Feature: Sensor technology
Figure 1: QDs are nanoscale semiconductors
Figure 2: QDs are commonly based on lead sulphide
QDs are nanoscale semiconductors that absorb and emit light across the near-infrared and SWIR spectrum. Commonly based on lead sulphide (PbS), they are fabricated with simple wet chemistry, allowing their large-scale production.
Sensor
technology: on the
threshold of a revolution
By Dr Hao Pang, CEO and Founder, Quantum Science
W
e stand on the threshold of a revolution in sensor technology. By the end of the decade, short-wave infrared (SWIR) sensing and imaging will be a common feature in many systems – from automotive, consumer
and medical to industrial automation – significantly enhancing their capabilities. It is expected that the market for SWIR sensing will explode
in just five years, to about $2.9bn from $322m in 2022 – largely thanks to advances in infrared quantum dot (QD) technology.
22 October 2023
www.electronicsworld.co.uk
SWIR sensing alternatives After years of intensive research, QD technology is now ready for commercial use in high-performance SWIR sensing. QDs are a very exciting new technology for the industry
because of the lack of alternatives suitable for widespread adoption. In terms of sensing capability, most other options on the market are missing certain critical functionalities, or face other barriers to their use in consumer applications. Silicon-germanium (SiGe) sensors are cheap but difficult
to fabricate. They are inherently low noise, easily meeting the signal-to-noise ratio required for most SWIR sensing and imaging applications. But, these sensors suffer from limited light detection ranges, peaking at around 1.4µm, which precludes them from use in many SWIR applications. By contrast, indium-gallium-arsenide (InGaAs) sensors
operate within the SWIR region of 0.9-1.7µm, with high quantum efficiency, reliability, low dark current and fast response speed. Extended InGaAs sensors with higher indium arsenide composition can even detect wavelengths to 2.6µm. InGaAs technology is much more mature than SiGe, and
is already used in machine-vision applications, defence and security. However, its primary downside is cost: individual InGaAs units can cost up to $10,000, due in part to the high defect rates during their manufacture. Creating an InGaAs sensor starts with epitaxially growing
the material onto indium phosphide (InP) wafers. These wafers are then diced into chips, before pixels are indium-bonded with silicon readout circuits, through a process known as “flip-chip hybridisation”. This process leads to limited pixel pitch and resolution, as well as being complex and expensive to run. The result is a low-yield product that is highly susceptible to defect formation and is difficult to scale to larger wafer sizes because of the InP fragility. These systems also require significant cooling to achieve the desired image quality, which further increases the size of an already bulky product. All these problems make InGaAs sensors suited only for niche markets, where performance matters more than cost and size.
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