Terahertz waves can now see electrical activity inside sealed chips - without touching them

Adelaide University / Hasso Plattner Institute / Virginia Diodes Inc.

Sealed inside their protective packaging, the chips that run our phones, cars, medical devices, and power grids become black boxes. Once packaged, there has been no practical way to see what is happening electrically inside a working chip without cutting it open, attaching physical probes, or switching it off. All of those options are either destructive, impractical, or defeat the purpose of observing a device in operation.

That limitation just got a workaround. An international research team has demonstrated that terahertz waves - electromagnetic radiation sitting between microwave and infrared on the spectrum - can detect tiny movements of electrical charge inside fully packaged semiconductor devices while they are running. No contact. No disassembly. No interruption.

How terahertz waves read a chip from the outside

Terahertz radiation occupies a frequency range (roughly 0.1 to 10 trillion cycles per second) that gives it useful properties for this application. It penetrates common packaging materials that block visible light. It is non-ionizing, meaning it does not damage biological tissue or sensitive electronics the way X-rays can. And it interacts with the movement of electrical charge carriers inside semiconductor materials.

The challenge has always been sensitivity. The electrical signals inside a working chip produce terahertz-scale perturbations that are extremely faint - far smaller than the wavelength of the terahertz radiation itself. Previous thinking held that detecting such small changes was impractical due to fundamental noise limits.

The research team, spanning Adelaide University in Australia, Virginia Diodes Inc. in the United States, and the Hasso Plattner Institute and University of Potsdam in Germany, solved this with an ultra-sensitive detection system built around a specialized homodyne quadrature receiver. This device can isolate extremely small changes in terahertz signals by canceling out background noise, leaving only the faint signature of electrical activity inside the device under test.

The result: a real-time view of electronics at work, even when the active region is buried deep inside sealed packaging.

Diodes, transistors, and proof the signal is real

The study, published in the IEEE Journal of Microwaves, demonstrated the technique across a range of commonly used semiconductor components, including diodes and transistors. The researchers verified that the signals they detected were caused by genuine electrical motion inside the devices - not by heat effects or electromagnetic interference from external sources.

This verification matters. Semiconductor devices generate heat when they operate, and heat can change the terahertz properties of materials in ways that might mimic an electrical signal. The team's detection system distinguished between thermal effects and actual charge carrier movement, confirming that the technique reads electrical activity rather than just temperature.

The method also worked across different device types and packaging configurations, suggesting it is broadly applicable rather than limited to a specific chip architecture or material system.

Safer than X-rays, more practical than probes

Current methods for inspecting semiconductor devices each come with trade-offs. Physical probing requires exposed chip surfaces and electrical contact, making it impractical for packaged devices in the field. X-ray inspection can see through packaging but uses ionizing radiation, raising safety concerns for operators and potentially damaging sensitive components with prolonged exposure. Electron microscopy offers extraordinary resolution but requires destroying the device.

Terahertz inspection sidesteps these problems. The radiation is non-ionizing and safe for both operators and devices. It requires no physical contact with the chip. And critically, it works while the device is running - meaning engineers can observe how a chip behaves under real operating conditions rather than inferring behavior from static images or powered-down measurements.

Professor Withawat Withayachumnankul, who leads Adelaide University's Terahertz Engineering Laboratory, frames the work as a first step toward solving a long-standing problem in electronics. The technique is demonstrated, but it is not yet a finished diagnostic tool.

Security, defense, and the integrity question

The potential applications extend beyond quality control in chip manufacturing. Dr. Chitchanok Chuengsatiansup, Professor of Cybersecurity at the Hasso Plattner Institute, points to security and defense uses. Being able to remotely assess electronic activity without physical access could help verify the integrity of critical hardware, detect malfunctioning or compromised components, and monitor systems in environments where hands-on inspection is difficult or dangerous.

In an era of growing concern about hardware supply chain security - where counterfeit or tampered chips can end up in military systems, critical infrastructure, or medical devices - a non-contact method for verifying that a chip is doing what it should be doing has obvious value.

The technique could also benefit high-power electronics, where devices operate under extreme conditions and cannot easily be taken offline for inspection. Power grid components, industrial motor controllers, and electric vehicle power systems are all candidates for in-operation monitoring.

Early-stage technique with unresolved questions

Several limitations should temper expectations. The study demonstrates proof of concept using relatively simple semiconductor components - diodes and transistors. Modern microprocessors contain billions of transistors packed into areas measured in square millimeters. Whether terahertz probing can achieve the spatial resolution needed to interrogate individual components within a densely integrated chip remains an open and difficult question.

The sensitivity of the homodyne receiver system, while sufficient for the demonstrated applications, may need significant improvement to detect the much smaller signals produced by the nanometer-scale features of modern processors. The researchers have not yet demonstrated the technique on cutting-edge chip architectures.

Signal interpretation also presents challenges. As devices grow more complex, distinguishing the terahertz signature of one component from its neighbors becomes harder. Developing the computational tools to decode terahertz data from complex integrated circuits will likely require substantial further work.

And while the technique is non-contact, it currently requires specialized laboratory equipment. Translating it into a portable or field-deployable diagnostic tool would require engineering the receiver system into something considerably more compact and robust than its current form.

Still, the fundamental barrier - proving that terahertz waves can detect electrical activity inside sealed, operating semiconductor devices - has been cleared. What follows is engineering, not physics. And for an industry that builds trillions of chips per year but has had no practical way to peek inside them while they run, that distinction matters.