The future $300 billion market for printed electronics is emerging via thin-film electronics. The contribution of organic materials to this is greatly publicized, but the best devices being developed usually rely on inorganic or combined inorganic/organic technology. The more select groups developing these inorganic materials and devices have a promising future.
Silicon chips have had a good run in the electronics industry, but the lowest cost chips have not changed much in price for decades; wide-area silicon, as with solar cells, is heavy, expensive, and in need of huge government subsidies to be sold in any volume. Truly flexible — as opposed to bendable — silicon is non-existent in practicable form. Enter thin-film electronics that increasingly can be printed, unlike silicon, and are potentially low cost and very versatile, useful for sensors, power, memory, logic, lighting, and more. Here, we are not just talking about semiconductors, but about dielectrics, conductors, and light emitters, for example.
Many companies and conferences use the terms organic or plastic electronics because, over the last ten years, huge developments have been made with organic-based devices, such as higher mobility and more stable materials, formulations that allow for printing organic semiconductors, and much more. The progress of this new industry is phenomenal. So is that the end of the story? Nothing could be further from the truth. While the contribution of organic materials is greatly publicized and has attracted over one thousand participants already, there have been significant developments with inorganic printed electronics or combinations of both.
For conductors with vastly better conductances and cost, for the best printed batteries, for quantum dot devices, and for transistor semiconductors with ten times the mobility, look to the new inorganics, that is, the emerging world of new nanoparticle metal and alloy inks that are superior in cost, conductivity, and stability, such as the flexible zinc oxide-based transistor semiconductors that work at ten times the frequency and with better stability and life, along with many other inorganic materials.
INORGANIC AND HYBRID CONSTRUCTIONS OFTEN BEST
Most companies that develop organic light emitting diodes (OLEDs) employ indium tin oxide (ITO) semitransparent electrodes and most other “organic” devices, including transistors, employ metal conductors. Indeed, given the mobility and, therefore, the operating frequency of organic transistor semiconductors, companies such as Motorola and Hewlett Packard in the U.S. are additionallyresearching inorganic semiconductors.
In other words, it is complementary to learn how to print a transparent inorganic semiconductor, with up to 400 times the mobility, alongside trying to invent stable, low cost organic semiconductors with device mobility that exceed 10 cm2/Vs, when even improving on one-tenth of that is proving tough.
It becomes a matter of “Shall I make the new inor-ganics printable?” or “Shall I make organics work better?” Not everyone is jumping the same way. Indeed there is a spectrum of choice as shown in Figure 1. Here we are simplifying by calling the right side “organic” because it almost always involves metal conductors, just as the left side often involves organic substrates. The technologies live together — and that is notjust an interim stage.
HOW IT IS PANNING OUT
Although the term inorganic printed electronics may not be on everyone’s lips any time soon, it is now recognized as an area of tremendous commercial potential and technical progress. The cohabitation of organics and inorganics will probably pan out in the manner below. This is, literally, a very fluid situation. Table 1 shows the likely impact of inorganic printed and potentiallyprinted technology by 2017 via the dominant chemistry by device and device element.See the legend for details.
FAST GROWTH IN INORGANIC PRINTED ELECTRONICS
Among the fastest growing companies in new electronics are those that offer flexible A.C. electroluminescent displays that can cover many tens of square meters, emitting a range of colors, or be incorporated in watch faces and instrument displays. They involve six to eight printed inorganic layers, including a copper-doped phosphor, the only organic material used as a routineplastic film substrate.
INORGANIC COMPOUNDS HOLD THE HIGH GROUND IN PHOTOVOLTAICS
Dye-sensitized solar cells (DSSCs) that reach the market are based on titanium dioxide. CIGS solar cells researched by IBM, commercialized successfully by Mia-solé in the U.S., and developed by several other companies are inorganic — based on copper, indium, and gallium diselenide. Theyare certainly wide area and flexible. Can they be printed?
It is little wonder that there is a rapidly growing number of organizations developing potentially printable inorganic and hybrid electronic materials and devices. Spectrolab in the U.S. recently demonstrated 40.7% efficiency with a gallium arsenide/germanium solar cell, eight times that of the best organic versions (which are improving only slowly at present) and approaching the best performance of heavy silicon. Spectrolab already offers commercially flexible solar cells based on various inorganic compounds.
SCOPE OF HYBRID INORGANIC/ ORGANIC SOLUTIONS
In the middle, there is much work on improving organics by adding inorganic materials, often in nanoparticle form. The new quantum dot devices and high-K printable dielectrics are usually based on inorganic materials. After all, organic materials always have low permittivity and are therefore rarely idealfor transistor dielectrics or compact high-value capacitors.
INORGANIC COMPOUND TRANSISTORS DRIVING FLEXIBLE DISPLAYS
Last year, Toppan Printing in Japan demonstrated a flexible electrophoret-ic display back plane driver that employs amorphous indium gallium zinc oxide semiconductors that are processed at room temperature. This is based on work at the Tokyo Institute of Technology in Japan. Toppan Printing claims much higher mobility and, therefore, potentially higher frequencies of operation than organic alternatives. Both companies have programs to commercialize their inventions, although Plastic Logic of the UK is ahead with flexible electrophoretic displays as it is already building a factory in Dresden,Germany to make them using its organic transistors.
DO NOT WAIT FOR HIGHLY CONDUCTIVE ORGANIC INKS
Progress in improving the rather resistive so-called organic conductors is also limited, so new inorganic conductors also are being developed by many companies, such as Cabot, Emerson & Cuming, Parelec, NanoDynamics, Fer-roCorp,and NanoMas Technologies of the U.S. Then there are nanotube carbon and inorganic inks coming along as both conductors and semiconductors from Unidym of the U.S. and others, although they may not be low in cost for some time. Despite this, there is some traction in the marketplace for the newer organic conductors,including semi-transparent ones, so the situation continues to evolve.
LIGHTING MAY GO EITHER WAY
The U.S. Department of Energy forecasts that the new laminar electrics will eventually achieve lighting at a very environmentally friendly 160 lumens per watt efficiency versus only 50 lumens per watt for fluorescent lighting today. However, it is conservative to say that it may be inorganic or organictechnology that is successful in this respect. The race is on.
STRONG MARKET GROWTH
In 2007, we are finding that the amount spent on inorganic electronic components and inorganic materials for composite components will be $482.7 million. Much of this is in fairly mature markets — metal flake ink used for conductors in heated windscreens, membrane keyboards, and circuit boards, and disposable sensors for the 2.2 billion glucose sensor labels sold yearly. However, also making an impact in 2007, included in this figure, are electrophoretic, electroluminescent, and electrochromic displays, laminar batteries, and thin film photovoltaics. In 2007, inorganic semiconductors are being developed but not yet sold, but by 2012, we anticipate that inorganic semiconductors will be 30% of the thin-film semiconductor market versus 70% for organicsemiconductors.
We anticipate that in 2017, of a total $48.18 billion market (which includes printed and thin-film displays, logic, memory, photovoltaics, power, and sensors), the amount spent on inorganic components as a whole or in composites with organics will be approximately 40.3%–$19.43 billion. This highlights the importanceof inorganic printed electronics and the opportunity for companies to be involved.
Dr. Peter Harrop is employed by IDTechEx. He can be contacted at +44 (0) 1256 862163; [email protected]; www.idtechex.com/inorganic.
All figures are from IDTechEx Inorganic Printed and Thin Film Electronics.
