Having followed the development of 3D, lightfield, and holographic displays for some time, I have come to believe that evolving the traditional raster pixel approach to smaller and smaller pixels is not going to get us to where we need to be to achieve high-fidelity lightfield or true holographic images. We need a breakthrough display technology. Based on a recent conversation with start-up SWAVE Photonics, they may have the answer we have been looking for. Their claim is the ability to create 0.2-micron pixels which is 10x smaller than what can be done today with the potential to get to 100X smaller. This is the order of magnitude increase that is needed for such high-fidelity light field and holographic displays.
SWAVE is a spin-out from IMEC, the Belgium research institute, which has raised 7M Euros in seed funding so far. Their technology has been in development for 6 years and now the company founders believe it is ready to transition to commercialization. This will still take time – perhaps 2 years, but now is the time to start engaging with potential customers, investors, and partners, noted Dimitri Choutov, one of the co-founders of SWAVE.
Choutov says they are developing a modulator technology that will create true holographic images (not to be confused with so-called holographic displays that are not true holographic displays). The technology is created in a semiconductor fab and display modulators need to be illuminated with RGB lasers to create a full-color display.
Laser-based holographic displays with LCOS modulators have been demonstrated before, but with a small modulator, the field of view of the resulting image is only a few degrees. Ever smaller pixels are the way to increase fidelity and field of view. SWAVE wants to offer modulators that can be tiled together to create holographic walls. When laser light illuminates the display, the first order is diffracted into a wide angle
This holodeck vision is one shared by Light Field Labs, but they have never revealed how their technology works. SWAVE is not revealing their technology details either, but it is based on phase change technology.
The phase change material is constructed with compounds of chalcogenide glass. It works by using a heating element, generally made of titanium nitride, to quickly heat and quench the glass, making it amorphous or crystalline. It stable in each binary state which may be how a diffraction pattern can be turned on or off. There is a CMOS driving backplane (22 nm node tech) with the phase change frontplane. Choutov described it as an electrical write and optical read approach.
Phase change materials have been commercialized for memory applications by Intel and STMicroelectronics. Elements as small as 20 nm have been demonstrated. But the memory applications have some reliability issues mainly from the fact that it is thermally driven with current running through the phase change material.
SWAVE has a different configuration than memory cells. The backplane contains the control circuits fabricated in a standard CMOS fab connected to heating elements. Current does not run through the phase change materials, thus avoiding many of the leakage, drift, and degradation issues of memory-based configurations.
The cell programming is very fast at 100-200 ns, but the modulator is not addressed like a display. Instead of raster addressing with rows and columns, it is updated by sectors – like a memory cell. The frame rate limitation is determined by the array size and power consumption, but Choutov believes 120 fps is achievable.
As for the phase change issues, memory cell resistance drift over time is not a concern as they only need to hold information for 2 frame periods so perhaps 10-30ms. Resistance degradation and material separation has not been observed either primarily due to not passing current through the phase change material.
One concern that has yet to be verified is the long-term reliability of the architecture. In phase change memory applications, the device can break down after 1E6 cycles from voiding and material separation – all the result of passing current through the phase change material. SWAVE is currently characterizing and optimizing the endurance with indications they are on a path to meeting customer requirements.
So far, Choutov says they have developed large chip versions (2 × 2 cm) for ultra-high–end holographic display applications and tiny versions (0.5 × 0.5 cm) for ultra-lightweight wearable devices.
SWAVE is a fabless chip company that has already started to engage with major customers to be sure they develop modulators that fit customer’s needs. They plan to offer modulators, not display solutions, and now has a developers’ kit to aid in customer evaluation of their technology. More details on their technology can be provided with an NDA.