Learn more about InVisage’s QuantumFilm™ technology and how it works.
QuantumFilm is a photosensitive layer that relies on InVisage’s newly invented class of materials to absorb light; specifically, the new material is made up of quantum dots, nanoparticles that can be dispersed to form a grid once they are synthesized. Just like paint, this dispersion of solid materials can be coated onto a substrate and allowed to dry.
The unprecedented light sensitivity and customizability of QuantumFilm set InVisage’s image sensor apart from traditional CMOS image sensors. Conventional sensors rely on a photosensitive layer made of silicon that also incorporates the circuitry necessary to read the electric output from the detected photons, as well as barriers isolating each pixel in order to prevent crosstalk. This means both less room for light sensing and less room for electric storage. InVisage has designed an innovative image sensor architecture with a dedicated QuantumFilm layer in order to maximize light sensing capability.
The above drawing shows a cross section of QuantumFilm pixels. Light passes through the color filter array, and is then detected by the quantum dots in the QuantumFilm layer. The metal wiring represents the sensor’s electrical circuitry. The higher positioning of the photosensitive layer allows the QuantumFilm pixel to detect more photons, store more electrons (and therefore more photographic information), and reproduce colors more accurately—all with a thinner camera module.
Across the visible spectrum, QuantumFilm™ absorbs the same amount of light as silicon in a layer ten times thinner. Silicon was designed to be an excellent electronic material, but its light absorption is inefficient: it is an excellent conductor of electrons, but a weak absorber of red light. Because of silicon’s indirect bandgap, light must pass through a thick layer of silicon before it can pass its energy to silicon’s electrons, and this leads to less efficient transfer of energy from light to the semiconductor. QuantumFilm’s bandgap is direct, so light passes its energy rapidly and efficiently to the electrons in QuantumFilm like a seamless hand-off of a baton in a relay race. This leads to a fast and efficient rate of conversion of light to an electrical signal, giving QuantumFilm superior quantum efficiency. The graph below shows how dramatic the difference is between the light absorption capabilities of equivalent thicknesses of QuantumFilm and silicon.
In InVisage’s QuantumPixel, light sensing is elevated to a new plane: the top surface of the wafer. InVisage coats the top surface of the silicon chip with QuantumFilm. In contrast to traditional CMOS sensors, which contain a silicon layer responsible for both light sensing and electronic read-out functions, and therefore can only absorb light with a limited area, QuantumFilm enables 100% fill factor (the light sensitive area to total area ratio in a pixel) because it is continuous—the entire area of the imaging array is occupied by a medium whose sole purpose is light sensing. This supplements QuantumFilm’s enhanced rate of light absorption and electron transport. The graph below shows the high percentage of photons the QuantumFilm sensor stores as electrons at different wavelengths. This measurement, called quantum efficiency, is a key indicator of image sensor sensitivity.
InVisage optimizes QuantumFilm for customer-driven applications by adjusting the size of our quantum dots.
The diagram below shows three formulations of QuantumFilm with dots of increasing size: QuantumFilm A (green, optimized for the visible range), QuantumFilm B (yellow, optimized for 850 nm. infrared), and QuantumFilm C (red, optimized for 940 nm. infrared). This change in size affects QuantumFilm’s bandgap—the energy required for a photon to excite an electron from its valence band to its conduction band (shown in the spatial band diagram at top). A smaller bandgap increases sensitivity to longer wavelengths of light, whose photons have less energy. As dot size increases from QuantumFilm A to C, QuantumFilm’s bandgap decreases and it becomes more sensitive to infrared light in addition to visible light. Using this process, we tune for the exact wavelength at which light absorption and sensing should stop for a particular application.