Browsing by Author "Chao, SC"

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Electrical characteristics of CO2-sensitive diode based on WO3 and IrO2 for microsensor applications
(1998-02-15)
Chao, SC
;
電子物理學系
;
Department of Electrophysics
Devices based on the contact of sputtered WO3 and IrO2 that are covered by an HCO3--containing polymer exhibit reversible and reproducible CO2-dependent, diodelike current rectification at 1 atm and room temperature. The gain or loss of current in the forward direction as a function of CO2 concentration is found to be tunable by controlling the thickness ratio of the WO3 and IrO2 films. The rectification mechanism is uniquely governed by the thermodynamic free energies; this is the key to the durability previously not attainable using conventional diodes in microsensor applications. These diodes are useful as a basis of construction for durable microsensors operating in gases or liquids.
Electrical characteristics of glucose-sensitive diode arrays based on WO3 and IrO2 for microsensor applications
(2003-11-01)
Chao, SC
;
電子物理學系
;
Department of Electrophysics
Arrays based on the contacts of sputtered WO3 and IrO2 that are covered by a glucose-oxidase-containing polymer exhibit reversible and reproducible glucose-dependent, diodelike current rectification. The glucose concentration as a function of current in the forward direction can be spatially resolved. These chemical-sensitive diode arrays are useful as a basis of construction of durable microsensors for tracing the concentration gradient of biological molecules, as in food freshness sensing.
Fabrication and characterization of IrO2-based microsensors for fast detection of carbon dioxide
(1997-04-01)
Lue, JC
;
Chao, SC
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
A pair of closely spaced IrO2 electrodes covered by a polymer film is employed as a new solid-state microsensor fur CO2 gas at 1 atm and room temperature. Its function is based on IrO2 sensitivity to the pH-lowering effect produced by CO2 equilibration in the polymer film. This sensitivity is made ''asymmetric'' by leaving one IrO2/polymer ''masked'' to CO2 gas exposure. The potential difference is measured and found to be reversible and reproducible for the concentration determination of CO2 between similar to 0.1-100% CO2 in N-2. Since the microsensor shows fast response, it can also be employed in transient flow-injection experiments for the volumetric analysis of CO2. When calibrated carefully and used with care, the new microsensor based on IrO2 is capable of measuring either the concentration or volume of CO2 with high precision and negligible baseline drift.
High-resolution MOS magnetic sensor with thin oxide in standard submicron CMOS process
(1996-10-01)
Yang, HM
;
Huang, YC
;
Lei, TF
;
Lee, CL
;
Chao, SC
In this paper, new results obtained with an NMOS magnetic-field sensor made by an industrial 0.8 mu m CMOS process are presented. The major disadvantage of MOS magnetic sensors, a larger noise, can be overcome by the submicron CMOS process with 19 nm gate oxide, The device with W/L=60 mu m/50 mu m biased at saturation region has a resolution of 150 nT (Hz)(-1/2) at 1 kHz and 400 nT (Hz)(-1/2) at 100 Hz, respectively. Even when the device size is scaled down to W/L=6 mu m/5 mu m, the resolution still has the value of 1.5 mu T (Hz)(-1/2) at 1 kHz. The dependence of sensitivity and current-related sensitivity for various bias conditions is discussed in detail and a simple model to explain these trends is established.
Material and ultrafast optoelectronic properties of furnace-annealed arsenic-ion-implanted GaAs
(1998-09-01)
Lin, GR
;
Chen, WC
;
Chang, CS
;
Chao, SC
;
Wu, KH
Structural, electrical, and ultrafast optical properties of furnace-annealed arsenic-ion-implanted GaAs (GaAs:As+) has been investigated for its applications in ultrafast optoelectronics, From these studies, we determine that GaAs substrates implanted with 200-keV arsenic ions at 10(16) ions/cm(2) and furnace-annealed at 500 degrees C-600 degrees C would have recovered its crystallinity, be highly resistive, and exhibit picosecond photo-excited carrier lifetimes. The duration of the electrical pulses generated by photoconductive switches (PCS's) fabricated on the optimized material was approximate to 4 ps, The risetime (10%-90%) and 1/e falltime were, respectively, approximate to 2 and 3 ps, These results were measurement-system limited, We estimated the actual response to be approximate to 2 ps, consistent with a photo-excited carrier lifetime of approximate to 1.8 ps. The peak responsivity was greater than or equal to 4x10(-3) A/W. The dark current for the GaAs:As+ PCS biased at 40 V was as low as 5 nA. The break down field was higher than 150 kV/cm, These characteristics are comparable to those of state-of-the-art photoconductors such as LT-GaAs.
Preparation and electronic properties of YBa2Cu3Ox films with controlled oxygen stoichiometries
(1998-08-01)
Wu, KH
;
Hsieh, MC
;
Chen, SP
;
Chao, SC
;
Juang, JY
We describe a novel technique capable of controlling the oxygen content of YBa2Cu3Ox (YBCO) films in a precise and reversible manner. The temperature dependence of resistivity and the distinct two-plateau behavior in critical temperature T-CO versus oxygen content plot of these films are consistent with those observed in the bulk and single crystals of YBCO. The O 1s and Cu 2p absorption spectra of these films were measured by polarization-dependent X-ray absorption spectroscopy (XAS). The intensity variations of the pre-edge peaks as a function of oxygen content are discussed. We also used these films to systematically study the electron-phonon coupling strength and the position of Fermi level by using a femtosecond pump-probe technique. A clear sign-reversal of the transient reflectivity, which was consistently explained by the thermomodulation model, was observed. Both of these optical measurements support the idea that the electronic structure of YBCO cuprates is based on the charge transfer model with hybridization between the Cu and O sites.