Sensors & Actuators: A. Physical (v.108, #1-3)

PREFACE (1).

Strongly pervoskite (1 0 0)-oriented lead zirconate titanate (PZT) films were prepared by the electrostatic spray deposition (ESD). The microstructure and crystalline-granular texture of the films were investigated by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. The films deposited at substrate temperature of 25 °C and 100 °C were found to have the same crystallite-size distribution around 150–200 nm. With given properties of the spray cloud and the precursor solution, well-crystallized PZT thick films with dense microstructure can be obtained at low deposition temperature. The relative dielectric constant of the 2 μm thick ESD-deposited PZT films with sol–gel PZT films as intermediate layers was as high as 960. The films also exhibit excellent remanent polarization and coercive fields of 12.5 μc/cm2 and 32 kV/cm, respectively.
Keywords: PZT; Film; Electrostatic spray deposition; Microelectromechanical system; MEMS;

In this paper, a microheater actuated by a Pb(Zr,Ti)O3 microcantilevers array was designed for parallel high density data storage with high data rate and long lifetime. The mechanisms of thermomechanical data writing and heat dissipation from the microheater were studied. The heat conduction through the cantilever to the base was found to be the dominant fact of heat dissipation, and the effects of the other two modes, convection and radiation, can be omitted. A 3D model of the microcantilever was built in ANSYS 5.7 and several simulations of the microheater thermal behavior were executed. As a result, an electrical pulse of 15 V in level, 0.2 μs in duration with a period of 10 μs is found to be a promising driving signal for the designed structure. The top temperature of the tip is about 200 °C, which is believed to be effective for softening polymethylmethacrylate film. Within the period of 10 μs, the tip can be cooled down to near the room temperature.
Keywords: Microheater; Simulation; High density data storage; Thermomechanical writing;

A microchip for electroporation of primary endothelial cells by Yu-Cheng Lin; Min Li; Chun-Sheng Fan; Li-Wha Wu (12-19).
Electroporation (EP) is a technique with which DNA molecules can be delivered into cells suspended in a chamber using high electric field pulses. We have utilized the MEMS technology to fabricate the EP microchip. In this device, the interdigitated electrodes should provide higher electric field on the chip surface and cells could be manipulated in situ without detachment if adherent cells were used for EP. Moreover, this EP microchip overcame the use of high voltage and the excess heat generated during electroporation, which are the main drawbacks of the current electroporation technology. One primary cell type, human umbilical vein endothelial cells (HUVEC), and two different cell lines, Huh-7 cell (human hepatocellular carcinoma cell line) and 293T cell (human embryonic kidney cell line) were used to test this device. Experimental results show that this EP microchip could successfully deliver green fluorescent protein (GFP) genes into these cells. In the case of primary HUVEC, the survival rates were greater than 31%, and the transfection rates were about 13–36% based on the number of surviving cells under the applied voltage ranging from 2 to 8 V. In summary, this EP microchip should provide many potential applications for gene therapy, particularly those using primary cells for gene delivery.
Keywords: Electroporation; Gene therapy; Gene transfection; Primary cell; MEMS;

Nano-indentation method for the measurement of the Poisson’s ratio of MEMS thin films by Jong-Hoon Kim; Soon-Chang Yeon; Yun-Kwang Jeon; Jeong-Gil Kim; Yong-Hyup Kim (20-27).
A nano-indentation method is presented to measure the Poisson’s ratio of thin films for micro-electro-mechanical systems (MEMS) applications. Double-ring shaped specimen is designed to facilitate the measurement of the Poisson’s ratio. The Poisson’s ratio can be obtained through analyzing the load–deflection data of the double ring specimen subjected to nano-indenter loading. The compatibility to the surface micromaching makes in situ measurement of the Poisson’s ratio feasible. The Poisson’s ratio is obtained as local quantity, not an average value over the wafer, due to the small size of the specimen. To validate the proposed method, the Poisson’s ratio of LPCVD polysilicon with thickness of 2.33 μm is measured. Experimental results reveal that the Poisson’s ratio of the polysilicon film is 0.254±0.0125.
Keywords: Poisson’s ratio; Nano-indentation; MEMS; Thin film; Material properties;

Polysilicon micromachined fiber-optical attenuator for DWDM applications by X.M. Zhang; A.Q. Liu; C. Lu; F. Wang; Z.S. Liu (28-35).
A high performance variable optical attenuator has been developed and its optical and mechanical models have also been established. The attenuator is fabricated by silicon surface micromachining technology and is then integrated with two single mode optical fibers that act as optical input and output. The attenuation is obtained by placing a 40  μm×40  μm gold-coated micromirror into the light path between two fibers. The attenuator has an overall layout size of 0.6  mm×1  mm (not including the fibers). It has 1.5 dB insertion loss and 45 dB attenuation range, and requires <8 V driving voltage to sweep the whole attenuation range. The specifications are promising for DWDM applications. The optical and mechanical models have been developed to fully characterize the VOA and therefore simplify the further design and optimization.
Keywords: Variable optical attenuator (VOA); Optical MEMS; DWDM; Fiber optics communication;

The mechanical modeling and experimental study of radio frequency (RF) micromachined capacitive switches is presented in this paper. The micromachined capacitive switch, fabricated using bulk and surface micromachining techniques, consists of a thin metal membrane suspended over a center conductor, and fixed at both ends to the ground conductors of a coplanar waveguide (CPW) line. A static mechanical model considering complicated geometry and the residual stress effect of the bridge is established to demonstrate the pull-in instability phenomenon of the micromachined capacitive switch, and to predict the effective stiffness constant and critical collapse voltage of the bridge for several typical bridge geometries. An optoelectronic laser interferometric system, based on a modified Michelson interferometer incorporated with optoelectronic devices is developed to evaluate the membrane deformation characteristics of the micromachined capacitive switch with different applied dc bias voltages. It is illustrated that the analytical solution is well agreed with the numerical simulation and experiment.
Keywords: RF MEMS; Microwave and wireless communication; Micromachined capacitive switch; Optical interferometry;

Single-/multi-mode tunable lasers using MEMS mirror and grating by A.Q. Liu; X.M. Zhang; J. Li; C. Lu (49-54).
The microelectromechanical systems (MEMS) technology has been widely applied to develop the miniaturized external cavity tunable lasers. In this paper, two integrated MEMS tunable lasers using different configurations are presented and discussed. One uses a deep-etched circular mirror as the external converging reflector. It works in multiple longitudinal modes and has mode hopping. The other employs a deep-etched rotary blazed grating as the reflector and filter simultaneously. Single-longitudinal mode operation is achieved and mode hopping can be avoided.
Keywords: Tunable laser; Blazed grating; DWDM; MEMS; Optical MEMS;

Study on piezoresistive effect of diamond films under magnetic field by W.L. Wang; K.J. Liao; C.G. Hu; S.X. Wang; C.Y. Kong; H.Y. Liao (55-58).
The piezoresistive effect of P-type diamond films was investigated under magnetic field. The diamond films in these studies were synthesized by microwave plasma chemical vapor deposition. The experimental results have shown that the change in the resistance was about 12.0% without magnetic field when microstrain was 100 at room temperature, but decreased by 9.5% under the magnetic field of 3 T at tensile stress. The origin of the piezoresistive effect in P-type diamond films can be explained by the strain-induced valence band split-off and the magnetoresistive effect in the films that was caused by additional hole movement in a magnetic field.
Keywords: Piezoresistive effect; Diamond films; Magnetoresistive effect; CVD;

Single crystal silicon rotary microactuator for hard disk drive by J.Q. Mou; Y. Lu; J.P. Yang; Q.H. Li (59-63).
A single crystal silicon rotary microactuator for hard disk drives (HDD) is described in this paper. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio 20:1 directly processed from a single crystal silicon substrate. It consists of a stator attached to the silicon substrate by bus bar, and a movable rotor connected to an anchored central column via spring beams. Both the stator and the rotor are suspended from the silicon substrate. When a voltage is applied to the actuator, the microactuator will drive the head to move in tracking direction by the rotational motion of the rotor. The microactuator prototype with overall dimensions 1.4  mm×1.4  mm×0.18  mm has been successfully fabricated. The results of finite element method (FEM) simulation demonstrate that the microactuator has a better dynamic performance in a Head Gimbal Assembly (HGA) for hard disk drives. Experiments show that ±0.6 μm equivalent displacement of the head element in tracking direction is achieved under the driving voltage 20 V. The frequency response testing results of the microactuator bonded with a slider indicate that the microactuator is feasible to operate as a fine actuator in HDD.
Keywords: Single crystal silicon; MEMS; Microactuator; Hard disk drive;

A circular-type thermal flow direction sensor free from temperature compensation by Seunghyun Kim; Sunghyun Kim; Yongduk Kim; Sekwang Park (64-68).
This research is about a thermal flow sensor, suggesting a new structure not only to improve the detection of airflow directions in any direction but also realize flow detection without temperature compensation. A flow direction sensor was fabricated using MEMS technology. The structure of the sensor, consisting of one heater and four sensing parts surrounding the heater, is a symmetrical circular-type to obtain uniform output regardless of various flow directions. The designed sensor operates based on the relative output difference of the four sensing parts in response to temperature variation induced by airflow. Even though the temperature of environments varies, the effect to the four sensing parts is equivalent due to its symmetrical structure. Because of its symmetrical structure and operating principle, the temperature variation caused by environments does not affect the conduct of the sensors. As a result, they do not need any temperature compensation for detecting flow direction.The fabricated sensors were tested at 22 and 32 °C. The response time was a few seconds and the maximum angle difference compared to flow angles was 5° for each test. This result demonstrates that the suggested structure of sensors could be applied to the detection of flow directions without any temperature compensation.
Keywords: Flow direction; Circular-type; MEMS; ASIC; Temperature compensation;

Laser assisted surface nanopatterning by M.H. Hong; S.M. Huang; B.S. Luk’yanchuk; T.C. Chong (69-74).
Pulsed laser irradiation combined with scanning probe microscopy (SPM) to achieve surface nanopatterning is investigated. A nanosecond pulsed laser beam is introduced to a gap between SPM tip and substrate surface. With the tip scanning over the surface, 10 nm resolution nanolines and nanocharacters can be obtained on metal and photoresist surfaces. With the fine-tuning of laser processing parameters, the depth and width of the nanolines can be controlled. Laser surface nanopatterning is also carried out by optical near-field effect with particles as lithography mask. Theory study shows that small particles work as efficient lenses. Light intensity under the particles is greatly enhanced dozens of times within a region <100 nm. Submicron particles were self-assembled as the mark to form nanopatterns on substrate surfaces with a 20 nm resolution.
Keywords: Nanofabrication; Laser; Scanning probe microscopy; Near-field optics;

A foveated-structure CMOS retina chip for edge detection with local light adaptation by Dae-Sik Park; Jung-Hwan Kim; Hyun-Soo Kim; Jong-Ho Park; Jang-Kyoo Shin; Minho Lee (75-80).
A foveated-structure CMOS retina chip for edge detection with local light adaptation is presented. The functions of photoreceptors, horizontal cells, and bipolar cells in the human retina are transformed to a simple equivalent circuit for detecting the edge of an input image. The unit pixel of the chip consists of only four MOSFETs and two photo-transistors. A 32×32 foveated-structure local light-adaptive retina chip for edge detection has been designed and fabricated using 0.6 μm double-poly triple-metal CMOS process. The fabricated retina chip measures 8  mm×8  mm and could detect the edges of an input image with a wide range of light intensity. It is anticipated that this local light-adaptive CMOS retina chip could find applications in the area of active vision systems for target tracking and recognition.
Keywords: Retina chip; Edge detection; Local light adaptation; Foveated-structure; Active vision system;

The objective of this work is to develop a surface micro-machining process that can be used to fabricate a heated micro-channel integrated with an array of both the pressure and the temperature sensors along the channel. With an air layer made underneath the channel for the purpose of insulation, this micro-channel can provide gas flow with measurement of both the local pressure and temperature distribution along the channel flow direction. This heated small size micro-channel can be used to study the channel flow and heat transfer process at the rarefied condition. The entire fabrication process is very complicated which has used a total of 21 photo masks and taken more than 320 times of fabrication procedures. Therefore, the channel has to be carefully designed and preliminary fabrication test has to be done before starting the complete fabrication process. The design consideration and fabrication procedures will be presented. Some of the difficulties encountered during the fabrication process will be discussed.
Keywords: Micro-channel fabrication; Micro-thermal system;

The objective of this study is to solve the difficulties encountered during planarization and etching of a polysilicon film that is deposited and used as a sacrificial layer in an oxide structure in a micro-thermal system such as a micro-channel device as mentioned in the previous paper. This polysilicon film has a relatively wide and deep ditch. Two different chemical–mechanical–polishing (CMP) processes that have been used to flatten the polysilicon-made sacrificial layer will be presented and the results are not very successful. A novel planarization technique using wet etch process is developed which has been shown to be able to flatten very effectively a surface with wide and deep ditch.
Keywords: Planarization process; CMP;

High-frequency one-chip multichannel quartz crystal microbalance fabricated by deep RIE by Vu Ngoc Hung; Takashi Abe; Phan Ngoc Minh; Masayoshi Esashi (91-96).
In this work, high-frequency one-chip multichannel quartz crystal microbalance (QCM) prepared by deep reactive ion etching (RIE) is presented. The quartz resonators in one-chip with the diameter in the range 0.05–1.0 mm and thickness in the range 18–82 μm were fabricated. The conductance measurements have shown that Q-factor of the resonators increases with decreasing quartz resonator thickness and reaches the value of about 30,000 for the 94 MHz quartz resonator. By decreasing the thickness, very small resonator with 100 μm diameter can be performed with Q-factor of 5700. The separation of spurious modes from fundamental mode is improved by reducing the diameters of the quartz resonators. The influence of the loading glycerol/water mixtures into the electrical properties of the sensor was conducted.
Keywords: Multichannel; Quartz crystal microbalance (QCM); Deep reactive ion etching (RIE);

Microfabrication of thermoelectric materials by silicon molding process by Jing-Feng Li; Shuji Tanaka; Toshiya Umeki; Shinya Sugimoto; Masayoshi Esashi; Ryuzo Watanabe (97-102).
Thermoelectric microgenerators and microcoolers are becoming technologically important for microelectromechanical systems (MEMS), but the conventional cutting and assembling techniques have limitation in miniaturizing the dimensions of thermoelectric devices to the micrometer order. We have combined MEMS technology and materials processing into a novel process to manufacture thermoelectric micro-modules with densely aligned fine-scale and high-aspect-ratio P–N elements. Our process consists of the following major steps: (1) micromachining a silicon mold; (2) filling the mold with thermoelectric materials; (3) connecting P- and N-type elements and assembling the whole module. By using the present process, Bi–Sb–Te system thermoelectric elements of 300 μm height and 40 μm cross-sectional width can be fabricated successfully.
Keywords: Microfabrication; Thermoelectric device; Silicon molding; Materials micro-processing;

3-D microarrays biochip for DNA amplification in polydimethylsiloxane (PDMS) elastomer by Xiaomei Yu; Dacheng Zhang; Ting Li; Lin Hao; Xiuhan Li (103-107).
In this paper, a rapid and low-cost fabrication technique for microarrays biochips is presented, and the fluorescence-based polymerase chain reactions (PCR) were performed in the chip for DNA amplification. The chip is consisted of 1064 column chambers. Each chamber has a volume of 25 nl, with the diameter of 460 μm and depth of 200 μm. The PCR chips were made of inexpensive silicone elastomer—polydimethylsiloxane (PDMS) and rapidly fabricated with micro-molding technique. The three-dimensional (3-D) PDMS replicas were molded directly from 3-D negative silicon master, which was fabricated by deep etching technique under the inductively coupled plasma (ICP) system. We demonstrated that the fluorescence-based PCR could be performed in the PDMS chip with nanoliter-volumes.
Keywords: Polymerase chain reaction (PCR); Polydimethlysiloxane (PDMS); Inductively coupled plasma (ICP);

A novel high temperature pressure sensor on the basis of SOI layers by Zhao Yulong; Zhao Libo; Jiang Zhuangde (108-111).
The principle of silicon-on-insulator (SOI) and low pressure chemical vapour deposited (LPCVD) to make the piezoresisitive pressure gauge is developed. A novel structure of the sensors for harsh environment is designed. In particular, the high temperature pressure sensors were used in: automotive industry, aviation engineering, as well as in oil fields, industrial measurement and control systems. The sensor could be used in 200 °C environment, and could endure the impact of instances high temperature (about 1000, and less than 0.5 s) because of it’s mechanical structure of cantilever bonded with SOI strain gauge. The test data of the sensor is obtained, and the result is satisfied.
Keywords: Pressure sensor; SOI strain gauge; Harsh environment;

Fabrication planar coil on oxide membrane hollowed with porous silicon as sacrificial layer by Zewen Liu; Yong Ding; Litian Liu; Zhijian Li (112-116).
This paper presents the preparation process of large area hollowed structure used for suspended planar inductor for CMOS compatible radio frequency (RF) circuits. Porous silicon (PS) is used as sacrificial layer, and SiO2 film is used as a support membrane. After aluminium coil structure fabrication an array of 4  μm×8  μm releasing holes is opened on the membrane. Tetramethyl ammonium hydroxide (TMAH) solution with additional Si powder and (NH4)2S2O8 is used to remove the PS layer through small releasing holes without eroding the uncovered Al. A 4 nH aluminium suspended inductor is obtained on a 450  μm×425  μm membrane hollowed with PS sacrifice method.
Keywords: RF; MEMS; CMOS; Porous silicon; Inductor; Sacrificial layer;

Fabrication and characterization of thick porous silicon layers for rf circuits by S.Z. You; Y.F. Long; Y.S. Xu; Z.Q. Zhu; Y.L. Shi; Z.S. Lai; Z.F. Li; W. Lu; A.Z. Li (117-120).
Porous silicon (PS) has been considered as a promising material for application to rf devices recently. In this paper, we present the characterization of PS layer in terms of Raman Spectroscopy and X-ray diffraction. The results obtained from the 400 μm-thick PS samples showed a shift of Raman peak position to 519 cm−1 and a lattice expansion of 0.1% compared with single crystal Si(1 0 0). Coplanar waveguides (CPWs) have been formed on the PS layers in attempt to obtain low-loss transmission lines for rf circuits.
Keywords: Porous silicon (PS); Raman spectrum; X-ray diffraction; Patterning;

Deep X-ray mask with integrated actuator for 3D microfabrication by Kwang-Cheol Lee; Seung S. Lee (121-127).
We present a novel method for 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a microactuator is integrated. The integrated microactuator oscillates the X-ray absorber, which is formed on the shuttle mass of the microactuator, during the X-ray exposures to modify the absorbed dose profile in X-ray resist, typically PMMA. The 3D PMMA microstructures according to the modulated dose contour are revealed after GG development. An X-ray mask with integrated comb drive actuator is fabricated using deep reactive ion etching, absorber electroplating, and bulk micromachining with silicon-on-insulator wafer. Silicon shuttle mass (1  mm×1  mm, 20 μm thick) as a mask blank is supported by four 1 mm long suspension beams and is driven by the comb electrodes. A 10 μm thick, 50 μm line and spaced gold absorber pattern is electroplated on the shuttle mass before the release step. The fundamental frequency and amplitude are around 3.6 kHz and 20 μm, respectively, for a dc bias of 100 V and an ac bias of 20 VP–P (peak–peak). Fabricated PMMA microstructure shows 15.4 μm deep, S-shaped cross-section in the case of 1.6 kJ cm−3 surface dose and GG development at 35 °C for 40 min.
Keywords: LIGA; Deep X-ray lithography; 3D microfabrication; Deep X-ray mask; Integrated microactuator; Comb drive actuator;

Study on low voltage actuated MEMS rf capacitive switches by F.M Guo; Z.Q Zhu; Y.F Long; W.M Wang; S.Z Zhu; Z.S Lai; N Li; G.Q Yang; W Lu (128-133).
We report the study on the MEMS rf switches with low actuated voltage. The switch structure has been optimized by the calculation on the dependence of actuated voltage on the Young’s modulus of membrane materials and geometrical sizes. Compared with gold material, AlSi0.04 is a good movable film material having lower actuated voltage (5 V). The switches array is made on the coplanar waveguide (CPW) transmission lines, which were fabricated on quartz, high resistivity (>2 kΩ cm) silicon and porous silicon substrates respectively. The pull-in voltage of the variable capacitor was below 20 V. Furthermore, the 21 bridges MEMS switch array had 372°/3.5 mm phase shift operating at 35 GHz. The chip is compacted into a size of 3.5  mm×0.5  mm .
Keywords: MEMS; rf switch; Actuation voltage; Young’s modulus; Low loss;

Research on electric field and electric breakdown problems of a micro-colloid thruster by Jijun Xiong; Zhaoying Zhou; Xiongying Ye; Xiaohao Wang; Yanyin Feng (134-137).
Electrodes are key components of a micro-colloid thruster. There are two unavoidable problems in the designing of electrodes of a micro-colloid thruster. Firstly, the electric field must be high enough to induce the propellant to form a droplet and then burst. Secondly the problem of electric breakdown between two electrodes of a micro-colloid thruster should be paid special attention to when high potential is applied between electrodes. This paper presents an equation to predict the minimum electric field value to start an electrospray, which is based on the balance between the surface tension and the electrostatic field force on the surface of a droplet at the tip of the source emitter of a micro-colloid thruster. Finite element analysis (FEA) results show that, this minimum value of electric field, about 107  V/m can be archived when 3000 V is applied between electrodes. Experiments conducted on the home-made micro electrodes verifies that electric breakdown does not occur at 8000 V when air pressure is below 10−3  Pa.
Keywords: MEMS; Micro-colloid thruster; Electric field; Electric breakdown; Electrode design;

Passive valves based on hydrophobic microfluidics by Yanying Feng; Zhaoying Zhou; Xiongying Ye; Jijun Xiong (138-143).
Fluid–surface interactions can become dominant in microfluidics, which is a central technology in a number of miniaturized systems for chemical, biological and medical applications. In this paper, two kinds of hydrophobic valves in microfluidic applications were presented. One is based on special geometrical designs and chemical modification for silicon dioxide and glass microchannels. Silicon dioxide and Pyrex glass surfaces, which are hydrophilic originally, are modified with octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) to be hydrophobic, with the contact angles up to ∼102 and 103°, respectively, for water. The formation of OTS SAMs takes <5 min. The OTS SAMs based stop valve can function well to enable stopping the flow of a liquid inside a microchannel in both directions. Tested for deionized water, the hydrophobic valve blocked successfully the liquid for many consecutive times and yielded pressure barrier up to ∼490 Pa, which is near to the theoretical prediction. The OTS SAMs, therefore the hydrophobic valve function, can be retained in a suitable environment for a long time and can rebirth conveniently when destroyed. The other kind of hydrophobic valve is based on hydrophobic pattern, which is formed by plasma depositing CHF3 patterns on the surfaces of silicon dioxide. The hydrophobic CHF3 patterns (measured for contact angle for water to be 102°) can block the liquid to flow forward. The theoretical analysis and the process design were presented.
Keywords: Valve; Surface tension; SAMs; Microfluidics;

Localized electrochemical micromachining with gap control by Li Yong; Zheng Yunfei; Yang Guang; Peng Liangqiang (144-148).
An approach to electrochemical micromachining is presented in which side-insulated electrode, micro gap control between the cathode and anode, and the pulsed current are synthetically utilized. An experimental set-up for electrochemical micromachining is constructed, which has machining process detection and gap control functions; also a pulsed power supply and a control computer are involved in. Microelectrodes are manufactured by micro electro-discharge machining (EDM) and side-insulated by chemical vapor deposition (CVD). A micro gap control strategy is proposed based on the fundamental experimental behavior of electrochemical machining current with the gap variance. Machining experiments on micro hole drilling, scanning machining layer-by-layer, and micro electrochemical deposition are carried out. Preliminary experimental results show the feasibility of electrochemical micromachining and its potential capability for better machining accuracy and smaller machining size.
Keywords: Electrochemical micromachining; Side-insulated electrode; Gap control; Pulsed current;

A homogeneously catalyzed micro-chemical thruster by Chen Xupeng; Li Yong; Zhou Zhaoying; Fan Ruili (149-154).
An advanced chemical thruster is proposed for the post-launch propulsion system of small satellites or other micro-spacecrafts, in which the homogeneously catalytic decomposition of hydrogen peroxide (H2O2) is used. The water solution of ferrous chloride (FeCl2) is chosen as the homogeneous catalyst. The core component of the thruster is the thrust chamber including the catalytic reaction tank and nozzle. Two kinds of thrust chamber prototypes have been fabricated by precision machining and silicon process, respectively. The former prototype has a conical nozzle with a throat diameter (φ) of 0.3 mm, while the latter has a planar nozzle with a throat section of 0.04  mm×0.2  mm. Controlled by two miniature electromagnetic valves, the thruster system can work in either continuous or pulse mode. Preliminary experiments on these prototypes have been carried out, and a smallest impulse per controlling pulse of less than 80 μN s is obtained.
Keywords: Micro-thruster; Homogeneous catalysis; H2O2; Specific impulse (I sp);

A 100-channel neurostimulation circuit comprising a complementary metal oxide semiconductor (CMOS), application specific integrated circuit (ASIC) and a 10×10 electrode array for interfacing with surviving neurons of the retina has been designed. We discuss the fabrication of the accompanying electrode array that is to be connected to the implant. Specifically, a technique is described that allows the consistent and accurate formation of platinum spheres.The technique uses a controlled discharge across an ionised air gap. The magnitude of the discharge energy (controlled by pre-selecting different discharge capacitors), allows for the control of sphere diameter.One hundred of the said spheres with attached 100 μm diameter platinum wires are then fabricated into an electrode array formed from a silicone base. We demonstrate that using our technique, it is possible to inexpensively fabricate uniform spheres for use in neuroprosthetic devices and that said spheres are suitable for both recording and stimulation of physiological functions.
Keywords: Vision prosthesis; Electrodes; Fabrication; Retina; Neurostimulation;

Monolithically integrated PCR biochip for DNA amplification by Zhan Zhao; Zheng Cui; Dafu Cui; Shanhong Xia (162-167).
A monolithically integrated microliter PCR (polymerase chain reaction) biochip has been designed and fabricated for DNA amplification. It consists of a vessel made in silicon, platinum thin film heater deposited on to the bottom of the vessel and a temperature sensor. A miniaturized thermal cycling system was designed with a PIC microcontroller to provide heating power and control of thermal cycling. The volume of PCR vessel is approximately 2 μl. It has a low time constant of thermal cycling, with the maximal heating rate over 15 °C/s and cooling rate at around 10 °C/s. This paper reports the PCR vessel structure, chip package problems and solutions, its thermal uniformity analysis, thermal cycling properties and the result of amplification. The result has demonstrated that the integrated PCR biochip can provide rapid heat generation and dissipation and improved temperature uniformity in DNA amplification.
Keywords: Polymerase chain reaction; Biochip; Integrated;

A piezoelectrically actuated micro synthetic jet for active flow control by Chester Lee; Guang Hong; Q.P. Ha; S.G. Mallinson (168-174).
The synthetic jet actuator (SJA) is a low power, highly compact microfluidic device which has potential application in boundary layer flow control. In recent work we have shown how synthetic jets work without cross flow and how effectively they modify the flow structure in the boundary layer under an adverse pressure gradient. This paper describes the piezoelectric synthetic jet actuator used in our experiments. The experimental set-up for flow control using this type of actuator is detailed. The results obtained show a significant enhancement of the jet effectiveness by forcing the boundary layer flow at the natural instability frequency. The actuators must have sufficient velocity output to produce strong enough vortices if they are to be effective for flow control. The forcing effect can occur at a frequency lower than the driving frequency of the actuator when used without cross flow. The forcing frequency appears to be an important parameter in synthetic jet boundary layer flow control.
Keywords: Synthetic jet; Piezoelectric actuation; Active flow control;

Fabrication and characterization of torsion-mirror actuators for optical networking applications by W.G. Wu; D.C. Li; W. Sun; Y.L. Hao; G.Z. Yan; S.J. Jin (175-181).
Novel torsion-mirror actuators with monolithically integrated new fiber holding structures, which can feature self-fixing and self-aligning of optical fibers, are fabricated in regular silicon wafers as well as in SOI wafers by using the mixed micromachining based on the surface and bulk silicon microelectronics. The electromechanical performances of the actuators and the optical properties of their micro-mirrors are investigated experimentally and theoretically. The electrostatic yielding voltages for driving the micro-mirrors of the actuators to tilt from 0° to 90° spontaneously are in the range of 270–290 V and the minimum holding voltages for keeping the tilting angle of the mirrors to be in 90° are found 55 V or so when the thickness of the torsion-beams suspending the mirrors is about 1 μm. Theoretical analysis manifests that the yielding voltage is most sensitive to the beam thickness among the series of design parameters about the torsion-mirror actuator structures. The micro-mirrors of the actuators can cyclically vibrate 108 times at least between 0° and 90°, and their shortest actuating time can reach an estimated less than 2 ms. The surface roughness and its distribution of the micro-mirrors of the actuators are small and smooth, respectively, which is acceptable for wavelength division multiplexing applications basically.
Keywords: MEMS; Torsion-mirror actuators; Fiber holding structures; Mixed micromachining; Surface roughness; Light scattering and reflection;

Experimental research on piezoelectric array microjet by Songmei Yuan; Zhaoying Zhou; Guohui Wang (182-186).
In this paper, a new type of piezoelectric array microjet for drug delivery will be introduced. The device consists of a fluid chamber, which is formed by a piezoelectric actuator bonded to a silicon chip with nozzles. Inside the silicon, an axis-symmetric vibration mode of a piezoelectric actuator can be transferred to dynamic energy of many droplets. In order to improve performance of droplets, its configuration and boundary conditions have been optimized by ANSYS finite elements method. At the same time, its driving circuit system has also been improved. Based on optimized structure and control circuit, microjet prototype has been experimented by particle dynamic analyzer (PDA), HP4194A impedance analyzer and Polytec-300 scanning laser vibrometer. After circuit matching, the distribution of droplets is more concentrated. It can be found that upward droplets have a long band shape or small diameter, and downward droplets have a large globe shape. The experimental results have been analyzed in great detail. The available and important conclusions have been obtained for potential applications of the microjet in drug delivery.
Keywords: Microjet; Piezoelectric transducer; Optimization; Matching circuit;

Thermal properties and spectroscopic properties of a new kind heavy fluoride glass Er:ZBLALiP microsphere were presented in this paper. Based on the thermalization effects between the upper levels responsible for green fluorescence at 522 and 546 nm in Er:ZBLALiP, we propose a new optical temperature sensing using micrometer-sized spherical cavity. The dependence of green emission intensity ratio (GEIR) on the surrounding temperature from 300 to 100 K was experimentally determined, which allows us to calibrate the sensing function of green intensity ratio versus temperature. Such a point temperature sensor is applicable for a large temperature range from 150 to 850 K with a resolution of the order of 1 K.
Keywords: Optical point sensing; Spectroscopy; Er:ZBLALiP; Modeling;

A novel micro-well array chip for liquid phase biomaterial processing and detection by Henry J.H. Chen; Tsai Fen Chen; Star R.S. Huang; Jeng Gong; J.C Li; Wei Chen Chen; T.H. Hseu; Ian C. Hsu (193-200).
This paper presents a novel micro-well array chip fabricated by micromachining and CMOS technology for biomedical application. The chip is designed to provide multi-function for liquid phase DNA or protein sample processing and detection, its function and structure includes heating, cooling, temperature sensing, vibration agitation, control circuits, array of micro-wells, and a transparent cover with liquid seal at each well. The embedded heater shows good linearity and can heat up to 101 °C with ∼20 mA current supply, liquid phase biomaterials such as probes and samples can be processed (hybridization, mixing, separation, washing, and detection) on the chip.
Keywords: Micro-well array; MEMS; Biochips; Liquid phase;

Effects of temperatures on microstructures and bonding strengths of Si–Si bonding using bisbenzocyclobutene by Yeon-Shik Choi; Joon-Shik Park; Hyo-Derk Park; Young-Hwa Song; Jin-Soo Jung; Sung-Goon Kang (201-205).
Thermal stability and characterizations of silicon to silicon wafer bonding at low temperature using B-staged polymer, bisbenzocyclobutene (BCB), were investigated. Bare silicon to bare silicon wafer (briefly, bare to bare) and patterned silicon by chemical etching to bare silicon wafer (pattern to bare) bonding with 4 in. size were achieved by heating BCB coated wafer pairs at 230 °C. In case of bare to bare bonding, interfaces of bonded wafers were mechanically stable and strong enough to withstand a tensile force of at least 190 kg/cm2 at room temperature. Bond strength was drastically decreased over 300 °C because of decomposition of polymer. In case of pattern to bare, interfaces of bonded wafers were dense and good enough to withstand a tensile force of at least 60 kg/cm2 at room temperature. Silicon to silicon wafer bonding using BCB was suitable for fabricating and packaging of microstructures for micro-electro-mechanical system (MEMS) devices at low temperatures (<300 °C).
Keywords: Wafer bonding; Thermal stability; Polymer bonding; Bisbenzocyclobutene;

Acoustic and electromechanical properties of 1–3 PZT composites for ultrasonic transducer arrays fabricated by sacrificial micro PMMA mold by Joon-Shik Park; Sun-Ho Lee; Soon-Sup Park; Jin-Woo Cho; Suk-Won Jung; Jin-Ho Han; Sung-Goon Kang (206-211).
Manufacturing method for 1–3 PZT composites for medical ultrasonic transducer array (UTA) using sacrificial polymethyl-methacrylate (PMMA) micro molds was investigated. The purpose of study was to compare this proposed method (briefly, micro-pressing) with conventional dicing method for UTA fabrication. The cell size was 135 μm × 135 μm with the 35 μm gap between cells, and the cell height was 170 μm. Microstructure of 1–3 PZT composites was dense and had uniform morphology. Dielectric constants at 1 kHz were 2627 for the dicing method and 2221 for the micro-pressing method. Two methods produced similar values for the thickness mode electromechanical coupling coefficients (K t): 73% for the dicing method and 68% for the micro-pressing method. Acoustic properties of fabricated ultrasonic transducer by the dicing method were similar to those of the micro-pressing method. Microstructure, electromechanical properties and acoustic properties of 1–3 PZT composites fabricated by the micro-pressing method were comparable to the properties obtained with the conventional dicing method. The micro-pressing method is a cost-effective way of manufacturing micro-ceramic rod arrays with high aspect ratio based on the batch type LIGA process.
Keywords: Transducer array; 1–3 Composite; Micro-pressing; PMMA; Injection molding;

Squeeze-film air damping of thick hole-plate by Minhang Bao; Heng Yang; Yuancheng Sun; Yuelin Wang (212-217).
The damping effect of air flow in holes is considered based on Poiseuille equation and the damping effect of lateral flow is considered by conventional Reynolds’ equation for infinite thick hole-plate. The expression for damping ratio is obtained and the conditions for minimum damping ratio can be found. A modified Reynolds’ equation is established for thick hole-plate with finite dimensions. The equation is a good approximation for hole-plates in typical MEMS devices. As it is also effective for non-hole-plate as well, it is more general than the conventional Reynolds’ equation. The distribution of damping pressure under a hole-plate can be found by solving the modified Reynolds’ equation with appropriate boundary conditions. As an example, the damping pressure of squeeze-film air damping of a long rectangular hole-plate is considered. Analytical expressions for the damping pressure, damping force and damping ratio are found.
Keywords: Squeeze-film air damping; Thick hole-plate; Reynolds’ equation;

A fast and accurate calibration method for high sensitivity pressure transducers by Minhang Bao; Yuancheng Sun; Heng Yang; Jinsuo Wang (218-223).
A novel calibration scheme for fast accurate calibration of high sensitivity pressure transducers is proposed and verified by experiments. Based on theoretical analysis, the accuracy of the calibration for non-linearity, hysteresis and repeatability can be much higher than 1×10−4 for pressure transducers with an operation range of 1 kPa or below. For accurate calibration of sensitivity, a single conventional measurement is needed at the full range pressure.A conventional compensation pressure gauge can be used for the new calibration method. The calibration is very accurate and very fast; only a few seconds for a test point (or 10–20 min for a device). As the operation pressure is self-generating, no expensive pressure source is needed. The performances can be further improved if the design of the apparatus is optimized for the new calibration method according to the theoretical analysis.
Keywords: Pressure transducer; Calibration; High sensitivity; Compensation pressure gauge;

Fabrication of X-ray masks and applications for optical switch molding by X.C. Shan; R. Maeda; T. Ikehara; H. Mekaru; T. Hattori (224-229).
Conventional X-ray masks for LIGA process are generally fabricated using Au electroplating. In this paper, a new approach of fabricating LIGA masks for X-ray lithography was demonstrated. The fabrication process started with deposition of a layer of Au film as thick as 5 μm on silicon substrate, then followed by electron cyclotron resonance (ECR) Ar+ etching, coating of negative resist SU-8 as a membrane for supporting and protection of patterned Au structures, and high aspect ratio reactive ion etching (RIE) from backside of the substrate. The fabricated Au masks were used for X-ray lithography. A PMMA mold-master of optical switch with a mirror height of 210 μm and verticality of 88.9° was obtained, which demonstrated a well acceptable performance.
Keywords: X-ray; Au mask; LIGA process; ECR; PMMA; Mold; Hot embossing;

A piezodriven XY-microstage for multiprobe nanorecording by Deyuan Zhang; Chienliu Chang; Takahito Ono; Masayoshi Esashi (230-233).
The properties of electrostatic, electromagnetic and piezoelectric actuators used for XY-microstage are compared to indicate high area efficiency but no good machinability of piezoelectric actuator, so that a novel planer fabrication method of the piezodriven XY-microstage with one PZT plate has been proposed. This fabrication method includes three processes, dicing, electroplating, femtosecond laser machining and so no. A parallelogram mechanism with flexure hinges, lever mechanisms and piezoelectrical actuators has been designed to make XY-displacement in monolayer plane structure. The area efficiency and volume efficiency of piezodriven XY-microstage are very higher than electrostaticdriven and electromagneticdriven one. The relationship of displacement characteristics with the sizes of parallelogram mechanism has been tested with the several principium prototypes fabricated by femtosecond laser machining of single nickel plate and assembly of PZT actuator. The test results show that the flexure hinges the shorter, the accuracy of the XY-displacement the better. Thirty micrometer displacement and 50% and above area efficiency have been obtained in the principium prototype.
Keywords: XY-stage; PZT; Multiprobe nanorecording;

An endpoint detectable plating process to avoid over-electroplating was proposed and performed in this work. The technology was developed for fabrication of Pyrex glass wafer with electrical feed-throughs. Thin film of gold was deposited on the glass wafer prior to the femtosecond laser drilling. When the growing metal in the through-holes was contacted to the metal, a resistance between the opposite two electrodes decreases suddenly. Thus, the endpoint detection was realized by in situ monitoring of applied voltage at constant current mode. After the endpoint detection, periodic reverse plating was applied to fill the through-holes uniformly. Finally, uniform copper deposition in the through-holes up to 12 aspect ratios was realized by this method. This technology was also applicable to the fabrication of microstructure based on electroforming.
Keywords: Through-hole plating; Endpoint detection; Femtosecond laser; Electrical interconnections; Glass;

A new type temperature-sensor of pn junction diode and micro-air-bridge heater combined with this one, are proposed and demonstrated. This pn junction diode temperature-sensor can cover very wide temperature range of about −200 to 500 °C (for about −200 to 150 °C by adjusting the forward bias-voltage; for about 150–500 °C by reverse bias-voltage of about 1 V) with very high sensitivity and accuracy like a NTC thermistor. It is confirmed that the heater combined with this pn junction temperature-sensor formed on the micro-air-bridge of 700  μm×700  μm has very quick response (thermal time constant of about 16 ms) and very high sensitivity and stability by feedback control.
Keywords: Heater; Air-bridge; Thermal sensor; Temperature-sensor; Silicon; pn junction;

Single crystal silicon piezoresistive nano-wire bridge by T. Toriyama; S. Sugiyama (244-249).
Air-bridge structure of p-type single crystal silicon nano-wire (NW) was fabricated by using 50 nm thick device layer and sacrificial layer etching of 130 nm thick buried oxide (BOX) in separation by implanted oxygen (SIMOX) substrate. The piezoresistance of the nano-wire bridge (NWB) was measured in order to verify its ability for sensing element of the nano-mechanical sensors. Longitudinal piezoresistance coefficient π l[1 1 0] and apparent transverse piezoresistance coefficient π t[1 1 0] were found to be 38.7×10−11 and 0 Pa−1, respectively, at surface concentration of N s=9×1019  cm−3. The value of π l[1 1 0] was in close agreement with that of NW without releasing from the substrate, and 54.8% larger than that of p+ diffused piezoresistor obtained by Tufte and Stelzer four decades ago (25×10−11  Pa−1 and at N s=9×1019  cm−3). The value of apparent π t[1 1 0] was much smaller than that of the NW without releasing from the substrate. An advantage of the vanished apparent π t[1 1 0] for design of the piezoresistive mechanical sensors will be discussed. Obtained results are useful for design consideration of nano-metric piezoresistive elements used in the nano-mechanical sensors.
Keywords: Piezoresistance coefficient; Nano-wire bridge; Single crystal silicon;

Fabrication of alloy and ceramic microstructures by LIGA–MA–SPS process by Naoki Miyano; Kazunori Tagaya; Kazunori Kawase; Kei Ameyama; Susumu Sugiyama (250-257).
Keywords: LIGA; Molding; SPS; Mechanical alloying; Shape memory alloy;

A novel glucose sensor based on microdialysis technique has been developed for continuous glucose monitoring. It includes: (1) The microdialysis sampling and interval perfusion system, it can prevent electrode from being fouled and it also provides enough time for glucose molecule traversing the microdialysis membrane to establish a dynamic balance, and the sensor can be recovered well, too. (2) A “sandwich” structure glucose sensor based on an aqueous glucose oxidase (GOD) and catalase solution, it is easy to replace the inactive enzyme solution. Au interdigital array (IDA) microelectrodes and microgrooves were fabricated on the silicon wafer for electrochemistry determinations. (3) Continuous glucose monitoring system. The results of in vitro experiments show this glucose sensor has short response time, high sensitivity and good linearity. To improve the stability of liquid enzyme, aqueous colloidal gold nanoparticles was mixed with coenzymes solution. The result of experiments shows the repeatability of sensor was improved, and the sensitivity of sensor was enhanced. To the best of our knowledge, this is the first demonstration that aqueous colloidal gold nanoparticles enhance the activity of aqueous enzymes.
Keywords: Microdialysis; Microelectrode; Glucose sensor; Electrochemistry; Enzyme; Gold nanoparticles;

Investigation of sol–gel prepared Ga–Zn oxide thin films for oxygen gas sensing by A. Trinchi; Y.X. Li; W. Wlodarski; S. Kaciulis; L. Pandolfi; S.P. Russo; J. Duplessis; S. Viticoli (263-270).
Gallium oxide–zinc oxide (Ga2O3–ZnO) thin films have been prepared by the sol–gel process and their oxygen gas sensing performance has been investigated. These semiconducting films were deposited on alumina substrates with interdigital electrodes and single crystal silicon substrates for the electrical and microstructural characterization. X-ray photoelectron spectroscopy (XPS) showed that the actual concentrations of Ga and Zn thin films differ from the nominal values in the prepared solutions. Additionally, the concentration of ZnO decreases when the annealing temperature increases. Scanning electron microscopy (SEM) revealed that films with Ga/Zn atomic ratio 90:10 possess cracks and are inhomogeneous when compared to those with that of 50:50. The sensors with Zn 50 at.% had a much larger response at lower operating temperature (<430 °C) compared to the Ga-dominated sensors, which operate above 450 °C. Furthermore, these sensors showed greatest performance at temperatures in the range of 380–420 °C. It was found that by increasing the amount of ZnO in the thin film sensors, the operating temperature decreased as well as the base resistance.
Keywords: Gallium oxide; Gas sensor; Zinc oxide; Sol–gel process; XPS;

Presented in this paper is a novel approach for the fabrication of low-cost integrated micromachined spatial light modulators based on electrostatic deformation of viscoelastic layers. The fabrication procedure is optimized so as to keep requirements on electronics and the mechanical layers as low as possible. In our approach, two silicon chips are bonded together with an intermediate 5 μm viscoelastic layer in between. When the bulk silicon of the top chip is etched away, a reflective surface results with very high optical quality. The top chip is coated with a 50 nm nitride layer to act as an etch stop and a 80 nm aluminum layer for reflectivity and conductivity. When alternating potentials are applied on the electrode structure, the surface deforms in a sinusoidal shape, resulting in a phase grating, as verified experimentally. Special low-stress etch holder technology was developed for back and sidewall protection of the device and its contact pads. Applications lie in the field of projection displays, optical communication networks and optical lithography.
Keywords: MEMS; Spatial light modulator; Viscoelastic layers; Projection displays;

List of conferences (278-279).

Author index (280).

Subject index (281-285).