Inspired by the human eye, CEA-Leti has produced the first monolithic curved infrared focal plane array. The device is an above-IC micro bolometer array of 320 x 356 pixels with a 25-µm pitch. The hemispherical shape has been obtained after silicon substrate removal, leading to impressive bending capabilities of the material.
As illustrated on the surface characterization (Figure 5
), there isn’t any defect to the perfect sphere exhibiting an 80-mm radius, in concave configuration (Figure 6
Figure 5: Surface profile of a 320 x 256, 25-µm pitch, pixel array (1cm²), R80mm
The infrared image in Figure 7
from the micro bolometer infrared focal plane array (IRFPA) illustrates the mechanical integrity of the MEMS-based micro bolometer architecture, and the non-modified electrical behavior of the semiconductor device (band-gap structure of the readout CMOS circuit), despite the stress induced in the device by the hemispherical shape.
Figure 6: 25-µm pitch 320 x 256 pixels array, R80mm
Figure 7: Infrared image - curved micro bolometer IRFPA
As shown by the image in Figure 7, the focal plane array is fully monolithic, characterized by a 100 percent fill factor. This first proof of concept on real devices will be transferred to the hybrid structures of infrared cooled focal plane arrays, typically used in astronomy. First simulations on E-ELT architectures show significant advantages in terms of throughput, optical design simplification and dimensions reduction. As O. Iwert from ESO noted in 20103: “with a flat detector often no camera design with an affordable number of lenses can be found with equivalent transmission and identical field of view.”