The tiny transistor is the heart of the electronics revolution, and Penn State materials scientists have just discovered a way to give the workhorse transistor a big boost, using a new technique to incorporate vanadium oxide, one of a family of materials called functional oxides, into the device.
The researchers knew that vanadium dioxide, which is just a specific combination of the elements vanadium and oxygen, had an unusual property called the metal-to-insulator transition. In the metal state, electrons move freely, while in the insulator state, electrons cannot flow. This on/off transition, inherent to vanadium dioxide, is also the basis of computer logic and memory.
The researchers had the idea that if they could add vanadium oxide close to the transistor it could boost the transistor’s performance. Likewise, by adding it to the memory cell, it could improve the stability and energy efficiency to read, write and maintain the information state. The major challenge they faced was that vanadium dioxide of sufficiently high quality had never been grown in a thin film form on the scale required to be of use to industry, the so-called wafer scale. Although vanadium dioxide, the targeted compound, looks simple, it is very difficult to synthesize. In order to create a sharp metal-to-insulator transition, the ratio of vanadium to oxygen needs to be precisely controlled. When the ratio is exactly right, the material will show a more than four-order-of-magnitude change in resistance, enough for a sufficiently strong on/off response.
In a paper in the online journal Nature Communications, the Penn State team reports for the first time the growth of thin films of vanadium dioxide on 3-inch sapphire wafers with a perfect 1:2 ratio of vanadium to oxygen across the entire wafer. The material can be used to make hybrid field effect transistors, called hyper-FETs, which could lead to more energy efficient transistors. In a paper published earlier this year, also in Nature Communications, the research group led by Prof. Suman Datta at Penn State showed that the addition of vanadium dioxide provided steep and reversible switching at room temperature, reducing the effects of self-heating and lowering the energy requirements of the transistor.
The implementation of vanadium dioxide can also benefit existing memory technologies, a quest that Penn State researchers are actively pursuing.