Thermal imaging camera with linear Pb1−xSnxSe-on-Si infrared sensor array and combined JFET/CMOS read-out electronics

A thermal imaging camera for the 8–12 μm wavelength range is described which employs a new infrared sensor device and read-out principle. A bilinear 2 × 128 element infrared sensor array is fabricated in a narrow gap Pb1−xSnxSe layer grown epitaxially on a Si-substrate. A ≈ 30 Å thick intermediate epitaxial CaF2 buffer layer is used for compatibility reasons. The read-out electronics chips contain, for each sensor, an integrator with a low noise JFET input transistor, correlated multiple sampling, and a sample and hold amplifier. They are wire-bonded to the sensor array and operated at 80–120 K. The JFET input transistors allow to amplify from much lower source impedances (down to <10 kΩ) than with CMOS design without adding significant noise. Therefore, infrared sensors with lower impedances can be used, which allows operation at higher temperature, or to use sensors with longer cut-off wavelengths.