zero-capacitor random-access memory

Z-RAM is a tradename of a now-obsolete dynamic random-access memory technology that did not require a capacitor to maintain its state. Z-RAM was developed between 2002 and 2010 by a now-defunct company named Innovative Silicon.

Z-RAM relies on the floating body effect, an artifact of the silicon on insulator (SOI) process which places transistors in isolated tubs (the transistor body voltages "float" with respect to the wafer substrate beneath the tubs). The floating body effect causes a variable capacitance to appear between the bottom of the tub and the underlying substrate. The floating body effect is usually a parasitic effect that bedevils circuit designs, but also allows a DRAM-like cell to be built without adding a separate capacitor, the floating body effect then taking the place of the conventional capacitor. Because the capacitor is located under the transistor (instead of adjacent to, or above the transistor as in conventional DRAMs), another connotation of the name "Z-RAM" is that it extends in the negative z-direction.