L. M. Schiavone

Electrochromic iridium oxide films prepared by reactive sputtering

We report the preparation and electrochromic properties of iridium oxide films deposited by reactively sputtering iridium in a humidified oxygen discharge. These sputtered iridium oxide films (SIROFs) have the fast coloring and bleaching kinetics and excellent stability previously observed for anodically grown iridium oxide films (AIROFs). SIROFs deposited on SnO2‐coated glass can be modulated from clear to blue‐gray with properties similar to those of AIROFs. In addition, SIROFs deposited on metal substrates exhibit a variety of colors which can be electrically altered. This adds a new dimension to the range of potential applications for iridium oxide displays.

Electrochromism of anodic iridium oxide films on transparent substrates

Anodic iridium oxide films (AIROF’s) can be grown and operated on transparent substrates. Using SnO2‐coated glass as the substrate we can monitor large, rapid, and persistent variations of the light intensity transmitted through the AIROF. The voltammogram of the AIROF on SnO2‐coated glass is essentially identical to that of an AIROF on iridium. This proves that the electrochemistry producing the coloration does not involve the substrate.

Solid‐state electrochromic cell with anodic iridium oxide film electrodes

A new solid‐state electrochromic cell has been fabricated using an anodic iridium oxide film (AIROF) display electrode. The cell has the symmetric sandwich structure AIROF‖Nafion‖AIROF, with the Nafion solid electrolyte opacified by an in situ precipitation technique. A symmetric square‐wave voltage of 1.5 V amplitude produces clearly perceivable color changes from pale to dark blue‐gray in ≈1 sec when viewed in diffuse reflection. Good open‐circuit optical memory is exhibited: (typical loss in attenuation of 8%/day).

Electrochromic cells with iridium oxide display electrodes

Abstract We report the fabrication and electrochromic behavior of iridium oxide film electrodes, including a specific display electrode design compatible with the high peak ion-insertion current densities accepted by this material and necessary for the shortest possible response time. The configuration of a complete two-terminal display cell, in which the high capacity counter electrode behaves as a pseudo-reference electrode, is presented. Cell performance, including the use of IR compensated constant-voltage address when response time is limited by impedances external to the iridium oxide itself, is reported.

Matrix‐addressable electrochromic display cell

We report an electrochromic display cell with intrinsic matrix addressability. The cell, based on a sputtered iridium oxide film (SIROF) and a tantalum‐oxide hysteretic counterelectrode, has electrochromic parameters (i.e., response times, operating voltages, and contrast) similar to those of other SIROF display devices, but in addition, has short‐circuit memory and voltage threshold. Memory and threshold are sufficiently large to allow, in principle, multiplexing of electrochromic display panels of large‐screen TV pixel size.

Temperature dependence of electrochromic processes in iridium oxide displays

We report measurements of the temperature dependence of coloration and bleaching times of electrochromic iridium oxide films in the range +20 to −43 °C. The intrinsic response times increase gradually with decreasing temperature according to an activation energy of ∼0.25 eV. For a contrast ratio of ∼4:1, suitable for a practical device, we find that the response times remain below ∼0.25 sec for T⩾−10 °C and below 1 sec for T⩾−25 °C. We have also found that the temperature variation of the response times is independent of pH, so that an optimized electrolyte can be chosen for a practical device. Moreover, its independence of pH suggests that the electrochromism of iridium oxide is due to insertion and fast‐ion diffusion of the same ion species in either basic or acidic aqueous electrolytes.