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Conductor in the oven

With the assistance of a household microwave oven, researchers develop new materials that increase the memory of computers by as much as 250 times

EDUARDO CESARA group of researchers from the Multidisciplinary Center for the Development of Ceramic Materials (CMDMC) has announced, in São Carlos, a new process and a new formulation for chips capable of increasing 250 times the memory of computers.  The novelty is important, because it may bring great benefits to consumers and to the course of the information technology and electrical/electronic industry in the country, and who knows, abroad. In Brazil, the production of semiconductors, essential components for every kind of electronic equipment, is one of the four points of the guidelines for industrial policy in Brazil, announced by the federal government in November, and which should be confirmed now, in March.  These products are made with silicon, and they make up the famous chips and other devices that, in turn, make up integrated circuits and do the processing and keep the information in any microprocessor, be it in the bank’s ATM, in cell phones, in a car’s fuel injection system, in a TV, or in computers.

Semiconductors are therefore are poised to receive, along with software, drugs, and capital goods, government and business incentives for a new development boost. Up until now, the discussion on the production of these components in Brazil has been mainly based on importing technology, with factories being set up here. With these prospects, the news announced in São Carlos may heat up the debate about the production of semiconductors in the country.

To arrive at the new materials that may serve a new generation of computer memory, the researchers from the CMDMC, one of the ten Research, Innovation, and Diffusion Centers (Cepids) funded by FAPESP, developed a cheap and simple process of chemical deposition with a home microwave oven that has now earned them the filing of a patent.  They also built an electrode (an element that conducts an electrical charge) that may replace platinum in integrated circuits. All these conquests are already a target for the interest of a multinational company whose the name the researchers involved in the negotiation are disclosing.

Small insulators
To understand the advance with the novelties presented by the researchers, you have to go into the world of semiconductors and their components.  The first great sign that the new material in the form of forms – called thin films,-  based on lead and barium titanate (PbBaTiO3) – has good characteristics for going into a computer memory lies with its high dielectric constant.  The greater this constant, the greater the quantity of electrons that can be filed in the memory. This parameter measures how much the material allows the movement of the electrical charge through its surface to other internal layers of the components.  Actually, these materials are insulators, incapable or inefficient for conducting an electric current, the opposite of a conductor, in which the charge flows normally. Then there are the semiconductors, materials made up of such chemical elements as germanium or gallium arsenide compounds, which have an intermediate electrical conductivity, storing fewer electrons than a metal, though allowing an easier and more orderly control over these particles.  In a dielectric material, the charge is shifted to another level within the electronic devices, known generically as chips (a sandwich of a semiconducting material separated by dielectric films), in the form of discharges, also called induction, when its dielectric rigidity is overcome.

The dielectric constant of the lead and barium titanate film produced in São Carlos is 1800, over 250 times more than that of a capacitor (a device that stores an electric charge in a very small space), used in integrated circuits.  The present-day films, based on silicon oxide and on silicon nitrate, have a dielectric constant equal to seven.  In other products that created the researchers from the CMDMC, besides American and Japanese ones, the biggest dielectric constants for these materials have reached the 700 mark, with sophisticated and costly methods.  “Present-day chips with a constant of seven are capable, for example, of processing 1 gigabyte (GB) of memory, while with the material we are developing they could reach 250 GB”, announces Professor Elson Longo, the coordinator of the Electrochemistry and ceramics Interdisciplinary Laboratory (Liec), of the Chemistry Department of the Federal University of São Carlos (UFScar) and of the CMDMC, called the Ceramics Cepid, which is made up as well by the Chemistry Institute (IQ) of the São Paulo State University (Unesp) of Araraquara, by the Institute of Nuclear Energy and Research, and by the São Carlos Chemistry Institute of the University of São Paulo.

“Nowadays, in the semiconductor pads of 1 square centimeter (cm2) in area, it is possible to file 1 megabyte of information.  With the new memory, it will be possible to file 250 MB in the same space”, says Longo.  “The high dielectric density, besides meaning an advance for the memory storage of capacitors, is necessary for keeping the concentration and storage of the electrical charge within the standards required for the future generations of dynamic random access memory, or Dram for short, which carries out the storage of the data and of the software information at the moment the computer is in use, which also results in a lower consumption of electricity.”

Thus, the research that resulted in the thin films of lead and barium titanate are part of a world-wide race, which has been going on for 20 years, to overcome one of the problems of microelectronics: the size of the memory cell. This part is being reduced year by year, with the goal of increasing the number of these devices and providing computers with greater storage and data processing capacity. A path that comes from the evolutionary demand from software, increasingly varied, disseminated, and sophisticated.  Making the memory devices smaller also facilitates miniaturization and the creation of new electronic equipment, or an increase in the functions of these devices s.

Since the 1970s, there has been a permanent quest for the multiplication of memory and space inside the semiconducting devices. The most famous prediction about this progress of information technology was made by electronic engineer Gordon Moore, one of the founders of the American Intel, the main manufacturer of semiconductors. He said that the growth of the computer industry would cause an increase in the processing capacity of chips, which should double every two years. Outlined in an article written by him, in 1965, for the magazine Electronics, the forecast came to be known later as Moor’s Law. During this time, the electrical/electronic industry has followed this evolution to the letter, or even with greater speed. The size of RAM memories, for example, has quadrupled every three years.

At the same time, it is becoming increasingly difficult to maintain the density of the capacitors using the present-day silicon products. One of the most important elements of this kind of device, the capacitor, has its dimensions reduced every year. At the beginning of the 1990s, the area of this component was 3.6 mm2.  Nowadays, it is 0.1 mm2. The estimate is that this area will shrink to 0.04 mm2 between 2007 and 2010.  Also decreasing in size and increasing in quantity are the transistors (amplifiers of electrical signals) in electronic equipment.  In 8086 processors, introduced onto the market in 1978, transistors numbered 29,000 units.  Today, with Pentium 4, the quantity has risen to 42 million transistors.

Temperature shock
The reduced sizes of these components brings another problem: the layers of silicon oxide overheat.  A few years ago, the industry that produces these devices plunged into an unceasing search to avoid, in future, in tiny capacitors, the loss of electrical current in integrated circuits, which is something that overturns the reliability of computers and other electronic equipment. High temperatures are no problem for the films developed by the team coordinated by Professor Elson Longo. “The systems are reliable, because barium and lead titanate is not degraded at the temperatures that damage the current devices. Another advantage of the new film is its ferroelectric condition, which gives it an advantage over the ferromagnetic ones used nowadays, because they have a low voltage in operation, besides being smaller in size, of low weight, and having a high speed in reading and writing, a process that stores, deletes, and imprints the characteristic 0 and 1 digital signals in the memories of a computer. “Large industrial groups from the United States, Europe, and Asia are investing millions of dollars in getting ferroelectric thin films, because they are competitive and easily integrated with the current technology for producing integrated circuits that use silicon and gallium arsenide chips”, says Longo.

But the great industrial advantage of the new film is the manufacturing process.  Using an organic solution of citrate obtained from citric acid (found in fruits like oranges and lemons), a solid compound is prepared, with a polymeric chemical structure (similar to plastics) that has barium, lead, and titanium as ingredients. This compound is taken to a simple oven at a temperature of up to 300º Celsius, to remove the organic material (carbon, mainly). “Next, we use a domestic microwave oven to steer the crystallization (essential for getting a good dielectric constant) and producing the barium and lead titanate film”, Longo explains. It is the first time that this compound is obtained by using this technique. “Perhaps Nasa (the American space agency) and the US military are already using this titanate in chips that need an advanced stage of stability.  It is not made industrially, though perhaps it is being produced in laboratories by expensive and complex methods, and without the dielectric constant that we have obtained”.

Contrary to the ultraclean rooms, without any kind of contaminating material in suspension, which make up high technology factories at the cost of many millions of dollars, the production of barium and lead titanate films can be done in any environment and without any special care.  “By the methods used today, these materials take about 40 hours to be ready. In the system we have developed, it takes two hours of burning in the ordinary oven, and another ten minutes in the microwave, to get the titanate”, is Longo’s comparison. FAPESP funded the patenting of this system, which was deposited in July 2003, hence before the publication, on January 12 this year, of the scientific article in Applied Physics Letters magazine, of the American Institute of Physics, signed by Professor Longo and the other researchers Fenelon Martinho Lima Pontes, Edson Leite, Geovane Pimenta Mambrini and Márcia Tsuyama Escote, from UFSCar, and also Professor José Arana Varela, from Unesp.

The same method was used to produce another innovation from the group of researchers: an electrode of lanthanum nickelate (LaNiO3). This material has replaced the layer of platinum in the sandwich that forms the chip. In the same way to be seen with barium titanate, the nickelate was produced from a compound, now formed of nickel and lanthanum, which guarantees the structural properties of the material before it goes to the oven, unlike the present-day films that undergo several processes of chemical or physical deposition. This means that the matrix, called a precursor polymer, now has the chemical memory that has the necessary structure for turning into a semiconducting or conducting material. “We made the material in the shape of a polymeric structure, and then, when we burned it, only the skeleton is left, which is the conductive or dielectric plate”, says Longo. “Another important point is that these materials are compatible amongst themselves in their chemical and molecular structure, facilitating the integration of these films into the same device, which usually has gold as its conductor, another chemically compatible element.”

Billions world-wide
The novelties presented by Professor Longo’s team should not diminish immediately Brazil’s dependence on imports of semiconductors, which in 2003 came to US$ 1.7 billion, according to the Brazilian Electrical and Electronics Industry Association (Abinee). Of this total, US$ 1.2 billion was in purchases from countries from Southeast Asia, like Taiwan, Singapore, and Hong Kong. “Brazil does not have the conditions, on its own, for financing semiconductor factories that need some billions of dollars to be set up”, says Longo.  “We showed, with this work, that Brazil has the competence for developing innovation, as well as training personnel with an excellent qualification for this sector.”  The production of the barium and lead titanate films and the lanthanum nickelate electrode with the technique developed by the Ceramics Cepid can be carried out both in Brazil and abroad, as may be indicated by the negotiation, if it comes to a positive result.

This is a billionaire market that is studying the new steps very closely.  Not without reason.  Last year, the world-wide sales of semiconductors reached the mark of US$ 166.4 billion, 18.3% higher than in 2002, according to the Semiconductor Industry Association (SIA), of the United States.  The forecast for the growth in sales formulated by the entity for this year is 19%.  An attractive market in a business that is increasingly fundamental.

The projects
Thin Films for Computer Memories; Modality Research, Innovation, and Diffusion Centers (Cepids); Coordinator Elson Longo – Multidisciplinary Center for the Development of Ceramic Materials; Investment R$ 1,200,000.00 every year for the Cepid
2. Apparatus and Method for Crystallizing Thin Films Using a Domestic Microwave Oven (nº 02/11415-2); Modality Intellectual Property Support Program; Coordinator Elson Longo – Multidisciplinary Center for theDevelopment of Ceramic Materials; Investment R$ 6,000.00