Hands-off approach scrutinises quantum chips

Editorial

Rebecca Pool

Tuesday, July 4, 2017 - 19:30
Image: Scanning microwave microscopy non-destructively generates images of patterned nanostructures in silicon.
 
Researchers have used scanning microwave microscopy to image and electronically characterise 3D phosphorous nanostructures fabricated via scanning tunnelling microscopy-based lithography.
 
STM is now used to pattern thin regions of dopant atoms, such as phosphorous, in silicon, to fabricate structures for quantum devices in next-generation electronics applications.
 
However, the characteristics of these nanostructures could only be inferred from destructive imaging methods, such as focused ion beam milling with scanning electron microscopy, as well as the performance of the final electronic device.
 
Given this, Dr Neil Curson from the London Centre for Nanotechnology, Imperial College, and colleagues, have devised a scanning microwave microscope set-up to directly image the structures with a resolution of 37 nm, lateral, and 4 nm in the vertical directions.
 
They first connect a vector network analyzer to a conducting atomic force microscope probe.
 
An electromagnetic wave is transmitted to the end of the microscope tip, which is pushed against the surface of the structure.
 
The tip then detects the reflected wave with the ratio of the incident and reflected signal power providing information on the local sample properties beneath the probe.
 
Microwave microscope visualizes 3D structures of atomically thin phosphorus layers buried 5-15 nm below a silicon surface.
 
As the researchers points out, the measurements are completely non-destructive and sensitive to as few as 1900 densely packed phosphorous atoms, up to 15 nm below a silicon surface.
 
What's more, the electrical and geometric results agree with properties obtained from electrical transport and secondary ion mass spectroscopy.
 
"The capabilities here are transformative for non-invasive diagnostics of atomic-scale components that will form the next generation of 'classical' and quantum devices," highlights Curson.
 
"If we can easily see all components of a chip in a non-destructive manner. it would be a game-changer," he adds. "What we have just done is a big step towards that."
 
Research is published in Science Advances.
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