The demand for more and ever smaller portable electronic devices has driven metal oxide semiconductor-based (CMOS) technology to its physical limit with the smallest possible feature sizes. This presents various size-related problems such as high power leakage, low-reliability, and thermal effects, and is a limit on further miniaturisation. To enable even smaller electronics, various nano-devices including carbon nanotube transistors, graphene transistors, tunnel transistors and memristors (collectively called post-CMOS devices) are emerging that could replace the traditional and ubiquitous silicon transistor.