Multi-stack Film Bolometer Absorber for Infrared Detection

The patent employs a multi-stack film absorber comprising alternating layers of metallic films (e.g., aluminum, copper, silver) and insulating films (e.g., silicon dioxide, silicon nitride). This composite structure leverages the complementary properties of different materials: metallic layers provide high infrared absorption through plasma resonance effects, while insulating layers provide thermal isolation and structural stability. The synergistic combination achieves superior absorption efficiency (exceeding 80% in certain configurations) compared to single-layer absorbers, while maintaining compatibility with standard ALD fabrication processes.

The absorber is segmented into multiple discrete thin film layers deposited in alternating sequences. Each layer has a specific function: metallic layers for absorption, insulating layers for thermal management. This segmentation allows independent optimization of each layer's thickness and material properties to maximize overall absorption efficiency while controlling thermal conduction pathways to the substrate.

Rather than using a single thick absorptive layer, the patent segments the absorber into multiple thin metallic layers separated by insulating barriers. This segmentation confines the absorptive function to thin metallic regions while the insulating layers interrupt thermal conduction pathways to the substrate. The result is enhanced absorption efficiency through increased light-matter interaction in the metallic layers while minimizing parasitic thermal loss to the substrate.

The insulating film layers act as thermal intermediaries between the metallic absorptive layers and the substrate. These intermediary layers (e.g., silicon dioxide, silicon nitride) provide thermal isolation, blocking heat flow from the absorber to the substrate while allowing the metallic layers to maintain their absorptive function. This mediator approach decouples the absorption efficiency requirement from thermal loss to the substrate.

The patent systematically varies critical parameters including layer thickness (typically 5-50 nm per layer), material composition (selecting from various metals and dielectrics), and stack configuration (number of repeats) to optimize absorption efficiency. These parameter changes are implemented within the framework of existing ALD fabrication capabilities, allowing precise control over film properties without requiring fundamentally new manufacturing equipment or processes.

The multi-stack film structure serves multiple functions simultaneously: the metallic layers provide infrared absorption, the insulating layers provide thermal isolation, and the alternating architecture provides mechanical stress management. This multi-functionality is achieved within a single fabrication sequence using standard ALD processes, avoiding the need for separate fabrication steps for each function and thereby limiting the increase in fabrication complexity.

The absorptive function is segmented across multiple thin metallic layers rather than concentrated in a single thick layer. Each thin metallic layer (5-20 nm) provides a contribution to absorption while maintaining thinness for thermal isolation. The cumulative effect of multiple segmented layers achieves high overall absorption efficiency while each individual layer remains thin enough to minimize thermal conduction to the substrate.

The patent creates a composite structure where thin metallic layers (for absorption with minimal thermal mass) are combined with insulating dielectric layers (for thermal isolation). This composite material approach allows the metallic components to be kept thin for thermal management while the insulating components compensate for the reduced absorptive path length, maintaining high absorption efficiency despite reduced individual metallic layer thickness.