Transistors repurposed as microchip “clocks” to address security concerns and supply chain vulnerabilities

A new method of creating the critical “clock” for all microprocessors from a specific set of transistors in a standard chip fab addresses security and supply chain concerns. Credit: Second Bay Studios

Microchip fab plants in the United States can cram billions of data-processing transistors onto a tiny silicon chip, but a critical device, essentially a “clock,” must be built separately to operate those transistors—a vulnerable Making the point. Chip security and supply line. A new approach uses commercial chip fab materials and techniques to fabricate specialized transistors that serve as the building blocks of this timing device, addressing the weak point and enabling new functionality through improved integration. Enable.

“Instead of multiple chips, multiple fabrication methods, and multiple sets of materials, everything has to be integrated,” said Dana Weinstein, a professor of electrical and computer engineering at Purdue University. often overseas” with the process used to manufacture industry-standard Fin Field Effect Transistors (FinFETs). “The U.S. needs to advance its capabilities in chip manufacturing, and this kind of advancement addresses a number of concerns in supply chain, national security and hardware security. By moving the entire clock inside the processor, you reduce clock errors. harden the device against attacks, and you enable new functionality such as acoustic fingerprinting of the packaged chip to detect tampering.”

Like all transistors – the devices that underlie modern microelectronics – FinFETs are a voltage-driven on/off gate. As its name suggests, a FinFET passes a current along a fin of semiconductor material that passes through the gate. In the off, or closed state, the fan does not conduct electricity. A voltage applied across the gate creates an electric charge in the fin, allowing electricity to flow in the open or on state.

But transistors must be compatible to perform operations for microprocessors, sensors and radios used in all electronic devices. Instruments that do this are built on sound, the resonant frequency that certain structures emit, such as a certain note when pinging a glass bowl. The regularly repeating wave of this so-called acoustic resonator acts as a cadence that is fed into a larger micro-electromechanical system and used to mark time. Current commercial microelectromechanical resonators cannot be fabricated in standard chip fabrication processes and must be fabricated separately and bundled with microchips for later use.

Weinstein’s innovation is to create an acoustic resonator with the current repertoire of materials and fabrication techniques available in a standard complementary metal-oxide semiconductor chip fab. In a recent journal article Nature Electronics, his research team reports their most advanced design to date. Using a commercial process operated at the GlobalFoundries Fab 8 facility in New York and described in the GlobalFoundries 14LPP FinFET Technology Design Manual, team members developed a specific set of FinFETs that generate frequencies in the 8-12 GHz range. Able to do, specific local clock rate of microprocessors.

The elegant solution essentially repurposes the data processing transistors into a timing device.

“With our approach, the chip fab runs the device through the same processes that they would use for a computer’s central processing unit or other application,” said Jackson Anderson, a Purdue graduate student in electrical and computer engineering. and first author of a Nature Electronics paper. . “When the microprocessor and other components are done, so is the resonator. It doesn’t need to go through further fabrication or be sent elsewhere for integration with a separate microprocessor chip.

Although the on or off state of a transistor usually directs current to act as the 0s and 1s of a binary code, all transistors can also be used as capacitors to store and release charge. Weinstein’s team does exactly that with arrays of “drive” transistors, squeezing a thin layer of dielectric material between the fan and the gate.

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

The size of the drive transistors guides and amplifies the vibration to build upon itself at a specific resonant frequency. This, in turn, expands and contracts the semiconductor material in an adjacent group of “sense” transistors, which changes the characteristics of the current across those transistors, translating the vibrations into an electrical signal.

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

Citation: “Integrated Acoustic Resonators in Commercial Fin Field-Effect Transistor Technology” by Jackson Anderson, Yanbo He, Bechuy Bahr and Dana Weinstein, 23 September 2022, Nature Electronics.
DOI: 10.1038/s41928-022-00827-6

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