Nonvolatile memories are memories that retain their contents even when unpowered. Nonvolatile memories have a variety of uses, from storage for portable devices to rewriteable memories in embedded systems. Several types of nonvolatile memories are commonly available, including electronically erasable programmable read only memory (EEPROM)-type memories such as flash memory. These memories can be slow and are therefore of limited utility as the throughput requirements of devices using nonvolatile memories increase.
Resistive random access memory (ReRAM) is an emerging memory type that is nonvolatile but potentially fast enough to replace both memories that are currently nonvolatile (e.g. flash memories), and random access memories (e.g. dynamic RAM) that currently use volatile memory technologies. ReRAM is a memory element that changes resistance when a voltage is applied across the element. One voltage (e.g. a “set” voltage Vset) is used to switch to a low resistance state, while another voltage (e.g. a “reset” voltage Vreset) is used to switch to a high resistance state. Another voltage can be applied to determine the resistance of the memory element, thereby reading the contents of the memory element.
In addition to set and reset voltages, various other operating parameters (e.g. on and off current ratios, forming voltages, etc.) of a ReRAM memory element can affect the performance of the memory element. For example, it may be desirable to use a ReRAM memory element that has low set, reset, and forming voltages, while having a high on and off current ratio. Thus, what is needed is a ReRAM memory element that has improved control over critical operating parameters.