Computer World
It is the declared objective of modern chip
technology to squeeze more and more strip conductors and transistors onto every computer
chip. Packing everything closer together speeds up the processes in the strip conductors,
which are now shorter; the transistors (the bits representing the 0 or 1 in the computer,
depending on the switching status) can also switch more quickly. Everything has its
limits, however. Today, a normal PC chip measuring just a few square centimetres contains
approximately 40 million transistors, each 130 nanometres wide – the equivalent of
about 2 thousandths of the thickness of a human hair. The more closely the bits and strip
conductors are packed together, however, the more difficult the chips are to make and
operate. With so many electrons racing about, they become extremely hot. Moreover, we are
beginning to enter the quantum universe. When things get smaller than 100 nanometres (100
billionths of a metre), the world is governed by the laws of quantum mechanics. A normal
electron no longer appears as something compact, but starts behaving like a wave. It can
only be tracked down by certain probabilities, and it can drift off into neighbouring
strip conductors, which doesn’t exactly enhance the chip’s reliability. Many
chip manufacturers are using all the tricks they can find to avoid this quantum world. The
chips are flat, stretched wafers. As a result, the strip conductors to the switching
elements or other connected chips are long – and this slows the computer down. One
suggestion for avoiding this dilemma is to simply stack several chips on top of each
other. The connections are then vertical, and this considerably shortens the signal paths
and speeds up the computer. Shorter strip conductors also generate less waste heat, and
since the electrical resistance also depends on distance, this would overcome a further
difficulty in chip technology. The vertical connections between the stacked chips can be
made via strip conductors fitted to the sides; there have also been attempts to attach
them, after stacking, by means of electrically conductive shafts distributed over the
chip. A further trick makes it possible to raise the switching rate of the transistors,
the bits. If they are etched out on the silicon substrate, they are surrounded by areas
that absorb electrons. This reduces the switching speed of the transistors, which are
constantly being switched between 0 and 1 when in operation. These areas are therefore
bombarded with oxygen ions; this converts them into silicon oxide, which serves as an
insulator. This coating in their environment improves the transistors’ switching rate
by 30 percent. Other gases such as hydrogen are also used for such a treatment to achieve
a strict electrical separation of the transistors. The computer chips can be speeded up
even more if the silicon substrate is subjected to mechanical tension, e.g. by connecting
it with another material. This stretches the silicon crystal lattice by a couple of
percent. This change in the lattice spacing makes the electrons more mobile and speeds up
the computer. People’s visions of the computers of the future go much further than
this, however. Like a computer, our brain also works with electrical voltages. They pass
on and process pieces of information. Up to now, these two worlds have been totally
separate from each other. But one initial barrier has now been overcome. A team of
researchers has managed to make a direct connection between nerve cells and the
transistors on a computer chip. To do this, nerve cells from a snail are grown directly on
a chip. These snail neurons link up, making it possible to read out signals from the chip
to the neuron and conversely. Perhaps this is the first step towards achieving a direct
interconnection between people and computers sometime in the future. However, operational
problems also crop up in conventional computers whenever two different systems are linked
together. For example, the electrical signals of the computer chips have to be converted
into optical signals, into light, in order to travel through optical fibres, and vice
versa. Work on optimizing computer chips is ongoing in many German institutes. This is the
kind of research that can move quickly from intensive pure research to technical
applications – an area that the researchers in Germany must keep a watch on more
intensively in the future.
The German physicist Herbert Kroemer was
awarded the Nobel Prize for Physics in 2000; he had improved the optoelectronic interface
by developing certain semiconductor elements.
(Courtesy: Deutschland Magazine Embassy
of Germany) |
