Electrical and optical characteristics of vacuum-sealed polysilicon microlamps

A silicon-filament vacuum-sealed incandescent light source has been fabricated using IC technology and subsurface micromachining. The incandescent source consists of a heavily doped p⁺ polysilicon filament coated with silicon nitride and enclosed in a vacuum-sealed (≈80-mT) cavity in the silicon-chip surface. The filament is formed beneath the surface and later released using sacrificial etching to obtain a microstructure that is protected from the external environment. The filament is electrically heated to reach incandescence at a temperature near 1400 K. The power required to achieve this temperature (for a filament 510×5×1 μm) is 5 mW. The emitted optical power is 250 μW, and the peak in the spectrum distribution is near 2.5 μm. The radiation approximately follows Lambert´s cosine law. The subsurface micromachining technique used to produce the evacuated cavity has applications in other micromechanical devices