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Controllable Persistence in Electrochromic Effect and Its Use in Beam Addressable Displays

IP.com Disclosure Number: IPCOM000083093D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR

Abstract

Electrochromic effect observed in an electrochemical redox system generally exhibits persistence or memory. However, this memory only persists when the electrochromic material is isolated from any possible current path between the electrodes, for otherwise the color image decays rapidly, i.e., exhibits a short persistence.

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Controllable Persistence in Electrochromic Effect and Its Use in Beam Addressable Displays

Electrochromic effect observed in an electrochemical redox system generally exhibits persistence or memory. However, this memory only persists when the electrochromic material is isolated from any possible current path between the electrodes, for otherwise the color image decays rapidly, i.e., exhibits a short persistence.

Such short persistence prevents the electrochromic (EC) cells from being addressed in a large-scan matrix, unless a high-impedance switch is incorporated at each cell, or special addressing techniques are used. The short persistence effect also limits the applicability of the EC cell as a beam-addressed device. Described is a beam addressable EC display in which a bias scheme is incorporated to control the EC persistence.

An electrochemical redox system exhibits the I-V and optical density characteristics shown in Figs. 1 and 2, respectively. As can be seen in Fig. 1, the system shows a clean threshold voltage V . A voltage greater than V(T)is required to cause a color layer to form at the cathode (a reduction process). When a color layer is formed at the cathode, its surface possesses a potential V(c) which is generally smaller than V(T). The potential V(c) (or charge in the color layer) will discharge if an external "controllable persistence".

One technique for obtaining a controllable EC persistence is to forward bias the EC medium, as shown in Fig. 3A. The optical density change observed as a function of this forward bias, V(bias), is plotted in Fig. 3B. As can be seen, the optical density or contrast may be arbitrarily controlled by varying the bias voltage, V(bias). Although the bias scheme shown in Fig. 3A is represented by a separate DC and AC voltage source, it is clear that the sources need not be separate but may comprise a single source to provide the desired waveforms. In this regard, any of a variety of biasing sc...