Optical sensitivity analysis of deformed mirrors for microcantilever array IR imaging

Abstract

Optical sensitivity is a major issue to improve the sensor responsivity and the spatial resolution of uncooled optomechanical focal plane arrays (FPA). The optical sensitivity is closely related to the mirror length and the undesired mirror deformation induced from the imbalanced residual stresses in different layers. In this paper, the influences of mirror length and deformation on the optical sensitivity are discussed by Fourier Optics. Theoretical analysis and experiments demonstrate that the optical sensitivity is seriously degraded by undesired mirror deformation, and that there exists an optimal mirror length which makes the optical sensitivity achieve its maximum under a certain mirror deformation. Based on the results, an optimized mirror configuration is presented to increase the optical sensitivity of substrate-free bi-material microcantilever array (SFBMA).

A holistic approach performance analysis of substrate-free focal plane array

“…Optical readout uncooled infrared imaging Figure 1(a) shows the principle layout of an optical readout uncooled infrared imaging system. 14,17 The key component of the system is the substrate-free bi-material microcantilever FPA. The micro-cantilever array structure of a recently fabricated FPA with 50 lm unit size is shown in the inset of Figure 1 Table I.…”

“…14 When the unit size is 60 lm, the calculated response is one order of magnitude lower than the experimental one. 14 The reason is that the supporting frame of the substrate-free FPA is much thinner, as compared with a traditional substrate FPA. As a result, the thermal capacity and the thermal conductivity of the FPA is greatly decreased, the frame becomes temperature-variable, which in turns enhances the value of H and S T and thus significantly improves the FPA temperature gray response.…”

“…The average value, 46.0 gray/K, can be regarded as the system temperature gray response and the system noise is 8 gray (as measured by the experiment described in Ref. 14). The NETD for the system is estimated to be about 170 mK.…”

“…From such FPAs with unit sizes of 200 lm, 120 lm, and 60 lm, one obtains an experimental response with noise equivalent temperature difference (NETD) of 320 mK. [12][13][14] Using the temperature-constant substrate FPA theoretical model, the calculated temperature gray responses of the substrate-free FPAs with unit sizes of 200 lm, 120 lm, and 60 lm are compared with experimental results. The results show that the calculated responses match the experiments when unit sizes are 200 lm and 120 lm, but the calculated response is only one-tenth of the experimental results when the unit size is decreased to 60 lm.…”

Research on bi-material MEMS detector arrays for THz imaging

“…One approach to overcome these difficulties is to incorporate MEMS-based bi-material detectors, which were successfully demonstrated in infrared imaging 6,7 . The structure of one pixel of the FPA is presented in figure 1 The FPA composed of bi-material (SiNx/Au) micro-cantilever pixels absorbs the THz radiation, resulting in the temperature increase of each pixel.…”