Near-infrared CMOS image sensors for no ambient light

Meanwhile, OmniVision’s R&D team has continued to refine its novel silicon semiconductor architectures and processes to achieve new records in quantum efficiency (QE), with Nyxel 2 now providing a 25% improvement in the invisible 940nm NIR light spectrum and a 17% bump at the barely visible 850nm NIR wavelength.

These sensitivity improvements enable image sensors to see even better and farther under the same amount of light, further extending the image detection range. Nyxel 2-based camera systems also require fewer LED lights, thus reducing overall power consumption and extending battery life. These added benefits make Nyxel 2 a well suited technology for surveillance systems, automotive in-cabin driving monitoring systems and the burgeoning under-display sensors in mobile devices.

“Nyxel 2 technology further extends OmniVision’s leadership in NIR image sensing,” said Lindsay Grant, Senior Vice President of Process Engineering at OmniVision. “Pushing the envelope of NIR performance opens new possibilities for applications that operate in near or total darkness, including more accurate driver-state monitoring, better surveillance capabilities for security systems and new under-display sensing applications for mobile devices.” 

Machine and night vision camera applications rely on NIR technology because NIR light illuminates objects with wavelengths outside the visible spectrum, avoiding any interference with the surrounding environment. Additionally, because the night sky contains more NIR photons than visible photons, greater NIR sensitivity allows for higher-resolution image capture with fewer power-hungry LEDs, which is highly desirable for battery-powered and night vision security camera applications.

Prior to the introduction of Nyxel technology in 2017, other NIR detection approaches fell short of the performance requirements for next-generation mobile and AR/VR products with embedded machine vision applications, as well as automotive and security cameras that require higher NIR sensitivity.

Competing CMOS approaches for NIR image sensing continue to rely solely on thick silicon to improve NIR sensitivity. However, this results in cross-talk and reduces the modulation transfer function (MTF). Attempts to overcome this by introducing deep trench isolation (DTI) often lead to defects that corrupt the dark area of the image. With Nyxel 2, OmniVision has further refined its revolutionary approach to NIR imaging that combines thick-silicon pixel architectures with careful management of wafer surface texture to improve QE, along with extended DTI to retain the MTF levels of the first generation without affecting the sensor’s dark current.

With these refinements, OmniVision’s Nyxel 2 can now achieve 50% QE at 940nm - a 25% improvement over the first generation, as measured using data from a 2.9 micron pixel. At the 850nm NIR wavelength, Nyxel 2 can provide 70% QE, which is not only a 17% improvement over the first generation, but it is now on par with the QE levels of top RGB sensors that operate with visible light. The results of these Nyxel 2 technology improvements are even higher and still unrivaled image quality, greater image detection range, and further reduction in light source requirements for even lower power consumption and extended battery life.

Nyxel 2’s performance improvements provide a range of new possibilities to designers. For surveillance systems, the number of IR LEDs around security camera lenses can be further reduced to save on both cost and power consumption, or the same number can be used to increase the brightness of captures taken in total darkness.

For automotive driver monitoring systems, accuracy can be increased while placing fewer LEDs in harder-to-see places within the cabin. For smartphones, the LEDs can be reduced to aid in the never-ending quest for extended battery life, while squeezing more components into compact form factors that both enable design innovation and reduce BOM costs.

OmniVision’s first image sensors with Nyxel 2 technology are expected to be available during the second half of 2020.