Small Size Does Matter
The megalithic structure known as Stonehenge has long fascinated mankind as a feat of engineering of a scale and complexity without parallel for its time. Fast forward a few thousand years to the present, when scientists at NUS have achieved another feat of engineering by successfully creating the world’s smallest three-dimensional (3-D) structure of Stonehenge.
Measuring only 80 micrometres in diameter, the Stonehenge microstructure was created by a process called silicon micromachining. This process uses a high-energy proton beam writer which can produce 3-D microshapes and structures of high structural accuracy on the surface of materials such as silicon. The proton beam writer, housed at the NUS Centre for Ion Beam Applications, can focus proton beams to diameters of less than 50 nanometres (about 2,000th the diameter of a human hair).
An NUS team comprising Associate Professor Mark Breese and Dr Teo Ee Jin of the Department of Physics, and Associate Professor Daniel Blackwood from the Department of Materials Science used the proton beam writer to control the precise depth of beam penetration to create a tiny replica of Stonehenge on a silicon wafer.
Their achievement demonstrates the potential of using silicon micromachining as a new approach for creating precise 3-D free-standing microstructures. By directly writing the required pattern or shape onto the surface of silicon wafers, micromachining has been able to overcome the limitation of conventional photolithography and silicon etching technologies that either cannot make such complex structures or can only do so by using many expensive repetitive processing steps.
World’s smallest 3-D silicon replica (left) of the original Stonehenge
at Salisbury Plain, England (right).
One of the areas which the fabrication of precise 3-D silicon microstructures will impact is a new technology called microelectromechanical systems (MEMS) or micromachines - integrated micro devices or systems with electrical, mechanical, optical, chemical and electronic components. Incorporating microstructures onto silicon chips will allow new types of functionality, enabling the chips to not only think but to sense, act and even to communicate. These enhanced chips could lead to the development of transistors, integrated circuits and microprocessors which are more intelligent and responsive to changes in their surroundings.
Such enhancements to the microprocessor ‘brain’ of MEMS could improve the overall decision-making and sensing capabilities of electromechanical products which incorporate MEMS technology. These enhancements could lead to smarter and more responsive products, for example tiny pumps that can deliver minute quantities of drugs to heal specific parts of the human body and deceleration-measuring sensors that can improve the trigger response time of car airbags to help save lives during accidents.
An array of nano-tips made of silicon
Apart from MEMS applications, silicon micromachining has been used to create tiny silicon waveguides or tracks which help channel light particles that can transmit data more quickly than electrons in today’s computers. Micromachining is also able to create silicon nano-tips, i.e. pointed structures that can emit electrons, which are being developed for use in products such as flat panel screens to display images of higher definition and quality.
Being the only researchers in Asia to use proton beam writing technology for silicon micromachining, the team hopes that the technology will become an established fabrication tool for constructing structures at the micrometre and nanometre scale in the future. If this is realised, there is no denying that size does matter – in this case, going small for big impact.
back to top |
