Semiconductor Integrated Device & Process Lab.


Home Research Selector


Selector (access) devices for X-point array

  • Suppression of leakage & sneak-path current is important when implementing X-point RRAM arrays
  • Selector devices can solve the sneak path issue by integrating them with RRAMs to configure a 1S-1R structure.
Insulator-to-Metal Transition (IMT) based selectors

  • Materials : VO2 and NbO2
  • Fast switching speed
  • NbO2 has better thermal stability, but suffers from high off current.
Tunnel-barrier Type Selector

  • Mechanism : band barrier controlling
  • Direct tunneling (DT) or Fowler-Nordheim (FN) tunneling is controlled by external bias.
  • Structure : Ta2O5 (Tunnel barrier) / TaOx / TiO2
Ovonic Threshold Switch (OTS)

  • Typical characteristics of chalcogenide materials.
  • One of the best candidate materials for a X-point array selector.
  • Advantages
    • Abrupt and fast switching speed
    • Purely electronic based switching
    • Simple and room temperature fabrication process
    • High thermal/electrical stability
Volatile CBRAM type switch

  • Mechanism: formation and dissolution of a metal filament
  • Volatile nature at low Icomp. due to instability of the filament
  • Advantages: abrupt transition, high on/off ratio, low off-state current level
Applications (1T1S using TS devices)
Volatile CBRAM type switch based selector

  • Conventional MOSFET has a subthreshold slope (SS) limit of 60mV/dec at RT.
  • Low off-state current and low SS (~4mV/dec) of transistors can be implemented by connecting CBRAM type switches to the drain side of MOSFET devices.
    Various types of selector devices (CBRAM selector, OTS, …) can also be adopted for this 1T1S application.
  1. 1.   E. Cha et al., "Nanoscale (∼ 10nm) 3D vertical ReRAM and NbO2 threshold selector with TiN electrode." Electron Devices Meeting (IEDM), 2013 IEEE International. IEEE, 2013.
  2. 2.   Y. Koo et al., "Te-based amorphous binary OTS device with excellent selector characteristics for X-point memory applications."  VLSI Technology, 2016 IEEE Symposium on. IEEE, 2016.
  3. 3.   J. Song et al., "Threshold selector with high selectivity and steep slope for cross-point memory array." IEEE Electron Device Letters 36.7 (2015): 681-683.