Consumer electronics have undergone a mini-revolution with the advent of non-volatile memories such as flash, which allow for easy storage of media and information.
Flash memory has enabled devices such as digital cameras, music players, and mobile phones to store considerable amounts of data. However, flash drives are still significantly more expensive than magnetic disk drives because of their complicated manufacturing process.
However, Frost & Sullivan has taken note of work being done by scientists from the National Institute of Standards and Technology (NIST), along with colleagues at George Mason University and Kwangwoon University. These researchers have succeeded in fabricating a new non-volatile memory device solution. By combining silicon nanowires with a more traditional type of data storage, they have developed a promising non-volatile storage option, which could prove far cheaper than flash memory.
A hybrid structure combining silicon nanowires and conventional data storage techniques makes this device far more reliable than earlier attempts at nanowire-based memory devices. Additionally, the hybrid approach also simplifies the integration into commercial applications.
The technology consists of a layered structure known as semiconductor-oxide-nitride-oxide-semiconductor, or SONOS for short. The unique feature of such a technology is its unique hands-off self-alignment technique for positioning the nanowires. Such a technique would significantly reduce fabrication costs, especially if these devices reach the high volumes market.
The researchers successfully grew the nanowires onto layered oxide-nitride-oxide substrates. Charge was stored by applying a voltage across the nanowires. A positive charge would result in electrons within the wire tunnelling down into the substrate, thereby charging it.
If a negative charge is applied, the reverse action takes place with the electron tunnelling back up the nanowire. This process is the key to the device's memory function: when fully charged, each nanowire device stores a single bit of information, either a '0' or a '1' depending on the position of the electrons. When no voltage is pre-sent, the stored information can be read.
Being a hybrid design, the device brings the best of both worlds. It combines excellent electronic properties of nanowires with established technology, and thus has several characteristics which make it very promising for applications in non-volatile memory.
Other advantages of the technology are its simple read, write and erase capabilities coupled with a large memory window (voltage range over which it stores information), which gives it good memory retention and a high resistance to disturbances from outside voltage fluctuations. Additionally, it boasts significantly higher on/off current ratios, which allows the circuit to easily differentiate between the '0' and '1' states.
NIST's hybrid approach also allows for better thermal stability especially at higher temperatures (a feature which is lacking in many alternative proposals for nanowire-based memory devices).
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, [email protected]
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