This same concept has been replicated in smartphone cameras to help them focus on an image through a technology called phase detection auto focus (PDAF).

SK hynix, though, recently unveiled a new technology called the All 4-Coupled (A4C) image sensor that provides a giant leap forward in camera sensor technology, much better than conventional PDAF. In this recent EE Times column [LINK], Tae-hyun (Ted) Kim, head of the CIS ISP at SK hynix, explains how A4C technology works and the benefits it delivers.

Similar to today’s Quad sensors, A4C uses a photodiode to convert light into an electric current and color filters to selectively absorb certain light wavelengths. Unlike Quad sensors, however, the A4C structure has one micro lens on each group of four-color filters of the same color pixels.

Using this unique structure, a subject is determined to be in focus if the different rays of light from the subject converge to one focal point. In other words, the intensity value is the same for the four pixels under one micro lens.

This unique structure and supporting SK hynix technology promises to dramatically improve smartphone cameras with faster and more accurate focus of images. The images captured also have higher-resolution, providing more detail for computer vision applications.

For more on this important technology, click on this link to read the column — SK hynix’s Next-Generation CMOS Image Sensor: All 4-Coupled (A4C) Sensor [LINK]

The post SK hynix’s Next – Generation CMOS Image Sensor: All 4-Coupled (A4C) Sensor first appeared on SK hynix Newsroom.

Picture This

Mobile devices – and their rapidly improving camera capabilities – are a huge part of our everyday lives. With the incredible technology contained in handheld devices today, it’s easier than ever before to capture, record and store imagery of ourselves and the world around us. As common as it might seem to us today, this capability didn’t arrive overnight. It is the result of many years, and decades, of research and development.
And as demand for higher quality images and smaller size devices continues, so does innovation, breakthrough and advancement. Below, we learn more about CMOS image sensor (CIS) technology development and SK hynix’s work with CIS in a contributed piece by Hoon Sang Oh, Fellow of SK hynix’s CIS Business.

Image Quality of CIS and Pixel

Most of the mobile devices we use today, such as cell phones, tablet PCs and laptop computers, are equipped with at least one or more camera sensors. The quality of the images we take on these devices is determined by an electric mechanism in the sensors called “pixel,” a key component which converts light into electric signal.

Among many indicators of the image quality, the most representative one is a definition and measurement procedure called “Image Signal-to-Noise Ratio (SNR)” (Fig. 1). In order to get high image SNR, we need to increase signal term and reduce noise term, which are mostly determined by major pixel performance indices such as full well capacity, sensitivity, pixel dark noise, readout-circuit noise and pixel crosstalk.

Under bright conditions, full well capacity and pixel crosstalk are the major factors in the image SNR, while under dark conditions, many factors, including sensitivity, pixel dark noise, readout-circuit noise and pixel crosstalk, contribute to image SNR. Therefore, technically, it is more difficult to get high image SNR, i.e. better image quality, under dark environment, since we need to control and improve many performance indices of pixel.

Fig. 1. Definition and Measurement procedure of Image SNR

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History of CIS Pixel Evolution

There have been constant needs for higher resolution sensor over the past decade, and continuous efforts to develop smaller pixel. The evolution history of CIS pixel technology is depicted in Fig. 2, where we see how the technical hurdles for pixel size scaling were overcome. Three phases have led the technical innovations for smaller pixel: (1) SENSITIVITY (2) CROSSTALK and (3) QUAD (or TETRA) PIXEL technology.

In the first phase, pixel engineers concentrated on making up for the sensitivity loss inevitably caused by the reduction of pixel size, developing many innovative technologies including on-chip-lens (or micro-lens), deep photodiode with thicker silicon, and backside illumination technology. As the pixel size reached about one micrometer, the second phase, which focused more on crosstalk reduction, began. During this time, novel technologies such as metal grid structure in color filter layer and deep trench isolation process for Si photodiode were developed in order to suppress the optical and electrical crosstalk, respectively.

As pixel size continued to shrink to sub-micrometer domain, a new concept of pixel operation mode based on QUAD or TETRA pixel structure was proposed as a solution to the sensitivity issue of small pixel under low illumination environment. The basic operation principle of the QUAD pixel is illustrated in Fig. 3. It is expected that all the sub-micrometer sized pixels to be developed in near future will also adopt this QUAD pixel scheme.

Fig 2. Evolution of CIS Pixel Technology

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Fig 3. QUAD pixel operation principle

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Image Sensors & SK hynix

SK hynix started its CIS business in 2007 and has produced 8-inch wafer-based image sensor products for more than a decade. With the advent of IoT and 5G-based ICT world, the image sensor market is growing rapidly today, and SK hynix is fostering the CIS business as the next growth engine beyond its memory business in order to meet this soaring demand. After a couple of years of preparation for the 12-inch fab CIS process, SK hynix launched a 12-inch wafer-based 1.0um product in 2019, which adopted its proprietary Black Pearl pixel technology and received good reviews from customers due to the highly competitive pixel performance. Black Pearl boasts improved noise characteristics, implementing clear images with little noise under low illumination conditions.

Looking Ahead

Continuously working to provide top-tier level sensor performance and productivity, SK hynix is committed to taking its efforts to the next level in the coming decade. SK hynix is now expanding its CIS product portfolio spectrum from mid-end to high-end products based on both performance and price competitiveness. Through its investment in the CIS space in 2020 and beyond, the company aims to quickly become one of the world’s leading CIS companies.

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The Golden Era of Multi Cameras Beyond Physical Limitations

One of the most considered specifications when customers purchase a new smartphone is the camera function. New smartphone designs, such as ‘hole-in displays’ and ‘notch-displays’ that maximize the screen size, are emerging as powerful industry trends. Therefore, minimizing the size of camera modules is more important than ever, and to accomplish this, and the size of the image sensor must be decreased along with pixel size.

An image sensor’s performance is defined by the number of image signals it can bring without a defect or noise. Therefore, one of the industry’s most important challenges lies in boosting the number of signals received with the same pixel unit size. As the front screen gets bigger, as many pixels as possible should be stored in the smaller module. However, decreasing the size of pixels to cut down on a smartphone’s camera module size results in poor image quality, due to less light being absorbed. At the same time, it is impossible to enlarge chip size to increase the number of pixels, which is why a technology that goes beyond physical limitations is essential, so that pixel size can be decreased while retaining high-quality camera performance that typically only large pixels can produce.

In this sense, ultra-high-resolution equipment is even more crucial for improving image quality than decreasing the pixel size. Recently, it is common to see smartphones boasting ultra-high-resolution cameras of over 20million pixels at the front, and over 40 million pixels at the back. For instance, Xiaomi is installing an image sensor in their new Mi Mix Alpha 5G smartphone that has 108 million pixels, which was released in September this year. 108 million pixels is the highest level among today’s commercially available smartphone cameras.

As it stands, the minimum pixel size of a mass-produced image sensor is 0.7 to 0.8μm (micrometer), with the maximum number of pixels at 108 million. Image sensor of 0.7μm pixels are expected to be mass-produced more and more from 2020.

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Competition to Secure Cutting-Edge Technologies is Fierce

Technological innovation for even smaller cutting-edge cameras is well underway. High-speed cameras can not only have a great impact on our daily lives, it can also be highly utilized in the ‘Automotive’ sector courtesy of its ability to meticulously measure the fast motion of moving cars. It is said that more than 10 cameras will be equipped to autonomous vehicles over level 4, which will be realized by 2023, and accordingly, demand for image sensors in the electronic device sector is expected to rise rapidly.

Competition in the advanced sensor market is fiercer than ever before. Global smartphone manufacturers are now applying intelligent 3D sensors to their flagship smartphones. As a major strength, 3D sensors can execute orders by understanding the shapes and motions of the human body, such as a person’s face or hand, which allows the smartphone to be controlled without even touching the screen.

Particularly, a Time of Flight (ToF) sensor, which measures distance from the time light from the camera travels to and from an object while simultaneously utilizing stereoscopic recognition – such as distance analysis, is now among the biggest trends in the industry. ToF is a cutting-edge 3D sensor that calculates space information, movement, and a three-dimensional look of an object via comprehensive distance analysis. While the Structured Light (SL) method was applied to the 3D sensor TrueDepth camera found in Apple’s 2017 iPhone X, it certainly had its limitation in terms of its distance calculations inferior to ToF. Currently, most smartphone manufacturers are applying superior ToF technology to their latest models, taking advantage of ToF’s diverse functions that allows highly regarded technologies such as biometric authentication, movement recognition, augmented reality (AR) and virtual reality (VR) to be realized. AR and VR content will benefit greatly from the advanced facial recognition technology, giving users the ability to create the perfect personal avatar or dance with their favorite game characters who can magically appear on their desk when the area is selected via the camera. The technology can even recommend the perfect furniture for any living room by analyzing the room’s three- dimensional structure with 3D CIS cameras.

Furthermore, the development of RGB + Infrared Radiation (IR) sensors that integrate the IR sector for better object recognition regardless of poor lighting, as well as research into vision sensors capable of pinpoint movement detection, is now at full throttle. For example, Dynamic Vision Sensor (DVS) is a super-speed motion sensor that reacts to changes in light intensity, incredibly effective in tracking positional changes. Because it solely captures movement, with faces not recorded, the innovation’s utmost strength for application lies in privacy protection. For this reason, this technology can be used in various sectors including VR, autonomous driving, movement recognition, danger detection, as well as important rescue and surveillance cameras.

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The semiconductor industry’s ultimate goal relates to the successful development of an effective AI sensor. This fast-paced sector aims to create technology that surpasses the human eyes’ capability of reaching an eye- watering 576-million pixels. The industry is now paying special attention to technology that can sense and process the movement of an obstacle or person ahead, even in complete darkness, and that can recognize positional changes and Region of Interest (ROI) in real time for more accurate and reliable autonomous driving. The development of image sensors that precisely measure high-speed movements in environments of limited lighting is assisting groundbreaking studies and research for technical progress, especially in the autonomous driving sector.

In conjunction with industrial trends relating to AI and 5G, the potential of CIS technology and its application in future innovations, such as 3D Vision, fully autonomous driving and Smart Security, is limitless.

The post New Era of CMOS Image Sensors… From Multi Camera to AI first appeared on SK hynix Newsroom.