Multispectral UV Imaging on Capacitive CMOS Arrays Enabled by Solution-Processed Metal-Oxide Nanoparticles

Abstract

Ultraviolet (UV) imagers are important for a variety of applications, such as quality inspection in the semiconductor industry, forensics and food quality inspection, but are often costly because they require dedicated semiconductor process flows. Here, an imaging chip is introduced that has been fabricated using standard 40 nm complementary metal-oxide-semiconductor (CMOS) technology. Instead of using a conventional charge-based photodetection principle, the imager uses a capacitive operation principle where UV-light causes capacitance changes via the photodielectric effect in a functionalization layer, which are measured by the underlying CMOS circuitry. This spin-coated or inkjet-printed functionalization layer consists of solution-processed, wide-bandgap, semiconducting metal-oxide nanoparticles, such as ZnO, SnO2 and Ga2O3. Owing to their bandgap-dependent optical absorption, these materials exhibit distinct capacitive responses across UV-A, UV-B, and UV-C spectral regions, thereby enabling band-selective detection and multispectral UV imaging. The sensors exhibit low noise-equivalent powers (17-138 fW Hz−1/2) across the UV bands. Unlike conventional silicon CMOS imagers, the present capacitive-CMOS platform is inherently visible-blind, providing selective UV detection. This work positions late-functionalized capacitive-CMOS arrays as a route toward reducing the fabrication complexity of UV imagers, which can lead to their more widespread implementation in consumer and low-volume application-specific products.