Finite element method as applied to the study of gratings embedded in complementary metal-oxide semiconductor image sensors

We present a new formulation of the finite element method (FEM) dedicated to the rigorous solution of Maxwell's equations and adapted to the calculation of the scalar diffracted field in optoelectronic subwavelength periodic structures [for both transverse electric (TE) and transverse magnetic (TM) polarization cases]. The advantage of this method is that its implementation remains independent of the number of layers in the structure, the number of diffractive patterns, the geometry of the diffractive object, and the properties of materials. The spectral response of large test photodiodes that can legitimately be represented in 2-D has been measured on a dedicated optical bench and compared to the theory. The validity of the model as well as the possibility of conceiving in this way simple processible diffractive spectral filters are discussed. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3139291]