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Leah wanted to know why the industry had stopped simply thinning the glass under the gate . For years the move had been the same : make the silicon dioxide thinner , so a shorter channel would still turn off when the gate said so . She had reached the claim that this move had run out , and she wanted the material that replaced it . Silicon dioxide stopped cooperating when the layer was only a few atoms thick . Electrons could then cross it even when the transistor was meant to be off . A thicker oxide would have blocked that leak , and it would also have loosened the gate's hold on the channel . The way through was a different oxide , a hafnium - based one , with a higher dielectric constant than silicon dioxide . Raise that constant , and a physically thicker film can still couple the gate to the channel as a thin film would . The new oxide did not sit well under the old polysilicon gate , so a metal gate replaced it . That pair is what Intel put into high - volume logic at the 45 nm generation , which the company described as the first time a high - volume logic process had used it . Intel formed the hafnium - based film by atomic layer deposition : each cycle adds a thin skin of material and then stops , so the thickness is counted in layers rather than poured . It was not a thinner copy of the old stack . It was a different stack that imitated a thin one . The shape of the channel had to change for a related reason . A flat transistor leaves the gate on one face of the silicon , so a very short channel can still leak past the gate . A FinFET stands a thin fin of silicon up and wraps the gate over three sides , which makes that sneak path harder . When three sides are no longer enough , the structure that follows is a nanosheet : the gate surrounds the channel on every side . The materials demand moves with the shape . The sheet has to be even to a few atoms , or the surround is only complete on the drawing . Leah stopped on that pair of changes . The oxide could not be thinned forever . The hafnium - based film let the gate keep its hold without a layer that leaked , and once a flat channel was no longer enough , the gate had to wrap the silicon instead of sitting on it .
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