Frequency-Modulated Bistable Display Using Electrowetting and Liquid Dielectrophoresis

Brief Description
This invention relates to information display devices that are based on electrowetting technology. It creates a bistable display that can hold a bright image, made possible by two capillarity-maintained hydrostatic equilibria that allow a liquid to exist in either of two configurations, and a frequency-dependent electromechanical force that facilitates movement of the liquid back and forth between these two equilibria by brief application of AC voltage at an appropriate frequency.  This invention can be used for a variety of display applications including small and large format electronic displays, computers, programmable signs, electronic paper systems, etc. 

Current electrowetting-based reflective display technologies require a continuous application of voltage to maintain an image.  Therefore these displays are not bistable, do not have inherent storage capability, and require external circuitry for image maintenance and refreshment.  In contrast the technology of this invention creates and holds a bistable image without the need for periodic refreshing.
The technology exploits the difference between the electrowetting-on-dielectric (EWOD) and liquid dielectrophoretic (DEP) regimes of the electromechanical force and modulates the frequency of the applied voltage between 'low' and 'high' values to move the liquid to a large or small gap, thereby creating on-or-off display pixels. Due to normal capillarity forces, the liquid maintains itself in either configuration indefinitely without the need for continued application of voltage. 
The principal advantage of this invention is that it is bistable and can hold a bright image without the continuous application of voltage or periodic refreshing of the image.  The pattern desired is written to the display pixel by pixel with the application of AC voltage.   This involves a very brief time and once written, the image is maintained without applying any further voltage.  This feature resolves a critical deficiency in previous electrowetting applications.
Overall, the invention provides excellent contrast and resolution and an improved viewing angle in a lightweight display. 

Patent Information:
Title Country Patent No. Issued Date
Frequency-Addressable Apparatus and Methods for Actuation of Liquids United States 8,228,657 7/24/2012
Computer Hardware
For Information, Contact:
Curtis Broadbent
Licensing Manager
University of Rochester
Thomas Jones
Weiqiang Wang
Adrian Bailey