Many night vision systems require cryogenic cooling to filter out background radiation, or “noise,” to create a reliable image. That complicates the design and adds to the cost and the unit’s bulkiness and rigidity.
Researchers at MIT, Harvard, Army Research Laboratory, and University of California Riverside, have developed an advanced device by integrating graphene with silicon microelectromechanical systems (MEMS) to make a flexible, transparent, and low-cost device for the mid-infrared range.
Testing showed it could be used to detect a person’s heat signature at room temperature without cryogenic cooling.
The researchers say that a thermal sensor could be based on a single layer of graphene, which would make it both transparent and flexible. Also, manufacturing could be simplified, which would bring costs down.
Graphene’s unique tunable Seebeck coefficient is leveraged for the demonstration of a graphene-based thermal imaging system. By integrating graphene based photothermo-electric detectors with micromachined silicon nitride membranes, researchers are able to achieve room temperature responsivities on the order of ∼7–9 V/W (at λ = 10.6 μm), with a time constant of ∼23 ms. The large responsivities, due to the combination of thermal isolation and broadband infrared absorption from the underlying SiN membrane, have enabled detection as well as stand-off imaging of an incoherent blackbody target (300–500 K). By comparing the fundamental achievable performance of these graphene-based thermopiles with standard thermocouple materials, they extrapolate that graphene’s high carrier mobility can enable improved performances with respect to two main figures of merit for infrared detectors: detectivity (over 800 million cm Hz1/2 per watt) and noise equivalent temperature difference (less than 100 mK). Furthermore, even average graphene carrier mobility (less than 1000 cm2 V–1 s–1) is still sufficient to detect the emitted thermal radiation from a human target.