Browsing by Author "Ren, Fan"

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A Reconfigurable, Pulse-shaping Potentiometric Readout System for Bio-Sensing Transistors
(2019-01-01)
Lu, Shao-Yung
;
Shan, Siang-Sin
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Yang, Jiancheng
;
Chang, Chin-Wei
;
Ren, Fan
This paper presents a new multi-modality readout system for potentiometric electrochemical sensors. The design adopts a pulse modulation at the gate and drain of the Bio-FET sensors to reduce the effects of charge accumulation between the surface of the electrodes and the ion analytes. The adjustable duration and amplitude of stimuli signals provide flexibility for different biosensing applications and a wide range of detectable concentration. Also, an oscillator-based architecture is proposed for digitization and integration. The counting time can be adjusted to enhance the resolution of the readout system. The proposed potentiometric sensing system was tested with 0.1-10 mM Potassium Ferricyanide (K-3[Fe(CN)(6)]), and the results are interpreted in the micro-LCD on the board. The design offers the opportunity for a handheld medical device with fast and real-time monitoring of biomarkers and ion analytes.
DC and dynamic switching characteristics of field-plated vertical geometry beta-Ga2O3 rectifiers
(2019-01-01)
Yang, Jiancheng
;
Carey, Patrick
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Ren, Fan
;
Chen, Yen-Ting
;
Liao, Y.
Reverse breakdown voltages larger than 1 kV have been reported for both unterminated Ga2O3 vertical rectifiers (1000-1600 V) and field-plated Schottky diodes (1076-2300 V) with an epi thickness of 8-20 mu m. If the doping is in the 10(16) cm range, the breakdown is usually in the 500-800V regime. Furthermore, the switching characteristics of discrete Ga2O3 vertical Schottky rectifiers exhibited reverse recovery times in the range of 20 to 30 ns. Large area (up to 0.2 cm(2)) Ga2O3 rectifiers were fabricated on a Si-doped n-Ga2O3 drift layer grown by halide vapor phase epitaxy on a Sn-doped n(+) Ga2O3 (001) substrate. A forward current of 2.2 A was achieved in single-sweep voltage mode, a record for Ga2O3 rectifiers. The on-state resistance was 0.26 Omega.cm(2) for these largest diodes, decreasing to 5.9 x 10 Omega.cm(2) for 40x40 mu m devices. We detail the design and fabrication of these devices. In addition, an inductive load test circuit was used to measure the switching performance of field-plated, edge-terminated Schottky rectifiers with a reverse breakdown voltage of 760 V (0.1 cm diameter, 7.85 x10(-3) cm(2) area) and an absolute forward current of 1 A on 8 mu m thick epitaxial beta-Ga2O3 drift layers. These devices were switched from 0.225 A to -700 V with t of 82 ns, and from 1 A to -300 V with t of 64 ns and no significant temperature dependence up to 125 degrees C. There was no significant temperature dependence of t(rr)up to 150 degrees C.
Dip Pen Nanolithography of Conductive Silver Traces
(2010-06-03)
Hung, Sheng-Chun
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Nafday, Omkar A.
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Haaheim, Jason R.
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Ren, Fan
;
Chi, G. C.
We report the first demonstration of sub mu m, sub-50-mu Omega.cm conductive traces directly written by Dip Pen Nanolithography (DPN). We achieved sub mu m Ag lines with 28.8 mu Omega.cm average resistivity after direct-write printing from a silver nanoparticle-based ink suspension and annealing at 150 degrees C for 10 min. This compares to Ag bulk resistivity of 1.63 mu Omega.cm, where the difference is within the range of previously reported variations in conductivity of Ag-based inks due to annealing conditions and larger width scales. We leveraged DPN's ability to directly place materials at specific locations in order to fabricate and characterize these conductive silver (Ag) traces on electrode patterns and multiple substrates (SiO(2), Kapton, mica). The low viscosity of the AgNP ink solution allowed write speeds up to 1600 mu m/s, almost 4 orders of magnitude higher than typical thiol-on-gold DPN writing speeds. This direct-write methodology paves the way for site-specific deposition of metallic materials for use in applications such as circuit repair, sensor element functionalization, failure analysis, gas sensing, and printable electronics.
Dynamic Switching Characteristics of 1 A Forward Current beta-Ga2O3 Rectifiers
(2019-01-01)
Yang, Jiancheng
;
Ren, Fan
;
Chen, Yen-Ting
;
Liao, Yu-Te
;
Chang, Chin-Wei
An inductive load test circuit was used to measure the switching performance of field-plated edge-terminated Schottky rectifiers with a reverse breakdown voltage of 760 V (0.1 cm diameter, 7.85 x 10(-3) cm(2) area) and an absolute forward current of 1 A on 8 mu m thick epitaxial beta-Ga2O3 drift layers. The recovery characteristics for these vertical geometry beta-Ga2O3 Schottky rectifiers switching from forward current of 1 A to reverse off-state voltage of -300 V showed a recovery time (trr) of 64 ns. There was no significant temperature dependence of trr up to 150 degrees C.
Effect of thermal annealing for W/beta-Ga2O3 Schottky diodes up to 600 degrees C
(2019-11-01)
Xian, Minghan
;
Fares, Chaker
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Ren, Fan
;
Gila, Brent P.
;
Chen, Yen-Ting
The electrical and structural properties of sputter-deposited W Schottky contacts with Au overlayers on n-type Ga2O3 are found to be basically stable up to 500 degrees C. The reverse leakage in diode structures increases markedly (factor of 2) for higher temperature annealing of 550-600 degrees C. The sputter deposition process introduces near-surface damage that reduces the Schottky barrier height in the as-deposited state (0.71 eV), but this increases to 0.81 eV after a 60 s anneal at 500 degrees C. This is significantly lower than conventional Ni/Au (1.07 eV), but W is much more thermally stable, as evidenced by Auger electron spectroscopy of the contact and interfacial region and the minimal change in contact morphology. The contacts are used to demonstrate 1.2 A switching of forward current to -300 V reverse bias with a reverse recovery time of 100 ns and a dI/dt value of 2.14 A/mu s. The on/off current ratios were >= 10(6) at -100V reverse bias, and the power figure-of-merit was 14.4 MW cm(-2). Published by the AVS.
Implementation of a 900 V Switching Circuit for High Breakdown Voltage beta-Ga2O3 Schottky Diodes
(2019-05-22)
Chen, Yen-Ting
;
Yang, Jiancheng
;
Ren, Fan
;
Chang, Chin-Wei
;
Lin, Jenshan
This paper presents a switching circuit for high breakdown-voltage Ga2O3 vertical Schottky rectifiers. Field-plated edge-terminated (FPET) vertical Schottky diodes were fabricated on a 20-mu m thick Si-doped n-type Ga2O3 drift layer which was grown on the 650-mu m thick beta-Ga2O3 substrate via halide vapor phase epitaxy (HVPE). The measured reverse recovery time of the proposed Ga2O3 Schottky diode was 81 ns when switched to a reverse bias voltage of -900 V. The implementation of a switching circuit with the novel Ga2O3 diode is the first demonstrated at such a high switching voltage. This paper also provides insights for the practical implementation of the Ga2O3 vertical Schottky rectifiers from device fabrication to circuit design. (C) The Author(s) 2019. Published by ECS.
Review-Opportunities for Rapid, Sensitive Detection of Troponin and Cerebral Spinal Fluid Using Semiconductor Sensors
(2019-11-20)
Carey, Patrick H.
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Lobo, Brian C.
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Gebhard, Michael P.
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Leon, Marino E.
;
Flax, Sherri D.
There are opportunities for development of modularized, inexpensive protein biomarker sensors in clinical applications. In this review we focus on two of these, namely early diagnosis of acute myocardial infarction (AMI) and detection of cerebral spinal fluid (CSF). Evaluation of patients with acute chest pain is challenging due to the heterogeneity of the underlying conditions, leading to patients with AMI being mistakenly sent home from emergency rooms or those at low risk for an adverse cardiac event being unnecessarily admitted without precise cardiac biomarker testing. Cardiac troponin I (cTnI) in cardiac muscle tissue is a standard clinical biomarker for AMI, as its concentration rises quickly in the blood during release from myocardial cells following cell death. The time-dependence of the cTnI concentration is the basis of antigen-antibody methodologies such as radioimmunoassay and enzyme-linked immunosorbent assay (ELISA). These methods are time consuming, leading to delays in diagnosis and higher costs. The challenge is to develop a real-time, accurate, low-cost point-of-care heart attack sensor. The coefficient of variation must be precise, within the parameters established by the American College of Cardiology. Similarly, leakage of cerebrospinal fluid (CSF) is a critical condition with a high risk of meningitis and potential mortality. The primary methods of detection for the biomarker beta 2-Transfferin (B2T) are immunofixation electrophoresis (IFE) and ELISA. Consistent IFE results down to 2 mu g/mL can be obtained in patient samples, but requires a minimum 2.5-hour testing period, which is not expedient for real time feedback during surgery in or around the central nervous system. Additionally, to achieve good sensitivity and handle the inherently low concentration of B2T in CSF, lab procedures require samples to be concentrated or run in duplicate to ensure accurate detection. Real time turnaround is on the order of days. To alleviate the slow turn-around times, there is strong interest in electronic detection methods for proteins using biologically functionalized transistors, which provide an electronic readout and are readily integrated with wireless data transmission. (C) The Author(s) 2019. Published by ECS.
Switching Behavior and Forward Bias Degradation of 700V, 0.2A, beta-Ga2O3 Vertical Geometry Rectifiers
(2019-01-30)
Yang, Jiancheng
;
Fares, Chaker
;
Ren, Fan
;
Chen, Yen-Ting
;
Liao, Yu-Te
We report the switching recovery characteristics of large area (contact dimension 0.04 x 0.04 cm(2)) vertical geometry beta-Ga2O3 Schottky rectifiers, consisting of Si-doped epitaxial layers on conducting bulk substrates. Devices that were switched from forward current of 0.225 A to reverse off-state voltage of -700 V in an inductive load test circuit showed a recovery time (t(rr)) of 82 ns, with a reverse recovery current (I-rr) of 38 mA and dI/dt of -2.28 A. mu sec(-1). This shows the potential of Ga2O3 rectifiers for power switching applications, provided effective thermal management schemes can be implemented. Devices deliberately tested to failure under forward bias conditions exhibit delamination and cracking of the Ni/Au contact and underlying epitaxial Ga2O3 due to the low thermal conductivity of the Ga2O3. This failure mode is different to that under high reverse breakdown conditions, where pits formed by material failure under the high field generated at the edge of the rectifying contact occurs. (C) The Author(s) 2019. Published by ECS.
UV ozone treatment for improving contact resistance on graphene
(2012-11-01)
Chen, Chung Wei
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Ren, Fan
;
Chi, Gou-Chung
;
Hung, Sheng-Chun
;
Huang, Y. P.
Optimized UV ozone cleaning of graphene layers on SiO2/Si substrates is shown to improve contact resistance of e-beam evaporated Ti/Au contacts by three orders of magnitude (3 x 10(-6) Omega-cm(2)) compared to untreated surfaces (4 x 10(-3) Omega-cm(2)). Subsequent annealing at 300 degrees C lowers the minimum value achieved to 7 x 10(-7) Omega-cm(2). Ozone exposure beyond an optimum time (6 min in these experiments) led to a sharp increase in sheet resistance of the graphene, producing degraded contact resistance. The UV ozone treatment is a simple and effective method for producing high quality contacts to graphene. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4754566]