Abstract
We investigate the generation of electrical signals by suspended thermoelectrically coupled nanoantennas (TECNAs) above a quasi-spherical reflector cavity in response to rapidly changing long-wave infrared radiation. These sensors use a resonant nanoantenna to couple the IR energy to a nanoscale thermocouple. They are positioned over a cavity, etched into the Si substrate, that provides thermal isolation and is designed as an optical element to focus the IR radiation to the antenna. We study the frequency-dependent response of such TECNAs to amplitude-modulated 10.6 μm IR signals. We experimentally demonstrate response times on the order of 3 μs, and a signal bandwidth of about 300 kHz. The observed electrical response is in excellent correlation with finite element method simulations based on the thermal properties of nanostructures. Both experiments and simulations show a key trade-off between sensitivity and response time for such structures and provide solutions for specific target applications.
Highlights
We investigate the generation of electrical signals by suspended thermoelectrically coupled nanoantennas (TECNAs) above a quasi-spherical reflector cavity in response to rapidly changing long-wave infrared radiation
We have previously shown that these combined effects result in about a 100 times enhancement of the thermal response compared to TECNAs on a SiO2/Si substrate[11,12], where the nanoantenna and the hot junction are in direct contact with the substrate
We have shown that suspended thermoelectrically coupled nanoantennas and nanoantenna thermopiles are capable of fast response to rapidly changing IR signals with a response time < 3 μs despite the conventional wisdom that thermal based IR sensors are slow and bulky
Summary
Design and fabrication Antenna designThe antenna is the receiving element that converts the optical energy through Joule heating by the radiation-induced antenna currents of the nanoantenna material. Maximum heating occurs when the antenna is at resonance, i.e., its length matches the effective wavelength of the incident radiation. For IR radiation at 10.6 μm, the resonant antenna length of a suspended IR antenna is 3.5 μm, as determined by COMSOL simulations. This provides an effective antenna aperture area of Pabs/E0 = 5.13 μm[2] which is slightly less than that for an ideal isotropic antenna (λ2/4π). When the cavity is included in the simulation the effective aperture rises to 38.5 μm[2]. This corresponds to an aperture efficiency of 22.6%. This can be improved by increasing the reflectivity of the cavity
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