Method for making electrochromic films having improved etch resistance

• US 4,233,339 A
• Filed: 10/23/1978
• Issued: 11/11/1980
• Est. Priority Date: 10/23/1978
• Status: Expired due to Term

• Current Assignee: Timex Corporation (Tanager Group BV)
• Original Assignee: Timex Corporation (Tanager Group BV)
• Inventors: Crandall, Richard, Leibowitz, Marshall, Faughnan, Brian
• Primary Examiner(s): Smith, John D.
• Application Number:
  US05/953,716
• Time in Patent Office: 750 Days
• Field of Search: 427/108, 427/109, 427/162, 427/164, 427/126, 427/377, 427/165, 427/166, 427/372.2, 350/357, 29/570, 204/192 P
• US Class Current: 427/108
• CPC Class Codes: G02F 1/1524 Transition metal compounds

Abstract

Thin, amorphous electrochromic layers deposited on substrate electrodes by, for example, vacuum deposition techniques, are subjected to a special heat treatment at a selected high temperature for a selected short time to convert at least a free portion of each layer to be exposed to the electrolyte from the amorphous form to a crystalline form while preventing excessive water loss which might adversely affect the electrochromic properties of the layer for display purposes. Crystallization of at least the free surface portion of the electrochromic layer significantly increases its etch resistance whereas retention of water in the electrochromic layer maintains satisfactory electrochromic properties for display purposes.

Claims

1. A method for improving the resistance of electrochromic material to the degrading effects, such as etching, resulting from contact with electrolyte means associated with electrochromic displays, comprising the steps of:

(a) forming an amorphous, water-bearing film of electrochromic material of selected thickness, said film having electrochromic properties suitable for display purposes but having a free surface susceptible to etching by said electrolyte means;

(b) subjecting the film to a heat treatment at a selected high temperature at least equivalent to the crystallization temperature of said electrochromic material for a selected short time of sufficient duration so as to cause crystallization through at least the free surface portion of the film thickness but of insufficient duration to cause substantial loss of water from said film,

whereby crystallization of at least said free surface portion substantially increases resistance of the film to etching while retention of water in the film preserves the electrochromic properties for display purposes.

2. The method of claim 1 wherein the amorphous, water-bearing film is formed by vacuum deposition techniques.

3. The method of claim 1 wherein the film of electrochromic material is selected from tungsten trioxide, molybdenum trioxide or admixtures thereof.

4. The method of claim 3 wherein the electrochromic material is tungsten trioxide and temperature of the heat treatment is at least 265°

C. and the time is from about 0.5 to 15 minutes.

5. The method of claim 4 wherein the time is from about 1 to 2 minutes at a temperature of at least 500°

C.

6. A method for making an electrochromic display having electrochromic material with improved resistance to the degrading effects, such as etching, resulting from the contact with electrolyte associated with electrochromic displays, comprising the steps of:

(a) providing a first substrate having transparent electrodes thereon;

(b) depositing a thin amorphous, water-bearing film of electrochromic material upon each electrode and subjecting each film to a heat treatment at a selected high temperature at least equivalent to the crystallization temperature of the electrochromic material for a selected short time of sufficient duration so as to cause crystallization through at least the free surface portion of the film but of insufficient duration to cause substantial loss of water therefrom;

(c) providing a second substrate having a counter electrode, the first and second substrates being positioned in spaced working relation;

(d) filling the space between the substrates with electrolyte; and

(e) sealing the first and second substrates together with adhesive means, whereby crystallization of at least said free surface portion of each electrochromic film in step (b) substantially increases resistance of the film to etching by said electrolyte, thereby increasing the useful life of said electrochromic display, while retention of water in said films preserves the electrochromic properties thereof for display purposes.

7. The method of claim 6 wherein the film of electrochromic material is deposited upon each transparent electrode by vacuum deposition techniques.

8. The method of claim 6 wherein the film of electrochromic material is selected from tungsten trioxide, molybdenum trioxide or admixtures thereof.

9. The method of claim 8 wherein the electrochromic material is tungsten trioxide and the temperature of the heat treatment is at least 265°

C. and the time is from about 0.5 to 15 minutes.