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May 24, 2024

Sony Reveals 8K LCOS Chip at Display Week

We’ve previously reported on the difficulties of making 8K projector imagers – they have to be very small and that means really, really tiny pixels. TI’s DLP technology, which is one of the key technology options for projector makers, would need a very large chip, given the current smallest pixel size available, and that would mean a high cost. Epson’s transmissive polysilicon LCDs would also struggle with very small pixels because of the challenge of getting enough light through the devices. However, LCOS chips have a potential advantage in terms of higher efficiency.

At Display Week in 2024, Sony’s Semiconductor Division presented a paper (15.2 Development of Novel Liquid Crystal on Silicon Microdisplays and Future Application) about a native 8K imaging LCOS chip that it has developed, although there is no news yet of a projector that will contain it. As the paper pointed out, LCOS has the advantage both of a high aperture ratio and a capability of supporting small pixels.

As Small as the Smallest Grain of Pollen

The new chip has a pixel size of just 2.6 microns – that’s as small as the smallest grain of pollen! High end projectors typically use three imagers, one for red, one for green and one for blue, so designers of the imagers don’t usually have to worry about sub-pixels. As is usual in LCOS chips, the imaging part of the device is built on a CMOS backplane which includes the driving circuitry. At this small pixel size there can be crosstalk between pixels as they are so close. Sony was able to use a thinner liquid crystal (LC) layer and a specialized alignment layer to reduce the crosstalk. 

Sony explained that the normal gap between pixels is typically 250nm but to optimise the area of each pixel, it was able to use lithography and a Krypton Fluoride excimer laser to reduce this to 160nm in the 8K device. It also created an extremely flat surface to allow a very uniform LC layer, optimizing contrast at 10,000:1 and reducing light loss.

Projection systems put a lot of light into the small area of the imager (the 8K device is just 0.9″ in diagonal) and that can cause the materials to degrade (older readers may remember that this was a problem in LCD projectors some years ago before better designs and inorganic alignment layers were introduced). Sony was aware of this issue and chose inorganic alignment film and optimized the LC material to counter this effect and allow a projector to be designed with 10,000 lumens of output power. 

While reducing the pixel size from 4.05 microns in its 4K LCOS device, the company was able to maintain a frame rate of 120Hz and support a 12 bit gray scale.

Sony also described in the paper that it used some of the technologies developed to create a ‘phase-only’ spatial light modulator (SLM) with FullHD resoloution and a 4.25 micron pitch This device is intended for use in innovative products such as holgraphic HUDs or even AR glasses.

8K Association Comment

This is the first 8K ‘native’ imager for projection that we have seen. Other 8K projectors are using 4K devices with ‘shifting’ to allow temporal dithering to achieve the perception of 8K. The persistence in the human visual system means that this is a reasonable way to achieve 8K, but having a native imager makes the system design more straightforward. 

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