# US 6,721,080 B1 · Optimum switching of a reversible electrochemical mirror device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,721,080 B1 - Document ID: US6721080B1 - Status: Granted - Kind: B1 - Application number: 10/256,841 - Filed: 2002-09-27 - Published: 2004-04-01 - Granted: 2004-04-13 - Earliest claimed: 2002-09-27 - Inventors: D Morgan Tench; Petra V. Rowell - Web page: https://patentgrep.com/patent/US6721080B1 ## CPC - G02F 1/1506: caused by electrodeposition, e.g. electrolytic deposition of an inorganic material on or close to an electrode - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS ## Abstract Reversible electrochemical mirror (REM) devices typically comprise a conductive oxide mirror electrode that is substantially transparent to radiation of some wavelengths, a counter electrode that may also be substantially transparent, and an electrolyte that contains ions of an electrodepositable metal. A voltage applied between the two electrodes causes electrodeposition of a mirror deposit on the mirror electrode and dissolution of the mirror deposit on the counter electrode, and these processes are reversed when the polarity of the applied voltage is changed. Such REM devices provide precise control over the reflection and transmission of radiation and can be used for a variety of applications, including smart windows and automatically adjusting automotive mirrors. According to the present invention, REM mirror uniformity is improved with minimal sacrifice in switching speed by utilizing a lower drive voltage when the mirror electrode sheet resistance is high, and a higher drive voltage when sufficient mirror metal is present to appreciably reduce the sheet resistance. Faster switching without damage to the electrode or decomposition of the electrolyte is provided by adjusting the applied voltage by the resistive loss in the electrolyte. Optimum results are provided by adjusting the drive voltages for the mirror metal plating and erasure processes based on real-time measurements of cell current, mirror electrode sheet resistance and temperature. Such sheet resistance measurements can also be used to monitor and control the reflectance of the device. ## Claims ### Claim 1 A method for optimizing the mirror uniformity and switching speed of a reversible electrochemical mirror of the type including a mirror electrode, a counter electrode, and an electrolyte disposed between and in electrical contact with the mirror and counter electrodes, wherein the electrolyte contains cations of an electrodepositable mirror metal, comprising the steps of: applying a first negative voltage to the mirror electrode relative to the counter electrode so that mirror metal is deposited onto the mirror electrode at a first rate; and applying a second negative voltage more negative than the first negative voltage to the mirror electrode relative to the counter electrode so that additional mirror metal is deposited onto the mirror electrode at a second rate which is faster than the first rate, wherein the second negative voltage does not exceed a predetermined maximum drive voltage. ### Claim 2 (depends on 1) The method of claim 1, wherein the second negative voltage is increased with time so that the rate at which additional mirror metal is deposited on the mirror electrode increases with time. ### Claim 3 (depends on 2) The method of claim 2, wherein the second negative voltage is increased with time continuously. ### Claim 4 (depends on 2) The method of claim 2, wherein the second negative voltage is increased with time in steps. ### Claim 5 (depends on 1) The method of claim 1, wherein the second negative voltage is increased based on the amount of charge passed between the mirror electrode and the counter electrode. ### Claim 6 (depends on 1) The method of claim 1, wherein the predetermined maximum drive voltage corresponds to a current that is less than the diffusion-limited current for electrodeposition of the mirror metal. ### Claim 7 (depends on 1) The method of claim 1, further comprising the steps of: measuring the sheet resistance between two locations on the mirror electrode; and measuring the current flowing between the mirror electrode and the counter electrode, wherein the second negative voltage is such that the multiplication product of the measured sheet resistance and the measured current is less than a predetermined maximum sheet IR drop. ### Claim 8 (depends on 7) The method of claim 7, wherein said step of measuring the sheet resistance comprises the steps of applying an alternating voltage between two electrical contacts on the mirror electrode and measuring an alternating current response to the alternating voltage. ### Claim 9 (depends on 7) The method of claim 7, wherein said step of measuring the sheet resistance comprises the steps of applying a direct voltage between two electrical contacts on the mirror electrode and measuring a direct current response to the direct voltage. ### Claim 10 (depends on 7) The method of claim 7, further comprising the step of: determining the electrical resistance of the electrolyte between the mirror electrode and the counter electrode, wherein the first negative voltage is a substantially safe voltage with respect to damage to the mirror electrode and breakdown of the electrolyte when no mirror metal is present on the mirror electrode, and wherein the magnitude of the second negative voltage is the smaller of: the predetermined maximum drive voltage; the sum of the safe voltage and the electrolyte voltage drop, the latter being equal to the multiplication product of the measured current and the measured electrolyte resistance; and that which will cause the multiplication product of the measured sheet resistance and the measured current to be less than the predetermined maximum sheet IR drop. ### Claim 11 (depends on 10) The method of claim 10, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second negative voltage to account for the temperature dependence of the electrolyte resistance. ### Claim 12 (depends on 10) The method of claim 10, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second negative voltage to account for the temperature dependence of the mirror electrode sheet resistance. ### Claim 13 A method for optimizing the mirror uniformity and switching speed of a reversible electrochemical mirror of the type including a mirror electrode, a counter electrode, and an electrolyte disposed between and in electrical contact with the mirror and counter electrodes, wherein the electrolyte contains cations of an electrodepositable mirror metal, comprising the steps of: applying a first positive voltage to the mirror electrode relative to the counter electrode so that mirror metal is dissolved from the mirror electrode at a first rate; and applying a second positive voltage less positive than the first positive voltage to the mirror electrode relative to the counter electrode so that additional mirror metal is dissolved from the mirror electrode at a second rate which is slower than the first rate, wherein the first positive voltage does not exceed a predetermined maximum drive voltage. ### Claim 14 (depends on 13) The method of claim 13, wherein the second positive voltage is decreased with time so that the rate at which mirror metal is dissolved from the mirror electrode decreases with time. ### Claim 15 (depends on 14) The method of claim 14, wherein the second positive voltage is decreased with time continuously. ### Claim 16 (depends on 14) The method of claim 14, wherein the second positive voltage is decreased with time in steps. ### Claim 17 (depends on 13) The method of claim 13, wherein the second positive voltage is decreased based on the amount of charge passed between the mirror electrode and the counter electrode. ### Claim 18 (depends on 13) The method of claim 13, wherein the predetermined maximum drive voltage corresponds to a current that is less than the diffusion-limited current for dissolution of the mirror metal. ### Claim 19 (depends on 13) The method of claim 13, further comprising the steps of: measuring the sheet resistance between two locations on the mirror electrode; and measuring the current flowing between the mirror electrode and the counter electrode, wherein the second positive voltage is such that the multiplication product of the measured sheet resistance and the measured current is less than a predetermined maximum sheet IR drop. ### Claim 20 (depends on 19) The method of claim 19, wherein said step of measuring the sheet resistance comprises the steps of applying an alternating voltage between two electrical contacts on the mirror electrode and measuring an alternating current response to the alternating voltage. ### Claim 21 (depends on 19) The method of claim 19, wherein said step of measuring the sheet resistance comprises the steps of applying a direct voltage between two electrical contacts on the mirror electrode and measuring a direct current response to the direct voltage. ### Claim 22 (depends on 19) The method of claim 19, further comprising the step of: determining the electrical resistance of the electrolyte between the mirror electrode and the counter electrode, wherein the first positive voltage is a substantially safe voltage with respect to damage to the mirror electrode and breakdown of the electrolyte when no mirror metal is present on the mirror electrode, and wherein the magnitude of the second positive voltage is the smaller of: the predetermined maximum drive voltage; the sum of the safe voltage and the electrolyte voltage drop, the latter being equal to the multiplication product of the measured current and the measured electrolyte resistance; and that which will cause the multiplication product of the measured sheet resistance and the measured current to be less than the predetermined maximum sheet IR drop. ### Claim 23 (depends on 22) The method of claim 22, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second positive voltage to account for the temperature dependence of the electrolyte resistance. ### Claim 24 (depends on 22) The method of claim 22, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second positive voltage to account for the temperature dependence of the mirror electrode sheet resistance. ### Claim 25 A method for optimizing the mirror uniformity and switching speed of a reversible electrochemical mirror of the type including a mirror electrode, a counter electrode, and an electrolyte disposed between and in electrical contact with the mirror and counter electrodes, wherein the electrolyte contains cations of an electrodepositable mirror metal, comprising the steps of: applying a first negative voltage to the mirror electrode relative to the counter electrode so that mirror metal is deposited onto the mirror electrode at a first rate, wherein the first negative voltage is a substantially safe voltage with respect to damage to the mirror electrode and breakdown of the electrolyte when no mirror metal is present on the mirror electrode; measuring the sheet resistance between two locations on the mirror electrode; measuring the current flowing between the mirror electrode and the counter electrode; determining the electrical resistance of the electrolyte between the mirror electrode and the counter electrode; and applying a second negative voltage more negative than the first negative voltage to the mirror electrode relative to the counter electrode so that additional mirror metal is deposited onto the mirror electrode at a second rate which is faster than the first rate, wherein the magnitude of the second negative voltage is the smaller of: a predetermined maximum drive voltage; the sum of the safe voltage and the electrolyte voltage drop, the latter being equal to the multiplication product of the measured current and the measured electrolyte resistance; and that which will cause the multiplication product of the measured sheet resistance and the measured current to be less than a predetermined maximum sheet IR drop. ### Claim 26 (depends on 25) The method of claim 25, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second negative voltage to account for the temperature dependence of the electrolyte resistance and the temperature dependence of the mirror electrode sheet resistance. ### Claim 27 A method for optimizing the mirror uniformity and switching speed of a reversible electrochemical mirror of the type including a mirror electrode, a counter electrode, and an electrolyte disposed between and in electrical contact with the mirror and counter electrodes, wherein the electrolyte contains cations of an electrodepositable mirror metal, comprising the steps of: applying a first positive voltage to the mirror electrode relative to the counter electrode so that mirror metal is dissolved from the mirror electrode at a first rate, wherein the first positive voltage does not exceed a predetermined maximum drive voltage; measuring the sheet resistance between two locations on the mirror electrode; measuring the current flowing between the mirror electrode and the counter electrode; determining the electrical resistance of the electrolyte between the mirror electrode and the counter electrode; and applying a second positive voltage less positive than the first positive voltage to the mirror electrode relative to the counter electrode so that additional mirror metal is dissolved from the mirror electrode at a second rate which is slower than the first rate, wherein the magnitude of the second positive voltage is the smaller of: the predetermined maximum drive voltage; the sum of a safe voltage with respect to damage to the mirror electrode and breakdown of the electrolyte when no mirror metal is present on the mirror electrode plus the electrolyte voltage drop, the latter being equal to the multiplication product of the measured current and the measured electrolyte resistance; and that which will cause the multiplication product of the measured sheet resistance and the measured current to be less than the predetermined maximum sheet IR drop. ### Claim 28 (depends on 27) The method of claim 27, further comprising the steps of: measuring the temperature of the mirror; and adjusting the second positive voltage to account for the temperature dependence of the electrolyte resistance and the temperature dependence of the mirror electrode sheet resistance.