Shinichi Yoneda

An 8 Mb Multi-Layered Cross-Point ReRAM Macro With 443 MB/s Write Throughput

Nonvolatile memories with fast write operation at low voltage are required as storage devices to exceed flash memory performance. We develop an 8Mb multi-layered cross-point ReRAM macro with 443MB/S write throughput (64b parallel write per 17.2ns cycle), which is almost twice as fast as existing methods, using the fast-switching performance of TaOχ ReRAM and the following three techniques to reduce the sneak current in bipolar type cross-point cell array structure in an 0.18μm process. First, memory cell and array technologies reduce the sneak current with a newly developed bidirectional diode as a memory cell select element for the first time. Second, we use a hierarchical bitline (BL) structure for multi-layered cross-point memory with fast and stable current control. Third, we implement a multi-bit write architecture that realizes fast write operation and suppresses sneak current. This work is applicable to both high-density stand-alone and embedded memory with more stacked memory arrays and/or scaling memory cells.

Distribution projecting the reliability for 40 nm ReRAM and beyond based on stochastic differential equation

A physical analytic formula based on Stochastic Differential Equation was successfully developed to describe intrinsic ReRAM variation. The formula was proved useful for projecting scaled ReRAM memory window and resistance distribution after long-term retention, verified by testing 40 nm 2-Mbit ReRAM. The formula also centered on practical and quantitative filament characterization.

True random number generator using current difference based on a fractional stochastic model in 40-nm embedded ReRAM

We have successfully developed a robust ReRAM true random number generator, using current difference, that does not require extra chip area. True random numbers are guaranteed by the current difference in the 1/fβ noise generated by Brownian motion, as tested using a fractional SDE model and verified using 1/fβ noise distribution. A highly reliable 40-nm ReRAM true random number generator circuit was designed and passed NIST SP800-22 randomness tests across all combinations of voltage (VDD ± 0.1 V) and temperature (−40 to 125 °C). The random number throughput achieves 32 Mbps with a low power consumption of 0.04 nJ/bit.