A 320 × 240 pixels quantum well infrared photodetector array for thermal imaging

Infrared pixel detectors sensitive to radiation in the wavelength range 8 to 9 µm have been fabricated and evaluated. The detectors have 320 × 240 pixels and consist of two parts. One is the infrared sensitive part with a quantum well structure based on n-doped AlGaAs/GaAs. The other part is a readout circuit in standard CMOS technology. The two parts are hybridized by a flip-chip technique using indium bumps. Optical coupling into the detectors is performed by using optimized, etched, two-dimensional gratings combined with GaAs substrate thinning down. The thinning removes the problem with thermal mismatch, enhances the absorption and eliminates optical crosstalk between pixels. The intended operating temperature range is 70–73 K, achievable by a miniature Stirling cooler. Excellent wafer uniformities resulting in responsivity uniformities of 3.3% across an array are found, and a temperature resolution NETD (noise equivalent temperature difference) = 20 mK is achieved.