write current is sufficiently large for speed and retention, the probability of MTJ breakdown needs to be considered. If the read current/write current ratio is not small enough, read disturb becomes more likely, i.e., a read error occurs during one of the many switching cycles. The read disturb error rate is given by , where τ is the relaxation time (1 ns) and Icrit is the critical write current. Higher endurance requires a sufficiently low . However, a lower Iread also reduces read speed. Endurance is mainly limited by the possible breakdown of the thin MgO layer. Overall MRAM has similar performance to SRAM, enabled by the use of sufficient write current. However, this dependence on write current also makes it a challenge to compete with the higher density comparable to mainstream DRAM and Flash. Nevertheless, some opportunities for MRAM exist where density need not be maximized. From a fundamental physics point of view, the spin-transfer torque approach to MRAM is bound to a "rectangle of death" formed by retention, endurance, speed, and power requirements, as covered above. While the power-speed tradeoff is universal for electronic devices, the endurance-retention tradeoff at high current and the degradation of both at low Δ is problematic. Endurance is largely limited to 108 cycles. Alternatives to MRAM Flash and EEPROM's limited write-cycles are a serious problem for any real RAM-like role. In addition, the high power needed to write the cells is a problem in low-power nodes, where non-volatile RAM is often used. The power also needs time to be "built up" in a device known as a charge pump, which makes writing dramatically slower than reading, often as low as 1/1000 as fast. While MRAM was certainly designed to address some of these issues, a number of other new memory devices are in production or have been proposed to address these shortcomings. To date, the only similar system to enter widespread production is ferroelectric RAM, or F-RAM (sometimes referred to as FeRAM). Also seeing renewed interest are silicon-oxide-nitride-oxide-silicon (SONOS) memory and ReRAM. 3D XPoint has also been in development, but is known to have a higher power budget than DRAM. History 1955 — Magnetic-core memory had the same reading writing principle as MRAM 1984 — Arthur V. Pohm and James M. Daughton, while working for Honeywell, developed the first magnetoresistance memory devices. 1988 — European scientists (Albert Fert and Peter Grünberg) discovered the