The evolution of mobile image sensors is ultimately linked to the advancement of pixel technology. The market's demand for high-quality images with smaller and thinner devices is becoming increasingly challenging, making 'fine pixel' technology a core task in the mobile image sensor industry.
In this trend, Samsung System LSI continues to advance its technology, drawing on its experience in the field of small-pixel image sensors. The recently released mobile image sensor ISOCELL JNP is the industry's first to apply Nanoprism, pushing the boundaries on the physical limitations of pixels.
Let's explore how Nanoprism, the first technology to apply Meta-Photonics to image sensors, was created and how it was implemented in ISOCELL JNP.
Smaller Pixels, More Light
Sensitivity in image sensors is a key factor in realizing clear and vivid images. Pixel technology has evolved over time to capture as much light as possible. Examples include the development from front-side illumination (FSI) to back-side illumination (BSI) and various technologies such as deep trench isolation (DTI).
In particular, technology has evolved in the direction of making pixels smaller and smaller to realize high-resolution images without increasing the size of smartphone camera modules. However, this has gradually reduced the sensitivity of unit pixels and caused image quality degradation due to crosstalk between pixels. As a result, it was hard to avoid the limitation of a sharp decline in image quality in low-light environments.
To solve this problem, Samsung introduced a Front Deep Trench Isolation (FDTI) structure that creates a physical barrier between pixels and also developed ISOCELL 2.0 , which isolates even the color filters on top of the pixels. Furthermore, Samsung considered an approach to innovate the optical structure of the pixel itself, which can utilize even the peripheral light that could not be accepted in the existing structure. Nanoprism was born out of this consideration.
More details on the pixel technology of Samsung can be found at the link below.
Nanoprism: Refracting Light to Collect More
Nanoprism is a new technology first proposed in 2017 based on Meta-Photonics source technology that Samsung Advanced Institute of Technology (SAIT) has accumulated for many years. Unlike meta-lens research, which was active in Meta-Photonics research at the time and minimized light dispersion, it used the reverse idea of maximizing dispersion to separate colors. The Nanoprism is a meta-surface-based prism structure that can perform color separation.
So, what has changed from the existing pixel structure? In the existing microlens-based optics, the microlens and the color filter of the pixel are matched 1:1, so only the light of the color corresponding to the color filter of each pixel can be accepted by the pixel. In other words, there was a physical limit that light could only be received as much as the size of the defined pixel.
However, Nanoprism sets an optimized optical path so that light can be directed to each color-matched pixel by placing a nanoscale structure in the microlens position. Simply put, the amount of light received by each pixel has increased, because light that was lost due to color mismatch can be sent to adjacent pixels using refraction and dispersion of light. Nanoprism allows pixels to receive more light than the existing microlens structure, and it was possible to improve the sensitivity reduction, which was a concern due to the smaller pixels.
Applying Nanoprism to Image Sensors
Commercializing Meta-Photonics technology in image sensors was a challenging task. Securing both customer reliability and technical completeness was vital. To operate properly as a product, not only the structure of Nanoprism had to be implemented, but also dozens of indicators had to be satisfied.
Samsung's relevant teams worked closely together, repeating the design-process-measurement loop, and made the best efforts to secure performance by considering and reflecting various scenarios from the initial design stage and establishing a reliable verification procedure.
As can be inferred from its name Nanoprism, it was especially difficult from process development to mass production because precise and complex nanometer (nm) structures had to be implemented in pixels. In order to bring the new technology to life, special techniques and methods were introduced, including CMP (Chemical Mechanical Polishing) and low-temperature processes for Nanoprism implementation as well as TDMS (Thermal Desorption Mass Spectrometry) for image sensor production.
ISOCELL JNP Enables Brighter and Clearer Images
ISOCELL JNP with Nanoprism has been in mass production this year, and is incorporated in recent smartphones, contributing to an enhanced user experience. Because more light can be received without loss, it is possible to take bright and clear pictures, especially in challenging light conditions. In fact, the ISOCELL JNP with Nanoprism has 25% improved sensitivity compared to the previous ISOCELL JN5 with the same specifications.
Of course, increasing the size of the image sensor can improve the overall performance of the camera, but in mobile, there is a limit to increasing the size of the image sensor indefinitely due to design constraints such as 'camera bump'. Samsung System LSI tried to break through this limitation head-on with Nanoprism. Even in situations where pixels are getting smaller, this technology has improved the sensitivity and color reproduction of each pixel, and applied to ISOCELL JNP.
More details on the product can be found at the link below.
The need for high-resolution image implementation in the mobile market will continue. Accordingly, the trend of pixel miniaturization will continue, and even if pixels become smaller, the development of pixel technology to secure high sensitivity, quantum efficiency, and noise reduction will be required. Nanoprism is a technology to increase sensitivity among these, and Samsung aims to move towards further innovation in a direction that goes beyond the existing physical limitations.
Building on this collaboration, continued cross-functional, cross-team efforts aim to explore new direction for next-generation image sensor technologies.
* All images shown are provided for illustrative purposes only and may not be an exact representation of the product. All images are digitally edited, modified, or enhanced.
* All product specifications reflect internal test results and are subject to variations by user's system configurations. Actual performance may vary depending on use conditions and environment.
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