Chun Sheng Yang

Fabrication of Metal Micro Needle Array by LIGA Process

Polymer materials, such as PMMA and PDMS, have been of great interest in the research and development of MEMS recently due to their relatively low cost and easy process. In this research, we are trying to fabricate Ni Micro needle array from PMMA master by through PDMS mold based on multi-mold transformation technology. The fabricated micro nickel needles array is 900 microneedles in 1 cm2 chip area and the height of each needle is about 150um.

Bulk PZT thick film preparation on silicon wafer and its application for MEMS power generator

The paper reports on the PZT thick films preparation method by bonding bulk PZT on Si and then lapping PZT to suitable thicknesses. Epoxy resins with preferable thermostability were used as the intermediate adhesive layer in bonding process. A tight bonding of more than 10MPa was attained at suitable gradient bonding temperatures in an oven which were from 30 oC up to 105 oC according to 15 oC per thirty minutes and holding for more than 3h at 105 oC, and a pressure of more than 0.05MPa. Some properties of the prepared PZT thick films were tested. Finally, a piezoelectric MEMS power generator was fabricated by using the described techniques of PZT thick films preparation on silicon. The maximum output voltage under the resonant operation was measured.

Evaluation of Properties of Lapped PZT Ceramics and Silicon Cantilever Based on Eutectic Bonding and Dicing Process

Piezoelectric sensor can produce voltage when deflected (function as an energy harvester) while piezoelectric actuator can deflect when a voltage is applied. Different device applications have different requirements on the thickness and in-plane geometry of the Lead Zirconate Titanate(PZT) piezoelectric layers and thus have their own processing difficulties. In this paper, PZT-Au-Si cantilever is fabricated by eutectic bonding and dicing process.The properties of lapped PZT ceramics and silicon cantilever is also evaluated. The PZT-Au-Si cantilever applications for both piezoelectric actuators and energy harvesters have been confirmed.

Biodegradable junctionless transistors with extremly simple structure

Biodegradable junctionless transistors with extremely simple structure are fabricated at room temperature. The free-standing sodium alginate (SA) membrane is used as both a substrate and the dielectric layer for the transistors. The source/drain electrodes and the channel region are made of one single patterned Al:ZnO (AZO) thin film. The proposed transistors can be operated at a low voltage of 1 V. Dissolution tests of those transistors in deionized water demonstrate their completely physical transience within 60 minutes. The operation mode of such transistors can be effectively tuned from depletion mode to enhancement mode by varying the thickness of the AZO film. Moreover, a resistor-loaded invertor was demonstrated by connecting those transistors in series with a 3 MQ resistor.

Enhanced Flexible Tubular Microelectrode with Conducting Polymer for Multi-Functional Implantable Tissue-Machine Interface

Implantable biomedical microdevices enable the restoration of body function and improvement of health condition. As the interface between artificial machines and natural tissue, various kinds of microelectrodes with high density and tiny size were developed to undertake precise and complex medical tasks through electrical stimulation and electrophysiological recording. However, if only the electrical interaction existed between electrodes and muscle or nerve tissue without nutrition factor delivery, it would eventually lead to a significant symptom of denervation-induced skeletal muscle atrophy. In this paper, we developed a novel flexible tubular microelectrode integrated with fluidic drug delivery channel for dynamic tissue implant. First, the whole microelectrode was made of biocompatible polymers, which could avoid the drawbacks of the stiff microelectrodes that are easy to be broken and damage tissue. Moreover, the microelectrode sites were circumferentially distributed on the surface of polymer microtube in three dimensions, which would be beneficial to the spatial selectivity. Finally, the in vivo results confirmed that our implantable tubular microelectrodes were suitable for dynamic electrophysiological recording and simultaneous fluidic drug delivery, and the electrode performance was further enhanced by the conducting polymer modification.

Comparison of Bonding of Bulk PZT to Silicon by Intermediate Glass Layer and by Intermediate Au Layer

As an energy conversion material, piezoelectric ceramic lead zirconate titanate (PZT) has been used in a wide range of areas. And a PZT wafer bonding with a silicon wafer technology is a promising method to fabricate micro-sensors and micro-actuators using well-established silicon machining techniques. In order to obtain the excellent piezoelectricity and suitable thickness from the bulk PZT, a method is presented. It is to bond a bulk PZT onto a silicon wafer via an intermediate layer. In this paper, two bonding methods are presented. One is to bond a bulk PZT with a silicon wafer by anodic bonding technique using a thin glass film as the intermediate layer. The other is to bond a bulk PZT with a silicon wafer by eutectic bonding using a thin gold film as the intermediate layer. The glass film is 2µm in thickness, deposited by sputtered method. Anodic bonding conditions are: 0.8MPa in pressure, 500 oC in temperature, 250V in voltage and different bonding time. The bonding strength test shows that the maximum bond strength is 13.93 MPa when the bonding time was 60 min. It is void-free structure in the interface of the PZT-Glass-Si structure. The gold film is 1.6µm in thickness, deposited by evaporation method. The eutectic bonding conditions are: 0.8MPa in pressure, 500 oC in temperature, and different bonding time. The bond strength of the PZT-Au-Si structure was tested and the maximum value was 13.19 MPa when the bonding time was 60 min.

Platinum Resistance Microsensor for Cryogenic Temperature Measurement

Platinum resistance temperature sensor is applied to the temperature range higher than 200K currently. Through studying the principle of platinum temperature sensor, the platinum resistance temperature microsensor can be used in the temperature region between 10K and 200K was studied. It employs symmetrical turn back structure, which effectively avoids the inductance caused by alternating current (AC). Fabrication process based on MEMS technology was illustrated. The platinum film was obtained by direct current (DC) magnetron sputtering deposition and the platinum resistance temperature microsensor was fabricated with 200nm thickness layer film. The relationship between resistance and temperature of platinum microsensor was tested by Quantum QD PPMS instrument. When T>30K and T<30K, TCR of platinum microsensor could achieve 16490ppm/K and 6430ppm/K respectively. Thus, the microsensor can be used as temperature sensing element between 10K and 200K in the cryogenics.

Two-Dimensional Motor Based on Surface Acoustic Wave

With the development of high precision processing, the miniaturization demand of motors with super-precision positioning and simple fabrication become an urgent problem. This paper illustrates a surface acoustic wave (SAW) motor for two-dimensional positioning. The SAW motor include a SAW stator and a slide. In order to realize the two-dimensional moving, four Interdigital Transducer (IDTs) are fabricated on the four directions of a 0.5-mm thick, 128°YX- LiNbO3 substrate. Comparing the aluminum material, the copper material selected to be used as IDT in our experiment has many advantages. Each of the four copper IDTs has 10 straight finger pairs in a simple repeating pattern, the IDT aperture is 10mm and the pitch is 400μm. The SAW stator is fabricated by the lift-off process. The dimension of the device is 29mm (width) X29mm (length). The slide consists of three ruby balls with the diameter of 1mm and an plastic disc with the thickness of 0.5mm and the diameter is 8mm. With the four radio frequency driving sources, two-dimensional motion is possible. The maximum speed of the slide that was placed on the SAW propagating surface was 5mm/s when the applied driving power was 28W and the applied driving frequency was 9.6MHz. The experiments indicate the two-dimensional motor based on SAW would be applicable to miniature motor and improve the resolution.

Fabrication of Piezoelectric Vibration Power Harvester using Bulk PZT

Piezoelectric energy harvester with high output and low resonant frequency is required in wireless sensors and portable devices. It can be fabricated by bonding of the bulk PZT ceramics with excellent piezoelectric properties to the Si wafer. Firstly, the basic design principles of piezoelectric energy harvester were analyzed. Then, the novel process flow to manufacture piezoelectric energy harvester using bulk PZT was explored. Using 2µm Au layer as the bonding layer, the bulk PZT was bonded to Si wafer at the temperature of 5500C for 2 hours. With the lapping technique, the thickness of bulk PZT is reduced from 300µm to 60µm. KOH was used to etch the backside of Si from 500µm to 20µm as the supporting layer of the piezoelectric beam. The last procedure was to dice the wafer into many cantilevers with different length or width. One of PZT piezoelectric cantilevers was tested using a mechanical shaker, by applying a sinusoidal oscillation at different frequencies. The resonant frequency is 815 Hz, and the voltage output is around 632 mV at 0.5g. The result shows that the sample has excellent ability to harvest energy of vibration and the novel bonding technology is quite feasible.

Fabrication and Performance of Piezoelectric MEMS Generators Using Bulk PZT Films

In this paper, a MEMS-based piezoelectric energy harvester is studied and the whole fabrication process is discussed. The generator structure of composite cantilever with nickel metal mass is devised. MEMS related techniques such as UV-LIGA, ion etching, XeF2 dry etching, wet chemical etching are developed to fabricate the device. This key process includes the bonding a bulk PZT to a Si wafer, and thinning the PZT down to about 15µm in thickness after bonding by mechanical lapping and polishing method. Epoxy resin with a thickness of about 4µm is used as the intermediate adhesive layer. The formed generator is measured on vibration testing setup. The energy under the first resonant mode can be harvested, corresponding to the resonant frequency of 810 Hz . The maximum output voltage under the resonant operation is about 1.23Vp-p.