Power/Performance Bits: Oct. 1

First Computer Based On Carbon Nanotubes
Pointing toward a new generation of energy-efficient electronics, a team of Stanford engineers has built a basic computer using carbon nanotubes (CNT), a semiconductor material that has the potential to launch a new generation of electronic devices that run faster, while using less energy, than those made from silicon chips.

People have been talking about a new era of carbon nanotube electronics moving beyond silicon but there have been few demonstrations of complete digital systems using this exciting technology until now.

This achievement is expected to galvanize efforts to find successors to silicon chips, which some expect will soon encounter physical limits that might prevent them from delivering smaller, faster, cheaper electronic devices.

Approximately 15 years ago carbon nanotubes were first fashioned into transistors, but an array of imperfections in them has long frustrated efforts to build complex circuits using CNTs. To this end, the Stanford team has put in place a process for fabricating CNT-based circuits, and have built a simple but effective circuit that shows that computation is doable using CNTs.

Better Electronics With Spirals Of Light?
A group of researchers at the California Institute of Technology (Caltech) has created the optical equivalent of a tuning fork—a device that can help steady the electrical currents needed to power high-end electronics and stabilize the signals of high-quality lasers—marking the first time that such a device has been miniaturized to fit on a chip. This development may pave the way to improvements in high-speed communications, navigation, and remote sensing.

When tuning a piano, a tuning fork gives a standardized pitch, or reference sound frequency. In optical resonators the ‘pitch’ corresponds to the color, or wavelength, of the light. This device provides a consistent light frequency that improves both optical and electronic devices when it is used as a reference, the researchers explained.

A photograph of the spiral chip-based optical resonator developed at Caltech, shown next to a quarter to provide scale. (Source: Caltech)
A miniaturized optical oscillator would represent a shift in the traditional roles of photonics and electronics. Currently, electronics perform signal processing while photonics rule in transporting information from one place to another over fiber-optic cable. Eventually, oscillators in high-performance electronics systems, while outwardly appearing to be electronic devices, will internally be purely optical.

A good tuning fork controls the release of its acoustical energy, ringing just one pitch at a particular sound frequency for a long time; this sustaining property is called the quality factor. The researchers transferred this concept to the optical resonator, focusing on the optical quality factor and other elements that affect frequency stability.

They were able to stabilize the light’s frequency by developing a silica glass chip resonator with a specially designed path for the photons in the shape of what is called an Archimedean spiral. Using this shape allows the longest path in the smallest area on a chip. They knew if they made the photons travel a longer path, the whole device would become more stable.

Frequency instability stems from energy surges within the optical resonator—which are unavoidable due to the laws of thermodynamics and because the new resonator has a longer path, the energy changes are diluted, so the power surges are dampened—greatly improving the consistency and quality of the resonator’s reference signal, which, in turn, improves the quality of the electronic or optical device.
In addition to its use as a frequency reference for lasers, a reference cavity could one day play a role equivalent to that of the ubiquitous quartz crystal in electronics. Most electronics systems use a device called an oscillator to provide power at very precise frequencies. In the past several years, optical-based oscillators—which require optical reference cavities—have become better than electronic oscillators at delivering stable microwave and radio frequencies. While these optical oscillators are currently too large for use in small electronics, there is an effort under way to miniaturize their key subcomponents.