Thermal system model and pyroelectric-thermal characterization method for infrared microsensor.

摘要

Pyroelectric infrared detectors are low-cost alternatives to conventional semiconductor-based infrared imaging systems. Their performance (responsivity) is strongly dependent on the thermal design of the system and the electrical and thermal properties of the pyroelectric element. The focus of this work is the optimization of the pyroelectric infrared focal plane array (IRFPA) system through thermal design, analysis and characterization. There have been few systematic analyses of the coupled electro-thermal phenomena that determine the performance of the IRFPA, and design of the system is susceptible to inaccuracies from varied material data in the literature. The unique contributions of the research include a formalized thermal modeling framework and a test technique to extract the material properties of a pyroelectric element. The research formalizes and integrates thermal system design with pyroelectric characterization in the framework of a simplified model of the electrical and thermal coupling in the system.; Analytical expressions are developed to examine the effects of geometric and material parameters on the system using compact models and Bayesian surrogate modeling. This way, the parameters that most influence the responsivity are identified through systematic analysis of the design space. Finite element models simulate the system-level energy transport in candidate designs and relate them to the RC network-based expressions. Geometry of the insulation pillars and gas pressure within the IRFPA package are shown to have the most influence on the thermal system. Large-array simulations up to 11x11 pixels show that a heat load on one pixel significantly influences adjacent pixels (thermal cross-talk) through lateral heat diffusion and this radius of influence extends approximately two pixels from the source pixel.; An electrical and thermal test method that allows simultaneous characterization of the pyroelectric element's thermal conductivity, diffusivity, and pyroelectric coefficient is outlined, demonstrated, fabricated, and validated. The technique combines thermoreflectance, temperature phase, and laser intensity modulation methods to eliminate uncertainties in the measurement from associating disparate data sets. Fabricating and testing the pyroelectric material using the same processes used in production also to eliminates variations in material properties due to fabrication methods. The sensitivity of the experiment to noise, analytical model parameters, and measurement uncertainties is analyzed through numerical case studies, to reveal how geometric variations in the sample influence the material property prediction. A composite error minimization algorithm is formulated to resolve the underconstrained nature of two unknown material properties in the thermal tests. The technique is general and versatile to other pyroelectric materials.