Next Chips: Organic Transistors and Memories and the Applications They Will Enable

The Second Coming of TFTs

NanoMarkets

There is nothing especially new about the thin-film transistor (TFT). It was invented by O. Heil in 1935, although commercialization work didn’t begin until the 1960s at RCA Labs. Back then, TFTs competed for a brief period of time with what was to become the silicon semiconductor industry, but the invention of the MOSFET put pay to any grandiose ambitions that TFT manufacturers might have had in this regard. Instead, these manufacturers turned to a less ambitious goal; applications in LCD and electroluminescent displays. By the late 1980s silicon TFTs had become widely used in LCD displays.

In the 21st Century, it suddenly seems that TFTs will have once again a broad role to play in electronics. Some observers (including NanoMarkets) now believe that thin film, organic and printed (TOP) electronics will grow into a very substantial industry over the coming decades. There are many reasons for believing this, but the main argument is essentially that a new kind of physical layer—capable of supporting electronics over a large area and on many kinds of substrates—will be needed to support the next wave of computing. TFTs will play a crucial role in that layer and new ways of producing them—printing especially—will help to lower their cost.

This next wave has various parts to it. At its simplest, low-cost TFTs could help bring existing functionality to new - and more cost sensitive -- markets. For example, low-cost TFTs could help bring higher resolution displays to handheld/cell phone markets via a new generation of active matrix LCD and OLED displays. Roll-up displays based on flexible TFT arrays would enable handheld users to utilize larger displays. Low-cost TFTs would enable the RFID concept to be extended from palettes to individual items and for new electronic capabilities to be provided in games, smartcards, and other disposables. Longer term TFTs would become a key component in making “pervasive computing;” a trend that the computer, consumer electronics and semiconductor industries are doing much to promote.

For this type of computing to evolve on the back of a TOP electronics physical layer, the TFT concept will have to be extended both in terms of device design and in terms of materials. At the present time, the most likely materials platform for this type of device would seem to be organic materials.

Organic Electronics and TFTs
Like TFTs, organic electronics is older than it looks; as far as the basic science goes it is a child of the 1960s. It also shares other things in common with TFT technology in that until very recently, its commercialization was confined to the display industry; organic LED (OLED) display sales are trending up to becoming a $1.0 billion market in the next few years. However, just as TFTs are breaking out of the markets to which they have previously been confined, so is organic electronics. OLED displays are no longer just for MP3 players and cell phone sub-displays; they have a future in cell phone main displays as well. More importantly in the context of this report, organic semiconductors now seem as if they are the obvious choice for the TFT products and memories that - as described above - will be required by the next wave of computing.

The specific advantages of organic TFTs (OTFTs) vary from application to application and they are discussed in detail in the main body of this report. However, they appear to have the ability compete successfully in various specialized applications environments with both mainstream semiconductor technology and silicon TFTs. What’s more, the potential advantages of OTFTs seem to be fairly broad based.

Cost is the big issue and here OTFTs hold out the promise of being manufactured using low-cost printing technology, or at least vapor deposition processes that are much less expensive than the optical lithography approaches used for standard CMOS chips and some silicon TFTs. The other important fact about OTFTs is that they can readily be created on flexible substrates, while conventional silicon devices (including most TFTs) tend to crack if flexed. Flexibility is a factor that helps to promote roll-to-roll manufacture, but almost more importantly, is vital if the rollable displays and embedded sensors and RFIDs that are expected to define the age of ubiquitous computing is to become a reality.

Commercialization of OTFTs (and organic electronics generally) are also encouraging. In the past year organic electronics firms, including those offering specialized organic semiconductor materials have received significant funding. In at least two cases - Plastic Electronics and Polymer Vision - such firms have announced the imminent arrival of full-scale production. Other TFT-oriented firms such as OrganicID, PolyIC and ORFID also seem headed in the same direction. And while the most attention in organic electronics goes to the smaller technology developers who deliberately court publicity, an examination of strategic investors and internal corporate R&D quickly shows that there are also giant firms that have involved themselves with OTFTs to one degree or another. Such firms include 3M, AMD, BASF, Canon, Dai Nippon Printing, H-P, Hitachi, IBM, Intel, Konica Minolta, LG, Matsushita, Philips, Pioneer, Ricoh, Samsung, Seiko Epson, Siemens, Sony, Spansion, ST Microelectronics, and Xerox. There are also numerous centers of academic research into OTFTs throughout the world.

Challenges to OTFTs
All this is obviously encouraging to those people - and there are now quite a few of them - who believe that one day organic electronics will one day be as big a business as the silicon electronics business is now. We think their judgments to be a bit premature. While the number of firms and research groups that are involved with developing OTFTs are impressive, there is no proof yet that the real addressable markets for these devices is such that a business can be built around them. In fact, it is probably fair to say that OTFT technology has already taken a couple of steps back from where the optimists thought it might be a couple of years back.

One example of this is that at the Society for Information Display (SID) annual conference in 2006 there was much talk about OTFT backplanes could lower the costs for LCD display makers. But two years later, there are few if any OTFT backplanes for LCD displays. They are being aimed now primarily at OLED and especially e-paper displays. Similarly printed OTFT-based RFID tags are widely seen as the way to get prices for such tags down to the point where RFID technology can be widely deployed at the item level. But printed RFID development is perhaps a year behind schedule when compared to where it was expected to be a couple of years ago. The first printed OTFT RFID tags are beginning to appear, but they are very basic products indeed. It is perhaps symptomatic that some now believe that the first significant revenues for OTFT-based products will come not from relatively complex products such as RFID tags and backplanes, but from games and novelties.

One reason that OTFTs have not lived up to the highest expectations for them is that organic semiconductors are not that impressive when it comes to performance. Indeed, when organic semiconductors were first discovered, they were seen more as a curiosity than as a practical material for electronics. Switching speeds for the first OTFTs do not compare even faintly with the speeds achievable by conventional CMOS chips, although they are potentially adequate for the large area, flexible electronics at which they are being targeted. The mobility of organic conductors is also quite unimpressive when compared to regular metals. And despite the promise of a new electronics paradigm that has been conjured up in the literature and trade press based on cheap “plastic” printed transistors, organic electronics materials are still very expensive. And although these materials have made great strides, they still cannot be said to be completely reliable in terms of being protectable against the ravages of water vapor and oxygen. In some cases - polymers in particular - they do not have the thermal stability that one might like to see when high-temperature processing is likely to be considered. Finally, there is some anecdotal evidence that printing - for all it virtues - does not have the applicability to TOP electronics that some hoped it would, at least not once full-scale production is being attempted.

The improvement of organic electronics continues apace, but there are some who are beginning to see that a different paradigm might apply in TOP electronics; one involving new inorganic materials - including nanoparticulate silicon. Such technologies that could restrict or eliminate the need for OTFTs are at a very early stage of development, but they have come a long way in the past year.

To summarize then OTFTs represent a new kind of electronic device that fits well with the direction that the semiconductor, electronics and display industries hope to take their products in the next decade or so. On the face of it then, this is a huge opportunity; an opportunity to be in on something as big as the creation of the transistor or the microprocessor. However, looking just beneath the surface exposes the fact that performance, manufacturing and economic issues will have to be addressed before anything like that potential can be addressed. And they will have to be addressed quickly, because other ways of creating TFTs are beginning to emerge. Indeed, important voices have been raised in support of an alternative future in which TOP electronics will ultimately progress using inorganic devices made from printed silicon, carbon nanotubes, etc. rather than OTFTs.

A Note on Organic Memory
OTFTs are the “logic” part of the emerging organic electronics paradigm, but this paradigm would not be complete without organic memory. Over the years, printed and organic memories have attracted attention of an impressive list of firms that includes AMD, H-P, Infineon, Intel, PolyIC, Philips, Xerox, Canon, Dai Nippon Printing, Matsushita, Pioneer, and Ricoh. However, there has been little to see by way of commercialization. Organic memories were proposed as a flash memory replacement a few years back - both Intel and AMD were quite interested in them at the time - but did not prove up to the task. They are now seeing a revival in a slightly different form as the memory solution for TOP electronics.

As with TFTs there is a lot of R&D that is being carried out in the field or organic memory that does not get much publicity. But at the commercial level, most of the activity is centered on one company, Thin Film Electronics (TFE). This was the company originally backed by Intel as a supplier of new technology that could ultimately replace flash. When Intel withdrew its support TFE, TFE was able to remake itself and has surrounded itself with a number of firms that are enabling it to pave a way towards printable organic memory. For example, one of TFE’s partners is Xaar, which is helping it develop industrial inkjet methods and processes for producing printed memory applications efficiently and in high volumes. On the manufacturing side, TFE is collaborating with OTB Engineering and Soligie.

Printed organic memory is seen as crucial to the future or printed RFID. But the opportunity is larger than this. Ultimately, printed organic memory is likely to be a critical element in the success of printable electronics as a whole.