Cheng-Yao Lo

MEMS-Controlled Paper-Like Transmissive Flexible Display

A novel microelectromechanical-systems (MEMS)-controlled paper-like transmissive flexible display device was modeled by a combination of a cantilever with a flat plate and was realized by roll-to-roll printing process for the first time. This model provides predictions as well as improvement suggestions to both mechanical and electrical designs. A newly developed roll-to-roll printing process which was composed of flexography, gravure, lift-off, and lamination techniques used to manufacture this device was proved applicable on flexible electronics with high-volume, low-cost, and large-area solutions. This 20 V-driven device provided distinguishable three primary colors with averaged transmittance of 50% in visible region for full color flexible display applications and showed commercialization compatibility. Its electrical, mechanical, and optical characteristics excelled previous similar works. The proved major advantages of mechanical reliability, low operation voltage, and process simplicity done by this work made the MEMS flexible display an important alternative to electrophoretic, electrowetting, and electrochromic systems.

Mutual Capacitive Flexible Tactile Sensor for 3-D Image Control

This study develops a novel mutual capacitive tactile sensor for a touch panel with shifted finger-type electrodes with high sensitivity and other benefits. This tactile sensor detects normal, shear, and pulling forces with good simultaneous visible transmittance and flexibility for the next generation of 3-D flexible portable displays. The tactile sensor is composed of polyethylene terephthalate, gold, indium tin oxide, and polydimethylsiloxane. It exhibits 75% transmittance on average in the visible region, 0.04-N force resolution, and 1.5-pF/N responsiveness. The finger-type electrode design improves sensitivity by 112%-4100%, depending on the number of fingers and shifted direction. This study conducts theoretical calculations, simulations, fabrication, and measurements.

Post-lithography pattern modification and its application to a tunable wire grid polarizer

This study reports a simple and cost-effective post-lithography solution for reducing the characteristic dimensions of structures on the nanometer scale using an external mechanical force without any modification of the existing exposure system. In particular, this study presents a tunable aluminum wire grid polarizer (WGP) made by a laser interference lithography and i-line (365 nm) exposure setup on polyethylene naphthalate. The WGP achieves a 58% maximum linewidth shrinkage of the metal nanowire on the polymer substrate, and further improved the polarization extinction ratio by 83% with a defined operation window and optimized strain. The simulations in this study prove the rise of the extinction ratio with the modulation of the WGP pattern. Physical evidence explains the fall of the extinction ratio for both the increase of the metal crack volume and the delaminated randomly oriented fall-on fragments under extensive operation.

Friction-Assisted Pulling Force Detection Mechanism for Tactile Sensors

This paper proposes a novel friction-assisted capacitance tactile sensing mechanism to simultaneously detect pulling, normal, and shear forces for 3D display image control applications with integrated transparency and flexibility. The sensing mechanism supports fingertip sensing ranges with ergonomic considerations, which is an improvement on previous studies. The mechanism produces demonstration sensitivities of 0.38, 0.28, 0.24, and 0.33 pF/N and sensing ranges 0-1 N, 0-1.6 N, 0-1.4 N, and 0-2.0 N for pulling (θ = 90°), friction-assisted pulling (θ = 30°), normal, and shear forces, respectively. In this paper, we proposed friction-assisted pulling force under θ = 30°, which fit a human fingertip and allowed it to control 3D virtual image. On average, the demonstration tactile sensor transparency is over 80% in the visible region. This study conducts and examines the theoretical design, simulation, fabrication, and measurement of the mechanism.

A High Sensitivity Three-Dimensional-Shape Sensing Patch Prepared by Lithography and Inkjet Printing

A process combining conventional photolithography and a novel inkjet printing method for the manufacture of high sensitivity three-dimensional-shape (3DS) sensing patches was proposed and demonstrated. The supporting curvature ranges from 1.41 to 6.24 × 10−2 mm−1 and the sensing patch has a thickness of less than 130 μm and 20 × 20 mm2 dimensions. A complete finite element method (FEM) model with simulation results was calculated and performed based on the buckling of columns and the deflection equation. The results show high compatibility of the drop-on-demand (DOD) inkjet printing with photolithography and the interferometer design also supports bi-directional detection of deformation. The 3DS sensing patch can be operated remotely without any power consumption. It provides a novel and alternative option compared with other optical curvature sensors.

Capacitive Tactile Sensor for Angle Detection and Its Accuracy Study

This paper proposes a capacitive tactile sensor for applications in normal force, shear force, and xy-plane shear angle sensing. This tactile sensor enabled shear force angle detection with less than 3° tolerance to be realized for the first time. The average sensitivity when applying the normal force was 4.43 pF/N, and the average sensitivity when applying the shear force ranged between 0.13 and 0.85 pF/N, depending on the angle. Angle detection errors caused by planar-, rotational-, and vertical-pattern shifts during the lamination process and operation are detailed. The results of an analysis indicated that both the planar and rotational shift greatly contributed to detection errors, whereas the contribution of the vertical shift was negligible. In addition to the experiment and analysis, simulations were performed to prove that the angle detection methodology yields consistent results in theory and in practice.

Fabricating a Silver Soft Mold on a Flexible Substrate for Roll-to-Roll Nanoimprinting

This study presents an efficient method for fabricating a silver soft mold with a three-dimensional (3-D) nanostructure on flexible polyethersulfone (PES) plastic substrates for a roll-to-roll (R2R) nanoimprint process by employing hot embossing in conjunction with inkjet printing. Prior to fabricating the silver soft mold, the researchers in this study used laser interference lithography (LIL) to fabricate the silicon mold of nanopillar arrays with diameters of 146 nm, heights of 201 nm, and pitches of 291 nm. Inkjet printing was used to coat the silver nanoparticle liquid uniformly on a PES substrate with the designed drop space and volume of droplets. By using hot embossing for 210 s, the researchers transferred the nanopillar arrays from the master Si mold to the liquid on the PES substrate. Finally, the silver nanoparticles of nanohole arrays were sintered on the PES by soft baking for 6 h. The results of this study showed that the silver soft mold could effectively transfer the nanostructures to the polymer substrate through the R2R process in various applications such as antireflection devices.

Critical dimension and pattern size enhancement using pre-strained lithography

This paper proposes a non-wavelength-shortening-related critical dimension and pattern size reduction solution for the integrated circuit industry that entails generating strain on the substrate prior to lithography. Pattern size reduction of up to 49% was achieved regardless of shape, location, and size on the xy plane, and complete theoretical calculations and process steps are described in this paper. This technique can be applied to enhance pattern resolution by employing materials and process parameters already in use and, thus, to enhance the capability of outdated lithography facilities, enabling them to particularly support the manufacturing of flexible electronic devices with polymer substrates.

Mechanical stress-controlled tunable active frequency-selective surface

This study proposes a tunable active frequency-selective surface (AFSS) realized by mechanically expanding or contracting a split-ring resonator (SRR) array. The proposed AFSS transfers mechanical stress from its elastic substrate to the top of the SRR, thereby achieving electromagnetic (EM) modulation without the need for an additional external power supply, meeting the requirements for the target application: the invisibility cloak. The operating mechanism of the proposed AFSS differs from those of other AFSSs, supporting modulations in arbitrary frequencies in the target range. The proposed stress-controlled or strain-induced EM modulation proves the existence of an identical and linear relationship between the strain gradient and the frequency shift, implying its suitability for other EM modulation ranges and applications.

Spatial resolution maximization for capacitive tactile sensors

Unlike conventional four-capacitor tactile sensors, this work presents a two-capacitor arrangement to reduce the size of sensing unit and to enhance the spatial resolution without losing sensitivity and accuracy. The shapes of the capacitors were simultaneously modified from squares to rectangles to realize balanced spatial resolutions in the x- and y-direction. Experiments showed identical results to the theoretical and simulation ones with less than 3° angle detection error and 0.3 pF/N sensitivity. The maximized spatial resolution of the proposed two-capacitor tactile sensor was more than doubled compared to that of the conventional four-capacitor ones.