Carbon Nanotubes with a Memory

Apr 03, 2006 feature
Carbon Nanotubes with a Memory
This image shows (a) the schematic structure of the flash-memory device and (b) a transmission electron microscope image of the device´s layered structure (the carbon-nanotube layer is labeled as "CNT").

Carbon nanotubes have successfully been made into a variety of nanoscale circuit components, including transistors, inverters, and switches. Now, a pair of scientists has made a rough, yet promising, flash memory device out of carbon nanotubes. The device is a long way from a finished, marketable product, but it nonetheless represents a significant step in the drive to incorporate carbon nanotubes into mainstream electronics.

“Unlike similar devices that have been made, which use carbon nanotubes but can only operate at very low, very impractical temperatures, our device displays impressive long-term information retention characteristics at room temperature,” said lead researcher Jiyan Dai, a physicist at The Hong Kong Polytechnic University, to PhysOrg.com. “This indicates that mainstream carbon nanotube-based flash memory devices are a real possibility.”

Flash memory devices are currently used to store data in many types of electronic items, including digital cameras, USB memory sticks, and cell phones. Flash memory is considered a “non-volatile” form of memory, meaning it can retain data without a constant supply of power.

A typical flash memory device stores information within a grid of transistors called cells. Each cell consists of three layers: a “control gate” compound and a “floating gate” compound separated by a thin layer of an insulating oxide compound. When a voltage is applied to the cell, electrons build up as negative electric charge in the floating gate. At a certain threshold of charge, the floating gate is considered closed and the cell is thought to have a value of “0.” When the charge drops below that level, the gate is open and the cell has a value of “1.” In this way, each cell is able to hold one bit of information (there are eight bits in one byte).

Dai and co-researcher X.B. Lu created their flash memory device using carbon nanotubes as the charge-storage layer. As described in a paper in the online edition of Applied Physics Letters, they embedded the nanotubes in a compound made of the elements hafnium, aluminum, and oxygen, abbreviated HfAlO, which serves as both the control gate and the oxide layer. This carbon-nanotube “sandwich,” with each layer only several nanometers in thickness, sits on a substrate of silicon.

Dai and Lu determined the charge-retention characteristics of the device by measuring, first, its capacitance (how well it stores electric charge) as a function of the voltage applied across it. They also measured how well the device held onto its charge as time elapsed, from fractions of a second up to nearly three hours. They found that the short-term charge retention wasn’t excellent. During the first couple of minutes, the “memory window” — the voltage range over which the device can retain information — became narrower, a property that is not desirable for flash memory devices. However, over the long term, the memory window remained at a value of about 0.5 V.

“We believe that the excellent long-term charge-retention characteristics of our device are due to the unique structure and electrical properties of carbon nanotubes,” said Dai.

Citation: “Memory effects of carbon nanotubes as charge storage nodes for floating gate memory applications,” Applied Physics Letters 88, 113104 (2006)

By Laura Mgrdichian, Copyright 2006 PhysOrg.com

Explore further: 3-D images of tiny objects down to 25 nanometres

Related Stories

Researchers explore longer life cycle for batteries

Mar 06, 2015

Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, no memory effect and only a ...

Novel crumpling method takes flat graphene from 2D to 3D

Feb 17, 2015

Researchers at the University of Illinois at Urbana-Champaign have developed a unique single-step process to achieve three-dimensional (3D) texturing of graphene and graphite. Using a commercially available ...

Recommended for you

From tobacco to cyberwood

12 hours ago

Swiss scientists from ETH Zurich have developed a thermometer that is at least 100 times more sensitive than previous temperature sensors. It consists of a bio-synthetic hybrid material of tobacco cells and nanotubes.

Scientists convert microbubbles to nanoparticles

15 hours ago

Biomedical researchers led by Dr. Gang Zheng at Princess Margaret Cancer Centre have successfully converted microbubble technology already used in diagnostic imaging into nanoparticles that stay trapped in tumours to potentially ...

'Atomic chicken-wire' is key to faster DNA sequencing

19 hours ago

An unusual and very exciting form of carbon - that can be created by drawing on paper- looks to hold the key to real-time, high throughput DNA sequencing, a technique that would revolutionise medical research ...

3-D images of tiny objects down to 25 nanometres

20 hours ago

Scientists at the Paul Scherrer Institute and ETH Zurich (Switzerland) have created 3D images of tiny objects showing details down to 25 nanometres. In addition to the shape, the scientists determined how ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.