New sensor shows faults in smallest circuits

Scientists at Brown University, Rhode Island, have created a magnetic-sensing microscope that allows them to watch electricity flow through the world’s smallest components.

The new scanning microscope can reportedly uncover defects in the smallest and most complex integrated circuits at a resolution 1,000 times greater than current technology.

‘This microscope will allow manufacturers to find defects in each embedded wire in ever-tinier circuits,’ said Brown University professor Gang Xiao, who developed the instrument’s hardware and software with Ben Schrag.

The microscope’s magnetic-scanning technology suggests a new small, non-invasive form of remote detection, said the researchers, who envision a ‘pass-over and detect’ magnetic-sensor-tipped pen, for use in finding internal cracks within aircraft, sensing biological agents in the environment or body, or recognising counterfeit bills or other objects.

Although magnetic sensing is used extensively, it is not applied widely for imaging electrical current flow, said Schrag. The only method that uses magnetic imaging to see current flow is restricted to extremely low temperatures, employing cryogenic aids such as liquid nitrogen. However, the Brown device works at room temperature. This design opens the way to greater use of magnetic sensing technology, he said.

‘The factor of 1,000 improvement in spatial resolution is how much better we can do than this cryogenic technology,’ Schrag said. ‘We are just scratching the surface of potential applications.’

Xiao and Schrag are using the technology to pinpoint how electrical current can form pinholes in state-of-the-art devices called magnetic tunnel junctions. These tiny sandwiches of ferromagnetic layers and insulating material are candidate memory storage cells to replace standard cells used in computer memory chips.

Until now, little or no technology existed for actually ‘watching’ electrical current flow, said Schrag. Whenever current runs through wires, such as those embedded within the semiconducting material of an integrated circuit, it creates a magnetic field. By measuring spatial changes in that magnetic field, the microscope visualises electrical current, even within wires buried under layers of advanced materials, he said.

‘The device allows us to see the evolution of hot spots on each wire in a circuit and how each defect moves down the wire in the form of electrons moving atoms,’ said Xiao. ‘To see a collection of atoms moving as a function of time is a capability that did not exist until now. We are witnessing the flow of electricity. It appears similar to an image of human blood flowing.’

About the size of a refrigerator, the microscope is being reduced to the size of a desktop computer. ‘The new design will allow a technician to sit in front of a monitoring screen, as integrated circuits pass through a small open door, under a scanner and out the door,’ Xiao said. Currently, the microscope takes a few minutes to scan a circuit. The researchers are working to reduce that time to as little as 30 seconds.

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