Introduction to integrated circuit technology

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

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:-

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

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)

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.

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.

Scale of Integration
Number of devices
Year
Zero Scale Integration
ZSI
1
1950
Small Scale Integration
SSI
2-30
1965
Medium Scale Integration
MSI
30-103
1970
Large Scale Integration
LSI
103-105
1980
Very Large Scale Integration
VLSI
105-107
1985
Ultra Large Scale Integration
ULSI
107-109
1990
Giga- Scale Integration
GSI
109-1011
2005
Tera- Scale Integration
TSI
1011-1013
2020

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.

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:

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.

Scaling the Intel Pentium processor
Minimum dimension
(micron)
0.80.6
Area of chip
(mm2)
284163
Maximum clock speed
(MHz)
66100
Supply voltage
(V)
53.3

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).