Flat Panel Displays --Principles, Materials and Processes Jing Zhang 04/06/2004 Outline • CRT (Cathode Ray Tube) Displays • Flat Panel Displays - Classification; - Liquid Crystal Displays; -
Download ReportTranscript Flat Panel Displays --Principles, Materials and Processes Jing Zhang 04/06/2004 Outline • CRT (Cathode Ray Tube) Displays • Flat Panel Displays - Classification; - Liquid Crystal Displays; -
Flat Panel Displays -- Principles, Materials and Processes
Jing Zhang
04/06/2004
Outline
• CRT (Cathode Ray Tube) Displays • Flat Panel Displays - Classification; - Liquid Crystal Displays; - Basic Principles; - Addressing Issues; - Modified LCD - Field Emission Displays; • Conclusions
CRT
•
CRT lives on
: 50s – VS EL; 60s – VS Plasma panels; now – VS LCD.
•
Advantage
: Available in a variety of sizes with a wide selection of phosphors; Fast response time; Low cost, etc.
•
Disadvantage
: Depth needed to focus or scan the beam; High power consumption.
CRT Displays – Basic Operations Left: Basic structure of Cathode-ray tube.
Right: Addressing method of CRT – Raster.
Flat Panel Displays
• Flatness Ratio: Depth to picture diagonal • Definition: Flat; Light; Require less power… • Classification: Emissive: Gas discharge; Plasma panel; Light emitting diode; Vacuum fluorescence; Electroluminescence; Flat cathode-ray tube; Non-emissive: Liquid crystal; Electromechanical; Electrochromatic; Electroactive solids;
Liquid Crystal
• Shape & Phases:
Liquid Crystal Displays
• Principle of a twisted nematic (TN) LCD • Supertwisted nematic LC cell: Larger twisted angle; Smaller voltage required
Addressing Schemes for LCD
Left: Direct Addressing Right: Passive Matrix LCD with row and column electrodes
TFT matrix Addressed LCD
• Motivation: To improve the response speed • Circuit & Schemes:
Fabrication of TFTs
• TFTs are Metal-Insulator-Semiconductor Field Effect Transistors, which are used more often as bottom-gate.
• For gate-dielectric: CdSe – aSi – PolySi • A-Si: Low mask count; Small number of mask alignments and processing steps • P-Si: Higher mobility; but needs to develop low temperature processing.
Guest – Host (GH) Displays
• TN & STN: Low transmittance; High power consumption.
• GH Displays: Fewer polarizer and color filters; Bright; Wide viewing angle.
• Host – Liquid Crystal; Guest – anisotropic dyes
Guest - Host Displays Left: Basic GH cell. Off state: Polarized white light is absorbed by the dye. Remaining spectrum exits as the colored light. On state: Dyes are tuned by electric field and allow the light to pass as white light.
Right: Double GH cell. The polarizer is replaced by the second cell, in which the LC molecule orientation is rotated by 90 degree with respect to the first cell.
Guest – Host Displays Left: Reflective GHD. Off state: Dye absorption yields a dark state. On state: Smooth metal electrode reflects almost 100 percent of the incoming light, which is forward scattered by the front scattering film. Right: Structure of a stacked three – layer GHD. It generates color without using a color filter, by relying on the combined absorption of the dyes. This sequence generates largest contrast.
Transflective with VA cells
Reflective:
If no E field: 2* (Pi/2); If E applied: 2* (Pi/2+Pi/2).
Transmissive:
If no E field applied: Two WRFs make no retardation, which obtains a dark state; If E applied: Polarization twisted by LC.
Field Emission Displays • Electrons are generated by field emission rather than thermal emission. • Less power consumption and instant turn-on; wide viewing angle; high color saturation.
• Sub-micron tips: Low work function material, sharp tips, suitable emitter materials.
FED enabled by nanotubes Wang QH, Yan M, Chang RPH, Applied Physics Letters, 78, p1294 (2001)
FED enabled by nanotubes • Fabricatio n Process:
Conclusion
• Flat panel displays are playing more important roles with increasing quality and decreasing cost; CRT displays still share the display market at the same time. • Mature technology is developed for liquid crystal displays, as well as other flat panel displays. • Performance on power, image quality can be improved.