Organic Semiconductors for Flexible Displays

Steve Kelly, CEO at SmartKem talks to AZoM about Organic Semiconductors for Flexible Displays.

How has SmartKem become a pioneer in the market for flexible semiconductors to be used in flexible displays?

From day one SmartKem established close relationships with all the key display manufacturers to ensure our materials would meet their current and future requirements. We invested a lot of resource in achieving this with a presence in Korea, Taiwan, Japan and with our Business Development Director, Dr Gary Tam who is based in Hong Kong.

This has allowed us to shape our technology roadmap and R&D programmes to ensure that we are now leaders in terms of performance, both electrical and physical, with our p-FLEX semiconductors for the flexible display sector.

We’ve also maintained our agility to adapt and offer customers bespoke formulations, as well as on-site engineering support to allow the smooth transfer of our technology platform into pilot line production.

Our focused approach in the development of our core p-FLEX product to meet market needs has allowed us to fully exploit our capability for molecular design, material synthesis, formulation into ink and exemplification in transistor form. It’s this complete skillset in materials, application and transfer that allows us to offer our customers comprehensive support.

It has to be said we also got lucky and brought on board many ex-employees of Avecia after its sale to Merck, experts who had worked in the development of organic semiconductors for decades. This allowed SmartKem to gain immediate traction within its R&D programme in its formative years and which we have built upon with a unique set of successfully launched products.

How do organic semi-conductors (OSCs) compare to silicon semi-conductors?

SmartKem’s p-FLEX materials have distinct advantages. Electrically they have great performance, high mobility (5 moving to 10 by y/e 2013) and high thermal and electrical stability. p-FLEX has already been proven to outperform a-Si in independent tests at centres of excellence such as CPI. The key differentiators for our customers are numerous but two standout factors are firstly inherent flexibility, which is critical as there are serious concerns as to whether inorganics can achieve this.

Secondly p-FLEX is an ink that can be processed at room temperature. Both open up the door to all sorts of continuous or semi-continuous narrow or wide area production systems with the end goal of roll-to-roll and all on plastic substrates.

With this in mind all of SmartKem’s material transistor (TFT) data has been generated at room temperature in air, on plastic (PEN) specifically to demonstrate its viability for these production methods.

We understand that large companies move in incremental steps when it comes to technology adoption. Indeed it makes sense to try and get a product enhancement with a technology you have a history with. That said we see inorganic materials as a stop-gap solution to achieve rigid (non-flexible) curved and ruggedized displays in the short-term before the end of the year.

This allows initial market entry of new form factor product but in the meantime we see significant efforts, in effect the transition in the short-medium term, to a new material technology for fully flexible displays with organic materials.

The market perspective from our standpoint is that inorganic materials are a quick fix; whereas, the medium to long-term needs of the flexible display industry will move towards organics where the material performance and process advantages are just too compelling to ignore.

SmartKem Flexible Tablet.

How do you plan on improving the electrical performance of OSCs to match that of silicon?

In comparison to many alternative materials we are already in a strong position with our semiconductors from both a performance and processing perspective. SmartKem already has a material system that outperforms amorphous silicon and is comparable to oxides, with the added advantage of ambient temperature processing which is a “must have” for most plastic substrates and inherent physical flexibility.

From an electrical performance standpoint, one significant issue with inorganics is the electrical stability, in particular bias stress stability. We have worked hard to ensure our materials exhibit minimal bias stress or hysteresis – as such our major focus at present is to deliver our target mobility of 10 by year end 2013.

Illustration of product positioning in relation to electrical and production process temperature. Image courtesy of SmartKem.

Where is there the biggest demand for flexible display technology and why is organic semiconductor technology likely to drive the market trend?

We believe the introduction into the market of flexible display products will be in incremental steps over the two to three years. The first products will be rigid but more robust products in both EPD and OLED displays overcoming the fragility of current display screens. The next increment will be in the adoption of rigid curved displays.

Due to the lack of need to flex in these introductory products, these will most likely be addressed with current inorganic materials in small form factor products such as mobile phones and e-readers. However, we do expect a respectable proportion of this early market to incorporate organic semiconductors as part of product development programs in the lead up to fully flexible products.  

In the meantime, commercial development programmes are driving the integration of organic materials as the move to bendable and fully flexible displays approaches in the next 18-24 months. This is where organic semiconductors will become ubiquitous with wide scale adoption of fully flexible backplanes incorporating a truly flexible semiconductor.

Market drivers will be led initially by electrical and physical performance and then ease of process and eventually cost of production. The ease of processing and cost of production  will become ever more important as the footprint of the display increases and the advent of fast, low temperature, continuous production techniques becomes more prevalent.  

What are the basic functional properties of OSC’s?

Organic semiconductors (OSCs) fall into two main categories of materials: polymeric and distinct molecular materials. A common feature is that both these types of materials are conjugated systems, that is to say they consist of alternating single and double bonds.

Key consideration has to be given to matching the highest electron energy level of the OSC to the work function of a metal contact to ensure efficient device operation.

For high performance high charge carrier mobility is required and this favours crystalline small molecule OSCs. The close packed and regular arrangement of the molecules in a crystal lattice gives rise to good π-overlap and efficient charge carrier mobility; however, these materials on their own tend to demonstrate anisotropy.

To overcome this SmartKem’s experts have perfected the development of small molecule OSCs formulated in polymer binders. Our polymer binders are designed and synthesised internally to allow a bespoke synergy between the small molecule and binder allowing us to achieve industry leading device performance.

How are you using printing and coating techniques to manufacture OSC’s?

As with most of our customers, we use simple spin cast techniques to make test arrays and devices. We have also generated a formulation for ink jet and are now finalising a programme for generation of a roll-to-roll formulation.

The spin cast process itself is very simple with material deposition being performed in air at ambient temperatures and can be done very quickly with basic kit, which is great.

Are there any challenges with the manufacturing processes for OSC’s?

There are manufacturing challenges with any material system and OSCs are no different in that regard. We have worked extremely hard to overcome any issues and this is part of the value that we offer to our customers with on-site support during the technology transfer process. In the early days, during the evolution of OSCs, one challenge was uniformity and it was quite common to hear “yields are great, all the transistors work…but differently..” (i.e., different threshold voltages).

Ultimately this comes down to control of material morphology and film thickness. SmartKem recognised all the historic concerns with typical OSC materials and this drove our development programme for p-FLEX with intensive efforts to both understand and control the material deposition through formulation of the material. We now have levels of uniformity that are making our customers very happy.

We are confident we can transfer this know-how and expertise as display product moves up the Gen scale in footprint.

The emergence of any new technology raises considerations with regard to standardisation of materials, processes, applications and equipment. There is a significant drive now to formalise the standards for the printed electronics industry, a significant part of which is flexible displays. SmartKem is actively involved in this process as an Expert Member of the IEC Technical Committee TC119 governing the worldwide standardisation of the printed electronics industry.

Do the structural properties to the material used for this technology hinder its application to a much wider and challenging market?

The degrees of freedom offered by p-FLEX in molecular design, formulation and processing are a real advantage rather than a hindrance.

In relation to the structural properties we formulate the material to offer high levels of uniformity and morphology (we are currently exemplifying at Gen 1 level). The fact that our materials can be processed as an ink at room temperature in air means that any print process can be used on any substrate.

We can formulate our materials to ensure optimum wetting on any substrate using these processes, which is a key differentiator and driver for customers using p-FLEX organic materials. It should also be appreciated that there is a complimentary processing and packaging overlap in the use of p-FLEX with OLED materials which makes practical sense as production systems move forward for flexible displays.

If we were to consider a recent report by HSBC on the demand for flexible display, how do you think your technology will help investment efficiency?

It’s clear from the recent TMT HSBC report the projected market for flexible EPD and OLED display is substantial. We believe SmartKem p-FLEX semiconductors are an enabler for this market growth, facilitating market entrance without significant capex on equipment, unlike inorganic equivalents. This can only help to bolster investment confidence in the sector.

p-FLEX’s electrical and physical specs already meet the requirements for both EPD and OLED and can be processed on a wide range of material surfaces using print processes such as ink jet, slot die or roll-to-roll. Critically this offers the end user the potential to make the transition to continuous print techniques and reduced cost of production as these systems come online. This potential gets people exited as a clear long-term product roadmap can be seen by the investment sector.

A recent news article by the designers of some of Apple’s product stated that flexible displays “will change the world” doesn’t do any harm either.

What are your growth plans for Asia?

Asia is a key market for SmartKem and we have worked hard to forge relationships with many of the key display manufactures and supply chain companies since the inception of the company. As previously mentioned, close collaboration with end users has been vital for us in refining our product specifications based on real world process and product requirements, in addition to transferring our technology to our customer base.

As well as MTAs (material test agreements) we are at the point of entering joint development agreements (JDA) with a number of companies and are also now shipping product to a number of Asian companies. Our strategy is to build on this and grow the team in Asia where necessary to support our activity.

We already have a representative based in Japan, Korea, Taiwan and our Business Development Director Dr Gary Tam is based in Hong Kong. In addition to this, our technical team has regularly visited Asia over the last 12 months to provide technical support.

China is also a very exciting market for SmartKem as we believe it will play a big part in the medium to long-term flexible display sector, so this will figure into our plans for future growth. We are currently in discussions with a number of companies in China and intend to establish a more substantial presence there this year.

You also have a novel evaluation kit. How will this streamline process for the manufacture of thin film transistors?

The adoption of any new technologies is a process that needs to be carefully managed. Our whole remit is to make this process as painless and as cost effective for our customer base.

We therefore like to encourage adoption in incremental steps, allowing low cost evaluation of a TFT array or evaluation kit by the customer, moving onto a MTA for further evaluation and lastly to JDA where we integrate p-FLEX into a customer process line. This allows any user of the material a high degree of confidence through good data to plan and budget the next steps in the adoption of our technology.

The supply of either a fully processed TFT array using p-FLEX or a partial or complete evaluation kit has proven a great success in product evaluation and exemplification within the display sector. The pre-fabricated TFT array with p-FLEX allows customers to measure and verify our data sheets. The evaluation kit – which includes a contact patterned PEN substrate, p-FLEX ink, organic gate insulator and a gate mask for evaporation of a gate pattern – allows any new customer with the most basic of equipment to make their own arrays using p-FLEX and exemplify.

Where can we find further information on your company’s expertise and your latest product?

We have regular news feeds on our website. Anyone interested in having a more detailed discussion can contact our Director of Business Development Gary Tam or our Head of Product Development Mike Cowin.

About Steve Kelly   

Steve Kelly founded SmartKem in 2008 to develop smart chemistry and processes for the printed electronics industry. As an experienced international business professional, he has spent over 20 years building successful technology ventures, particularly early stage. Steve has extensive experience in Intellectual Property exploitation, VC funding and launching new technology to market.