Leakage mechanism in AlxGa1-xN/GaN heterostructures with AlN interlayer

Leakage of AlxGa1-xN/GaN heterostructures was investigated by admittance–voltage profiling. Nominally undoped structures were grown by low-pressure metal-organic vapor-phase epitaxy (MOVPE). The investigated structures had an Al-content of 30 %. They are compared to structures with an additional 1 nm thick AlN interlayer placed before the Al0.3Ga0.7N layer growth, originally to improve device performance. Conductance of FET devices with AlN interlayer, measured from depletion of the two-dimensional electron gas (2DEG) to zero volt bias at frequencies ranging from 50 Hz to 10 kHz, could be described by free charge carriers using a Drude model. The voltage dependent conductance shows a behavior described by either Poole-Frenkel emission or Schottky emission. From the size of the conductance, as well as simulation of the tunneling current injected from the gate under off-state conditions by universal Schottky tunnelling, Schottky Emission is obvious. Evaluating the data by Schottky emission, we can locate the leakage path, of tens of nm in the range between gate and drain/source with contact to the 2DEG, originating from the AlN interlayer. The static dielectric constant in growth direction, necessary for the evaluation, is determined from various AlxGa1 xN/GaN heterostructures to ε||(0) = 10.7 +/- 0.1.

Multi-Level Resistive Switching of Pt/HfO2/TaN Memory Device

This work characterizes resistive switching and neuromorphic simulation of Pt/HfO2/TaN stack as an artificial synaptic device. A stable bipolar resistive switching operation is performed by repetitive DC sweep cycles. Furthermore, endurance (DC 100 cycles) and retention (5000 s) are demonstrated for reliable resistive operation. Low-resistance and high-resistance states follow the Ohmic conduction and Poole–Frenkel emission, respectively, which is verified through the fitting process. For practical operation, the set and reset processes are performed through pulses. Further, potentiation and depression are demonstrated for neuromorphic application. Finally, neuromorphic system simulation is performed through a neural network for pattern recognition accuracy of the Fashion Modified National Institute of Standards and Technology dataset.

Influence of AlN and GaN Pulse Ratios in Thermal Atomic Layer Deposited AlGaN on the Electrical Properties of AlGaN/GaN Schottky Diodes

Atomic layer deposited AlGaN with different AlN and GaN pulse ratios (2:1, 1:1, and 1:2) was used to prepare AlGaN/GaN Schottky diodes, and their current transport mechanisms were investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. Under low reverse bias condition, the sample with the pulse ratio of 2:1 was explained by Poole–Frenkel emission and the negative temperature dependence for the sample with the pulse ratio of 1:2 was associated with the acceptor levels in the AlGaN layer. Fast interface traps at 0.24–0.29 eV were observed for the samples with the pulse ratios of 1:1 and 1:2, whereas bulk traps at ~0.34 eV were observed for the sample with the pulse ratio of 2:1. Higher trap densities were obtained from the C–V hysteresis measurements when the pulse ratios were 1:1 and 1:2, indicating the presence of a charge trapping interfacial layer. According to the X-ray photoelectron spectroscopy spectra, the pulse ratio of 2:1 was found to have less oxygen-related defects in the AlGaN layer.

The I–V Characteristics of M–BaxSr1–xTiO3–M Thin Film Structures with Oxygen Vacancies. Part 2

In Part 2 of the paper, based on the results and assumptions pointed in Part 1, analytical expressions were derived for Schottky barrier thermal/field assisted and Poole-Frenkel emission currents. The computer modeling theoretical dependencies of the I–V characteristics has been compared with the experimental measured results and obtained good agreements.

Poole–Frenkel Emission Saturation and Its Effects on Time-to-Failure in Ta-Ta2O5-MnO2 Capacitors

I-V characterization of Ta-Ta2O5-MnO2 capacitors was investigated at different temperatures, and Poole–Frenkel (PF) emission saturation was experimentally observed. Under the saturation voltage, the I-V curves at different temperature converged, and the temperature dependency was vanished. Above the saturation voltage, the leakage current was decreasing as the temperature increased. In order to evaluate the effects of saturation voltages (VS) on time-to-failure (TTF) of the capacitors, VS were first determined at +2°C and +25°C, then voltage accelerating tests were conducted at 85°C under 1.6 times of rated voltage. The distribution of VS and TTF of the samples were plotted and compared. It was shown that samples with lower saturation voltage failed earlier in the distribution of time-dependent dielectric breakdown. Comparing conventional methods for evaluating the quality of tantalum capacitors by measuring the leakage current at elevated temperature, the nondestructive measurement of saturation voltage at +2°C and +25°C may provide a novel and practicing approach tool to screening out capacitors with defected Ta2O5 layers.

Comprehensive Examination on Resistive Random Access Memory

With the latest advances in materials science, resistive random access memory (RRAM) devices are attracting non-volatile, low power consumption, non-destructive read, and high density memory. Related performance parameters for RRAM devices include operating voltage, operating speed, resistivity, durability, retention time, device yield, and multi-level storage. Numerous resistive mechanisms, such as conductive filaments, space charge limited conduction, trap charging and discharging, Schottky emission, and pool-Frenkel emission, have been proposed to explain the resistance switches of RRAM devices. Therefore, in this work, different oxide-based random access memories (RRAMs) were provided for comprehensive investigation of neuromorphiccalculations. With the development of RRAM, the physical mechanism of conduction, the basic history of neuromorphic calculations begins. Finally, suggestions for future research, as well as waiting for the challenges of RRAM equipment, are given.

ELECTRICAL CHARACTERIZATION OF METAL JUNCTION FORMED WITH PURE AND POLYANILINE-BLENDED POLY(SCHIFF BASE) POLYMER

In this paper, we demonstrate the formation of Schottky contact formed by Al with a new class of synthesized conjugated pure poly(Schiff base) (PSB) and its blend with varied concentrations of polyaniline (PANI). The Schottky behavior was transformed into Ohmic in the blended polymer. PSB was synthesized from the solution of polycondensation of terephthaloyl chloride (T) and 4-(4-hydroxybenzylideneamino)phenol (SB). The polymer showed good thermal stability with [Formula: see text] of 312∘C as determined by thermal gravimetric analysis–differential scanning calorimetry TGA–DSC and high molecular weight [Formula: see text] (g/mol) with coiled conformation as determined by laser light scattering. PBS was blended with various weight percentage ratios of PANI (0, 3, 6, 9, 12, 15 percent by weight of the pristine polymer). The metal contact (Au) was formed and studied in the temperature range of 293–373[Formula: see text]K, which showed that Schottky behavior in the intrinsic polymer with an ideality factor was close to 2 and then reduced to 1.0–1.2 in the blended polymers. In blended polymers, the conduction across the junction was characterized by Schottky emission at low field and Poole–Frenkel emission at high field. The Schottky barrier height showed a small increase with temperature, which was attributed to reduction in the built up of image charge. The Schottky and Poole–Frenkel emission coefficients were also determined and Schottky emission coefficient agreed with the theoretical value, while Poole–Frenkel emission coefficient was small. In short, the metal–semiconductor junction was affected by the blending, while conduction within the polymer remained independent of PANI concentration.