Field-Emission Displays (FED´s)

Transcription

Field-Emission Displays
(FED´s)
Stephanie Dirksmeyer, 671197
Contents
1. Working Principle
2. Applied Phosphors
2. Features
3. Developments
http://www.prad.de/new/news/shownews_tv871.html
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Stephanie Dirksmeyer | Field-Emission Displays
26.06.2016
generation of electrons
acceleration of electrons
excitation of phosphors
emission by phosphors
taken from:
http://elektroniktutor.de/technologien/te_pict/microtip.gif
 comparable to cathode ray tubes!
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generation of electrons: via field emission
electrical fields above 109 V/cm set free electrons from metal
surfaces via tunneling
potential drop
due to E-field
http://en.wikipedia.org/wiki/File:Fig
216_Field_Emission.PNG
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high field strength is reached by special
geometry
high density of field lines at sharply curved
surfaces
http://cnx.org/content/m42317
/latest/?collection=col11406/latest
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use of Spindt-type emitters
cones of molybdenum
mechanically and thermally stable
low work function
diameter at base and height:
ca. 1 µm
http://en.wikipedia.org/wiki/File:Fig218_Field_Emitter_Array.
PNG
application of field via extraction grid/ gate (U ≈ 50 V)
arranged as array: up to 1000 emitters per pixel
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further acceleration towards cathode
(V > 500 V)
gate is used for easier control
excitation of phosphor pixels
alternative emitter materials:
carbon nanotubes (CNT´s)
silicon (in the beginning)
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requirements to phosphors:
colour point (red, blue, green pixels)
high quantum efficiency
short decay time
stability
in general the same as for CRT displays
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special requirement to FED phosphors:
excitation energy is lower
(30 kV in CRT´s ↔ max. 8 kV in FED´s)
excitation only at surface
decreasing number of involved luminescent
centers: efficiency saturation
more defects at surface: quenching
high current density: fast degradation
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2. Applied phosphors
suited phosphors:
red
green
blue
Y2O3:Eu
ZnO:Zn
ZnGa2O4
YVO4:Eu
Gd2O2S:Tb
Y2SiO5:Ce
use of oxidic hosts
or inorganic protective coating
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mechanism of cathodoluminescence
excitation of the host  formation of excitons
luminescent centres trap excitons
relaxation under luminescence under 3 mechanisms
centre luminescence
characteristic luminescence
donor-acceptor luminescence
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mechanisms of luminescence
centre luminescence:
at an activator ion influenced by its environment (crystal field theory)
broad bands
typical for transition metals (e.g. Mn2+) and complex anions (e.g.
(VO4)3-)
characteristic luminescence:
based on f-f- transitions of rare earth ions
line emitters
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donor-acceptor luminescence:
trapping of single charge carriers
recombination under luminescence
broad, unstructured bands due to vibrations
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3. features
advantages
flat screen: ca. 2 mm
self-emissive
wide viewing angle (no polarisation filters)
quick response time: µs-range
low power consumption
high contrast (black matrix)
experience from CRT-technique can be adapted
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3. features
disadvantages
high accuracy needed in production
sealing: high vacuum inside
stability of phosphors
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3. Developments
effect of field emission known since 19th century
theoretical explanation 1928 by Fowler and Nordheim
early use in field-emission microscope
development of FED technique since ≈ 1990 by different
companies
many campaigns stopped
only prototypes were build
today research on CNT emitters
demonstration by Sony
http://www.prad.de/new/news/shownews_tv871.html
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Sources
Bredol, M., Kynast, U., & Ronda, C. (1994). Leuchtstoffe für Kathodenstrahlröhren. Angewandte Chemie, S. 36 - 43.
Cathey, D. (1995). Field Emission Display. VLSI Technology, Systems and Applications, (S. 131 - 136). Taipei.
Itoh, S., & Tanaka, M. (4 2002). Current Status of Field-Emission Displays. Proceedings of the IEEE(90).
Jüstel, T., Feldmann, C., & Ronda, C. (2000). Leuchstoffe für aktive Displays. Physikalische Blätter(56), S. 55 - 58.
Jüstel, T., Nikol, H., & Ronda, C. (1998). New Developments in the Field of Luminescent Materials for Lightning and
Displays. Angewandte Chemie, International Edition(37), S. 3084 - 3103.
Shah, I. (6 1997). Field-emission displays. Physics World.
Mietke, D. www.elektroniktutor.de. Abgerufen am 11. 4 2014 von http://elektroniktutor.de/technologien/fed.html
www.cnx.org. (6. 6 2012). Abgerufen am 11. 4 2014 von http://cnx.org/content/m42317/latest/?collection=col11406/latest
http://de.wikipedia.org/wiki/Feldemission
http://en.wikipedia.org/wiki/Field_emission_display#History
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Field-Emission Displays (FED´s)

Transcription

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