MEMS cavity-coating layers and methods

#1. Technical Field

#This application is generally related to microelectromechanical systems (MEMS), and more particularly, to coatings within MEMS cavities and methods for forming the same.

#2. Description of the Related Art

#FIG. 1 is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position.

#FIG. 2 is a system block diagram illustrating one embodiment of an electronic device incorporating a 3×3 interferometric modulator display.

#FIG. 3 is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of FIG. 1.

#The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices.

#Embodiments described herein include methods of lining MEMS cavities by atomic layer deposition (ALD) after removal of sacrificial material. The deposited material can conformally coat all cavity surfaces, serving as an optical dielectric layer, or serving as a supplemental dielectric that seals pin holes in a previously formed dielectric, in either case resulting in a thinner dielectric for a given insulation quality. Materials can be chosen to exhibit combinations of reduced stiction between relatively moving electrodes, reduced surface charge build-up, improved mechanical properties, and/or improved electrical properties. In another embodiment, ALD conditions are selected to deposit a nonconformal layer preferentially in regions proximate openings into the cavity, thereby reducing contact area and thus stiction when the MEMS electrodes are actuated to collapse the cavity. Removal of sacrificial material and subsequent ALD coating can be performed before or after assembly of the MEMS substrate with a backplate.

#One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in FIG. 1. In these devices, the pixels are in either a bright or dark state. In the bright (“on” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“off” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white.