A new method to approximate the receive minimum distance is presented. In the proposed approximation, the geometric mean of the singular values of the channel matrix is used instead of the conventional minimum singular value. Numerical experiments show that the proposed approximation has less mean squared error than the minimum singular value bound and outperforms the minimum singular value bound in terms of bit error rate when they are applied to the antenna subgroup selection system.

Effects of conductive defects on unipolar resistive random access memory (RRAM) are investigated in order to reduce the operation current for high density and low power RRAM applications. It is clarified that forming voltage decreases with increasing charged conductive defects which are a source of conductive filament (CF) path and with decreasing cell thickness. Random circuit breaker (RCB) network simulation model which is a dynamic percolation simulation model is used to elucidate these effects. From this simulation results, the optimal cell thickness with sufficient conductive defect shows improved resistive switching characteristics such as low forming voltage, small set voltage distribution and low reset current. From the deep understanding of relationship between conductive defect in various cell thickness and other resistive switching parameters, RRAM with low forming voltage and reset current can be obtained and it will be one of the most promising next generation nonvolatile memories.

In this work, resistive switching random-access memory (RRAM) devices having a structure of metal/Si$_{3}$N$_{4}$/Si with different top electrode metals were fabricated to investigate the changes in switching and conduction mechanisms depending on electrode metals. It is shown that the metal workfunction is not strongly related with either high-resistance state (HRS) and forming voltage. Top electrodes (TEs) of Al, Cu, and Ni show both bipolar and unipolar switching characteristics. The changes of resistances in these devices can be explained by the different defect arrangements in the switching layer (SL). Among the devices with different TE metals, one with Ag electrode does not show unipolar switching unlike the others. The conducting filaments of Ag-electrode device in the low-resistance state (LRS) demonstrated metallic behaviors in the temperature-controlled experiments, which supports that Ag substantially participates in the conduction as a filament source. Moreover, the difference in switching speed is identified depending on TE metals.