Reliable Fire Detection Systems with Low-cost SiC-based Solar-blind UV Photodiodes

New and improved low-cost flame monitoring systems are needed that can quickly and reliably detect a fast-spreading fire. The most reliable fire monitors today are based on solar-blind UV detection systms with Geiger counter-type tubes that are costly, fragile, and require high voltage. Spire has recently demonstrated feasibility of hydrogen flame monitors based on silicon-on-insulator (SOI) UV photodiodes. In the SOI structure, active layer thickness is chosen so that UV is detected within the device, while longer wavelengths are absorbed in the electrically isolated substrate. Spire proposes new and improved fire monitors based an low-cost filterless solar-blind UV photodiodes built on novel SiC-On-Insulator (SICOI) structure. We will investigate detectors with superior UV selectivity based on SiCOI structures capable of operating at elevated temperatures (up to 500¿C) . Cubic SiC has a bandgap of about 2.2 eV, twice that of Si, which makes it ideal for absorbing UV photons while transmitting much of the visible wavelengths. Spire recently demonstrated that crystalline Sic layers can be grown epitaxially by high temperature carbonization of ultrathin Si layers on Sol wafers to form SiCOI structures. In Phase I, we plan to fabricate PN junction UV photodiodes on SiCOI substrates and compare their performance to similar devices fabricated on bulk Si, bulk SiC and SOI wafers. Particular emphasis will be placed on the selective optical responsivity in the 200 to 400 nm wavelength range (critical for flame detection) as a function of temperature. In Phase II, we will optimize device process parameters and prototype fire monitors integrated with an audible warning system will be tested and delivered. Solar-blind UV detectors and image sensors have a wide range of military and commercial applications. These devices could be used for detecting fires in munitions depots, aircraft engines and the UV signature from rocket plumes or residual cannon-bore fire. Other applications of these photodiodes include, atomospheric ozone density measurements, flame monitoring of residential land industrial boilers and furnaces, and UV imaging and dosimetry in medical applications