Broadband thermal detector with a plurality of quarter-wave cavities

A thermal detector, configured to absorb electromagnetic radiation in a predefined spectral band, the detector comprising:

• a readout substrate, having:
• a readout circuit;
• and a reflector configured to reflect the electromagnetic radiation;
• and
• an absorbent membrane suspended above the readout substrate, thermally insulated from the readout substrate, having a thermometer transducer electrically connected to the readout circuit, and having:
• a first thin-film absorber, with a total surface area S1, thermally coupled to the thermometer transducer, and configured to absorb the electromagnetic radiation in a spectral sub-band Δλ1 of the spectral band, centered on a wavelength λc1, and is spaced from the reflector by a value h1 equal to αc1/4neq1 so as to form therewith a first quarter-wave cavity C1 for the wavelength λc1, neq1 being a refractive index of the medium associated with the first quarter-wave cavity C1;
• and
• at least one second thin-film absorber, with a total surface area S2, thermally coupled to said thermometer transducer, arranged in the absorbent membrane so as not to be covered by the first absorber, and the second absorber being configured to absorb the electromagnetic radiation in a spectral sub-band Δλ2 of the spectral band, centered on a wavelength λc2, and being spaced from the reflector by a value h2 equal to λc2/4neq2 so as to form therewith a second quarter-wave cavity C2 for the wavelength λc2, neq2 being a refractive index of the medium associated with the second quarter-wave cavity C2, the spectral sub-band Δλ2 being centred on the wavelength λc2 equal to λc1/2 within plus or minus 2 μm,
• the first and second absorbers having total surface areas such that a surface area ratio S2/S1 is comprised between 0.5 and 3.