Development of a Cryogenic Test Bench for Spectral MTF Measurement on Midwave Infrared Focal Plane Arrays
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https://doi.org/10.1007/s11664-020-08388-0 Ó 2020 The Minerals, Metals & Materials Society
TOPICAL COLLECTION: U.S. WORKSHOP ON PHYSICS AND CHEMISTRY OF II-VI MATERIALS 2019
Development of a Cryogenic Test Bench for Spectral MTF Measurement on Midwave Infrared Focal Plane Arrays EDOUARD HUARD ,1,3 SOPHIE DERELLE,1 JULIEN JAECK,1 ˆ ME PRIMOT1 ´ RO OLIVIER GRAVRAND,2 and JE 1.—ONERA/DOTA – Chemin de la Vauve aux Granges, 91120 Palaiseau, France. 2.—CEA – Leti, 17 Avenue des Martyrs, 38054 Grenoble, France. 3.—e-mail: [email protected]
The modulation transfer function (MTF) is one of the key figures of merit for the characterization of infrared focal plane arrays (FPA). Moreover, with both the trend of reduced pixel pitch and the variety of pixel structures observed in the industry, the study of the impact of wavelength on the MTF is also of great interest, and thus needs a spectro-spatial measurement. In this paper, we demonstrate such spectral MTF measurements in the mid-wavelength infrared (MWIR) band by the use of several spectral bandpass filters. We realize those measurements at 80 K on a specific n/p 320 9 256 HgCdTe MWIR FPA, divided into different areas. The pixel pitch is the same for all areas (30 lm), the only difference being the fill factor, which differs from one zone to another. The MTF measurement bench is based on a continuously self-imaging grating interferometer integrated in a specific cryogenic set-up. Key words: Modulation transfer function, cryogenic bench, spectral measurement, pixel confinement
INTRODUCTION In the infrared range, the influence of wavelength on the pixel modulation transfer function (MTF) is usually not taken into account since, in the vast majority of cases, this effect is considered to be negligible. However, in the context of pixel pitch reduction,1,2 with the emergence of multispectral and hyperspectral imagers3,4 along with the evolution of the structure of the pixels (filters, integrated optics, metamaterials, etc.),5,6 some unusual spectral effects can be expected for the future generation of infrared focal plane arrays (FPAs). Therefore, in this paper, we introduce a specific test bench for spectral MTF measurements, by the use of an interferential method using a continuously selfimaging grating (CSIG) interferometer7 and spectral filters, in a specific cryogenic environment. The bench is tested on a particular 30 lm pixel pitch
(Received February 24, 2020; accepted August 1, 2020)
mid-wavelength infrared (MWIR) HgCdTe detector manufactured by CEA in 2011 for specific studies on low-fill-factor pixels.8 This detector is a good candidate for a first test of our bench, since spectral effects can be expected on low-fill-factor diodes. The detector presents several zones with different structures: high-fill-factor square diodes and low-fillfactor circular diodes. In this paper, we present MTF measurements of three of those distinct structures. The experimental set-up will first be detailed, and then the MTF results will be presented, leading finally to an interp
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