Thermal Imprint Research Articles

An Ediacaran–Cambrian thermal imprint in Rajasthan, western India: Evidence from 40Ar–39Ar geochronology of the Sindreth volcanics

The Sindreth Group exposed near Sirohi in southern Rajasthan, western India, is a volcanosedimentary sequence. Zircons from Sindreth rhyolite lavas and tuffs have yielded U–Pb crystallization ages of ~768–761 Ma, suggesting that the Sindreth Group is a part of the Malani magmatic event. Earlier 40Ar–39Ar studies of other Malani volcanic and plutonic rocks yielded disturbed argon release spectra, ascribed to a ~550 Ma thermal event possibly related to the Pan-African orogeny. To test and confirm this possibility, we dated two whole-rock and three feldspar separate samples of the Sindreth volcanics by the 40Ar–39Ar method. All samples yield disturbed argon release spectra suggesting radiogenic argon loss and with plateau segments at 550 Ma or 490 Ma. We interpret these as events of argon loss at 550–490 Ma related to an Ediacaran–Cambrian thermal event, possibly related to the Malagasy orogeny. The combined older and new 40Ar–39Ar results are significant in showing that whereas Ediacaran–Cambrian magmatic and metamorphic events are well known from many parts of India, they left thermal imprints in much of Trans-Aravalli Rajasthan as well. The overall evidence is consistent with a model of multiphase assembly of Gondwanaland from separate continental landmasses.

Highly Flexible Magnetoelectronic Device Integrated With Embedded Ag Nanoparticle Electrode

A flexible magnetoresistance (MR) device is fabricated through the hybrid process of embedding an Ag nanoparticle electrode by thermal imprinting and magnetic multilayer sensor element by sputtering on a polyethylene naphthalate (PEN) substrate. The MR signal profiles for a ring type sensor deposited on the PEN substrate show typical anti-symmetric curves centered for the field H=0, and the maximum signal and its field sensitivity are nearly the same as those of sensors deposited on Si and glass substrates. The root mean square (rms) roughnesses and magnetic properties of magnetic thin film deposited on the different substrates show that Hex was decreased with increasing roughness. Further, MR change with temperature had no significant effect on the sensor performance. The stability of Au electrode and Ag paste electrode were compared during the bending of MR sensor, revealing the cracking of Au electrode above 45°. However, Ag paste electrode was stable up to 90°. The field sensitivity of the MR signal for the full range of fields is inversely proportional to the effective anisotropy field, which is the sum of exchange-bias and stress-induced anisotropy fields. As a whole, the field sensitivity of MR signal depends on bending stress at the sensor position.

Simplified Cu/Polyimide Damascene Approach Based on Imprint Process of Soluble Block Copolymer Polyimide

In this study, a Cu/polyimide damascene approach based on an imprint technique was demonstrated aiming at developing a low-cost fabrication process for high-density interconnections in polyimide. First, a UV-assisted thermal imprint process that utilizes the high formability and low shrinkage of a soluble block copolymer polyimide was proposed as a high precision patterning process for polyimide. As a result, fine patterns (line widths ranging from 3 to 50 µm) with rectangular cross sections and clear line edges were fabricated in soluble block copolymer polyimide films by UV-assisted thermal imprinting followed by curing. Additionally, Cu damascene structures with a minimum line width of 3 µm were fabricated in the polyimide by performing subsequent Cu electroplating and chemical mechanical polishing (CMP), and the feasibility of the process was verified.

Size Error and Modification of V-Groove in Thermal Microimprint

Thermal microimprint is a promising technology for polymer microstructure, so it is used to form V-groove on the surface of optical devices. However, it is difficult to control the size accuracy of V-groove because of the elastic recovery of polymer. In order to solve the problem, the influencing factors on the polymer elastic recovery were firstly analyzed in this article. Then, it was proposed that the embossment height of mold should be modified according to the depth of V-groove and the modifier formulas should be constructed based on the theory of polymer viscoelasticity. In the end, the optimal technological parameters of thermal microimprint were obtained through the thermal imprint experiments, and the embossment height of the mold after modification was calculated according to the experimental data, and thus a new mold was produced as to verify the accuracy of the modifier formulas. The results showed that the approach of modification could not only ensure dimension accuracy of V-groove, by keeping the error within 1μm, but also shorten the imprint time, consequently the efficiency of thermal microimprint would be improved.

Polycarbonate as an Elasto-Plastic Material Model for Simulation of the Microstructure Hot Imprint Process

The thermal imprint process of polymer micro-patterning is widely applied in areas such as manufacturing of optical parts, solar energy, bio-mechanical devices and chemical chips. Polycarbonate (PC), as an amorphous polymer, is often used in thermoforming processes because of its good replication characteristics. In order to obtain replicas of the best quality, the imprint parameters (e.g., pressure, temperature, time, etc.) must be determined. Therefore finite element model of the hot imprint process of lamellar periodical microstructure into PC has been created using COMSOL Multiphysics. The mathematical model of the hot imprint process includes three steps: heating, imprinting and demolding. The material properties of amorphous PC strongly depend on the imprint temperature and loading pressure. Polycarbonate was modelled as an elasto-plastic material, since it was analyzed below the glass transition temperature. The hot imprint model was solved using the heat transfer and the solid stress-strain application modes with thermal contact problem between the mold and polycarbonate. It was used for the evaluation of temperature and stress distributions in the polycarbonate during the hot imprint process. The quality of the replica, by means of lands filling ratio, was determined as well.

Emplacement of hot Lesser Himalayan nappes from 15 to 10 Ma in the Jumla-Surkhet region, western Nepal, and their thermal imprint on the underlying Early Miocene fluvial Dumri Formation

A multichronological study of the weakly metamorphosed Early Miocene fluvial Dumri Formation and the overlying Kuncha and Lesser Himalayan Crystalline nappes has helped to clarify the timing and heat source of the metamorphism, as well as the history of emplacement and cooling of the nappes. U–Pb ages of detrital zircons from the Dumri Formation show peaks at ca 1 Ga and 500–600 Ma, and fission-track dating indicates a thermal imprint on the formation at 11–10 Ma. In the Naudanda Quartzite, overlying the Kuncha Formation, reset fission-track detrital zircon ages are 9.5 Ma, but the U–Pb ages are older than 1.7 Ga. The differences in the U–Pb ages for detrital zircons from the Dumri and Kuncha Formations indicate that the Kuncha nappe was never exposed at the surface during the Early Miocene when the Dumri Formation was deposited. Two-mica garnet schists of the Main Central Thrust (MCT) zone have fission-track detrital zircon ages of 7.8 Ma and 40Ar–39Ar muscovite ages of 19 Ma, though the zircons have U–Pb ages older than 600 Ma. Our interpretation is that the heat for the Dumri Formation metamorphism came from the overlying nappes. The timing of the thermal imprint on the Dumri Formation indicates that the metamorphic nappe reached its present position before ca 10 Ma. The Parajul Khola granite in the frontal zone of the Kuncha nappe yields U–Pb zircon ages of 1.89 Ga, and it underwent an Early Miocene thermal event, cooling below 240°C at 14.7 Ma and below 100°C at 10.3 Ma. These thermochronological data suggest that the frontal part of the Kuncha nappe was exposed at the surface around 15–14 Ma and cooled immediately, but inner parts of the nappe were still hot during its emplacement.

Room temperature wafer bonding of metal films using flattening by thermal imprint process

This paper reports on the surface flattening of metal films on wafers by the thermal imprint process and its application to wafer direct bonding. The ultraflat surface of a sapphire wafer was pressed onto the surface of a sputter-deposited Au film on a Si wafer for 600s at 200°C with an applied pressure of 5MPa by compressed air. As a result, the Au film surface was successfully flattened by thermal imprint process. The flattened Au films were bonded in a vacuum chamber after surface activation by Ar beam sputtering. In the case of bonding between two Au films on a Si wafer, the surface flattening of the Au films was determined to be effective when the bonding load is small and/or the Au films are relatively thick. In the case of bonding between a Si wafer and a Au film on a Si wafer, defects at the bonding interface were found to be dramatically reduced by the flattening of the Au film surface. Additionally, the Au–Si bonding using the flattened Au film was significantly stronger than that without flattening.

Property Measurement and Processing Parameter Optimization for Polylactide Micro Structure Fabrication by Thermal Imprint

Polylactide (PLA) is a thermoplastic polymer derived from renewable resources. In this study, we measured the material properties and forming conditions of PLA under the thermal imprint process. The properties of PLA were investigated under various imprint temperatures and imprint times. The results show that increasing the imprint temperature and imprint time results in a progressive rise in Young's modulus and a decrease in elongation at break. Furthermore, if the imprint time exceeds 10 min, crystallinity at imprint temperatures 90 and 110 °C increases visibly. Measurements of rheology properties was performed and the results show viscoelastic behaviors which are combination of irreversible viscous flow and reversible elastic deformation at the temperature of 110–180 °C. The forming conditions of PLA micro structures under thermal imprint technology were studied based on the Taguchi method. The experimental results show that the transfer rate was enhanced to 96.3%. This study therefore contributes to research on the fabrication of biomedical devices using biodegradable polymers produced by the thermal imprint process.

Geochronological constraints on Meso- and Neoarchean regional metamorphism and magmatism in the Dharwar craton, southern India

This contribution addresses the time framework of the regional metamorphism in the three crustal provinces making the Archean Dharwar craton. We present results of texturally controlled in situ EPMA chemical dating of monazites, chemical dating of monazite separates, as well as Sm–Nd garnet–whole rock isochrons and SHRIMP U–Pb zircon ages for pelites, amphibolites and granitoids over target areas typical of the various crustal levels of the provinces. The Western Dharwar craton has undergone a major thermal pulse at 2.52Ga followed by slow cooling to ca. 2.4Ga and recorded earlier thermal events around 3.0Ga and 3.1Ga. The Central Dharwar craton records a major high-grade thermal imprint at ca. 2.55–2.51Ga followed by cooling up to 2.45Ga and earlier thermal events at ca. 2.62 and 3.20Ga. In the Eastern Dharwar craton the widespread thermal pulse between 2.55 and 2.52Ga is best recorded. From 2.52Ga on, the entire craton ultimately and contemporaneously undergoes the main event of regional HT–LP metamorphism. The contrasted thermal records of the three provinces reflect their accretion age(s) and their degree of involvement in a wide Latest Archean hot orogen, which sets the capacity of these lithospheric segments to be impact by deformation and mantle fluxes. The tectonic setting of Latest Archean hot orogeny is compatible with active plate margin processes having interacted with mantle instabilities (i.e., plumes?). The tectonic setting of pre-2.5Ga thermal pulses is difficult to assess, but considering their systematic links with documented magmatic pulses, they may have been generated in contexts comparable that of Latest Archean hot orogeny where lateral constrictional flow of hot orogenic crust achieves gravity driven flow, 3D mass redistribution of viscous lower crust submitted to convergence.

High-speed imprinting on plastic optical fibers using cylindrical mold with hybrid microstructures

• We developed a cylinder mold with hybrid-layered patterns. • A precise cutting was combined with 3-D photolithography using a flexible mask. • The imprint speed was improved by changing a press-force control method. • We succeeded in continuous imprinting on a POF at a feeding speed of 20 m/min. We are developing flexible and large-size e-textiles by weaving in a smart fiber. On the surface of the fiber, micro-electro-mechanical-systems (MEMS) structures, electronic circuit patterns, and guide structures for positioning during the weaving process are fabricated. In order to manufacture smart fibers in large quantities, we developed a cylindrical mold with hybrid-layered structures consisting of 260-μm-wide macro patterns and several 10-μm-wide patterns fabricated by precise cutting of substrate employing forming tools and 3-D photolithography, and using a micro-patterned flexible photomask. Initially, the polished surface of the cylinder is covered with an electroless-plated Ni–P alloy; and convex structures with rectangular cross-sections and arc shaped convex structures are cut. Next, the surface of the cylinder is coated with a positive-tone photoresist by a dipping process. Ultraviolet (UV) lights are then irradiated on the photoresist through a flexible micro-patterned photomask wrapped around the cylinder; and then the micro-patterns on the photomask are thus transferred onto the cylindrical surface. Next, following a Cu electroplating, hybrid-layered patterns are made that comprise 260-μm-wide macro and several 10-μm-wide microstructures. In the final step, the photoresist is then removed. And moreover, in order to realize high-speed imprinting, the mechanical stiffness of a reel-to-reel thermal imprint system is improved, and the press-force control method is changed. The imprint system is equipped with a completed cylindrical mold; and using the system, a plastic optical fiber (POF) comprising a 240-μm-diameter PMMA core with a 5-μm-thick fluoride clad is imprinted for a demonstration. The cylindrical mold heated up to 50 °C with an infrared lamp, is pushed into the surface of the POF to a depth of 4.5–6.7 μm. As a result, a continuous imprinting on the POF is achieved at an imprint speed of 20 m/min.

Experimental testing and FEM simulation for thermal imprinting of micro/nano glass-optical devices

Thermal imprinting of glass-optical devices and its numerical simulation using the finite element method were investigated. The constitutive equation of the glass material was estimated using compression creep tests based on conventional thermoviscoelastic theory. The relaxation modulus of D263 glass was approximated by the generalized Maxwell model. For glass thermal imprinting, a glassy carbon die was used on which line and space or microlens array patterns were machined with a focused ion beam (FIB). The optimum molding-temperature condition that gives precise transcription profile was investigated in detail. Finite element analyses were performed to simulate the experimental glass thermal imprinting. In comparing experimental and numerical results, the transcription heights of groove or microlens obtained by experimental tests approximately agreed with numerical values. Finite element analyses using thermoviscoelastic property of glass are reliable in estimating suitable conditions for glass thermal imprinting.

Fabrication of Ni-W Electroformed Mold for Thermal Imprint of Borosilicate Glass

Fabrication of Ni-W Electroformed Mold for Thermal Imprint of Borosilicate Glass

Effect of Micro-Patterned Membranes on the Cathode Performances for PEM Fuel Cells under Low Humidity

Although micro-patterned membranes improve the performances of proton exchange membrane fuel cells, their intrinsic effect has not been clarified. This paper aims to clarify the effect of the patterned surfaces in terms of the overvoltage by fabricating well-defined micro-pillar structures on the cathode side of the membrane via thermal imprint lithography. Cell performance data and numerical simulation revealed that the pillar structures reduce the proton transport resistance and mass transport loss in the cathode catalyst layers. The reduced proton transport resistance expands the catalyst layers contributing the power generation toward the interface between the catalyst and gas diffusion layers. This decreases the average permeation distance of oxygen to react at the catalyst, which would explain the observed reduction of the concentration overvoltage. The pillar structures reduce the ohmic overvoltage predominantly at a relative humidity of <25% and a current density of <500 mA/cm2. The concentration overvoltage suppression becomes more significant at higher humidity and current densities where the oxygen diffusion to the catalyst is blocked by water. Our findings are useful to design optimum pillar structures that maximize the fuel cell cathode performances.

アモルファス材料の熱インプリント用モールドへの適用とその加工方法

アモルファス材料の熱インプリント用モールドへの適用とその加工方法

Thermal Imprint of P3HT and PCPDTBT: Layer Preparation and Imprint Temperature

Thermal Imprint of P3HT and PCPDTBT: Layer Preparation and Imprint Temperature

Wafer level silicon mould fabrication and imprinting of high density microstructures

Wafer level mould fabrication and its imprinting technology are of great interest for cost effective mass fabrication of nano or microsized patterns. Although the process for making a silicon mould involves only several steps such as photolithography, deep reactive ion etching (DRIE) and nanoimprinting, there are still many issues to be overcome in order to achieve uniformly imprinted patterns on the whole wafer. Taking a 4'' wafer full of high density 3x3@mm squares with a depth of 10@mm as an example, this paper investigates the pitfalls in silicon mould fabrication and imprinting, and provides feasible solutions as a good reference to researchers seeking to mass fabricate micron-sized patterns by thermal imprinting.

Transparent conductive film with printable embedded patterns for organic solar cells

We report a development of a highly transparent conductive film (TCF) which is the first embedded metal grid of fine lines on a flexible substrate. The TCF reveals excellent electrical and optical performance as transparent conductive film with an extremely high σDC/σOP value of 237 due to 80.35% transmittance and 6.85Ω/□ sheet resistance. Furthermore, the extremely high performance is realized with new features of the TCFs: roll-to-roll printability on flexible substrates, thermal imprinting of channels at 10μm widths, water-based nano-silver paste to fill the narrow channels, and doctor blade as a facile method to fill the paste into the channels. The TCF electrode is implemented to fabrication of an organic solar cell (OSC) which shows a power conversion efficiency of 1.40%. This is non-optimized yet but approaching that of an ITO-based OSC (1.70%). Thus, we demonstrate a printable TCF to replace the ITO films toward low-cost large area roll-to-roll fabrication of organic solar cells.

Using thermal imagings in the study of periglacial forms and processes

Periglacial morphogenetic domain is marked by the presence of landforms whose genesis and evolution is closely related to thermal conditions. It goes without saying therefore of interest to know the thermal characteristics of these periglacial landforms. To achieve this objective, the use of clasical thermometers is also expensive and laborious process, but in our opinion, the most expeditious way is to use a infrared termocamera. Tacking into account that radiant temperature of the Earth surface is a a function of their internal temperature or kinetic temperature, and their ability to emit radiation, strongly dependent on the thermal properties of the material - with physical and compositional differences -, we consider that a thermal image can also reveal just some of the differences in the morphological structures. Energy flux that occurs at topographic surface interactions with the atmosphere cause individualization of microclimates, with implications for the appearance and development of the periglacial morphogenetic processes like creep, fros heaving, solifluction, thermal sorting and weathering. A way of understanding of these processes and highlighting small-scale differentiation knowing as much detail as possible, is knowing the thermal image, thermal imprint of each microform.

Control of inclination angle of glass-like carbon mold by defocus UV exposure on Si-containing photoresist

The authors fabricated micropatterns with inclined sidewalls in a glass-like carbon (GC) mold to thermal imprint on a glass substrate, and succeeded in controlling its inclination angle. The technology comprised three features: (1) A Si-containing photoresist was used with its etching resistance higher than that of the conventional photoresist; (2) the inclination angle of pattern's sidewalls was controlled by a defocus UV exposure technique; and (3) a GC substrate was etched to form a mold by using a Si-containing photoresist structure with inclined sidewalls as a masking layer; the technique was also used to control the inclination angle of the trench's sidewalls in the GC mold. The authors input different focus offset values to defocus the image in order to control the intensity distribution of UV lights within a film of Si-containing photoresist that was spin-coated on a polished GC wafer. In the next step, GC was etched by a 19:1 mixture of O2 and CHF3 which then created a trench structure with inclined sidewalls according to the variations in local masking thicknesses. By changing the focus offset in the UV exposure system from 0 to −12 μm, the inclination angle of the Si-containing photoresist microstructures was varied from 17° to 40°. With these changes, the range of the angles of GC molds became 6° to 17°. Then by thermal imprinting on Pyrex glass and quartz, these numbers expanded from 10° to 32°.

Sidewall-angle dependent mold filling of three-dimensional microcavities in thermal nanoimprint lithography

Nanoimprint stamp cavities with vertical and sloped sidewalls show different filling behaviors during thermal nanoimprinting resulting from the varying ability of the viscous polymer to wet the surface during the thermal imprint step. In this paper, the authors describe the formation of prefill states already in the pressure-less contact phase, before squeeze flow begins to fill the cavities. These stable states are created by a constant contact angle formed at the sidewall, and the states themselves generate surface topographies in the resist below the imprint cavities which are dependent upon the surface energy, the geometry of the stamp cavities, and the resist thickness. Therefore, prefilling topographies, formed once a stamp is in contact with a liquid polymer surface and resulting in a transformation of the resist layer with homogeneous thickness into a thickness modulated film, have to be considered as the standard case in molding. Furthermore, due to the local balance of material pinning and wetting mechanisms, cavities preferentially fill from the sloped sidewall and, therefore, this observed phenomenon is highly relevant for the defect-free replication of 3-D surface topographies.