Micromachined Infrared Thermopile Detectors

Infrared detectors are the key devices in infrared technology, and military requirements greatly drove their development. Infrared thermopile detectors are the detectors without cooling, and possessing other merits like no bias. These made them attracting devices and were put into use in many fields. Since the emergence of Micro-Electro-Mechanical System (MEMS) in 1980's, studies of micromachined infrared thermopile detectors have been carrying on. The research included both single element and array. But the process of commercializing thess detectors was slow because they were difficult to fabricate. Combined with their theory, this thesis focused on the processing of micromachined infrared thermopile detectors.Based on one dimensional steady thermal conduct equation and other thermal theory, the relations of the components of detectors including membrane, absorber, thermocouple and packaging with the properties-esponsivity (Rv), detectivity (D*) and time constant T were established. And optimal design was discussed combined with processing and resulting in some novel discoveries like unequal width of thermocouple and the suitable size of infrared absorber.Novel front etching process experimented and detectors with diagonal cantilever supporting membrane were raised in cantilever series. Integrated devices were obtained and the feasibility of the process was proved. The most troublesome thing of applying the process was that it needed too long the etching time. During the processing, the influence of film stress, step covering and surface tension were discovered. Some suggestions were suggested and implemented in the experiment.The fabrication of detectors based on close membrane supporting structure proved the consistency of current process. Linear and planar arrays were obtained. It was difficult of welding during packaging process. Mo boat and galvanization of Ni were tried to solve such problem. Both attempts gained some good results. The thickness of Au was obviously increased using former idea and self align deposition of Ni was realized in latter method. Galvanization had great potential in the process because of its easiness especially.With respect to the problems of ohm contacting, step covering and device packaging, substituting Al for Au was adopted in infrared thermopile detectors withclose membrane. After solving the difficulty of silicon etching without attacking aluminium, and changing the supporting dielectric membrane to SiOa - SisN^ integrated devices with Al/PolySi thermocouples were gained.A testing system was established by ourselves with respect to micromachined infrared thermopile detectors. Using direct and comparing testing methods, characterization of single element detectors with close membrane were measured. The resistance of the detectors was 200Kohm. In the detectors without infrared absorbing layer, the properties were Rv 15V/W, D* 4.0 X 107cmHzwW1 and T 10-20ms. With infrared absorbing layer, Rv and D* were increased several times than before, and T was increased even greater.