Purdue University Puts a Processor's Clock Source Right Inside the Processor by Repurposing FinFETs

Researchers from Purdue University's Department of Electrical and Computer Engineering, working with Skyworks Solutions and Texas Instruments' Kilby Labs, have come up with a way to use a microchip's own transistors as a clock source — addressing supply chain issues by taking a critical component out of the equation.

"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," explains Dana Weinstein of the potential impact of the team's work. "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. 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."

Microchips need a way to "tick" from instruction to instruction, and typically use an external clock source like a crystal oscillator. The Purdue device, by contrast, uses the fin-shaped field-effect transistors (FinFETS) already found inside modern microprocessors and repurposes them as acoustic resonators — creating a clock source directly within the processor and which, crucially, can be constructed using existing manufacturing techniques.

"With our approach, the chip fab runs this device through the same process they would use for a computer's central processing unit [CPU] or other application," explains first author Jackson Anderson. "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.

"We're squeezing those layers between the gate and the semiconductor, pushing and pulling on that thin region between the gate and the fin. We do this alternately on adjacent transistors – one compressing, one stretching – building vibrations laterally in the device."

The concept is similar, in principle at least, to a recent project by Rue Mohr that turned an off-the-shelf EEPROM chip into its own clock source, using either an inductor-capacitor (LC) or resistor-capacitor (RC) delay circuit — allowing a seven-segment display system to run entirely without a clock crystal, with surprisingly usable results. Where Mohr's creation topped out at around 3.5MHz, though, the Purdue device — manufactured at a GlobalFoundries facility on a 14LPP FinFET node — proved capable of reaching between 8GHz and 12GHz.

The team's work has been published under open-access terms in the journal Nature Electronics.