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Capturing Light: New Ergonomic Photodetector for the Trillion-sensor Era

Capturing Light: New Ergonomic Photodetector for the Trillion-sensor Era


Scientists develop a compact and robust optical sensor that can convert light to digital signals for use in flexible electronics


Light-to-frequency conversion circuits (LFCs) are often used to overcome setbacks faced by conventional ultra-low power light sensors. However, use of LFCs can lead to chip area wastage and poor performance of photosensors. Researchers from Incheon National University, South Korea have now developed a highly photosensitive LFC with improved chip area economy, high tuneability, and superior compatibility with flexible electronics. This novel photodetector system can be used in the newly envisioned Internet-of-things (IOT) sensor systems.


Incheon National University researchers have developed a highly efficient multi-functional photodetector with ergonomic architecture and superior signal processing ability, which can be a useful addition to the Internet-of-things sensor systems

Photo courtesy: Pixabay

The world is heading towards a trillion-sensor economy where billions of devices using multiple sensors will be connected under the umbrella of Internet-of-things. An important part of this economy is constituted of light/photo sensors, which are tiny semiconductor-based electronic components that detect light and convert them to electrical signals. Light sensors can be found everywhere around us, from household electronic gadgets and health-care equipment to optical communication systems and automobiles.

Over the years, there has been marked progress in research on photosensors. Scientists have endeavored to develop sensors that can detect a high dynamic range of lights and are easy to manufacture and energy efficient. Most light sensors used in cost-effective consumer products are energy efficient but are susceptible to noiseunwanted light informationin the external environment, which adversely affects their performance. To tackle this issue, products have been designed using light-to-frequency conversion circuits (LFCs), which show better signal to noise ratio. However, most LFCs are made of silicon-based photodetectors that can limit the range of light detection. Also, use of LFCs leads to chip area wastage, which becomes a problem when designing multi-functional electronic circuits for compact devices.

Now a team of researchers from Incheon National University, South Korea, led by Prof. Sung Hun Jin, has demonstrated a highly efficient system of photodetectors that can overcome the limitations of conventional LFCs. In their study, which was made available online on 10 June 2021 and subsequently published in volume 17, issue 26 of the journal Small, they report developing complimentary photosensitive inverters with p-type single walled carbon nanotubes (SWNT) and n-type amorphous indium-gallium-zinc-oxide (a-IGZO/SWNT) thin film transistors. Prof Jin explains “Our photodetector applies a different approach with regard to the light-to-frequency conversion. We have used components that are light dependent and not voltage dependent, unlike conventional LFCs.”

The new design architecture allowed the team to design LFC with superior chip area efficiency and compact form factor, making it suitable for use in flexible electronic devices. Experiments conducted using the photosensor system indicated excellent optical properties, including high tunability and responsiveness over a broad range of light. The LFC also showed possibility of large area scalability and easy integration into state-of-the-art silicon wafer-based chips.

The LFC system developed in this study can be used to build optical sensor systems that have high-level signal integrity, as well as excellent signal processing and transmitting abilities. These promising properties make it a strong contender for application in future Internet-of-Things sensor scenarios. “LFCs based on low dimensional semiconductors will become one of the core components in the trillion sensors area. Our LFC scheme will find application in medical SpO2 detection, auto-lighting in agriculture, or in advanced displays for virtual and augmented reality” concludes Prof Jin.



Jinheon Jeong, Seung Gi Seo, Seung-Myeong Yu, Yunha Kang, Junyoung Song,*

and Sung Hun Jin*

Title of original paper:

Flexible Light-to-Frequency Conversion Circuits Built

with Si-Based Frequency-to-Digital Converters via

Complementary Photosensitive Ring Oscillators with

p-Type SWNT and n-Type a-IGZO Thin Film Transistors






Department of Electronic Engineering

Incheon National University, Republic of Korea

*Corresponding author’s email:

About Incheon National University

Incheon National University (INU) is a comprehensive, student-focused university. It was founded in 1979 and given university status in 1988. One of the largest universities in South Korea, it houses nearly 14,000 students and 500 faculty members. In 2010, INU merged with Incheon City College to expand capacity and open more curricula. With its commitment to academic excellence and an unrelenting devotion to innovative research, INU offers its students real-world internship experiences. INU not only focuses on studying and learning but also strives to provide a supportive environment for students to follow their passion, grow, and, as their slogan says, be INspired.


Website: /mbshome/mbs/inuengl/index.html



About the author

Dr. Sung Hun Jin obtained M.S. and Ph. D degrees in electrical engineering from Seoul National University in 2000 and 2006, respectively. Subsequently, he worked as a senior engineer in Samsung Electronics for 4 years. He joined Prof. John A. Rogers’ group at University of Illinois at Urbana-Champaign in 2009 for researching nano and flexible electronics. Currently he is working as an Associate Professor in the department of electronics engineering in Incheon National University. His current research interests include low dimensional nanomaterials-based FETs and logic circuits for flexible smart systems. Recently, he has extended his research scope toward super-capacitors, bio-and chemical-sensors, neuromorphic devices, as well as transient electronics for bio- and eco-friendly security-related applications.