Novel Dielectrics for TOP Electronics

NanoMarkets will soon be issuing a report on dielectric materials. More details available here.

Until recently, the focus of materials development for thin-film, organic printable (TOP) electronics was on conductors and semiconductors. However, as this rapidly growing area of electronics becomes more sophisticated, there is a growing need for new or enhanced dielectric materials for both processors and memories. The search for such materials has been particularly important as electronics materials firms begin to talk about organic versions of CMOS and new dielectric materials have to meet the needs of flexible substrates.

Electronics based on printable and largely organic conductors, dielectrics, and semiconductors, with OFETs as the core devices, have become a research area in their own right and have spurred significant investment by established and emerging companies such as BASF, DuPont, Evonik, Merck, Polyera and Thin Film Electronics, and also by leading research institutions including Cambridge University, Max Planck Institute, North Western University, PARC and University of Groningen.

NanoMarkets believes that novel dielectrics for TOP electronics will find great suitability in providing higher performance at lower cost initially for low-end item-level tags over the next few years and then thrive, evolving and specializing over time to support a broader range of high-end applications.

The fastest growing segments for dielectrics are in TFTs and memory using organic, inorganic or hybrid (a mixture of the two) compounds that will enable complementary organic circuits (flexible).

Organic Material Sets and "Organic CMOS"
Inorganic based CMOS has been the standard for decades in the microelectronics industry. With the advent of TOP, the future looks especially promising on the new materials front (e.g. hybrimers and nanodielectrics). The new concept of low power "organic CMOS" or organic electronic circuits seems likely to provide the organic computing power that will ultimately drive the much talked about pervasive computing. In fact, partial or entire material sets are already being offered by firms including Merck, Polyera and PolyIC.

Organic Thin-Film Transistors
One reason that OTFT dielectrics have not been widely discussed until now is that one fairly conventional inorganic material, silicon oxide (SiO2), has been the mainstay material used in this application. However, as discussed in this report, several different types of dielectric materials are being proposed, which offer low temperature processability—and therefore combine well with the processing advantages of organic semiconductors in both top-gate and bottom-gate device architectures.

Considerable attention is being given to the role of the interface between the dielectric layer and the semiconductor layer in OTFTs, since it is realized that both the physical and chemical nature of this interface plays a vital role in device performance. A simple OTFT can be created using vapor deposition to deposit organic semiconductor material on SiO2, but without additional treatment the interface can be highly disordered. Warming the substrate and slowing down the deposition process seems to help, but this is rather impractial for commercial-scale processing. Several alternative approaches are now being utilized, such as: coating the insulator with a monolayer of organic material (self-absorbed monolayers); metal oxides—printed barium or strontium titanate nanocomposites; single (mobilities of >0.5 cm2Vs) or bilayer polymer dielectrics (mobilities of 3 cm2/Vs) with polyvinyl phenol, poly vinyl alcohol, poly methylmethacrylate or polyimides; crosslinked polymer blends; and new photocurable dielectrics, which are discussed in detail in this report.

The immediate opportunity for organic dielectrics is with the top-gate structured OFET, since the organic dielectric does not destroy the underlying organic semiconductors. Top-gate/bottom-contact-structured devices allow patterning of the bottom source-drain electrodes on top of any flexible or rigid substrate prior to fabricating the rest of the device. Top-gate/top-contact devices allow organic semiconductor films to grow on top of any flexible or rigid substrate and there are ways of arranging the device elements.

Organic Memory - Alive and Well
On the organic memory front, Thin Film Electronics is building a strong alliance of materials, equipment and manufacturing firms with the objective of bringing its ferroelectric polymer memory to market soon. Meanwhile, academics at a surprisingly large number of universities around the world—especially in Korea, Taiwan and Japan—are gradually improving the speed of OTFTs and coming up with new approaches to organic memory.