Global shutter is a feature of some CMOS image sensors that allows capture of an entire image at a single point in time. We discuss how the device architecture of InVisage’s QuantumFilm enables global shutter operation by controlling the bias on the device stack without an additional transistor, giving high shutter efficiency in a 1.1 μm pixel CMOS image sensor. We use drift-diffusion device simulations to inform our design and reveal device and material properties that are key for carrier selectivity. Based on our device model, we fabricated global-shutter-enabled QuantumFilm devices for near infrared sensing applications and present a characterization of our devices.
At the 940 nm wavelength, solar background irradiance is relatively low and device-mounted monochromatic LED emission can be used to illuminate and assess the shape, distance, and optical properties of objects. We report here NIR imaging that outperforms existing CMOS sensors by achieving record 42% quantum efficiency at 940 nm for a 1.1 μm pixel. The rationally engineered material properties of QuantumFilm allow tuning of the spectral response to the desired wavelength to achieve quantum efficiency that exceeds 40%. In addition, the combination of high QE with QuantumFilm’s distinctive film-based electronic global shutter mechanism allows for extremely low illumination power and therefore lowers time-averaged system power when imaging with active illumination.
This work presents the development of a quantum dot-based photosensitive film engineered to be integrated on standard CMOS process wafers. It enables the design of exceptionally high performance, reliable image sensors. Quantum dot solids absorb light much more rapidly than typical silicon-based photodiodes do, and with the ability to tune the effective material bandgap, quantum dot-based imagers enable higher quantum efficiency over extended spectral bands, both in the Visible and IR regions of the spectrum. Moreover, a quantum dot-based image sensor enables desirable functions such as ultra-small pixels with low crosstalk, high full well capacity, global shutter and wide dynamic range at a relatively low manufacturing cost. At InVisage, we have optimized the manufacturing process flow and are now able to produce high-end image sensors for both visible and NIR in quantity.