Evolutionary 2D organic crystals for optoelectronic transistors and neuromorphic computing

Brain-inspired neuromorphic computing has been extensively researched, taking advantage of increased computer power, the acquisition of massive data, and algorithm optimization. Neuromorphic computing requires mimicking synaptic plasticity and enables near-in-sensor computing. In synaptic transistors, how to elaborate and examine the link between microstructure and characteristics is a major difficulty. Due to the absence of interlayer shielding effects, defect-free interfaces, and wide spectrum responses, reducing the thickness of organic crystals to the 2D limit has a lot of application possibilities in this computing paradigm. This paper presents an update on the progress of 2D organic crystal-based transistors for data storage and neuromorphic computing. The promises and synthesis methodologies of 2D organic crystals are summarized. Following that, applications of 2D organic crystals for ferroelectric nonvolatile memory, circuit-type optoelectronic synapses, and neuromorphic computing are addressed. Finally, new insights and challenges for the field's future prospects are presented, pushing the boundaries of neuromorphic computing even farther.

Investigation of random telegraph noise characteristics of Hf-based MONOS nonvolatile memory devices with HfO2 and HfON tunneling layer

This paper investigated the low frequency noise (LFN) utilizing 1/f noise and random telegraph noise (RTN) characteristics of Hf-based metal/oxide/nitride/oxide/silicon (MONOS) nonvolatile memory (NVM) device with HfO2 and HfON tunneling layer (TL). The low frequency noise spectral density (SID ) was investigated to evaluate the interface characteristics with fresh and after programming/erasing (P/E) cycles of 104. Both devices show similar slope of ~1/f in all of the frequency regions. Although HfON TL shows high SID compared to HfO2 TL, increased ratio is 15.4 which is low compared to HfO2 TL of 21.3. As decreasing the channel length from 10 to 2 μm, HfON TL shows small increased ratio of SID . Due to the nitrided characteristics, HfON TL suppress the degradation of interface. Finally, it is found that trap site of HfO2 TL is located near the interface by RTN measurement with capture (τC) and emission time constant (τE).

Characterization of Graphenic Carbon Produced by Pulsed Laser Ablation of Sacrificial Carbon Tapes

This paper reports on the pulsed laser deposition of nanocarbon films on metal and dielectric substrates, using high-purity sacrificial carbon tape as a carbon source on a neutral gas background. The films were characterized by X-ray diffraction (XRD), photoelectron (XPS) and Raman spectroscopy. The XRD and Raman structural analyses revealed that the synthesized films have a graphenic nanocrystalline turbostratic structure, with sp2 clusters about 15–18 nm in size, depending on the laser fluence. A significant decrease in the oxygen and hydrogen contents in the films, in comparison with the target material, was established using XPS, as well as a significant decrease in the sp3 carbon content. The deposited films were found to be similar to reduced graphene oxide (rGO) in composition, with a surprisingly low number of defects in the sp2-matrix. The method proposed in the work may have good prospects of application in the production of energy storage and nonvolatile memory devices.

Improvement of the Charge Retention of a Non-Volatile Memory by a Bandgap-Engineered Charge Trap Layer

In recent years, research based on HfO2 as a charge trap memory has become increasingly popular. This material, with its advantages of moderate dielectric constant, good interface thermal stability and high charge trap density, is currently gaining in prominence in the next generation of nonvolatile memory devices. In this study, memory devices based on a-IGZO thin-film transistor (TFT) with HfO2/Al2O3/HfO2 charge trap layer (CTL) were fabricated using atomic layer deposition. The effect of the Al2O3 layer thickness (1, 2, and 3 nm) in the CTL on memory performance was studied. The results show that the device with a 2-nm Al2O3 layer in the CTL has a 2.47 V memory window for 12 V programming voltage. The use of the HfO2/Al2O3/HfO2 structure as a CTL lowered the concentration of electrons near the tunnel layer and the loss of trapped electrons. At room temperature, the memory window is expected to decrease by 0.61 V after 10 years. The large storage window (2.47 V) and good charge retention (75.6% in 10 years) of the device under low-voltage conditions are highly advantageous. The charge retention of the HfO2/Al2O3/HfO2 trap layer affords a feasible method for fabricating memory devices based on a-IGZO TFT.

Modeling and Simulation of Hafnium Oxide RRAM Based on Oxygen Vacancy Conduction

The resistive memory has become one of the most promising new memory types because of its excellent performance, and HfO2 resistive material has attracted extensive attention. The conduction mechanism based on oxygen vacancy is widely recognized in the research of new nonvolatile memory. An RRAM electrothermal coupling model based on the oxygen vacancy conduction mechanism was constructed using COMSOL. The resistance process of the device is simulated by solving the coefficient partial differential equation, and the distribution of oxygen vacancy concentration, temperature, electric field, electric potential and other parameters in the dielectric layer at different voltages are obtained. The effects of temperature, dielectric layer thickness, top electrode thermal conductivity and conductive wire size on the resistance characteristics of the device are studied. It has guiding significance to further study the RRAM mechanism.