The advancement of silicon electronic technology is slowing down as the field becomes more mature and the technology scaling approaches the quantum limit. However, there are many current and emerging impactful open areas of research such as digitally assisted mm-wave and THz self-correcting systems, quantum engineering assisted electronics, non-planar transistor based electronic systems, and low power mm-wave and THz signal generation, processing, and imaging. At the same time, the field of silicon electronics is rapidly becoming inter-disciplinary to advance further.
For a given silicon electronic technology, the performance of the active and passive devices are mainly limited by the parasitic components (such as undesired capacitance and resistance) and the substrate loss. The active device level limitations make the signal generation and processing rather challenging at sub-mm-wave and THz regimes. Also, parasitic components of the active devices together with the limited quality factor of passive components make the design of low phase noise oscillators and efficient power amplifiers rather challenging. Additionally, the loss and limited bandwidth in the high-frequency electrical interconnects, increase the power consumption of chip-to-chip or board-to-board data links significantly. Quantum engineering and innovative new devices (such as non-planar active and passive devices) may overcome some of the active and passive device level challenges and are important and promising open areas of research. Moreover, the performance of some of the RF, mm-wave, and sub-mm-wave systems that are designed in silicon based technologies may be improved through the concept of optically assisted electronics. The low loss of the optical medium (such as waveguides), as well as high bandwidth available in optical frequencies can be employed to improve the performance of an existing electronic system. Low-loss optical delays and high quality factor resonators available in the photonic integrated circuits can be used to perform optically assisted electrical signal processing. Due to the small size of these photonic resonators, the optically assisted electrical signal processing may be performed in a smaller area compared to an equivalent all-electrical system. In opto-electronic oscillators, the high optical carrier frequency and low loss optical delay lines enable realization of low phase noise RF and mm-wave and sub-mm-wave oscillators.
Similarly, use of sophisticated analog, RF, mm-wave, and sub-mm-wave architectures in addition to near-zero incremental cost of transistors in high node technologies can improve the performance of photonic systems. Examples are RF assisted phase noise reduction of semiconductor lasers and electronically controlled laser phased arrays. In the concept of electronic-photonic co-design, combining the advantages of devices, circuits, and architectures in both electronic and photonic domains can profoundly impact both fields resulting in advances in several areas such as communications, signal processing, imaging, and sensing. Under the DARPA DODOS program, we are in the process of developing a highly stable optical synthesizer with mHz level resolution across 5THz range. As another example of electronic-photonic co-design, we have demonstrated laser phase noise reduction and stabilization using a hybrid integration of an electronic chip and a photonic chip.
With the rapid growth of social media, video streaming, and cloud services, we are witnessing an ever-increasing capacity demand from the inter-rack links to the global IP network. This requires the next generation transceivers to be low cost, highly scalable, and energy efficient. All-silicon transceivers have the potential to be mass-produced at low costs. By leveraging the CMOS-compatible silicon photonics and the advanced electronic processes, we are developing optical transceivers for next generation networks. The co-design of the photonic devices and mm-wave electronic circuitry enables realization of high-speed low-power and low-cost integrated transceivers.
Near-zero incremental cost of transistors in advanced silicon processes with operation frequencies approaching THz regime opens up many impactful and exciting research topics that may result in new applications in detection and sensing, communication, and bio-technology. Meanwhile, despite important achievements in battery technology, the recent trends show that the advancements in battery technology have been significantly slower than that of silicon electronic technologies. At the same time, the market demands more functionalities and better performance from new electronic devices making it essential for RF and mm-wave engineers to come up with new components, techniques, and more importantly architectures to improve the performance while reducing the power consumption.