4. Problems in Microelectronic Circuit Technology

The manufacture of silicon microcircuits consists of a number of carefully controlled processes, all of which have to be performed to well-defined specifications.

The semiconductors are similar to insulators in that they have their lower bands completely filled; they will conduct if more than a certain voltage is applied. A crystal of pure silicon is a poor conductor of electricity, so, conductivity poses a problem. Most semiconductor devices are known to be made by introducing controlled numbers of impurity atoms in a crystal, the process called doping.

Two independent lines of developments are considered to lead to microscopic technique that produced the present integrated circuits: the semiconductor and film technologies.

Silicon crystals may be doped with different elements. Silicon doped with phosphorus or another pentavalent element is called an n-type semiconductor, doping with trivalent element gives rise to a p-type semiconductor.

Impurities may be introduced by the diffusion process. At each diffusion step in which n-type or p-type regions are to be created in certain areas, the adjacent areas are protected by surface layer of silicon dioxide, which effectively blocks the passage of impurity atoms. This protective layer is created very simply by exposing the silicon wafer at high temperatures to an oxidizing atmosphere.

A transistor can be made by adding a third doped region to a diode so that, for example, a p-type region is said to be sandwiched between two n-type regions. One of the n-doped areas is called the emitter and the other, the collector, the p-region between them is the base; this is called an npn-transistor, there may be pnp-transistors.

The success of silicon in microelectronics is believed to be largely attributed to excellent properties of SiO interface and ease of thermal oxidation of silicon. An important aspect of the oxidation process is its low cost. Several hundred wafers can be oxidized simultaneously in a single operation.

Reactive gas plasma technology is being applied to the deposition and removal of selected materials during the manufacture of semiconductor devices. Epitaxial growth in combination with oxide masking and diffusion has given the device designer extremely flexible tools for making an almost limitless variety of structures. Advances in silicon crystal growth technology have encouraged advances in the automation of crystal growing equipment.

The evaporation, sputtering and anodization are the major techniques used in integrated thin film circuit construction and are also applicable to silicon integrated circuitry and device work. These methods singly or in combination enable a variety of resistive, insulating and constructive materials to be laid down onto a suitable substrate. The two most important processes for the deposition of thin films are chemical-vapour deposition and evaporation.

Plasma etching, which is expected to play an important role in manufacture of semiconductor and other devices requiring fine-line lithography, involves the use of a glow discharge to generate reactive species from relatively inert molecular gases. This plasma-etching process has been shown to have important advantages in terms of cost, cleanliness, fine-line resolution, and potential for production line automation.

Nowadays much of the procedure by which ICs are transformed from the conception of the circuit designer to a physical reality is done with the aid of computers. A computer can simulate the operations of the circuit. Computer simulation is less expensive than assembling a “bread-board” circuit made up of discrete circuit elements; it is also more accurate.

Increasing interest in submicron layer now poses new problems. New developments in materials are believed to be due to new manufacturing forms and vice versa. Integrated circuit technology is evolving so rapidly that even a period as short as six months can produce a significant change. (29)

5. Computer As It Is

The word “computer” comes from a Latin word which means to count. Today it would be difficult to find any task calling for the processing of large amounts of information that is not performed by a computer. Computers are using in science, in commerce, in industry, in government and others. Nowadays computer-aided design can no longer be separated from computer-aided manufacturing; they are one and the same. The list of applications is large and growing rapidly.

Every computer now in existence must be told what to do: it must have a set of instructions are called a program. Regardless of their size or purpose most computer systems consist of three elements: the input-output ports, the memory hierarchy and the central processing unit. The input-output ports are known to be paths whereby information is fed into the computer or taken out of it. Items of information can be written to, stored in, retrieved from memory on demand by CPU, or erased to make room for other information. The CPU controls the operation of the entire system by issuing commands to other parts of the system and by acting on the responses.

Computers are classified by size and capability as microcomputers, mainframes and supercomputers, depending on the size of their main memories and on their processing speed. The boundaries separating the categories change frequently as computer technology advances.

Several developments have helped to reduce programming effort. One of the most important causes of the man-machine communication barrier is that an interactive computer system typically responds only to commands phrased with total accuracy in a highly restricted artificial language designed specifically for this system. Many scientists are known to have been conducting a research on man-machine communication.

The problem that hinders man-machine communication is language barrier. A good deal of work is now being done on automated program optimization. Algorithms are especially important to take advantage of vector and microprocessor parallelism. Once we have designed algorithms, we must provide better languages to allow more efficient expression and execution of these algorithms. True portability requires a high-level representation of algorithms, with no machine-dependent semantics.

New programming languages that can support parallel and distributed computing are in great demand. There are currently two approaches to this special issue. One is to adapt currently available popular programming languages and equip them with special library; another is to design conceptually new languages that exploit the fundamental principle of parallel and distributed computing.

In information systems the fields of computers and communications are merging. The integration and coordination of the individual information systems and computers introduces new requirements, design parameters, and tradeoff.

Still there is a critical issue that is the security of computers. Computer networks will always be vulnerable to attack, but there are ways to make a network much more resistant to attack. (27)

6. Computer Trends

The earliest computers were developing during the Second World War for specific defense applications - some of the first computers were used to calculate artillery firing coordinates. These systems did not become commercially marketable for a number of reasons: they were special-purpose, designed for military applications; they were extremely large, occuping huge warehouses; they consumed enormous amounts of electricity, generated immense amounts of heat, required tons of chilled air, and broke down every few hours.

The first commercial systems ran such “business” applications as accounting, billing, payroll, and inventory control. These early computer system processed data in batches, they executed one program at a time and handled transactions one at a time from a predefined sequence of transactions. They required considerable amounts of manual intervention and the applications they performed were limited in scope.

The computers on the 1950s also tended to be physically large, internally slow, and somewhat unreliable in terms of system availability. They used vacuum tubes which limited their price-performance ratio and both the numbers and kinds of applications that were run on them.

Next systems came in 1960s with the invention of the transistor were smaller, faster and more reliable.

In the 1970s, the arrival of integrated circuitry resulted in fast and reliable computer systems. Data communications systems enabled more and more applications to be accessed from remote locations by employees working on Cathode Ray Tube terminals. The applications began to provide information that resulted in a wide range of benefits, from significantly improved customer service to tighter management control over widely dispersed operations and functions.

In the 1980s, the microcomputer brought low-cost computer power to virtually anyone who wishes to use it. In the 1990s, administrative applications evolved into tools for the strategic use of an organization’s information assets to create a competitive advantage for the organization. Advances in electronic technology improved in cost-performance of computer systems. They continued to shrink in size and increase in power.

Advances in communication technology placed more and more information at the fingertips of the average worker, as systems were tied into local, national, and international networks. The use of the Internet has become ubiquitous in a few short years. (17)

7. Effect on Health

Statistics show that the average sixth-grade student watches four hours of television per day. But that does not include the time he spends playing games while staring at a computer or TV screen.

A Japanese study showed that computer games stimulated only a limited part of a child’s brain. According to the study, children need more reading, writing, and arithmetic. But they also need the stimulation of playing outside with the other children and interacting with others.

Some 40 percent of US children between five and eight years of age are clinically obese. They haven’t a time for some exercises because of too much time spent in front of TV or computer screen. One company has even developed exercise equipment that can be used while playing computer games. It would be far better to limit the time spent playing such games, leaving ample time for other activities that help a child to develop a well-rounded personality.

Eye problems may result from staring at the screen for great lengths of time. Surveys show that at least a quarter of all computer users experience visual problems. One reason is that the blink rate may slow down, cause dryness or irritation of the eye. Blinking clears the eye, simulating tear production and washing out contaminants.

Children can play computer games for hours on end, with few breaks. This may cause eyestrain and focusing problems. Experts suggest taking regular breaks of several minutes after each hour of computer use. (16)