ACTFELACTFEL Alternating Current Thin Film Electroluminescent Lamps

ObjectiveObjective

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

Preparation and PrimingPreparation and Priming

Prepare the substrate (glass, with ITO):Wash with appropriate solvent to remove any dirt and other impurities

– Acetone, MeOHDry with Nitrogen

Deposit PrimerChemical that coats the substrate and allows for better adhesion of the resist, HMDS

Spin-Coating the ResistSpin-Coating the Resist

Spin-coat the photoresist onto the surface of the glass

RPM: 4500Time: 42 secProduces a thin uniform layer of photoresist on the glass surface.

Use red/amber safe light at this stage

Soft-BakingSoft-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 ExposureMask 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 DeveloperPhotoresist DeveloperHighly 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 ITOEtching the ITO

Put glass in a beaker of 20% HCl, 5% HNO3 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.1st phosphor2nd dielectric3rd conductive silver rear electrode

Applying Thin FilmsApplying 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 ConstraintsThe phosphor layer should be as thin as possible

Applying Thin Films 2Applying 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 60-2000 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 LampsPowering Lamps