Maskless Lithography Research Articles

P‐8.6: Elimination of Nanorods by Tetramethylammonium Hydroxide for the Fabrication of AlGaN‐based UV‐C Micro‐LED Array

Short‐wavelength ultraviolet (UV‐C) micro light‐emitting diode (Micro‐LED) array greatly benefits the optogenetic applications in neuroscience, optical communications, and maskless lithography. In this work, UV‐C Micro‐LED arrays with each pixel size of 10×10 μm2 were fabricated, and the nanorods introduced by inductively coupled plasma (ICP) etching were eliminated by post‐ICP tetramethylammonium hydroxide (TMAH) treatment. The pixel‐level electrical characteristics were analyzed, and the peak wavelength stability under variable injected current densities was demonstrated. The results indicated the potential of applying the TMAH treatment in the fabrication of the UV‐C Micro‐LED array.

Consistent pattern printing of the gap structure in femtosecond laser DMD projection lithography.

Maskless lithography technologies have been developed and played an important role in the fabrication of functional micronano devices for microelectronics, biochips and photonics. Optical projection lithography based on digital micromirror device (DMD) is an efficient maskless lithography technology that can rapidly fabricate complex structures. The precise modulation of gap width by DMD maskless optical projection lithography (MOPL) using femtosecond laser becomes important for achieving micronano structures. Herein, we have investigated the relationship between the structure morphology and the light intensity distribution at the image plane by multi-slit diffraction model and Abbe imaging principle, and optimized the gap width more accurately by modulating exposure energy. The aperture diameter of the objective lens has a substantial effect on the pattern consistency. The continuously adjustable structural gap widths of 2144 nm, 2158 nm and 1703 nm corresponding to 6, 12, 24 pixels are obtained by varying the exposure energy in the home-built MOPL system. However, the ideal gap structure cannot be obtained only by adjusting the exposure energy when the gap width is small, such as 1 or 2 pixels. Furthermore, we have proposed an alternative way to achieve fine gap structures through the structural decomposition design and precise control of exposure energy in different regions without changing the MOPL optical system. This study would provide a promising protocol for fabricating gap microstructures with controllable configuration using MOPL technique.

Making monolayer graphene photoluminescent by electron-beam-activated fluorination approach

• Electron-beam-activated fluorination method was used to open the bandgap of graphene. • Semiconducting C 4 F patterns were directly written on monolayer graphene. • C 4 F with a bandgap of 3.26 eV can emit sharp and strong photoluminescence at ∼380 nm. The past one and half decades have witnessed a tremendous development of graphene electronics, and the key to the success of graphene is its exceptional properties. The lacking of an inherent bandgap endows graphene with excellent electrical properties but considerably limits its applications in light-emitting and high-performance graphene-based devices. Herein, an approach for the direct writing of semiconducting and photoluminescent fluorinated graphene (C 4 F) patterns on monolayer graphene by an optimized electron-beam-activated fluorination technique is reported. A series of characterization approaches, such as atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy were used to demonstrate the successful preparation of C 4 F for maskless lithography. Specially, a sharp and strong photoluminescence located at the purple light range of ∼380 nm was observed in C 4 F, demonstrating a desirable semiconducting nature, and the bandgap was further confirmed by follow-up electrical measurements, where the C 4 F filed-effect transistor exhibited a p-type semiconductor behavior and significantly enhanced on/off ratio. Therefore, this work provides a novel technique for the fabrication of graphene devices for promising electronic and optoelectronic applications, but also opens a route towards the tailoring and engineering of electronic properties of graphene.

Evolution in Lithography Techniques: Microlithography to Nanolithography.

In this era, electronic devices such as mobile phones, computers, laptops, sensors, and many more have become a necessity in healthcare, for a pleasant lifestyle, and for carrying out tasks quickly and easily. Different types of temperature sensors, biosensors, photosensors, etc., have been developed to meet the necessities of people. All these devices have chips inside them fabricated using diodes, transistors, logic gates, and ICs. The patterning of the substrate which is used for the further development of these devices is done with the help of a technique known as lithography. In the present work, we have carried out a review on different types of lithographic techniques such as optical lithography, extreme ultraviolet lithography, electron beam lithography, X-ray lithography, and ion beam lithography. The evolution of these techniques with time and their application in device fabrication are discussed. The different exposure tools developed in the past decade to enhance the resolution of these devices are also discussed. Chemically amplified and non-chemically amplified resists with their bonding and thickness are discussed. Mask and maskless lithography techniques are discussed along with their merits and demerits. Device fabrication at micro and nano scale has been discussed. Advancements that can be made to improve the performance of these techniques are also suggested.

Atmospheric micro-sized cold plasma jet created by a long and ultra-flexible generator with sputtered gold thin film electrode

Atmospheric cold plasma jets with various configurations have drawn intense interests in diverse applications, such as surface modification and endoscopic applications. In this paper, a long and ultra-flexible micro-sized cold plasma jet generator is presented and its characteristics are analyzed. The generator mainly consists of two concentric silicone tubes with the inner one acting as the gas channel and the outer one acting as insulating layer of heat and high voltage. Gold thin film was sputtered on the circular surface of inner tube to work as the electrode as well as separation layer of ultraviolet radiation. Electrical, optical and thermal characteristics of this generator were investigated. Cold microplasma jet can be generated and ejected to the ambient air with the length varied from 0.1 m to 2.5 m, and it can impact on the finger without electric and heat sensation. Optical emission spectra analysis indicated that reactive species like OH and O atoms were generated in the plasma. This device exhibits ultra-flexible property which can be arbitrarily bent and plugged into complex and deep environment. Localized internal surface modification of polyvinyl chloride tube using this microplasma jet was also demonstrated and the result showed that surface wettability can be greatly improved after plasma treatment. This generator shows great potential for internal surface processing, plasma endoscopic and maskless lithography applications.

Assembly method of biological lens array based on maskless lithography

<p indent="0mm">In the field of micro and nano optics, transparent dielectric microspheres and living biological cells have attracted more and more attention due to their optical imaging capabilities. However, it is difficult to integrate them directly onto optical systems because of their size and bioactivity limitations. Although multi-physics field methods based on optical tweezers and acoustic tweezers can manipulate microspheres and cells for imaging, they tend to have specific requirements for imaging samples. Here, we proposed a method for the preparation of microsphere/cellular lens array modules based on maskless lithography. Natural sedimentation principle is utilized to form microlens arrays by assembling SiO₂ microspheres and MCF-7 cells on the hydrogel microporous module. The experimental and simulation results show that the SiO₂ microsphere array embedded in the hydrogel still maintains its super-resolution imaging capability, and the MCF-7 cells can achieve the image magnification. As a result of the arrayed imaging, a larger viewing field can be obtained than that of individual microspheres or cells. The modular imaging method proposed in this paper is expected to be applied in the field of biophotonic devices and <italic>in vivo</italic> optical imaging.

Microflow multi-layer diffraction optical element processed by hybrid manufacturing technology.

Traditional planar diffractive optical elements (DOEs) are challenged in imaging systems due to diffraction efficiency and chromatic dispersion. In this paper, we have designed a microfluidic diffractive optical element (MFDOE), which is processed by digital micromirror device (DMD) maskless lithography (DMDML) assisted femtosecond laser direct writing (FsLDW). MFDOE is a combination of photoresist-based multi-layer harmonic diffraction surface and liquid, realizing diffraction efficiency of more than 90% in the visible band. And it shows achromatic characteristics in the two bands of 469 nm (±20 nm) and 625 nm (±20 nm). These results show that MFDOE has good imaging performance.

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Method for improving the speed and pattern quality of a DMD maskless lithography system using a pulse exposure method.

Maskless lithography based on a digital micromirror device (DMD) has the advantages of high process flexibility and a low production cost. However, due to the trade-off relationship between the pixel size and exposure area, it is challenging to achieve high resolutions and high patterning speeds at the same time, which hinders the wider application of this technology in micro- and nano-fabrication processes. In addition, micromirrors in DMDs create pixelated edges that limit the pattern quality. In this paper, we propose a novel DMD maskless lithography method to improve the pattern quality during high-speed continuous patterning by means of pulse exposure and oblique scanning processes. A unique criterion, the pixel occupancy, was devised to determine the parameters related to the pulse exposure and oblique scanning optimally. We also studied how the duty cycle of the pulse exposure affects the pattern quality. As a result, we were able to increase the scanning speed up to the speed limit considering the damage threshold of the DMD and improve the pattern quality by resolving the pixelation problem. We anticipate that this method can be used in various microfabrication fields with short product life cycles or in those that require custom designs, such as the manufacturing of PCBs, MEMS devices, and micro-optics devices, among others.

P‐76: Elimination of Nanorods by Tetramethylammonium Hydroxide for the Fabrication of AlGaN‐based UV‐C Micro‐LED Array

Short‐wavelength ultraviolet (UV‐C) micro light‐emitting diode (Micro‐LED) array greatly benefits the optogenetic applications in neuroscience, optical communications, and maskless lithography. In this work, UV‐C Micro‐LED arrays with each pixel size of 10×10 μm2 were fabricated, and the nanorods introduced by inductively coupled plasma (ICP) etching were eliminated by post‐ICP tetramethylammonium hydroxide (TMAH) treatment. The pixel‐level electrical characteristics were analyzed, and the peak wavelength stability under variable injected current densities was demonstrated. The results indicated the potential of applying the TMAH treatment in the fabrication of the UV‐C Micro‐LED array.

Focused electron beam deposited silicon dioxide derivatives for nano-electronic applications

The material and electrical properties of silicon dioxide derived insulators formed with a focused electron beam in the presence of a TEOS or TMCTS precursor are presented. Raman and energy dispersive X-ray spectroscopy were used to analyse the chemical structure and composition of the deposited dielectric. It was found that the TEOS precursor induced a purer dielectric with a reduced carbon percentage ( ∼ 3 % ) which was independent of the electron beam energy. An investigation with TMCTS showed the importance of using an additional water vapour supply as an in-situ oxidising co-reactant, suppressing the deposited carbon content by up to a factor of six. Leakage current and voltage breakdown measurements were used to calculate the effective resistance and the dielectric strength of the insulator. The two precursors formed insulators with similar electrical properties with effective resistances on the order of G Ω for < 100 nm thick depositions and dielectric strengths of 7 MV cm −1 , equivalent to those found in sputtered silicon dioxides, but allowing high-resolution maskless lithography.

Triboelectric nanogenerator based on direct image lithography and surface fluorination for biomechanical energy harvesting and self-powered sterilization

Due to the high electric output, triboelectric nanogenerators (TENG) have gained extensive attention in recent years for their abilities to power the wearable and portable electronic devices. Surface charge density and effective contact area are pivotal for the electric output of the TENG. In this work, the maskless direct image lithography (DIL) method with high precision and rapid prototyping was used to fabricate the polyurethane (PU) layers with surface microcones within 3 min for increasing the contact electrification area. After chemically modified with trichloro (1 H,1 H,2 H,2 H-perfluorooctyl) silane (FOTS) vapor, the contact area further increases accompanying with the enlarged electron affinity difference because of the roughened morphology in micro-nanoscale and the introduced surface fluorine. The TENG based on PU and fluorinated polyurethane (F-PU) layer with microcones can achieve a high current of 22 μA, which is 5 times higher than that of the flat PU and F-PU layers. The microcones, surface roughened morphology and fluorine on the microcones have conjunct effects on the enhancement of electric output. Moreover, because of the customizability of DIL method and the prominent stability and favorable flexibility of PU and F-PU layers, the TENG can be fabricated into different shapes to harvest mechanical energy from various human motions. Furthermore, when the TENG was connected with the cuprous oxide (Cu2O) nanowire electrode and served as the electric supply, the antibacterial and antifungal properties of the nanowire show obvious enhancement. Thus, this work provides a rapid and effective way to enhance the output of TENG from perspectives of surface microstructure design without any templates.

Rapid photolithographic fabrication of high density optical interconnects using refractive index contrast polymers

We have developed new polymer optical interconnect materials that we term refractive index contrast (RIC) polymers that are ideally suited to a wide variety of photonic interconnect applications as the refractive index can be tuned over the range of n = 1.42 to 1.56, while index contrast Δn can be precisely tuned through composition and ultraviolet exposure; the waveguides can be directly patterned in dry films with no wet or dry etching processes required. RIC polymer interconnects thus have the ability to access numerous photonic platforms, including silicon photonic chips, ion-exchange (IOX) glass optical substrates, and optical fiber arrays. We demonstrate for the first time efficient single-mode polymer interconnect fabrication via a maskless lithography approach that exhibits low loss adiabatic coupling (∼1.5dB at 1550nm) to IOX waveguides through the formation of grayscale tapers.

Nanoscale flexible organic thin-film transistors.

Direct-write electron-beam lithography has been used to fabricate low-voltage p-channel and n-channel organic thin-film transistors with channel lengths as small as 200 nm and gate-to-contact overlaps as small as 100 nm on glass and on flexible transparent polymeric substrates. The p-channel transistors have on/off current ratios as large as 4 × 109 and subthreshold swings as small as 70 mV/decade, and the n-channel transistors have on/off ratios up to 108 and subthreshold swings as low as 80 mV/decade. These are the largest on/off current ratios reported to date for nanoscale organic transistors. Inverters based on two p-channel transistors with a channel length of 200 nm and gate-to-contact overlaps of 100 nm display characteristic switching-delay time constants between 80 and 40 ns at supply voltages between 1 and 2 V, corresponding to a supply voltage-normalized frequency of about 6 MHz/V. This is the highest voltage-normalized dynamic performance reported to date for organic transistors fabricated by maskless lithography.

Anti-Counterfeiting Tags Using Flexible Substrate with Gradient Micropatterning of Silver Nanowires.

Anti-counterfeiting technologies for small products are being developed. We present an anti-counterfeiting tag, a grayscale pattern of silver nanowires (AgNWs) on a flexible substrate. The anti-counterfeiting tag that is observable with a thermal imaging camera was fabricated using the characteristics of silver nanowires with high visible light transmittance and high infrared emissivity. AgNWs were patterned at microscale via a maskless lithography method using UV dicing tape with UV patterns. By attaching and detaching an AgNW coated glass slide and UV dicing tape irradiated with multiple levels of UV, we obtained AgNW patterns with four or more grayscales. Peel tests confirmed that the adhesive strength of the UV dicing tape varied according to the amount of UV irradiation, and electrical resistance and IR image intensity measurements confirmed that the pattern obtained using this tape has multi-level AgNW concentrations. When applied for anti-counterfeiting, the gradient-concentration AgNW micropattern could contain more information than a single-concentration micropattern. In addition, the gradient AgNW micropattern could be transferred to a flexible polymer substrate using a simple method and then attached to various surfaces for use as an anti-counterfeiting tag.

Research progress of maskless lithography based on digital micromirror devices

Research progress of maskless lithography based on digital micromirror devices

Ampoule‐Like Microvolume Containers with Transparent Code for Easy‐to‐Use and Space‐Saving Storage of Small‐Volume Biospecimens

AbstractThe importance of storing, transporting, and managing biospecimens for analysis and research has increased. Biospecimens, such as DNA and cells, have a volume of several micrometers or less for practical storage, management, and usage, and high space efficiency can be achieved if stored in an appropriate indexed container. However, although previous studies have highlighted the importance of small‐volume biospecimens, containers suitable for easily handling microscale samples and space‐saving storage are lacking. Here, easy‐to‐use and space‐saving biospecimen storage with ampoule‐like microvolume containers and transparent codes are introduced. The high‐durability epoxy‐based containers are suitable for storing and using microscale biospecimens, and protecting internal biospecimens from the external environment. To identify the biospecimens, microsized transparent QR codes on microparticles for indexing sample information and storage conditions are fabricated via optofluidic maskless lithography, enabling on‐demand fabrication. Both the microsized QR code and microvolume container are highly transparent, making the observation of even minimal volumes of internal material convenient. Similar to an ampoule, the microvolume container can be broken with a needle or blade to release the biospecimen. The storage efficiency of the container is verified by storing and releasing DNA, antibiotics, and cells. This container will save space for biospecimens in biobank systems.

Composite Structure of Ag Colloidal Particles and Au Sinusoidal Nanograting with Large-Scale Ultra-High Field Enhancement for SERS Detection

In this study, a novel composite Surface-Enhanced Raman Scattering (SERS) substrate is proposed for ultrasensitive detection. Consisting of gold sinusoidal nanograting and silver colloidal nanoparticles (AgNPs-AuSG), this type of SERS substrate is easy for fabrication by maskless laser interference lithography, and capable of providing large-scale ultra-high field enhancement, attributed to localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs). The enhancement factor (EF) of this composite substrate is as high as up to 10 orders of magnitude in the simulation experiment. Experimental results show that this large-area, productive SERS substrate of AgNPs-AuSG has realized sensitive TNT and RDX detection with the limit of detection (LOD) of 10−10 M, which may be a potential candidate for trace explosives detection.

Sidewall profiles in thick resist with direct image lithography

Maskless lithography is an increasingly popular method of micro-patterning in research settings. This technical note presents methods for controlling the feature size and sidewall profile of thick-resist features, when exposed using maskless direct imaging systems. Maskless lithographic systems use focussed, uncollimated light, and therefore do not naturally produce the vertical sidewalls that may be required for soft lithography and other secondary processes. We explore exposure dose energy, placement of the focal plane, and the use of multiple focal planes to optimize features in thick (∼800 μm) SU-8 resist. We find that placing the image plane at the mid-height of the resist film produces structures with a good compromise of sidewall angle and feature sharpness. We also find that using multiple exposures at multiple heights can produce sidewall angles that are stable over a range of dose energies.

Rapid and Label-Free Electrochemical Detection of Fumonisin-B1 Using Microfluidic Biosensing Platform Based on Ag-CeO2 Nanocomposite

Food contamination by mycotoxins is a major problem. Fumonisin-B1 (FU-B1) is one of the most abundantly found mycotoxins in products such as corn, rice, maize, and wheat, causing some of the most contagious diseases, such as pulmonary edema, hydrothorax, and immunosuppression, and is possibly carcinogenic. Its rapid and early detection in food products is therefore vital. We have fabricated an electrochemical microfluidic biosensing platform to detect FU-B1 with silver-ceria nanocomposite using maskless lithography. Structural characterizations confirmed nanocubes formation (CeO2) and spherical structures (Ag) with no impurities. The resulting nanobiochip showed an excellent linear response to antigen-FU-B1. linear detection was obtained from 10 pg ml−1−100 ng ml−1 with high sensitivity as 7.33 μA (log (ng. ml−1))−1cm−2. Limit of detection and limit of quantification were obtained as 1.5 pg. ml−1, and 3.9 pg. ml−1, respectively. Reynold’s number was found to be 0.79, showing the fluid’s laminar flow inside the channel. Interference studies showed specificity toward FU-B1 detection. Applicability in real food samples was assessed using spiked corn samples and showed recovery of up to 85% with excellent linear response. These results indicate that an electrochemical microfluidic nanobiochip can be used for rapid, label-free, and highly sensitive detection of antigen FU-B1.