In a recent progress update NASA has revealed the development of its Complementary Metal-Oxide-Semiconductor (CMOS) image sensors. These single-photon imaging devices will be crucial for upcoming missions such as the Habitable Worlds Observatory (HWO).
The sensors are engineered to detect individual photons with extraordinary efficiency while enduring the punishing conditions of space, including high-energy radiation. Their ability to operate with minimal noise makes them vital for future space telescopes that aim to capture faint atmospheric signals or biosignatures such as oxygen, methane, or carbon dioxide from exoplanets orbiting faraway stars.
Detecting these biosignatures depends on measuring incredibly weak optical signals, often just a few photons arriving from a distant planet. Conventional imaging detectors struggle under these conditions, as read noise, dark current, and radiation damage can overwhelm the signal.
Single-photon CMOS technology is designed to overcome these problems by incorporating a high-gain floating diffusion sense node. These sensors can register individual photons and convert them into measurable signals, maintaining high precision across the broad temperature ranges encountered in space.
The Current Study
To refine these detectors, NASA researchers combined detailed simulations with practical prototyping. Using Technology Computer-Aided Design (TCAD), they modelled the optical and electrical behavior of different CMOS architectures, comparing semiconductor materials such as silicon and mercury cadmium telluride (HgCdTe).
These models were particularly important for evaluating sensitivity in the near-infrared (NIR) range, where many biosignature molecules leave their spectral fingerprints.
After modelling, the team developed prototypes with an emphasis on low capacitance and high gain at the sense node, which are key design choices for resolving single photoelectrons. In the lab, engineers tested their performance across multiple metrics: dark current, quantum efficiency, and read noise, both before and after controlled radiation exposure.
To simulate the thermal environment of space, the detectors were mounted in a vacuum Dewar with precise temperature control, including colder conditions than those typically tested in past designs.
Radiation testing was central to the study. The sensors were exposed to protons and gamma rays at intensities that mimic years of spaceflight. Researchers tracked how performance degraded under irradiation, focusing on rising noise and dark current. They also trialed new readout strategies to counter these effects. One promising method involved ramping signals over time and segmenting data acquisition, which allowed cosmic ray artifacts to be identified and removed, and preserved the integrity of faint astronomical measurements.
Finally, to validate performance outside the lab, prototypes were mounted on telescopes at ground-based observatories. Observing star fields, nebulae, and even passing satellites tested their resilience under real-world conditions, including background light and atmospheric noise.
Results and Discussion
The findings confirm that the sensors can reliably detect single photons in the near-infrared, aligning closely with predictions from the simulation models. Quantum efficiency was high, with the devices converting faint photon fluxes into usable electrical signals suitable for astronomical observations.
Even after irradiation, the sensors retained functionality sufficient for space missions. Performance degradation was modest, and the advanced readout modes successfully suppressed cosmic ray artifacts and noise. Dark current remained exceptionally low, measured at just one electron every 30 minutes at 250 K. This exceptional performance makes these devices particularly well-suited for detecting biosignatures, where every photon counts.
Mechanical and thermal testing confirmed that the sensors could operate effectively across a wide range of temperatures and under radiation exposure comparable to long-duration missions. Real-sky trials revealed their practical capability, showing high sensitivity, accurate photometry, and resilience to environmental challenges.
The study also highlighted ongoing challenges. Extending efficient operation into the mid- and far-infrared ranges will be essential for fully characterizing exoplanet atmospheres, as will improving radiation hardness to ensure longevity in orbit. Continued refinement of materials, sensor architecture, and readout strategies will be required before deployment on flagship missions.
Conclusion
The development of SPSCMOS sensors represents a major step toward equipping space telescopes with the sensitivity needed to probe exoplanet atmospheres for traces of life. With their ability to register single photons, operate at low noise levels, and withstand radiation damage, these devices are well on track for integration into future missions such as the Habitable Worlds Observatory.
By combining modelling, laboratory testing, and in-sky validation, NASA researchers are laying the groundwork for detectors that could help scientists answer a long-pondered question. Are we alone in the universe?
Reference
Press Release. NASA. Advancing Single-Photon Sensing Image Sensors to Enable the Search for Life Beyond Earth. Accessed on 4th September 2025. https://science.nasa.gov/directorates/stmd/advancing-single-photon-sensing-image-sensors-to-enable-the-search-for-life-beyond-earth/