Low-temperature characteristics of magnesium fluoride based bipolar RRAM devices

Effect of long chain fatty acids on the memory switching behavior of tetraindolyl derivatives

Non-volatile memory devices using organic materials have attracted much attention due to their excellent scalability, fast switching speed, low power consumption, low cost etc. Here, we report both volatile as well as non-volatile resistive switching behavior of p-di[3,3'-bis(2-methylindolyl)methane]benzene (Indole2) and its mixture with stearic acid (SA). Previously, we have reported the bipolar resistive switching (BRS) behavior using 1,4-bis(di(1H-indol-3-yl)methyl)benzene (Indole1) molecules under ambient conditions [Langmuir 37 (2021) 4449-4459] and complementary resistive switching (CRS) behavior when the device was exposed to 353 K or higher temperature [Langmuir 38 (2022) 9229-9238]. However, the present study revealed that when the H of -NH group of Indole1 is replaced by -CH3, the resultant Indole2 molecule-based device showed volatile threshold switching behaviour. On the other hand, when Indole2 is mixed with SA at a particular mole fraction, dynamic evolution of an Au/Indole2-SA/ITO device from volatile to non-volatile switching occurred with very good device stability (>285 days), memory window (6.69 × 102), endurance (210 times), data retention (6.8 × 104 s) and device yield of the order of 78.5%. Trap controlled SCLC as well as electric field driven conduction was the key behind the observed switching behaviour of the devices. In the active layer, trap centers due to the SA network may be responsible for non-volatile characteristics of the device. Observed non-volatile switching may be a potential candidate for write once read many (WORM) memory applications in future.

Effects of Top and Bottom Electrodes Materials and Operating Ambiance on the Characteristics of MgFx Based Bipolar RRAMs

The effects of electrode materials (top and bottom) and the operating ambiances (open-air and vacuum) on the MgF_x-based resistive random-access memory (RRAM) devices are studied. Experiment results show that the device's performance and stability depend on the difference between the top and bottom electrodes' work functions. Devices are robust in both environments if the work function difference between the bottom and top electrodes is greater than or equal to 0.70 eV. The operating environment-independent device performance depends on the surface roughness of the bottom electrode materials. Reducing the bottom electrodes' surface roughness will reduce moisture absorption, minimizing the impact of the operating environment. Ti/MgF_x/p⁺-Si memory devices with the minimum surface roughness of the p⁺-Si bottom electrode show operating environment-independent electroforming-free stable resistive switching properties. The stable memory devices show promising data retentions of >10⁴ s in both environments with DC endurance properties of more than 100 cycles.

Vacuum and Low-Temperature Characteristics of Silicon Oxynitride-Based Bipolar RRAM

This study investigates the switching characteristics of the silicon oxynitride (SiOxNy)-based bipolar resistive random-access memory (RRAM) devices at different operating ambiances at temperatures ranging from 300 K to 77 K. The operating ambiances (open air or vacuum) and temperature affect the device’s performance. The electroforming-free multilevel bipolar Au/Ni/SiOxNy/p+-Si RRAM device (in open-air) becomes bilevel in a vacuum with an on/off ratio >104 and promising data retention properties. The device becomes more resistive with cryogenic temperatures. The experimental results indicate that the presence and absence of moisture (hydrogen and hydroxyl groups) in open air and vacuum, respectively, alter the elemental composition of the amorphous SiOxNy active layer and Ni/SiOxNy interface region. Consequently, this affects the overall device performance. Filament-type resistive switching and trap-controlled space charge limited conduction (SCLC) mechanisms in the bulk SiOxNy layer are confirmed.