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 midinfrared absorber structure. The fabricated absorber structure has shown an absorption of more than 95% in the wavelength range of 3.2-5.47 μm. The detector was fabricated with standard cleanroom process techniques and equipment. The serial resistance was measured at about 315 kΩ at room temperature. The photosensitivity of the detector was characterized for a signle wavelength (4.26 µm) and a band of wavelength ranging from 2.5-5.5 µm through two different measurement setups. In the first measurement setup, the photosensitivity was estimated at 57.5 V•mm 2 •W-1 through a MEMS-based infrared radiation source and with an optical band-pass filter of wavelength 4.26µm. The following characterization was performed to characterise 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 (D*) of the fabricated detector were measured to values of 30-92 V•W-1 and 8.0×10 7-2.4×10 8 cm•Hz 1/2 •W-1 , respectively, in the wavelength range of 2.8-5 µm. The time constant was estimated to around 21 ms.

Micromachined Infrared Thermopile Detector Based on a Suspended Film Structure

“…Shen et al [7] designed an umbrella structured absorber embedded in the overhanging beam of the thermocouple by a strut, which achieved a better heat flow path and increased the temperature difference between the hot and cold junction. Ashraf et al [8] improved the performance by integrating SU-8 into the absorber structure of the thermopile detector, resulting in improved absorption rates and enhanced hot end temperatures. In addition, there are many scholars who have achieved performance enhancement of thermopiles through process control.…”

Designing Optically & Utilization of Thermopile Chip with Resonant Cavity Absorber Structure as IR Absorber

“…The porous materials with dendritic and soft structure, like gold-black, can have great absorption at ultra-wide wavelength range and are typically used as the absorber of thermopile chip [12][13][14][15][16][17]. However, these porous materials are generally too fragile and not compatible with CMOS [18,19]. Owing to the interference of light, the resonant cavity absorber structures can also have great absorption at a specific band and are also often used as the absorber of thermopile chips.…”

Design and Fabrication of a Low-Cost Thermopile Infrared Detector

“…Covering the hot end with different types of absorber materials is a common method to improve the performance of thermopiles. Shakeel Ashraf integrated the SU-8 into the absorber structure of the thermopile detector, which leads to an improved absorption rate and improved performance [ 5 ]. Ting-Wei Shen improved thermopile response by a factor of 2.6 by embedding an umbrella-shaped absorber [ 6 ].…”