Small print Printing technology has already revolutionised the world twice.

The next revolution will apply to countless manufactured products, warns Michael Ward

f all manufacturing tech- nologies, the one that has arguably had the greatest single impact on our society

is printing. Before Caxton’s printing press, books were rare, hand-crafted and precious. Once the printing process was developed, for the first time, the recordmg and dmemination of infor- mation became automated and stan- dardised, available to artisans and merchants, the middle classes.

It is scarcely an exaggeration to say that this development made technology, in the modern sense, possible. (Try to imagine a world in which the working of the internal-combustion engine is a jealously guarded mystery, passed on in secret ii-om master to apprentice within a closed guild.) Thus printing, as a manufacturing technique, has led to liberating all of the great ideas of modern times.

Interestingly it is the direct descend- ant of printing that has powered the more recent, and more familiar, infor- mation revolution. Lithography which uses optical exposure of a photosensitive material to enable images to be created, can be viewed as a specialised kind of printing technique. And, of course, it is also closely associated with data storage and dmemination.

Now lithography has become a core process in the microelectronics industry, helping to bring cheap and powerful components to a global market. In contrast to the hand-crafted radio technology of the early 20th century, advanced electronic products are literally printed on the production line. The very term ‘printed circuit board’ represents a revolution in the tech- nology of electronic manufacture, indmting as it does the change from manual wiring of electronic products to

mass-producing printing technology. Developments of this printing tech-

nology are now used to form the microchips at the heart of the computer network that is the Internet. Thus lithography is underpinning the latest information revolution, not only making possible information storage and dissemination but now also process- ing of data, bringing ever better access to information and entertainment.

So a particularly intriguing question for futurologists is: what next for lithography?

The same technology that has been developed to support the manufac- turing process in microelectronics is now been exploited to produce minia- ture mechanical devices, such as motors and sensors, for a whole range of completely new applications. This new generation of lithographically produced devices extends beyond the logical realm of data recording and processing into the physical areas of data acquisi-

tion and actuation. The new activity is known as microengineering or, particularly in the USA, MEMS (micro-electro-mechanical systems) or, increasingly in Europe, microsystems.

At the heart of this emerging technology is the deposition-litho- graphy-etch cycle. A layer of material, such as metal or oxide, is deposited on to a suitable substrate, often silicon. The substrate can be several tens of centimetres in size, while the deposited layer may be just 10 or 1 pm in thickness. O n to this deposited layer, photosensitive resist is deposited, and then a pattern is projected on to the photoresist through a glass mask, using ultraviolet light to give the sharpest dimensional control, resulting in a negative or positive image of the mask pattern.

The next stage is to transfer the pattern in the resist into the deposited layer. To do this, we apply various etch technologies that selectively remove the deposited layer while leaving the photoresist pattern intact. Finally the resist itself can be removed.

By repeatedly applying this dep-lith- etch sequence, it is possible to build up complex structures. To support a free structure in three dimensions, we use sacrificial layers that are then removed at a later stage of processing.

Fig. 1 shows a small electrostatically- operated electrical switch or relay. This device is typical of the sort of structures that can be fabricated using this type of process.

The device has many useful properties. Although it is a mechanical switch, it has a mechanical resonant frequency in excess of 10 kHz-indeed, it is possible to build mechanical devices with even higher frequency of opera- tion, such as R F filters. Ths high-

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kequency response is a result of the low mass and great stifhess of micron-sized devices. Further, since the switch does not rely on minority carriers, it can work at much higher temperatures than the usual 200°C upper limit of silicon switches.

Furthermore, the device will have near ideal switch characteristics: when it is off, it really d be off. All this makes it possible to imagine an electro- mechanical data processing element that could compete with shcon at low processor speeds, but could offer enhanced hgh-temperature operation and low-power capabilities.

The features of this process that make it attractive as a mechanical manu- facturing method are similar to those associated with printing. Once the process has been developed, a compo- nent designed and masks obtained, the process can just run, and a complete device can be fabricated without the need for the macroscopic assembly of individual components such as gears and cogs. It is well suited to mass production: 10000 devices can be produced at one go, just as easily as a single device. Since each device is very small, many hundreds of thousands of components can be obtained from a single 10 cm diameter substrate.

Traditionaliy, process development and device design have been very expensive issues in the microsystems sector. However, when large markets are involved, the costs can be recovered over many products.

The microsystems industry has now reached a stage where fabrication processes are available to be exploited by many customers-much as the sllicon industry uses its very expensive foundries for many products. Moreover, design tools are now available with specialist support to make access much more reliable to these new manu- facturing processes.

A forthcoming seminar (organised by IEE Professional Group S11) on ‘Demonstrated micromachining tech- nologies for industry’ will bring together leading UK research specialists and suppliers ofmicroengineering tech- nology. The seminar will be held at Austin Court, Birmingham, on 30 March. The aim of the event is to give

Fig. I : Electrostatically operated switch

industrial engineers an insight into what microengineering can achleve, how they can take advantage of it, and most importantly, how to gain access to this exciting manufacturing technology

Highlights of the event wd include the presentation of a micromachined resonator, and other devices, such as PCR reactors. These examples show clearly what the current generation of technology is capable of, even before we start dreaming of the next generation. The idea is that this will encourage industry representatives to consider how they can use the technology in their future development plans. Fortunately for us, many applications of micro- systems are in the health care, environ- ment and leisure industries, which are all set to be major growth areas in the future economy.

Of course, access to the manu- facturing base is essential, and speakers from various sectors of the industry wd describe the available processes and how to access them. The presentation will include descriptions of the develop- ments that have recently been made in establishing a sofmare design system that can be used to access the tech- nology base, similar to those commonly used within the CMOS microelec- tronics sector.

As with any area of product develop- ment, it is important to exploit the existing processes wherever possible, and not invent new devices that

require new processes unless absolutely necessary. By using existing, stable processes, the designer can capitalise on previous investment in process develop- ment, and be able to concentrate on innovation within the device design.

Finally, it is worth remembering that the USA and Japan are recognised as being world leaders in the technology and its exploitation. Closer to home, countries such as Germany and Switzerland have an excellent repu- tation, but if Europe, and the UK in particular, are to compete then substantial investment, sustaining a long-term programme of continuous development, is needed.

Within the UK there are some impressive commercial applications of microsystems, which are truly world class, exemplified by companies such as BAe and Druck. However, the UK lags behind in its uptake of micro- engineering concepts and products. In Japan, schoolchildren enter compe- titions to design micromachines.

The seminar represents your chance to learn about this growing area, and what microsystems could possibly do for your company, its products and its balance sheet.

For more information and to reserve places on the seuninau, contact Helen Pope on 020 7344 5439.

0 IEE: 2000

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