Flexible and sustainable – low temperature display manufacturing

Paul Cain, Strategy Director

April 06, 2020

The manufacture of transistors has always been an energy intensive endeavour. There are many types of transistors, the majority of which are made from silicon. Whilst the manufacturing processes for different types of silicon transistors differ, they all involve multiple process steps that consume high amounts of energy - for example, high temperature and vacuum processes, such as Chemical Vapour Deposition (CVD), ion implantation and sputtering. In some cases this can involve processes up to 1000°C.

Energy consumption

Nearly all transistors in the world are manufactured either for microchips (on wafers) or displays (on glass or plastic). In the world of microchip manufacturing, as transistors get smaller, the manufacturing energy cost per transistor (along with several other metrics) gets better.

However, in the displays industry, the economics are different – the energy consumption is bigger. This is because the transistors need to be produced over large areas - for example to cover your TV screen (and TVs are getting bigger, not smaller). Each year we, as a planet, manufacture around 250 million square meters of transistors for displays. Whilst the temperatures involved in making silicon thin-film transistors used in displays are lower than for semiconductor wafer processing, they still require 300-500°C, depending on type and performance requirements.

In the past few years we have also seen the arrival of flexible OLED displays built onto plastic films instead of glass. This feat of engineering has been achieved by taking the same 500°C silicon thin film transistor process, but building it directly onto a special plastic (polyimide) film substrate that has been designed to withstand these very high temperatures. In the world of flexible displays, high temperature and high cost go hand in hand.

Low-temperature manufacturing

FlexEnable looks to roll to roll electronicsFlexEnable has adopted a different approach to flexible display manufacture – one that is much lower cost, as well as being lower energy and more sustainable - all three of these advantages originate from the very low processing temperature of the organic thin-film transistors (OTFTs) used to make glass-free Organic LCDs (OLCDs). FlexEnable’s OTFT process means transistors can, for the first time, be manufactured at temperatures less than those used to boil an egg. The entire OTFT manufacturing process is carried out at under 100°C – it uses FlexEnable’s FlexiOM™ organic semiconductor materials in place of silicon, and removes the need for other energy intensive processes such as CVD and ion implantation. As a result, the OTFT process drastically reduces the manufacturing energy requirements compared to silicon TFTs – by around a factor 10!

Bio-based substrates

Indeed, the temperature of FlexEnable’s flexible display process is so low that it can choose from a wide range of films for the flexible substrate, including those which are bio-based (not oil-based) and biodegradable. For example, the OLCD process uses a transparent flexible film called “TAC” – tri acetyl cellulose. This, as the name says, is actually a type of cellulose that is usually made from wood pulp – in other words, TAC is made from the same natural raw materials as paper. Indeed cellulose film is increasingly common as a sustainable alternative to plastic in food packaging.

TAC has been used in the displays supply chain for decades – often within the polarisers that sit either side of the glass display cell that you’re probably reading this on. It is used because it has optically excellent properties, is low cost to manufacture and as a result is already manufactured in hundreds of millions of square meters each year.

During the manufacturing process the TAC film is attached to a flat sheet of display glass. At the end of the process the TAC is removed from the glass with a very simple “release” process that requires no expensive capex. This simple process is a key part of why OLCD has low cost – not only because the yield is high, but also because the flat glass carrier is reused for the next display.

FlexEnable’s TFT process is the lowest temperature transistor process ever industrialised. Low temperature is not only about saving energy, it is also about allowing the widest choice of substrates to choose from, including those which are more sustainable, and in doing so bringing the cost of flexible displays down.

Repurposing existing display factories

The OTFT process developed by FlexEnable has been specifically designed to be implemented in existing flat panel display (FPD) factories, utilising existing equipment. Apart from requiring less investment, it also reduces environmental impact by removing the need to build a factory from scratch or disposing of equipment.

For more information on flexible OLCD manufacture, please get in touch with FlexEnable at info@flexenable.com.

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