Maskless Process Research Articles

Highly improved light extraction with a reduced spectrum distortion of organic light-emitting diodes composed by the sub-visible wavelength nano-scale periodic (∼250 nm) structure and micro-lens array

Out-coupling enhanced organic light-emitting diodes (OLEDs) with micro-lens arrays and a nano-scale periodic light-extraction structure—a photonic crystal (PC)—utilizing laser interference lithography (LIL) are demonstrated. Generally, PC-based OLEDs suffer from a distorted and shifted spectrum, despite a highly improved intensity. However, in this study, we demonstrate PC-based OLEDs with a distortion-free spectrum and a highly improved out-coupling performance. It was found that spectrum distortion decreased with the pitch size of the PC. The PC-based OLED with a 250nm pitch size showed a dramatically reduced spectral shift: International Commission on Illumination 1931 color coordinate of (Δ0.00, Δ0.00) and Δpeak wavelength of 0nm as compared with the reference. Simultaneously, the external quantum efficiency and the power efficiency were enhanced by up to 178% and 264%, respectively, as compared with the reference. Moreover, through the LIL, simple and maskless processes were achieved for a light-extraction structure over a large area.

Control of geometry in Si-based photonic nanostructures formed by maskless wet etching process and its impact on optical properties

We demonstrate that maskless wet etching of self-assembled Ge quantum dot (QD) multilayers can create large-area photonic nanostructures, and the geometry can be tuned by changing wet etching conditions. It is found that the reflectance in the near-infrared wavelength can be decreased by controlling geometry, and an increase in the depth of the photonic nanostructures results in enhancement of photoluminescence intensity from Ge QDs. These results show that control of geometry in photonic nanostructures is useful for enhancement of optical absorption in the Ge QD multilayers.

Fabrication of an ultra-thin silicon solar cell and nano-scale honeycomb structure by thermal-stress-induced pattern transfer method

A 3μm thick silicon layers with nano-scale honeycomb structure on the surface were fabricated using the mask-less process, “Thermal-stress Induced Pattern Transfer method”. The thin silicon layer was deposited on a patterned sapphire substrate with nano-scale pyramids, followed by a metal layer printing on the top of the thin silicon layer. After thermal treatment, a thin silicon layer was peeled off from the patterned sapphire substrate and was transferred to the metal layer. Meanwhile, the periodic patterns on the sapphire substrate were transferred to the thin silicon layer forming the honeycomb structure on the surface of the silicon layer. The whole process was operated at a low temperature below 250°C without any mask process. Finally, the solar cell was fabricated on the silicon thin layer and its performance was measured. The short circuit current density is 0.11mA/cm2.

Improving the Electrical Contact Property of Single-Walled Carbon Nanotube Arrays by Electrodeposition

Abstract A parallel method for the fabrication of metal contacts on single-walled carbon nanotube (SWNT) arrays was presented and the electrical contact property was evaluated by a SWNT-field effect transistor structure. Copper and gold contacts were fabricated on both semiconducting SWNTs and metallic SWNTs by using a maskless electrodeposition process. The SWNT array remained a p-type semiconductor after the electrodeposition. The contact resistance between SWNT array and microelectrodes was reduced more than 50% by the established copper contacts. The source-drain current of the carbon nanotube field-effect transistor (CNT-FET) structure can be further increased from 7.9 μA to 9.2 μA when the copper contacts were replaced by gold ones, which is probably due to the better contact property to SWNT of gold contacts with fine grain size.

Improving the Electrical Contact Property of Single-Walled Carbon Nanotube Arrays by Electrodeposition

A parallel method for the fabrication of metal contacts on single-walled carbon nanotube (SWNT) arrays was presented and the electrical contact property was evaluated by a SWNT-field effect transistor structure. Copper and gold contacts were fabricated on both semiconducting SWNTs and metallic SWNTs by using a maskless electrodeposition process. The SWNT array remained a p-type semiconductor after the electrodeposition. The contact resistance between SWNT array and microelectrodes was reduced more than 50% by the established copper contacts. The source-drain current of the carbon nanotube field-effect transistor (CNT-FET) structure can be further increased from 7.9 μA to 9.2 μA when the copper contacts were replaced by gold ones, which is probably due to the better contact property to SWNT of gold contacts with fine grain size.

Nano-patterned dual-layer ITO electrode of high brightness blue light emitting diodes using maskless wet etching

We propose a dual-layer transparent Indium Tin Oxide (ITO) top electrode scheme and demonstrate the enhancement of the optical output power of GaN-based light emitting diodes (LEDs). The proposed dual-layer structure is composed of a layer with randomly distributed sphere-like nano-patterns obtained solely by a maskless wet etching process and a pre-annealed bottom layer to maintain current spreading of the electrode. It was observed that the surface morphologies and optoelectronic properties are dependent on etching duration. This electrode significantly improves the optical output power of GaN-based LEDs with an enhancement factor of 2.18 at 100 mA without degradation in electrical property when compared to a reference LED.

Formation of SiO2 surface textures via CHF3/Ar plasma etching process of poly methyl methacrylate self-formed masks

This work presents a simplified technique for nanotexturing SiO2 surfaces. Nanotextures were obtained by a mask-less dry-etching process of a spin-coated polymethylmethacrylate (PMMA) on a SiO2 surface. Dot-like nanostructures containing small Al particles were initially formed through reactive ion etching (RIE) using CHF3/Ar etchants for an etching duration of 60 s. The etching duration was increased to 2 min to obtain high-density ring-shaped nanomasks with an outer diameter of 80 nm and a wall thickness of 20 nm. The SiO2 surface was textured with ring-shaped nanomasks after 6 min of RIE. The optical reflectance of the nanotextured SiO2 surface after 6 min of etching was around 15% within the spectral interval of 400–1000 nm, which is suitable for optical devices such as solar cells.

Non-enzymatic glucose sensing on long and short diamond nanowire electrodes

In this paper the fabrication of micrometer long boron-doped diamond nanowire (L-BDD NWs) electrodes is reported. The diamond nanowires were obtained by a maskless reactive ion etching process with oxygen plasma using 15μm thick polycrystalline boron-doped diamond (BDD) films as starting material. The resulting nanowire interfaces showed enhanced electrochemical activity towards the direct electrochemical detection of glucose under strong basic (pH12) condition when compared to flat BDD and short nanowires (S-BDD NWs). The robust response of these nanostructures with a detection limit of 60μM and a linear range up to 8mM and the ease of formation make L-BDD NWs a promising platform for real time applications.

Mesmoproc – implementation of a maskless electrochemical surface modification process

Conventional approaches to the fabrication of fine features in the printed circuit board and metal finishing industries typically employ a multistage photolithography stage to process each individual substrate, which is both inefficient and wasteful of valuable materials. By developing and implementing a maskless electrochemical process that decreases the use of lithography, the Mesmoproc project aims to assist European industry in these sectors.

Mesmoproc – implementation of a maskless electrochemical surface modification process

Conventional approaches to the fabrication of fine features in the printed circuit board and metal finishing industries typically employ a multistage photolithography stage to process each individual substrate, which is both inefficient and wasteful of valuable materials. By developing and implementing a maskless electrochemical process that decreases the use of lithography, the Mesmoproc project aims to assist European industry in these sectors.

Ultra-violet laser processing of graphene on SiO2/Si

A graphene transparent electrode might be used in industry in the near future instead of indium tin oxide (ITO). For patterning of ITO, the maskless laser process was reported as a simple and fast process. In this paper, effects of ultra-violet laser irradiation to graphene on SiO2/Si are investigated. The experimental results show that the threshold thickness of graphene for complete removal from the SiO2/Si substrate by laser irradiation is approximately 10nm. Thinner graphene layers than the threshold thickness were removed by laser irradiation with a power density of larger than approximately 3.5MW/cm^2. The mechanism for the observed complete removal of graphene should be ejection due to the supersonic elastic vibration of the substrate caused by pulsed laser irradiation.

Generic Methods for Micrometer- And Nanometer-Scale Surface Derivatization Based on Photochemical Coupling of Primary Amines to Monolayers of Aryl Azides on Gold and Aluminum Oxide Surfaces

A series of aryl azide terminated thiols and phosphonic acids has been synthesized, and used to prepare self-assembled monolayers on (respectively) gold and aluminum oxide surfaces. The rates of photoactivation were determined using contact angle measurement and X-ray photoelectron spectroscopy (XPS). The behavior of a diazirine functionalized aryl thiol was also studied. The rates of activation were found to be similar for all five adsorbates. However, the extent of photochemical coupling of a primary amine was significantly greater for the aryl azides than for the diazirine. A range of primary amines was successfully coupled to all of the azides with high yield. Little difference in reactivity was observed following perfluorination of the aromatic ring. Micrometer-scale patterns were fabricated by carrying out exposures of the aryl azide terminated SAMs through a mask submerged under a film of primary amine. Contrasting amines could be introduced to unreacted regions in a subsequent maskless step. A scanning near-field optical microscope was used to fabricate nanopatterns. Exposure of the azides to irradiation at 325 nm in air enabled selective deactivation of azides. The surrounding surface was functionalized with a primary amine in a maskless process; when a protein-resistant oligo(ethylene glycol) functionalized amine was used it was possible to produce protein nanopatterns, by adsorbing protein to features defined using near-field exposure.

Formation of a Honeycomb Texture for Silicon-Based Solar Cells Using a Mask-Less Process

The honeycomb structure could reduce the reflection of a crystalline silicon solar cell, which usually generated by mask process and etching process. In this Letter, a 3 μm silicon thin film with the honeycomb surface was successfully fabricated by mask-less process. The silicon thin films were deposited on the honeycomb pattern sapphire substrate (PSS) and the metal paste was printed on the silicon thin films. After thermal annealing treatment, the silicon layer together with the metal paste will be peeled off from the sapphire substrate because of the large differences of thermal expansion coefficient between the silicon-metal layer and a sapphire substrate. The honeycomb structure can be obtained easily by transferring the patterns from the well-designed PSSs to the obtained silicon layer.

Self-biased Dual-phase Energy Harvesting System

ABSTRACTIn this study, we report the design and fabrication of a dual-phase energy harvester which can synchronously harvest both mechanical and magnetic energy in the absence of DC magnetic field. The harvester consists of a magnetostrictive cantilever beam and a magnetostrictive/ piezoelectric (M/P) self-biased laminate composite structure. This structure allows us to utilize piezoelectric and self-biased magnetoelectric effect simultaneously. By combining these mechanisms together, a sum effect for harvesting both magnetic and vibration energy was realized under DC magnetic field free condition. The bilayer structure provides a simplified geometry that can be easily incorporated into MEMS devices. We demonstrate a hybrid synthesis method for fabrication of complex three-dimensional thin films using a cost-effective and mask-less aerosol jet deposition process. The combination of the hybrid aerosol jet process with dual phase harvester design provides the opportunity to fabricate small scale power sources required for structural health monitoring applications.

Thermally Activated Bumping Process using Sn3.0Ag0.5Cu Solder Powder for Low-Cost Interposers

A novel bumping process using solder bump maker (SBM) is developed for fine-pitch flip chip bonding. It features maskless screen printing process with the result that a fine-pitch, low-cost, and lead-free solder-on-pad (SoP) technology can be easily implemented. The process includes two main steps: one is the thermally activated aggregation of solder powder on the metal pads on a substrate and the other is the reflow of the deposited powder on the pads. Only a small quantity of solder powder adjacent to the pads can join the first step, so a quite uniform SoP array on the substrate can be easily obtained regardless of the pad configurations. Through this process, an SoP array on an organic substrate with a pitch of 130 μm is, successfully, formed.

A Review On Variable MEMS Mirrors For Photo-Lithographic Masks

This paper presents a review on using MEMS based mirror arrays to achieve maskless lithography in order to eliminate mask costs in the micro fabrication processes. With the advanced technology nodes, it becomes more and more costly to produce the lithography masks. Especially with the extreme ultraviolet lithography technique, the necessity to use maskless lithography becomes more obvious. Several universities and companies fabricated tilting mirror style or piston style mirror arrays to propose a solution to maskless lithography processes.

Sub-Micron Lithography Using InGaN Micro-LEDs: Mask-Free Fabrication of LED Arrays

The fabrication of gallium-nitride (GaN)-based light-emitting diode (LED) arrays by a direct writing technique, itself using micron-sized LEDs (micro-LEDs), is reported. CMOS-driven ultraviolet GaN-based micro-LED arrays are used to pattern photoresist layers with feature sizes as small as 500 nm. Checkerboard-type square LED array devices are then fabricated using such photoresist patterns based on either single pixel or multipixel direct writing, and implemented as part of a completely mask-less process flow. These exemplar arrays are composed of either 450-nm-emitting 199 $\,\times\,$ 199 $\mu{\rm m}^{2}$ pixels on a 200- $\mu{\rm m}$ pitch or 520-nm-emitting 21 $\,\times\,$ 18 $\mu{\rm m}^{2}$ pixels on a 23- $\mu{\rm m}$ pitch. Fill factors of 99% and 71.5% are achieved with optical output power densities per pixel of 5 and 20 ${\rm W}/{\rm cm}^{2}$ at 90- and 6-mA dc-injected currents, respectively.

Guided Assembly of Gold Colloidal Nanoparticles on Silicon Substrates Prepatterned by Charged Particle Beams

Colloidal gold nanoparticles represent technological building blocks which are easy to fabricate while keeping full control of their shape and dimensions. Here, we report on a simple two-step maskless process to assemble gold nanoparticles from a water colloidal solution at specific sites of a silicon surface. First, the silicon substrate covered by native oxide is exposed to a charged particle beam (ions or electrons) and then immersed in a HF-modified solution of colloidal nanoparticles. The irradiation of the native oxide layer by a low-fluence charged particle beam causes changes in the type of surface-terminating groups, while the large fluences induce even more profound modification of surface composition. Hence, by a proper selection of the initial substrate termination, solution pH, and beam fluence, either positive or negative deposition of the colloidal nanoparticles can be achieved.

Closed-loop control of laser assisted chemical vapor deposition growth of carbon nanotubes

Laser-assisted chemical vapor deposition growth is an attractive mask-less process for growing locally aligned nanotubes in selected places on temperature sensitive substrates. An essential parameter for a successful and reproducible synthesis of nanotubes is the temperature during growth. Here, we demonstrate a temperature feedback control mechanism based on the dynamic, in situ monitoring of the infrared radiation coupled with reflectivity information. With the information provided by these sensors, an infrared laser, focused on a silicon substrate covered with aluminum-oxide and iron catalyst layers, can be controlled. The growth takes place in a gaseous mixture of argon (carrier gas), hydrogen (process gas), and ethylene (carbon-containing gas). Scanning electron microscopy and Raman spectroscopy analysis demonstrate the excellent reproducibility of the closed-loop control process over multiple experiments. Furthermore, we developed a unique method to identify the onset for catalyst formation and activation by monitoring the fluctuation of the reflected laser beam.

Miniature Fabry-Perot pressure sensor created by using UV-molding process with an optical fiber based mold

We present a miniature Fabry-Perot pressure sensor fabricated at the tip of an optical fiber with a pre-written Bragg grating by using UV-molding polymer process. The mold is constructed by integrating an optical fiber of 80 μm diameter with a zirconia ferrule. The optical fiber based mold makes it possible to use optical aligning method to monitor the coupled intensity between the mold-side and replica-side fibers, rendering a maskless alignment process with a submicrometer accuracy. A polymer-metal composite thin diaphragm is employed as the pressure transducer. The overall sensor size is around 200 μm in diameter. Experimental study shows that the sensor exhibits a good linearity over a pressure range of 1.9-7.9 psi, with a sensitivity of 0.0106 μm/psi. The fiber Bragg grating is exploited for simultaneous temperature measurements or compensation for temperature effects in pressure readings. The sensor is expected to benefit many fronts that require miniature and inexpensive sensors for reliable pressure measurement, especially biomedical applications.