ONE consequence of the growth of microelectronics has been an exploration of the periodic table reminiscent of European navigators' search for the spice islands half a millennium ago. Then, as now, the objective was material of great rarity and value, which was needed in only small quantities but which did jobs that nothing else could manage. In the case of nutmeg, cloves and mace, the job was to enhance the taste of food and demonstrate wealth and sophistication. They were so valuable that wars were fought to control the supply of some. In the case of indium, gallium and tantalum it is their unique electrical properties that are of interest. Indium-tin oxide, for example, is both transparent and electrically conductive. Without it, liquid-crystal display screens would be much harder to make. Meanwhile tantalum (used as an insulator in mobile-phone chips) once became so valuable that it, too, helped drive a war—the civil war in eastern Congo, where its ore has been dusted over the countryside like icing sugar by ancient volcanic eruptions.

The latest element to be dragged out of obscurity by the chemist-descendants of Prince Henry the Navigator is hafnium. This metal (or, rather, its oxide) is the magic ingredient that computer-chip designers hope will enable them to carry on shrinking the transistors on their products in obedience to Gordon Moore's famous law that the number of such transistors on a given area of chip will double every two years or so. Indeed, it is the most significant change of recipe since Dr Moore and his colleagues invented the microprocessor back in the 1960s. Intel, the firm that Dr Moore helped to found on the back of the invention, will introduce its new hafnium-based chip, called Penryn, on November 12th. Its competitors are expected to follow suit as soon as they can.

At bottom, transistors are electronic valves that use a small voltage at a place called a gate to regulate the flow of current through the rest of the device. This switching of current is what produces the zeros and ones of binary arithmetic, and is the basic process of computing. Gates, which are made of silicon, must be electrically isolated. Until now, that has been done using silicon dioxide—in other words, quartz. The insulating layer is made by exposing the silicon of the gates to pure oxygen, which is a well-honed manufacturing process.

As transistors have got smaller, though, the silicon-dioxide layer has been made thinner and thinner. It is now a mere five atoms thick, which is already too thin to be a perfect insulator. As a result, modern transistors have to accommodate some current leakage. This has been regarded as a price worth paying to avoid having to reorganise the manufacturing process to accommodate new materials. Any thinner, however, and the insulation would break down altogether.

Researchers at Intel and elsewhere have seen this problem coming for some time. In the late 1990s they started to look for a material that could serve as silicon dioxide's replacement. They rejected oxides of aluminium (which is abundant) and lanthanum (which isn't) and eventually lighted upon hafnium. Hafnium oxide is a very good insulator indeed. Unfortunately, using it requires completely rebuilding the gate, by including a metal connection between the insulator and the underlying silicon. (Exactly which metal, all of the companies involved are being cagey about.) This is a lot harder than just baking the chip in oxygen at the appropriate point in its manufacture, which is why engineers have held out until the last possible moment before making the change.

The new combination of materials is, however, just what Dr Moore ordered. Penryn chips have twice as many transistors as their predecessors (about a billion). Just as important, they waste only one-fifth the amount of power in the gate. With luck, though, the quantities needed for microelectronics will not be worth fighting over.



