Jin Xie

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.

A MEMS rotary comb mechanism for harvesting the kinetic energy of planar vibrations

A capacitive energy harvester based on in-plane rotary combs is proposed and studied. It is capable of collecting kinetic energy from planar ambient vibrations for low frequency operation. The design and simulation of capacitance among rotary combs, ladder spring and resonant frequency of the whole rotary comb energy harvester are presented in this paper. This device is fabricated in SOI (silicon-on-insulator) wafers by deep silicon etching technology. The dimensions of the prototype are about 7.5 mm × 7.5 mm × 0.7 mm. A maximum measured output power in air for vibrations of 0.5 g, 1 g, 1.5 g, 2 g and 2.5 g is 0.11 µW, 0.17 µW, 0.24 µW, 0.3 µW and 0.35 µW, respectively, when the loading resistance matches the parasitic resistance of 80 MΩ at the resonant frequency of 110 Hz. In order to reduce the air damping effect, the prototype is packaged by having a metal cap to form the vacuum level of 3 Torr. The testing results in vacuum level of 3 Torr show that the resonant frequency decreases from 110 Hz in air to 63 Hz, and the maximum electrical output power at 0.25 g is 0.39 µW.

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.

Novel piezoelectric actuation mechanism for a gimbal-less mirror in 2D raster scanning applications

In this paper, we present the design, fabrication and measurement results of a 2D scanning mirror actuated by 1 × 10 piezoelectric Pb(Zr,Ti)O3 (PZT) cantilever actuators integrated on a thin silicon beam. A combination of bulk silicon micromachining based on a silicon-on-insulator (SOI) substrate and thin-film surface micromachining on a 5 µm thick Si device layer is used to fabricate the device. Multi-layers of Pt/Ti/PZT/Pt/Ti are deposited as electrode materials. A large silicon mirror plate (5 mm × 5 mm) and a 1 × 10 PZT cantilever array arranged in parallel are formed after the backside release process. The ten PZT cantilever actuators are electrically isolated from one another. The device can operate in three modes: bending, torsional and mixed (or combinational) modes. In bending mode, the first resonant frequency was measured to be 30 Hz and an optical deflection angle of ±8° was obtained when all ten cantilevers were actuated at 9 Vpp. In torsional mode, the resonant frequency was measured to be 89 Hz and an optical deflection angle of ±4.6° was obtained by applying a gradually declining ac voltage started at 8 Vpp to two sets of actuators, where each set comprises five cantilever actuators of the said 1 × 10 array, i.e. 1–5 and 6–10. A 2D raster scanning pattern was achieved in the mixed mode when the bending mode was carried out by cantilever actuators of 4–7 and the torsional modes were exercised by two different sets of cantilever actuators, i.e. 1–3 and 8–10, under opposite biasing direction. This mixed mode operation mechanism demonstrates the first 2D raster scanning mirror-driven beam actuators.

A high-sensitivity biaxial resonant accelerometer with two-stage microleverage mechanisms

This paper presents a design and experimental evaluation of a micro-electro-mechanical system biaxial resonant accelerometer with two-stage microleverage mechanisms. The device incorporates two pairs of double-ended tuning fork resonators coupled to a single proof mass. The two-stage microleverage mechanisms possess a higher amplification factor than single-stage microleverage mechanisms, so that the proposed accelerometer has a high level of sensitivity. In addition, a low level of cross-axis sensitivity is realized because of the decoupling beams. The accelerometer is theoretically analyzed and then simulated in the system level by the finite element method. The device is fabricated in a silicon-on-insulator wafer. The experimental results demonstrate that the average differential sensitivity of the resonant accelerometer is 275 Hz g?1 at a resonant frequency of 290?kHz under a polarization voltage of 5?V. The measured cross-axis sensitivity is lower than 3.4%.

Design and optimization of wafer bonding packaged microelectromechanical systems thermoelectric power generators with heat dissipation path

A new concept of microelectromechanical system based thermoelectric power generator (TPG) with unique heat dissipation path is investigated in this study. By using solder based wafer bonding technology, the authors can bond three pieces of wafers to form vacuum packaged TPG. According to the finite element method and analytical modeling results, the output power per area of device is derived as 68.6μW∕cm2 for temperature difference of about 6°C between two ends of thermocouple junctions. It shows that the proposed device concept is an effective and low cost approach to enhance the output voltage.

The fine patterning of diamond thin film

Due to its unique properties (high nicchanical strength, low friction coeficicnt, high wear rcsistance and cheniical incrtncss), diamond is an esccllcnt candidate matcrial for micromechanical application. One of the important considerations in the fabrication of diamond MERlS is fine patterning. Direct patterning of diamond is difficult due to its extreme resistance to chemical attack. An alternative approach is to grow a prepattemcd film through selective nucleation. However, nucleation selectivity (<IO5) reported in previous were not high enough to realize patterning in mixon scale. The authors have developed a i x w l sc!cctia dcposition method in which a high sclectivity (5x lo6) was achieved and perfcct diamond patterns with narrowest width I . 8 p i were obtained at the first tinic[I. ~n tlie present paper, we rcport tlie rcccnt dcvclopmcnt in the fabrication of diamond micromotor structure bascd on this patterning proccss as well as boron-doping technique.

Compact electrode design for an in-plane accelerometer on SOI with refilled isolation trench

A two-axis in-plane capacitive accelerometer fabricated on silicon-on-insulator (SOI) is developed. With each stationary electrode separated to two sub stationary electrodes by refilled isolation trench, the presented accelerometer has compact differential capacitance electrodes to improve capacitance sensitivity per sensing area. In addition, the overlap area-changed capacitor enables good linearity and low damping coefficient.

Microfabricated endoscopic probe integrated MEMS micromirror for optical coherence tomography bioimaging

In this paper, we present a miniaturized endoscopic probe, consisted of MEMS micromirror, silicon optical bench (SiOB), grade index (GRIN) lens, single mode optical fiber (SMF) and transparent housing, for optical coherence tomography (OCT) bioimaging. Due to the use of the MEMS micromirror, the endoscopic OCT system is highly suitable for non-invasive imaging diagnosis of a wide variety of inner organs. The probe engineering and proof of concept were demonstrated by obtaining the two-dimensional OCT images with a cover slide and an onion used as standard samples and the axial resolution was around 10µm.