Every time we hear the word transistors we immediately, refer to silicon as building block of transistors, but the truth is different. 70 years ago two physicists, at Bell Telephone Laboratories- John Bardeen and Walter Brattain, made the first transistor with Germanium. This was the greatest invention of the 20th century. With help of Moore’s law the transistors have delivered computer far beyond anyone thought in 1950’s.
Despite germanium’s starring role in the transistor’s history, it was soon replaced by silicon. But now the germanium is up for come back. World’s leading edge chip makers are thinking about replacing silicon with germanium.
The basic idea is to replace the silicon in transistors with a material that can move current at grater rates. Building transistors with such channels could help engineers continue to make faster and more energy-efficient circuits, which would mean better computers, smartphones, and countless other gadgets for years to come.
For long time, the excitement over alternative channels revolved around the materials like gallium arsenide, which are made from the atoms that lie in the columns just to left and right of silicon in the periodic table of elements. But researchers soon discovered that those materials have some fundamental physical limitations. Plus it is likely to be too expensive and difficult to integrate with existing silicon technology. So after few years’ researchers decided to go back to germanium.
The first Complementary –metal oxide semiconductor (CMOS) circuits – made with germanium, were build on existing silicon wafers of today. Researchers have also constructed a range of different transistor architectures using the material. These include nanowire devices, which may be next in line when the present state-of-the-art transistor design, known as the FinFET, can’t be miniaturized any longer.
It turns out that putting germanium back into the mix isn’t as big a challenge as it might seem. Transistors that use a combination of silicon and germanium in the channel can reportedly be found in some recent chips, and they made an appearance in a 2015 demonstration of future chip-manufacturing technology by IBM and partners.
WHY WAS SILICON ABLE TO REPLACE GERMANIUM?
There are some good reasons why silicon dominated. For one thing, silicon is far more abundant and thus a lot cheaper. Silicon also has a wider bandgap, the energy hurdle that must be overcome in order for a transistor to carry current. The larger the bandgap, the harder it is for current to leak across the device when it’s supposed to be off, draining power. As an added benefit, silicon also has better thermal conductivity, making it easier to draw away heat so that circuits don’t overheat.
So if silicon has so many advantages why are engineers and researcher considering to replace silicon with germanium now ?????
Well the answer is simple and is called mobility. Electrons move three times faster in germanium than in silicon in room temperatures. And holes—the electron voids in a material that is treated like positive charges—move about four times as easily.
Since both electrons and holes are so mobile in germanium, that makes the material a continent candidate for constructing CMOS circuits. As we know CMOS circuits use two different kind transistors – p channel and n channel FET. P -channel FET contains excess of free moving holes. N- channel FET has excess of free electrons. The faster these electrons and holes can move, the faster the resulting circuits can be. And because less voltage must be applied to draw those charge carriers along, circuits can also consume considerably less energy.
Of course germanium is not the only high Mobil material. Materials such as indium arsenide and gallium arsenide, also boast excellent electron mobility. In fact, electrons in indium arsenide are nearly 30 times as mobile as they are in silicon. So far, so good. The problem is that this amazing property does not extend to the holes in indium arsenide, which are not much more mobile than holes in silicon. That limitation makes it almost impossible to make a high-performance pFET, and the lack of a fast pFET rules out speedy CMOS circuitry, which is not designed to tolerate a very large difference in the speed between nFETs and pFETs.
Due to all these reasons, researchers are lining towards germanium to be used in place of silicon. But nothing is final yet the research in making faster transistors is still going and is on the peak. There is an existing debate in weather to use Nano electronics with transistors or to replace the silicon. The answer to this question holds the key to future of electronics. This answer will be reveled in coming 5-7 years!! This answer will mark the new beginning of electronics.
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