ULIS bolometer improvements for fast imaging applications

Abstract

Thermal Image Sensor performances for high end applications can be compared using a Factor of Merit (FoM) based on NETD and thermal time constant (τ_th). This FoM is defined as FoM = NETD × τ_th and is expressed in mK.ms. Best bolometers FoM range from 500 to 720 mK.ms. When fast response is required from the detector due to short events or fast moving objects in the scene, bolometers can be limited by their τ_th , today around 12 ms for ULIS 17 μm components, leading to blurred images or poorer signal to noise ratio. Adjusting the bolometer τ_th can be achieved simply by lowering the pixel responsivity, keeping FoM globally unchanged and leading to unacceptable NETD performance. This paper discusses the bolometer key parameters and tradeoffs that can lead to improved FoM associated with drastically decreased thermal time constant. Thanks to a multi-parameter design optimization, ULIS has developed an improved 17μm pixel with an exceptional FoM of 125 mK.ms and thermal time constant below 3 ms, which is 4 times better than the state of the art. Prototypes characterization will be presented and the image quality will be compared with the one of a standard camera.