ou nanolab/nsf nue/bumm & johnson electroluminescent lamps the luxprint electroluminescent inks...

OU NanoLab/NSF NUE/Bumm & JohnsonOU NanoLab/NSF NUE/Bumm & Johnson

Electroluminescent LampsElectroluminescent Lamps

The Luxprint Electroluminescent InksThe Luxprint Electroluminescent Inksfor this activity were donated by DuPont.for this activity were donated by DuPont.

http://www2.dupont.com/DuPont_Home/en_US/


OutlineOutline Motivation Motivation HistoryHistory Final SchematicFinal Schematic Useful PhysicsUseful Physics

Thin film Capacitors (AC)Thin film Capacitors (AC) Luminescence from phosphorsLuminescence from phosphors

How to make one:How to make one: OverviewOverview Lithography: patterning ITOLithography: patterning ITO Applying the phosphorApplying the phosphor Power up/ testing/ trouble Power up/ testing/ trouble

shootingshooting Definitions/ GlossaryDefinitions/ Glossary


MotivationMotivation Electroluminescence is the direct conversion of Electroluminescence is the direct conversion of

electricity to light.electricity to light. Electroluminescence is cool light, unlike incandescent Electroluminescence is cool light, unlike incandescent

lamps where light is generated by heating a filament lamps where light is generated by heating a filament to high temperatures.to high temperatures.

The heat from the lamps barely increase by 1The heat from the lamps barely increase by 1°° C C above ambient temperature. above ambient temperature.

Solid state lighting.Solid state lighting. Unlike incandescent lighting there is no filament and Unlike incandescent lighting there is no filament and

therefore no critical failure. Light output decays with therefore no critical failure. Light output decays with age.age.

EL lamps are probably the most rugged lighting EL lamps are probably the most rugged lighting technology available.technology available.

A promising futureA promising future Thanks to recent advances in electronics and Thanks to recent advances in electronics and

materials chemistry, EL lamps have re-emerged as an materials chemistry, EL lamps have re-emerged as an innovative and exciting lighting technique.innovative and exciting lighting technique.

Facts taken from An Introduction to Dupont's Screenprintable EL Material System


History of ElectroluminescenceHistory of Electroluminescence

1936: 1936: EL was discovered by a G. Destriau.EL was discovered by a G. Destriau.

1940's:1940's: Chrysler tested EL for Automotive Chrysler tested EL for Automotive Applications.Applications.

1950's: 1950's: Sylvania developed and sold EL night lights.Sylvania developed and sold EL night lights.

1960's: 1960's: The industry saw decline.The industry saw decline.

1970's:1970's: Acceptance of EL lamps in the aircraft Acceptance of EL lamps in the aircraft industry.industry.

1980's: 1980's: EL hit the automotive market and held on to EL hit the automotive market and held on to aviation.aviation.

1990's: 1990's: EL continues in automotive, aviation, and is EL continues in automotive, aviation, and is entering consumer markets.entering consumer markets.

Taken from An Introduction to Dupont's Screenprintable EL Material System


Types of Electroluminescent Types of Electroluminescent DevicesDevices

from ETRIfrom ETRI


ACTFEL Lamps: Schematic of Final LampACTFEL Lamps: Schematic of Final Lamp

The ITO and Silver layers act as two plates of a capacitor. The ITO The ITO and Silver layers act as two plates of a capacitor. The ITO is transparent, so the photons can pass through the layer.is transparent, so the photons can pass through the layer.

The AC current produces a changing electric field in the capacitor The AC current produces a changing electric field in the capacitor that excites the phosphor. The excited phosphors emit light.that excites the phosphor. The excited phosphors emit light.

The dielectric evens out the E field, reflects light, and prevents the The dielectric evens out the E field, reflects light, and prevents the capacitor from shorting.capacitor from shorting.

glass

ITO

Silver Layer

Phosphor

Dielectric

h

AC current

(1-3 µm)

(Rear Electrode)

(30µm)


ACTFEL Lamps: Cross-section of Final ACTFEL Lamps: Cross-section of Final LampLamp

Dielectric Layer(1-3 µm particles)

Silver Layer(Rear

Electrode)

Phosphor Layer(30µm particles)

ITO coated Glass


ACTFEL Lamps: Basic PhysicsACTFEL Lamps: Basic Physics Alternating Current Thin Alternating Current Thin

Film Electroluminescent Film Electroluminescent Lamps are essentially Lamps are essentially just capacitors.just capacitors.

The electric field found The electric field found inside a parallel plate inside a parallel plate capacitor is used to capacitor is used to excite phosphor excite phosphor molecules.molecules.

The excited phosphor The excited phosphor emits light.emits light.


ACTFEL Lamps: Basic Physics, ContinuedACTFEL Lamps: Basic Physics, Continued

Small green circles are Small green circles are manganese atoms.manganese atoms.

Large blue circles are Large blue circles are excited manganese atoms.excited manganese atoms.

The horizontal dashes The horizontal dashes represent mobile electrons represent mobile electrons in the phosphor particle.in the phosphor particle.

Electrons in the phosphor particles are driven by the electric Electrons in the phosphor particles are driven by the electric field. These electrons slam into manganese atoms in the field. These electrons slam into manganese atoms in the phosphor and excite them.phosphor and excite them.

The excited manganese atoms relax by emitting a visible photon.The excited manganese atoms relax by emitting a visible photon.

The motion of the electrons is proportional to the electric field.The motion of the electrons is proportional to the electric field.

The electric field is proportional to the applied voltage and The electric field is proportional to the applied voltage and inversely proportional to the electrode separation. Thus the inversely proportional to the electrode separation. Thus the brightness will increase by raising the voltage or thinning the brightness will increase by raising the voltage or thinning the phosphor and the dielectric layers.phosphor and the dielectric layers.

phosphor particle

electrodesZnS:Mn


Energy Band Diagram for ACTFELEnergy Band Diagram for ACTFEL


Making an EL Lamp: OverviewMaking an EL Lamp: Overview

Photolithography: patterning ITOPhotolithography: patterning ITO

Applying the phosphor, dielectric, and silver Applying the phosphor, dielectric, and silver layerslayers

Power up/ testing/ trouble shootingPower up/ testing/ trouble shooting


Patterning the ITO by PhotolithographyPatterning the ITO by Photolithography One way to shape the EL lamp One way to shape the EL lamp

is by patterning the ITO is by patterning the ITO electrode.electrode.

Only the phosphor under the ITO Only the phosphor under the ITO electrode will be excited.electrode will be excited.

Photolithography is used to Photolithography is used to transfer a pattern.transfer a pattern.

1.1. The ITO coated glass is covered The ITO coated glass is covered with a photo resistwith a photo resist

2.2. The resist is exposed under a mask The resist is exposed under a mask of the desired pattern.of the desired pattern.

3.3. The resist is developed. The The resist is developed. The exposed sections of the resist exposed sections of the resist dissolve while the unexposed dissolve while the unexposed sections harden (positive type sections harden (positive type resist).resist).

See the photolithography slideshow See the photolithography slideshow for further details.for further details.


Patterning ITO coated slidesPatterning ITO coated slides

After a pattern has been transferred, After a pattern has been transferred, the ITO layer of the ACTFEL lamp can the ITO layer of the ACTFEL lamp can be etched.be etched. A solution of hydrochloric acid and nitric A solution of hydrochloric acid and nitric

acid will oxidize and remove the acid will oxidize and remove the conductive metal oxide.conductive metal oxide.

The etched pattern shown below was The etched pattern shown below was created by photolithography using the created by photolithography using the mask shown to the right.mask shown to the right.

Other lithographic techniques (such as Other lithographic techniques (such as molecular beam epitaxy) can be used molecular beam epitaxy) can be used to etch the ITOto etch the ITO

NoteNote: The pattern is reversed because : The pattern is reversed because the lamp will be viewed from the the lamp will be viewed from the opposite side of the glass.opposite side of the glass.


Notes on Etching:Notes on Etching: What type of patterns don’t work? What type of patterns don’t work?

The pattern to the right represents The pattern to the right represents an etched ITO pattern on glass. an etched ITO pattern on glass. The black parts are where ITO is The black parts are where ITO is present. (positive resist)present. (positive resist)

The ITO connects to a power The ITO connects to a power source that makes contact along source that makes contact along the right edge of the display (the the right edge of the display (the red bar).red bar).

The phosphor under the ITO electrode will only be excited if The phosphor under the ITO electrode will only be excited if the ITO has current running through it. the ITO has current running through it. Notice that the ITO inside the capital "D" is not connected to the Notice that the ITO inside the capital "D" is not connected to the

rest of the ITO.rest of the ITO. This section of ITO lacks current. This section of ITO lacks current.


What type of patterns work?What type of patterns work?

The pattern to the right is the The pattern to the right is the same as the pattern in the same as the pattern in the last slide, but the inside of last slide, but the inside of the “D” has been connected the “D” has been connected to the rest of the ITO. Now to the rest of the ITO. Now this section of the ITO will this section of the ITO will have power. have power.

The design problem in the last example can be The design problem in the last example can be fixed by modifying the etched pattern.fixed by modifying the etched pattern.

To illuminate the pattern, all the ITO must be To illuminate the pattern, all the ITO must be connected to the power source.connected to the power source.


Applying Thin FilmsApplying Thin Films After the ITO is patterned the ACTFEL lamp can made.After the ITO is patterned the ACTFEL lamp can made. Each layer comes packaged separately as a thick paste Each layer comes packaged separately as a thick paste

(stir before using).(stir before using). The thickness of each layer is controlled by using scotch The thickness of each layer is controlled by using scotch

tape as a spacer.tape as a spacer. Apply scotch tape along 3-5mm on two parallel sides of Apply scotch tape along 3-5mm on two parallel sides of

the plate.the plate. Apply the pastes in sequence using a Apply the pastes in sequence using a

spatula. Thin them by scraping a spatula. Thin them by scraping a microscope slide across the layer.microscope slide across the layer.

Dry and cure each layer before Dry and cure each layer before application of the nextapplication of the next Each layer is dried in an oven at 130°C for Each layer is dried in an oven at 130°C for

~15 minutes.~15 minutes. 11stst phosphor (Luxprint 8152) phosphor (Luxprint 8152) 22ndnd dielectric (Luxprint 8153) dielectric (Luxprint 8153) 33rdrd conductive silver rear conductive silver rear

electrodeelectrode (Luxprint 9145) (Luxprint 9145)


Applying Thin FilmsApplying Thin Films

The dielectric layer should cover all of the phosphor layer and be as thin as The dielectric layer should cover all of the phosphor layer and be as thin as possible without risking a short in the capacitor.possible without risking a short in the capacitor.

The silver layer must The silver layer must notnot touch the ITO. Parts of the ITO layer are removed 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 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.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 The thin films must be applied to the substrate within defined boundaries to substrate within defined boundaries to avoid shorting the capacitor.avoid shorting the capacitor.

Layer ConstraintsLayer Constraints The phosphor layer should be as thin as The phosphor layer should be as thin as

possiblepossible


Power UpPower Up 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.


Trouble Shooting: Non-uniformity of LightingTrouble Shooting: Non-uniformity of Lighting

Notice the dark regions along the bottom and upper left corner of the display.

This non-uniformity is caused by an irregularity in the thickness of the thin films.

The difference in thickness between the center of the display and the dark band at the bottom is about 16 microns.

Areas where the film is thinner will be brighter because the electric field is larger here. Thicker areas will be dimmer.


Definitions/ Glossary:Definitions/ Glossary:

ACTFELACTFEL – alternating current thin film electroluminescence; gives off light when – alternating current thin film electroluminescence; gives off light when influenced by electrical current.influenced by electrical current.

Electroluminescence Electroluminescence – the direct conversion of electrical energy into light.– the direct conversion of electrical energy into light. Thin layerThin layer - a very thin deposition of a colloidal substance (phosphor, dielectric, - a very thin deposition of a colloidal substance (phosphor, dielectric,

silver) onto the ITO coated glass plate.silver) onto the ITO coated glass plate. ITOITO – Indium Tin Oxide (In – Indium Tin Oxide (In220033:Sn0:Sn022) A thin layer of indium oxide that has been ) A thin layer of indium oxide that has been

doped with tin; transparent, conductive coating on glass plate.doped with tin; transparent, conductive coating on glass plate. PhosphorPhosphor – powders made of materials such as zinc sulfide, doped with either – powders made of materials such as zinc sulfide, doped with either

copper or manganese to achieve the emission colors when exposed to an electric copper or manganese to achieve the emission colors when exposed to an electric field. field.

Dielectric layerDielectric layer – an insulating layer that serves to even out the electric field – an insulating layer that serves to even out the electric field across the phosphor layer and prevents short circuits. The dielectric in this case is across the phosphor layer and prevents short circuits. The dielectric in this case is barium titanate. barium titanate.

ElectrodesElectrodes – form the plates of the capacitor; one front electrode of transparent – form the plates of the capacitor; one front electrode of transparent ITO and one back electrode of silver.ITO and one back electrode of silver.

AcknowledgementsAcknowledgements The Luxprint Electroluminescent Inks for this lab were donated by DuPont The Luxprint Electroluminescent Inks for this lab were donated by DuPont

Microcircuit Materials. Microcircuit Materials. http://http://www.mcm.dupont.comwww.mcm.dupont.com Initial development of this lab activity was performed by James Dizikes and Lloyd Initial development of this lab activity was performed by James Dizikes and Lloyd

Bumm with the support of a Nanotechnology Undergraduate Education program Bumm with the support of a Nanotechnology Undergraduate Education program grant. grant. NSF DMR-0304664NSF DMR-0304664

http://www.mcm.dupont.com/

http://www.mcm.dupont.com/

http://www2.dupont.com/DuPont_Home/en_US/

ou nanolab/nsf nue/bumm & johnson electroluminescent lamps the luxprint electroluminescent inks...

Documents

incandescent lamps

phosphor particles

phosphor power

phosphor molecules

film electroluminescent

excited manganese atoms

cool light

changing electric field