Combined use of thermal analysis techniques can realize complementarity of different characterization methods. Comprehensive thermal analysis with both thermogravimetric analysis and differential thermal analysis (TG/DTA) can measure not only mass change of a sample but also its temperature change during programmed heating-induced reaction or phase transition processes, thereby obtaining multiaspect thermal information of the material such as dehydration, structural decomposition, phase change and thermal stability. This study proposes and develops a MEMS chip-based TG/DTA microsystem that integrates both programmed heating and detecting elements into a TG chip and a DTA chip to enable the microinstrument performing TG/DTA joint characterization under microscope observation. The TG chip contains a self-heating resonant microcantilever to measure heating-induced mass change of a sample and the DTA chip is with a microheater and a temperature-detecting thermopile integrated on a suspended thermal-insulating diaphragm. Only nanogram and microgram-level samples are needed for the TG and DTA chips, thereby achieving safe measurement to energetic materials such as strong oxidants. The chip-based microinstrument surpasses the state-of-the-art commercial TG/DTA instruments that have, in the long term, suffered from large sample-amount (milligram level) requirements and have been unable to measure energetic materials. Compared with commercial instruments, the chip-based microinstrument is advantageous given its more accurate analysis, much higher heating rate, much smaller instrument volume and much lower power consumption, etc. The microinstrument has been fabricated by using wafer-level MEMS techniques. Testing results show that the mass-detection sensitivity of the TG-chip is as high as 0.45 Hz/pg in air and the temperature sensitivity of the DTA chip achieves 2.9 mV/K under the high heating rate of 25 °C/s. The strong oxidant of KMnO₄ is analyzed with the TG/DTA joint characterization under microscopic observation. At the same time as microscope observation of the thermal decomposition phenomena, two-step thermal decomposition process of KMnO₄ is identified and the thermal decomposition temperatures are obtained. The TG/DTA microinstrument is promising to be applied for study of various materials.

This article presents a 96 μm x 106 μm sized single-crystalline silicon (SC-Si) /Au thermopile infrared (IR) detector, with the thermopile and IR absorber located at different layers of a double-deck micromechanical structure for improving detectivity. In order to enhance IR-heat absorption within such a tiny device size, an umbrella-shaped SiN IR absorbing membrane instead of traditional plane IR-absorbing film occupies the whole area of the top layer structure. The umbrella-shaped IR absorber is suspended on top of the IR-detecting thermopile layer, with a central umbrella-stick to support the suspending and conducting the absorbed IR-heat to the bottom thermopile layer. The bottom thermopile layer consists of six pairs of spiral-shaped SC-Si/Au thermocouples that feature several times higher Seebeck coefficient compared to the traditional polysilicon/metal thermocouples. By combining surface-micromachining technique with a specific bulk-micromachining process performed in (111) silicon wafer, the double-deck structured IR-detector is successfully fabricated only from the front side of a single (111) silicon wafer for IC-foundry compatible low-cost manufacturing. Testing results show that this device of about 100-μm scale achieves an ultrahigh IR detectivity of 1.01 x 10⁸ cm·Hz $^{{1/2}}·$ W⁻¹, which is two times improvement compared to the recently reported thermopile IR detectors, though the counterparts had larger device area. Featuring tiny size and batch fabrication capability, the proposed high-performance IR-detector is promising in both single-point detection and multipixel arrayed temperature imaging applications.

This paper reports an ultra-small pixel (100 µm × 100 µm) infrared (IR) thermopile sensing array with double-level suspended films structure fabricated by a front-side Post-CMOS compatible process. Benefit from the optimized heat dissipation control, the ultra-small thermopile pixel achieves the normalized detectivity of 2.1 × 10 ⁷ cm·Hz ^1/2 ·W ⁻¹ and the responsivity of 52 V/W in air. Owing to the design of the double-level structure, the device obtains a high fill factor of 0.94. Test results show that the responsivity deviation of each pixel is less than ± 6.6 % and the response time is 1.4 ms. The designed thermopile array indicates a high potential for low-cost and high-resolution IR focal-plane array (IRFPA).