Performance Analysis And Research Of Substrate-free Focal Plane Array

Optical read-out uncooled infrared imaging technique has attracted much attention in recent years due to its low cost and high performance. Base on the technique, our group proposed and fabricated the substrate-free focal plane array (FPA) successfully. It not only simplified the production process, but also improved the infrared imaging quality. In this paper, mechanical noise, thermal and thermo-mechanical characteristic about substrate-free FPA is studied.The substrate-free FPA is susceptible to mechanical noise (NETDTM) due to low resonance frequency of monolayer membrane structure, which could lead to the raise of noise equivalent temperature difference (NETD). In order to solve the problem, three kinds of novel structure with enhanced beam are proposed in this paper. Based on finite element analysis and experimental results by using simplified model and laser displacement sensor, the three structures are proved to have a significantly increase of resonance frequency (from 74Hz to 835Hz, 404Hz and 1120Hz) and reduce NETDTM by two orders of magnitude, which consequently carry out the structural optimization of FPA.A simplified model is proposed in this paper, in order to resolve the limitation of computer performance, and get accurate FPA resonance frequency. Meanwhile, the model is validated by experimental result and simulation result, which provide much more convenience for future structural optimization analysis.Through thermal stress analysis, substrate-free FPA is found to have a tremendous advantage, compare to traditional substrate FPA, on heat conversion efficiency and thermo-mechanical response. According to the result, physical model base on the hypothesis of constant temperature substrate is modified, including total thermal conductance and thermo-mechanical response of each microcantilever.For substrate-free FPA, frame thermal conductance is in the same magnitude with beam thermal conductance (10-8 W/K), which is a large decrease comparing to substrate FPA, whose frame thermal conductance is infinite. Due to the large decrease in thermal conductance, frame functions as a'thermal isolation'frame which reduces the total thermal conductance and therefore increases the temperature change. Meanwhile, frame also functions as a'thermal diffusion'frame which certainly results in the temperature pre-change in the ones not absorbing radiation. The linear superposition of the temperature pre-change by the other ones thus will greatly increase the temperature change. Both characteristics will significantly increase the heat conversion efficiency of substrate-free FPA, which can be the twice of substrate FPA.Because of the temperature-variable characteristic of frame, temperature change ratio of frame and absorber can up to 94%, which result in the same level temperature change in bi-material microcantilevers. Therefore, a potential of 33 % improvement in thermo-mechanical response is envisioned...