Researchers Turn Transistors into High-Frequency Clock Sources

03-02-2023 | By Robin Mitchell

Researchers from Purdue University have demonstrated a new technique for turning regular transistors used in microprocessors into high-frequency clock sources, something that may help reduce supply chain issues in the future. Why are electronic devices so susceptible to supply chain issues, what did the researchers demonstrate, and what other components could be integrated into single packages?

Why are electronic devices so susceptible to supply chain issues?

Of all the creature comforts that humanity has developed, none have become as critical to modern life as electronics. From paying bills to receiving a salary, electronic devices are involved in almost everything we do. To demonstrate this fact of life, try living without electronics for a single day, and it is unlikely that you would be able to. That isn’t to say that you couldn’t survive for a day without having personal access to electrical equipment, but trying to do so without having some aspect of your life governed by an electrical device at some point is impossible.

As such, it goes without saying that modern society with disrupted access to electronic devices will suffer massive consequences. In fact, this was made abundantly clear during the 2020 COVID pandemic, where semiconductor supply chain issues resulted in massive failings across all areas of industry. The inability to access chips meant that electronic device manufacturers couldn’t make products, and this lack of sales resulted in falling revenues, which in turn either saw companies shrink to survive or simply went under. 

But the reason why electronic devices are so susceptible to supply chain issues boils down to two reasons; their complexity and modern manufacturing practices. To start with, the first reason the modern complexity of electronic devices can see hundreds of components are used in a single device. Many of these components will likely be sourced from a dozen or more manufacturers, and these manufacturers will be spread across the globe. This results in a situation whereby one local disaster can prevent the manufacturer of the end product. Such situations could include local natural disasters, political changes, war, material shortages, and even major holidays.

The second reason, modern manufacturing practices, refers to the common use of production models such as Just-In-Time (something that is highly popular in Japan). In these cases, products are manufactured to meet current demand instead of manufacturing surplus in anticipation of future demand. While this enables manufacturers to be highly streamlined and efficient, the lack of surplus in both raw materials and end-product means that any disruption to the supply chain effectively halts manufacture.

Researchers turn transistors into high-frequency clock sources

All digital computers that have ever been created (even those based on vacuum tubes) have all relied on a centralised clock source for synchronisation. While many microcontrollers can integrate clock sources internally (such as internal RC oscillators), most systems will utilise some external clock source based on a piezoelectric material (such as a quartz crystal). The advantage of such clock sources is that they are highly accurate and resistant to changes in temperature, meaning that they can provide computers with a stable and reliable clock. 

However, these crystals, being located outside of the main processor, introduce supply chain challenges to engineers as they need to be sourced separately. At the same time, the use of additional external components introduces higher costs to engineers (which is why internal RC oscillators are used in low-cost microcontroller applications). 

Recognising the challenges faced by engineers in supply chain security, researchers from Purdue University recently demonstrated a new technique that can turn transistors into high-frequency clock sources. Taking advantage of modern processor technologies, the researchers were able to convert FinFET devices into clock sources with frequencies in the 8GHz to 12GHz range, which is well above the current clock frequencies used in processors.

To achieve this feat, the researchers took advantage of the capacitive gates on FinFET transistors that undergo a minute deflection when charged and discharged. By carefully lining up multiple FinFET transistors and using multiple drive FETs, the resulting charge/discharge induces high-frequency resonance vibration. These changes in mechanical forces can be detected by sense amplifiers, and this can result in a carefully tuned clock source that can be integrated alongside a processor in the same semiconductor die. 

What other components can be integrated into a single package?

The ability to integrate the clock source and processor into a single design enables engineers to eliminate the need for an external clock, therefore improving supply chain security (albeit a small amount). However, numerous other components could also be integrated into the same semiconductor die as the processor, and the more components that can be integrated, the more resistant electronic device supply chains can become.

While not the case for mainstream desktop processors, microcontrollers already integrate most systems components into a single package, including the CPU, RAM, ROM, and peripherals. Voltage regulation is another peripheral that modern microcontrollers are beginning to integrate, and this is especially helpful for those wanting to eliminate external power supply chips. 

The continuing miniaturisation of transistors could also bring about new concepts in the field of computing. Traditionally, smaller transistors have always resulted in more powerful processors with more cores and slightly larger caches, but as we approach the 3nm barrier, engineers may consider dropping additional cores in favour of integrated SRAM. The entirely transistor nature of SRAM makes it easy to integrate alongside digital circuitry, and the close proximity of integrated RAM to the processor would massively speed up memory access times. This could even see flash memory integrated into the same package, thus creating an entire computer on a single chip, whereby SRAM provides system RAM, and Flash provides OS ROM. 

Overall, there are many system components that can be integrated into the same silicon as the main processor, and reducing the number of external components in a design not only helps to reduce costs but also improves supply chain strength. 


By Robin Mitchell

Robin Mitchell is an electronic engineer who has been involved in electronics since the age of 13. After completing a BEng at the University of Warwick, Robin moved into the field of online content creation, developing articles, news pieces, and projects aimed at professionals and makers alike. Currently, Robin runs a small electronics business, MitchElectronics, which produces educational kits and resources.