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Micro-electro-mechanical Systems (MEMS) Drive IMOD Reflective Technology
The core building blocks of mirasol displays, the Interferometric Modulator (IMOD) element is a simple MEMS (micro-electro-mechanical system) device.
The IMOD element has two stable states. When no voltage is applied, the plates are separated, and light hitting the substrate is reflected. When a small voltage is applied, the plates are pulled together by electrostatic attraction and the light is absorbed, turning the element black.
This is the fundamental building block from which Qualcomm's mirasol displays are made and produce color.
How Color Is Created
At the most basic level, a mirasol display is an optically resonant cavity. The device consists of a self-supporting deformable reflective membrane and a thin-film stack (each of which acts as one mirror of an optically resonant cavity), both residing on a transparent substrate.
When ambient light hits the structure, it is reflected both off the top of the thin-film stack and off the reflective membrane. Depending on the height of the optical cavity, light of certain wavelengths reflecting off the membrane will be slightly out of phase with the light reflecting off the thin-film structure. Based on the phase difference, some wavelengths will constructively interfere, while others will destructively interfere.
The human eye will perceive a color as certain wavelengths will be amplified with respect to others. The image on a mirasol display can switch between the selected color and black by changing the membrane state. This is accomplished by applying a voltage to the thin-film stack, which is electrically conducting and is protected by an insulating layer. When a voltage is applied, electrostatic forces cause the membrane to collapse.
The change in the optical cavity now results in constructive interference at ultraviolet wavelengths, which are not visible to the human eye. Hence, the image on the screen appears black.
A full-color display is assembled by spatially ordering IMOD elements reflecting in the red, green and blue wavelengths.