Metal Shadow Research Articles

Patterned Surface Activation of Cyclo-Olefin Polymers for Biochip Applications

Two different surface activation methods (UV/ozone and oxygen plasma treatment) were applied for patterned surface activation of cyclo-olefin polymer (COP) surfaces combined with different masking techniques (metal shadow mask and protective tape). Surface properties were characterized by various methods such as contact angle measurement, ATR-IR, XPS and Surface enhanced ellipsometric contrast (SEEC) microscopy. UV/ozone and oxygen plasma allowed for patterned surface modification of COP leading to the formation of carboxylic and hydroxyl groups on the activated part of the surface. Stability against organic solvents was determined by rinsing the activated substrates with 2-propanol. For UV/ozone treatment it was found that a thin film of degradation products remains on the COP surface and is at least partly removed in the following washing or rinsing steps.

Simple, Fast, and Cost‐Effective Fabrication of Wafer‐Scale Nanohole Arrays on Silicon for Antireflection

A simple, fast, and cost‐effective method was developed in this paper for the high‐throughput fabrication of nanohole arrays on silicon (Si), which is utilized for antireflection. Wafer‐scale polystyrene (PS) monolayer colloidal crystal was developed as templates by spin‐coating method. Metallic shadow mask was prepared by lifting off the oxygen etched PS beads from the deposited chromium film. Nanohole arrays were fabricated by Si dry etching. A series of nanohole arrays were fabricated with the similar diameter but with different depth. It is found that the maximum depth of the Si‐hole was determined by the diameter of the Cr‐mask. The antireflection ability of these Si‐hole arrays was investigated. The results show that the reflection decreases with the depth of the Si‐hole. The deepest Si‐hole arrays show the best antireflection ability (reflection < 9%) at long wavelengths (>600 nm), which was about 28 percent of the nonpatterned silicon wafer’s reflection. The proposed method has the potential for high‐throughput fabrication of patterned Si wafer, and the low reflectivity allows the application of these wafers in crystalline silicon solar cells.

Metal shadowing for electron microscopy.

Metal shadowing of bacteria, viruses, isolated molecules, and macromolecular assemblies is another high-resolution method for observing the ultrastructure of biological specimens. The actual procedure for producing a metal shadow is relatively simple; a heavy metal is evaporated from a source at an oblique angle to the specimen. The metal atoms pile up on the surfaces that face the source, but the surfaces away from the source are shielded and receive little metal deposit, creating a “shadow.” However, the process of producing biological specimens that are suitable for metal shadowing can be very complex. There are a whole host of specimen preparation techniques that can precede metal shadowing, and all provide superior preservation in comparison to air drying, a required step in negative staining procedures. The physical forces present during air drying (i.e., surface tension of the water–air interface) will literally crush most biological specimens as they dry. In this chapter I explain the development of and procedures for the production of biological specimens from macromolecular assemblies (e.g., DNA and RNA), purified isolated molecules (e.g., proteins), and isolated viruses and bacteria preparations suitable for metal shadowing. A variation on this basic technique is to rotate the specimen during the metal deposition to produce a high-resolution three-dimensional rendering of the specimen.

Magnetoelectric properties of Tb0.3Dy0.7Fe1.92/Pb(Zr x Ti1−x )O3 bilayer thin films

Magnetoelectric Tb0.3Dy0.7Fe1.92(Terfenol-D)/PbZrxTi1−xO3(PZT) bilayer thin films were deposited on (111)-oriented Pt/Ti/SiO2/Si substrates. The PZT layers with different compositions (x = 0.3 and 0.52) were grown on the substrates by using the sol-gel method. Terfenol-D layers were deposited on the PZT-film-coated substrate by ion beam sputtering at room temperature with a dot-type patterned metal shadow mask. The structural characteristics and the ferroelectric, ferromagnetic and magnetoelectric(ME) properties of the Terfenol-D/PZT bilayer thin films were investigated. In our results, the maximum remnant polarization, 2Pr were ∼60 µC/cm2 for Terfenol-D/PZT(30/70) (Zr/Ti ratio = 30/70). The magnetization and the ME voltage coefficients were identical regardless of the Zr/Ti composition of PZT. The ME voltage coefficients of the films were over 400 mV/cm·Oe, which were about 4 times higher than the values reported for other bilayer structures.

P-Doped SiO<sub>2</sub> Proton Conducting Films for Low Voltage Thin Film Transistors

P-doped SiO2 were prepared by PECVD and one metal shadow mask self-assembled method was used for fabricating oxide thin film transistors gated by such proton conductors. Proton conduction of these films was demonstrated and electrical characteristics of oxide thin film transistors gated by such proton conductors were discussed. Due to excellent proton conduction and big capacitance density, oxide thin film transistors gated by such proton conductors have obtained excellent performances with mobility of 48.39 cm2/Vs, threshold voltage of-0.36 V, subthreshold swing of 0.13 V/decade, Ion/off ratio of 3.2×106 with the relative humidity of 30% at the room temperature.

Characteristics of GaN-Based High-Voltage LEDs Compared to Traditional High Power LEDs

In this letter, GaN-based high-voltage light-emitting diodes (HV-LEDs) arrays with 16 microchips connected in series are fabricated. The light output power-current-voltage (LOP-I-V) characteristic of HV-LEDs is measured. Under input power of 1.1 W, the LOP of HV-LEDs is enhanced by 11.9% compared to traditional high power light-emitting diodes (THP-LEDs) with the same chip size. Due to the reduced metal shadow effect and better current spread, the HV-LEDs exhibit higher light extraction efficiency under the same current density, which is simulated by a 3-D ray tracing method. As a result, the luminous efficiency of HV-LEDs is 21.6% higher than that of THP-LEDs under input power of 1.1 W. Furthermore, the efficiency droop of HV-LEDs is reduced to half of that of THP-LEDs.

Gas Sensors Based on Ceramic MEMS Structures Made of Anodic Alumina and Yttria Stabilized Zirconia Films

The application of thin ceramic films for the fabrication of MEMS devices enables the extension of their working temperature range up to 600°C, a decrease in heating power consumption, and a very considerable decrease in production cost of sensors and actuators based on this technology. These advantages are very important for the application of gas sensors under harsh environmental conditions, in autonomous and wireless sensor networks. The methods of the fabrication of MEMS platforms for metal oxide semiconductor and thermocatalytic gas sensors, fast thermometers, and flowmeters based on yttria stabilized zirconia (YSZ) and alumina membranes for gas sensors are described. Alumina membranes stable up to 800°C have thickness of about 12 microns and are produced by anodic oxidation of aluminum foil in diluted oxalic acid followed by high-temperature annealing. YSZ membrane with the same thickness is made by slip casting with consequent annealing under mechanic load. Platinum heaters are deposited onto the surface of the membrane by magnetron sputtering through metallic shadow mask. Perfect adhesion of platinum to ceramic material permits us to avoid the application of adhesive sub-layers, and, therefore, improves long-term stability of the heater at high temperature. The sensor chip has a shape of triangle cut by laser beam; the heater meander is located in the vertex of triangle. This approach simplifies the technology of the fabrication of the platform and decreases power necessary for the heating of the sensing layer up to working temperature of 400 – 600°C. It is shown that the application of such triangle shaped membranes permits a decrease in power consumption of the MEMS working at 450°C down to ~ 40 mW at continuous and down to < 1 mW at pulse heating of gas sensor with duty cycle of 1 %. Thermal response time of the microheater is of about 80 ms.

Mechanisms of (NH4)2Sx-treated III-V compound triple-junction solar cells incorporating with hybrid electrode

A hybrid electrode composed of the metal contact pads and the transparent indium-tin-oxide film was incorporated with the (NH4)2Sx-treated InGaP/InGaAs/Ge triple-junction solar cells. The hybrid electrode structure was used to reduce the metal shadow area. The passivation function enabled by the (NH4)2Sx surface treatment was used to enhance the photoluminescence intensity and carrier lifetime of the (NH4)2Sx-treated n-type AlInP window layer. The conversion efficiency of (NH4)2Sx-treated solar cells with the hybrid electrode structure was improved up to 35.73% due to an increase in the absorption of the incident light along with the surface passivation.

Surface characterization of plasma‐polymerized polyethylene glycol thin film modified by plasma treatment

Polyethylene glycol (PEG) is a well‐known non‐fouling material used for protein adsorption and cellular adhesion. Recently, we successfully fabricated plasma‐polymerized PEG (PP‐PEG) thin films on various substrates by using a plasma enhanced chemical vapor deposition method and PEG200 as a precursor. The structure of our PP‐PEG thin film was found to be very similar to the chemical structure of a PEG polymer and also bore a non‐fouling characteristic for numerous proteins and cells without in vitro or in vivo toxicity. In this study, we modified this PP‐PEG thin film with a simple H2/He plasma treatment to change the non‐fouling surface property to a fouling one for proteins and cells. To make the patterned surfaces for proteins or cells on the protein‐ or cell‐resistant areas, depositing a new fouling PP thin film was unnecessary since it was possible to perform a simple H2/He plasma treatment through a metal shadow mask on the PP‐PEG thin film. Various surface analysis techniques such as water contact angle, atomic force microscopy, X‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry were used to confirm the drastic changes in the surface chemical properties resulting from the plasma treatment. These results show that a PP‐PEG film, together with its plasma treatment through a shadow mask, is a very simple and useful patterning technique for various biological applications. Copyright © 2012 John Wiley & Sons, Ltd.

Tuning the Threshold Voltage of Double-Gate Low-Voltage Transparent Oxide-Based TFTs by a Lateral In-Plane Gate

Double-gate low-voltage transparent oxide-based thin-film transistors (TFTs) with a lateral in-plane gate are self aligned by only one metal shadow mask. The threshold voltage of such devices can be tuned in a wide range from -1.07 to 0.78 V by the lateral in-plane gate, which allows the device switching from a depletion to an enhancement-mode operation. High performance with a field-effect mobility of >; 10 cm2/V · s, a current on/off ratio of ~3 × 105, and a low subthreshold swing of ~195 mV/decade is obtained at various voltage biases of the in-plane gate. Such double-gate TFTs are promising for next-generation transparent electronics with low power consumption.

Low-Voltage Organic/Inorganic Hybrid Transparent Thin-Film Transistors Gated by Chitosan-Based Proton Conductors

Solution-processed solid chitosan-based proton conductor film shows a large specific gate capacitance of ~7.47 μF/cm2 due to the interfacial electric-double-layer effect. Low-voltage (1.5 V) organic/inorganic hybrid transparent thin-film transistors with patterned indium-tin-oxide channels gated by chitosan films are self-assembled on glass substrates by only one metal shadow mask. The subthreshold gate voltage swing, current on/off ratio, and field-effect mobility are estimated to be 93 mV/dec, ~106, and 5.74 cm2·V-1·s-1, respectively. The reproducibility of pulse respond of such device is also demonstrated, which indicates the absence of electrochemical doping of the channel at the interface.

Full color organic electroluminescent display with shared blue light-emitting layer for reducing one fine metal shadow mask

To make a full color organic electroluminescent display, conventionally it requires three fine metal shadow masks (FMM) to pattern the red, green and blue light-emitting layer. In this work, by arranging the blue light-emitting layer as a shared layer for all sub-pixels, we demonstrate that a full color display can be achieved by two FMM processes, thus reducing one FMM process compared to conventional method. The red, green and blue sub-pixels can be optimized independently despite the reduction of one FMM process. Also, the performance of the red and green sub-pixels is not degraded by the shared blue light-emitting layer. Due to elimination of one FMM, the process TACT time, mask cost and alignment error can all be reduced, thus cutting down the manufacturing cost of full color organic electroluminescent display.

Surface Potential Measurement of Tris(8-hydroxyquinolinato)aluminum and Bis[N-(1-naphthyl)-N-phenyl]benzidine Thin Films Fabricated on Indium–Tin Oxide by Kelvin Probe Force Microscopy

To clarify the interfacial properties of an organic light-emitting diode (OLED), we discuss the surface potential of organic semiconductor thin films fabricated on an electrode that was measured by noncontact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KFM) utilizing frequency modulation (FM). The organic semiconductor films were deposited on a glass/indium–tin-oxide (ITO) substrate by the vacuum evaporation technique using intersecting metal shadow masks. This deposition technique enables us to fabricate four different areas on the same substrate. The surface potentials of the crossover area of the deposited thin films were investigated by the nc-AFM/KFM technique. The energy band diagram was depicted, and we observed that the charge behavior of the organic semiconductor depended on the material and the structure.

38.2: Invited Paper: Fabrication of Thin Film Transistor Circuits Using Shadow Masking: A Low Cost Alternative to Conventional Lithography

AbstractThin film transistors with micron size features are fabricated by evaporation printing (a combination of evaporation deposition through a fine metal shadow mask). Using successive deposition steps and better than lum mask to mask registry, transistor circuits are realized without conventional lithography. These components are useful in active matrix backplanes for top emitting OLED and e‐paper displays.

Low-Voltage Transparent Indium–Zinc–Oxide Coplanar Homojunction TFTs Self-Assembled on Inorganic Proton Conductors

H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -incorporated nanocolumnar SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based proton conductors show an enhanced electric double layer (EDL) capacitance value of ~8 μF/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 20 Hz. The upper frequency limit of EDL formation is found to be higher than 10 kHz. Transparent indium-zinc-oxide (IZO) coplanar homojunction thin-film transistors gated by such proton conductors are fabricated by one metal shadow mask self-assembled method. The operating voltage is found to be as low as 0.6 V. The current ON/OFF ratio, the subthreshold swing, and field-effect mobility are estimated to be 6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , 68 mV/dec, and 12 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V · s, respectively. Such transparent transistors hold promise for low cost and portable electrochromic devices and invisible biochemical sensors.

Surface analysis of protein‐resistant, plasma‐polymerized ethylene glycol thin films

AbstractPoly(ethylene glycol) (PEG) has been widely used in biomedical applications because of its protein‐resistant and nontoxic properties. In this study, a plasma‐polymerized ethylene glycol (PPEG) thin film was deposited on a substrate using a capacitively coupled plasma chemical vapour deposition (CCP‐CVD) method with various plasma powers and ethylene glycol as a precursor. The surfaces of the PPEG thin films were characterized using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) along with a principal component analysis (PCA), and XPS. We confirmed that the PPEG thin film deposited at low plasma power closely resembles PEG polymers in terms of surface chemical composition and protein‐resistant property. To make patterned surfaces with protein‐resistant property for proteins, a PPEG thin film was first uniformly deposited on a glass slide and patterns were produced on the PPEG coated surface by depositing a plasma‐polymerized amine film through a metal shadow mask. When we spotted proteins on the patterned surface, they were immobilized only onto the plasma‐polymerized amine areas but not onto the PPEG areas. These results show that PPEG surfaces would be useful for the construction of various protein arrays. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Nucleotide-Dependent Shape Changes in the Reverse Direction Motor, Myosin VI

We have studied the shape of myosin VI, the actin minus-end directed motor, by negative stain and metal shadow electron microscopy. Single particle processing was used to make two-dimensional averages of the stain images, which greatly increases the clarity and allows detailed comparisons with crystal structures. A total of 169,964 particle images were obtained from two different constructs in six different states (four nucleotide states and with and without Ca 2+). The shape of truncated apo myosin VI was very similar to the apo crystal structure, with the lever arm bent strongly backward and around the motor domain. In the full-length molecule, the C-terminal part of the tail has an additional bend taking it back across the motor domain, which may reflect a regulated state. Addition of ATP, ADP, or ATP- γS resulted in a large change, straightening the molecule from the bent shape and swinging the lever by ∼140°. Although these nucleotides would not be expected to produce the pre-powerstroke state, myosin VI in their presence was most similar to the truncated crystal structure with bound ADP-VO 4, which is thought to show the pre-powerstroke shape. The nucleotide data were therefore substantially different from expectation based on crystal structures. The full-length molecule was almost completely monomeric; only ∼1% were dimers, joined through the ends of the tail. Addition of calcium ions appeared to result in release of the second calmodulin light chain. In negatively stained molecules there was little indication of extended α-helical structure in the tail, but molecules viewed by metal shadowing had a tail ∼3× longer, 29 vs. 9 nm, part of which is likely to be a single α-helix.

Normalized metal artifact reduction (NMAR) in computed tomography

While modern clinical CT scanners under normal circumstances produce high quality images, severe artifacts degrade the image quality and the diagnostic value if metal prostheses or other metal objects are present in the field of measurement. Standard methods for metal artifact reduction (MAR) replace those parts of the projection data that are affected by metal (the so-called metal trace or metal shadow) by interpolation. However, while sinogram interpolation methods efficiently remove metal artifacts, new artifacts are often introduced, as interpolation cannot completely recover the information from the metal trace. The purpose of this work is to introduce a generalized normalization technique for MAR, allowing for efficient reduction of metal artifacts while adding almost no new ones. The method presented is compared to a standard MAR method, as well as MAR using simple length normalization. In the first step, metal is segmented in the image domain by thresholding. A 3D forward projection identifies the metal trace in the original projections. Before interpolation, the projections are normalized based on a 3D forward projection of a prior image. This prior image is obtained, for example, by a multithreshold segmentation of the initial image. The original rawdata are divided by the projection data of the prior image and, after interpolation, denormalized again. Simulations and measurements are performed to compare normalized metal artifact reduction (NMAR) to standard MAR with linear interpolation and MAR based on simple length normalization. Promising results for clinical spiral cone-beam data are presented in this work. Included are patients with hip prostheses, dental fillings, and spine fixation, which were scanned at pitch values ranging from 0.9 to 3.2. Image quality is improved considerably, particularly for metal implants within bone structures or in their proximity. The improvements are evaluated by comparing profiles through images and sinograms for the different methods and by inspecting ROIs. NMAR outperforms both other methods in all cases. It reduces metal artifacts to a minimum, even close to metal regions. Even for patients with dental fillings, which cause most severe artifacts, satisfactory results are obtained with NMAR. In contrast to other methods, NMAR prevents the usual blurring of structures close to metal implants if the metal artifacts are moderate. NMAR clearly outperforms the other methods for both moderate and severe artifacts. The proposed method reliably reduces metal artifacts from simulated as well as from clinical CT data. Computationally efficient and inexpensive compared to iterative methods, NMAR can be used as an additional step in any conventional sinogram inpainting-based MAR method.

Metal-Semiconductor Contact Behavior of Solution-Processed ZnSnO Thin Film Transistors

We studied the influence of different types of metal electrodes on the performance of solution-processed zinc tin oxide (ZTO) thin-film transistors. The ZTO thin-film was obtained by spin-coating the sol-gel solution made from zinc acetate and tin acetate dissolved in 2-methoxyethanol. Various metals, Al, Au, Ag and Cu, were used to make contacts with the solution-deposited ZTO layers by selective deposition through a metal shadow mask. Contact resistance between the metal electrode and the semiconductor was obtained by a transmission line method (TLM). The device based on an Al electrode exhibited superior performance as compared to those based on other metals. Kelvin probe force microscopy (KPFM) allowed us to measure the work function of the oxide semiconductor to understand the variation of the device performance as a function of the types metal electrode. The solution-processed ZTO contained nanopores that resulted from the burnout of the organic species during the annealing. This different surface structure associated with the solution-processed ZTO gave a rise to a different work function value as compared to the vacuum-deposited counterpart. More oxygen could be adsorbed on the nanoporous solution-processed ZTO with large accessible surface areas, which increased its work function. This observation explained why the solution-processed ZTO makes an ohmic contact with the Al electrode.

3-dimensional electrode patterning within a microfluidic channel using metal ion implantation

The application of electrical fields within a microfluidic channel enables many forms of manipulation necessary for lab-on-a-chip devices. Patterning electrodes inside the microfluidic channel generally requires multi-step optical lithography. Here, we utilize an ion-implantation process to pattern 3D electrodes within a fluidic channel made of polydimethylsiloxane (PDMS). Electrode structuring within the channel is achieved by ion implantation at a 40 degrees angle with a metal shadow mask. The advantages of three-dimensional structuring of electrodes within a fluidic channel over traditional planar electrode designs are discussed. Two possible applications are presented: asymmetric particles can be aligned in any of the three axial dimensions with electro-orientation; colloidal focusing and concentration within a fluidic channel can be achieved through dielectrophoresis. Demonstrations are shown with E. coli, a rod shaped bacteria, and indicate the potential that ion-implanted microfluidic channels have for manipulations in the context of lab-on-a-chip devices.