In Part 1 of this mini-series on alternative and future technologies, we pondered buckyballs, nanotubes, and the use of diamond films as substrates (base layers) for integrated circuits and system-in-package (SiP) assemblies.

Now, these are certainly jolly interesting topics, but but there's so much more out there...

Superconductors

One of the Holy Grails of the electronics industry is to have access to conductors with zero resistance to the flow of electrons, and for such conductors, known as superconductors, to operate at room temperatures.

As a concept, superconductivity is relatively easy to understand: consider two sloping ramps into which a number of pegs are driven. In the case of the first ramp, the pegs are arranged randomly across the surface, while in the second the pegs are arranged in orderly lines. Now consider what happens when balls are released at the top of each surface as illustrated in Figure 1.

Figure 1. Graphical representation of superconductivity.

In the case of the randomly arranged pegs, the ball's progress is repeatedly interrupted, while in the case of the pegs arranged in orderly lines, the ball slips through "like water off a duck's back."

Although analogies are always suspect (and this one doubly so!), the ramps may be considered to represent conducting materials, the gravity accelerating the balls takes on the role of voltage differentials applied across the ends of the conductors, the balls play the part of electrons, and the pegs portray atoms.

The atoms in materials vibrate due to the thermal energy contained in the material: the higher the temperature, the more the atoms vibrate. An ordinary conductor's electrical resistance is caused by these atomic vibrations, which obstruct the movement of the electrons forming the current.

The Kelvin (or Absolute) scale of temperature was invented by the British mathematician and physicist William Thomson (1824-1907), first Baron of Kelvin. Using the Kelvin scale, 0 K (corresponding to -273° C) is the coldest possible temperature and is known "as absolute zero."

If an ordinary conductor were cooled to a temperature of absolute zero, atomic vibrations would cease, electrons could flow without obstruction, and electrical resistance would fall to zero. A temperature of absolute zero cannot be achieved in practice, but some materials exhibit superconducting characteristics at higher temperatures. (See note.)

Note: If I happened to be an expert in superconductivity, this is the point where I might be tempted to start muttering about Correlated electron movements in conducting planes separated by insulating layers of mesoscopic thickness, under which conditions the wave properties of electrons assert themselves and electrons behave like waves rather than particles. But I'm not, so I won't.

In 1911, the Dutch physicist Heike Kamerlingh Onnes (1853-1926) discovered superconductivity in mercury at a temperature of approximately 4K (-269°C). Many other superconducting metals and alloys were subsequently discovered. However, until 1986, the highest temperature at which superconducting properties could be achieved was around 23K (-250°C) with the niobium-germanium alloy (Nb₃Ge).

In 1986, Georg Bednorz and Alex Müller discovered a metal oxide that exhibited superconductivity at the relatively high temperature of 30K (-243°C). This led to the discovery of ceramic oxides that superconduct at even higher temperatures. In 1988, an oxide of thallium, calcium, barium and copper (Tl²Ca²Ba₂Cu₃O₁₀) displayed superconductivity at 125K (-148°C), and, in 1993, a family based on copper oxide and mercury attained superconductivity at 160K (-113°C). These "high-temperature" superconductors are all the more noteworthy because ceramics are usually extremely good insulators.

Like ceramics, most organic compounds are strong insulators; however, some organic materials known as organic synthetic metals do display both conductivity and superconductivity. In the early 1990s, one such compound was shown to superconduct at approximately 33K (-240°C). Although this is well below the temperatures achieved for ceramic oxides, organic superconductors are considered to have great potential for the future.

New superconducting materials are being discovered on a regular basis (a new family of iron-based superconductors was announced as recently as May 2008, for example), and the search is on for room temperature superconductors, which, if discovered, are expected to revolutionize electronics as we know it.

Protein Switches

Another area receiving a lot of interest is that of switches and memories based on proteins (I should perhaps commence by pointing out that this concept doesn't imply anything gross like liquidizing hamsters to extract their proteins!)