We present a method to characterize the temperature dynamics of miniaturized thermal IR sources. The method circumvents the limitations of current IR photodetectors, by relying only on an electrical measurement rather than on optical detection. Thus, it enables the characterization of the light emission of IR sources over their full operation frequency range. Moreover, we develop a model of thermal IR sources allowing simulations of their thermal and electrical behavior. By combining measurements and modeling, we achieve a comprehensive characterization of a Pt nanowire IR source: the reference resistance R0 = 17.7Ω, the TCR α = 2.0 × 10-3 K-1, the thermal mass C = 2.7 × 10-14 J/K, and the thermal conductance G = 1.3 × 10-6 W/K. The thermal time constant could not be measured, because of the frequency limitation of our setup. However, the operation of the source has been tested and proved to function up to 1 MHz, indicating that the thermal time constant of the source is smaller than 1 μs.
Electronic properties and sensitivity of metallic bolometers were studied as a function of thin-film thickness in the active area. Our devices are made of platinum and chromium, with an active area of lateral dimensions 1 μm by 300 nm. The thickness of the metallic film was varied between 3.3 nm and 82.3 nm. Temperature coefficient of resistance and resisitvity were characterized, and are respectively increasing and decreasing with the thickness increasing. A threshold thickness of 40 nm is revealed where both parameters reach a constant value. Responsivity and detectivity were evaluated, unveiling the importance of 1/f noise. Responsivity reaches a maximum value of 2×105 V.W-1 for bolometers with a 7.5 nm thickness. Detectivity keeps a constant value of 1×108 cmHz1/2/W for samples thicker than 40 nm, before dropping considerably as the thickness is decreased. This loss in detectivity is believed to be due to the prominence of 1/f noise in such thin samples.
We present novel nanoscale bolometers made of lithographically defined platinum wires. The cores of our structures are
narrow wires with fixed width of 300 nm and length ranging from 300 nm to 17 μm. Some are significantly smaller in
size than the wavelengths they are exposed to from a 1200 K blackbody source. The response of the wire's resistance to
the external radiation reflects its temperature and can be monitored in real-time. Previously, we have reported a steep rise
in responsivity and detectivity with decreasing wire length under such infrared exposure, for a constant Joule power
dissipation in the wire (drive power). In this work, we aim to enhance the performance of the bolometers by changing
physical and driving parameters, i.e. the insulating layer thickness or the external bias. We find that after such
optimization, structures can reach a responsivity R of 4.5x105 V/W and a detectivity D* of 2.3x1010 cmHz1/2/W. With a
reduced size and a high performance, these devices could improve the infrared sensors technology.
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