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Electronics Teaching | The School of Enginering and Electronics |
The University of Edinburgh is recognised as the primary European site for the design and fabrication of ferroelectric liquid crystal SLMs and the world leader in post-processing of the silicon backplanes. This capability is the result of a close collaboration between the University's Departments of Electrical Engineering and Physics (The Applied Optics Group). Several devices which were designed at Edinburgh (either exclusively or as part of a collaboration) are available commercially as shown in the table below. It is an important part of our policy to make our designs and our post processing capability available to organisations wishing to capitalise on our expertise in this field.
| Resolution | Aperture | Frame Rate | Status |
| (mm2) | (kHz) | ||
| 176 × 176 | 3.2 × 3.2 | 1 | Commercially available from GEC Marconi |
| 256 x 256 | 10 x 10 | 4 | Commercially available from CRL Smectic Technology |
| 512 × 512 | 10 × 10 | * | Samples available |
| 1024 × 768 | 12.3 × 9.2 | * | Samples available |
* commercially sensitive
Figure 1 shows a very early example of a 16X16 SLM although it can be observed from the above table that the resolution of the devices is now approaching VGA quality. Figure 2 shows a schematic section of an assembled microdisplay.
Figure 2 a cross-section through the assembled device.
Figure 3 and 4 show examples of a planarised and non-planarised 256 X 256 device and it can be observed that the optical efficiency of the planarised device is considerably improved.
Figure 3. A planarised 256 × 256 SLM.
Figure 4. A non-planarised 256 × 256 SLM.
The array of applications areas for these devices is enormous. The most obvious and probably the largest market in terms of device numbers is in displays. These devices are not only of high pixel count but also very small and light in comparison with competing technologies. Niche markets being targeted include projection displays and head mounted displays. Figure 5. shows the image obtained from a 176×176 SLM.
Figure 5. Image displayed on a 176×176 SLM.
Figure 6 demonstrates how the picture is built up from 3 bit planes.
Figure 6. Simple SLM Colour Operation (3 bit planes = 8 colours)
The latter are likely to be of use in fields such as medicine and surgery, the emergency services and, of course, recreational virtual reality.
Other uses likely to generate smaller markets in terms of numbers of devices, but in which performance requirements will command a much higher unit cost, include dynamic holography (holograms which can be altered in real time), optical correlators (optical pattern recognition systems), free space optical switching networks for computer and telecommunications
Each new generation of devices puts further demands on the crucial post processing, which is performed in-house, on commercial wafers. Shrinking feature sizes and larger die sizes require continual refinement of all of the microfabrication techniques involved in post-processing of SLM wafers. In addition to this general process improvement, access to state of the art microfabrication techniques allows us to consider more exotic advances. Our current plans include the deployment of multiple overlapping metal layers above the circuitry to prevent stray light from reaching the substrate (this prevention is necessary for any application involving high intensity light); the use of microfabrication techniques to deposit spacer and alignment layers for the liquid crystal; the deposition of exotic metals for the top mirror layer; through wafer contacts to allow mirrors to be placed on the rear of the wafer; deposition of transparent conducting layers for transmission mode operation.
The UK Electronics Weekly Magazine has featured a device designed at Edinburgh and we have also made the front cover of GEC's Journal of Research 12/02 (August 1995).
Some more SLMs images are available
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Revision Date: 15th May 1999
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