How chips in computers work is not a big mystery. They process information by sending electrical signals through billions of tiny transistors. These switch between "on" and "off" – 0 and 1 – thereby creating binary data. At least in theory. What actually happens inside a chip during operation has, however, remained largely invisible—especially without physical access to the device.
X-ray vision without radiation damage
The problem: chips in operation are firmly embedded within their devices—sealed and inaccessible. To observe what they are doing, the device may need to be opened and its operation interrupted. Observation during operation is therefore not possible in many cases.
However, a research group led by HPI professor Chitchanok Chuengsatiansup and professor Withawat Withayachumnankul from the University of Adelaide, together with researchers from the U.S. technology company Virginia Diodes Inc., has now developed a method to observe chips without touching, dismantling, or shutting them down.
Their approach relies on so-called terahertz waves. The method works similarly to X-rays—but with a crucial difference. X-rays are ionizing and could potentially damage a chip. Terahertz waves are non-ionizing, making them ideally suited to observe the tiny movements of electrical charges inside operating chips. They are also sensitive enough to detect even the smallest changes within a chip—even those smaller than the wavelength of the terahertz radiation itself.
Security for critical infrastructure
This new method opens up the possibility of looking inside a wide range of electronic devices, including smartphones, medical equipment, vehicles, power grids, and defense systems. The researchers’ next step is to scale the method and apply it to more complex systems.
The approach is also highly relevant to Prof. Chuengsatiansup’s research. Observing chips with terahertz waves is not only useful for detecting defects—it may also pose security risks that need to be understood:
Cryptographic algorithms typically operate on secret data such as keys,” she explains. “If one can observe what is being computed during execution, it may be possible to extract those keys. That is why we investigate such potential information leaks.
At the same time, the method holds significant potential for improving the security of critical infrastructure. In many cases, systems in this domain cannot simply be taken offline for inspection—making non-invasive analysis techniques like this especially valuable.
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