| Infrared (IR) detection technology has been widely used in both military and civilian fields, of which core is IR detector. Thermopile IR detectors based on Seebeck effect are one of the most important IR devices, which has become one of the research hotspots in current infrared technology field as they have following characters:requiring neither cooling systems nor alternative radiation controllers, wide spectrum of infrared radiation response, low cost, and simple output circuit etc. Firstly, through analysis of the development situation of the infrared detectors at home and abroad, the existing problems in structure and fabrication process of the thermopile detectors are proposed. Then the analysis of the effect of structure and material composition on the performances of thermopile detectors is conducted. Based on above analysis, a MEMS thermopile-based IR sensor with high duty cycle is presented and more details are displayed in following paragraphs:(1) The surface area of the conventional thermopile devices based on four-end-beam (FEB) structure cannot be effectively utilized, resulting in a lower duty cycle of the device. In order to solve above problems, the one based on double-end-beam (DEB) structure is proposed. Structural sizes of the DEB based thermopiles may be further scaled down and maintain relatively higher responsivity and detectivity when compared with the FEB based thermopiles.(2) In this paper, the model of theory and analysis of thermopile infrared detector based on thermal-conductive-electrical-isolated (TCEI) structures is built for analyzing the relations between contact heat resistance and performance of the device. High contact thermal resistances would limit the performance of the thermopile sensors. Meanwhile, SiNx material serving as thermal-conductive-electrical-isolated (TCEI) structures, with a relatively large thermal conductivity and a small electrical conductivity, are adopted both under the cold junctions and the hot junctions so as to improve the performance of the detector.(3) The thermopiles proposed in this paper adopt Xenon difluoride (XeF2) gas to release the structures. However, such an isotropic etching step from the front-side would easily lead to excessive release, as a result, the cold junctions and the electrodes might be floated to damage. In order to solve these drawbacks, etching barrier structures are integrated in our device to prevent floating of the cold junctions and the electrodes in case of excessive release.With all these efforts, layout design and flow processing of the thermopile devices are completed. Preliminary measurement results demonstrate that the DLTS-based IR device achieves a responsivity of 1151.15 V/W, a detectivity of 4.15×108 cm Hz1/2/W, and a time constant of 14.46 ms and has higher performance than that of the FEB-based one which has been reported. Besides, in measurements of varied temperatures and vacuum pressures, the thermopile proposed in this work could reach relatively high sensitivities in temperature response and wide response range in vacuum pressure. This indicates that such a device can also function as a temperature sensor and a vacuum sensor. Meanwhile, nanofiber forests with different morphology are fabricated by the plasma repolymerization technology; After that, whether black silicon fabricated by the plasma repolymerization technology can be function as absorber material is also analyzed and discussed. The preparation process of the black silicon has high flexibility, controllability and repeatability, and for the whole thermopile devices can be fully compatible.
|
PDF Full Text Request