In electronics graphene is quickly becoming the great hope for replacing and improving upon silicon semiconductors. Since silicon semiconductors are the basis of much commercial electronics (especially computing), we’re talking the Big Time here. This attracts a lot of research money, which in turn attracts researchers to probe opportunities in a number of directions. One of the main directions is to use graphene in transistors. [SciTechStory: Graphene Transistors]. Another approach in development by a research team under Sung-Yool Choi at the Electronics and Telecommunication Research Institute (Daejeon, South Korea) combines two alternatives to the graphene transistor: The memristor instead of a transistor and graphene oxide instead of pure graphene. What’s the advantage?
In theory, not only does memristor technology work well with graphene oxide, but the combination provides more flexibility (physically) and lowers cost. As described in a paper published in Nano Letters [Graphene Oxide Thin Films for Flexible Nonvolatile Memory Applications] this type of circuit commonly used for computer memory could be printed on plastic sheets and used wherever flexibility is needed, such as in wearable electronics.
In applications such as computer memory (RAM) transistors work by storing an electrical charge. Memristors work by storing electrical resistance. That is, when a current is passed through a memristor, its level of resistance to electricity (in Ohms) changes. The change is retained, and the value associated with it is in memory. The memristor was first theorized in 1971 but made practical by Hewlett-Packard only a couple of years ago. The Korean team chose this type of circuit because of the compatibility in electronic behavior and manufacturing suitability of graphene oxide.
Graphene oxide is graphene with some additional atoms of hydrogen and oxygen. It retains the 1-atom thickness and most of the electrical properties of graphene but is easier to handle in manufacturing. In this case, the South Korean researchers used a design similar to that employed by Hewlett-Packard in their memristors. This is built upon arrays of parallel wires perpendicular (right angles) to each other with a layer of titanium oxide sandwiched between them. Each crossing point of the wires makes one memristor. The researchers approach substituted the much less expensive graphene oxide for titanium oxide.
The resulting memristor is about 1000 times larger than HP design, but it is much cheaper to make and flexible. The thinking is that in terms of densely packed circuits, it’s hard to beat silicon for performance, so the graphene oxide memristor doesn’t compete in that arena. What it can do is cycle between ‘on’ and ‘off’ about 100,000 times, which about the same as flash memory. The researchers expect that 1 million cycles is possible. It can also be flexed at least 1,000 times before it deteriorates.
Perhaps graphene oxide memristors should be considered a niche technology, rather than a challenge to silicon transistors. However, it sometimes happens that ‘good enough’ and ‘cheap’ make a formidable combination. That remains to be seen as the real challenge for Choi and his team will be to develop a successful manufacturing process at the scale needed to compete.