ACTFEL Alternating Current Thin Film Electroluminescent Lamps

Objective  Use photolithography to pattern ITO  Develop photoresist and etch ITO  Apply layers of phosphors, dielectric, and silver  Power up lamp  Troubleshoot

Preparation and Priming  Prepare the substrate (glass, with ITO): Wash with appropriate solvent to remove any dirt and other impurities –Acetone, MeOH Dry with Nitrogen  Deposit Primer Chemical that coats the substrate and allows for better adhesion of the resist, HMDS

Spin-Coating the Resist  Spin-coat the photoresist onto the surface of the glass RPM: 4500 Time: 42 sec Produces a thin uniform layer of photoresist on the glass surface.  Use red/amber safe light at this stage

Soft-Baking  Put on hotplate Temperature: 115°C, Time: 5 min  Removes volatile solvents from the coating  Makes photoresist imageable  Hardens to amorphous solid  Be careful not to overbake and destroy the sensitizer  Be careful not to not soft-bake

Mask Alignment and Exposure  Photomask is a square piece of transparency printed on by a laser printer  Maximize light intensity using photo-detector  Remove all shadows from exposure area  After alignment, the photoresist is exposed to the UV lamp

Photoresist Developer Highly pure buffered alkaline solution  Removes proper layer of photoresist upon contact or immersion  Degree of exposure affects the resolution curves of the resist  Immerse wafer in developer and swirl around for 90 seconds  Wash developed wafer with deionized water and dry with nitrogen

Etching the ITO  Put glass in a beaker of 20% HCl, 5% HNO 3  Heat beaker for 10 minutes in water bubble bath  Check for infinite resistance across The Gap  Fix Gap with razor blade if necessary  Remove wafers and wash in acetone  Dry with Nitrogen

 After the ITO is patterned the ACTFEL lamp can be made.  Each layer comes packaged separately as a thick paste (stir before using).  The thickness of each layer is controlled by using scotch tape as a spacer.  Apply scotch tape along 3-5mm on two parallel sides of the plate.  Apply the pastes in sequence using a spatula. Thin them by scraping a microscope slide across the layer.  Dry and cure each layer before application of the next Each layer is dried in an oven at 130°C for 15 minutes.  1 st phosphor  2 nd dielectric  3 rd conductive silver rear electrode Applying Thin Films

The dielectric layer should cover all of the phosphor layer and be as thin as possible without risking a short in the capacitor. The silver layer must not touch the ITO. Parts of the ITO layer are removed in order to extend the silver layer to the edge of the glass. This makes it easier to connect the lamp to a power source. The black lines mark the etched ITO pattern, and are used to accurately place the scotch tape; they’re later removed with acetone. Phosphor Layer Dielectric Layer Silver Layer (Rear Electrode) Cross-section of TFEL display  The thin films must be applied to the substrate within defined boundaries to avoid shorting the capacitor.  Layer Constraints The phosphor layer should be as thin as possible Applying Thin Films 2

 After the thin films are dry, the lamp needs a power source.  Copper tape is used to make good contacts without damaging the lamp. Small pieces of tape are attached to the ITO layer and the silver layer separately.  The phosphor requires a changing electric field in order to fluoresce. A DC voltage will only produce a changing electric field in a capacitor as it charges. In order to produce continuous lighting an AC voltage is required.  Normal 110V 60Hz AC power can be used to light your lamp. In the lab we use a high frequency power supply Hz and a few hundred volts, which gives a brighter light. Front and back of device Device with leads on, powered, and in darkness. Powering Lamps