Liquid crystal on silicon
Liquid crystal on silicon (LCOS) is a type of manufacturing process for making microdisplays and SLMs.
Liquid crystal on silicon (LCoS or LCOS) is a miniaturized reflective active-matrix liquid-crystal display or "microdisplay" using a layer of liquid crystal on top of a silicon backplane. It is a type of spatial light modulator. LCoS initially was developed for projection televisions, but has since been used in near-eye displays.
LCOS phase only SLMs operate on the principle of the birefringence of the liquid crystal material.
ConstructionEdit
LayersEdit
An LCOS module is layered.
The first layer is the top layer. It is the counter electrode (CE). It is made of a standard glass (such as Corning 1737F) covered by a layer of indium tin oxide (ITO).[1]
There is a top layer of ITO and a bottom layer of ITO. Between them is the liquid crystal. Underneath the bottom layer of ITO is a CMOS backplane.
ParametersEdit
The counter electrode glass must have a thermal expansion coefficient that matches the backplane's as closely as possible.
The liquid crystal material used in LCOS gadgets is typically a nematic liquid crystal.
The distance from the backplane to the glass substrate may be around 2 microns.
ManufacturingEdit
Manufacturing of LCOS gadgets can be separated from the process of etching the silicon. A manufacturing facility may be able to receive pre-etched and pixelated backplane CMOS wafers from a fab. Then the facility can simply fill the liquid crystal, do layer alignment, and packaging.
InputsEdit
The inputs to the manufacturing process are:
- CMOS silicon wafers with a TFT pattern etched into them
- cover glass wafers
- indium tin oxide
- liquid crystal
- polyamide or inorganic material for an alignment layer
The CMOS silicon wafers already have CMOS patterns in them.
The CMOS silicon wafer is known as a backplane.
StepsEdit
- Liquid crystal fill and seal
- Electrode attachment
- Packaging
HistoryEdit
Some of the first LCOS modulators were made at Hughes Research Laboratories.
Display product companiesEdit
Silicon foundriesEdit
- Amkor[2]
- SMIC
- TSMC
- UMC