Transistors Used as Microchip ‘Clock’ Address Supply Chain Weakness

by Carolyn Mathas

Billions of data processing transistors are crammed onto a tiny silicon chip; however, a “clock,” to time the operation of those transistors must be made separately. This represents a security risk for the supply line.

A more recent approach uses commercial chip fab materials and techniques to fabricate specialized transistors used as the building block of this timing device, addressing weak points and enabling greater functionality via more integration.

Dana WeinsteinPurdue University professor of electrical and computer engineering, is developing acoustic resonators with the processes used to produce industry-standard fin field-effect transistors (FinFETs). The advances address multiple supply chain, national security, and hardware security concerns. Moving the whole clock inside the processor hardens the device against clock-glitching attacks and enables acoustic fingerprinting of the packaged chip for tamper detection.

The alternative method is to build an acoustic resonator with existing materials and fabrication techniques available in a standard CMOS. The findings are published in Nature Electronics. Team members fabricated a specialized set of FinFETs capable of producing a frequency of 8-12 gigahertz, which exceeds the typical native clock rates of microprocessors. The solution essentially repurposes data processing transistors into a timing device.

Although a transistor’s on or off state directs current to serve as the 0s and 1s of binary code, all transistors can be used as capacitors to store and release a charge. Weinstein’s team takes arrays of “drive” transistors, squeezing and releasing a thin layer of dielectric materials between the fin and the gate. The transistors are sized to guide and amplify the vibrations into building themselves into a specific resonant frequency. This stretches and compresses the semiconductor material in an adjacent group of “sense” transistors. The result is an altering of the characteristics of a current across those transistors, translating the vibration into an electrical signal.


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