How To Make A Practical Diamond Device

Diamond has some phenomenal properties. Many of these are due to the fact that the carbon atoms that make diamond what it is, are held together by very tight chemical bonds in a close packed structure. Compounded by the small size of the carbon atom this makes it challenging (but not impossible) to dope diamond in the same way you would with silicon. A good analogy is that with most dopants it's rather like trying to squeeze a tennis ball into a tight packed array of ping-pong balls. The resulting distortion to the regular crystal structure of diamond compromises the performance of the material.

To make practical working devices in diamond, you need to start by tearing up the semiconductor rulebook. The first principle of working with diamond is that it is not a classical semiconductor - rather it's an electrical insulator with some phenomenal charge transport properties.

Our technology takes diamond, one of the world's best electrical insulators, and turns it at will into a controllable conductor. We do this by exploiting one of diamond's unique properties, which is that it is virtually transparent to free electrons. This phenomenon is widely known and has been used to make switching devices in the past. To make such a device the free electrons were generated from an external source such as a hot filament (just as in a thermionic tube) and therefore needed to operate under a vacuum.

What these devices did show was that they could handle very high power levels (kiloamps per cm²) and they were capable of very fast picosecond switching times. As everyone who's ever had to change a lightbulb will know, filaments are fragile, so an improvement to the original design was proposed. In the Mark II version, the hot filament was replaced by a cold cathode - which utilised lots of needle like structures (just like those room ionisers that were so popular in the 1990's) engineered using semiconductor fabrication techniques. This type of cathode generated electrons by a process known as field emission and the had the big advantage that you didn't need to apply large amounts of power to heat a filament:

The problem with this Mark II idea was that a vacuum was still required, so still not practical. Evince's innovation was to realise that superior dielectric properties of diamond could sustain the conditions needed to support field emission within the material itself. Using proprietary surface engineering techniques we have developed a process by which we embed tens of thousands of nano-scale electron emitters into a diamond substrate that provide the charge necessary to switch diamond from being an insulator to an efficient conductor...

... and no vacuum is required!

The result is a new class of devices - unique to diamond - that exhibit the superior high voltage and high frequency switching properties of much loved thermionic valve but none of their drawbacks.