Low-dark-current 640×512 Type-II superlattice long-wave infrared focal plane array enabled by photolithographic vacuum contact pressure optimization

This paper systematically investigates the effect of vacuum contact pressure during contact photolithography on the mesa morphology and device performance of long-wave infrared (LWIR) focal plane arrays (FPAs). By comparing lithography fidelity, mesa sidewall morphology, and dark current, we demonstrate that increasing the vacuum contact pressure can effectively suppress Fresnel diffraction, yielding a smoother lithography pattern edge by forming a more uniform, smooth inverted-trapezoid mesa sidewall during etching. This optimization of the mesa morphology significantly reduces the dark current induced by dangling bonds, crystal lattice defects, and polymer residues. Experimental results show that the FPAs fabricated at 62 kPa exhibit a dark current one order of magnitude lower than that fabricated at 53 kPa, along with a 50-fold reduction in standard deviation. The bad pixel rate decreases from 15.5% to 0.6%, while the noise equivalent temperature difference (NETD) improved to 17 mK. Compared with recent similar studies, this work achieved a state-of-the-art NETD of 17 mK and a low dark current density of 5.424 × 10^-5 A/cm², demonstrating that tuning the vacuum contact pressure is an effective approach to enhancing LWIR FPA imaging performance.