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

Abstract

This paper reports on the fabrication and characterization of a thermopile detector with an integrated mid-infrared absorber structure. The fabricated absorber structure has shown an absorption of more than 95% in the wavelength range of 3.2–5.47 ${\mu }\text{m}$ . The detector was fabricated with standard cleanroom process techniques and equipments. The serial resistance was measured at about 315 $\text{k}{\Omega }$ at room temperature. The photosensitivity of the detector was characterized for a signal wavelength (4.26 ${\mu }\text{m}$ ) and a band of wavelength ranging from 2.5–5.5 ${\mu }\text{m}$ through two different measurement setups. In the first measurement setup, the photosensitivity was estimated at 57.5 $\textrm {V}\cdot \textrm {mm}^{ {2}}\cdot {W}^{-1}$ through a MEMS-based infrared radiation source and with an optical band-pass filter of wavelength 4.26 ${\mu }\text{m}$ . The following characterization was performed to characterize the photosensitivity of the detector in a broader wavelength range. This measurement was taken using a monochromator setup utilizing a reference photodetector for calculations of the optical power of the infrared source. The photosensitivity and the specific detectivity ( $\text{D}^{\ast }$ ) of the fabricated detector were measured to values of 30–92 $\textrm {V}\cdot \textrm {W}^{-1}$ and $8.0\times 10^{7}-2.4\times 10^{ {8}}\,\,\textrm {cm}\cdot \textrm {Hz}^{1/2}\cdot \textrm {W}^{-1}$ , respectively, in the wavelength range of 2.8–5 ${\mu }\text{m}$ . The time constant was estimated to around 21 ms.