Hanhua Feng

Electromagnetic energy harvesting from vibrations of multiple frequencies

A novel multi-frequency energy harvester has been designed and fabricated, which consists of three permanent magnets, three sets of two-layer copper coils and a supported beam of acrylic, while these coils are made of thin fire resistant 4 (FR4) substrates using a standard printed circuit board. The energy under the first, second and third resonant modes can be harvested, corresponding to the resonant frequencies of 369 Hz, 938 Hz and 1184 Hz, respectively. The maximum output voltage and power of the first and second vibration modes are 1.38 mV, 0.6 µW and 3.2 mV, 3.2 µW for a 14 µm exciting vibration amplitude and a 0.4 mm gap between the magnet and coils, respectively. The feasibility study results are in good agreement with the theoretical calculations and show promising application potentials.

Design, Fabrication, and Characterization of CMOS MEMS-Based Thermoelectric Power Generators

This paper presents the design, modeling, fabrication, and characterization of CMOS microelectromechanical-systems-based thermoelectric power generators (TPGs) to convert waste heat into a few microwatts of electrical power. Phosphorus and boron heavily doped polysilicon thin films are patterned and electrically connected to consist thermopiles in the TPGs. To optimize heat flux, the thermal legs are embedded between the top and bottom vacuum cavities, which are sealed on the wafer level at low temperature. A heat-sink layer is coated on the cold side of the device to effectively disperse heat from the cold side of the device to ambient air. The peripheral cavity is designed to isolate heat from the surrounding silicon substrate. Both simulation and experiments are implemented to validate that the energy conversion efficiency is highly improved due to the aforementioned three unique designs. The device has been fabricated by a CMOS-compatible process. Properties of thermoelectric material, such as the Seebeck coefficient, electrical resistivity, and specific contact resistance are measured through test structures. For a device in the size of 1 cm2 and with a 5-K temperature difference across the two sides, the open-circuit voltage is 16.7 V and the output power is 1.3 ¿W under matched load resistance. Such energy can be efficiently accumulated as useful electricity over time and can prolong the battery life.

Microfluidic device as a new platform for immunofluorescent detection of viruses

A bead-based microfluidic device was developed and demonstrated to achieve rapid and sensitive enzyme-linked immunosorbent assay (ELISA) with quantum dots as the labeling fluorophore for virus detection. In comparison to standard ELISA performed on the same virus, the minimal detectable concentration of the target virus was improved from 360 to 22 ng mL-1, the detection time was shortened from >3.25 h to <30 min, and the amount of antibody consumed was reduced by a factor of 14.3.

Characterization of heavily doped polysilicon films for CMOS-MEMS thermoelectric power generators

This paper presents the material characterization of boron- and phosphorus-doped LPCVD polysilicon films for the application of thermoelectric power generators. Electrical resistivity, Seebeck coefficient and thermal conductivity of polysilicon films doped with doses from 4 × 1015 to 10 × 1015 at cm−2 have been measured at room temperature. Specific contact resistance between polysilicon and aluminum is studied and nickel silicidation is formed to reduce the contact resistance. The overall thermoelectric properties, as characterized by the figure of merit, are reported for polysilicon doped with different doping concentrations. For the most heavily doping dose of 10 × 1015 at cm−2, figure of merit for p- and n-type polysilicon is found as 0.012 and 0.014, respectively. Based on the characterization results, a CMOS compatible thermoelectric power generator composed of boron- and phosphorus-doped polysilicon thermopiles is fabricated. When 5 K temperature difference is maintained across two sides of a device of size of 1 cm2, the output power is 1.3 µW under a matched electrical resistance load.

Si nanophotonics based cantilever sensor

We present design and simulation results of a novel nanomechanical sensor using silicon cantilever embedded with a two-dimensional photonic crystal microcavity resonator. Both of resonant wavelength and resonant wavelength shift could be measured as a function of various physical parameters such as applied force, strain, and displacement. Rather linear relationship is derived for strain and resonant wavelength shift. This new nanomechanical sensor shows promising features for biomolecules detection.

High-speed, high-optical-efficiency laser scanning using a MEMS-based in-plane vibratory sub-wavelength diffraction grating

In this paper, we report the modeling, fabrication and characterization of a microelectromechanical systems (MEMS)-based sub-wavelength diffraction grating under in-plane motion for high-optical-efficiency high-speed laser-scanning applications. The scanner utilizes in-plane rotational vibration of a planar microstructure to change the orientation of the diffraction grating, hence causing a diffracted laser beam to scan with less dynamic wavefront deformation as compared with conventional scanning micromirrors. An optical efficiency of more than 75% is experimentally achieved with a simple gold-coated binary sub-wavelength grating. When operated in air and electrostatically driven by 45 V dc bias and 84 V peak-to-peak ac voltages, the 1 mm diameter grating is capable of scanning an optical scan angle of 13.7° with a 632.8 nm wavelength incident laser beam at a resonant frequency of 20.35 kHz. The measured optical resolution is around 310 pixels per unidirectional scan.

Fatigue and Bridging Study of High-Aspect-Ratio Multicopper-Column Flip-Chip Interconnects Through Solder Joint Shape Modeling

This paper addresses fatigue and bridging issues by numerical analysis for an ultra-fine-pitch flip-chip interconnect that consists of multiple copper columns (MCC) and a solder joint. First, the processing flow is briefly presented, which enables prototyping of high-aspect-ratio (~6) copper columns, and hence, enhanced thermomechanical reliability of the interconnects. A public software, Surface Evolver (SE), has been used through this work to predict the solder joint geometry evolution. By integrating SE solder joint shape modeling, stress/strain analysis within ANSYS, and design of experiment (DoE) techniques as well, detailed numerical analysis has been conducted on the solder joint fatigue response to various factors such as the Cu-Solder wetting angle, loading direction, and solder geometry parameters. Finally, by applying the DoE techniques and the most updated features of SE, bridging risks of this interconnect with a fine pitch of 40mum is investigated, in which critical solder volume is calculated as a function of the interconnect geometry parameters. Based on these results, a solid basis for the design and processing of this advanced flip-chip interconnect has been established

Double-Layered Vibratory Grating Scanners for High-Speed High-Resolution Laser Scanning

A novel micromachined electrostatic double-layered vibratory grating scanner has been successfully developed for high-speed high-resolution laser scanning applications. This paper presents its design, modeling, fabrication, and measurement results. A comprehensive dynamic model considering the geometric nonlinearity of the platform suspension flexures is also proposed to predict the dynamic performance of the device at large scanning amplitudes. Compared with previously reported single-layered vibratory grating scanners, double-layered scanners - in which the diffraction grating and its driving actuator are located in different layers - have the potential to scan at large amplitudes and at high scanning speeds with large aperture sizes. We have demonstrated a prototype with a 2-mm-diameter diffraction grating which is capable of scanning at 23.391 kHz with an optical scan angle of around 33° and a resulting θopticalD product (product of the optical scan angle and diameter of the diffraction grating) of 66 deg mm.

A 2-DOF Circular-Resonator-Driven In-Plane Vibratory Grating Laser Scanner

In this paper, we present the design, modeling, fabrication, and measurement results of a microelectromechanical systems (MEMS)-based in-plane vibratory grating scanner driven by a two-degree-of-freedom (2-DOF) comb-driven circular resonator for high-speed laser scanning applications. Diffraction grating driven by a 2-DOF circular resonator has the potential to scan at large amplitudes compared with those driven by a one-degree-of-freedom (1-DOF) comb-driven circular resonator or a 2-DOF electrical comb-driven lateral-to-rotational resonator. We have demonstrated that our prototype device, with a 1-mm-diameter diffraction grating is capable of scanning at 20.289 kHz with an optical scan angle of around 25deg. A refined theoretical model with fewer assumptions is proposed, which can make the prediction of dynamic performance much more accurate.

Compact MEMS-driven pyramidal polygon reflector for circumferential scanned endoscopic imaging probe

A novel prototype of an electrothermal chevron-beam actuator based microelectromechanical systems (MEMS) platform has been successfully developed for circumferential scan. Microassembly technology is utilized to construct this platform, which consists of a MEMS chevron-beam type microactuator and a micro-reflector. The proposed electrothermal microactuators with a two-stage electrothermal cascaded chevron-beam driving mechanism provide displacement amplification, thus enabling a highly reflective micro-pyramidal polygon reflector to rotate a large angle for light beam scanning. This MEMS platform is ultra-compact, supports circumferential imaging capability and is suitable for endoscopic optical coherence tomography (EOCT) applications, for example, for intravascular cancer detection.