Dzung Viet Dao - Academia.edu (original) (raw)

Papers by Dzung Viet Dao

This paper reports the top-down fabrication of carbon nanotube (CNT) thin film on microelectrical... more This paper reports the top-down fabrication of carbon nanotube (CNT) thin film on microelectrical mechanical systems (MEMS) and the characterization of the thermoelectric coefficients of aligned single-walled carbon nanotube (SWNT) forest film. The film was synthesized by water-assisted chemical vapor deposition (CVD), a process known as 'super-growth'. CNT film was then condensed, manually maneuvered, and conveniently patterned by electron beam (EB) lithography to form desirable shapes. We demonstrate this process by patterning an array of Au-CNT thermocouples; measurement under room temperature conditions reveals the Seebeck coefficient of aligned SWNT film to be 18-20 μV C −1 .

Technical Digest. MEMS 2002 IEEE International Conference. Fifteenth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.02CH37266), 2002

This paper presents the design concept, fabrication and calibration of a six-degree of freedom (6... more This paper presents the design concept, fabrication and calibration of a six-degree of freedom (6-DOF) turbulent flow micro sensor utilizing the piezoresistive effects in silicon. The proposed sensor can independently detect six components of force and moment on a test particle in a turbulent flow. By combining p-type conventional and shear piezoresistors in Si (1 1 l), and arranging them suitably on the sensing area, the total number of piezoresistors used in this sensing chip is only eighteen, much fewer than the forty eight piezoresistors of the prior art piezoresistive 6-DOF force sensor [l]. Calibration for six components of force versus output voltages was carried out. The sensitivities are linear, close to the design values, and high enough to measure the forces and moments expected to act on the particles in turbulent flow in geophysics.

IEEJ Transactions on Sensors and Micromachines, 2008

In this paper, a thermoelectric generator with a flexible structure is presented. The thermoelect... more In this paper, a thermoelectric generator with a flexible structure is presented. The thermoelectric generator consists of 1625 thermocouples made from two materials, i.e. n-type BiTe and Cu thin films, on a flexible polyimide sheet by utilizing micromachining technology. The prototype of the flexible thermoelectric generator has dimensions of 100mm × 80mm × 3mm (length × width × thickness). Theoretical calculations show an output voltage of 317mV/K and a power of 7.8muW/K2. Preliminary experimental results measured on the test thermocouple samples show an average Seebeck voltage of 58.8muV/K per one thermocouple was obtained. This thermoelectric generator structure can be bent flexibly, so it can be used on both flat and cylindrical surfaces, e.g. on the skin of human body.

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2012

Polymethyl methacrylate (PMMA) has been proposed as a material for micro-electromechanical system... more Polymethyl methacrylate (PMMA) has been proposed as a material for micro-electromechanical systems (MEMS) to initiate the research on environmentally friendly micro-nano machining technology using polymer materials. A polymer MEMS process has been developed using hot embossing and precision machining. MEMS structures less than 2 µm were successfully embossed. The PMMA layer that remained after hot embossing was removed by a polishing process to release the movable parts. A PMMA electrostatic comb-drive microactuator was fabricated. Both finger width and gap between fingers were 5 µm, and thickness was larger than 70 µm. An operated displacement of 11 µm at a drive voltage of 100 V was obtained. It was 20 times larger than that of an identical silicon device. A torsional micro mirror device driving with vertical comb actuator was fabricated. The size of the mirror was 1 × 1 mm 2 . The maximum tilt angle of 5.6 was obtained with driving voltage of 100 V and frequency up to 100 Hz. A chevron-shaped PMMA thermal actuator with a thickness of about 50 µm has been fabricated and tested successfully. The displacement was about 5 times larger than that of a Si counterpart at the same power consumption.

2006 IEEE International Symposium on MicroNanoMechanical and Human Science, 2006

Micro electrostatic comb-drive actuators are important components in micro electromechanical syst... more Micro electrostatic comb-drive actuators are important components in micro electromechanical systems (MEMS) [1]. Especially, polymer materials like PMMA have been of great interest in the research and development of integrated circuits (IC) and MEMS recently due to their relatively low cost and easy process [2]. In this research, we are trying to fabricate a PMMA-based electrostatic comb-drive actuator by X-ray lithography, which serves for a Micro Conveyer System.

Procedia Engineering, 2011

We present a micromachined gas sensor which can detect dilute NH 3 gas at ppb (parts per billion)... more We present a micromachined gas sensor which can detect dilute NH 3 gas at ppb (parts per billion) concentration based on chemoresistive effect of semiconducting tungsten trioxide (WO 3 ). The sensor structure consists of a poly-Si diaphragm-heater suspended on four tiny beams, which are connected to a frame with overall chip size of 1×1×0.3 mm 3 . Thanks to the diaphragm-beam structure, the power loss due to thermal conduction effect decreases and uniformed temperature on whole diaphragm is obtained. The sensor has been fabricated and tested. Thermal efficiency of the heater was measured to be 10 o C/mW. The optimal working temperature was found to be around 300 o C, and the sensor could detect NH 3 gas at ppb concentration in a background of wet air. The nano-gap effect of the interdigitated electrodes in improvement of the sensitivity was also confirmed. Our estimation based on the measurement results and system noise showed a limit-of-detection of NH 3 gas could be down to 2.5 ppb concentration.

IEEJ Transactions on Sensors and Micromachines, 2011

Nanostrain Sensing Based on Piezo-Optic Property of a Photonic Crystal Cavity

TRANSDUCERS 2009 - 2009 International Solid-State Sensors, Actuators and Microsystems Conference, 2009

This paper presents comprehensive improvements of micro motion transmission systems (MTS), which ... more This paper presents comprehensive improvements of micro motion transmission systems (MTS), which driven by electrostatic comb-drive actuators through ratchet mechanism to move micro objects unidirectionally in straight, curved and rotational paths. The first MTS is the tangential driving MTS, in which the driven objects are moved by tangential force. A rotational gearing MTS and micro conveyance system (MCS) based on this driving mode will be presented. Thanks to the new designs of directional guider of the micro containers and new turning module, the containers can move in both straight and curved paths in the tangential MCS. The second MTS is the perpendicular driving MCS, which drives micro containers by the perpendicular driving force, i.e. the moving direction of the container is perpendicular to the actuation direction. Movement velocities of the containers can be controlled by changing the driving frequency.

IEEJ Transactions on Sensors and Micromachines, 2007

In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossi... more In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossing process. Silicon molds were fabricated from silicon wafer with thickness of 500mum. First, DRIE technique was performed after optimized etching time and deposition (passivation) time to obtain a depth of 30mum with positive tapered sidewall of 1°. This is very important for de-molding process

TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference, 2007

This paper describes a design and fabrication of Si micro transportation systems (MTS) to drive m... more This paper describes a design and fabrication of Si micro transportation systems (MTS) to drive microcars based on ratchet mechanism and electrostatic comb-drive actuators. This MTS consists of linear and rotational comb actuators, microcars, and micro ratchet mechanism. The microcars can be moved with different velocities by comb-drive actuators through ratchet teeth. In this study, the MTS was fabricated by using SOI wafer with device layer of 30µm, buried SiO 2 layer of 4µm, and with only one mask. In our experiments, the movement of the microcar has been tested with driving frequency ranges from 5Hz to 40Hz. The velocity of the microcar was proportional to the driving frequency, and it matched well with theoretical calculation.

2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008

This paper presents a novel micro transportation system (MTS), which can drive micro containers i... more This paper presents a novel micro transportation system (MTS), which can drive micro containers in both straight and curved paths, based on electrostatic and ratchet mechanism. The micro container, which has driving-wings and anti-reverse-wings attached to the central 'backbone', is driven by electrostatic actuator through the ratchet racks in perpendicular direction. The container with the length and width of 450µm and 250µm, respectively, moves like a water strider with desirable velocity up to 200µm/sec in the straight and curved paths. In order to create the smart and flexible MTS, the elemental modules, e.g. straight, turning and separation modules with the same size (6mm×6mm) have been developed. Therefore, different configurations of the MTS can be created flexibly by assembling the elemental modules.

2007 International Symposium on Micro-NanoMechatronics and Human Science, 2007

motors to move a sliding shuttle. In this case, the This paper presents a novel micro transportat... more motors to move a sliding shuttle. In this case, the This paper presents a novel micro transportation driving mechanism requires at least two groups of system (MTS), which can drive micro carts by bidirectional XY actuators which were turned on and off utilizing electrostatic actuator and ratchet at suitable times, alternately holding and driving a mechanism. The micro cart, which has driving-wings shuttle. In another work [5], Fujimasa reported the and anti-reverse-wings attached to its central integrated actuator which was actuated by vibration and 'backbone', is driven by electrostatic actuator

IEEE International Symposium on Micro-NanoMechatronics and Human Science, 2005, 2005

We report a design and fabrication of micro conveyer system (MCS) based on electrostatic comb-dri... more We report a design and fabrication of micro conveyer system (MCS) based on electrostatic comb-drive actuators using SOI wafer. This MCS consists of linear comb actuator, rotational comb actuator, micro containers, and ratchet mechanism. Micro containers, used for carrying micro and nano samples such as protein, cells, are moved by comb-actuators through ratchet teeth. Each MCS, which has dimension of

2008 International Symposium on Micro-NanoMechatronics and Human Science, 2008

This paper presents design and fabrication of a silicon micro ratcheting transmission system (RTS... more This paper presents design and fabrication of a silicon micro ratcheting transmission system (RTS) that utilizes electrostatic comb-drive actuators to rotate a gear ring (or rotor) through a ratchet mechanism. The rotational actuator is engaged with the gear ring through ratchet teeth at one end, and reciprocally rotates around an elastic point at the other end based on electrostatic force.

Microsystem Technologies, 2014

hence, rF MeMS featuring small size, low weight and high performance can be considered as a futur... more hence, rF MeMS featuring small size, low weight and high performance can be considered as a future enabling technology to replace off-chip passive elements (Girbau et al. 2006).

Microsystem Technologies, 2009

This paper presents a systematic approach to fabricate optically smooth, through-wafer silicon (S... more This paper presents a systematic approach to fabricate optically smooth, through-wafer silicon (Si) molds for polymer optical devices, in particular poly(dimethylsiloxane) (PDMS) total internal reflection (TIR)-based devices. First, the Si molds were fabricated by an optimized, through-wafer deep reactive ion etching (DRIE) process to achieve small roughness. To further reduce the roughness, the Si molds were then oxidized and etched in BHF for three times to achieve surface roughness average (R a ) and root mean square (RMS) roughness below 25 nm while peakto-valley (P-V) roughness is below 150 nm. We monitored the surface roughness and morphology of the sidewalls of Si mold through three cycles of oxidation and BHF etching using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). We found that further oxidation and BHF etching might not have much effect in further reducing the roughness while the device feature definitions might be compromised. Finally, the PDMS TIR-based devices replicated from the Si molds were evaluated by means of FESEM, AFM and by imaging of the fluorescent evanescent spots.

Microsystem Technologies, 2013

This paper presents the design and fabrication of a silicon micro gearing system (MGS) that utili... more This paper presents the design and fabrication of a silicon micro gearing system (MGS) that utilizes electrostatic comb-drive actuators to rotate a gear ring through a ratchet mechanism. The rotational comb-drive actuator is engaged with the gear ring through a spring system and ratchet teeth at one end, reciprocally rotates around an elastic point at the other end based on the electrostatic force. Rotational motion and torque from the driving gear ring are transmitted smoothly to driven gears through involute-shaped gear teeth. Smart design of antigap structures helps to overcome the unavoidable gap problem occurred in deep reactive ion etching (deep-RIE) process of silicon. The MGS has been fabricated and tested successfully by using SOI (silicon-on-insulator) wafer and one mask only. The angular velocity of the gear ring is proportional to the driving frequency up to 40 Hz.

Microsystem Technologies, 2014

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Journal of Microelectromechanical Systems, 2000

We report a dual-color total-internal-reflection (TIR)-based chip that can generate two overlappi... more We report a dual-color total-internal-reflection (TIR)-based chip that can generate two overlapping evanescent fields with different wavelengths for simultaneous imaging of two types of fluorophores. We derived a general relationship among the dimensions of the components of the chip to guarantee the overlap of two evanescent fields. Optical simulation results also confirm the generation and overlap of two evanescent fields. Using Si bulk micromachining and poly(dimethylsiloxane) (PDMS) casting, our fabrication method integrates all miniaturized optical components into one monolithic PDMS chip. Thus, assembly is unnecessary, and misalignment is avoided. Our PDMS chip can be employed with various sample delivery platforms, such as glass slide, flow cell, microchannel, etc. We first demonstrated the capability of the chip by imaging TIR fluorescent spots of a mixture of two fluorophores, namely, fluorescein and tetramethylrhodamine. We then employed the chip to observe the Brownian motion of a mixture of nile-red and dragon-green 500-nm microbeads. Our chip could potentially be integrated into a micro-total analysis system for highly sensitive and high-resolution dual-fluorescence imaging applications. . His current research interests are the design and fabrication of optical MEMS, optical biosensors, and microfluidics.

This paper reports the top-down fabrication of carbon nanotube (CNT) thin film on microelectrical... more This paper reports the top-down fabrication of carbon nanotube (CNT) thin film on microelectrical mechanical systems (MEMS) and the characterization of the thermoelectric coefficients of aligned single-walled carbon nanotube (SWNT) forest film. The film was synthesized by water-assisted chemical vapor deposition (CVD), a process known as 'super-growth'. CNT film was then condensed, manually maneuvered, and conveniently patterned by electron beam (EB) lithography to form desirable shapes. We demonstrate this process by patterning an array of Au-CNT thermocouples; measurement under room temperature conditions reveals the Seebeck coefficient of aligned SWNT film to be 18-20 μV C −1 .

Technical Digest. MEMS 2002 IEEE International Conference. Fifteenth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.02CH37266), 2002

This paper presents the design concept, fabrication and calibration of a six-degree of freedom (6... more This paper presents the design concept, fabrication and calibration of a six-degree of freedom (6-DOF) turbulent flow micro sensor utilizing the piezoresistive effects in silicon. The proposed sensor can independently detect six components of force and moment on a test particle in a turbulent flow. By combining p-type conventional and shear piezoresistors in Si (1 1 l), and arranging them suitably on the sensing area, the total number of piezoresistors used in this sensing chip is only eighteen, much fewer than the forty eight piezoresistors of the prior art piezoresistive 6-DOF force sensor [l]. Calibration for six components of force versus output voltages was carried out. The sensitivities are linear, close to the design values, and high enough to measure the forces and moments expected to act on the particles in turbulent flow in geophysics.

IEEJ Transactions on Sensors and Micromachines, 2008

In this paper, a thermoelectric generator with a flexible structure is presented. The thermoelect... more In this paper, a thermoelectric generator with a flexible structure is presented. The thermoelectric generator consists of 1625 thermocouples made from two materials, i.e. n-type BiTe and Cu thin films, on a flexible polyimide sheet by utilizing micromachining technology. The prototype of the flexible thermoelectric generator has dimensions of 100mm × 80mm × 3mm (length × width × thickness). Theoretical calculations show an output voltage of 317mV/K and a power of 7.8muW/K2. Preliminary experimental results measured on the test thermocouple samples show an average Seebeck voltage of 58.8muV/K per one thermocouple was obtained. This thermoelectric generator structure can be bent flexibly, so it can be used on both flat and cylindrical surfaces, e.g. on the skin of human body.

Advances in Natural Sciences: Nanoscience and Nanotechnology, 2012

Polymethyl methacrylate (PMMA) has been proposed as a material for micro-electromechanical system... more Polymethyl methacrylate (PMMA) has been proposed as a material for micro-electromechanical systems (MEMS) to initiate the research on environmentally friendly micro-nano machining technology using polymer materials. A polymer MEMS process has been developed using hot embossing and precision machining. MEMS structures less than 2 µm were successfully embossed. The PMMA layer that remained after hot embossing was removed by a polishing process to release the movable parts. A PMMA electrostatic comb-drive microactuator was fabricated. Both finger width and gap between fingers were 5 µm, and thickness was larger than 70 µm. An operated displacement of 11 µm at a drive voltage of 100 V was obtained. It was 20 times larger than that of an identical silicon device. A torsional micro mirror device driving with vertical comb actuator was fabricated. The size of the mirror was 1 × 1 mm 2 . The maximum tilt angle of 5.6 was obtained with driving voltage of 100 V and frequency up to 100 Hz. A chevron-shaped PMMA thermal actuator with a thickness of about 50 µm has been fabricated and tested successfully. The displacement was about 5 times larger than that of a Si counterpart at the same power consumption.

2006 IEEE International Symposium on MicroNanoMechanical and Human Science, 2006

Micro electrostatic comb-drive actuators are important components in micro electromechanical syst... more Micro electrostatic comb-drive actuators are important components in micro electromechanical systems (MEMS) [1]. Especially, polymer materials like PMMA have been of great interest in the research and development of integrated circuits (IC) and MEMS recently due to their relatively low cost and easy process [2]. In this research, we are trying to fabricate a PMMA-based electrostatic comb-drive actuator by X-ray lithography, which serves for a Micro Conveyer System.

Procedia Engineering, 2011

We present a micromachined gas sensor which can detect dilute NH 3 gas at ppb (parts per billion)... more We present a micromachined gas sensor which can detect dilute NH 3 gas at ppb (parts per billion) concentration based on chemoresistive effect of semiconducting tungsten trioxide (WO 3 ). The sensor structure consists of a poly-Si diaphragm-heater suspended on four tiny beams, which are connected to a frame with overall chip size of 1×1×0.3 mm 3 . Thanks to the diaphragm-beam structure, the power loss due to thermal conduction effect decreases and uniformed temperature on whole diaphragm is obtained. The sensor has been fabricated and tested. Thermal efficiency of the heater was measured to be 10 o C/mW. The optimal working temperature was found to be around 300 o C, and the sensor could detect NH 3 gas at ppb concentration in a background of wet air. The nano-gap effect of the interdigitated electrodes in improvement of the sensitivity was also confirmed. Our estimation based on the measurement results and system noise showed a limit-of-detection of NH 3 gas could be down to 2.5 ppb concentration.

IEEJ Transactions on Sensors and Micromachines, 2011

Nanostrain Sensing Based on Piezo-Optic Property of a Photonic Crystal Cavity

TRANSDUCERS 2009 - 2009 International Solid-State Sensors, Actuators and Microsystems Conference, 2009

This paper presents comprehensive improvements of micro motion transmission systems (MTS), which ... more This paper presents comprehensive improvements of micro motion transmission systems (MTS), which driven by electrostatic comb-drive actuators through ratchet mechanism to move micro objects unidirectionally in straight, curved and rotational paths. The first MTS is the tangential driving MTS, in which the driven objects are moved by tangential force. A rotational gearing MTS and micro conveyance system (MCS) based on this driving mode will be presented. Thanks to the new designs of directional guider of the micro containers and new turning module, the containers can move in both straight and curved paths in the tangential MCS. The second MTS is the perpendicular driving MCS, which drives micro containers by the perpendicular driving force, i.e. the moving direction of the container is perpendicular to the actuation direction. Movement velocities of the containers can be controlled by changing the driving frequency.

IEEJ Transactions on Sensors and Micromachines, 2007

In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossi... more In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossing process. Silicon molds were fabricated from silicon wafer with thickness of 500mum. First, DRIE technique was performed after optimized etching time and deposition (passivation) time to obtain a depth of 30mum with positive tapered sidewall of 1°. This is very important for de-molding process

TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference, 2007

This paper describes a design and fabrication of Si micro transportation systems (MTS) to drive m... more This paper describes a design and fabrication of Si micro transportation systems (MTS) to drive microcars based on ratchet mechanism and electrostatic comb-drive actuators. This MTS consists of linear and rotational comb actuators, microcars, and micro ratchet mechanism. The microcars can be moved with different velocities by comb-drive actuators through ratchet teeth. In this study, the MTS was fabricated by using SOI wafer with device layer of 30µm, buried SiO 2 layer of 4µm, and with only one mask. In our experiments, the movement of the microcar has been tested with driving frequency ranges from 5Hz to 40Hz. The velocity of the microcar was proportional to the driving frequency, and it matched well with theoretical calculation.

2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008

This paper presents a novel micro transportation system (MTS), which can drive micro containers i... more This paper presents a novel micro transportation system (MTS), which can drive micro containers in both straight and curved paths, based on electrostatic and ratchet mechanism. The micro container, which has driving-wings and anti-reverse-wings attached to the central 'backbone', is driven by electrostatic actuator through the ratchet racks in perpendicular direction. The container with the length and width of 450µm and 250µm, respectively, moves like a water strider with desirable velocity up to 200µm/sec in the straight and curved paths. In order to create the smart and flexible MTS, the elemental modules, e.g. straight, turning and separation modules with the same size (6mm×6mm) have been developed. Therefore, different configurations of the MTS can be created flexibly by assembling the elemental modules.

2007 International Symposium on Micro-NanoMechatronics and Human Science, 2007

motors to move a sliding shuttle. In this case, the This paper presents a novel micro transportat... more motors to move a sliding shuttle. In this case, the This paper presents a novel micro transportation driving mechanism requires at least two groups of system (MTS), which can drive micro carts by bidirectional XY actuators which were turned on and off utilizing electrostatic actuator and ratchet at suitable times, alternately holding and driving a mechanism. The micro cart, which has driving-wings shuttle. In another work [5], Fujimasa reported the and anti-reverse-wings attached to its central integrated actuator which was actuated by vibration and 'backbone', is driven by electrostatic actuator

IEEE International Symposium on Micro-NanoMechatronics and Human Science, 2005, 2005

We report a design and fabrication of micro conveyer system (MCS) based on electrostatic comb-dri... more We report a design and fabrication of micro conveyer system (MCS) based on electrostatic comb-drive actuators using SOI wafer. This MCS consists of linear comb actuator, rotational comb actuator, micro containers, and ratchet mechanism. Micro containers, used for carrying micro and nano samples such as protein, cells, are moved by comb-actuators through ratchet teeth. Each MCS, which has dimension of

2008 International Symposium on Micro-NanoMechatronics and Human Science, 2008

This paper presents design and fabrication of a silicon micro ratcheting transmission system (RTS... more This paper presents design and fabrication of a silicon micro ratcheting transmission system (RTS) that utilizes electrostatic comb-drive actuators to rotate a gear ring (or rotor) through a ratchet mechanism. The rotational actuator is engaged with the gear ring through ratchet teeth at one end, and reciprocally rotates around an elastic point at the other end based on electrostatic force.

Microsystem Technologies, 2014

hence, rF MeMS featuring small size, low weight and high performance can be considered as a futur... more hence, rF MeMS featuring small size, low weight and high performance can be considered as a future enabling technology to replace off-chip passive elements (Girbau et al. 2006).

Microsystem Technologies, 2009

This paper presents a systematic approach to fabricate optically smooth, through-wafer silicon (S... more This paper presents a systematic approach to fabricate optically smooth, through-wafer silicon (Si) molds for polymer optical devices, in particular poly(dimethylsiloxane) (PDMS) total internal reflection (TIR)-based devices. First, the Si molds were fabricated by an optimized, through-wafer deep reactive ion etching (DRIE) process to achieve small roughness. To further reduce the roughness, the Si molds were then oxidized and etched in BHF for three times to achieve surface roughness average (R a ) and root mean square (RMS) roughness below 25 nm while peakto-valley (P-V) roughness is below 150 nm. We monitored the surface roughness and morphology of the sidewalls of Si mold through three cycles of oxidation and BHF etching using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). We found that further oxidation and BHF etching might not have much effect in further reducing the roughness while the device feature definitions might be compromised. Finally, the PDMS TIR-based devices replicated from the Si molds were evaluated by means of FESEM, AFM and by imaging of the fluorescent evanescent spots.

Microsystem Technologies, 2013

This paper presents the design and fabrication of a silicon micro gearing system (MGS) that utili... more This paper presents the design and fabrication of a silicon micro gearing system (MGS) that utilizes electrostatic comb-drive actuators to rotate a gear ring through a ratchet mechanism. The rotational comb-drive actuator is engaged with the gear ring through a spring system and ratchet teeth at one end, reciprocally rotates around an elastic point at the other end based on the electrostatic force. Rotational motion and torque from the driving gear ring are transmitted smoothly to driven gears through involute-shaped gear teeth. Smart design of antigap structures helps to overcome the unavoidable gap problem occurred in deep reactive ion etching (deep-RIE) process of silicon. The MGS has been fabricated and tested successfully by using SOI (silicon-on-insulator) wafer and one mask only. The angular velocity of the gear ring is proportional to the driving frequency up to 40 Hz.

Microsystem Technologies, 2014

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Journal of Microelectromechanical Systems, 2000

We report a dual-color total-internal-reflection (TIR)-based chip that can generate two overlappi... more We report a dual-color total-internal-reflection (TIR)-based chip that can generate two overlapping evanescent fields with different wavelengths for simultaneous imaging of two types of fluorophores. We derived a general relationship among the dimensions of the components of the chip to guarantee the overlap of two evanescent fields. Optical simulation results also confirm the generation and overlap of two evanescent fields. Using Si bulk micromachining and poly(dimethylsiloxane) (PDMS) casting, our fabrication method integrates all miniaturized optical components into one monolithic PDMS chip. Thus, assembly is unnecessary, and misalignment is avoided. Our PDMS chip can be employed with various sample delivery platforms, such as glass slide, flow cell, microchannel, etc. We first demonstrated the capability of the chip by imaging TIR fluorescent spots of a mixture of two fluorophores, namely, fluorescein and tetramethylrhodamine. We then employed the chip to observe the Brownian motion of a mixture of nile-red and dragon-green 500-nm microbeads. Our chip could potentially be integrated into a micro-total analysis system for highly sensitive and high-resolution dual-fluorescence imaging applications. . His current research interests are the design and fabrication of optical MEMS, optical biosensors, and microfluidics.