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 capacitor against the insulated substrate. The charge accumulates on this capacitor and may cause adverse effects, for example, opening of parasitic transistors in the structure and causing off-state leakages, resulting in higher current consumption and in case of DRAM in loss of information from the memory cells. It also causes the history effect, the dependence of the threshold voltage of the transistor on its previous states. In analog devices, the floating body effect is known as the kink effect.
One countermeasure to floating body effect involves use of fully depleted devices. The insulator layer in FD devices is significantly thinner than the channel depletion width. The charge and thus also the body potential of the transistors is therefore fixed. However, the short-channel effect is worsened in the FD devices, the body may still charge up if both source and drain are high, and the architecture is unsuitable for some analog devices that require contact with the body. Hybrid trench isolation is another approach.
While floating body effect presents a problem in SOI DRAM chips, it is exploited as the underlying principle for ZRAM and TTRAM technologies. For this reason, the effect is sometimes called the Cinderella effect in the context of these technologies, because it transforms a disadvantage into an advantage.
Famous quotes containing the words floating, body and/or effect:
“We sank a foot deep in water and mud at every step, and sometimes up to our knees, and the trail was almost obliterated, being no more than that a musquash leaves in similar places, where he parts the floating sedge. In fact, it probably was a musquash trail in some places.”
—Henry David Thoreau (18171862)
“The elephant, not only the largest but the most intelligent of animals, provides us with an excellent example. It is faithful and tenderly loving to the female of its choice, mating only every third year and then for no more than five days, and so secretly as never to be seen, until, on the sixth day, it appears and goes at once to wash its whole body in the river, unwilling to return to the herd until thus purified. Such good and modest habits are an example to husband and wife.”
—St. Francis De Sales (15671622)
“The attention of those who frequent the camp-meetings at Eastham is said to be divided between the preaching of the Methodists and the preaching of the billows on the back side of the Cape, for they all stream over here in the course of their stay. I trust that in this case the loudest voice carries it. With what effect may we suppose the ocean to say, My hearers! to the multitude on the bank. On that side some John N. Maffit; on this, the Reverend Poluphloisboios Thalassa.”
—Henry David Thoreau (18171862)