Showing papers by "Chien-Hung Liu published in 2010"

Ultraviolet ZnO Nanorod Photosensors

Abstract: This study fabricates and characterizes ultraviolet (UV) photosensors with ZnO nanorods (NRs). The NR arrays were selectively grown in the gap between interdigitated (IDT) electrodes of devices using hydrothermal solution processes and a lithography-based technique. Compared with a conventional ZnO photosensor without NRs, the proposed UV NR photosensors have much higher photoresponse in the UV region. Additionally, the photoconductive gain of an NR photosensor increased as UV illumination time increased; it varied at 34.45−5.32 × 102 under illumination by 18.28 mW/cm2 optical power. Consequently, the substantial photoconductive gain can be attributed to high surface-to-volume ratio of ZnO NRs. The high density of hole-trap states on NR surfaces lead to a persistent photoconductivity (PPC) state, promoting the transport of carriers through devices.

Design and control of a long-traveling nano-positioning stage

Abstract: In this paper, a Dual-Axis Long-Traveling Nano-Positioning Stage (DALTNPS) is presented. In order to extend the traveling and increase the accuracy, the two sorts of stages, a traditional ball-screw stage and a three-degrees-of-freedom (3-DOF) piezo-stage, were composed. The traditional ball-screw stage which is composed of two guide-ways and a ball-screw at each axis is a long-travel stage, and the 3-DOF piezo-stage, which is composed of three piezoelectric actuators and four translation–rotation mechanisms, is a high precision stage. In addition, a 3-DOF measuring system and a PID controller are composed of a 3-DOF closed-loop controller and applied to implement the DALTNPS. The measuring system which is composed of two laser interferometers and two plane mirrors is a 3-DOF optical measuring system. Thus, the position at the x and y axes and the rotation around the z axis can be obtained and they are the responses of DALTNPS. Finally, the experiment results evidence that the DALTNPS is characterized by long-travel, high linear accuracy, high rotation accuracy, high contouring accuracy and high motion speed.

Characteristic Improvements of ZnO-Based Metal–Semiconductor–Metal Photodetector on Flexible Substrate with ZnO Cap Layer

Abstract: In this work, ZnO-based metal–semiconductor–metal photodetectors with and without a ZnO cap layer were fabricated on flexible substrates of poly(ethylene terephthalate) (PET) for comparative analysis. The ZnO films were prepared by a low-temperature sputtering process. The photodetector with a ZnO cap layer (stack structure: ZnO/Ag/ZnO/PET) shows a much higher UV-to-visible rejection ratio of 1.56 ×103 than that without. This can be attributed to the photocurrents that are not only significantly increased in the UV region but also slightly suppressed in the visible region for such a novel structure. With an incident wavelength of 370 nm and an applied bias of 3 V, the responsivities of both photodetectors with and without a ZnO cap layer are 3.80 ×10-2 and 2.36 ×10-3 A/W, which correspond to quantum efficiencies of 1.13 and 0.07%, respectively. The Schottky barrier height at the Ag/ZnO interface is also determined to be 0.782 eV.

Thickness measurement system for transparent plates using dual digital versatile disc (DVD) pickups

Abstract: A low-cost high-precision thickness measurement system for transparent plates that uses dual digital versatile disc (DVD) pickups is proposed. The two DVD pickups are used as the transmitter and the receiver in the measurement system, respectively. One of the DVD pickups emits a laser to the other DVD pickup (receiver) and projects on the photodiode integrated circuit of the receiver. The transparent plate is placed in the optical path to change the focused point that will affect the focusing error signal (FES) of the receiver. Using the FES, a mathematical model for thickness measurement based on the geometric optical method is developed. The experimental results show that the accuracy is 1.5 μm, and the uncertainty is estimated to be ±1.37 μm for the measured thickness of 150μm.

Development of a DVD pickup-based four-degrees- of-freedom motion error measuring system for a single-axis linear moving platform

Abstract: In this study, a simple and high-resolution four-degrees-of-freedom (4-DOF) motion error measuring system based on DVD pickup has been proposed. it can simultaneously measure the horizontal straightness error and three angular errors of a single-axis linear moving platform. The horizontal straightness error is measured based on the focus technique of DVD pickup and the inverse algorithm is used to solve pitch, yaw, and roll angular errors through the kinematic analysis. The grating is mounted on the moving axis of a single-axis linear moving platform and reflects incident laser beam into several diffractive rays. Photodiode IC (PDIC) of DVD pickup is set up for detecting the focus error signal (FES) of zero-order diffraction ray from grating and quadrant detectors are set up for detecting the position of ±1st-order diffraction rays from grating. The 4-DOF motion error measuring system detected the three angular errors with a related accuracy of about ±1 arc sec for a measuring range of ±100 arc sec, and detected horizontal straightness with a related accuracy of about ±2 μm for a measuring range of ±150 μm.

Preparation and Characteristics of Flexible Nanorod-Based Photodetectors

Abstract: Metal-semiconductor-metal ultraviolet photodetectors on flexible polyethylene terephthalate (PET) substrates with ZnO nanorods have been characterized. The photoresponsity and UV-to-visible rejection ratio of the ZnO nanorod-based sensor were 0.0409 A/W and 282.59, respectively. Compared to a traditional ZnO photodetector without nanorods, the fabricated novel photodetector showed much higher photoresponsity which could strongly depend on oxygen adsorption and desorption in the presence of trap states at the nanorods surface. It can be attributed to high surface-to-volume ratio of ZnO nanorods.

Method of detecting a dynamic path of a five-axis machine tool and dectecting assembly for the same

Abstract: A method of detecting a dynamic path of a five-axis machine tool having a spindle and a turntable and has a preparing step, a correcting step and a detecting step. The preparing step includes mounting a detector on the spindle, mounting a cat-eye reflector on the turntable, emitting a laser light to the cat-eye reflector, reflecting the laser light to the detector and splitting into two light beams. One of the light beams is emitted to a four-quadrant position sensitive detector. The correcting step includes rotating the detector, detecting a signal of the laser light by the four-quadrant position sensitive detector to eliminate an offset between the detecting assembly and the spindle. The detecting step includes detecting the dynamic path of the five-axis machine tool by detecting the positions of at least two of the linear axes and at least one of the rotation axes of the five-axis machine tool.

Development of a straightness measuring system and compensation technique using multiple corner cubes for precision stages

Abstract: At present, the accuracy of precision manufacture is most affected by straightness errors, so the measurement and compensation of these errors are very important. In the current paper, thre...

Development of a middle-range six-degrees-of-freedom system

Abstract: This paper describes the successful development of a middle-range six-degrees-of- freedom stage, using the features of a flexible structure. The system includes two parts: a middle- range positioning X-Y stage and a four-degrees-of-freedom stage. The flexible structure of the four-degrees-of-freedom stage is built from two kinds of flexible bodies: circular hinges and a new two-degrees-of-freedom flexible body. The four-degrees-of-freedom stage was designed to compensate movement errors including linear displacement, pitch, and roll errors. The linear displacement reaches 20mm along the X-axis, 20mm along the Y-axis, and 5mm along the Z-axis. The rotation angle around the X-axis (ux), Y-axis (uy), and Z-axis (uz) were all 10 arcsec. A novel six-degrees-of-freedom measuring system was also designed. Precision feedback control is demonstrated in a series of experiments performed using the proposed measurement system.

Detecting assembly for a multi-axis machine tool

Abstract: A detecting assembly for multi-axis machine tools having a spindle and a turntable and has a detector, a lens device and a computer. The detector is connected to the spindle and has a mounting frame and two detecting segments. The mounting frame is connected to the spindle and has a connecting rod, a bottom board and multiple mounting boards. The detecting segments are mounted on the mounting boards and each has a light source and a sensor. The lens device is mounted on the turntable, extends into the detector and has a supporting shaft and a spherical lens. The spherical lens is mounted on an upper end of the supporting shaft to align light emitted from the light sources with corresponding sensors via the spherical lens. The computer is electrically connected to the detector to receive signals of the detecting segments of the detector and has a signal processor.

The development of A 3‐dimensional vibration measuring system with corner cubes and quadrant detectors(Invited)

Abstract: In this paper, a new optical 3‐dimensional vibrometer is presented. This system is composed of two orthogonally set up corner cubes (CC), a collimated laser source, two quadrant detectors (QD) and three beam‐splitters (BS). The corner cubes are designed to be fixed to the vibrating object and reflect the laser source onto the quadrant detectors. Due to the optical characteristics of the corner cubes, the measuring results of the QD can be magnified twice and it is not affected by micrometer‐angle. So, the three‐dimensional vibration amplitude can be obtained. The resolution is about 50 nm. This system is characterized by three‐dimensional measurement, high resolution, low cost, simple set up and wide bandwidth.

Characteristics of ZnO-based MSM photodetectors with ZnO cap layer on flexible substrates

Abstract: In this work, both of ZnO based metal-semiconductor-metal photodetectors with and without ZnO cap layer were fabricated on flexible substrates (polyethylene terephthalate, PET) for comparative analysis. The ZnO films were prepared by a low temperature sputtering process. The photodetector with ZnO cap layer (stack structure: ZnO/Ag/ZnO/PET) shows a much higher UV-to-visible rejection ratio of 1.56×103 than one without. It can be attributed to the photocurrents significantly enhanced under UV light illumination in such a novel structure. With an incident wavelength of 370 nm and 3 V applied bias, the responsivities of both photodetectors with and without ZnO cap layer are 3.80×10−2 and 2.36×10−3 A/W, respectively, which correspond to quantum efficiencies of 1.13 % and 0.07 %. The Schottky barrier height on Ag/ZnO interfaces is also obtained to be 0.782 eV.

Development of the precision long-stroke 3-DOF nano-stage for the photonic crystal process

Abstract: In this paper, it develops a precision long-stroke 3-DOF nano-stage for the nano photonic crystal process. It integrates a linear motor driven long-stroke stage, a piezoelectric driven three-degrees-of-freedom (3-DOF) nano stage, multi-degrees-of-freedom (MDOF) laser interferometer measurement system and their control systems. The long-stroke nano-stage is a hybrid precision stage that can provide long-stroke and high precision positioning. The common focus horizon regulation system is used to keep the parallelism between writing instrument and the target while the laser direct writing instrument is used to write the nano structure needed. Furthermore, the automatic focusing and horizon control system can compensate the defocusing and angular errors that caused by machining automatically. With this precision 3-DOF nano-stage, the laser direct writing system can improve the process speed, overcome the optical limit of interference to reduce the writing spot, generate arbitrary patterns.

Measurement and tracking control of the Z‐tilts error compensating stage of the nano‐measuring machine

Abstract: Purpose – The purpose of this paper is to develop the multi‐degree‐of‐freedom measurement system to test, verify, and control the nano‐measuring machine.Design/methodology/approach – A generic differential model approach is constructed to numerically describe the hysteresis effects of piezoelectric actuators. Based on the generic differential model, a feedforward compensator with a proportional integral (PI) type controller is designed to compensate for the hysteresis nonlinearity of a piezoelectric actuated three degree‐of‐freedom coplanar nanostage which can provide high‐precision applications.Findings – The Z‐tilts (z, pitch, and roll motion) error compensation stage of the nano‐measuring machine is accomplished. Moreover, a high‐resolution laser interferometer is used to measure position accurately.Originality/value – This paper contributes to develop a tracking control design method for the piezoelectric motion platform which combines a closed‐loop feedforward compensator with a PI type controller.