Range infrared detector issues in the SWAPc and pitch reduction context

Abstract

Joining their technological skills and strengths, SOFRADIR and ULIS merged in a new High Tech Company named LYNRED. This new company will be oriented towards excellence in II-VI, III-V and bolometers technologies, covering all Society’s needs in term of infrared detection. Nowadays one noticeable trend in infrared market sensors is the optimization of two key metrics: sensor range and image quality. These metrics depend mostly on three criteria: modulation transfer function (MTF), Noise Equivalent Temperature Difference (NETD) and Residual Fixed Pattern Noise (RFPN). MTF improvement was previously achieved by reducing pixel pitch to 30μm [1] to 10μm [2]. NETD and RFPN were improving thanks to a better material quality. The improvement of NETD and RFPN can also be used to increase the operating temperature. The Modulation Transfer Function performance is directly linked to the ability to distinguish objects details and sharpness of the imaging system. MTF value determines, with NETD and RFPN, the system range via the so -called Minimum Resolvable Temperature Range (MRTD). We need to keep in mind that not only MTF has to be optimized but also MRTD, which is very challenging in the context of High Operating Temperature (HOT) and pixel pitch reduction. There are many challenges to be addressed for future small pitch, large format and HOT+ (> 160K) detectors. Electrical and optical crosstalks are one of the prime concerns for detectors with sub-10μm pixel pitch. We will compare several existing materials and their optical and electronic transport properties, elementary sensors designs, such as III-V superlattice, II-VI materials, MESA, loophole, planar and depleted photodiodes. This discussion will be based on measurements on improved HgCdTe 10μm and 7.5μm pitch technology completed by simulation using Finite Element Modelization (FEM) coupled with Finite Difference Time Domain (FDTD).