Yao-Joe Yang

A flexible capacitive tactile sensing array with floating electrodes

In this work, we present the development of a capacitive tactile sensing array realized by using MEMS fabrication techniques and flexible printed circuit board (FPCB) technologies. The sensing array, which consists of two micromachined polydimethlysiloxane (PDMS) structures and a FPCB, will be used as the artificial skin for robot applications. Each capacitive sensing element comprises two sensing electrodes and a common floating electrode. The sensing electrodes and the metal interconnect for signal scanning are implemented on the FPCB, while the floating electrode is patterned on one of the PDMS structures. This special design can effectively reduce the complexity of the device structure and thus makes the device highly manufacturable. The characteristics of the devices with different dimensions are measured and discussed. The corresponding scanning circuits are also designed and implemented. The tactile images induced by the PMMA stamps of different shapes are also successfully captured by a fabricated 8 × 8 array.

Flexible Temperature Sensor Array Based on a Graphite-Polydimethylsiloxane Composite

This paper presents a novel method to fabricate temperature sensor arrays by dispensing a graphite-polydimethylsiloxane composite on flexible polyimide films. The fabricated temperature sensor array has 64 sensing cells in a 4 × 4 cm2 area. The sensor array can be used as humanoid artificial skin for sensation system of robots. Interdigitated copper electrodes were patterned on the flexible polyimide substrate for determining the resistivity change of the composites subjected to ambient temperature variations. Polydimethylsiloxane was used as the matrix. Composites of different graphite volume fractions for large dynamic range from 30 °C to 110 °C have been investigated. Our experiments showed that graphite powder provided the composite high temperature sensitivity. The fabricated temperature sensor array has been tested. The detected temperature contours are in good agreement with the shapes and magnitudes of different heat sources.

White light from polymer light-emitting diodes: Utilization of fluorenone defects and exciplex

A white light polymer light-emitting diode was demonstrated with a double layer configuration: poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) blended with poly(N-vinylcarbazole) as both hole-transporting layer and electron-blocking layer, blue-emissive poly(9,9-dihexylfluorene-alt-co-2,5-dioctyloxy-para-phenylene) (PDHFDOOP) blended with green-emissive poly[6,6′-bi-(9,9′-dihexylfluorene)-co-(9,9′-dihexylfluorene-3-thiophene-5′-yl)] as an emissive layer. By annealing the emissive layer at a relatively high temperature, fluorenone defects were generated into PDHFDOOP, which formed an exciplex with poly-TPD, as a red emitter. The devices exhibit a maximum brightness of ∼4800cd∕m2 and a maximum luminous efficiency of ∼3cd∕A. Moreover, the Commission Internationale de L’Eclairage coordinates of the emitted light is close to that of pure white light and is insensitive to the applied voltages.

Effect of air damping on the dynamics of nonuniform deformations of microstructures

In this paper, we present a methodology for extracting macromodel parameters of compressible isothermal squeezed-film damping (CISQFD) for flexible structures of MEMS under small amplitude oscillation. The theoretical derivation, which is based on structural modal analysis and CISQFD numerical simulation, is presented. The spring and damping components of CISQFD of any oscillation mode can be extracted by this methodology, and thus the generic parameters of CISQFD can be obtained for any flexible structure with given oscillation modes. We successfully formulated an accurate and concise second order dynamics equation for a flexible MEMS devices by using the CISQFD parameters and the modal spring constant and mass. Simulation results of resonance shift and quality factor are consistent with experimental results.

Low-order models for fast dynamical simulation of MEMS microstructures

In this paper, are describe how a few simulations of fully meshed dynamical problems can be used to construct efficient low-order models for system-level design of microstructures. We report on the use of this method to capture the measured behaviour of a pressure sensor based on the pull-in time of a beam. Results show that the reduced order model decreases simulation time by at least a factor of 37 while achieving good agreement with experimental data.

A novel 2 ? 2 MEMS optical switch using the split cross-bar design

In this paper, a novel 2 × 2 MEMS optical switch is presented. The switch, which employs the proposed split cross-bar (SCB) design, intrinsically possesses advantages over typical 2 × 2 MEMS switches of traditional designs, such as the cross-bar design and the mirror-array design. In comparison to the cross-bar switches, the SCB switch does not have the constraint on the mirror thickness which affects fiber alignment significantly. In comparison to the mirror-array switches, the SCB switch requires fewer movable mirrors and thus gives better fabrication yield. The SCB device can be easily fabricated by employing inductively-coupled-plasma etching (ICP) on a silicon-on-insulator (SOI) wafer with one photo-mask. Electro-thermal V-beam actuators integrated with the bi-stable mechanisms are employed to move and latch the movable mirrors of the proposed device. The displacement of the movable mirrors is at least 60 µm under a driving voltage of 40 V. The optical performance and the dynamic response of the SCB switch are also investigated. The measured average insertion loss is less than −1.4 dB with a deviation of 0.08 dB. Also, the measured switching time is about 10 ms.

Enhanced performance of white polymer light-emitting diodes using polymer blends as hole-transporting layers

AU: PLEASE CONFIRM CHANGES MADE IN THE BYLINE.White polymer light-emitting diodes (WPLEDs) with the Commission Internationale de l’Enclairage coordinates of (0.32, 0.34) are demonstrated with poly(9,9-dioctylfluorene-2,7-diyl) as host and poly(5-methoxy-2-(2′-ethyl-hexylthio)-p-phenylenevinylene) as guest. Blends of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and poly(N-vinyl-carbazole) (PVK) are introduced into bilayer devices as hole-transporting layers (HTLs). Because the blends combined the hole-injection and hole-transporting capabilities of poly-TPD with electron-blocking capability of PVK, WPLEDs with the blends as HTLs exhibit enhanced performance in comparison with single-layer device and bilayer devices with pure poly-TPD or pure PVK as HTL. With a 1:1 weight ratio of poly-TPD to PVK in the blend, the WPLED achieves a maximum brightness of ∼5000cd∕m2 with a maximum electroluminescent efficiency of 3.15cd∕A.

Nonlinear heat-transfer macromodeling for MEMS thermal devices

In this paper, we present a nonlinear heat-transfer macromodeling technique using the trajectory piecewise-linear model-order-reduction (TPWLMOR) method. A 3D nonlinear heat-transfer model, which is capable of accounting for the temperature-dependent material properties as well as the radiation effect, is implemented using the finite-difference method (FDM). The numerical models generated by the FDM are reduced into compact models using the TPWLMOR technique, which is based on the concept of a piecewise-linear approximation and an Arnoldi-based model-order-reduction (MOR) algorithm. Nonlinear macromodeling case studies of different MEMS thermal devices are demonstrated using the TPWLMOR technique. The calculated steady and transient characteristics of the thermal devices are discussed. In terms of computational cost, the TPWLMOR models are at least 2 orders of magnitude faster than the original nonlinear full-meshed models with a negligible compromise in accuracy. The simulated results by the TPWLMOR models are also verified with the experimentally measured results.

Extraction of heat-transfer macromodels for MEMS devices*

In this paper, a model order reduction technique for MEMS heat-transfer system-level modeling is presented. A 3D heat-transfer solver, which is appropriate for MEMS thermal analysis, is implemented using the finite-difference method (FDM). The numerical models generated by the FDM solver can be reduced into low-order macromodels by an Arnoldi-based technique. This order reduction operation has been implemented as an automatic process. Because the macromodels are generated from the finite-element or the finite-difference (FEM/FDM) approximation of the original solid models, they preserve the original characteristics for most operation conditions. Also, since the orders of the macromodels are much less than those of their original FEM/FDM models, the computational costs are significantly reduced by about two to four orders of magnitude. This performance improvement thus makes the macromodels compatible for system-level or circuit simulations, which is essential for overall performance prediction. We also demonstrate that the macromodel results are in good agreement with the experimental results. The macromodels are also converted into the circuit component modules written by the hardware description language, and are inserted into a circuit simulator for system-level simulations with other circuit components.

Macromodeling of coupled-domain MEMS devices with electrostatic and electrothermal effects

In this paper, a macromodeling procedure for coupled-domain MEMS devices with electrostatic and electrothermal effects is presented. Transient fully-meshed simulations using finite-element or finite-difference methods (FEM/FDM) for coupled-domain systems require tremendous computational cost. Therefore, in this work, we use the Karhunen-Loeve/Galerkin technique for extracting the macromodels that capture the systems nonlinear behaviors, such as the structural dynamics, the squeeze-film damping and the electrostatic actuation. In addition, using the Arnoldi-based technique, the thermal macromodels are reduced from the linear FEM/FDM models. The system dynamic behavior is successfully reproduced by using these macromodels. Compared with the fully-meshed model, the computational cost of the macromodels is reduced by at least a factor of 500 with less than 1% error. Experimental verifications for the simulated results are also provided.