Uncooled infrared bolometer arrays operating in a low to medium vacuum atmosphere: performance model and tradeoffs

Abstract

In this paper we present a comprehensive calculational model for the noise equivalent temperature difference (NETD) of infrared imaging systems based on uncooled bolometer arrays. The NETD model is validated and benchmarked using published performance data of state-of-the-art uncooled infrared bolometer arrays. The calculational model is used to evaluate possible infrared sensor and system design tradeoffs that allow optimization for low-cost infrared systems with improved reliability and lifetime, while still achieving a NETD of about 150 mK, required for pedestrian injury mitigation systems. We propose an approach in which high performance crystalline semiconductor materials with very low 1/f-noise properties and a temperature coefficient of resistance (TCR) of 3 %/K are used as thermistor material for the bolometers. The resulting increased bolometer performance can be used to operate the infrared imaging arrays in a vacuum atmosphere with increased gas pressure while still achieving useful NETD levels. The proposed calculational model suggests that a NETD on the order of 150 mK can be reached with uncooled infrared bolometer arrays operating in vacuum pressures on the order of 6 mbar. Such specifications for the bolometer vacuum package dramatically simplify wafer-level vacuum packaging and ease long-term reliability issues, contributing to lowering the vacuum packaging and thus, the overall infrared imaging chip costs.