Chien-Hsing Hsu

Electrochemical Performances of Cu Nanodots Modified Amorphous Si Thin Films for Lithium–Ion Batteries

Amorphous Si thin films have been prepared using radio-frequency magnetron sputtering. Cu nanodots of 2-10 nm in diameter were sputter deposited on the surface of Si films. The Si films modified with Cu nanodots (n-Cu/Si) were used as anodes for lithium-ion batteries. The performances of the n-Cu/Si anodes with different thickness of Si films, 120 and 1000 nm, were characterized and compared. The Cu nanodots can greatly improve the cycling stability. The amount of capacity fading was 66% after 150 cycles for the thinner Si films (120 nm), and was over 90% after 50 cycles for thicker films (1000 nm). For the n-Cu/Si films, the amount of capacity fading was 33% for thin films and 45% for thicker films.

Study of hydrogen detection response time with Pt-gated diodes fabricated on AlGaN/GaN heterostructure

The hydrogen detection response time of Pt-gated diode sensors fabricated on AlGaN/GaN heterostructure as a function of the hydrogen concentration was investigated. A new method to extract the response time, taking the derivative of diode current, was proposed and shown to reduce the response time of detecting 1% hydrogen by about 60% as compared to the response time defined as the diode current reaching 90% of its total changes, t90. Hydrogen-sensing experiments were conducted at different temperatures, and an Arrhenius plot of the data determined an activation energy of 17.7 kJ/mole for the sensing process.

Carbon monoxide detection sensitivity of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors in different temperature environments

The effect of ambient temperature on the detection sensitivity of carbon monoxide (CO) using ZnO nanorod-gated AlGaN/GaN high electron mobility transistor (HEMT) sensors was studied over a range of temperatures from 25 to 400 °C. An increase of the HEMT drain current was observed for exposure to the CO-containing ambients, due to chemisorbed oxygen on the ZnO surface reacting with CO to form CO2 and releasing electrons to the oxide surface, increasing the counter charges in the two-dimensional electron gas channel of the HEMT. By increasing the detection temperature from 25 °C to 150 °C, the CO detection sensitivity, ΔI/I, and detection limit were significantly improved from 0.23% to 7.5% and from 100 ppm to ∼30 ppm, respectively. However, the sensitivity of the CO detection was degraded by the decrease of mobility and saturation drain current of HEMT at temperatures higher than 200 °C.

The effect of N2 plasma damage on AlGaAs/InGaAs/GaAs high electron mobility transistors. I. DC characteristics

Abstract 0.25 μm gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors were exposed to inductively coupled plasma (ICP) N 2 discharges at varied source power and rf chuck power. The plasma damage was characterized by evaluating device extrinsic transconductance and saturated drain–source current, as well as Schottky gate ideality factor and reverse breakdown voltage as a function of both ICP source power and rf chuck power. Auger and atomic force microscopy were also used to characterize the atomic ratio and roughness of plasma damaged surface, respectively. At a lower range of ICP source power (between 100 and 300 W) with a constant rf power of 10 W, the device performance was barely changed. But at higher ICP source power (greater than 400 W) and rf power (greater than 20 W), device characteristics including gate ideality factor, reverse breakdown voltage and saturated drain–source current were seriously degraded. In this plasma damage study, two device degradation mechanisms were identified. The first was ion bombardment induced lattice disorder that created generation–recombination centers and reduced the free carrier concentration. The second was preferential loss of As from GaAs surface and this also created deep level states, which gave rise to gate leakage current.

Wireless Hydrogen Sensor Networks Using AlGaN/GaN High Electron Mobility Transistor Based Differential Diodes Sensor

1. University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611 2. University of Florida, Department of Chemical Engineering, Gainesville, FL 32611 3. University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611 4. Feng Chia University, Department of Chemical Engineering, Taichung, Taiwan 40724 5. SVT Associates, Eden Prairie, MN 55344 6. University of Florida, Gainesville, FL 32611 7. J Painter Consulting LLC, Deltona, FL 32738

A novel potentiometric sensor based on urease/ bovine serum albumin-poly(3,4-ethylenedioxythiophene)/Pt for urea detection

Abstract We have presented a potentiometric urea sensor using an urease/bovine serum albumin (BSA)-poly(3,4-ethylenedioxythiophene)(PEDOT)/Pt electrode. A urea detection sensitivity of 15.2 mV/decade (order of magnitude) has been achieved. BSA trapped in the PEDOT matrix was employed to bond urease molecules on the surface of a BSA-PEDOT/Pt electrode via amide bonds formed between the carboxyl functional groups on the enzyme and the amines on the BSA. The effects of PEDOT thickness, pH value of the urea solution, urease concentration, and temperature on the urea detection sensitivity were also studied. The lifetime of the sensor was studied for a period of 10 weeks, and the average sensing degradation rate was about 9 % per week. This sensor displayed a high selectivity to urea over glucose, KCl, and NaCl.

Effects of N2 or Ar plasma exposure on GaAs/AlGaAs heterojunction bipolar transistors

Abstract The effects of N 2 and Ar plasma exposure on GaAs/AlGaAs heterojunction bipolar transistors (HBT) were investigated with an inductively coupled plasma (ICP) system. The plasma damage was characterized by evaluating device dc current gain and base–collector reverse breakdown voltage as functions of ICP source power and rf chuck power. Recombination centers, surface damage, and deep level defects created by the N 2 and Ar discharges are the dominant mechanisms for device degradations. Exposure time and chamber pressure are also critical to device dc characteristics. We also found that HBT devices degrade more seriously in N 2 plasma than in Ar plasma.