To develop computer memories that can store more data than dynamic random access memory (DRAM), scientists are developing a form of memory chip called resistive random access memory (RRAM). Common types of memory such as DRAM and Flash use electrical charges to store data, but RRAM uses resistance to store each bit of information. The resistance is changed using voltage and, also being a non-volatile memory type, the data remain intact even when no energy is being applied. Each component involved in switching is located in between two electrodes and the features of the memory chip are sub-microscopic.
Very small increments of power are needed to store data on RRAM. While it generally includes a metal oxide layer and a capping layer, there are different resistive memory types that integrate certain kinds of materials. The kind of material can make a difference in how long the access time to information is, how well data are retained, and how long the memory lasts without failure. How much power that is used during operation can also be influenced by the material type for the layers.
One kind of RRAM uses titanium oxide which is an insulator. One side of it is mixed with oxygen molecules that can move to the other side if voltage is turned on across the barrier. Conduction can begin once with switch state of the memory is turned on. When the oxygen molecules return to the other side then the memory is returned to the off state. It takes fractions of a second for the on and off cycles to take place.
Another type of resistive memory lines up titanium oxide into horizontal microscopic strips between conducting wires. Most kinds of memory arrange similar components into a vertical arrangement. The resistance could be controlled across each individual strip, and the ability to alter the resistance in varying degrees could create a learning-like capability for memory systems. Electronics companies continue to work toward developing concepts for how the memory will work.
Phase-change memory is another kind that is being developed along with RRAM. Also called conductive bridging random access memory (CBRAM), it uses a great deal of heat to change material properties for resistance states to be altered. Several electronics manufacturers are focusing on RRAM as a viable replacement to memory such as DRAM that is about as small as possible to operate efficiently.