The performances of conductive-bridging random access memory (CBRAM) have been reviewed for different switching materials such as chalcogenides, oxides, and bilayers in different structures. The structure consists of an inert electrode and one oxidized electrode of copper (Cu) or silver (Ag). The switching mechanism is the formation/dissolution of a metallic filament in the switching materials under external bias. However, the growth dynamics of the metallic filament in different switching materials are still debated. All CBRAM devices are switching under an operation current of 0.1 μA to 1 mA, and an operation voltage of ±2 V is also needed. The device can reach a low current of 5 pA; however, current compliance-dependent reliability is a challenging issue. Although a chalcogenide-based material has opportunity to have better endurance as compared to an oxide-based material, data retention and integration with the complementary metal-oxide-semiconductor (CMOS) process are also issues. Devices with bilayer switching materials show better resistive switching characteristics as compared to those with a single switching layer, especially a program/erase endurance of >105 cycles with a high speed of few nanoseconds. Multi-level cell operation is possible, but the stability of the high resistance state is also an important reliability concern. These devices show a good data retention of >105 s at >85°C. However, more study is needed to achieve a 10-year guarantee of data retention for non-volatile memory application. The crossbar memory is benefited for high density with low power operation. Some CBRAM devices as a chip have been reported for proto-typical production. This review shows that operation current should be optimized for few microamperes with a maintaining speed of few nanoseconds, which will have challenges and also opportunities for three-dimensional (3D) architecture.

Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, sputtered SiGe layers and thermally grown tunnel oxide were fabricated on p-Si substrates. The trilayer structures were rapid thermal annealed at 1000 °C in nitrogen atmosphere for different durations. Cross-sectional transmission electron micrographs revealed the complete isolation of Ge nanocrystals in the sandwiched structure annealed for a longer duration. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. Under optimized annealing conditions, an enhancement of the charge storage capability of nanocrystals was observed in agreement with the optical emission characteristics.

High-quality single-crystal ZnO nanowire arrays with diameter ranging from 30 to 110 nm were synthesized using a two-step process: (1) synthesis of ZnO thin film by sol–gel technique, which was used as seed layer, and (2) oriented ZnO nanowire arrays were grown on ZnO seed layer using a hydrothermal reaction process at a low temperature of 90 °C. Experimental results reveal an ultrahigh sensitivity of ∼98% to 100 ppm of H2 gas and 93% to 200 ppm of CO gas, an ultrafast recovery of 1 to 2 ms to CO gas with high repeatability. The current transients demonstrate the reversible type sensing to reducing gas (H2 or CO) detection using as-grown ZnO nanowire arrays sensor. The hydrothermally grown ZnO nanowire-array-based gas sensors may have potential application in industry without much modification.

The effect of carbon contamination on the electrical properties of metal-insulator-metal (MIM) capacitor using HfO2 dielectric has been reported. The HfO2 film with lower carbon contamination shows an overall high performance, such as a higher capacitance density of 5.21 fF/μm2, a lower leakage current of 1.3×10−7 A/cm2 at 1 V, lower-voltage coefficients of capacitance, and better frequency and temperature dispersion properties compared with the capacitor of theHfO2 film with higher carbon contamination. The calculated ac barrier heights by electrode polarization model from capacitance-voltage (C-V) characteristics are 0.58 eV for the HfO2 film with high carbon contamination and 0.95 eV for the HfO2 film with negligible carbon contamination. The dc barrier heights extracted from current-voltage (I-V) characteristics are 0.26 eV for the HfO2 film with high carbon contamination and 1.1 eV for the HfO2 film with negligible carbon contamination. All of these experimental results exhibit that the increase in defect density in HfO2 films generated from carbon impurities results in the degradation of barrier heights and poor performance of the MIM capacitor. It is important to point out that, during the fabrication process of the MIM capacitor, the carbon contamination must be minimized.