Z-RAM is a tradename of a now-obsolete

dynamic random-access memory Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxi ...

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 The floating body effect is the effect of dependence of the body potential of a transistor realized by the silicon on insulator (SOI) technology on the history of its biasing and the carrier recombination processes. The transistor's body forms a ...

, an artifact of the

silicon on insulator In semiconductor manufacturing, silicon on insulator (SOI) technology is fabrication of silicon semiconductor devices in a layered silicon–insulator–silicon substrate, to reduce parasitic capacitance within the device, thereby improving perfo ...

(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 Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized a ...

to appear between the bottom of the tub and the underlying

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

. 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

DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxi ...

s), another connotation of the name "Z-RAM" is that it extends in the negative z-direction. Theoretically, a reduced cell size would have allowed denser storage, which in turn could (when used with large blocks) have improved access times by reducing the physical distance that data would have to travel to exit a block. For a large

cache memory In computing, a cache ( ) is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewher ...

(as typically found in a high-performance microprocessor), Z-RAM would then have been potentially as fast as the SRAM used for conventional on-processor (L1/L2) caches, but with lower surface area (and thus cost). However, with advances in manufacturing techniques for conventional SRAM (most importantly, the transition to 32nm fabrication node), Z-RAM lost its size advantage. Although

AMD Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufact ...

licensed the second generation Z-RAM in 2006, the processor manufacturer abandoned its Z-RAM plans in January 2010. Similarly, DRAM producer

Hynix SK hynix Inc. is a South Korean supplier of dynamic random-access memory (DRAM) chips and flash memory chips. Hynix is the world's second-largest memory chipmaker (after Samsung Electronics) and the world's third-largest semiconductor company. ...

had also licensed Z-RAM for use in DRAM chips in 2007, and Innovative Silicon announced it was jointly developing a non-SOI version of Z-RAM that could be manufactured on lower cost bulk CMOS technology in March 2010, but Innovative Silicon closed on June 29, 2010. Its patent portfolio was acquired by

Micron Technology Micron Technology, Inc. is an American producer of computer memory and computer data storage including dynamic random-access memory, flash memory, and USB flash drives. It is headquartered in Boise, Idaho. Its consumer products, including ...

in December 2010.

References

Types of RAM {{Primary storage technologies