METHOD FOR PREPARING INVISIBLE ANODIC ALUMINUM OXIDE PATTERN

• US 20200131659A1
• Filed: 10/24/2018
• Published: 04/30/2020
• Est. Priority Date: 10/24/2018
• Status: Active Grant

• Current Assignee: National Cheng KUNG University (Government of The Republic of China)
• Original Assignee: National Cheng KUNG University (Government of The Republic of China)
• Inventors: CHUNG, CHEN-KUEI, CHEN, YUN, YU, CHUNG-YU
• Granted Patent: US 10,947,634 B2
• Time in Patent Office: Days
• CPC Class Codes: B01D 67/0065 by anodic oxidation
• CPC Class Codes: B01D 71/025 Aluminium oxide
• CPC Class Codes: C25D 11/022 Anodisation on selected surface areas
• CPC Class Codes: C25D 11/024 Anodisation under pulsed or modulated current or potential
• CPC Class Codes: C25D 11/045 for forming AAO templates
• CPC Class Codes: C25D 11/06 characterised by the electrolytes used
• CPC Class Codes: C25D 11/10 containing organic acids
• CPC Class Codes: C25D 11/12 Anodising more than once, e.g. in different baths
• CPC Class Codes: C25D 11/18 After-treatment, e.g. pore-sealing
• CPC Class Codes: C25D 11/24 Chemical after-treatment

Abstract

A method for preparing invisible anodic aluminum oxide (AAO) patterns is revealed. The method includes a plurality of steps. First take an aluminum substrate. Then anodize the aluminum substrate for the first time to get a first anodic aluminum oxide (AAO). Next perform photolithography so that a photoresist forms a pattern on the aluminum substrate with the first AAO. Lastly anodize the aluminum substrate for the second time so that a second AAO is formed on the pattern and the pattern becomes invisible.

Claims

1. A method for preparing invisible anodic aluminum oxide patterns comprising the steps of:

Step 1;

taking an aluminum substrate;

Step 2;

anodizing the aluminum substrate for the first time to get a first anodic aluminum oxide (AAO);

Step 3;

performing photolithography so that a photoresist forms a pattern on the aluminum substrate with the first AAO;

Step 4;

anodizing the aluminum substrate for the second time so that a second AAO is formed on the pattern and the pattern becomes invisible.

2. The method as claimed in claim 1, wherein the invisible pattern is further treated by annealing or pore-widening so that the invisible pattern can be later made visible.

3. The method as claimed in claim 2, wherein the invisible pattern treated by annealing is made visible by ultraviolet (UV) light while the invisible pattern treated by pore-widening is rendered visible by droplet addition.

4. The method as claimed in claim 2, wherein the annealing is performed in an annealing furnace at a temperature between 200 degrees Celsius (°

C.) and 500°

C. for 3-6 hours.

5. The method as claimed in claim 4, wherein the temperature of the annealing is 400°

C. over a period of 3 hours.

6. The method as claimed in claim 2, wherein the aluminum substrate is immersed in a phosphoric acid solution during the pore-widening.

7. The method as claimed in claim 6, wherein the concentration of the phosphoric acid solution is 1 wt %-20 wt % and the temperature thereof is 10°

C.-45°

C.;

the second AAO without being covered with the photoresist is treated by pore-widening for 30-1800 seconds.

8. The method as claimed in claim 2, wherein a layer of metal is electroplated on a surface of the aluminum substrate already treated by pore-widening;

the metal is selected from the group consisting of platinum (Pt), aluminum (Al), silver (Ag), gold (Au), iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), titanium (Ti), tantalum, (Ta), copper (Cu) or a combination thereof.

9. The method as claimed in claim 2, wherein a layer of metal or alloy whose reflectivity is higher than 70% is electroplated on the surface of the aluminum substrate and the thickness of the layer is 5-25 nm.

10. The method as claimed in claim 1, wherein the aluminum substrate is selected from the group consisting of a pure aluminum substrate, an aluminized substrate and an aluminum alloy substrate.

11. The method as claimed in claim 1, wherein a pulse voltage is applied to the aluminum substrate for 30-500 seconds during the first anodizing;

the pulse voltage can be positive voltage ranging from 30 V to 120 V or negative voltage ranging from −

2 V to −

4 V.

12. The method as claimed in claim 1, wherein during the photolithography, a photoresist is coated on the aluminum substrate with the first AAO and then soft baked at 70°

C. for 1 minute for removal of a part of solvents;

the pattern is transferred from a photomask to the photoresist and next the photoresist is hard baked at 120°

C. for 1 minute to remove any residual solvents;

a developer solution is used for washing away the exposed photoresist if the photoresist is the positive photoresist;

once the photoresist is the negative photoresist, the developer solution is used for washing away the unexposed photoresist.

13. The method as claimed in claim 1, wherein a pulse voltage is applied to the aluminum substrate for 30-500 seconds during the second anodizing;

the pulse voltage can be positive voltage ranging from 30 V to 120 V or negative voltage ranging from −

2 V to −

4 V.