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SCIENCE CHINA Information Sciences, Volume 61, Issue 6: 060413(2018) https://doi.org/10.1007/s11432-017-9352-0

Flexible cation-based threshold selector for resistive switching memory integration

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  • ReceivedOct 31, 2017
  • AcceptedJan 12, 2018
  • PublishedApr 18, 2018

Abstract

Emerging resistive switching random access memory (RRAM), considered as the most promising candidate of flash memory, is favorable for in flexible electronic system. However, in high density flexible crossbar RRAM array, crosstalk issue that currents from the neighboring unselected cell lead to failure of write and read operations, still keeps a main bottleneck. Therefore, flexible selector compatible with the flexibility of the RRAM array should be focused on to configure one selector-one resistor (1S1R) system, which is immune to crosstalk issue. In this paper, flexible cation-based threshold switching (TS) selectors (Pt/Ag/HfO$_{2}$/Pt/Ti/parylene) are fabricated and the compressive performance is studied systematically. The device shows excellent bidirectional volatile TS characteristics, including high selectivity ratio (10$^{9}$), low operating voltages ($|~V_{\rm~TH}|~<~1$ V), ultra-low leakage current ($\sim$10$^{-13}$ A) and good flexibility. The successful demonstration of the wire connected 1S1R unit comprising this flexible selector and one bipolar resistor cell indicates the great potential of this cation-based selector to restrain the crosstalk issue in a large flexible RRAM array.


Acknowledgment

This work was supported by National Key RD Program (Grant No. 2017YFB0405603), Beijing Training Project for the Leading Talents in ST (Grant No. ljrc201508), Youth Innovation Promotion Association, Chinese Academy of Sciences (Grant No. 2015096), Opening Project of Key Laboratory of Microelectronics Devices and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences (Grant No. Y7YS033003).


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  • Figure 1

    (Color online)Configuration of the devices. (a) Schematic illustration of the Pt/Ag/HfO$_{2}$/Pt/Ti/parylene cation-based RS device; (b) SEM image of the crossbar devices; (c) peeling-off process of the fresh sample; (d) optional photograph of the coiled sample on one finger.

  • Figure 2

    (Color online) The unidirectional volatile TS behavior of the Ag/HfO$_{2}$/Pt/Ti/parylene devices. (a) Typical unidirectional TS I-V curves of the devices, after forming (left panel), the LRSs after SET operation (right panel) are all volatile regardless of the $I_{\rm~CC}$ (10, 50, and 100 $\mu$A); (b) $V_{\rm~TH}$ from three devices, each performed under 10, 50, and 100 $\mu$A $I_{\rm~CC}$ for 200 successive switching cycles; (c) statistical distribution of the $V_{\rm~TH}$ from (b); (d) spontaneous rupture of the fragile Ag CF under small bias generates a filament gap, while the length of the gap is strongly dependent on CF size.

  • Figure 3

    (Color online) Under 500 $\mu$A $I_{\rm~CC}$, the Pt/Ag/HfO$_{2}$/Pt/Ti/parylene devices show stable nonvolatile RS behavior. (a) Typical I-V curves of the Pt/Ag/HfO$_{2}$/Pt/Ti/parylene device under 500 $\mu$A $I_{\rm~CC}$; (b) HRS and LRS (read at 0.2 V) of the device for 100 DC sweep cycles.

  • Figure 4

    (Color online) The bidirectional volatile TS behavior of the pristine Pt/Ag/HfO$_{2}$/Pt/Ti/parylene devices.protectłinebreak (a) Typical bidirectional TS I-V curves of the devices under 100 $\mu$A $I_{\rm~CC}$, the LRS is volatile for both biasing polarities generating a selectivity of about 10$^{9}$; (b) $\pm~V_{\rm~TH}$ from 200 forward-backward switching cycles; (c) single positive sweep of the device with a rate of 7.5 mV$\cdot$step$^{-1}$, indicating a sharp ON switching slope of about 1 mV$\cdot$dec$^{-1}$; (d) DC stress test of the device at room temperature for 10$^{4}$ s.

  • Figure 5

    (Color online) Coil measurement of the bidirectional Pt/Ag/HfO$_{2}$/Pt/Ti/parylene selector. (a) Optional photograph of the coiled sample on a tube with 0.2 mm diameter; (b) photograph of the test situation on the probe station; (c) I-V curves of 200 switching cycles of the coiled TS selector after being coiled and stretched for 1000 times on the tube; (d) $\pm~V_{\rm~TH}$ of the 200 forward-backward switching cycles in (c); (e) sharp ON switching slope of about 1 mV$\cdot$dec$^{-1}$ can also be observed after coiled; (f) the coiled selector still shows nice DC stress tolerance for 10$^{4}$ s.

  • Figure 6

    (Color online) Measurement of the wire-connected 1S1R unit. (a) The typical I-V curves of the Cu/HfO$_{2}$/Pt device; (b) I-V curves of the Cu/HfO$_{2}$/Pt memory in series with the Pt/Ag/HfO$_{2}$/Pt/Ti/parylene cation-based selector under 100 $\mu$A $I_{\rm~CC}$.

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