Probing the States of Single Molecules for Sensing and Multi-value Memory Applications

Flash memories are used to store phone numbers, music, pictures and videos in mobile phones and are also frequently now used in place of magnetic hard disks in laptop computers. Such memories are non-volatile retaining information even if a battery looses all charge. Consumers constantly want more memory on their portable electronic devices to allow more video and music to be stored but flash memory is already close to the scaling limits preventing significant increases to memory sizes in the future.

A flash memory consists of a floating gate charge node where the a single bit of digital information is stored as a "1" when the node is charged and "0" when the node is discharged. As the floating gate is reduced in size, there are more errors when electrons leak out of or onto the floating gate. These errors result from variation in floating gate size by just a few atomic layers which are sufficient to substantially change the applied voltage required to tunnel electrons onto or off the floating gate. This limit has been reached with present production.

Our approach to improve flash memory and allow smaller memories is to use molecules which are produced chemically to allow charges to be stored as the digital memory and as the molecules are all identical, they do not suffer the same variability errors as the present silicon floating gate flash memories. Out ultimate aim is to use single molecules to enable further scaling thereby aiming to increase the amount of memory available in the future. We will also investigate molecules that can store more than "0" and "1" known as multi-valued memory. This multi-valued memory approach allows more bits to be stored on a single floating gate thereby allowing higher memory density expanding further what could be stored on a mobile phone or laptop computer.

The approach we are taking requires the ability to measure the state an electron occupies on a single molecule. Therefore the technique developed here could be used to measure the properties of single molecules. This has potential applications for measuring the electronic properties of single molecules directly allowing the full characterisation of the molecular levels which at present is difficult to achieve. We believe these techniques can benefit a wide range of researchers in chemistry, physics, materials science and engineering in achieving far cheaper characterisation of materials at the nanoscale.