Integrated infrared spectrometers and spectral image sensors for non-invasive monitoring of biomarkers

Introduction 

Proliferation of wearable devices brought optical sensing technologies directly to customers, which enabled them to monitor their vital signs such as oxygen saturation, blood pressure and pulse, effortlessly and continuously. These technologies collect information (either in transmission or reflection) in the visible to near-infrared (NIR, up to 1 μm wavelength) spectral range where efficient and affordable light sources and photodetectors are available. On the other hand, SWIR light (Short Wave Infra-Red; wavelength range 1-2 μm) can penetrate deeper in the tissue and many relevant molecules (water, proteins, sugars, lipids etc.) have distinct absorption features in SWIR. Hence, extending the operating spectral range to SWIR could greatly expand and enrich the collected information and give consumers deeper insights about their health condition. Unfortunately, commercially available light sources and photodetectors for the SWIR range are too expensive and bulky to be integrated into wearable devices. As an alternative, imec is developing SWIR photodetectors and image sensors based on colloidal quantum dot (CQD) thin-film semiconductors, which have a potential to break the current limitations of SWIR sensors regarding the price, size, and resolution.  CQDs are chemically synthesized nanocrystals with remarkable emissive and absorption properties, and they can be deposited in form of thin films over large areas, enabling scalability not possible with the current SWIR technologies. By pairing CQD-based SWIR emitters with photodetectors, new possibilities for miniaturized and affordable SWIR spectrometers emerge, which can ultimately deliver powerful and real-time monitoring of biomarkers to consumers.