Design and fabrication of resonator-QWIP for SF6 gas sensor application

The infrared absorption of SF6 gas is of narrowband and peaks at 10.6 mu m. This narrow band absorption posts a stringent requirement on the corresponding sensors as they need to collect enough signal from this limited spectral range to maintain a high sensitivity. Resonator-Quantum Well Infrared Photo detectors (R-QWIPs) are the next generation of QWIP detectors that use resonances to increase the quantum efficiency (QE) for more efficient signal collection. Since the resonant approach is applicable to narrowband as well as broadband, it is particularly suitable for this application. We designed and fabricated R-QWIPs for SF6 gas detection. To achieve the expected performance, the detector geometry must be produced according to precise specifications. In particular, the height of the diffractive elements (DE) and the thickness of the active resonator must be uniform, and accurately realized to within 0.05 mu m. additionally, the substrates of the detectors must be removed totally to prevent the escape of unabsorbed light in the detectors. To achieve these specifications, two optimized inductively coupled plasma (ICP) etching processes are developed. Due to submicron detector feature sizes and overlay tolerance, we use an ASML stepper instead of a contact mask aligner to pattern wafers. Using these etching techniques and tool, we have fabricated FPAs with 30 mu m pixel pitch and 320x256 format. The initial test results showed promising results.