Yigui Li

Fabrication and analysis of high-performance piezoelectric MEMS generators

In this paper, we have designed a fabrication process for microgenerators by bonding a piezoelectric ceramic Pb(Zr,Ti)O3?(PZT) plate to a silicon on insulator (SOI) wafer. The key techniques of the process include the low-temperature bonding technique using conductive epoxy resin, thinning of the bulk PZT using mechanical lapping and wet-etching combined method, and the micromachining of bulk ceramics by dicing. Through the development and optimization of the process, a piezoelectric MEMS power generator array was successfully fabricated. The typical device is selected to characterize the output performance of the microgenerators, while the composite beam dimension of PZT and silicon layer is about 3080 ?m???800 ?m???31 ?m and the dimension of Ni proof mass is about 900 ?m?? 800 ?m???450 ?m. The experimental results show that the output voltage, output power and power density of this device are 2.72 VP-P, 11.56 ?W and 28?856.7 ?W cm?3?at the resonant frequency of 514.1 Hz when it matches an optimal resistive load of 70 k? under the excitation of 1g acceleration. The output performance of this device is higher, compared with that of other reported MEMS power generators, which demonstrates that this novel technique has great potential to fabricate high-performance piezoelectric MEMS energy harvester.

A generator with nonlinear spring oscillator to provide vibrations of multi-frequency

A piezoelectric generator with nonlinear spring oscillator is proposed to provide multiple resonant modes for operation and improve conversion efficiency. In order to scavenge the vibration energy of multiple frequencies from a certain vibration source, two types of nonlinear springs have been employed and tested. The maximum output power of 5, 17.83, and 23.39 μW for the nonlinear spring of 8.3 N/m with 1 g acceleration has been obtained under the resonant frequency of 89, 104, and 130 Hz, respectively. Its total output power of 46.22 μW is obviously larger than the one of 28.35 μW for traditional second-order spring-mass linear system.

X-ray lithography mask fabricated by excimer laser process

LIGA process technique is a three-dimensional micromachining technology which is applied to fabricate 3D micromechanical parts. Because the LIGA process requires LIGA mask for deep-etch X-ray lithography, the mask fabrication is a complex technique. The use of micro optical systems in commercial applications (as sensors or in telecommunication) is not only depending on the performance but also on the price of the system. It is highly dominated by fabrication and assembly costs. In order to solve this problem, many efforts have been made in the world. Direct laser patterning of absorber thin films of LIGA mask allows the possibility of rapid prototyping and low cost manufacture of X-ray lithography mask. Excimer laser mask projection techniques have been used in order to directly manufacture LIGA mask for X-ray lithography. The mask pattern with circles structures with 25µm pitch have been fabricated by sequential direct laser ablation of thin gold film using mask projection techniques. This paper describes the X-ray mask design and fabrication processes in details. The fabricated LIGA mask is used as a pattern for x-ray exposure onto a polymethyl-methacrylate (PMMA) resist. A fine micro structures of PMMA in a low cost and a short fabrication period is obtained using the mask. It is confirmed that such LIGA mask is important for rapid prototyping in the areas of medical and biosensors.

X-ray lithography fabrication of Poly-L-Lactides microstructures

The lubrication technique to generate the PLLA microstructures with the very smooth surface is demonstrated. The function of X-ray on PLLA polymer material is breaking the PLLA polymer main chain and generating intermediates which can be degraded further and finally dissolved by the solvent interaction. In this paper, we have illustrated a novel micromachining method for PLLA polymer material. Various polymer structures are fabricated using this novel X-ray lithography technique. The data of exposure doses against the processed depth on the PLLA sheet is shown

Novel device of passive and fixed alignment of optical fiber using SU-8 photoresist

In the microoptics field, precise alignment is very important to reduce the coupling losses in optical links. In this paper, a novel device of passive and fixed alignment of optical fiber is proposed. The rectangular V-groove formed by one sidewall of SU-8 resist and the substrate is used to position the optical fiber, and the leaf spring with flexure hinge clamps it. The spring is fabricated by the sacrificial layer technique. The clamping force provided by the spring acts on the upper semi-circle of the optical fibers cross section, so that the device need not use the additional cover on the optical fiber to perform the vertical location and the final fixing. It has simple structure and process, and is convenient to assemble and integrate with other microparts. The coupling of two optical fibers using the devices in our experiment has less than 1.5dB insert loss.

Piezoelectric energy harvesting from ultrasonic vibration in fluid environments

This paper presents the development of piezoelectric energy harvesting from ultrasonic vibration in fluid environments. The ultrasonic is emitted by the transducer in the ultrasonic cleaner and propagated in fluid environments which causes the piezoelectric bimorph bending up and down, thus the PZT layer generates electrical charges. Some preliminary experiments including output voltages in different fluid environments and in draft angles of the piezoelectric device relative to the level surface have been investigated. The experimental result shows that the output voltages vary with the fluid environment, the maximum voltage is generated in clean water and then physiological saline and sea water. Additionally, different draft angle lead to various output voltages with the maximum voltage been present at 45°to 60°or 105°to 120°region and the minimum value at 90°in the same fluid environment. Some possible causes about this phenomenon are also analyzed.

Study on Fabrication of Polymer Electrostatic Comb-drive Actuator by DXRL Technique

This paper reports a novel approach to fabricate poly-methyl-meth-acrylate (PMMA) electrostatic comb-drive actuator using the deep X-ray lithography (DXRL) technique. The designed actuator consists of 140 units of interdigitated parallel capacitors with the finger gap and width being 2mum and 4mum respectively, and the thickness of the structure is 200 mum, which makes the aspect ratio 50:1. A brief description of the design and simulation with ANSYS are also presented in this paper

Microfabrication of PLLA polymer by x-ray lithography

Poly-L-Lactides(PLLA) is a biodegradable polymer material which is sensitive to X-ray as a resist and free of stress crack formation. The fabrication technique to generate the PLLA micro structures with the very smooth sidewall is demonstrated. The function of X-ray on PLLA polymer material is breaking the PLLA polymer main chain and generating intermediates which can be degraded further and finally dissolved by the solvent interaction. In this paper, we have illustrated PLLA polymer is a new resist material for x-ray lithography and can be developed in alkaline developers after x-ray exposure. Various polymer structures are fabricated using this novel X-ray lithography technique. The PLLA structure sidewall obtained by this process is very smooth compared with that of other micromachining methods. The result after 0.02Ahour X-ray exposure dosage and developed in NaOH (1N) developer for 1 hour at room temperature shows the smooth sidewall by consuming PLLA to generate lactic acid salts. The depth of the micro PLLA structure is about 150μm and the RMS value of the sidewall roughness was within 200nm. The data of exposure doses against the processed depth on the PLLA sheet is shown.

Fabrication and test of square prism shaped dye micro laser based on photoresist molding process

A dielectric microcavity of dye doped polydimethylsiloxane (PDMS) is fabricated by SU-8 photoresist molding technique. The molding technique by fabricating a solid polymer dye microcavity laser is described in detail. The dye laser microcavity resonators properties are confirmed

The fabrication and test of a square prism shaped dye micro laser based on the SU-8 molding process

A dielectric micro cavity of dye doped polydimethylsiloxane (PDMS) is fabricated by the SU-8 photoresist molding technique. The orthogonal array was adopted in our experiments for improving the pattern quality and analyzing the interaction among the process parameters. The molding technique by fabricating a solid polymer dye micro cavity laser is described in detail. The dye laser operation of the micro cavity has been confirmed.