Photolithography Method Research Articles

Development and integration of near atmospheric N2 ambient sputtered Au thin film for enhanced infrared absorption

The exceedingly fragile nature of thermally grown Au-black coating makes handling and patterning a critical issue. Infrared absorption characteristics of near atmospheric, N2 ambient DC sputtered Au thin films are studied for this purpose. The thin Au films are sputtered at different chamber pressures in Ar and N2/Ar gas ambient from 4.5 to 8.0mbar and optimized for enhanced infrared absorption. The absorber film sputtered in N2/Ar ambient at 8.0mbar chamber pressure offers significant absorption of medium to long wave infrared radiations. The micro-patterning of sputtered Au thin film is carried out by using conventional photolithography and metal lift off methods on a prefabricated µ-infrared detector array on Si (100) substrate. The steady state temperature response of sputtered film has been examined using nondestructive thermal imaging method under external heating of the detector array.

Continuous electrochemical detection of hydrogen peroxide by Au-Ag bimetallic nanoparticles in microfluidic devices

We developed electrochemical microfluidic devices containing Au-Ag bimetallic nanoparticles on single-walled carbon nanotube (SWCNT) electrodes for precise, rapid and non-enzymatic electrochemical detection of hydrogen peroxide (H2O2). A homogeneous SWCNT layer on a glass substrate was patterned by a standard photolithography method and an O2-plasma technique. The patterned SWCNT layers were used as working electrode, counter electrode, and reference electrode in a 1mm wide and 23μm deep microchannel. To enhance the electrochemical catalytic properties of the working electrode, Au covered Ag nanoparticles (NPs) were electrochemically deposited on the SWCNT working electrode with current streaming solution into a microfluidic channel. The AgNPs had catalytic activity to improve the reduction of H2O2 combined with AuNPs, which could support catalytic reaction of AgNPs. The reduction in H2O2 in fabricated devices was monitored at an optimized condition and was linear with H2O2 concentration, resulting in a sensitivity of 13.1μA·cm−2·mM−1, a correlation coefficient of r2=0.985, and limit of detection 26.8μM (S/N=3). For the analysis of real samples, diluted antiseptic solutions containing 3wt% H2O2 were used to determine the concentration of H2O2 in the pharmaceutical sample. The recovery values ranged from 97% to 107%, and relative standard deviations were below 5%. We expect that the developed microfluidic sensor is a prospective electrochemical platform for accurate, reproducible non-enzymatic detection of H2O2.

A Mechanism to Enhance Antenna Performance using Notch and Defected Ground Structure

Objectives: This paper has proposed the mechanism to enhance antenna performance. The antennas are designed to be applied in communication devices. Methods/Statistical analysis: The proposed antenna characteristics had been analyzed by means of Finite Difference Time Domain (FDTD) method and had been fabricated by photolithography method on FR-4 Printed Circuit Board (PCB). Both simulation and measurement result show that the proposed antenna had three resonant frequencies 2.45GHz, 3.75GHz, and 5GHz with Return Loss (RL) are -40dB, -25dB and -20dB, respectively. Findings: All four antenna designs show characteristics of the mechanism. The antenna 1 is the reference design, after the first mechanism of antenna 2 which is to give the notch line on the both side of the antenna 2. The improvement of this first mechanism shows the RL. The second mechanism is rotated 60 degrees of the resonator of the antenna 2, show that the surface current adds more significant and give better RL. The third mechanism adds the defected ground structure on the both ground plane, the result gives the antenna a better RL from all the mechanism. The mechanism steps that applied on proposed antenna give enhance on such as RL, bandwidth, and radiation pattern. Application/Improvements: The radiation patterns show the omni direction in frequency 2.45 GHz and bi-direction in both 3.75 and 5 GHz with HPBW around 80 degrees. The proposed antenna was suitable for communication devices.

Performance Improvement in Polymer-based Thin Film Transistors Using Modified Bottom-contact Structures with Etched SiO2Layers

Polymer-based thin film transistors (TFTs) with a modified bottom-contact structure and etched SiO2 layer were developed and investigated. An increase in the field-effect mobility in the developed TFTs compared to TFTs with a normal bottom-contact structure was ascertained. A bottom-contact structure and the photolithographic processing method were used to ensure that the developed TFTs were suitable for commercial applications. Increased mobility of the modified bottom-contact structure was attributed to direct contact of the Au electrode with the active polymer layer.

Detection ofAeromonas hydrophilaUsing Fiber Optic Microchannel Sensor

This research focuses on the detection ofAeromonas hydrophilausing fiber optic microchannel biosensor. Microchannel was fabricated by photolithography method. The fiber optic was chosen as signal transmitting medium and light absorption characteristic of different microorganisms was investigated for possible detection. Experimental results showed thatAeromonas hydrophilacan be detected at the region of UV-Vis spectra between 352 nm and 354 nm which was comparable to measurement provided by UV spectrophotometer and also theoretical calculation by Beer-Lambert Absorption Law. The entire detection can be done in less than 10 minutes using a total volume of 3 μL only.This result promises good potential of this fiber optic microchannel sensor as a reliable, portable, and disposable sensor.

Detection and sizing of nanoparticles and DNA on PDMS nanofluidic chips based on differential resistive pulse sensing.

The RPS (Resistive Pulse Sensing) technique is a popular tool for the label-free detection of particles. This paper describes a simple, cost-effective PDMS nanofluidic chip for the detection and characterization of nanoparticles based on the differential RPS technique with high resolution and sensitivity. The chip is composed of two layers of PDMS slabs. Microchannel systems fabricated by the photolithography method on the top layer are used for sample loading and differential signal acquisition, and a straight nanochannel on the bottom layer fabricated by an unconventional approach bridging the gap between the microchannels works as an RPS sensing gate. A single-stage differential amplifier is used to amplify the RPS signals when particles or DNA pass through the sensing gate. It was demonstrated that this nanofluidic RPS chip can detect nanoparticles as small as 23 nm with a high SNR (Signal-to-Noise Ratio). The experimental results also show that the device is able to distinguish nanoparticles of smaller size differences such as 60 nm and 83 nm with high resolution, showing superior performance in comparison with the results obtained from DLS (Dynamic Light Scattering). This differential nano-RPS chip was also applied to detect the translocation of dsDNA molecules.

Proposal of Ultrafine and High Reliable Trench Wiring Process for Organic Interposer

An organic interposer technology with ultrafine line and space is required to achieve high-density interconnection between chips. In this article, we propose a high reliability, ultrafine trench wiring process. Currently, trench wiring is made by laser ablation of dielectric, sputtering, copper plating, and then chemical mechanical polishing (CMP). However, it is challenging to achieve fine trench with smooth side wall using laser ablation, and CMP is also not suitable because of its high assembly cost. Reliability is another challenge because of the narrower and thinner insulator. We have developed a photosensitive insulation film (PIF) with fine resolution. The trench wiring of 2/2 μm line and space has been successfully assembled by photolithography, plating, and surface planer method as the alternative to CMP. The wiring layer of 2/2 μm line and space, which is covered with a thin barrier metal layer and PIF, has passed the biased highly accelerated temperature and humidity stress test (HAST) screening. A copper paste is applied as a seed layer instead of sputtering. The sintered copper filled with adhesive paste into the copper pores is compatible as the seed layer, and the wiring layer of 10/10 μm line and space has passed the reliability tests such as moisture sensitivity level 2 (MSL2), thermal cycling test, and biased HAST.

3D Neural Culture in Dual Hydrogel Systems.

3D in vitro culture systems may yield physiological outcomes that more closely approximate in vivo behavior. A number of fabrication techniques and hydrogel scaffold materials are available to researchers, but often their implementation is complex and seemingly prohibitive. Herein, we describe a simplistic and adaptable dual hydrogel photolithography method utilized to engineer advanced in vitro systems for studies of neuronal development and characterization.

A microfluidic electrochemical cell with integrated PdH reference electrode for high current experiments

An on-chip thin-film palladium hydride reference electrode is described for use with microfluidic electrochemical cells. A Pd electrode fabricated by photolithographic methods is charged with hydrogen in-situ with a simple current step technique. The placement of the reference electrode in a side channel means that it is unaffected by species in the main channel. Placement upstream of the working and sense electrodes is shown to be a significant improvement over cells with the reference electrode placed externally. The adverse effects of solution resistance are investigated quantitatively, and it is shown that the described configuration allows for high current experiments while maintaining accurate potential measurement. A simple formula for calculating the maximum current density for a certain cell geometry and electrolyte resistivity is presented.

Diamond photonics platform enabled by femtosecond laser writing.

Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV’s states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, still lacking is an efficient photonic fabrication method for diamond akin to the photolithographic methods that have revolutionized silicon photonics. Here, we report the first demonstration of three dimensional buried optical waveguides in diamond, inscribed by focused femtosecond high repetition rate laser pulses. Within the waveguides, high quality NV properties are observed, making them promising for integrated magnetometer or quantum information systems on a diamond chip.

Proposal of Ultra-fine and High Reliable Trench Wiring Process for Organic Interposer

Abstract An organic interposer technology with ultra-fine line and space is required in order to achieve high density interconnection between chips. In this paper we propose a high reliability, ultra-fine trench wiring process. Current trench wiring is made by laser ablation of dielectric, spattering, copper plating and then Chemical mechanical polishing (CMP). However, it is challenging for laser ablation to achieve fine trench with smooth side wall and CMP is not suitable because of high assembly cost. Reliability is another challenge because of the narrower and thinner insulator. We have developed photosensitive insulation film (PIF) with fine resolution. The trench wiring of 2/2 μm line and space has been successfully assembled by photolithography, plating and surface planer method as the alternative to CMP. The wiring layer of 2/2 μm line and space, which was covered with the thin barrier metal layer and PIF, has passed the biased highly accelerated temperature and humidity stress test (HAST) screening. In addition to the above process a copper paste has been applied as a seed layer instead of the spattering. The sintered copper filled with adhesive paste into the copper porous is compatible as the seed layer and the wiring layer of 10/10 μm line and space has passed the reliability tests such as MSL2, thermal cycling test and biased HAST.

Direct growth of nanocrystalline graphene/graphite all carbon transparent electrode for graphene glass and photodetectors

Nanocrystalline graphene/graphite hybrids all carbon transparent electrodes were fabricated from photoresist with a photolithography method by the carbonization and graphitization of the aromatic molecules in the photoresist. The sheet resistance and transmittance of the hybrids transparent electrodes can be easily optimized by modulating the photoresist grid size and gridline width. The optimized hybrids were fabricated on quartz for graphene glass that exhibits excellent properties for heating device. They were also engaged on Si with a thin oxide layer by a catalyst-free and direct growth method for high-performance Schottky junction photodetectors that exhibit remarkable properties on photodetection with the photovoltage responsivity exceeding up to 105 V/W under the incident light power of 0.05 μW, which make it suitable as weak-light-signal detectors. This study should be helpful on the various applications of catalyst-free, cost-effective, transparent, electrically and thermally conductive graphene.

Layer Number Dependence of Li+ Intercalation on Few-Layer Graphene and Electrochemical Imaging of Its Solid-Electrolyte Interphase Evolution

Bulk and surface electrochemical reactivity converge on ultrathin electrochemical interfaces such as few-layer graphene (FLG). In spite of the many recent works regarding the use of exfoliated graphene materials for charge storage, we still lack a detailed mechanistic understanding of how Li+ intercalates in FLG. Li+ intercalation in graphitic carbon is known to proceed through a staging mechanism, where intercalation occurs at selected interlayers at a time, rather than randomly on any available empty interlayer galleries, until reaching the nominal composition LiC6. Thus, on graphite this process is strongly dependent on the number of neighboring empty galleries at any given time. FLG naturally displays a limited number of galleries, therefore, we hypothesize that this process will also necessarily be distributed unevenly. In this study, we applied FLG (1-10 layers) to explore the alkaline ion uptake mechanisms. Chemical vapor deposition methods with varies recipes were applied to grow double and multilayer graphene. By multicycle wet transfer of bilayer graphene, 2-8 layer graphene with well-defined area and low defect density. Direct growth of multilayer graphene (>10 layers) serves as control group. Photolithography method was used to generate micro patterns on graphene as “point of entry” for Li+intercalation. Lithium ion intercalation on FLG, as measured via cyclic voltammetry, shows a staging-type process, which has strong dependence on the number of layers of graphene sheets that compose the electrode. On a graphene electrode with less than five layers, the numbers of intercalation/de-intercalation peaks were limited due to the lack of graphene interlayer galleries to stabilize Li ions. Those peaks broaden and increase in number as the layer number increases to six. Despite these mechanistic differences on ion intercalation, the formation of a solid-electrolyte interphase (SEI) was observed on all electrodes. Scanning electrochemical microscopy (SECM) in the feedback mode was used to demonstrate spatial resolved changes in the surface conductivity of FLG during SEI evolution. The fabrication of “ionic channels” on the FLG electrode provided preferential positions for Li ion insertion. The role of these channels can be evidenced using a Li-ion sensitive SECM imaging technique through localized flux measurements. This work highlights the impact of nano-structure and micro-structure on macroscopic electrochemical behavior and provides guidance to the mechanistic control of ion intercalation using atomically thin graphene interface. Figure 1

Improvement of TFT Characteristics for Low-Temperature Solution-Processed Oxide Semiconductors with Hydrogen Injection and Oxidation Process

Thin-film transistors (TFTs) using oxide semiconductors have attracted much attention for switching and driving devices in large-screen, high-resolution liquid crystal display (LCD) and organic light-emitting diode (OLED) displays because of their high mobility1-3. As an advanced oxide TFT fabrication method, the solution-process is widely researched due to advantages such as its low process cost, large-scale fabrication capacity, and the simplicity of the process. However, several drawbacks of the solution-process must be addressed for display applications. One of the key points is the trade-off between the processing temperature and the TFT characteristics. From previous research on solution-processed oxide TFTs, it has been reported that low-temperature-processed TFTs are generally inactive below 400 °C due to a lack of metal-oxide-metal bond formation and decomposition of the residual species4,5. However, a low-temperature process is strongly required for application to plastic substrates for flexible displays and flexible electronics devices.In addition, a low-temperature process is important to achieve low fabrication costs. Here, we demonstrate improvement of the TFT characteristics by application of a hydrogen injection and oxidation (HIO) process for low-temperature solution-processed oxide TFTs. From a technical standpoint, we consider that the important factor is how to efficiently decompose the residual species. The solution-processed oxide TFTs exhibit inferior device performance when a few residual species remain. Therefore, a reduction reaction is initiated by a hydrogen injection process to decompose the residual spices. The characteristics of a TFT based on indium gallium zinc oxide (IGZO) were evaluated, such as the field effect mobility and the threshold voltage (Vth) shift under positive and negative bias stress. The maximum temperature for the entire fabrication process was as low as 300 °C. Solution-processed IGZO thin films were fabricated by a spin-coating method onto 200 nm thick thermally oxidized SiO2/n+-Si substrates and annealing at 300 °C for 1 h. The IGZO precursor was prepared from 0.3 M solutions of indium nitrate hydrate (In(NO3)3·xH2O), gallium nitrate hydrate (Ga(NO3)3·xH2O), and zinc nitrate hydrate (Zn(NO3)2·xH2O) in pure water. The composition ratio for In:Ga:Zn was set to 4:1:1. Hydrogen plasma treatment was adopted for the hydrogen injection process with subsequent annealing at 300 °C for 1 h. After fabrication of the IGZO film, the active area of the IGZO film was defined using a conventional photolithography method. Patterned source/drain (S/D) electrodes (Mo) were formed on the IGZO thin films using a shadow mask. Figure 1 shows the transfer characteristics of the IGZO TFT with and without the HIO process. The transfer characteristics of these IGZO TFTs for gate voltages (Vg) ranging from -30 to 30 V were measured at a fixed drain voltage (Vd) of 30 V. After the HIO process for the IGZO TFTs, the field effect mobility was significantly improved from 2.1 cm2/Vs to 4.8 cm2/Vs. Figure 2 shows the results for the threshold voltage shift (ΔVth) under a positive gate bias stress (PBS) of 20 V and a negative gate bias stress (NBS) of -20 V, with and without the HIO process. The stress time was set to 1 h at the maximum. Improvement of the reliability was confirmed: the Vth shift was less than 0.25 V for PBS and -2 V for NBS. The trap sites of any residual species or defect states in active channels were thus efficiently suppressed by the hydrogen injection process. In addition, the oxidation process may enhance the metal-oxide-metal bond formation. In conclusion, the HIO process as a combination of hydrogen reduction reaction and oxidation was demonstrated as effective for the improvement of solution-processed oxide TFTs. Improvement of the TFT characteristics was confirmed in terms of the field effect mobility and the Vthshift under PBS and NBS. Therefore, we consider that this new approach will lead to the development of high-performance solution-processed oxide TFTs in future. 1K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, Nature 432, 488 (2004). 2K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M. Hirano, and H. Hosono, Science 300, 1269 (2003). 3L. Wang, M. Yoon, G. Lu, Y. Yang, A. Facchetti, and T.J. Marks, Nature materials 5, 893 (2006). 4 M. G. Kim, M. G. Kanatzidis, A. Facchetti, and T. J. Marks, Nature materials 5, 382 (2011) 5 S. Jeong, Y. G. Ha, J. Moon, A. Faccchetti, T. J. Marks, Advanced materials 22, 1346 (2010) Figure 1

On the Use of Scalable NanoISFET Arrays of Silicon with Highly Reproducible Sensor Performance for Biosensor Applications.

As a prerequisite to the development of real label-free bioassay applications, a high-throughput top–down nanofabrication process is carried out with a combination of nanoimprint lithography, anisotropic wet-etching, and photolithography methods realizing nanoISFET arrays that are then analyzed for identical sensor characteristics. Here, a newly designed array-based sensor chip exhibits 32 high aspect ratio silicon nanowires (SiNWs) laid out in parallel with 8 unit groups that are connected to a very highly doped, Π-shaped common source and individual drain contacts. Intricately designed contact lines exert equal feed-line resistances and capacitances to homogenize the sensor response as well as to minimize parasitic transport effects and to render easy integration of a fluidic layer on top. The scalable nanofabrication process as outlined in this article casts out a total of 2496 nanowires (NWs) on a 4 inch p-type silicon-on-insulator (SOI) wafer, yielding 78 sensor chips based on nanoISFET arrays. The sensor platform exhibiting high-performance transistor characteristics in buffer solutions is thoroughly characterized using state-of-the-art surface and electrical measurement techniques. Deploying a pH sensor in liquid buffers after high-quality gas-phase silanization, nanoISEFT arrays demonstrate typical pH sensor behavior with sensitivity as high as 43 ± 3 mV·pH–1 and a device-to-device variation of 7% at the wafer scale. Demonstration of a high-density sensor platform with uniform characteristics such as nanoISFET arrays of silicon (Si) in a routine and refined nanofabrication process may serve as an ideal solution deployable for real assay-based applications.

Monitoring Volumetric Changes in Silicon Thin-Film Anodes through In Situ Optical Diffraction Microscopy.

A high-resolution in situ spectroelectrochemical optical diffraction experiment has been developed to understand the volume expansion/contraction process of amorphous silicon (a-Si) thin-film anodes. Electrodes consisting of 1D transmissive gratings of silicon have been produced through photolithographic methods. After glovebox assembly in a home-built Teflon cell, monitoring of the diffraction efficiency of these gratings during the lithiation/delithiation process is performed using an optical microscope equipped with a Bertrand lens. When the diffraction efficiency along with optical constants obtained from in situ spectroscopic ellipsometry is utilized, volume changes of the active materials can be deduced. Unlike transmission electron microscopy and atomic force microscopy characterization methods of observing silicon's volume expansion, this experiment allows for real-time monitoring of the volume change at charge/discharge cycles greater than just the first few along with an experimental environment that directly mimics that of a real battery. This technique shows promising results that provide needed insight into understanding the lithium alloying reaction and subsequent induced capacity fade during the cycling of alloying anodes in lithium-ion batteries.

Local Magnetization Measurements on GdBCO Coated Conductors With Narrow Strands: A Comparative Study

The local magnetization of the GdBCO coated conductors was investigated with external magnetic fields applied parallel to the c-axis by using low-temperature scanning Hall probe microscopy. The GdBCO coated conductors were patterned to be bridge shapes by photolithography method. The experimental results are in quantitatively good agreement with the modified Bean's critical state model. In addition, the normalized local hysteresis loss was justified to be accordant to the normalized remanent field distribution.

Integration of Flexible and Microscale Organic Nonvolatile Resistive Memory Devices Using Orthogonal Photolithography.

We present the integration of flexible and microscale organic nonvolatile resistive memory devices fabricated in a cross-bar array structure on plastic substrates. This microscale integration was made via orthogonal photolithography method using fluorinated photoresist and solvents and was achieved without causing damage to the underlying organic memory materials. Our flexible microscale organic devices exhibited high ON/OFF ratio (I(ON/I(OFF) > 10(4)) under bending conditions. In addition, the ON and OFF states of our flexible and microscale memory devices were maintained for 10,000 seconds without any serious degradation.

Formation of silver and zinc selenide relief patterns by the lift-off photolithography method

Conducting the lift-off photolithography on silicon wafers with thicknesses of the FP-383 photoresist layers varying from 1.60 ± 0.20 to 4.20 ± 0.20 μm is considered. As a lift-off layer, either a silver layer or zinc selenide layer with a thickness of 80–90 nm was deposited. The edge roughness of the image elements after the lift-off is 5.00 ± 0.20 μm.

A facile method for fabrication of highly integrated organic field-effect transistors on photoresist-unwettable insulators with remarkable stability

Environmental stability is one of the most important parameters for high-performance organic field-effect transistors (OFETs). Hydrophobic insulators usually possess much better air stability than some conventional inorganic and hydrophilic organic insulators. However, fabrication of devices with high integration by photolithography method cannot be directly performed on hydrophobic insulators due to their photoresist-unwettable properties. In this work, a simple yet efficient metal-assisted photolithography method is developed to achieve large-scale fabrication of highly integrated organic electronic devices on photoresist-unwettable insulators. By using copper (Cu) as sacrificial layer, photolithography can be performed on these insulators with nearly the same resolution, uniformity, and reproducibility as the conventional photolithography. This method shows excellent flexibility and is capable of fabricating high-integrated devices on a variety of hydrophobic insulators including hydrophobic amorphous fluoropolymer (CYTOP), poly(dimethylsiloxane) (PDMS), and octadecyltrichlorosilane (OTS)-modified SiO2. OFETs based on 6,13-dichloropentacene (DCP) microwires (MWs) with CYTOP as the insulator layer were fabricated, which exhibited excellent device performance. Much improved device stability with very low mobility degradation (less than 9%) was observed after 24 days. While devices fabricated on hydrophilic insulators of poly-(vinyl phenol) (PVP) and bare SiO2 experienced dramatic performances decay within 24 days. Furthermore, by using metal-assisted photolithography method, flexible OFETs arrays could be further fabricated on polyethylene naphthalate (PEN) substrate, which showed excellent mechanical bending flexibility and stability. This work unveils the great potential of metal-assisted photolithography method for long-term stable high-integration organic electronic devices.