Objective With the increasing requirements for the resolution, large field of view, and multi spectral range of infrared detectors in fields such as astronomical telescope, military warning, and space remote sensing, staring large-scale array and scanning long line array infrared detectors have been developed. The size of the infrared focal plane is limited by the size of the readout circuit of the detector chip and the size of the detector material. The large format infrared detector has the problems of high cost, unstable performance and low uniformity. Therefore, infrared detector splicing technology is an important means to solve this problem. The splicing methods of infrared detector are mainly divided into optical splicing and mechanical splicing. The mechanical splicing method receives the optical system image directly on the focal plane because it does not add redundant optical components, and has the advantages of small energy loss and simple system structure. At present, many international projects, including astronomical telescopes, dark energy detection telescopes or ground-based telescopes, have gradually begun to carry the splicing large format infrared detector load as the core detection component, and the detector module as the splicing unit is getting larger and larger, and the total scale of the splicing detector is also getting larger and larger. Subsequently, the technical requirements of temperature control, high precision splicing and mechanical properties of splicing large array infrared detector components have been improved. According to the performance requirements of multi-module splicing of large format infrared focal plane package, the structure of Dewar component was analyzed and designed, and the mechanical and thermal properties of the component were verified. Finally, the large format infrared detector Dewar component met the requirements of the project.

Methods The key structure of the multi-module spliced large format infrared detector Dewar was designed. A three-point adjustable module structure based on precision shim was adopted (Fig.3), and a multi-point coupled flexible cold strap structure with high thermal conductivity, as well as SiC cold platform structure with low stress and high uniform temperature, were designed (Fig.4). In addition, key technologies such as precision splicing of detector module, temperature uniformity of large format focal plane, low heat loss of large Dewar component, and mechanical reliability of cold platform component were studied. Liquid nitrogen refrigeration was used to test the low temperature field of large format infrared detector Dewar (Fig.8), and the flatness of the focal plane array was measured by three-dimensional imaging instrument. Finally, the mechanical vibration test of the component was carried out (Fig.10).

Results and Discussions The 2 k×2 k infrared detector module was spliced with a 3×3 array, and the total size of the focal plane array reached 6 k×6 k. The temperature uniformity of the 9 module array was ± 0.45 K, and the 9 module array was ± 0.45 K, and the flatness of the focal plane array after module splicing was better than ± 10 µm. The heat loss of the large Dewar component at room temperature was 7.53 W. The mechanical vibration test of Dewar component shows that the minimum fundamental frequency of XYZ three directions is 557 Hz, and after 9 grms random vibration, the function of the component is normal, without obvious changes, and can meet the requirements of engineering applications.

Conclusions Design the package structure for the spliced large format infrared detector Dewar, by using the zirconia support structure with high stiffness and low thermal conductivity, the SiC cold platform with high thermal conductivity and low thermal expansion coefficient, as well as the interface material with high elasticity and high thermal conductivity, and analyze and design the key structure of Dewar component such as the detector module installation structure based on three-point adjustment, the cold platform structure and the multi-point coupling cold strap structure. Implemented a 6 k×6 k large format infrared detector Dewar module based on a 2 k×2 k 18 µm center to center distance detector module assembled in a 3×3 array. Mechanical vibration and thermal tests are carried out to verify that the components meet the index requirements of the large format infrared detector Dewar component. After the detector module is spliced, the flatness of the focal plane array is better than ± 10 µm, the focal plane temperature uniformity is better than ± 1 K, the heat loss of the Dewar component is better than 7.53 W, and the Dewar component passes the 9 grms random vibration test. The fundamental frequency of the Dewar component reaches up to 557 Hz. The key performance index is basically equivalent to the main international spliced large format infrared detector component, which meets the engineering application requirements.