Nanotechnology and sub-miniaturised sensors

Citation

White, N. (2004), "Nanotechnology and sub-miniaturised sensors", Sensor Review, Vol. 24 No. 3. https://doi.org/10.1108/sr.2004.08724caa.002

Nanotechnology and sub-miniaturised sensors

Nanotechnology and sub-miniaturised sensors

It is particularly timely to have an issue of Sensor Review dedicated to the subject of miniaturised sensors. Many of the major advancements in this field have taken place within the past 20 years or so. Some of the ideas for such devices, however, came about as a result of some very creative thinking much earlier in the 20th century. For those who have not read the seminal paper “there's plenty of room at the bottom” (Feynman, 1992), it is worth noting that in 1959 the famous physicist, Richard Feynman, discussed issues such as the manipulation of matter on an atomic scale and the feasibility of fabricating denser electronic circuits for computers. Many people consider this paper as the first to introduce the concepts of micro electromechanical systems (MEMS) and nanotechnology. He described a vision of using machines that could construct smaller machines and these, in turn, would make even smaller machines down to the molecular level. Basically, this was a “bottom-up” approach to micromachine design. Feynman actually offered a prize (subsequently claimed in 1960) to the first person to make an electric motor 1/64 in.³ (about 0.4 mm³). These size limits turned out to be slightly too large and the motor was actually made using conventional mechanical engineering methods that did not require any new technological developments.

Much of the earliest documented evidence of MEMS research was published in the 1970s. In the following decade, various types of pressure sensor began to emerge. The first major commercial MEMS device, however, was the impact sensor for airbag deployment in cars and this did not appear until the 1990s. Today, there are many examples of MEMS devices available in the market place including inertial sensors, pressure sensors, biomedical sensors, microfluidic systems and inkjet nozzles. One of the reasons that MEMS have proved to be so popular is that the fabrication processes are essentially the same as those used to make integrated circuits. Another reason is that, in addition to possessing well-suited electrical characteristics, silicon also possesses excellent mechanical properties.

The area of nanotechnology would once have been treated as science fiction, but it is now being put forward by some, as one of the most exciting research fields in contemporary science – the next “big thing”. Of course, all the hype has stirred up much debate on the topic and the many discussions on applications are wide-ranging, to say the least. I am not going to try to define the “nanotechnology” in the limited space here, but suffice to say that the term encompasses more than just devices fabricated in the nanometre scale. Anyway, what is all this got to do with sensors?

Well, some of the advances in the area of nanotechnology will have direct influence on future miniaturised sensors. Take, for example, the case of a silicon resonant sensor; typical dimensions of a MEMS resonator would be of the order a few tens microns, giving a resonant frequency of several hundreds of kilohertz at the most. The “nano” equivalent (or NEMS device), being much smaller, would have a resonant frequency in the gigahertz range. NEMS beam- based resonators have been shown to be capable of measuring masses down to 10⁻¹⁸ g (1 attogram) – that is almost on a par with the performance of mass spectrometers.

There seems to be little doubt that nanotechnology will play a major role in future miniaturised sensors, but it is also clear that microtechnologies still have much to offer. With all the publicity surrounding the former let us hope that the latter does not get completely overlooked.

Neil WhiteSchool of Electronics and Computer Science, University of Southampton, Southampton, UK.

ReferenceFeynman, R.P. (1992), “There's plenty of room at the bottom”, Journal of Microelectromechanical Systems, Vol. 1 No. 1, pp. 60-6.