16 February 2010 Development of micro-incandescent light sources on silicon substrate
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In this work we report one simple fabrication process to build incandescent microlamps over silicon microtips. By taking advantage of the underetch observed when the Si substrate is anisotropically etched in KOH solutions, specific silicon microtips are created which serve as mechanical supports for the incandescent light sources. A thin film of chrome is deposited by sputtering technique above the microtip and defined by photolitography in order to create an electrical resistance. Consequently, the electrical energy transformed in heat is concentrated in a small spot achieving temperatures high enough to produce incandescent light similar to a blackbody spectrum. To reduce the heat loss caused by the high thermal conductivity of silicon, a layer of silicon dioxide (SiO2) placed between substrate and metal was necessary to avoid the use of large electrical currents to generate the incandescence in the light source. A SiO2 film is also used as a protection layer against moisture and specially oxygen, since at high temperatures chrome can easily oxidize losing its electrical conductivity. As the microtips are very tall compared to photoresist thickness, the lift-off process was needed in order to guarantee that the top of the microtip would be covered by chrome. The results showed that it is possible to produce light in all visible spectrum by applying electrical power higher than 4 W.
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A. H. Gollub, A. H. Gollub, D. O. Carvalho, D. O. Carvalho, G. Rehder, G. Rehder, M. I. Alayo, M. I. Alayo, } "Development of micro-incandescent light sources on silicon substrate", Proc. SPIE 7590, Micromachining and Microfabrication Process Technology XV, 75900E (16 February 2010); doi: 10.1117/12.842432; https://doi.org/10.1117/12.842432

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