Complementary and bipolar regimes of resistive switching in TiN/HfO 2 /TiN stacks grown by atomic‐layer deposition

Han

Adv Materials Technologies

et al. 2018

179

126

required. Several types of emerging mem ories have been researched in the past few decades such as magnetic memory, phase change memory, ferroelectric tunnel junc tions, and resistive switching memory. Among these emerging devices, resistive switching memory called memristors, introduced by Chua in 1971, [1] have strong points of small cell size, nonvolatile and random data access possibility, easy fabri cation process, and simple structure. [2,3] Because of these advantages, various mate rials are examined for achieving memris tive properties.In addition, different from the past sev eral decades, information is being made depending on experiences or repeated stimuli similar to that in the human brain. The human brain contains ≈10 11 neurons and 10 15 synapses, occupies a small space, and consumes less than 20 W, which is lower than the power required to run a household light bulb. [4][5][6] Moreover, the human brain is currently considered as the most intelligent and fastest operation system. Therefore, neuromorphic computing, which emu lates the human brain, has been regarded as a promising nextgeneration computing system. Studies on neuromorphic computing have been rapidly growing and highlighted for various applications such as artificial intelligence, sensors, robotic devices, and memory devices.Existing neural networks are implemented by the combination of machine learning as software and the von Neumann archi tecture as hardware based on the complementary metaloxide semiconductor (CMOS) technology. However, CMOSbased cir cuits require 6-12 transistors and the design is not flexible. [7] The present computing system with the von Neumann architecture is implemented by a serial operation through a central processing unit (CPU). Because of the von Neumann bottleneck, memory devices have limitations in data processing speed between memory and CPU and require high power and large space. [8][9][10] Therefore, a new neuromorphic computing system that is exe cuted by parallel operation with a high operation speed, low energy consumption, and small volume is critically required.To achieve such requirement, memristive materials have been actively examined as emulating several functions of human brain. A memristor could act as a single unit of synapse without software programming supports. Memristorbased neu romorphic architecture is implemented by parallel operation with efficient power, small volume, and high data processing Neuromorphic architectures are in the spotlight as promising candidates for substituting current computing systems owing to their high operation speed, scale-down ability, and, especially, low energy consumption. Among candidate materials, memristors have shown excellent synaptic behaviors such as spike time-dependent plasticity and spike rate-dependent plasticity by gradually changing their resistance state according to electrical input stimuli. Memristor can work as a single synapse without programming support, which remarkably satisfies the requirements of neuromorphic computing. Here, the mo...

Section: Metal Oxidesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recent Advances in Memristive Materials for Artificial Synapses

Han

Adv Materials Technologies

et al. 2018

179

126

Applied Physics Letters

“…Using Equation (1), the hopping distance is found to be approximately 0.58 nm, which is close to the reported value of 1 6 0.1 nm using TiN/HfO 2 /TiN structure. 10 Chen et al 18 have also reported the hopping distance ranging from 1.4 to 0.3 nm with current compliances of 10 to 100 lA using a Pt/ Zn:SiO 2 /TiN structure. On the other hand, the linear nature of ln(J/E) vs. E 1/2 curve confirms the Poole-Frenkel conduction mechanism at "1" state for a high field regime (À1 to À4 V) of the S2 devices ( Fig.…”

mentioning

confidence: 93%

Evolution of complementary resistive switching characteristics using IrOx/GdOx/Al2O3/TiN structure

Jana

Samanta

Maikap

et al. 2016

The complementary resistive switching (CRS) characteristics using an IrOx/GdOx/Al2O3/TiN single cell are observed whereas the bipolar resistive switching (BRS) characteristics are observed for the IrOx/GdOx/TiN structure. Transmission electron microscope and energy dispersive X-ray spectroscopy depth profile show crystalline GdOx film and the presence of higher amount of oxygen at both IrOx/GdOx interface and Al2O3 layer. Inserting thin Al2O3 layer, the BRS is changed to CRS. This CRS has hopping distance of 0.58 nm and Poole-Frenkel current conductions for the “0” and “1” states, respectively. A schematic model using oxygen vacancy filament formation/rupture at the TE/GdOx interface and Al2O3 layer has been illustrated. This CRS device has good endurance of 1000 cycles with a pulse width of 1 μs, which is very useful for future crossbar architecture.

“…Besides, Egorov et al have also shown the transition between CRS ↔ BRS can be achieved by applying an asymmetrical sweeping voltage in TiN/HfO x /TiN memory structure 53. Although, during the BRS operation in a 1T1R bipolar RRAM test array, the activation of unwanted self-CRS from BRS is very risky.…”

mentioning

confidence: 97%

The Role of Ti Buffer Layer Thickness on the Resistive Switching Properties of Hafnium Oxide-Based Resistive Switching Memories

et al. 2017

Ti/HfO-based resistive random access memory (RRAM) has been extensively investigated as an emerging nonvolatile memory (NVM) candidate due to its excellent memory performance and CMOS process compatibility. Although the importance of the role of the Ti buffer layer is well recognized, detailed understanding about the nature of Ti thickness-dependent asymmetric switching is still missing. To realize this, the present work addresses the effects of Ti buffer layer thickness on the switching properties of TiN/Ti/HfO/TiN 1T1R RRAM. Consequently, we have demonstrated a simple strategy to regulate the FORMING voltage, leakage current, memory window, and decrease the operation current, etc. by varying the thickness of the Ti layer on the HfO dielectrics. Accordingly, controllable and reliable bipolar, complementary, and reverse bipolar resistive switching (BRS, CRS, and R-BRS) properties have been demonstrated. This work also provides the direction to avoid unwanted CRS properties during the first RESET operation by decreasing the FORMING voltage. Furthermore, the memory device shows good nonvolatility at ∼1 μA programming current by selecting a proper thickness of Ti buffer layer. To achieve reliable BRS properties for low power application, the operation current has been further optimized, whereas the memory device shows pulse endurance of more than 7 million cycles at a low pulse width of 50 ns and excellent data retention properties of more than 40 h at 150 °C measurement temperature.