Wen-Yang Chang

A Large Area Flexible Array Sensors Using Screen Printing Technology

A flexible electronics sensor for large area sensing was developed using a screen printing technology with the thixotropy sol-gel materials to form the microstructure patterns on two polyimide (PI) sheets. A flexible sensor is 150times150 mm2, including posts, resistances, bumps, and electrode traces. The space between the top electrode and the resistance layer provided a buffer distance for large bending. Experimental results show that array microstructures have good morphological profiles at a screen speed of 10 mm/s, a squeegee pressure of 213 kPa, and a separation speed of 0.4 mm/s using the print-print mode. A membrane with a bump protrusion had a large displacement and a quick sensitive response because the bump provided a concentrated force of von Mises stress on the membrane center. For printing thick structures, diffusion effects and dimensional shrinkages can be reduced when a paste material with a higher viscosity is used. The results exhibit a potential for using in the flexible sensing and higher temperatures. In additional, the fabrication is the low cost and potential higher throughput in flexible electronics applications.

Flexible electronics sensors for tactile multi-touching.

Flexible electronics sensors for tactile applications in multi-touch sensing and large scale manufacturing were designed and fabricated. The sensors are based on polyimide substrates, with thixotropy materials used to print organic resistances and a bump on the top polyimide layer. The gap between the bottom electrode layer and the resistance layer provides a buffer distance to reduce erroneous contact during large bending. Experimental results show that the top membrane with a bump protrusion and a resistance layer had a large deflection and a quick sensitive response. The bump and resistance layer provided a concentrated von Mises stress force and inertial force on the top membrane center. When the top membrane had no bump, it had a transient response delay time and took longer to reach steady-state. For printing thick structures of flexible electronics sensors, diffusion effects and dimensional shrinkages can be improved by using a paste material with a high viscosity. Linear algorithm matrixes with Gaussian elimination and control system scanning were used for multi-touch detection. Flexible electronics sensors were printed with a resistance thickness of about 32 μm and a bump thickness of about 0.2 mm. Feasibility studies show that printing technology is appropriate for large scale manufacturing, producing sensors at a low cost.

A Flexible Piezoelectric Sensor for Microfluidic Applications Using Polyvinylidene Fluoride

A flexible technology for microfluidic applications using piezoelectric polyvinylidene fluoride (PVDF) and polydimethylsiloxane (PDMS) was developed. The flexible piezoelectric PVDF detects the flow rates and impulse pressure signal using piezoelectric characteristics. This study uses microelectromechanical systems (MEMS) technology to fabricate the sensing patterns on PVDF sheets, designs a molding transfer to form the microfluidic channels of the PDMS, and integrates them together. Experimental results show that PVDF films has good piezoelectricity at stretching ratio of 4, the flow rates ranged from 100 to 450 mL/min at dynamic controlling sensing, the miniature curvature radius is about 3 cm, and the cross section of the flexible microchannels is about 200 times 200 mum2. The feasibility studies show that molding transfer is an appropriate low-cost technology for fabricating the flexible piezoelectric channels. The PVDF can be easily manufactured using MEMS process because it has a good mechanical strength and electrochemical stability in polymers.

Phase Detection of the Two-Port FPW Sensor for Biosensing

This study reports the phase detection of the two-port flexural plate wave (FPW) sensor for designing and integrating the miniature system and provides a comprehensive methodology for portable using in the biosensor applications of severe acute respiratory syndrome coronavirus (SARS-CoV). The miniature system mainly utilizes the concept of the frequency divider that involves a divider, a time-based oscillator and a gate to reduce the high frequency, and the FPW sensor is fabricated using microelectromechanical systems (MEMS) technologies for producing a potable biosensing detector. The results demonstrate that the insertion loss decreased about -1.15% dB/degC, and the phase delay was about 2.05deg/(1000 cP). The phaseshift resolution was about 10 mV per degree, and the original frequency of 4.2 MHz was divided by 100 to reduce the frequency to 42 kHz. The SARS-CoV could be detected via the S protein binds to the human angiotensin-converting enzyme 2 (hACE2) as a functional receptor, which would cause the phase delay due to the combining of the antibody with the antigen. Therefore, the feasibility studies provide the information that phase detection is an appropriate low-cost technology via frequency divider for fabricating of the miniature biosensors.

Interface dynamics and mechanisms of nanoindented alkanethiol self-assembled monolayers using molecular simulations

The interface and nanoindentation mechanisms of alkanethiol self-assembled monolayers (SAMs) chemisorbed on a gold surface are investigated using molecular dynamics simulation. The mechanisms include the nanoindentation depths, the workpiece temperatures, the numbers of SAM layers, the length of united-atoms per chain, and the shapes of the indenters. The simulation results show that the disorder and the plastic mobility of SAM chains increased with increasing indentation depth. The relaxation force and the plastic energy almost linearly increased with increasing indentation depth. The disorder region after indentation at high temperature is larger than that at low temperature. The adhesive force shows a dependence on temperature during indentation. The potential energy decreases with increasing number of SAM layers. The structural morphologies of the SAMs were not affected at the third layers for SAM film with four layers. The maximum load quickly decreases for film with two SAM layers. The structures of the SAM can be easily tilted and bent when the united-atoms per chain length is long. The SAM atoms become more disorderly and the elastic recovery is smaller when the SAM length of the united-atoms per chain is long after indentation.

Nanoindentation response of nickel surface using molecular dynamics simulation

The mechanisms of dislocation nucleation on a nickel (Ni) (001) surface under nanoindentation behaviours are investigated using molecular dynamics simulation. The characteristic mechanisms include the molecular models of a thermal layer (TL) and thermal with a free layer (TFL), multi-step load/unload cycles, tilt angles and shapes of the indenter, and slip vectors. The model of a TL has higher reaction force than a TFL. The maximum forces of nanoindentation decrease with increasing time of the multi-step load/unload cycle. The indenter with the tilt angle has larger force to act on the molecular model than the indenter along the normal direction. The effect of the indentation shape is presented such that the conical tip has larger load force to act on the molecular model. The defects along Shockley partials on the (111) plane are produced during nanoindentation involving nucleation, glide and slip.

Flexible electronics sensors for tactile multiscanning

Flexible electronics sensors are designed and fabricated for tactile multiscanning and large area applications. The algorithm matrix is derived for multiscanning switch of tactile sensing. The thixotropy materials, bump, and resistance material are printed on the polyimide substrate. A gap between the top electrode and the resistance layers provides a buffer distance to increase the radius of curvature for large bending. Experiment results show that a flexible electronics sensor with a printed a resistance layer and an algorithm matrix performed the multiscanning functions. The membrane without a bump had a delay time of about 0.2 s at the transient response and took a longer time to reach the stable state after a force is applied. For printing thick structures on the flexible substrates, diffusion effects, and dimensional shrinkages can be reduced by using a thixotropy material with a high viscosity. The probability distribution density of the printed resistance values, a thickness of about 23.2 microm, at two standard deviations from the mean values is about 81.2%. Feasibility studies show that screen printing is appropriate for large area applications and is a low-cost technology for fabricating flexible electronics sensors.

Molecular dynamics on interface and nanoscratch mechanisms of alkanethiol self-assembled monolayers.

The interface dynamics and nanoscratched mechanisms of alkanethiol self-assembled monolayers (SAM) chemisorbed on a gold surface are investigated using molecular dynamics simulation. The characteristic mechanisms mainly include the nanoscratched depths, the workpiece temperatures, the scratched speed, the SAM chain lengths, and the shapes of the indenters. The simulation results show that the disorder and the plastic mobility of SAM structures increased with increasing nanoscratched depth. The scratched forces, the potential energy, the friction force, and the friction coefficient increased with increasing scratched depth. The larger scratched depth required a larger force to overcome the resistance, which leads to the increases in the friction force. The variations of the scratched forces and the friction forces after scratching at various temperatures are very similar. An increase in the scratched force, friction force, and friction coefficient with increasing scratched speed is observed. The scratched shape after scratching is clearer for a longer SAM chain. The SAM structures are easily tilted and bent when the chain length is longer. The reaction forces after scratching using a spherical indenter are higher than those after scratching using a Vickers indenter.

Phase Detection of the Two-port FPW Sensor for Biosensing

In this study, we provided a comprehensive methodology for designing and integrating miniature system in the biosensor application. In general, the network analyzer is commonly used for acoustic wave sensor measurement. However, it is remarkably inconvenient for portable use. Therefore, we presented a readout concept, which was focused on the miniaturization of the flexural plate wave (FPW) sensor system by integrating phase detection circuit. The miniature system includes a Wien-Bridge oscillator, a voltage following, a FPW device, a phase-locked loop, a phase detector, a MCU, and a LCM display. This work succeeded in integrating all the subsystems. And the core technology of the system is the phase detection function. The results showed the phase shift resolution is 10 mV/1deg

Using Pt Dopant and Sol Gel Technology for Sensitivity Enhancement of TiO 2 /SnO 2 Humidity Sensors

The sensitivity of the humidity sensor based on hybrid thin films of nanostructure TiO2/SnO2 with Pt dopant was successfully increased. The humidity-sensitive materials, TiO2/SnO2, were prepared by sol gel technology. The microstructure of the sensing film after calcination was investigated by the field emission gun scanning electron microscopy (FESEM) and revealed that the metal oxide hybrid had about 10 nm grain size. For studying the effect of Pt dopant on the humidity-sensitive responses, 1 ml to 10 ml of Pt standard solution was added into the colloidal solution. To compare the humidity sensor of Pt dopant with that of no Pt dopant, operational frequencies and electrode spacing were set under the relative humidity from 30% to 95% at the ambient temperature of 22degC. We demonstrated that adding Pt dopant remarkably enhanced the sensitivity of TiO2/SnO2 humidity sensor, and further decreased the TiO2/SnO2 resistance, which was 3.3 times lower than that without Pt dopant at the high humidity