Introduction to integrated circuit technology

There is no doubt that our daily lives are significantly affected by electronic engineering technology. This is true:-

• in our professional disciplines,
• on the domestic scene,
• in the workplace,
• in school and university
• in leisure activities.

We are accustomed to being exposed to, and to coming to terms with quite sophisticated electronic devices and systems. There is no doubt that revolutionary changes have taken place in a very short time. Furthermore, the revolutionary advances in technology have not yet by any means run their full course and the potential for future developments is exciting to say the least.

Electronics as we know it today is characterised by:-

• reliability,
• low power dissipation,
• extremely low weight and volume, and low cost,
• an ability to cope easily with a high degree of sophistication and complexity.

Integrated circuit technology, has made possible the design of powerful and flexible processors which provide highly intelligent and adaptable devices for the user. Integrated circuit memories have provided the essential elements to complement these processors and, together with a wide range of logic and analogue integrated circuitry,

The beginning of the revolution

• The beginning of the revolution is hailed by many as the discovery of the germanium bipolar transistor by John Bardeen, William Shockley and Walter Brattain at Bell Laboratories in the USA in December 1947.

1947

A device called a transistor, which has several applications in radio where a vacuum tube ordinarily is employed, was demonstrated for the first time yesterday at Bell Telephone Laboratories, 463 West Street, where it was invented. (23rd December 1947)

• The recognition in 1954 that the use of silicon instead of germanium could produce better transistors, and the development of the much simpler field-effect transistor paved the way for the microelectronics revolution that was to follow.

• In 1958, Jack Kilby at Texas Instruments invented the monolithic integrated circuit, in which for the first time four transistors were integrated into a single substrate to form a complete amplifier.

1958

Jack Kilby, a young electrical engineer at Texas Instruments, figured out how to put all the circuit elements - transistors, resistors, and capacitors, along with their interconnecting wiring - into a single piece of germanium. His rough prototype was a thin piece of germanium about one-half inch long containing five separate components linked together by tiny wires.

(Kilby's circuit was an awkward looking thing, very hard to manufacture). Commercial integrated circuit production had to await the development of the improved manufacturing methods for silicon devices, and for interconnecting them with deposited Al, all based on carefully controlled chemical, physical and optical (photographic) processes, which led to the monolithic integrated circuit.

• This was man's first hesitant step into the era of microcircuit engineering.

• Although progress was at first slow, other manufacturers gradually followed suit; the development of the logic gate (c. 1960), the semiconductor memory and the microprocessor soon followed, and marked the dawn of the computer age.

• The first commercial ICs began to emerge at the beginning of 1960

Since that time there have already been four generations of ICs: SSI (small scale integration), MSI (medium scale integration), LSI (large scale integration), and VLSI (very large scale integration), all of these being fuelled by an unrelenting drive towards greater and greater miniaturisation.

A brief review of the history of the microprocessor using Intel products as examples.

Intel = INTegrated Electronics

1968
Robert Noyce & Gordon Moore establish Intel in Santa Clara, California.

Intel produces the first 1K RAM (random access memory).

1971
Intel (Ted Hoff) invents the microprocessor (4004), roughly equal in power to ENIAC. The 4-bit 4004 ran at 108 kHz & contained 2300 transistors. The speed of this 1971 device is estimated at 0.06 MIPS (million instructions/s). By comparison, Intel's new P6 runs at 133 MHz, contains 5.5 million transistors, and executes 300 MIPS.

1978

The 8086/8088 Microprocessor. A pivotal sale to IBM's new personal computer division made the 8088 the brains of IBM's new 'hit product' -- the IBM PC. This was followed in 1982 by the 80286, on which was based the IBM PC/AT (Advanced Technology) computer.

1981
IBM PC is released.

In April the UK government launches a £4 million Micros in Schools scheme.

1985

The Intel '386 contained 275,000 transistors. It was Intel's first '32-bit' chip, and was capable of 'multi-tasking'.

1989

The '486 (shown) was significantly more powerful, and was the first to offer a built-in mathematical co-processor, greatly speeding up transcendental functions.

1993

The Pentium was first introduced in 1993 - it was designed to allow computers to handle "real-world" data such as speech, sound and images.

1997

The latest Pentium II (1997) contains 7.5 million transistors and is packaged in a unique format ..

Moore's Law

Silicon technology has become the dominant fabrication process for relatively high performance and cost effective VLSI circuits.

Such has been the potential of the silicon integrated circuit that in less than three decades, the number of transistors (as a measure of complexity) being integrated into circuits on a single silicon chip has risen from tens to millions, as can be seen in the Figure.

Now we are beginning to see the emergence of the fifth generation, ULSI (ultra large scale integration), which is characterised by complexities in excess of 5 million devices on a single IC chip. Further miniaturisation is still to come, and more revolutionary advances. The figure sets out what has become known as 'Moore's first law' after predictions made by Gordon Moore (of Intel) in the 1960s. It may be seen that his predictions held true with remarkable accuracy, right up to the 1980s.

To try and get some idea of the degree of complexity and the manufacturing challenges associated with a modern-day integrated circuit, we can think of it like this: if the circuit were magnified such that the individual transistors were of the size of office buildings, and the interconnections between them were of the size of the streets and avenues, then the entire circuit at this scale would stretch from London to San Francisco.

We can see that the scale of integration achieved in microcircuits has risen in a meteoric way, and integrated circuits may now contain millions of transistors on a chip of silicon the size of a fingertip, and cost but a few pence. It has been estimated that in the brief history of microelectronics, in excess of 10¹⁶ transistors have been manufactured world-wide.

• That's on average about 10⁷ per second, continuously, over the forty years that integrated devices have been manufactured.

• If all the devices manufactured since 1947 were stacked end to end - they would stretch halfway to the sun …

It is difficult to think of any other endeavour in the history of man that has been brought to such a state of refinement.

One commentator has put it like this:

• If the motor car had undergone the same degree of development as the integrated circuit, the journey by car from Cambridge to London would nowadays take just a couple of seconds, using half a teaspoonful of petrol.

• There would be no need to find a parking meter at the other end, because the cost of buying a replacement car would be about 10p, a fraction of the parking fee!"

Scaling

But what is the irresistible attraction of making devices progressively smaller? Apart from the obvious benefits, of offering more devices and hence greater functionality within a single package, there are a number of other important advantages that accrue from scaling integrated circuits to smaller dimensions. For example, if transistor dimensions are reduced by a factor k, the area occupied by each device is evidently reduced by k². Analysis shows that the time taken for a signal to pass through the transistor falls, also by a factor k, and the power consumed by it is also reduced by k². So smaller devices are faster, require less power, and cost less. These are the powerful incentives which drive chip manufacturers inexorably towards smaller and smaller devices.

To take a well-known example, the Intel Pentium processor in the PC (widely used in the office and the home) was originally manufactured using transistors with minimum dimensions of 0.8 micrometres. Its clock speed was limited to 66 MHz. By reducing the minimum dimension to 0.6 micrometres, the clock speed can be raised to 100 MHz, allowing the processor to carry out 50% more instructions per second. The latest Pentium Pro has minimum dimensions of 0.35 micrometres, and can run at 200 MHz.

Unfortunately the enhanced performance brought about by scaling devices comes at the expense of enormous technical investment. The manufacture of integrated circuits involves hundreds of separate procedures, all of which must be carried out perfectly correctly to produce working devices. In addition, it calls for microscopic precision, measured in fractions of micrometres. The process, by which the patterns describing the shapes and sizes of the circuit elements are transferred to the surface of the wafer (lithography) is a key factor. Up to now, this has been often been accomplished by photographic reduction of patterns created with the help of a computer-aided design tool. But as the size of the features imaged becomes comparable to the wavelength of light, fidelity suffers, and the proportion of working devices declines. Maintaining the necessary level of precision also calls for chip production environments that are thousands of times cleaner than today's cleanest surgical operating theatres.

One of the reasons for the divergence in more recent years from Moore's Law is the increasing difficulty and escalating cost of servicing these demands.

This is not the only reason for the recent 'failure' of Moore's Law. In addition, there are real problems associated with the sheer complexity of designing and testing such very large circuits (embodying millions or tens of millions of transistors).