Another dimension

Three-year UK project aims to develop a solid-state chip device that will measure and assess nano-scale surfaces on the production line. Siobhan Wagner reports.

For years people have discussed future applications for nanotechnology — everything from PCs that boot up instantly to pacemakers that are less likely to be rejected by human tissue. But engineers know that nanotechnologies will not be able to develop further without progress in nanometrology.

The precise control of dimensions of objects is the key issue of nanotechnology and the science of nano-objects. The dimensions of these objects are below 100nm, and the precision required is frequently around 0.1nm. This requires new methods of measurement to be developed.

Researchers at Huddersfield University will be trying to do just that next month when they begin a three-year project to develop a solid-state chip device that will measure and assess nano-scale surfaces on the production line. The aim is to integrate into a single chip the essential components of an interferometer — an optical device that can measure surfaces with the use of interfering light beams.

It works by splitting a beam of light into two paths, bouncing them back and re-combining them. The different paths may vary in length or comprise different materials to create a re-combined beam that has an altered light intensity on a back detector. The power of this beam can then be used for a measurement.

With current technology, interferometers only work efficiently off the production line because of their susceptibility to inaccuracies due to disturbances in a manufacturing atmosphere.

‘There are accurate instruments for measuring, but they only work in a laboratory environment where the temperature and vibration are controlled,’ said project leader Prof Xiangqian Jiang of Huddersfield’s computing and engineering department. ‘These kind of instruments can’t be used on the production line, so we want to develop a very robust device that is also so small you can fit it in the machine.’

This way, the nano-scale properties and diameters of a product can be analysed and measured as it is being manufactured. Jiang said this will cut down on material waste, saving both time and money. She said it will also shrink the size and cost of machinery.

The Ipswich-based Centre for Integrated Photonics (CIP) has been sub-contracted to deliver the advanced optoelectronic devices and the final optoelectronic hybrid chip. The company was chosen because of its proven capabilities for integrating optical elements, such as interferometers, into silicon chips.

CIP accomplishes this in a process similar to assembling printed circuit boards. The technique includes plugging micro-machined silicon daughterboards, which carry individual optical components, into a micromachined planar silica motherboard. The company’s 2R signal regenerator, used in fibreoptic communications, integrates a planar silica Mach-Zehnder interferometer (MZI) and a monolithic quad semiconductor optical amplifier array to create a dual-channel 2R regenerator with just a 1dB loss at daughterboard/motherboard interface.

While the technology to create these chips is already available, their application in nano-manufacturing and nanometrology is innovative. ‘No-one has ever made this kind of chip for this purpose before,’ said Jiang.

CIP’s research programme vice- president, Michael Robertson, estimates that the chips will be robust enough to withstand a harsh manufacturing environment because they are so small and compact.

When they are commercially available, it is likely that industry demand will be high — if the current market for nanostructured surfaces is any indication.

The rapidly increasing use of nano-scale and ultra-precision structured surfaces is wide ranging and covers optics, hard disks, medical devices and the micro moulding industries — all relying on ultra-precision surfaces.

The scale of the products does not limit the need for the surface precision. The James Webb Space Telescope project, for example, requires complex freeform surface segmented telescope mirrors 1.3m across, with less than 10nm form deviation.

Yet with some applications, such as medical devices, an even smaller deviation is required. As Jiang points out: ‘Just one nanometre could make a difference.’