Fabrication of TiO2 memristive arrays by step and flash imprint lithography.

Identical patterns and characteristics of sub-100 nm TiO2-based memristive systems on 4 inch silicon substrates were demonstrated using Step and flash imprint lithography (SFIL). SFIL is a nanoimprint lithography technique that offers the advantagess of a high aspect-ratio, reliable nano-patterns, and a transparent stamp that can be used to facilitate overlay techniques. The overlay process from the alignment system in IMPRIO 100 was appropriate for the fabrication of nanoscale crossbar arrays in this study. High-density crossbar arrays that consisted of TiO2 resistive switching material that was sandwiched between Pt electrodes with a width of 80 nm and a half-pitch of 100 nm were in turn replicated through successive imprinting and etching processes. The use of the direct metal etching process enhanced the uniformity of the TiO2/Pt interface. The electrical property of the crossbar arrays showed the bipolar switching behavior that resulted in the application of the nonvolatile resistive memory.

Pattern-definable and low cost fabrication of nanopatterned conducting polymer film on flexible substrates.

This study reports the pattern definable and low cost fabrication of nanopatterned conducting polymer film on flexible substrates. Noble nanopatterned polymer hard template was fabricated by using nanoimprint lithography (NIL) and used for electropolymerization of conducting polymer. Conducting polymer was electrochemically deposited on the template and transferred over to flexible substrates. Eventually conducting polymer films with various nanopatterns were fabricated on flexible substrates. High pattern definability was achieved by nanoimprinted polymer template, which was molded from lithographically fabricated stamp. Low cost fabrication was accomplished due to low cost NIL, reusable polymer templates, and low material consumption of electrodeposition. The electrodeposited films were transferred using double sided tape. Because the templates are made of flexible polymer, the transfer bonding method applied in this study is adaptable to both wafers and flexible polymer substrates. The fabricated nanopatterned conducting polymer film can be applied to gas sensors, super capacitors, super wetting films, and neuron interfaces due to its characteristic of high surface to volume. For an illustrative application, the gas sensing properties of films were tested. The result showed enhanced sensing characteristic with nanopatterned film, which are attributed to the high surface to volume ratio of nanopatterned films.

An Antireflective Nanostructure Array Fabricated by Nanosilver Colloidal Lithography on a Silicon Substrate.

An alternative method is presented for fabricating an antireflective nanostructure array using nanosilver colloidal lithography. Spin coating was used to produce the multilayered silver nanoparticles, which grew by self-assembly and were transformed into randomly distributed nanosilver islands through the thermodynamic action of dewetting and Oswald ripening. The average size and coverage rate of the islands increased with concentration in the range of 50-90 nm and 40-65%, respectively. The nanosilver islands were critically affected by concentration and spin speed. The effects of these two parameters were investigated, after etching and wet removal of nanosilver residues. The reflection nearly disappeared in the ultraviolet wavelength range and was 17% of the reflection of a bare silicon wafer in the visible range.

Mass fabrication of resistive random access crossbar arrays by step and flash imprint lithography.

Step and flash imprint lithography (SFIL) is a promising method recently used for next generation lithographic technology because it is a high-speed process that can be carried out at room temperature and low pressures. Improvements made to SFIL enable the replication of crossbar patterns with a high resolution and the development of suitable materials and techniques to achieve high resolution capability. In this study, SFIL is used to fabricate high-density random access crossbar arrays based on a NiO resistive switching system. The bottom and top electrodes are transferred onto silicon wafers perpendicular to each electrode using the inductively coupled plasma reactive ion etching (ICP-RIE) technique. Direct metal etching without a wet-based process minimizes damage to the electrode surface. The I-V curves of individual active cells (70 x 70 nm(2)) for crossbar arrays reveal the unipolar resistive switching (RS) behaviour of the fabricated device. A high off/on resistance ratio (>10(4)) and reproducible resistance switching characteristics for each active cell were found in different fields and for different wafers. The experimental data indicate that high-density crossbar arrays can be well replicated and that the electrical performance of these arrays is reliable.

Measurement of surface adhesion force of adhesion promoter and release layer for UV-nanoimprint lithography.

In this work, we investigated the effect of surface treatment as release layer and adhesion promoter for UV-Nanoimprint lithography and measured the surface adhesion force by using tensile separation force of Instron equipment. Several Self-Assembled Monolayers (SAMs) of 3-Acryloxypropyl methyl dichlorosilane (APMDS) 3-Aminopropyl-triethoxysilane (APTS), and 3-Glycidoxypropyltrimethoxysilane (GPTS) as adhesion promoters and (1H,1H,2H,2H-perfluorooctyl)trichlorosilane (FOTS) as release layer were fabricated by vapor deposition method and were compared with oxygen plasma treatment. APMDS could strongly improve the adhesion force between UV-curable acrylate resin and silicon substrate because of strong covalent bonding. Finally, we could successfully fabricate various imprint patterns by using proper surface treatment of SAMs.

Stamping-based planarization of flexible substrate for low-pressure UV nanoimprint lithography.

Patterning flexible substrates in nano scale is an important and challenging issue in the fabrication of next-generation devices based on a non-silicon substrate. Step and Flash imprint lithography (S-FIL) which is a room temperature and low pressure process offers several important advantages, such as the use of a smaller and therefore cheaper stamp or the possibility of the overlay imprinting, as a transparent stamp is utilized. However, it is very difficult to perform S-FIL on a flexible substrate successfully due to the high waviness. The waviness of a flexible substrate is not a constant value in contrast to a rigid substrate. It depends on the imprint pressure applied onto the substrate. In this paper, in section two, the effect of the imprint pressure on the waviness of the surface of the flexible substrate is examined. It is proved that the waviness of the surface of the flexible substrate could not be reduced sufficiently to assure a successful imprint at low imprint pressures. In the third section, a method of patterning polymer substrates using ultra-violet nanoimprint lithography (UV-NIL) is presented. The method consists of two stages, stamping-based planarization and S-FIL. In stamping-based planarization, a planarization layer of transparent polymer is formed onto the flexible substrate. Waviness of the blank stamp (in this study, glass wafer) is transferred to the planarization layer. S-FIL is performed with the nanoimprint tool IMPRIO100 directly onto the planarization layer employing a 1 x 1 in. quartz stamp. Optical microscope and SEM images of the successfully imprinted patterns were also presented.

A mushroom lectin from ascomycete Cordyceps militaris.

A mushroom lectin has been purified from ascomycete Cordyceps militaris, which is one of the most popular mushrooms in eastern Asia used as a nutraceutical and in traditional Chinese medicine. This lectin, designated CML, exhibited hemagglutination activity in mouse and rat erythrocytes, but not in human ABO erythrocytes. SDS-PAGE of CML revealed a single band with a molecular mass of 31.0 kDa under both nonreducing and reducing conditions that was stained by silver nitrate, and a 31.4 kDa peak in a Superdex-200 HR gel-filtration column. The hemagglutination activity was inhibited by sialoglycoproteins, but not in by mono- or disaccharides, asialoglycoproteins, or de-O-acetylated glycoprotein. The activity was maximal at pH 6.0-9.1 and at temperatures below 50 degrees C. Circular dichroism spectrum analysis revealed that CML comprises 27% alpha-helix, 12% beta-sheets, 29% beta-turns, and 32% random coils. Its binding specificity and secondary structure are similar to those of a fungal lectin from Arthrobotrys oligospora. However, the N-terminal amino acid sequence of CML differs greatly from those of other lectins. CML exhibits mitogenic activity against mouse splenocytes.

Boron nitride stamp for ultra-violet nanoimprinting lithography fabricated by focused ion beam lithography.

Cubic boron nitride (c-BN) is one of the hardest known materials (second after diamond). It has a high level of chemical resistance and high UV transmittance. In this study, a stamp for ultra-violet nanoimprint lithography (UV-NIL) was fabricated using a bi-layered BN film deposited on a quartz substrate. Deposition of the BN was done using RF magnetron sputtering. A hexagonal boron nitride (h-BN) layer was deposited for 30 min before c-BN was deposited for 30 min. The thickness of the film was measured as 160 nm. The phase of the c-BN layer was investigated using Fourier transform infrared (FTIR) spectrometry, and it was found that the c-BN layer has a 40% cubic phase. The deposited film was patterned using focused ion beam (FIB) lithography for use as a UV-NIL stamp. Line patterns were fabricated with the line width and line distance set at 150 and 150 nm, respectively. The patterning process was performed by applying different currents to observe the effect of the current value on the pattern profile. The fabricated patterns were investigated using AFM, and it was found that the pattern fabricated by applying a current value of 50 picoamperes (pA) has a better profile with a 65 nm line depth. The UV transmittance of the 160 nm thick film was measured to be 70-86%. The hardness and modulus of the BN was measured to be 12 and 150 GPa, respectively. The water contact angle of the stamp surface was measured at 75°. The stamp was applied to UV-NIL without coating with an anti-adhesion layer. Successful imprinting was proved via scanning electron microscope (SEM) images of the imprinted resin.

Fabrication of nano- and micro-scale UV imprint stamp using diamond-like carbon coating technology.

Two-dimensional (2-D) and three-dimensional (3-D) diamond-like carbon (DLC) stamps for ultraviolet nanoimprint lithography were fabricated with two methods: namely, a DLC coating process, followed by focused ion beam lithography; and two-photon polymerization patterning, followed by nanoscale-thick DLC coating. We used focused ion beam lithography to fabricate 70 nm deep lines with a width of 100 nm, as well as 70 nm deep lines with a width of 150 nm, on 100 nm thick DLC layers coated on quartz substrates. We also used two-photon polymerization patterning and a DLC coating process to successfully fabricate 200 nm wide lines, as well as 3-D rings with a diameter of 1.35 microm and a height of 1.97 microm, and a 3-D cone with a bottom diameter of 2.88 microm and a height of 1.97 microm. The wafers were successfully printed on an UV-NIL using the DLC stamps without an anti-adhesive layer. The correlation between the dimensions of the stamp's features and the corresponding imprinted features was excellent.