The development of a new thermometer material at Lynred has opened new opportunities towards a smaller pixel pitch. This pixel pitch reduction leads to several challenges and technological breakthroughs that are necessary both for the bolometer pixel design and the readout circuit architecture. The symposium presentation and the associated article will present a recent development at CEA-leti and Lynred of a 8.5μm bolometer pixel pitch Focal Plane Array (FPA). The drastic reduction of the pixel area leads to important changes of the micro bolometer features, especially a strong decrease of thermal capacitance Cth and increase of the thermal resistance Rth in order to maintain a high detector responsivity. The rise of the noise due to temperature fluctuation or 1/f contributions have also to be considered. The consequences of those modifications and resulting trade-offs, such as pixel fill factor and optical absorption yields in the 8-14 μm band ; pixel self-heating and Read-Out IC (ROIC) dynamic range, will be discussed. Finally, the electro-optical performances of our 640x480 FPAs are presented, and perspectives will be given.
Historically LYNRED (created from the merger of SOFRADIR and ULIS in 2019) has used amorphous silicon materials (“a-Si”) as thermistor materials for its uncooled microbolometer products. If a-Si materials present several advantages that made the success of LYNRED’s products (easy to use and integrate in thermal camera), their intrinsic bolometric performances (i.e. TCR and 1/f noise) are still lower than the commonly used oxides thermistors[1] (i.e. VOx[2] and TiOx[3]). In order to stay in a leading position regarding sensor performances without any trade-off, LYNRED, with the support of its historical R&D partner the CEA-LETI, developed new materials. This strategy has led to new cutting edge products. At the end of 2020 a new 17 µm pixel pitch product (Pico640s[4]), with one of the highest sensor performance reported on the market (typical thermal sensitivity of 25 mK (f/1, 300K, 30Hz)), has been introduced in our product portfolio. We also launched our state of the art 12 µm product range with performances equivalent to our current 17µm product range. More generally, these developments open up new opportunities toward smaller pixel pitch. The symposium presentation and the associated article will present how we have increased the "Signal to Noise Ratio" (SNR) of our products while keeping all the elements which have been our hallmark. Special attention will be paid to NETD, stability of product characteristics during operation and manufacturing excellence. All these features were obtained only by hardware (at the pixel level) improvements without the need to use sophisticated algorithms or specific ROIC functions, in the spirit of LYNRED’s FPA products.
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