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22 Jan 2020
Adoption of germanium-on-silicon light absorption layer extends sensing range to 1550 nm for higher performance.
The giant image sensor vendor OmniVision is collaborating with the Taiwan-based 3D imaging specialist Artilux on new devices that promise improved performance in the near-infrared spectrum.
Fabricated with a germanium-on-silicon (GeSi) light absorption layer, the Artilux sensors are able to detect out to 1550 nm in the near-infrared spectrum - meaning that 3D sensing solutions can take advantage of eye safety regulations that permit the use of more powerful light sources than at shorter wavelengths.
The two companies say that the main objective of the new collaboration is to combine that GeSi technology with OmniVision's more conventional CMOS approach for applications in mobile phones and beyond.
“The new product offerings will not only cover the mainstream light sensing spectrum from visible light to 850nm/940nm, but will further extend to 1350nm/1550nm, which can provide a superior outdoor experience and improved eye safety for multiple growing digital imaging market segments,” announced the pair.
ToF depth sensing
Zhubei City-headquartered Artilux unveiled the technology in the form of its Explore Series product at the Consumer Electronics Show (CES) in Las Vegas earlier this month, describing it as “the world's first wide-spectrum 3D time-of-flight (ToF) sensor based on GeSi photonic innovation”.
Operating at the longer near-infared wavelengths is regarded as being ten times safer than at the conventional 940 nm, while also offering better sensing accuracy and performance under sunlight.
However, the usual trade-off is that laser emitters at these longer wavelengths are much more difficult to produce. They must be fabricated using indium phosphide (InP) semiconductor material, rather than the more developed gallium arsenide (GaAs) - and are therefore significantly more expensive to make.
At CES, Artilux demonstrated a color depth-sensing camera for logistics applications and robot vision, as well as a 3D camera able to operate at the longer wavelength.
“The sensor is projected to enter mass production in Q1 2020 and targets applications that will benefit from the improved 3D sensing performance such as mobile devices, automotive lidar, and machine vision,” announced the company.
Eye safety
Artilux also referenced recent work by its internal research team concluding that when the GeSi pixel is operated at the longer near-IR wavelength, it is “substantially safer” than at 940 nm, thus allowing the use of a much higher laser power but still in compliance with laser safety regulations.
The company claims that means ten times more laser power can be deployed safely at 1200-1400 nm than at 940 nm.
Its research team, whose devices were produced by foundry partner Taiwan Semiconductor Manufacturing Company (TSMC), added: “The system performance comparison between a silicon pixel and a GeSi pixel at 940 nm indicates that the GeSi features lower depth errors compared to the silicon pixel in both indoor and outdoor scenarios.”
By adopting both the longer wavelength and new algorithms, Artilux claims to have “redefined” the performance of 3D sensing, and overcome an industry bottleneck with an approach it believes will fundamentally transform 3D sensing technology and applications.
Coupling the GeSi layer with a CMOS process, the company said last summer that the technology delivered a quantum efficiency of 70 per cent at 940 nm, and of 50 per cent at 1550 nm.
That is combined with a modulation frequency of 300 MHz or more, with Artilux insisting that the approach is ready for mass production at an affordable price.
According to a LinkedIn profile, Artilux co-founder and CEO Erik Chen previously worked at both TSMC and Intel, and completed a PhD at Stanford University before setting up Artilux in 2014.
California-headquartered OmniVision is one of the world's largest providers of cameras and sensor devices used in consumer electronics, automotive, medical, and various other applications. In early 2016, the company was acquired by a consortium of Chinese investors led by Hua Capital Management.
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