Sometime in the coming decades, chipmakers will no longer be able to make silicon chips faster by packing smaller transistors onto a chip. That’s because silicon transistors will simply be too leaky and expensive to make any smaller.
People working on materials that could succeed silicon have to overcome many challenges. Now researchers at the University of California, Berkeley, have found a way past one such hurdle: they’ve developed a reliable way to make fast, low-power, nanoscopic transistors out of a compound semiconductor material. Their method is simpler, and promises to be less expensive, than existing ones.
Compound semiconductors have better electrical properties than silicon, which means that transistors made from them require less power to operate at faster speeds. These materials are already in some expensive niche applications such as military telecommunications equipment, which gives them a leg up over more exotic potential silicon replacements like graphene and carbon nanotubes.
But wafers of compound semiconductor materials are also very fragile and expensive, “which is only okay where cost doesn’t matter,” says Ali Javey, associate professor of electrical engineering and computer sciences at the University of California, Berkeley. Compound semiconductors are on the market in expensive communications chips for the military, for example.
Researchers believe they can overcome this fragility and expense by growing compound-semiconductor transistors on top of a supportive silicon wafer—a trick that should be compatible with existing manufacturing infrastructure.
However, compound semiconductors cannot be grown on silicon—there’s a mismatch between the crystalline structures of the two materials that makes this difficult to do well. The Berkeley group has now shown that transistors made from compound semiconductors can be grown on another surface and then transferred to a silicon wafer. “That’s a plausible path for dealing with the fact that compound semiconductors are difficult to grow,” says Jesús del Alamo, professor of electrical engineering and computer science at MIT who was not involved with Javey’s work.