LoGHeD: An effective approach for negative differential resistance effect suppression in negative capacitance transistors

A negative capacitance transistor (NCFET) with fully depleted silicon-on-insulator (FDSOI) technology (NC-FDSOI) is one of the promising candidates for next-generation low-power devices. However, it suffers from the inherent negative differential resistance (NDR) effect, which is very detrimental to device and circuit designs. Aiming at overcoming this shortcoming, this paper proposes for the first time to use local Gaussian heavy doping technology (LoGHeD) in the channel near the drain side to suppress the NDR effect in the NC-FDSOI. The technical computer-aided design (TCAD) simulation results have validated that the output conductance (GDS) with LoGHeD, which is used to measure the NDR effect, increases compared to the conventional NC-FDSOI counterpart and approaches zero. With the increase in doping concentration, the inhibitory capability of the NDR effect shows a monotonously increasing trend. In addition, the proposed approach maintains and even enhances performances of the NC-FDSOI transistor regarding the electrical parameters, such as threshold voltage (VTH), sub-threshold swing (SS), switching current ratio (ION/IOFF), and drain-induced barrier lowering (DIBL).

Conductance Quantization Behavior in Pt/SiN/TaN RRAM Device for Multilevel Cell

In this work, we fabricated a Pt/SiN/TaN memristor device and characterized its resistive switching by controlling the compliance current and switching polarity. The chemical and material properties of SiN and TaN were investigated by X-ray photoelectron spectroscopy. Compared with the case of a high compliance current (5 mA), the resistive switching was more gradual in the set and reset processes when a low compliance current (1 mA) was applied by DC sweep and pulse train. In particular, low-power resistive switching was demonstrated in the first reset process, and was achieved by employing the negative differential resistance effect. Furthermore, conductance quantization was observed in the reset process upon decreasing the DC sweep speed. These results have the potential for multilevel cell (MLC) operation. Additionally, the conduction mechanism of the memristor device was investigated by I-V fitting.

Magnetic tunneling junctions based on 2D CrI3 and CrBr3: spin filtering effects and high tunnel magnetoresistance via energy band difference

Recently, the study on two-dimensional materials expands to the field of spintronics. The intrinsically ferromagnetic van der Waals materials such as CrI3 and CrBr3 receive much attention due to nearly 100% spin polarization and good stability, resulting in excellent performance in magnetic tunnel junctions. In this work, we design the magnetic tunnel junctions of Cu/CrI3/Cu and Cu/CrBr3/Cu with the electrodes of Cu(111) and the tunneling barrier of 4-monolayer CrI3 or CrBr3. Our first-principle calculations combined with nonequilibrium Green’s function method indicate that the CrBr3-based MTJ has a larger maximum tunneling magnetoresistance ratio than the CrI3-based MTJ. In a wide bias voltage range, the CrI3-based MTJ can maintain high spin filtering performance, while that of the CrBr3-based MTJ degrades sharply as the bias voltage increases. It is noted that negative differential resistance effect is observed in the CrBr3-based MTJ. The differences of spin transport properties between the CrI3-based MTJ and the CrBr3-based MTJ are clarified in terms of the inside device physics, including the spin-dependent projected density of states, band structures, Bloch states, and the electron density difference. This work provides some physical insights for the design of 2D van der Waals MTJ.

Synaptic Characteristics from Homogeneous Resistive Switching in Pt/Al2O3/TiN Stack

In this work, we propose three types of resistive switching behaviors by controlling operation conditions. We confirmed well-known filamentary switching in Al2O3-based resistive switching memory using the conventional device working operation with a forming process. Here, filamentary switching can be classified into two types depending on the compliance current. On top of that, the homogeneous switching is obtained by using a negative differential resistance effect before the forming or setting process in a negative bias. The variations of the low-resistance and high-resistance states in the homogeneous switching are comparable to the filamentary switching cases. However, the drift characteristics of the low-resistance and high-resistance states in the homogeneous switching are unstable with time. Therefore, the short-term plasticity effects, such as the current decay in repeated pulses and paired pulses facilitation, are demonstrated when using the resistance drift characteristics. Finally, the conductance can be increased and decreased by 50 consecutive potentiation pulses and 50 consecutive depression pulses, respectively. The linear conductance update in homogeneous switching is achieved compared to the filamentary switching, which ensures the high pattern-recognition accuracy.