Perspectives on Organic Electronics and Manufacturing

Organic semiconductors represent an important new opportunity in thin film electronic devices. Conjugated organic materials can exhibit semiconducting and optoelectronic functionalities with processing conditions much milder than those used to make crystalline and amorphous inorganic semiconductors. This has allowed the development of several new devices, which can be processed at lower temperature, with greater speed, and with potentially lower cost, than traditional devices in their categories. The difference between organic semiconductors and inorganic systems is that organic semiconductors are held together by van der Waals bonds, which are relatively weak and require only a small energetic investment to make and break. This weak intermolecular bonding makes it straightforward to use thermal evaporation and solution processes to deposit the material uniformly over large surfaces. These processes are straightforward to apply to large surfaces enabling applications, which require significant areal coverage and low production costs. Solution processes can use printing techniques to pattern material, potentially leading to significant throughput and cost improvement.
It has been known since the late 1930s that organic solids can be semiconductors; anthracene was one of the first materials discovered to be photoconducting and was used by Chester Carlson in his early work leading to the first photocopier system. Xerography was an application where crystalline semiconductors (especially those of that era) were unsuitable because a large plate of the semiconductor material was required. Charge and toner had to be applied to a sheet of the semiconductor as large as a piece of paper, and organic semiconductors could be ground into a suspension and applied onto large plates (and later, drums) for charging and image duplication. Interest in organic semiconductors waned as inorganic amorphous semiconductors such as selenium and silicon established themselves as more durable alternatives for electrophotography.
Research in organic semiconductors continued at a number of firms interested in xerography, photography, and printing, examining mostly photoconductivity and photosensitization of film products. A revolution occurred in 1986 when researchers at Kodak published two papers describing a solar cell and a light emitter made using evaporated thin-film organic semiconductors. This development launched worldwide interest in organic semiconductors as a vehicle for implementing large area electronics. Today, after 20 years of research and development, we have already begun to see the first few generations of commercial products based on this material system reaching the market.
There are a number of potential applications for organic semiconductor-based systems, and each has its own appropriate material set and manufacturing challenges. This report will examine a number of commercial and pre-commercial device manufacturing strategies, and in particular examine through these processes both the materials and equipment involved in the process. The devices that will be examined in greatest detail are:

  • Organic light emitting diodes (OLED)
  • Organic thin-film transistors (OTFT)
  • Organic photovoltaics (OPV)
  • Organic photodetectors (OPD)

There are four perspectives on manufacturing in particular that we believe are critical to the production of each of these devices, each of which points to different opportunities, and to which much of the analysis in this report is therefore devoted.
Perspective #1: Availability of Equipment
Much of the small-scale development work in organic semiconductor devices has been performed using general purpose laboratory equipment. While it is possible to examine the properties of material stacks and to develop interesting device concepts in this way, specialized equipment is required for both the transition from the laboratory scale to pilot stage manufacturing (where the process is proven scalable), and subsequently to large scale manufacturing (where the process needs to be profitable). This is especially true for materials that are highly air-sensitive and require processing in a controlled environment as well as specialized packaging.
Evaporated thin-film organic devices are easily made a few at a time even in simple homemade systems. The intermolecular attraction between organic small molecules generally can be thermally disrupted, and a material flux can be formed using a heated boat, crucible, or other material source. Metals can also typically be deposited using thermal evaporation and usually share the same equipment set. Air sensitive devices, on the other hand, require some additional infrastructure; devices need to be emerge from the protected deposition environment already packaged against water vapor and oxygen exposure or unloaded into a glovebox or other inert environment for further handling and packaging. Most pilot lines for multi-layer thermal evaporation use a star-configuration cluster tool with integrated surface preparation, masking, and packaging. Manufacturing systems using either star clusters or inline configurations have been demonstrated, depending on the application and masking requirements.
Solution deposited materials face a different set of challenges. The same weak intermolecular attraction also makes solution deposition relatively straightforward if the component materials have been functionalized so as to be soluble. A great deal of coating equipment for unstructured coatings (e.g. slot coating, gravure coating, etc.) is available on an industrial scale, but unavailable and relatively impractical to develop in laboratory or pilot-scale systems. The high cost of the equipment and tooling used in the coating industry makes it difficult to perform the iterative testing and development required to commercialize a process without the support of a large industrial organization. A notable exception is for inkjet printing. Several developmental inkjet printers are available for research and development purposes that allow direct scale-up to industrial systems, often using the same heads or heads with the same orifice and reservoir characteristics as the development systems. This allows both process and ink development to proceed at a faster pace. Virtually all solution-based devices still require some vacuum evaporation steps (e.g. for electrode deposition), but more often than not, the requirements on the evaporation are significantly relaxed thanks to the spatial definition provided by the solution processing step when printing is used. Creative processes (such as GE's OLED lamination process) can also move the vacuum coating steps to points in the process flow where integration is easier.
Several small-scale and pilot systems exist for slot and gravure coating. These systems are suitable for coatings on the lab and pilot-line scale. While these systems are primarily seen by their manufacturers as part of a scale-up path to larger and more capable equipment, their capacities may be adequate for many limited volume applications.
OLED production lines represent a significant market for manufacturing equipment, and are by far the largest equipment segment for modern organic semiconductor devices. This demand has led several large vacuum and inkjet deposition equipment companies to invest in the development of sophisticated equipment for OLED deposition, handling, and packaging. This infrastructure has significantly improved the availability of equipment for manufacturing and R&D of air-sensitive vacuum and solution deposited devices. Turnkey cluster tools, which integrate substrate preparation, aligned shadow masking, and encapsulation are available at price points suitable for research and pilot line production. Non-OLED devices, which can leverage this equipment set are at a clear advantage for production scaling.
Perspective #2: Availability of Materials
The availability of semiconductor and substrate materials is a significant issue for the development of organic semiconductor devices and systems. There are some materials which have been developed for other applications, such as indium tin oxide (ITO) coated glass, that can be applied to OSC devices with minimal optimization; for example, in the case of OLEDs, ITO with minimized surface roughness in addition to the usual transparency/conductivity tradeoff can be used. However, in general, OSC devices require specialized materials in reasonable volumes to achieve commercial success. Market opportunities exist in filling the gaps in the material supply chain and in providing materials that meet the needs of target markets, especially those outside of OLEDs.
Organic semiconductors were initially produced in large quantity for use in dyes and electrophotography. Many of the R&D-scale material suppliers, such as American Dye Source (ADS) and HW Sands, have their roots in supplying materials for film sensitization and electrophotography.
There are three general business models used in the semiconductor materials market, each of which has its advantages. The type of materials available from each is somewhat different. The first model is pure-play material sale. These firms include all costs in the charge for materials and will sell to any customer. A number of small firms such as Luminescence Technology and the aforementioned ADS and HW Sands in addition to some larger catalog distributors such as Sigma-Aldrich and synthesis houses such as Tokyo Chemical Industry (TCI) use this business model. These firms typically produce materials, but not much know-how. Proprietary materials may be available, but these typically will not carry any device licenses. This model allows sales to a broad market of large and small players. Contracts with large industrial users will be limited by the confidence that the customers have in a uniform long-term supply. Margins are linked to the scarcity of the materials being produced; materials under exclusive license can carry higher margins, but other materials will generally be sold in a competitive market. Revenue is not realized from customer production—only material volume sales. Production customers must separately license any device stacks, which use these materials if a proprietary arrangement is used.
The second model is used by a group of firms that have developed and aggregated a significant material and IP portfolio and that seek to monetize their know-how. These firms share proprietary manufacturing and handling process know-how under license and will only sell materials through partnership agreements (often using third parties to perform the bulk synthesis). The large OLED IP hubs, including Kodak, Universal Display Corporation, and Cambridge Display Technology, and a few large chemical companies including Idemitsu Kosan operate through this model. This model has a number of advantages. Revenue can be realized as royalties against customer-produced products, which allows for a revenue stream to continue as the covered devices are deployed even if the constituent material value decreases. It also aligns the interests of the IP suppliers and customers, making the supplier hold a stake in the success of the product, and decreasing the risk to the licensee. A limitation of this model is that it can be difficult for small firms to enter these agreements, creating an incentive to develop independent IP for what are perhaps some of the more innovative firms in the space. Material sales will also be limited to licensees, which can be a small market for many of these materials. Licenses for proprietary device configurations are included with these agreements, allowing their use, and the most advanced high-R&D cost OLED materials are typically only available under this type of arrangement.
The third group is comprised of vertically integrated synthesis and manufacturing operations, such as DuPont and, previously, SK Display. While some of these organizations (or related divisions) may also sell materials and know-how separately, the main goal is to integrate in-house developed materials and panel manufacturing processes. This model has the potential to capture more of the finished product value chain, with the downside of incurring all of the associated development and commercialization expenses for a single customer. This model is difficult to execute as a pure play, partners have proven almost always necessary to allow the use of externally developed IP and know-how to reduce overall costs and accelerate market deployment.
The market demand for OLEDs has significantly improved the availability of organic semiconductors for other application areas as well. Many of the same firms involved with OLED development have also established the infrastructure necessary to synthesize and purify other organic semiconductors on a large scale.
The substrate infrastructure is also now reasonably well established. OLED-grade ITO glass sheet is widely available. ITO coated polyethylene terephthalate (PET) and, more recently, polyethylene naphthalate (PEN) are also available in commercial quantities with surface qualities suitable for thin-film organic electronic applications such as OLEDs and solar cells. Substrates with integrated encapsulation functionalities, while widely promised, are still not available in commercial quantities and represent an untapped market opportunity.
Perspective #3: Device and Process Readiness
An important element in any analysis of new devices is the readiness of the technology to deliver adequate performance, and to be fabricated on a volume scale appropriate for the target market.
Many devices that can be made at the laboratory or pilot scale using one process will not necessarily scale well to larger volumes or substrate sizes using the same fabrication techniques. This is partially because the techniques and costs strategies used in R&D are different from those in manufacturing. The techniques used in the lab are often chosen for research convenience and low capital investment. Few parts are processed in an R&D laboratory, so any capital infrastructure is most economical when it is maximally flexible in technique, materials used, etc. and has a relatively low initial expense. In manufacturing, the most important parameter is the cost per finished part; considerations such as TACT time (time allotted to produce one unit), material utilization efficiency, and equipment downtime become more important than the initial capital investment. Operating and maintenance costs often eclipse that of the initial capital investment and this affects which techniques are viable for manufacturing. Whether a process has been adapted to manufacturing-ready techniques critically affects the viability of the process for the move into manufacturing.
Perspective #4: Market Readiness
While there has been great excitement for many of the applications, which it is believed organic and other thin-film semiconductors enable, it has been less clear which market opportunities are immediately ready for commercial success. The first mover assumes both the risk and potential rewards of establishing the market first, and until very recently, this has meant a reluctance to invest in anything beyond the pilot line stage.
For each potential market and device it is essential to assess the market readiness relative to competitors in the space (if any), the market's ability to sell the product at a reasonable price, and the ability of the product to meet the market&#25s demands for quantity and performance. For some devices (such as OLED cell phone displays), a vertically integrated captive customer can make this process easier, and it has been in these systems that many developmental products are first released.

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