**8. References**

566 Recent Advances in Nanofabrication Techniques and Applications

printing can be used in continuous mode as well as drop-on-demand mode. The main benefit of the electrohydrodynamic inkjet printing is generation of pattern smaller than the nozzle size, because the printing is performed by pulling the liquid rather than pushing of the liquid, which is limitation in other inkjet technology such as thermal and piezoelectric printing. The advantage of electrohydrodynamic printing over conventional printing is high resolution can be obtained. The other advantage of this direct patterning method is the flexibility in the process in terms of material to be used as well as patterns can be made on different kinds of substrate. In continuous mode the patterning is performed by achieving through thing continuous jet in the stable cone-jet mode, however the thin is difficult to stabilize due to electric field. The drop-on-demand mode can be used as alternative to continuous electrohydrodynamic printing. In drop-on-demand the stable cone-jet is achieved for shorter period of time by applying the pulse voltage. Single nozzle electrohydrodynamic printing has low throughput, in order to increase the efficiency multinozzle printing can be performed as reported. The other advantage of electrohydrodynamic printing is thin film deposition in electrospray mode. Thin films can be deposited on the surface of different substrate without changing the experimental setup. This combination of both the technologies (patterning and thin film deposition) can help in fabrication of the

electronic devices such as TFT, OLED or Solar Cells etc. through single technology.

There is lot of research is being performed in the field of the electrohydrodynamic printing by patterning the functional materials even in submicron level (Schirmer et al. 2010). However the functional materials meeting these requirements are a challenge, which can be used for the patterning purpose. The inks containing these functional materials impact the morphology, adhesion, chemical and environmental stability, these factors affect the performance. In addition to this the material used in direct patterning technologies has drawbacks in functional performance such as ion mobility, on-off voltage, threshold voltage and off current. Many researchers are working in the field of chemical and material technologies to overcome these limitations, by introducing the different materials that can be used for fabrication of devices through direct fabrication technology. Inorganic material such as carbon nanotube (single-wall and multi-wall) and metal nanoparticles (silver, gold and copper) based inks and pastes are commercially available for the direct patterning applications. Recently there researches are also working on the organic materials that can be used as the insulation material for electronic devices and also conductive organic material such as PEDOT, which can used for the fabrication of the conductive tracks. Recently composite polymers have received interests in the field of direct patterning material due to improvement in mechanical, thermal, optical and conductive properties. But the major drawback is still the performance of devices fabricated through the direct patterning

In electrohydrodynamic inkjet printing, for large area manufacturing the design of multinozzle printing head is another bottle neck due to interfering of electric field between nozzles. The miniaturization of the nozzles dimensions cause problems in obtaining the symmetric and stable cone-jet for printing. Other limitation is the fabrication of such small size nozzles. To optimize the performance of small nozzles, the physics and chemistry of the nozzle has to optimize to ensure the printability of different functional materials, with damaging the nozzles. When using the micron size nozzle, the issue of the clogging arises

**6. Challenges and future trends** 

technology as compared to conventional electronic.


**28** 

*Japan* 

**Lithography-Free Nanostructure Fabrication** 

Fabricating nanoscale patterns with sub-10 nm feature size has been an important research target for potential applications in next-generation memories, microprocessors, logic circuits and other novel functional devices. Typically, according to the International Technology Roadmap for Semiconductor (ITRS) from 2009, an 8.9 nm node device is targeted for the year 2024. To achieve this milestone, liquid immersion lithography and extreme ultraviolet (EUV) lithography can be expected to be among the most commonly used techniques for the fabrication of nanopatterns. With liquid immersion lithography using a wavelength of 193 nm and a high numerical aperture (NA), it has been demonstrated that 32 nm features can be patterned (Finders et al., 2008; Sewell et al., 2009). EUV lithography using a short wavelength of 13.5 nm and 0.3-NA exposure tool has also enabled the printing of 22 nm

On the other hand, attractive patterning techniques, such as a superlattice nanowire pattern transfer (SNAP) method (Melosh et al., 2003; Green et al., 2007), a mold-to-mold cross imprint (MTMCI) process (Kwon et al., 2005) and a surface sol-gel process combined with photolithography (Fujikawa et al., 2006), are currently proposed and pursued actively. The SNAP method, which is based on translating thin film growth thickness control into planar wire arrays, has enabled the production of molecular memories consisting of 16 nm wide titanium/silicon nanowires. The MTMCI process using silicon nanowires formed by spacer lithography, in which nanoscale line features are defined by the residual part of a conformal film on the edges of a support structure with the linewidth controlled by the film thickness, has been used to produce a large array of 30 nm wide silicon nanopillars. With the surface sol-gel process combined with photolithography, where the linewidth is determined by the thickness of coating silica layer on the resist pattern, the size reduction and the large area of

Recently, we have proposed a double nano-baumkuchen (DNB) structure, in which two thin slices of alternating metal/insulator nano-baumkuchen are attached so that the metal/insulator stripes cross each other, as part of a lithography-free nanostructure fabrication technology (Ishibashi, 2003 & 2004; Kaiju et al., 2008; Kondo et al., 2008). The schematic illustration of the fabrication procedure is shown in Fig. 1. First, the metal/insulator spiral heterostructure is fabricated using a vacuum evaporator including a film-rolled-up system. Then, two thin slices of the metal/insulator nano-baumkuchen

**1. Introduction** 

half-pitch lines (Naulleau et al., 2009).

sub-20 nm silica walls have been achieved.

**Techniques Utilizing Thin-Film Edges** 

Hideo Kaiju1,2, Kenji Kondo1 and Akira Ishibashi1 *1Research Institute for Electronic Science, Hokkaido University* 

*2PRESTO, Japan Science and Technology Agency* 

