Shortwave infrared (SWIR) light is an invisible yet powerful tool that has the potential to revolutionize various industries, including robotics, automotive, and consumer electronics. It offers reliability, function, and performance even in adverse conditions such as bright sunlight, fog, haze, and smoke. The use of SWIR-sensitive image sensors can provide eye-safe illumination and enable molecular imaging to detect material properties. However, the integration of SWIR technology has faced challenges due to the presence of heavy metals in quantum dots. In a recent study published in Nature Photonics, researchers at ICFO have made a breakthrough by successfully developing non-toxic, high-performance SWIR image sensors using colloidal quantum dots (CQDs). This article explores the implications of this research and its potential impact on high-volume markets.
Traditional SWIR image sensors use quantum dots that contain heavy metals like lead or mercury. These materials pose a risk to human health and the environment, leading to strict regulations set by the Restriction of Hazardous Substances (RoHS) directive. The study conducted by ICFO researchers aimed to address this challenge and develop a technology platform that is compliant with RoHS standards.
During their exploration, the researchers stumbled upon silver telluride (Ag2Te) quantum dots as a by-product of their research on silver bismuth telluride nanocrystals. They discovered that these non-toxic quantum dots exhibited quantum-confined absorption similar to their heavy-metal counterparts. This finding sparked their interest in developing a method to synthesize phosphine-free versions of silver telluride quantum dots, as phosphine had a negative impact on the optoelectronic properties of the dots.
The team successfully synthesized phosphine-free silver telluride quantum dots using different phosphine-free complexes. This led to the production of quantum dots with well-controlled size distribution and excitonic peaks spanning a broad range of the spectrum, including distinct excitonic peaks over 1,500nm. These quantum dots demonstrated remarkable performance, making them a promising material for SWIR photodetectors.
To integrate the phosphine-free quantum dots into photodetectors, the researchers faced the challenge of reverting the device setup. They resolved this issue by incorporating a buffer layer, resulting in a significant improvement in the photodetector performance. The SWIR photodiode achieved a spectral range from 350nm to 1,600nm, a linear dynamic range exceeding 118 dB, and a room temperature detectivity of the order 10^12 Jones. These performance metrics were on par with heavy-metal-containing photodiodes.
After successfully developing the non-toxic quantum dot photodetector, the researchers collaborated with Qurv, an ICFO spin-off, to create a proof-of-concept SWIR image sensor. The team integrated the photodiode with a CMOS-based read-out integrated circuit (ROIC) focal plane array (FPA), resulting in the first non-toxic, room temperature-operating SWIR quantum dot image sensor. The sensor demonstrated its capabilities by capturing images of transmission through silicon wafers and visualizing the content of opaque plastic bottles under SWIR light.
The development of a non-toxic, high-performance SWIR image sensor opens up a world of possibilities for various industries. Consumer electronics can leverage SWIR technology for improved vision systems, enabling safe driving under adverse weather conditions. The eye-safe window provided by SWIR light also allows for long-range light detection and ranging (LiDAR), three-dimensional imaging in automotive, augmented reality, and virtual reality applications. The potential of SWIR technology is immense, and the use of non-toxic quantum dots paves the way for its widespread adoption in high-volume markets.
The researchers are now focused on further enhancing the performance of photodiodes by engineering the stack of layers in the photodetector device. Additionally, they aim to explore new surface chemistries for the non-toxic quantum dots, improving their performance, thermal stability, and environmental compatibility. By addressing these challenges, the team aims to bring SWIR image sensors using non-toxic quantum dots to the market, effectively revolutionizing various industries that rely on high-performance computer vision applications.
The successful development of non-toxic quantum dot-based SWIR image sensors represents a significant milestone in the field of computer vision. The use of colloidal quantum dots offers a promising solution to overcome the limitations posed by heavy metals in SWIR technology. With the potential for high-volume compatibility and compliance with RoHS regulations, these non-toxic quantum dots have the power to unlock the full potential of SWIR technology in robotics, automotive, and consumer electronics markets. As researchers continue to innovate and refine the technology, we can expect to witness an exciting wave of advancements in SWIR applications in the near future.
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