Kerwin Wang

A capacitance level sensor design and sensor signal enhancement

This paper introduces a novel fringe field capacitive sensor. To enhance the sensor signal, various sensor electrode design strategies and a surface modification method are introduced, discussed and compared. The sensors are characterized by both simulations and experiments. The experiment results demonstrate the sensor capability of water level measuring. In addition, fringing field sensor of the field strength across the target by the dielectric strength can be used to measure the dielectric constant or component of a solution. The experiment results show that nitrogen plasma surface modification can improve the sensitivity from 69pF/mm to 97pF/mm.

Electrowetting enabled magnetic particle immunoassay with on-chip magnetic washing

This work demonstrates a unique DMF (Digital Microfluidics) immunoassay chip with 17 microelectrodes in an area of 6×6 mm2, which manipulates both electric and magnetic fields, to carry magnetic particle based immunoassay. Superparamagentic particles act as a label for the analyte in measurement and Hall sensor response indicates the presence of target analyte. This report describes magnetic washing (pulling of unbound magnetic beads) on DMF chip without any external magnet or additional component. The chip has a novel fabrication process where 600×600 micron electrodes are interspaced with a gap of 22 micron. The movement of the droplet on the chip is controlled automatically by using FPGA Altera DE0.

Multi-step three dimensional micro assembly for a flexible LED display

This paper presents a novel multi-step three dimensional microassembly of passive-circuit-mesh, conductive beads, and LED chips to fabricate a flexible, bright, and wide viewing angle display. A novel flexible display architecture is proposed. To deliver this design, we focus our efforts on the multi-batch assembly integration. A 3-by-3 light-emitting diode array with a chip size of 610µm by 610µm by 90µm is successfully prototyped with device fill factor up to 37.97%. It yields a 990µm squared monochromatic pixel.

Position determination of a ball grid array by automated optical inspection method

This paper introduces a novel automated optical inspection (AOI) method to measure the positions and diameters of micro-solder balls of a ball grid array (BGA). The method is focused on the refinement of optical configuration, image acquisition platform design to improve the time efficiency of AOI. We use a white LED ring as a light source. It is combined with the platform. The system can perform multiple image processing and object detection steps to locate the center of each ball. This paper also presents two methods to estimate the diameters of the balls. A dummy BGA, consists of misaligned solder balls, are assembled to a conductive substrate to evaluate the platform. Test result shows that the platform is capable of performing continuous image acquisition of a 15fps, 640 × 480, 8-bite grayscale video.

Using a canny-edge-detection based method to characterize in-plane micro-actuators

This paper developed an automatic optical inspection (AOI) technology for characterizing the motion amplitude and the vibration mode shape of in-plane micro-actuators. The technology involves a multi-stage image process method. It includes an image contrast enhancement step and a Canny edge detection method. To evaluate this approach, a rotational electrostatic actuator has been prepared for testing. This actuator performed low contrast optical micrographs under first vibration mode. The testing result shows that the technology can handle low contrast microscopic images quite well. The suggested method successfully provides quantitative information to identify the vibration amplitudes and mode shape of the tested actuator with a space resolution of 0.46μm/pixel.

Using a self-organized metallic microsphere array to enhance image brightness and contrast for volumetric 3D displays

This paper presents a self-organized microsphere array to enhance image brightness and contrast of a volumetric 3D display. This display, using a swept-volume technique, exhibits 3D images by 2D projective-image-frame sweeping. These images are projected from a programmable LED array and a focusing lens system. The sweeping screen consists of a self-organized metallic microsphere array, which acts like a reflective screen to enhance the image brightness and contrast from a multitude of viewing directions. The voxels can be controlled by manipulating the frequency of flashing LEDs and the sweeping screen. The experiment results successfully demonstrate 500 voxels in a 6cm3 tetragonal imaging space. This paper also shows the effectiveness of using a metallic self-organized microsphere array to increase the brightness of voxels. Compared to the voxels generated by original reference screen, it can increase image brightness up to 300%.

Deterministic three-dimensional micro-assembly in parallel

This paper introduces a novel deterministic three-dimensional micro-assembly method to tackle the difficulty of micro-part assembling at unstable equilibrium region. We design, characterize and manufacture an parallel assembly system, which is capable of connecting micro-parts from almost arbitrary direction into desired structures in batch processes. This paper also introduces a non-contact method to measurement the surface adhesion forces among parts, donor and receiver substrates. Five successive 3D micro-assembly processes have be tested with yield ratio investigation to demonstrate this technology. Table 1. A comparison of this study to some published three-dimensional assembly technologies

Vibration Feature Extraction Using Audio Spectrum Analyzer Based Machine Learning

To develop a tool to identify different mechanical vibrations, this paper presents a novel instrument to extract the vibration features of rotating machinery. The instrument consists of an audio spectrum analyzer, a signal processing circuit and a single-board computer. This architecture offers a cost-effective solution for machine status monitoring and analyzing. The experiment results show that the training data collected from audio spectrum analyzer can work well with both KNN and SVM methods to construct accurate machine-learning models with the 95.8% and 97.2% accuracy respectively.

Capacitor discharge sintering with silver-nickel nano-composite in the interconnection of thermoelectric generators

This paper presents a capacitor discharge sintering process with a homemade silver-nickel paste for thermoelectric element interconnections. The paste is a 75 nm silver/nickel composite mixture. Without using any specific atmosphere control, the capacitor discharge is capable of nanoparticle sintering with time-efficient process at room temperature. A 0.01 F capacitor is serially connected to the sample and charged to 10 V (0.5 Joule) for the sintering process. To evaluate the conductivity of the sintered composite, the conductive material is screen-printed on an Al2O3 ceramic substrate; it forms a rectangular tunnel to bridge two silver electrodes. After sintering process, the resistance of the screened conductive pass-way is dropped from 9.47 Ω to 0.35 Ω. The bonding strength and high temperature resistance test results of the sintered composite is also presented in this paper. Without generating a lot of heat, the sintering process can be applicable to flexible electronics.

Filling through-silicon vias with conductive ferromagnetic silver-iron composite

This paper demonstrates a novel magnetic induced injection method of ferromagnetic composite to build electrically conductive through-silicon vias (TSVs). The through conductive via is filled with conductive ferromagnetic composite by attractive magnetic force. The composite is made of the mixture of silver and iron nanoparticles. SU-8 2002 is covered on the side walls of via as an insulating material by a low vacuum suction. After thermal curing process, the dielectric layer can possess an electric field as high as 5×106 V/cm. All of the fabrication steps are completed below 100 C. The TSVs can allow a current density of 6×107 A/m2. The leakage current is 2×10-6 A at 50 V. After DC electrical sintering, the resistances of each TSV is less than 0.85 Ω.