
INTRODUCTION Downscaling of actual non-volatile memory technology (Flash) becomes more and more challenging due to physical limitations and increasing processing complexity. Use of resistiveswitching materials (oxide resistive random access memory [1], phase change memory [2], programmable metallization cell [3],Ö) incorporated in nanometer-size via structures can be a solution for memory cells with very small footprint. Organic semiconductors are currently investigated as alternative to inorganic (metal-oxide) resistive-switching material for future memory generations. CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) is an organometallic material known since 1979 to exhibit bistable reproducible electrical resistive switching [4] in presence of an electric field (∆E) according to equation 1 [5], with x≤n: ∆E + 0 0 + ↔ Cu x + (TCNQ )x + [Cu (TCNQ )]n-x (eq.1) [Cu (TCNQ )]n high impedance ("OFF" state) low impedance ("ON" state) Since CuTCNQ can be prepared from copper metal by a spontaneous chemical reaction with TCNQ solution [4] or gas [6], integration of this memory material into the Cu complementary metal oxide semiconductor (CMOS) back end-of-line (BEOL) wafers could be achieved [6]. In a previous work we have shown that CuTCNQ nanowire memories, with a Cu
bottom and an Al top electrode, could be integrated on Cu interconnect structures (250 nm via diameter) in a standard CMOS BEOL process [7,8]. Corresponding Cu/CuTCNQ/Al memory elements achieved up to 40 write/erase cycles, with ON/OFF currents ratios between 10 and 100. In this contribution we report on endurance improvements and perform a thorough investigation of electrical properties of CuTCNQ based organic memories.
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