Conventional Photolithography Research Articles

Single-Step Dual-Layer Photolithography for Tunable and Scalable Nanopatterning.

Conventional photolithography, due to its scalability, robustness, and straightforward processes, has been widely applied to micro- and nanostructure manufacturing in electronics, optics, and biology. However, optical diffraction limits the ultimate resolution of conventional photolithography, which hinders its potential in nanoscale patterning for broader applications. Here, we introduce a derivative of conventional photolithography for nanoscale patterning called dual-layer photolithography (DLPL), which is based on the controlled exposure and development of overlapping positive and negative photoresists. In a typical experiment, substrates are sequentially coated by two layers of photoresists (both positive and negative). Then, we purposefully control the exposure time to generate slightly larger features in the positive photoresist than those in the negative photoresist. After development, their overlapping areas become the final features, which outline the original features. We demonstrate line widths down to 300 nm here, which can be readily improved with more precise control. By adjusting the lithography parameters and material deposition, the feature sizes, shapes (e.g., rings, numbers, letters), line widths (300-900 nm), and materials (e.g., SiO2, Cr, and Ag) of these features can be independently controlled. Combined with anisotropic etching, more complex three-dimensional nanostructures can be fabricated as well, as we demonstrate here with Si. We further fabricate photodetectors as an example application to show that these nanostructures fabricated by DLPL can be used to promote light-trapping MAPbI3 perovskite films to achieve good photoelectric properties. This strategy is not limited to ultraviolet photolithography and may also be incorporated into other energetic beam-based lithographic approaches, including deep and extreme ultraviolet photolithographies and electron beam lithography, to enhance their resolution.

Fabrication and Characterization of Nanonet-Channel LTPS TFTs Using a Nanosphere-Assisted Patterning Technique.

We present the fabrication and electrical characteristics of nanonet-channel (NET) low-temperature polysilicon channel (LTPS) thin-film transistors (TFTs) using a nanosphere-assisted patterning (NAP) technique. The NAP technique is introduced to form a nanonet-channel instead of the electron beam lithography (EBL) or conventional photolithography method. The size and space of the holes in the nanonet structure are well controlled by oxygen plasma treatment and a metal lift-off process. The nanonet-channel TFTs show improved electrical characteristics in terms of the ION/IOFF, threshold voltage, and subthreshold swing compared with conventional planar devices. The nanonet-channel devices also show a high immunity to hot-carrier injection and a lower variation of electrical characteristics. The standard deviation of VTH (σVTH) is reduced by 33% for a nanonet-channel device with a gate length of 3 μm, which is mainly attributed to the reduction of the grain boundary traps and enhanced gate controllability. These results suggest that the cost-effective NAP technique is promising for manufacturing high-performance nanonet-channel LTPS TFTs with lower electrical variations.

Research on piezo-phototronic effect in ZnO/AZO heterojunction flexible ultraviolet photodetectors

A novel Al-doped (3 wt%) ZnO (AZO) UV photodetector (PD) and ZnO/AZO heterojunction double-layer UV PD were prepared on a polyethylene terephthalate (PET) substrate by utilizing the radio frequency (RF) sputtering technology and conventional photolithography. Because the ZnO/AZO heterojunction possesses the ability to improve the separation of the photogenerated electron-hole pairs, the responsivity of the ZnO/AZO PD is higher than that of the pure AZO PD under the same bias voltage. Moreover, the responsivity of the obtained ZnO/AZO PD showed a 1.13 fold increase from 5.91 to 6.70 A/W when the tensile variable ɛ was 0.16. These findings also provide a new alternative for the preparation of flexible UV PDs with piezo-phototronic effect, which is low-cost and offers environmental sustainability.

Skin-Compatible Amorphous Oxide Thin-Film-Transistors with a Stress-Released Elastic Architecture

A highly reliable reverse-trapezoid-structured polydimethylsiloxane (PDMS) is demonstrated to achieve mechanically enhanced amorphous indium-gallium-zinc oxide (a-IGZO) thin-film-transistors (TFTs) for skin-compatible electronics. Finite element analysis (FEA) simulation reveals that the stress within a-IGZO TFTs can be efficiently reduced compared to conventional substrates. Based on the results, a conventional photolithography process was employed to implement the reverse-trapezoid homogeneous structures using a negative photoresist (NPR). Simply accessible photolithography using NPR enabled high-resolution patterning and thus large-area scalable device architectures could be obtained. The a-IGZO TFTs on the reverse-trapezoid-structured PDMS exhibited a maximum saturation mobility of 6.06 cm2V−1s−1 under a drain bias voltage of 10 V with minimal strain stress. As a result, the proposed a-IGZO TFTs, including stress-released architecture, exhibited highly enhanced mechanical properties, showing saturation mobility variation within 12% under a strain of 15%, whereas conventional planar a-IGZO TFTs on PDMS showed mobility variation over 10% even under a 1% strain and failed to operate beyond a 2% strain.

Sensitivity of Surface Acoustic Wave Sensors Based LiNbO3 128° Y-X and at-Quartz to PM10 and PM2.5

IntroductionParticulate matter (PM) was estimated to cause around 7 million premature deaths worldwide per year according to World Health organization [1]. These particles can cause diseases leading to premature death [2]. Over the last decade, the monitoring of PM became an important issue on a worldwide scale. The miniaturization of the existing bulky systems has also become necessary to reduce their cost. To address this need, a new miniaturized system for PM monitoring was previously developed in our team [3]. It takes advantage of both a 3 Lpm cascade impactor and surface acoustic waves (SAW) sensors to respectively separate and measure particles. The present study aims to compare the sensitivity of two SAW devices. The first exploits Love waves on an AT cut Quartz substrate and the second is based on Rayleigh waves from a LiNbO3 Y-X 128° substrates. The latter presents a high electromechanical coupling factor that could be exploited for the self-cleaning of the device after the measurement. This could allow overcoming the fouling issue faced with impactors that wouldn’t be solved with quartz based sensors which suffer from an insufficient electromechanical coupling. Method In this study we used a dedicated 3 Lpm cascade impactor equipped with SAW delay lines as collecting plate. The Rayleigh wave sensor and the Love wave sensor were designed and fabricated respectively on LiNbO3 Y-X 128° cut and AT-Quartz cut substrates using a conventional photolithography process. The interdigital transducers (IDT) consist of double finger pairs made of 200 nm thick aluminum with a periodicity p=10 µm and a wavelength λ=40 µm. Hence, the working frequency is 125 MHz for the Love mode and 98 MHz for the Rayleigh mode. The propagation of Love wave needs a guiding layer. For that purpose, a silica layer was deposited using sputtering technique with shear velocity lower than the piezoelectric substrates. The region between the two IDTs constitutes the sensing area.Preliminary tests have been performed using candle smoke. As the obtained PM concentrations were unstable and difficult to reproduce, we have developed an experimental set-up bench consisting of a 1m3 chamber, a particle’s generator AGK 2000 and an optical system FIDAS® 100. Thus, sodium chloride (NaCl) was used to produce PM2.5 while PM10 were generated from silicon carbide (SiC) in the 0 to 200 μg/m3 concentration range. When the particles impact on the sensor surface, the velocity of the acoustic waves decreases due to the sensors’ high gravimetric sensitivity. Accordingly, the wave phase velocity shift is measured by monitoring the phase at constant frequency with an open loop interrogation [4]. It’s then correlated to the particles concentration. Results and Conclusions Figure 1 and 2 shows plots of phase derivative dϕ/dt of sensors based AT-Quartz (black) and LiNbO3 (red) with the concentration of PM10 and PM2.5 respectively measured with the optical system FIDAS®. As expected, the sensitivity of the Rayleigh wave sensor based on LiNbO3 is lower than the Love wave sensor based on quartz for both PM10 and PM2.5. The sensor’s sensitivity is estimated by applying a linear fit of the plotted data. The sensitivity of sensors based on quartz is 3.10-4 °/s.μg/m3 for PM 2.5 and 5.10-5 °/s.μg/m3 for PM10. For sensors based on LiNbO3, the sensitivity is 1.10-4 °/s.μg/m3 for PM2.5 and 1.10-5 °/s.μg/m3 for PM10. The feature that the sensors’ response is greater with PM2.5 than with PM10 can be explained by the fact that most adhesion forces are linearly dependent on particle diameter [5] which is often described as the rebound effect. As a result, the smaller particles settle more on the surface of the sensor resulting in a more significant slowdown of the wave. To ensure that each stage is measuring the targeted size range, we took images of the sensors surface at the end of the experiment using a microscope. Figures 3, 4 show the surface of the PM2.5 stage and figures 5, 6 the one of the PM10 stage. One can observe that, as expected, the PM2.5 contain more particles than the PM10 and that the particle sizes correspond well to the ranges [0.3 μm, 2.5 μm] and [2.5 μm, 10 μm]. It has therefore been shown that LiNbO3 sensors, although less sensitive, can also be used for fine particles detection. They still need work to improve their performance and limit the rebound effect, but they remain very promising for the development of self-cleaning systems.

Design of line seeds for glancing angle deposition

This paper presents an enhanced seeding rule for the design and fabrication of line seeds for glancing angle deposition (GLAD). GLAD is capable of creating nanometer-level three-dimensional (3D) features by ballistic shadowing from natural/artificial nuclei at oblique incident angles in physical vapor deposition processes. The GLAD features, including columns, springs, zigzags, and ribbons, are building blocks of a wide range of optical, mechanical, and sensing applications. Nanoribbons can be obtained from sub-100 nm-wide line seeds from GLAD; however, volume production of the ultralong fine lines is difficult by conventional fabrication techniques. Additionally, a general process for designing line seeds for creating nanoribbons, especially line seeds with two-dimensional cross sections, is lacking. This paper fills the gaps by integrating the design, fabrication, and optimization of line seeds for obtaining nanoribbons by GLAD. In this paper, a new seeding theory for line seeds for GLAD is proposed by first introducing an empirical model for accurately determining the percent coverage of the deposition for an incident angle over 70°. We discuss the optimum shape and size of the lines for obtaining continuous solid ribbons by matching the percent coverage under predetermined incident angles in a GLAD process. The thickness of the GLAD ribbons is controllable by the geometric parameters of the seeds; ∼100 nm-thick ribbons are obtained from micrometer-width lines created using conventional photolithography. The design process of parabolic cross-sectional line seeds is demonstrated as an example of applying the upgraded seeding rule. Finally, the fabrication of centimeter-long nanoribbons and the use of the ribbons as templates for nanochannels are demonstrated.

Development of a flexible dielectric-barrier-discharge plasma actuator fabricated by inkjet printing using silver nanoparticles-based ink

We demonstrate that a flexible dielectric-barrier-discharge (DBD) plasma actuator fabricated by an inkjet printing process using metallic inks generates stable surface discharge and ionic wind for active airflow control. The establishment of a practical fabrication method for DBD plasma actuators is a critical issue to be tackled for industrial applications. The inkjet process requires just the printing of the metallic inks and sintering processes while the conventional photolithography technology requires a lot of processes for the fabrication of the DBD plasma actuators. The electrical and mechanical characteristics of a multi-stage DBD plasma actuator fabricated by this printed electronics technology are investigated and are compared with the DBD plasma actuator made by the conventional method using copper tape. The DBD plasma actuator developed in this study induces a similar or even stronger ionic wind than that of the conventional one. Also, a thin exposed electrode (≃1 μm), which is preferable in terms of airflow control applications, is achieved by the inkjet printing process. The development of the fabrication method using printed electronics expands the application field of the DBD plasma actuator, including complex curved surfaces and full-scale size applications.

Interconnect Fabrication by Electroless Plating on 3D-Printed Electroplated Patterns.

The metallic interconnects are essential components of energy devices such as fuel cells and electrolysis cells, batteries, as well as electronics and optoelectronic devices. In recent years, 3D printing processes have offered complementary routes to the conventional photolithography- and vacuum-based processes for interconnect fabrication. Among these methods, the confined electrodeposition (CED) process has enabled a great control over the microstructure of the printed metal, direct printing of high electrical conductivity (close to the bulk values) metals on flexible substrates without a need to sintering, printing alloys with controlled composition, printing functional metals for various applications including magnetic applications, and for in situ scanning electron microscope (SEM) nanomechanical experiments. However, the metal deposition rate (or the overall printing speed) of this process is reasonably slow because of the chemical nature of the process. Here, we propose using the CED process to print a single layer of a metallic trace as the seed layer for the subsequent selected-area electroless plating. By controlling the activation sites through printing by the CED process, we control, where the metal grows by electroless plating, and demonstrate the fabrication of complex thin-film patterns. Our results show that this combined process improves the processing time by more than 2 orders of magnitude compared to the layer-by-layer printing process by CED. Additionally, we obtained Cu and Ni films with an electrical resistivity as low as ∼1.3 and ∼2 times of the bulk Cu and Ni, respectively, without any thermal annealing. Furthermore, our quantitative experiments show that the obtained films exhibit mechanical properties close to the bulk metals with an excellent adhesion to the substrate. We demonstrate potential applications for radio frequency identification (RFID) tags, for complex printed circuit board patterns, and resistive sensors in a Petri dish for potential biological applications.

Numerical Simulation and Experimental Verification of Droplet Generation in Microfluidic Digital PCR Chip.

The generation of droplets is one of the most critical steps in the droplet digital polymerase chain reaction (ddPCR) procedure. In this study, the mechanism of droplet formation in microchannel structure and factors affecting droplet formation were studied. The physical field of laminar two-phase flow level was used to simulate the process of droplet generation through microfluidic technology. The effect of the parameters including flow rate, surface tension, and viscosity on the generated droplet size were evaluated by the simulation. After that, the microfluidic chip that has the same dimension as the simulation was then, fabricated and evaluated. The chip was made by conventional SU-8 photolithography and injection molding. The accuracy of the simulation was validated by comparing the generated droplets in the real scenario with the simulation result. The relative error (RE) between experimentally measured droplet diameter and simulation results under different flow rate, viscosity, surface tension and contact angle was found less than 3.5%, 1.8%, 1.4%, and 1.2%, respectively. Besides, the coefficient of variation (CV) of the droplet diameter was less than 1%, which indicates the experimental droplet generation was of high stability and reliability. This study provides not only fundamental information for the design and experiment of droplet generation by microfluidic technology but also a reliable and efficient investigation method in the ddPCR field.

Spatially-resolved insulator-metal transition for rewritable optical gratings

Optical relief gratings are usually composed of physical grooves with a constant periodicity, and typically suffer from light scattering, are mechanically fragile and are single function. Here, we develop WO3-based gratings by using a recently reported electron-proton synergistic doping route under ambient conditions. This doping strategy is compatible with conventional ultraviolet photolithography, and we show that it induces a selective insulator-metal phase transition and coloration in WO3, with spatial-resolution up to micron-scale. Due to the electrochromic-induced-contrast, a WO3 volume phase grating without grooves and a WO3 relief grating with tunable periodicity are demonstrated. Both gratings can be rewritten after a reset procedure by annealing in air. Our experiments demonstrate WO3–based gratings and an attractive technique for rewritable oxides.

Tunable characteristic of phase-locked quantum cascade laser arrays* *Project supported by the National Basic Research Program of China (Grant Nos. 2018YFA0209103 and 2018YFB2200504), the National Natural Science Foundation of China (Grant Nos. 61991430, 61774146, 61790583, 61674144, 61774150, and 61805168), the Beijing Municipal Science & Technology Commission, China (Grant No. Z201100004020006), and the Key Projects of the Chinese Academy of Sciences

A multimode interference (MMI) structure is designed to simplify the fabrication of quantum cascade laser (QCL) phase-locked arrays. The MMI geometry is optimized with a sufficient output channel distance to accommodate conventional photolithography and wet etching process by which power amplifier array is fabricated without using the complicated two-step etching-regrowth or dry etching technique. The far-field pattern with periodically modulated peaks reveals that the beams from the arrays are phase-locked. Furthermore, the frequency tuning performance of the MMI-based phase-locked arrays is studied using the Littrow-configuration external cavity structure. A wavelength tuning range of more than 60 cm−1 is demonstrated, which will eventually realize the high power, frequency tunable, large-scale phase-locked arrays, and their application in spectroscopy.

Study of Self-Patterned Zinc Tin Oxide Thin-Film Transistors Prepared from Photocurable Precursor Solution with Photoacid Generator

Solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) have great potential uses in next-generation wearable and flexible electronic products. Zinc and tin precursor materials are naturally abundant and have low fabrication costs. To integrate a single ZTO TFT into logic circuits including inverters, NAND, and NOR gates will require the development of a facile patterning process to replace conventional and complicated photolithography techniques which are usually time-consuming and toxic. In this study, self-patterned ZTO thin films were prepared using a photo-patternable precursor solution including a photoacid generator, (4-methylthiophenyl)methyl phenyl sulfonium triflate. Solution-processed ZTO precursor films fabricated with the photoacid generator were successfully micropatterned by UV exposure, and transitioned to a semiconducting ZTO thin film by heat treatment. The UV-irradiated precursor films became insoluble in developing solvent as the generated proton from the photoacid generator affected the metal-containing ligand and changed the solubility of the metal oxide precursors. The resulting ZTO thin films were utilized as the active layers of n-type TFTs, which exhibited a typical n-type transfer, and output characteristics with appropriate threshold voltage, on/off current ratio, and field-effect mobility. We believe that our work provides a convenient solution-based route to the fabrication of metal-oxide semiconductor patterns.

Electronic transport in submicrometric channels at the LaAlO3/SrTiO3 interface

Nanoscale channels realized at the conducting interface between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ provide a perfect playground to explore the effect of dimensionality on the electronic properties of complex oxides. Here we compare the electric transport properties of devices realized using the atomic force microscope-writing technique and conventional photolithography. We find that the lateral size of the conducting paths has a strong effect on their transport behavior at low temperature. We observe a crossover from a metallic to an insulating regime occurring at about 50 K for channels narrower than 100 nm. The insulating upturn can be suppressed by the application of a positive backgate. We compare the behavior of nanometric constrictions in lithographically patterned channels with the result of model calculations, and we conclude that the experimental observations are compatible with the physics of a quantum point contact.

Resist‐ and Etching‐Free Patterning Mediated by Predefined Photosensitive Polyimide for Two‐Dimensional Semiconductor‐Based Photodetectors

AbstractEven though molybdenum disulfide (MoS2) possesses superb features, its practical application in optoelectronics is hindered by the lack of a reliable synthetic route for producing large‐scale two‐dimensional (2D) MoS2 with spatial homogeneity and a pertinent patterning technique that can be used to realize 2D MoS2‐based photodetector arrays. To resolve these issues, the effectiveness of an unprecedented combination of a solution‐based synthetic route with resist‐ and etching‐free patterning of 2D MoS2 mediated by pre‐defined photosensitive polyimide (PSPI) for realizing 2D MoS2‐based photodetector arrays is demonstrated. A solution‐based large‐area compatible approach is adopted for the synthesis of MoS2. Comprehensive structural and chemical analysis of the MoS2 synthesized by altering the concentration of ammonium tetrathiomolybdate is performed to determine the optimum conditions for enhancing the photoelectrical responses of MoS2‐based photodetectors. It is ascertained that the photocurrent of MoS2‐based photodetectors fabricated by PSPI‐assisted patterning is unequivocally greater than that of photodetectors produced via the conventional photolithography process owing to the absence of photoresist residues associated with impeding photon absorption and providing scattering centers of photogenerated carriers.

Epoxy thermoset coatings with fine controllable hierarchical structures prepared from bio-inspired photo-/colloidal lithography technique for anticorrosion application

Several epoxy thermoset (ET) composite coatings with artificial fine controllable micro/nano hierarchical structures were prepared through photolithography/colloidal lithography and subsequently applied in anticorrosion field. Firstly, several silicon wafers with fine controllable interspacing and width of micro-scaled cylindrical structures were fabricated through conventional photolithography. Subsequently, nano-scaled tips were fabricated upon a smooth clean surface on the previous silicon wafer with micro-scaled cylinders to generate nano-scaled tips through colloidal lithography. Moreover, ET coatings were duplicated by nano-casting technique with polydimethylsiloxane (PDMS) as a soft negative template. Surface morphology and contact angle (CA) of as-prepared hard silicon template and ET coatings were identified. The CA of water droplets on ET coating with bio-inspired micro/nano hierarchical structures (denoted by BET) was 160°, which meant that this coating was more hydrophobic than ET coatings with distinctive surface structures. Anticorrosion studies of as-prepared ET coating with/without distinctive structures showed that cold rod steel (CRS) electrode coated with BET had better anticorrosion performance than other ET coating for short- and long-term studies. This procedure of fine controllable micro/nano structure coatings opens the door for further innovative investigations of corrosion protection methods and material designs.

Distinguishing normal and aggregated alpha-synuclein interaction on gold nanorod incorporated zinc oxide nanocomposite by electrochemical technique

Misfolding and accumulation of the protein alpha synuclein in the brain cells characterize Parkinson's disease (PD). Electrochemical based aluminum interdigitated electrodes (ALIDEs) was fabricated by using conventional photolithography method and modified the surfaces with zinc oxide and gold nanorod by using spin coating method for the analysis of PD protein biomarker. The device surface modified with gold nanorod of 25 nm diameter was used. The bare devices and the surface modified devices were characterized by Scanning Electron Microscope, 3D-Profilometer, Atomic Force Microscope and high-power microscope. The above measurement was also performed to measure the interaction of antibody with aggregated alpha-synuclein for normal, aggregated and aggregated alpha synuclein in human serum and distinguished against 3 control proteins (PARK1, DJ-1 and Factor IX). The detection limit for normal alpha synuclein was 1 f. with the sensitivity of 1 f. on a linear regression (R2 = 0.9759). The detection limit for aggregated alpha synuclein was 10 aM with the sensitivity of 1 aM on a linear regression (R2 = 0.9797). Also, the detection limit of aggregated alpha synuclein in serum was 10 aM with the sensitivity of 1 aM on a linear regression (R2 = 0.9739). These results however indicate that, serum has only minimal amount of alpha synuclein.

High resolution patterning of PbS quantum dots/graphene photodetectors with high responsivity via photolithography with a top graphene layer to protect surface ligands.

Photodetectors based on colloidal quantum dots (CQDs) and single layer graphene (SLG) have shown high responsivity due to the synergy of strong light absorption from CQDs and high mobility from SLG. However, it is still challenging to achieve high-density and small-footprint devices on a chip to meet the demand for their integration into electronic devices. Even though there are numerous approaches to pattern the chemically fragile CQD films, usually they require non-conventional approaches such as stamping and surface modification that may be non-compatible with semiconductor processing. In this study, we show that conventional lithography and dry etching can be used to pattern QD active films by employing a graphene monolayer passivation/protective layer that protects the surface ligands of CQDs. This protective layer avoids damage induced by lithography process solvents that deteriorate the carrier mobility of CQDs and therefore the photoresponse. Herein we report patterning of CQDs using conventional UV photolithography, achieving reproducible five-micron length PbS CQDs/SLG photodetectors with a responsivity of 108 A W−1. We have also fabricated thirty-six PbS CQDs/SLG photodetectors on a single chip to establish micron size photodetectors. This process offers an approach to pattern QDs with conventional UV lithography and dry etching semiconductor technology to facilitate their integration into current semiconductor commercial technology.

Visible-light-stimulated synaptic InGaZnO phototransistors enabled by wavelength-tunable perovskite quantum dots.

Neuromorphic vision sensors are designed to mimic the human visual system, which allows image recognition with low power computational requirements. Photonic synaptic devices are one of the most viable building blocks for constructing neuromorphic vision sensors. Herein, a photonic synaptic sensor based on an inorganic perovskite quantum dot (QD) embedded InGaZnO (IGZO) thin-film phototransistor is demonstrated. The photodetection wavelength ranges of the transistor can be adjusted by changing the halogen ions (Cl, Br) of the perovskite QDs. Under low intensity 450 and 550 nm illumination, the CsPbBr3 QD embedded phototransistor sensor shows a responsivity of 6.7 × 102 and 4.2 × 10−2 A W−1, respectively. The perovskite QD embedded transistor not only presents high responsivity to visible light, but also features excellent synaptic behavior, including an excitatory postsynaptic current (EPSC), pair-pulse facilitation (PPF), long-term memory, and memory erasure through gate voltage regulation. Moreover, the sensor fabrication process in this work is compatible with conventional photolithography processes. Taking these merits into account, the proposed QD embedded IGZO transistor presents a promising route by which to construct artificial visual sensors with color-distinguishable optical signal sensing and processing.

Effects of O2 Plasma Treatments on the Photolithographic Patterning of PEDOT:PSS

Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is known for its potential to replace indium–tin oxide in various devices. Herein, when fabricating finger-type PEDOT:PSS electrodes using conventional photolithography, the cross-sectional profiles of the patterns are U-shaped instead of rectangular. The films initially suffer from non-uniformity and fragility as well as defects owing to undesirable patterns. Adding a small amount of hydrolyzed silane crosslinker to PEDOT:PSS suspensions increases the mechanical durability of PEDOT:PSS patterns while lifting off the photoresist. To further improve their microfabrication, we observe the effects of two additional oxygen (O2) plasma treatments on conventional photolithography processes for patterning PEDOT:PSS, expecting to observe how O2 plasma increases the uniformity of the patterns and changes the thickness and U-shaped cross-sectional profiles of the patterns. Appropriately exposing the patterned photoresist to O2 plasma before spin-coating PEDOT:PSS improves the wettability of its surface, including its sidewalls, and a similar treatment before lifting off the photoresist helps partially remove the spin-coated PEDOT:PSS that impedes the lift-off process. These two additional processes enable fabricating more uniform, defect-free PEDOT:PSS patterns. Both increasing the wettability of the photoresist patters before spin-coating PEDOT:PSS and reducing its conformal coverage are key to improving the photolithographic microfabrication of PEDOT:PSS.

High Detectivity Ammonia Gas Sensor of Pentacene Based Organic Material with OXIDE MESH

Ammonia gas sensing properties of pentacene based organic gas sensor fabricated by thermal evaporation method on amorphous oxide semiconductor (a-SiInZnO) mesh. The amorphous oxide semiconductor mesh layer was fabricated by RF sputtering and conventional photolithography. Insertion of a dense mesh layer has been found to significantly improve gas sensing properties. In the case of a conventional pentacene thin film, the SEM image analysis resulted in a uniform surface. This means that ammonia gas cannot be adsorbed well on the surface. The insertion of the mesh layer improves the surface volume ratio of the organic thin film and induces more ammonia gas to be adsorbed on the pentacene surface. As a result, it was confirmed that even when the ammonia gas concentration was 5 ppm or less, the detection rate was higher than that of a conventional pentacene thin film. It is expected to be applied to various high-sensitivity organic-based gas sensors.