Gold nanohole arrays for biochemical sensing fabricated by soft UV nanoimprint lithography

We report on results of fabrication and optical characterisation of sub-250 nm periodic gold nanohole arrays on glass by using UV nanoimprint lithography (UV-NIL) combined with both reactive ion etching (RIE) and Cr/Au lift-off processes. The transmission spectra of the fabricated nanohole gratings were measured for different hole diameters and periods. We also show preliminary results of chemical sensing after surface modification of the gold hole arrays. In agreement with the theoretical prediction, we found that any change in the dielectric index of the surrounding environment of the metallic array produces a transmission peak red shift.     

A versatile pattern inversion process based on thermal and soft UV nanoimprint lithography techniques

Si master molds are generally patterned by electron-beam lithography (EBL) that is known to be a time-consuming nanopatterning technique. Thus, developing mold duplication process based on high throughput technique such as nanoimprint lithography can be helpful in reducing its fabrication time and cost. Moreover, it could be of interest to get inverted patterns (holes instead of pillars) without changing the master EBL process. In this paper, we propose a two step process based on thermal nanoimprint lithography (T-NIL) (step 1) and soft UV assisted nanoimprint lithography (UV-NIL) (step 2) to invert a master EBL mold. After the two inversion steps, the grand-daughter Si mold exhibits the same pattern polarity as the EBL mold. For step 1, pattern transfer using ion beam etching (IBE) of a thin metallic underlayer is the critical step for dimension control due to the low NXR1020 resistance. For step 2, the optimized reactive ion etching (RIE) step allows transfer with good anisotropy even for nanostructures at the 50 nm-scale. For structures larger than 100 nm, this inversion process has been successfully applied to large field replication (up to 1.5 cm²) on whole wafer.     

Residue-free room temperature UV-nanoimprinting of submicron organic thin film transistors

In this study we report on an innovative nanoimprint process for the fabrication of entirely patterned submicron OTFTs in a bottom-gate configuration. The method is based on UV-Nanoimprint Lithography (UV-NIL) combined with a novel imprint resist whose outstanding chemical and physical properties are responsible for the excellent results in structure transfer. In combination with a pretreated stamp the UV-curable resist enables residue-free imprinting thus making etching obsolete. A subsequent lift-off can be done with water. The UV-NIL process implies no extra temperature budget, is time saving due to short curing times, eco-friendly due to a water-based lift-off, simple because it is etch-free and completely r2r compatible. It works perfectly even if ultra-thin organic and hybrid films are used as gate dielectrics. On this basis entirely patterned functional submicron OTFTs with pentacene as the semiconductor are fabricated showing clear saturation, low switch-on voltage (～3 V) and a sufficiently high on–off ratio (10³).     

Inkjet and microcontact printing of functional materials on foil for the fabrication of pixel-like capacitive vapor microsensors

The work presented demonstrates the utilization of micro-contact printing of self-assembled monolayers (SAMs) of gold nanoparticles (NPs) to pattern the porous thin metallic film composing the top electrode of an ultra-fast capacitive relative humidity sensor based on miniaturized parallel-plates electrodes. The rest of the device, which occupies an area of only 0.0314 mm², is fabricated by inkjet printing stacked individual drops of functional materials, namely gold NPs for the bottom electrode and a polymeric humidity sensing layer, on a polymeric foil. Compared to other printing methods, the use of microcontact printing to pattern the top electrode enables the additive transfer of a solvent-free metallic layer that does not interact chemically with the sensing layer, permitting the thinning of the latter without risk of short-circuits between electrodes, and broadening the range of usable sensing materials for detection of other gases. Thinning the sensing layer yields to ultra-fast response devices with high values of capacitance and sensitivity per surface area. The fabrication process is compatible with low heat-resistant polymeric substrates and scalable to large-area and large-scale fabrication, foreseeing the development of low-cost vapor sensing sheets with high space–time resolution, where every sensor would correspond to a pixel of a large array.     

Promising methane gas sensor synthesized by microwave-assisted Co3O4 nanoparticles

The morphology and gas sensing characteristics of Co₃O₄ nanoparticles prepared using the microwave irradiation were investigated. XRD and TEM are used to analyze the structural and the morphological properties of the prepared nanoparticles. XRD results confirmed the formation of pure phase of these nanoparticles. The gas sensor based on the synthesis Co₃O₄ nanoparticles reveals faster response and recovery time at low temperature detection toward methane gas. Specifically, for methane concentration of 1%, the response and the recovery times at 200 °C are 100 s and 50 s, respectively. Furthermore, the sensing characteristics of Co₃O₄ nanoparticles were improved by increasing the operating temperatures and gas concentrations as well. The experimental results clearly demonstrate the potential use of Co₃O₄ nanoparticles as a sensing material in the fabrication of CH₄ sensors.     

UV nanoimprint lithography with rigid polymer molds

Transparent polymers are considered as alternative low-cost mold materials in UV nanoimprint lithography (UV-NIL). Here, we demonstrate a nanoimprint process with molds made of rigid polymers novel for this application. These polymer molds are found to show high performance in the patterning with UV-NIL. Sub-50 nm structures were fabricated with this process.     

The UV-nanoimprint lithography equipment with multi-head imprinting unit for sub-50 nm half-pitch patterns

Nanoimprinting lithography (NIL) is a promising technology to produce sub-50 nm half-pitch features on silicon- and/or quartz-based substrates. It is well-known as the next generation lithography. Especially, the UV-nanoimprint lithography technology has advantages of the simple process, low cost, high replication fidelity and relatively high throughput. In this paper, chip-size multi-head imprinting unit with compliance stage and overlay/alignment system with moiré and dual grating unit are proposed in order to fabricate sub-50 nm half-pitch patterns. These systems are set-up and performed in single-step nanoimprinting tool (ANT-4) which has several functional units for nanoimprinting process. Using the UV-NIL tool, 50 nm, 70 nm and 100 nm half-pitch dot and line patterns are obtained. Also, 20 nm overlay/alignment accuracy is obtained by means of the proposed method.     

Process control for 32 nm imprint masks using variable shape beam pattern generators

Step and Flash Imprint Lithography (S-FIL^®) is a unique method that has been designed from the beginning to enable precise overlay for creating multi-level devices. However, since the technology is 1X, it is critical to address the infrastructure associated with the fabrication of templates (imprint masks).For device manufacturing, one of the major technical challenges remains the fabrication of full-field 1X templates with commercially viable write times. Recent progress in the writing of sub-40 nm patterns using commercial variable shape e-beam tools and non-chemically amplified resists has demonstrated a very promising route to realizing these objectives, and in doing so, has considerably strengthened imprint lithography as a competitive manufacturing technology for the sub-32 nm node. Here we report the critical dimension (CD) uniformity and process latitude of dense 32 nm patterns from templates written with variable shape beam pattern generators. Uniformity on the template and in the imprinted field was 3.22 and 3.45 nm, 3σ. Process latitude during the writing of the template was improved by increasing both feature bias and exposure dose. As an example, the slopes for the 36 and 32 nm features are approximately 0.30 and 0.25 nm/μC/cm², respectively, indicating a substantial process window for exposure dose.     

Technique for transfer of high-density,high-aspect-ratio nanoscale patterns in UV nanoimprint lithography and measurement of the release force

Ultraviolet nanoimprint lithography (UV-NIL) is a powerful tool for nanoscale fabrication. However, the replication of high-density, high-aspect-ratio mold patterns by UV-NIL is very difficult because of the strong forces required to release the replicate from the mold. We used a glassy carbon (GC) mold with an antireflective structure, fabricated by irradiation with an oxygen-ion beam, to produce a high-density, high-aspect-ratio pattern, and we evaluated its release properties. The fabricated GC surface contained high-aspect-ratio conical structures with pitch of less than 100 nm. After fabrication of the antireflective structure, the mold surface was coated with chromium and a fluorinated silane coupling agent. By using this treatment and a peel motion during mold release, faithful replication of the mold structure in photocurable resin was possible. The release force increased with increasing mold surface area; the surface area effect is therefore the main factor in the mold-release step.     

3D structures for UV-NIL template fabrication with grayscale e-beam lithography

The individual steps in fabrication of templates for UV-NIL processes are described. After spin coating a conductive copolymer (ESPACER 300) on top of the resist, insulating substrates have been structured by use of electron beam lithography at 20 keV beam energy. A three-dimensional (3D) pattern has been created in a low contrast positive tone resist PMMA 35k. By RIE in a CHF₃ – O₂ – process, the pattern has been transferred into the quartz substrate. Finally, the 3D structures have been replicated in a UV-NIL process.     

Soft UV-NIL at 20 nm scale using flexible bi-layer stamp casted on HSQ master mold

In this paper we present a comparative study of two e-Beam Lithography (EBL) processes for Nanoimprinting Lithography (NIL) master mold, i.e. the standard PMMA based EBL Si patterning process and the HSQ process. 20 nm features with minimal sidewall roughness and high uniformity are demonstrated on large surface by using HSQ process. Moreover, to validate this ultra-high resolution HSQ EBL process and to check NIL resolution performances, soft UV-NIL replications were performed using soft hard-PDMS/PDMS bi-layer stamps casted on the HSQ master mold. We demonstrate the replication of sub-20 nm nanodots of high density (pitch 60 nm) with a good uniformity on the whole field area.     

Optimizing the fabrication process for high performance graphene field effect transistors

As an emerging material, graphene has attracted vast interest in solid-state physics, materials science, nanoelectronics and bioscience. Graphene has zero bandgap with its valence and conduction bands are cone-shaped and meet at the K points of the Brillouin zone. Due to its high intrinsic carrier mobility, large saturation velocity, and high on state current density, graphene is also considered as a promising candidate for high-frequency devices. To improve the reliability of graphene FETs, which include shifting the Dirac point voltage toward zero, increasing the channel mobility and decreasing the source/drain contact resistance, we optimized the device fabrication process. For CVD grown graphene, the film transfer and the device fabrication processes may produce interfacial states between graphene and the substrate and make graphene p or n-type, which shift the fermi level far away from the Dirac point. We have found that after graphene film transfer, an annealing process at 400 °C under N₂ ambient will shift Dirac point toward zero gate voltage. Ti/Au, Ni, and Ti/Pd/Au source/drain structures have been studied to minimize the contact resistance. According to the measured data, Ti/Pd/Au structure gives the lowest contact resistance (～500 ohm μm). By controlling the process of graphene growth, transfer and device fabrication, we have achieved graphene FETs with a field effective mobility of 16,000 cm²/V s after subtraction of contact resistance. The contact resistivity was estimated in the range of 1.1 × 10^?6 Ω cm² to 8.8 × 10^?6 Ω cm², which is close to state of the art III–V technology. The maximum transconductance was found to be 280 mS/mm at V_D = 0.5 V, which is the highest value among CVD graphene FETs published to date.     

All solution roll-to-roll processed polymer solar cells free from indium-tin-oxide and vacuum coating steps

A roll-to-roll process enabling fabrication of polymer solar cells comprising five layers on flexible substrates is presented. The device geometry is inverted and allow for fabrication on both transparent and non-transparent flexible substrates. The process is illustrated in this work by formation of a bottom electrode comprising silver nanoparticles on a 130 micron thick polyethyleneternaphthalate (PEN) substrate. Subsequently an electron transporting layer of zinc oxide nanoparticles was applied from solution followed by an active layer of P3HT-PCBM and a hole transporting layer of PEDOT:PSS. These first four layers were applied by slot-die coating. The final electrode was applied by screen printing a grid structure that allowed for transmission of 80% of the light. The materials were patterned into stripes allowing for formation of a single cell device and serially connected modules comprising 2, 3 and 8 stripes. All five layers in the device were processed from solution in air and no vacuum steps were employed. An additional advantage is that the use of indium-tin-oxide (ITO) is avoided in this process. The devices were tested under simulated sunlight (1000 W m^?2, AM1.5G) and gave a typical performance 0.3% in terms of power conversion efficiency (PCE) for the active layer. The low PCE was due to poor transmission of light through the back electrode.     

SnO2 gas sensor fabricated by low frequency alternating field electrophoretic deposition

SnO₂ thick film gas sensor has been prepared by applying low frequency (0.1 Hz) AC electric fields to a stable suspension of SnO₂ nanoparticles in acetylacetone. Parallel gold electrodes were used as the deposition substrate. Effect of CO, O₂ and H₂ gas exposure as well as ethanol vapor on conductivity of the SnO₂ film at 300 °C is investigated. Results show that the sensor is sensitive and its response is repeatable. This work shows that ACEPD can be used as an easy and cheap technique for fabrication of electronic devices such as ceramic-based gas sensors.     

Low temperature fabrication of a ZnO nanoparticle thin-film transistor suitable for flexible electronics

A bottom-gate/top-drain/source contact ZnO nanoparticle thin-film transistor was fabricated using a low temperature annealing process (150 °C) suitable for flexible electronics. Additionally, a high-k resin filled with TiO₂ nanoparticles was used as gate dielectric. After fabrication, the transistors presented almost no hysteresis in the I–V curve, a threshold voltage (V_T) of 2.2 V, a field-effect mobility on the order of 0.1 cm²/V s and an I_ON/I_OFF ratio of about 10⁴. However, the transistor is sensitive to aging effects due to interactions with the ambient air, resulting in current level reduction caused by trapped oxygen at the nanoparticle surface, and an anti-clockwise hysteresis in the transfer curve. It was demonstrated, conjointly, the possible desorption of oxygen by voltage stress and UV light exposure.     

Nanostructured nickel oxide ultrafine nanoparticles: Synthesis,characterization, and supercapacitive behavior

Well-dispersed NiO nanoparticles were prepared via cathodic electrodeposition followed by a heat-treatment method. The supercapacitive performance of the prepared nanoparticles was analyzed by means of cyclic voltammetry (CV) and galvanostatic charge–discharge tests at −0.2–0.5 V potential windows in 1 M KOH. The nanoparticles exhibited high specific capacitance (1623.1 F g⁻¹ at the scan rate of 5 mV s⁻¹) and good long-term cycling stability (9.6% capacity decay after 1000 cycling at the current density of 2 A g⁻¹).     

Integration of organic semiconductor lasers and single-mode passive waveguides into a PMMA substrate

Efficiently combining active and passive elements in integrated optics is a key ingredient for their successful employment. Here, we present the fabrication of an optimized PMMA substrate structure for improved coupling of laser light generated by organic semiconductor distributed feedback lasers into single-mode deep ultraviolet induced waveguides. For production, electron beam lithography on an oxidized silicon wafer and subsequent reactive ion etching is used to form the feedback grating of the laser. Afterwards, an aligned second electron beam lithography step on top of the grating allows the fabrication of a topographical step of 1.67 μm on the edges of the grating area. Metal is evaporated on this resulting master structure serving as a plating base for electroforming of a Ni tool. The tool is then used for hot embossing of the structure into PMMA bulk material. On a length of 500 μm the imprinted grating lines, having a period of 200 nm, are 100 nm wide and 60 nm high. Aligned deep ultraviolet exposure to induce a passive single- or multi-mode waveguide and co-evaporation of the active material Alq₃:DCM finish the coupling region. This structure optimizes the coupling of laser light generated in the laser structure into the passive waveguide. In combination with microfluidic channels, the laser light can be considered for sensing applications on a PMMA lab-on-chip system.     

Fabrication of hp 32 nm resist patterns using near-field lithography

Near-field lithography (NFL) has no fundamental limit such as the diffraction limit of light. However, in order to fabricate resist patterns with hp 32 nm, thorough optimization of various processes are indispensable. Previously, we reported on the use of fine and ultra-thin top-layer resist, and designs and fabrication of our special masks. In this paper, the effect of the total resist thickness on the near-field distribution is analyzed by the finite-difference time domain analyses and compared with our experiments. For the fabrication of hp 32 nm patterns, the total resist thickness as well as the tri-layer resist process are accordingly optimized. By the near-field exposure using an i-line mercury lamp and the dry-etching process for thin top-layer photo-resist, we have successfully fabricated the hp 32 nm resist pattern of 120 nm height.     

Filling behavior of UV nanoimprint resin observed by using a midair structure mold

The filling behavior of resin during UV nanoimprint lithography (UV-NIL) was observed by using a “midair structure mold” and by changing the imprint pressure. The midair structure molds were fabricated by electron beam lithography (EBL) using hydrogen silsesquioxane (HSQ) as a negative tone resist. After the fabrication of midair structure mold, two types of surface treatment molds, which were with or without release coating, were prepared. Using these molds, the filling behavior of a UV curable resin was investigated at various pressures. The results indicate that a pressure of approximately 1.2 MPa is necessary for complete filling in the case of molds treated with a release agent. This method demonstrates effect of a release coating for UV-NIL.     

Fabrication and application of temperature triggered MEMS switch for active cooling control in Solid State Lighting system

As the power of Solid State Lighting (SSL) system continuously rising and consequently high temperature occurred in the light source, active cooling solutions with controlling were widely used and smart controlling was indispensable for less energy consuming. In this work, a micro–electro-mechanical-system (MEMS) based, temperature triggered, switch was developed as a cost-effective solution for smart cooling control in SSL systems. The switch (1.0 × 0.4 mm²) was embedded in a silicon substrate and fabricated with a single-mask 3D micro-machining process. The device switched on at a designed temperature threshold with a contact resistance less than 2 ohm, and switched off when the temperature dropped below that limit. In this way, this device can enhance the automatic control of a cooling system without any need of additional electronic components and the used standard semiconductor manufacturing process gives highly possibility for integration and fabrication for future silicon based SSL systems.