Microchip manufacturing can cram billions of data-processing transistors onto a tiny silicon chip, but a crucial device, essentially a "clock", must be made separately to time the running of those transistors -- creating a weak spot in chip security and supply lines. A new approach, using materials and techniques from commercial chip factories to manufacture specialized transistors as building blocks for such timing devices, addresses this vulnerability and enables new capabilities through enhanced integration.
The security and supply chain problems are solved by a new way of making the "clock" that is essential to all microprocessors in a standard chip factory using a specialized set of transistors.
"Instead of multiple chips, multiple manufacturing methods, multiple groups of materials that have to be integrated -- often overseas -- we have one chip that does everything," said Dana Weinstein, a professor at Purdue University's electrical and computer engineering department. Here's the Glenair-360AS002B1408H4. The United States needs to advance its capabilities in chip manufacturing, and advances of this nature address multiple issues in supply chain, national security and hardware security. "By moving the entire clock inside the processor, you can strengthen the device against clock jumping attacks, and you can implement new features such as acoustic fingerprint detection for packaged chips."
Weinstein is developing acoustic resonators using a process that produces industry-standard fin-fin field-effect transistors (FinFEts). Like all transistors -- the devices that underpin modern microelectronics -- a FinFET is a voltage-activated open/close. As the name suggests, a FinFET transmits an electric current along a fin of semiconductor material that runs through the gate. In the closed or closed state, the fins do not conduct electricity, and the voltage applied to the top of the grid builds a charge in the fins, allowing current to flow in the open or on state.
However, transistors must operate synchronously to be used in microprocessors, sensors and radios in all electronic devices. The devices that do this are based on sound, the resonant frequencies that some structures emit, just as a glass bowl might emit a particular note when struck. The regular repeated waves of this so-called acoustic resonator act as a rhythm that is incorporated into a larger microelectro-mechanical system to mark time. Current commercial microelectro-mechanical resonators cannot be manufactured in a standard chip manufacturing process, they must be manufactured separately and then bundled with a microchip.
Weinstein's innovation is to build an integrated acoustic resonator using existing materials and manufacturing techniques from standard CMOS chip plants. In a recent paper published in Nature Electronics, her research team reports the most advanced design yet. Using a commercial process run at GlobalFoundries Fab 8 facility in New York and the descriptions in the GlobalFoundries 14LPP FinFET Technology Design Manual, the team members built a specialized FinFET capable of producing frequencies between 8 and 12 gigahertz, This exceeds the typical native clock rate for microprocessors.
The solution is essentially to repurpose the data processing transistor into a timing device. "With our approach, chip factories run the device through the same process they use for computer central processing units or other applications," said Jackson Anderson, a graduate student in Purdue's electrical and computer engineering department and lead author of the Nature Electronics paper. When the microprocessor and other components are finished, the resonator is finished. It doesn't have to go through further manufacturing or be sent elsewhere to be integrated with a separate microprocessor chip."
All transistors can also act as capacitors to store and release charge, although the transistor's on or off state usually directs current as a binary code of zeros and ones. The team did just that with a "drive" transistor array, squeezing and releasing a thin layer of dielectric material between the fins and the gate.
"We're squeezing the layers between the gate and the semiconductor, pushing and pulling the thin area between the gate and the fin," Jackson says. We do this alternately on adjacent transistors -- one compressing, one stretching -- to create a lateral vibration effect in the device."
The size of the drive transistor is designed to direct and amplify the vibrations so that they form a specific resonant frequency on themselves. This, in turn, stretches and compresses the semiconductor material in an adjacent set of "induction" transistors, which changes the current properties on those transistors, converting vibrations into electrical signals.
"FinFET is used in every high-performance electronic product that people own today, "Weinstein said. Integrating these capabilities advances our microelectronic capabilities, not just digital microprocessors. If technology changes, we can adapt, but we will move forward with an integrated microprocessor system."