With recent development of digital technology for electric equipment, requirements for nonvolatile memories have been increasing in order to store data such as images. Specifically, requirements for larger capacity of memories, reduction of power necessary for writing, higher write/read speed, longer life and others have been further increasing. At present, flash memories that achieve nonvolatility by utilizing a mechanism in which electrons are injected into a floating gate provided at the gate of a semiconductor transistor are in practical use as nonvolatile memories and are widely used as external memories for digital cameras and personal computers.
However, such flash memories have many drawbacks, e.g., high write power, long write time, short rewritable life and difficulty in increasing the capacity (device miniaturization). Therefore, to overcome these drawbacks of flash memories, new nonvolatile memories such as a semiconductor memory (FeRAM) using a ferroelectric material, a semiconductor memory (MRAM) using a TMR (tunnel MR) material, a semiconductor memory (OUM) using a phase-change material have been actively developed to date. Nevertheless, these memories also have drawbacks, e.g., difficulty in device miniaturization for the FeRAM, high write power for the MRAM and short rewritable life for the OUM. Until now, no memories satisfy all the requirements for nonvolatile solid-state memories. As a recording method to overcome the drawbacks, a technique of changing the resistance value of an oxide with a perovskite structure by utilizing a pulse voltage was invented by Houston University (U.S. Pat. No. 6,204,139). However, this technique still has great difficulties in obtaining stable operation as a memory and high mass-production yield.
USPTO Backgrounds
USPTO Backgrounds