Multilevel resistive random access memory achieved by MoO3/Hf/MoO3stack and its application in tunable high-pass filter.

In this work, the multilevel resistive random access memories (RRAMs) have been achieved by using the structure of Pt/MoO3/Hf/MoO3/Pt with four stable resistance states. The devices show good retention property of each state (>104s) and large memory window (>104). The simulation and experimental study reveal that the resistive switching mechanism is ascribed to combination of the conductive filament in the stack of MoO3/Hf next to the top electrode and redox reaction at the interface of Hf/MoO3next to bottom electrode. The fitting results of current-voltage characteristics under low sweep voltage indicate that the conduction of HRSs is dominated by the Poole-Frenkel emission and that of LRS is governed by the Ohmic conduction. Based on the RRAM, the tunable high-pass filter (HPF) with configurable filtering characteristics has been realized. The gain-frequency characteristics of the programmable HPF show that the filter has high resolution and wide programming range, demonstrating the viability of the multilevel RRAMs for future spiking neural network and shrinking the programmable filters with low power consumption.

Gas Sensor Based on Surface Enhanced Raman Scattering.

In order to address problems of safety and identification in gas detection, an optical detection method based on surface enhanced Raman scattering (SERS) was studied to detect ethanol vapor. A SERS device of silver nanoparticles modified polyvinylpyrrolidone (PVP) was realized by freeze-drying method. This SERS device was placed in a micro transparent cavity in order to inject ethanol vapor of 4% and obtain Raman signals by confocal Raman spectrometer. We compared different types of SERS devices and found that the modification of polyvinylpyrrolidone improves adsorption of ethanol molecules on surfaces of silver nanoparticle, and finally we provide the mechanism by theory and experiment. Finite Difference Time Domain(FDTD) simulation shows that single layer close-packed Ag nanoparticles have strong local electric field in a wide spectral range. In this study, we provide a case for safety and fingerprint recognition of ethanol vapor at room temperature and atmospheric pressure.