A collaborative research effort between Korea and the United States has yielded next-generation image sensor technology with superior resolution, enhanced power efficiency, and reduced size compared to existing models. The team has also secured foundational technology for ultra-high-resolution shortwave infrared (SWIR) image sensors, potentially disrupting a market currently led by Sony.
Schematic diagram of the InGaAs photodiode image sensor integrated on the Guided-Mode Resonance (GMR) structure proposed in this study (left), a photograph of the fabricated wafer, and a scanning electron microscope (SEM) image of the periodic patterns (right). Image Credit: Korea Advanced Institute of Science & Technology
On November 20th, 2024, KAIST announced that a research team led by Professor SangHyeon Kim from the School of Electrical Engineering, in partnership with researchers from Inha University and Yale University, has developed an ultra-thin broadband photodiode (PD). This advancement marks a pivotal moment in high-performance image sensor development.
The research significantly enhances the trade-off between absorption layer thickness and quantum efficiency in traditional photodiode designs. The new photodiode achieves a quantum efficiency exceeding 70 %, even with an absorption layer thinner than one micrometer—approximately 70 % thinner than conventional technologies.
This innovation simplifies pixel processing, enabling higher resolution, improved carrier diffusion, and lower production costs. However, thinner absorption layers typically struggle to capture long-wavelength light, posing a challenge that the research team was able to effectively address.
To overcome the limitations of thinner absorption layers, the researchers incorporated a guided-mode resonance (GMR) structure. This advanced design facilitates efficient light absorption across a broad spectrum, ranging from 400 nanometers (nm) to 1700 nm. This range includes both visible and SWIR light, making it valuable for industrial applications such as medical imaging, security systems, and autonomous driving.
The GMR structure, a concept from electromagnetics, enhances light absorption efficiency by creating resonant conditions at specific wavelengths. This innovation not only broadens the absorption spectrum but also supports hybrid and monolithic 3D integration with CMOS-based readout integrated circuits (ROIC), paving the way for next-generation ultra-high-resolution image sensors.
The improved performance in the SWIR region positions this technology as a frontrunner in developing ultra-high-resolution sensors. These advancements promise significant applications in digital cameras, aerospace, autonomous vehicles, and satellite observation. The thinner absorption layer reduces costs and power requirements while maintaining high quantum efficiency, enhancing international competitiveness in imaging technology.
This research demonstrates that significantly higher performance than existing technologies can be achieved even with ultra-thin absorption layers.
Sang Hyun Kim, Study Lead Researcher and Professor, Korea Advanced Institute of Science & Technology