Novel technology for microlenses for imaging applications.

Microlenses are an important functional element of a modern imaging device. Typically, they are fabricated from organic materials on top of individual pixels. Though they are widely used, they do exhibit a number of limitations. These are, but not limited to, thermal stability, radiation sensitivity, outgassing properties, additional topography, and difficulty in manufacturing asymmetrical, noncircular microlens designs using conventional manufacturing techniques. In this paper, we present a novel approach for the fabrication of microlenses. We report on the design, manufacturing, and characterization of microlenses fabricated from classical dielectric materials used in the manufacturing of CMOS semiconductor devices. These microlenses rely on a Fresnel optical design, provide functionality similar to the classical microlenses, and do not suffer from their limitations. We subjected these microlenses to several environmental reliability stress conditions, including pressure, temperature, humidity, and their variation. Moreover, we test their sensitivity to gamma rays and protons.

Thin-Film Quantum Dot Photodiode for Monolithic Infrared Image Sensors.

Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10-6 A/cm² at -2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors.