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DIGITAL memory. We want more of it. Memory in your cellphone that will store every message you have ever received, or that will keep computer data safe if the plug is pulled.

For now, that remains a pipe dream. But advances in creating next-generation digital memories are coming thick and fast. This week, Philips Research Laboratories in Eindhoven, the Netherlands, announced a new material for a technology known as a phase-change random-access memory (RAM) that has brought the dream a crucial step closer.

For now, the main standard for electronic non-volatile memory 鈥� chips that keep data even with the current switched off 鈥� is the kind called flash memory. But it comes with problems. Because it is difficult to make flash memory cells small, the amount of data that can be packed onto a single chip is limited. Flash is also too slow and expensive to use in PCs.

Couple this to the insatiable demand for extra storage in portable gadgets such as mobile phones, digital cameras and USB memory sticks, and it is not hard to see why 鈥渢he whole world is working on replacing flash memories鈥�, as Rob Wolters from Philips puts it. The race is on to find alternatives: ideally a cheap memory that, like flash, stores data without needing power.

Some approaches use memory based on arrays of magnetic switches (MRAM). But Samsung, Intel and STMicroelectronics are, like Philips, interested in phase-change RAM, which uses a data-storage technique inspired by optical discs such as DVDs.

In rewritable CDs and DVDs, a laser beam is used to melt bits of the coating materials, changing them reversibly between two states. One state is ordered and crystalline, the other is disordered and amorphous. These two phases represent data encoded as binary 1s and 0s, which can be read out by a weak laser because the two states reflect different amounts of light.

The patches of material that store a binary bit can be made incredibly small, so in principle they need only contain a few tens of atoms, Wolters says. This means phase-change memories could allow super-dense storage.

There has been some success in making experimental phase-change RAM from standard silicon chips. In June 2004 Samsung announced a 64-megabit prototype RAM. These memories use electrical pulses rather than a laser to melt the bits, and read the data by comparing the electrical resistance of the two phases.

But problems remain. 鈥淥ne of the fundamental deficiencies of phase-change RAM is that it requires a large current,鈥� says Peter Haring Bolivar from the University of Siegen in Germany. He has proposed changing the shape of the memory cell to cut the current required to melt it. Philips has taken that idea and has designed a new material for building phase-change RAM. 鈥淲e have found a material that switches with electric field,鈥� Wolters says.

Philips is proposing to use antimony telluride, doped with a secret mix of elements, to replace the standard gallium antimony telluride used in PC RAM. The phase change is triggered when the electric field crosses a certain threshold, and an avalanche of electrons causes the material to break down electronically. The process is efficient even for small memory cells (Nature Materials, DOI: 10.1038/nmat1350).

Wolters admits that it鈥檚 too early to tell whether this new material will make phase-change RAM the winner in the race to replace flash memory. But it looks promising. At stake is a gigantic prize: a universal digital memory that could replace all existing technologies. While the market for flash was a sizeable $15.5 billion in 2004, a digital memory that could do everything would be worth almost $50 billion a year.