When he first joined as a staff engineer at IBM Research, studying new devices and circuits for logic and memory applications, Bob Dennard often joked that he planned to spend "a couple of years at most" learning the ropes. Fifty years later, IBM is celebrating one of its most honored inventors.
Bob made a unique contribution to computer technology with his invention of the one-transistor dynamic random-access memory (DRAM) cell -- now the worldwide standard for low-cost digital memory. DRAM is an array of memory cells integrated on a silicon chip in which each cell consists of a metal-oxide-semiconductor (MOS) transistor and a MOS capacitor.
How DRAM works
Information is stored as a charge on the capacitor and the transistor is used to control reading and writing. This simple DRAM arrangement required less power and cost much less than the previous magnetic memory. Moreover, it was much simpler and allowed higher cell density than the other semiconductor memory elements then being developed. The patent was granted in 1968 and the one-transistor memory cell first appeared in products in the 1970's. Today all computer component and systems manufacturers worldwide use this type of memory.
DRAM is Bob's most prominent contribution. DRAM technology leads the semiconductor industry in volume, with revenues of about $30 billion per year.
Bob himself is well known in his field for his contributions to miniaturization of semiconductor devices and integrated circuits used in all computers. In the early l970's, Bob and coworkers at IBM Research developed a concept of MOS transistor and circuit scaling that provides for systematic reduction of MOS integrated circuit dimensions and predicts the benefits of such reduction in improved circuit performance, lower power and greater density.
Industry debt to DRAM
DRAM and the MOS integrated-circuit scaling concept have been among the most influential and visible developments in microelectronics. The explosive growth of the semiconductor industry in the past three decades has been propelled by the growth in memory chip production, through increased density and reduced cost, as well as by the increased performance of microprocessors made possible by scaling.
These developments have in turn made increased computer power and new communications tools broadly available. The consequences have been profound for human well-being and for the economic strength of the world.
In 1988, Bob was awarded the National Medal of Technology from President Ronald Reagan. He was also inducted into the National Inventors Hall of Fame.
An honored IBM Fellow since 1979, Bob continues working at the IBM Thomas J. Watson Research Center in Yorktown Heights, NY. He shows no signs of slowing down any time soon.
A version of this article by Philip Bender originally appeared on the IBM intranet.
Last updated on August 22, 2008