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Electrochromic Display Employing Multiple Reference Electrodes

IP.com Disclosure Number: IPCOM000042016D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Bird, CL: AUTHOR [+3]

Abstract

A continuously available stable reference potential for the potentiostatic control of erasure of an electrochromic display can be derived successively from multiple reference electrodes. While one electrode is being used as a reference, another is erased and rewritten with a deposit of the electrochromic substance sufficient to stabilize its potential with respect to the electrochromic solution. To prevent a cumulative build-up of non-erasable deposit on the reference electrodes, it has been found necessary, periodically, to ensure total erasure of each electrode by the use of an extended cleaning cycle.

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Electrochromic Display Employing Multiple Reference Electrodes

A continuously available stable reference potential for the potentiostatic control of erasure of an electrochromic display can be derived successively from multiple reference electrodes. While one electrode is being used as a reference, another is erased and rewritten with a deposit of the electrochromic substance sufficient to stabilize its potential with respect to the electrochromic solution. To prevent a cumulative build-up of non-erasable deposit on the reference electrodes, it has been found necessary, periodically, to ensure total erasure of each electrode by the use of an extended cleaning cycle. Although this can be achieved by employing more than two reference electrodes, it is preferred to employ only two reference electrodes having different asymmetric primary and cleaning cycles which are periodically interchanged. Fig. 1 shows the variation of current to the reference electrode with time for the two types of cycle. The cycles are described as follows: Primary Cycle In a viologen electrochromic system employing silver electrodes, the reference electrode is written at constant current of 0.1 mA for a time tw1, typically 20 ms, to deposit a sufficient amount of charge to ensure a stable potential. The electrode is then relaxed by holding it open circuit for a further time tr1, typically 200 ms, to allow the potential to stabilize. It is now ready to be used as a reference electrode for the bulk of the cycle, for example, to control potentiostatic erasure of the display. Eventually, to prevent the deposit becoming difficult to erase, the reference electrode itself must be erased and rewritten. This erase step is also potentiostatically controlled, employing the other electrode as reference, and takes a time te1, typically 500 ms, during which the primary reference electrode is held approximately 400 mV anodic of the alternate reference. If the total cycle time tc is 10 seconds, the electrode to which the primary cycle is applied provides the reference function for approximately 95% of the time. Cleaning Cycle While one electrode is subjected to the primary cycle, the second electrode is subjected to the cleaning cycle shown in the lower waveform. The second electrode is held at the erase potential with respect to the primary reference for a time te2, which is almost as long as the time for which the primary reference is available, i.e., 95% of the cycle time. Just before the primary is erased, the second electrode is written briefly for a time tw2, typically 10 ms, and allowed to relax for a further time tr2, typically 50 ms. The second electrode is...