Transistors Repurposed as Microchip Clock Address Security Flaws

Purdue University, West Lafayette, IN

A method of repurposing existing techniques to produce a microprocessor timing device in a standard chip fab plant could address supply chain and security weak points. (Image: Second Bay Studios)

United States microchip fab plants can cram billions of data-processing transistors onto a tiny silicon chip, but the “clock,” which times the transistors’ operations, must be made separately, which creates a flaw in chip security as well as the supply line. However, a new approach uses commercial chip fab materials and techniques to fabricate specialized transistors to serve as the building block of the timing device.

“You would have one chip that does everything instead of multiple chips, multiple fabrication methods, and multiple material sets that must be integrated — often overseas,” said Dana Weinstein, a Purdue University Professor who’s developing acoustic resonators with the processes used to produce industry-standard fin field-effect transistors (FinFETs).

Like all transistors, FinFETs are a voltage-activated on/off gate. A FinFET passes a current along a fin of semiconducting material that runs through the gate. In the off state, the fin does not conduct electricity. A voltage applied to the top of the gate builds an electric charge in the fin, allowing electricity to flow in an on state.

“There’s a need for America to advance its capabilities in chip manufacturing, and an advance of this nature addresses multiple concerns in supply chain, national security, and hardware security,” she added. “By moving the whole clock inside the processor, you harden the device against clock-glitching attacks, and you enable new functionality such as acoustic fingerprinting of the packaged chip for tamper detection.”

Transistors, though, must be synchronized to perform operations for microprocessors, sensors, and radios used in all electronic devices. The devices that do this are built on sound, the resonant frequency that some structures emit. The regular repeating wave of this acoustic resonator serves as a cadence that’s incorporated into a larger microelectromechanical system and used to mark time. Current commercial microelectromechanical resonators can’t be fabricated in a standard chip fabrication process and must be made separately and then bundled with microchips for use.

Weinstein’s innovation is to build an acoustic resonator with the existing repertoire of materials and fabrication techniques available in a standard complementary metal oxide semiconductor chip fab. Her research team reported, in Nature Electronics, that they fabricated a specialized set of Fin-FETs capable of producing a frequency in the range of 8-12 gigahertz, which exceeds the typical native clock rates of microprocessors.

“With our approach, the chip fab runs this device through the same process they would use for a computer’s central processing unit or other application,” said Jackson Anderson, a Purdue grad student and first author on the paper. “When the microprocessor and other components are done, so is the resonator. It doesn’t have to undergo further fabrication or be sent somewhere else for integration with a separate microprocessor chip.”

Although the transistor’s on/off state ordinarily directs current to serve as the 0s and 1s of binary code, all transistors can also be used as capacitors to store and release a charge.

“We’re squeezing those layers between the gate and the semiconductor, pushing and pulling on that thin region between the gate and the fin,” Jackson said. “We do this alternately on adjacent transistors — one compressing, one stretching — building vibrations laterally in the device.”

“Every single piece of high-performance electronics that you have uses FinFETs,” Weinstein said. “Integrating these functions advances our microelectronics capabilities beyond just digital microprocessors. If the technology changes, we can adapt, but we would be moving forward with an integrated microprocessor system.”

For more information, contact Mary Martialay at This email address is being protected from spambots. You need JavaScript enabled to view it..