Quantum mechanics may explain how microelectronic devices operate but it has little to do with the practical applications. However, with this article STMicroelectronics delves into the realms of theoretical physics - an opportunity that has arisen because it has been chosen to supply critical components for one of the world's most ambitious scientific collaborations: the Large Hadron Collider (LHC) being constructed by CERN, the European organisation for nuclear research.
ST will supply specially designed silicon sensors that will detect nuclear particles generated in the LHC experiments, including experiments designed to detect the particle known as the 'Higgs Boson' whose existence, if verified, has crucial implications for theoretical physics.
Unfortunately, the particle has so far eluded all attempts to detect its existence. If it does exist, it will only be seen by making other particles collide at very high energies and examining the results of the collisions. CERN's Large Electron-Positron collider has now been shut down while CERN builds its Large Hadron Collider (LHC), which will be the world's most powerful cyclotron scheduled for operation in 2005.
One of the most important experiments that will be performed when the LHC starts operation is called the Compact Muon Solenoid (CMS) experiment, designed to provide, among other things, a definitive answer to the question that has tantalised nuclear physicists for more than 30 years: does the Higgs Boson exist?
ST has been chosen to supply the critical sensors that will help answer this question. ST will manufacture some 20 000 sensors, of eight different types, which will be used to measure the properties of sub-atomic particles created by the collision of other particles that have been accelerated to achieve very high collision energies. Because the sensors have an area around 100 times larger than conventional silicon chips, their manufacture requires the most stringent precautions to eliminate impurities and defects in the silicon crystal.
The sensors used are so large that there is only one sensor on each wafer. Manufacturing quality is therefore critical. These sensors have an area around 100 times larger than conventional silicon chips. They will be manufactured at ST's M3 fab in Catania, Italy, using a technology similar in complexity to that used to produce power MOSFET transistors. However, because each sensor measures around 9 x 9 cm, it is only possible to fit a single sensor on each wafer that passes through the manufacturing cycle, which involves eight basic stages of processing.
Physicists have calculated that the Higgs Boson, if it exists, will be produced by only one in every thousand billion collisions between high-energy protons. This means that only the highest performance sensors could detect it. "Semiconductor manufacturers normally make hundreds of chips simultaneously on each wafer and expect a few of them to be defective due to normal manufacturing tolerances. We will be making just one sensor on each wafer and making sure that each one works perfectly", says Giuseppe Ferla, R&D Director of ST's Discrete and Standard Circuits Group in Catania.
Meanwhile, attention has shifted to the USA's Fermi National Acceleration Laboratory (Fermilab) in Illinois, which has a collider called the Tevatron, which is smaller than LHC will be, but bigger than LEP. Just before CERN closed down the LEP, its researchers thought they saw signs of the Higgs Boson but the evidence was inconclusive. If the Higgs Boson does exist, the energies achievable with the LHC will almost certainly find it, say scientists. In the next few years, however, US physicists will have the world's biggest collider and are engaged in a race to detect the Higgs Boson before the LHC starts operation.
"No-one knows whether Fermilab will succeed before the LHC becomes operational but, in any case, we are proud to be taking part in one of the most wide reaching collaborations in scientific history," adds Ferla.
ST is one company that is uniquely qualified to play its part in this endeavour because its close links with universities such as Florence and Pisa means it has the highly specialised and rare expertise required to work with the CERN physicists, while the excellence of its manufacturing processes means that it can meet the very demanding specifications.
For more information contact Avnet Kopp, 011 809 6100, [email protected], www.avnet.co.za
The Higgs Boson is a hypothetical particle that was proposed in the 1960s by British physicist, Peter Higgs, as a way to achieve Einstein's dream of uniting relativity and quantum mechanics into a single theory that could explain - among other things - why some sub-atomic particles have zero mass and some do not.
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