Tunable voltage polarity-dependent resistive switching characteristics by interface energy barrier modulation in ceria-based bilayer memristors for neuromorphic computing

Enhanced linear and symmetric synaptic weight update characteristics in a Pt/p-LiCoOx/p-NiO/Pt memristor through interface energy barrier modulation by Li ion redistribution

“…6 For a more efficient computing operation, the synaptic weight update is pursued to be analog, linear, and symmetric and to have a wide dynamic range to enhance the range of memory states. 7,8…”

“…To date, RRAM devices with a variety of oxides have been researched for synaptic device application, such as HfO 2 , 13–15 Ta 2 O 3 , 16–18 WO x , 19–21 TiO 2 , 22–24 CeO 2 , 7,25,26 ZnO, 27–29 NiO, 30–32 SrFeO x , 33 and PCMO. 34,35 With respect to the resistance change mechanism, filamentary-type CBRAM and VCM suffer from a non-linear, digital-type and asymmetric resistance change with a large device-to-device variation due to the abrupt and stochastic nature of filament formation.…”

“…5,36 In comparison, interfacial-type RRAM with the resistance change associated with ion redistribution is thought to be more promising to achieve a precise and gradual resistance change in an analog manner as well as resulting in various biological synaptic behaviors such as short-term and long-term plasticity (STP and LTP), and paired pulse facilitation or depression (PPF and PPD). In order to achieve more reliable control of ionic redistribution, bilayer structures were also employed such as GDC/CeO 2 , 7 WO x /TaO x , 37 TiO 2 /Al 2 O 3 , 38 AlO x /HfO 2 , 39 HfO 2 /Al 2 O 3 , 40 TaO x /TiO 2 , 41 HfO 2 /HfO 2− x , 42 and HfO y /HfO x . 43…”

“…6 For a more efficient computing operation, the synaptic weight update is pursued to be analog, linear, and symmetric and to have a wide dynamic range to enhance the range of memory states. 7,8 Among various candidate devices for artificial synapses, two-terminal memristors have been extensively explored due to their advantage of having a similar structure to the biological neuron-synapse-neuron structure. Memristors exhibit tunable conductance states depending on historical electrical signals emulating the dynamic synaptic weight update behavior.…”

“…9 As among the two-terminal memristor devices, resistive random access memory devices (RRAM), including conductive bridge random access memory (CBRAM) using a metallic filament, valence change memory (VCM) with an oxygen-vacancy filament, and interfacial-type RRAM with oxygen redistribution particularly at the interface, have been reported to have low energy consumption down to sub-pJ per synaptic event and good scalability for high-density integration, forming a crossbar array structure with CMOS compatibility. [10][11][12] To date, RRAM devices with a variety of oxides have been researched for synaptic device application, such as HfO 2 , [13][14][15] Ta 2 O 3 , [16][17][18] WO x , [19][20][21] TiO 2 , [22][23][24] CeO 2 , 7,25,26 ZnO, [27][28][29] NiO, [30][31][32] SrFeO x , 33 and PCMO. 34,35 With respect to the resistance change mechanism, filamentary-type CBRAM and VCM suffer from a non-linear, digital-type and asymmetric resistance change with a large device-to-device variation due to the abrupt and stochastic nature of filament formation.…”