Non-volatile memory such as the flash memory used in portable memory sticks has become integral to the electronics industry because they can store data without a power source and are cheap to manufacture. Another type of non-volatile memory technology being actively developed is resistive memory, which has a relatively simple structure consisting of a semiconducting or insulating material placed between two metallic electrodes. With the emergence of demand for low-cost, flexible ‘plastic’ electronics, resistive memory based on organic materials, which can be easily deposited on flexible substrates, has become a target of research. Ching-Ting Lee and colleagues from the National Cheng Kung University in Taiwan1 have now successfully built an organic resistive memory device with an additional metallic gate that allows its properties to be tuned, greatly expanding the device’s versatility.

The research team started with a standard two-terminal organic resistive memory device consisting of a layer of 9,10-di(2-naphthyl)anthracene (ADN), a small organic molecule, sandwiched between two thermally deposited gold electrodes. Gold atoms that penetrate into the ADN layer serve as charge-trapping sites where charge can accumulate when a high voltage is applied across the organic layer. This effect increases the current passed between the electrodes by four orders of magnitude, turning the memory element ‘on’.

Fig. 1: Schematic illustration of the three-gate organic resistive memory device.Adapted from Ref. 1. Reproduced with permission. © 2010 ACS

The researchers added functional versatility to this device by adding a third metallic terminal to control the density of charge in the ADN layer (Fig. 1). Lee and his colleagues found that a higher third-gate voltage reduced the voltage required to switch the memory from ‘on’ to ‘off’, increased the current levels in both the ‘on’ and ‘off’ states, and increased the ratio of ‘on’ current to ‘off’ current.

This added control makes the organic resistive memory element more useful in applications such as displays, which require low current for pixel control but high current for pixel emission. Future work on these devices will focus on obtaining a better understanding of how switching occurs, says Lee. ”The influence of the metal/organic interface on switching behavior is still unknown, and this can be better understood by trying different active layer materials.”