Multispectral image fusion via heterogeneous integration of broadband image sensor and sub‑Boltzmann Transistors on CMOS.

Broadband multispectral imaging from ultraviolet to near-infrared enables spectral information fusion into a single composite, enriching inputs for machine vision and medical diagnostics. Conventional fusion systems require multiple photodetectors and co-registration algorithms, leading to resolution mismatch, area overhead, and computational burden, while readout circuitry increases chip area and power. Scaled transistors also suffer from off-state leakage and thermionic limits, increasing dark current and degrading signal-to-noise ratio. Here, we report a heterogeneously integrated quantum-dot-sensitized phototransistor active pixel sensor array incorporating series-connected CMOS-based steep-subthreshold switching transistors in a vertically stacked architecture. The switches operate below the Boltzmann limit, achieving a subthreshold swing of ~3.27 mV/dec over six decades, ~52-fold lower than CMOS, with ~0.1 pA leakage. The array exhibits ultralow dark current of ~36 fA, >120 dB linear dynamic range, and ~30 fJ/pixel switching energy. The phototransistor exhibits ~2 × 106 A/W responsivity and ~1.3 × 1014 Jones detectivity, enabling single-sensor pixel-level multispectral fusion for medical imaging.