Display systems

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Microdisplay research history

Active matrix TFT displays

Our microdisplay research was the natural successor of the "active matrix TFT display" research we performed during the late eighties / early nineties.

• Monocrystalline active matrices on a 4 inch wafer (for reflective projection) (48K)
• Detail of the above (88K)
• Detail of the above (71K)
• Detail of the above (81K)

First generation microdisplay: 160x120 pixels

Our first microdisplay was designed and fabricated more than 10 years ago. In those early days it served as a feasibility demonstrator and helped us to get acquainted with the technological challenges that are typical for microdisplays. It has also made it possible to get other people interested in microdisplays, resulting in several bilateral as well as EC funded projects starting in 1997.

Technology description and specifications: (pictures are here)

• ASIC approach: the active plate is a chip that was designed and fabricated in the Alcatel Microelectronics 2 um HBiMOS process.
• Design details:
  • 160x120 pixel active matrix with integrated drivers
  • left and right row driver, one column driver (analogue bidirectional scanner type)
  • analogue grey level capability
  • dimensions:
    • chip size: 24.4 by 19.5 mm
    • pixel size and shape: 80 um square (including inter-pixel gap)
    • active area size: 12.8 by 9.6 mm
• Back-end process:
  • A modified low-cost back-end process (completely implemented in 5 um thin-film technology) provided flat and highly reflecting pixel electrodes as well as sufficient light shielding of the underlying silicon circuits. See these pictures of a few pixels in normal (38 KB) and dark field (43 KB) illumination
  • Reflecting electrodes: cold sputtered aluminium
  • Planarisation: OLIN + Brewer Science materials
  • Light Shield: Brewer Science's DARC material
• Liquid crystal technology:
  • Introduction: Two different types of LC effects are used:
    • Some cells are filled with a PDLC (Merck) or a PNLC mixture (kindly provided by Dainippon Ink & Chemicals), sealed and cured. No alignment layers or polarizers are needed with these liquid crystals. These scattering LCD types yield excellent direct-view behaviour (see for example this picture taken in direct view)
    • Other cells are filled with DAP (Deformation of Aligned Phase) liquid crystals. This (almost) vertically aligned effect is excellent for projection applications, because of the high contrast ratio that is achieved. In this technology, an alignment layer is needed, but still no rubbing. A very good alignment layer technology based on oblique sputtering of SiO2 was invented by the "Labor fur Bildschirmtechnik" in the university of Stuttgart.
  • Alignment layers:
    • PDLC/PNLC : no alignment layers or rubbing process needed
    • DAP : obliquely sputtered SiO2 alignment layer, no rubbing required
  • Liquid crystal material:
    • PDLC and DAP material from Merck
    • PNLC material from Dainippon Ink & Chemicals
  • Spacers were kindly provided by Sekisui.
  • A cover glass with ITO is used as the backplane electrode.
  • Assembly:
    • PDLC/PNLC : low cost cell assembly (GBV 'one-drop'- method)
    • DAP: standard vacuum filling

After a few years, our back-end technology had improved considerably. The latest PDLC/PNLC displays were much brighter than the first ones, closely approaching true paper-white behaviour. The vias had also been scaled down, leading to a better black state and a better contrast. In the latest cells, there were no more line defects.

• Text and graphics capabilities (first batch) (64K)
• Girl's face (first batch) (42K)
• PDA-type application (second batch) (55K)
• Detail showing individual pixels (second batch) (19K)

• Same girl's face in 8 grey levels (first batch) (34K)
• Portion of windows display (first batch) (54K)
• Face, 8 grey levels (second batch) (72K)
• Watching an ice hockey game (second batch) (45K)

• an 11-second, 12 fps AVI movie (old batch) (1160K)
   
• a 5-second AVI movie of a projected image of a DAP cell (1405K);
• Same movie as an MPEG file (489K)

The module electronics has evolved from a bulky assembly (68K) to a single hybrid circuit, leading to a much more compact module (65K).
The following picture gives an impression of the real display dimensions (active area only 12.8 by 9.6 mm)
Assembled display with external electronics integrated on a hybrid circuit (104K)

Second generation microdisplay : XGA

We have designed this microdisplay and its external electronics for the Taiwanese company TMDC (Taiwan Micro Display Corporation).

Main specs:

• XGA: 1024x768 pixels (1056x800 actual)
• 0.9" diagonal
• 17.6 um pixels
• 92% geometrical aperture ratio
• Vertically Aligned Nematic (VAN) liquid crystal
• contrast 800:1

Download a PDF document with complete specs. (108K).

Some pictures taken in direct view (some of them taken through a magnifier lens):

         the designers

Some pictures taken from a projected image (courtesy TMDC)

click thumbnails to enlarge 

Third Generation microdisplay: WXGA

 
click thumbnails to enlarge

Press release (29th of April 2003)

Finished microdisplay research projects

In the framework of the European Esprit project Mosarel, this 2560x2048 pixel microdisplay was developed. Some projected images of a working cell can be found on the Mosarel page.
 

In the European IST project LCOS4LCOS, a single-LCOS projector for consumer applications was developed

Microdisplay publications

Papers presented at the Eurodisplay 2002 conference organized by Le Club Visu SID France in Nice, 1-4 October 2002:
Download: A XGA VAN-LCoS Projector
Download: Assembly of an XGA 0.9” LCoS Display using Inorganic Alignment Layers for VAN LC

Consult our complete publication list