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SCIENCE CHINA Information Sciences, Volume 64 , Issue 4 : 142402(2021) https://doi.org/10.1007/s11432-020-2960-x

A bidirectional threshold switching selector with a symmetric multilayer structure

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  • ReceivedMay 3, 2020
  • AcceptedJun 18, 2020
  • PublishedNov 23, 2020

Abstract

Selectors have been proposed as a highly effective tool for suppressing substantial leakage currents without sacrificing the high density of resistive random-access memory (RRAM) crossbar arrays. Among various selector types, the programmable metallization cell (PMC) selector is promising due to its simple structure and high selectivity. In this work, we demonstrate a new PMC selector that exhibits bidirectional threshold switching behavior by implementing symmetric multilayer dielectrics. The proposed Ag/SiTe/HfO$_{2}$/SiTe/Ag selector device has a low off current ($<10^{-10}$ A), high selectivity ($>10^{5}$), and low threshold voltage variation ($<$ 0.05). Upon connection to a bipolar RRAM cell via a wire, the proposed selector successfully suppresses the leakage current of an unselected device below the threshold voltage.


Acknowledgment

This work was supported by National Natural Science Foundation of China (Grant Nos. 61604177, 61704191, 61471377).


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  • Figure 1

    (Color online) Schematic of the fabrication process. First, the bottom Ag electrode was patterned and grown on a Si substrate with SiO$_{2}$ via ion sputtering (a). SiTe and HfO$_{2}$ were grown over the bottom layer using magnetron sputtering and atomic layer deposition, and the samples were then annealed (b). The bottom electrode was removed by etching (c), and subsequently, the top electrode was grown (d). (e) presents a structural schematic of the as-fabricated device.

  • Figure 2

    (Color online) DC sweep characteristics. (a) Bidirectional threshold switching phenomena under various compliance currents. (b) Volatile threshold switching with high selectivity. (c) Low switching slope. (d) DC stress test under a 0.2-V bias.

  • Figure 3

    (Color online) Transient tests. (a) Positive pulse test with a 2-$\mu$s delay before threshold switching. (b) Negative pulse test with a 3-$\mu$s delay before switching. (c) Double-pulse test in which the device turns on and off.

  • Figure 4

    (Color online) Endurance test. (a) DC sweep of 100 cycles with threshold switching in both polarities. (b) Cumulative probability of the threshold voltage and hold voltage in DC sweeps. (c) A total of 10$^{6}$ pulse tests with a large on/off resistance difference. (d) A 10-M$\Omega~$ resistor test with the same pulse applied in the selector test.

  • Figure 5

    (Color online) Mechanism analysis. (a) Initial state with a few Ag atoms doped during fabrication. (b) Conductive filaments are formed when a voltage is applied, and the filaments automatically rupture after the voltage is removed, with only a small gap remaining. (c) Residual filaments provide a preferred path for filament reformation when a voltage is applied again.protect łinebreak (d) Ag atoms return to the minimum interfacial energy position after the voltage is removed, and filaments in the SiTe layer near the interface rupture.

  • Figure 6

    (Color online) DC characteristics for 1R (a) and 1S1R (b). The cell current is suppressed by the selector when the voltage is lower than the threshold voltage.