Integration of an interferometric IR absorber into an epoxy membrane based CO₂detector

Abstract

Measurements of carbon dioxide levels in the environment are commonly performed by using non-dispersive infrared technology (NDIR). Thermopile detectors are often used in NDIR systems because of their non-cooling advantages. The infrared absorber has a major influence on the detector responsivity. In this paper, the fabrication of a SU-8 epoxy membrane based Al/Bi thermopile detector and the integration of an interferometric infrared absorber structure of wavelength around 4 µm into the detector is reported. The membrane of thermopile detector has been utilized as a dielectric medium in an interferometric absorption structure. By doing so, a reduction in both thermal conductance and capacitance is achieved. In the fabrication of the thermopile, metal evaporation and lift off process had been used for the deposition of serially interconnected Al/Bi thermocouples. Serial resistance of fabricated thermopile was measured as 220 kΩ. The response of fabricated thermopile detector was measured using a visible to infrared source of radiation flux 3.23 mW mm −2 . The radiation incident on the detector was limited using a band pass filter of wavelength 4.26 µm in front of the detector. A responsivity of 27.86 V mm 2 W −1 at room temperature was achieved using this setup. The fabricated detector was compared to a reference detector with a broad band absorber. From the comparison it was concluded that the integrated interferometric absorber is functioning correctly.

Fabrication and Characterization of a SU-8 Epoxy Membrane-Based Thermopile Detector With an Integrated Multilayered Absorber Structure for the Mid-IR Region

“…Absorption in the structure was calculated by using 5, where, Top = transmittance, Aop = absorption, Rop = reflectance, and reflectance and transmittance coefficients were calculated by using the transfer matrix theory of multilayer structures [12]. The transfer matrix for each layer in the structure is described by (6).…”

“…In theory, this structure has an absorption of 100% at a specific wavelength reported in [10], [11]. The construction of a λ/4 IR absorber structure based on SU-8 epoxy (as a dielectric medium) and its integration into the thermopile detector has been reported in [12], where the absorber structure, which was designed for a wavelength of 4.26 µm, covers 81% of the detector surfacethe surface area of the detector was 4 mm 2 andthe absorber had an area of 3.24 mm 2 . The FTIR measurement showed more than 97% absorption for the structure.…”

A Highly Accurate Method for Measuring Response Time of MEMS Thermopiles

“…MEMS thermopiles can convert infrared radiation into electrical signals and have been widely used in non—contact thermometers [ 1 , 2 ], uncooled infrared cameras [ 3 , 4 ], gas flow sensors [ 5 , 6 , 7 ], heat flow sensors [ 8 , 9 , 10 ], nondispersive infrared sensors [ 11 , 12 , 13 , 14 , 15 ], and vacuum gauges [ 16 , 17 ], etc. The performance of thermopiles can be evaluated by various parameters, including responsivity, detectivity, response time, etc.…”

Characterization of non-dispersive infrared gas detection system for multi gas applications

“…Despite this fact the detection of further gases, for example humidity and hazardous gases and not only CO 2 in indoor gas monitoring [1] or CO 2 and hydrogen sulphide additionally to CH 4 in biogas are interesting [2]. Non dispersive infrared (NDIR) gas measurement systems are widely used because of their high selectivity, sensitivity, simplicity, and long-term stability [3]. These systems are based on the detection of light intensity variation caused by IR absorption of specific molecules.…”