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Sensors and Actuators B 205 (2014) 199–205

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

jo ur nal home page: www.elsev ier .com/ locate /snb

ighly sensitive palladium oxide thin film extended gate FETss pH sensor

tanu Dasa, Danny Hsu Koa, Chia-Hsin Chena, Liann-Be Changa, Chao-Sung Laia,u-Chuan Chua, Lee Chowb, Ray-Ming Lina,∗

Department of Electronic Engineering and Green Technology Research Center, Chang Gung University, 259 Wen-Hwa 1st Road, Kwei-Shan,aoyuan 33302, TaiwanDepartment of Physics, University of Central Florida, Orlando 32816, USA

r t i c l e i n f o

rticle history:eceived 13 May 2014eceived in revised form 19 August 2014ccepted 19 August 2014vailable online 3 September 2014

a b s t r a c t

It is well-known that palladium readily absorbs hydrogen gas at room temperature. Based on this uniqueproperty of palladium, palladium oxide (PdO)-sensitive membrane in the extended gate field-effect tran-sistor (EGFET) configurations have been evaluated as a detector for hydrogen ions in pH buffer solutions.The PdO thin film was prepared by a two-step process through reactive electron beam evaporation andsubsequent thermal oxidation in an optimal O2 flow. Our results indicate that the PdO-based EGFET sensor

eywords:GFETalladium oxideH sensoruper-Nernstian sensitivity

showed super-Nernstian sensitivity approximately 62.87 mV/pH, while exhibiting good linearity as wellas good stability between pH 2 and pH 12. Our research demonstrates that PdO membrane can be usedin EGFET structure without compromising sensitivity achieved by conventional methods. Furthermore,the disposable PdO sensor shows great potential for low cost biochemical detection due to its simplifiedfabrication and measurement system.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

The detection of ions and molecules in a biochemical environ-ent plays a significant role in chemical science and biotechnolo-

ical application. The basis of an ion-sensitive field-effect transistorISFET) is derived from a metal-oxide semiconductor field-effectransistor (MOSFET), of which the metal gate is hereby substitutedy an ion-sensitive membrane with direct contact with a bufferolution [1]. Since the invention of the first ISFET by Bergveld in970 [2], various techniques and sensing membranes have beenxploited. The potential of these solid-state devices have attracted

great deal of attention, due to their numerous advantages suchs miniaturization, chip-circuit design and low cost in manufactur-ng. In particular, they are an excellent candidate for the integrationf biochemical sensors in microelectronics. Several ISFET-basediochemical sensors have been proposed [3,4]. However, owingo the fragile nature of membrane degradation in extreme condi-

ions, extended gate field-effect transistor (EGFET) configurationas been developed to prolong stable operation. The mecha-ism of surface ion adsorption in ISFET and EGFET are essentially

∗ Corresponding author. Tel.: +886 3 2118800x5790; fax: +886 3 2118507.E-mail address: rmlin@mail.cgu.edu.tw (R.-M. Lin).

ttp://dx.doi.org/10.1016/j.snb.2014.08.057925-4005/© 2014 Elsevier B.V. All rights reserved.

the same, with the major difference that EGFET configuration canonly be used in low impedance membranes. EGFET is a subset ofthe ISFET family line, which modifies the ISFET into a two-partdesign. The sensing membrane is immersed in the solution, whileconnected to a remote FET IC chip for real-time analysis [1,5,6].This approach enables us to swap the sensing membrane from anychemical damage instead of fabricating a whole new device.

Prompted by the demand for low cost chemical sensors,researchers looked into SiO2 initially for pH sensitive membrane.The search for a more compatible material continued as sensitivityand stability impacted the performance of these chips. Since therealization of Ta2O5 as a pH-sensing membrane in 1981 by Mat-suo et al. [7], various research groups have demonstrated the useof different sensing membranes such as Al2O3 [8], Si3N4 [4], SnO2[9], Er2O3 [10], Si nanowire/SiO2/Al2O3 [11], IrOX [12], Gd2O3/SiO2stacked oxide [13], silicon nanowire [14], Ru-doped TiO2 [15] film inorder to enhance detection capabilities. As the Nernst limit of pHsensitivity is 59 mV/pH, “super-Nernstian” sensitivity >59 mV/pHcould promise a far more precise detection in monitoring the pHlevels in blood and extracellular fluids.

In the 1980s, both Grubb and King [16] and Liu et al. [17]demonstrated the use of palladium–palladium oxide as a wireform electrode for their sensor fabrication. Both fabricated sensorsrevealed merits in pH detection, with the exception reported by

2 ctuators B 205 (2014) 199–205

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Fig. 1. Photograph of (a) bare PCB mounting template, (b) encapsulated PdO sensor

00 A. Das et al. / Sensors and A

iu et al., for exceeding Nernstian behavior with 71.4 ± 5 mV/pH.rubb and King employed high temperature thermal oxidationf the palladium wire, whereas Liu et al. used electrochemicalnodization. This was followed by the works of Kinoshita et al.18] and Bloor et al. [19], whose groups also fabricated Pd–PdO pHlectrode via thermal oxidation and electrochemical route respec-ively. Then in 1986, Karagounis et al. [20] demonstrated theossibility of fabricating Pd–Pdo thin film potentiometric pH sensorhrough RF reactive sputtering technique, reaching a pH sensitivityf 54 mV/pH in the pH range between 3 and 9.

Despite the promising developments in biochemical sensors,d–PdO-based sensors in EGFET configurations have not yet beeneported. Therefore in this investigation, we propose a highly sen-itive membrane consisting of PdO thin film as a pH sensor in theGFET format. The sensor’s performances in sensitivity, stabilitynd reversibility were measured and analyzed. The experimentalesults have demonstrated that super-Nernstian pH response waseached with similar sensitivities achieved by conventional meth-ds. These findings demonstrate a novel and effective design of

biochemical sensor by unifying the compound semiconductorensing membrane with the silicon integrated chip technology.

. Experimental details

.1. PdO film preparation

Extended gate field-effect transistors, comprised of PdO thinlm sensing membranes were fabricated on sapphire substrate andncapsulated on a copper clad FR-4 printed circuit board (PCB) lam-nate sheet. To begin with, 130 nm thickness of palladium oxidelm was deposited by reactive electron beam (E-Beam) evaporation

rom a 99.999% pure Pd slug on a two inch sapphire substrate under2 flow of 20 sccm. The PdO thin film on sapphire then underwentn annealing in furnace at 973 K for an hour in O2 flow of 1 slm.he two-step process was employed for the enhanced formationf PdO film. Morphology analysis was done using field emissioncanning electron microscopy (FE-SEM). In addition, X-ray photo-lectron spectroscopy (XPS) study was employed to characterizealladium–oxygen species on the surface of PdO film. Analysishrough Hall measurement revealed the p-type semiconductiveature of PdO film with sheet resistivity, sheet carrier concen-ration and mobility of about 1221 �/�, 5.93 × 1014 cm−2 and.61 cm2 V−1 s−1 respectively.

.2. PdO sensor chip fabrication

Copper Clad FR-4 – PCB laminate sheet was first etched to fabri-ate a mounting template for the sensor chip as shown in Fig. 1(a).amples of 1 × 1 cm2 size were scribed from the native waferor sensor chip fabrication. For pH detection studies, 1 × 1 cm2

dO/sapphire sample was mounted on square shaped area andonded via silver paste. Silver paste was then applied carefully inhe surrounding edges of the PdO layer and extended to copperlate, as to form the conductive line between sensing membranend PCB. A homemade epoxy package was employed to encapsu-ate sensor chip and copper line while exposing a sensing area ofpproximately 0.25 cm2 free from epoxy. The completed sensor ashown in Fig. 1(b) chip was immersed in pH 7 buffer solution for4 h, allowing sensing surface to stabilize prior to current–voltageI–V) measurement. A Texas Instruments n-MOSFET CD4007UBE

as used as the FET in the EGFET device. The dimension n-MOSFETsed for our measurement consists of gate length and gate widthf 10 �m and 30 �m, respectively. We have used signal line of co-xial cable to connect copper metal line of fabricated PdO sensor

chip and (c) final PdO sensor chip connected to the gate of n-MOSFET; schematicillustration of the (d) fabricated PdO sensor chip and (e) I–V measurement setup forthe PdO pH-EGFET sensor.

chip and the gate of n-MOSFET as shown in Fig. 1(c). Fig. 1(d) showsthe schematic diagram of completed PdO pH sensor chip.

2.3. Measurement of sensor chip

All current–voltage measurements took place in a shieldingbox in order to prevent any light exposure or electromagnetic

A. Das et al. / Sensors and Actuators B 205 (2014) 199–205 201

Fig. 2. (a) Surface morphology of PdO film by FE-SEM (×2.2 K). X-ray photoelectronsl

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threshold voltages shifts from the left to the right as the hydrogen

pectra showing binding energy of (b) Pd 3d5/2, Pd 3d3/2 and (c) O 1s, Pd 3p5/2 coreevel electrons of PdO film.

nterference. Variation in the solution temperature also can affecthe sensor sensitivity as Nernst law is proportional to temperature.

e have performed all the measurement of PdO sensor in roomemperature (300 ± 2 K). Buffer solutions of pH 2, 4, 6, 8, 10 and 12ere obtained from Merck Chemicals. The pH-sensing properties

n terms of sensitivity, linearity, hysteresis, drift were measured inarious pH buffer solutions through Ag/AgCl reference electrodey Agilent B1500A semiconductor parameter analyzer. Fig. 1(e)hows the schematic diagram of the I–V measurement setup fordO EGFET pH sensor.

. Results and discussion

.1. PdO film characterizations

Fig. 2(a) shows the top-view FE-SEM images of the surface mor-hology of PdO film, which suggests a relatively smooth surfacef the film. The XPS spectrum of PdO film is presented in Fig. 2(b)nd (c). The Pd 3d5/2 and Pd 3d3/2 doublet binding energy situatedt 336.6 eV and 342.0 eV (Fig. 2(b)) respectively corresponds to thehemical state of PdO. The binding energy peak of the O 1s situatedt 529.8 eV and the Pd 3p5/2 signal situated at 533.7 eV (Fig. 2(c))hich also correspond to the chemical state of PdO. The binding

nergy peaks determined are in agreement with that previouslyeported values for palladium oxide [21]. Taken together, it is ver-fied that the formation of PdO layer during the combined processf reactive EB deposition in O2 flow and furnace annealing processn O2 ambient.

Analysis on PdO membrane’s pH sensitivity, linearity, real-timeesponse, hysteresis and drift were examined in order to determinets sensing characteristics.

Fig. 3. (a) Transfer characteristics (IDS–VREF) for the PdO ion-sensitive EGFET sensorin the linear regime for different pH values from 2 to 12. (b) Linearity of PdO EGFETsensor in linear region.

3.2. Sensitivity and linearity (linear region)

In accordance to the EGFET theory, the relationship between IDSvs. VREF in the linear region can be expressed as follows:

IDS = W�nCox

2L[2(VREF − VT(EGFET))VDS − V2

DS] (1)

where W/L denotes the channel width to length ratio, �n denotesthe electron mobility in the channel, Cox denotes the gate capaci-tance per unit area, VT(EGFET) denotes the threshold voltage of EGFETsensor, VREF and VDS are the reference and the drain-source vol-tages. The VT(EGFET) could be expressed in the following formula[15],

VT(EGFET) = VT(MOSFET) − ˚M

q+ EREF + �Sol − � (2)

where the VT(MOSFET) is the threshold voltage of MOSFET, ˚M is thework function of the metal gate (reference electrode) relative to thevacuum, EREF is the potential of the reference electrode, �Sol is thesurface dipole potential of the buffer solution, and ϕ is the surfacepotential at the electrolyte/sensing film interface.

The IDS–VREF characteristics are shown in Fig. 3(a) for PdO EGFETsensors in the linear region. The IDS–VREF curve in linear regionshows a uniform shift of the threshold voltage to higher voltagewith the decreasing concentration of the hydrogen ions, i.e., the

ions concentration decreased. The pH sensitivity and linearity ofthe PdO film was derived from the IDS–VREF curves at IDS = 100 �Ain pH solutions ranging from pH 2 to pH 12 as shown in Fig. 3(b).

2 ctuators B 205 (2014) 199–205

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Fig. 4. Output characteristics (IDS–VDS) for the pH-EGFET sensors in the saturation

Software that monitored the drain current as a function of time,while keeping the drain bias (VD) and gate bias (VG) constant. Fig. 5shows the real-time responses of IDS for PdO sensor chip dipped

02 A. Das et al. / Sensors and A

he pH voltage sensitivity and linearity can then be extracted asollows,

pH voltage sensitivity = VT(EGFET)(x2) − VT(EGFET)(x1)pH(x2) − pH(x1)

= �VT(EGFET)

�pH

(3)

The sensitivity of the PdO EGFET sensor was calculated to be2.87 mV/pH and linearity was revealed to be 99.97%. These resultsave demonstrated that the PdO sensing membrane exhibits a

inear pH change. We have measured five different PdO sensorhip prepared in different batches. The sensitivity values in pHange from 2 to 12 are found to be 60.38, 60.43, 61.60, 62.87,5.31 mV/pH. All of the sensor chips have shown sensitivity greaterhan 59 mV/pH. The average sensitivity is 62.11 mV/pH. The calcu-ated standard deviation is 2.05. We have presented data from theensor chip of sensitivity 62.87 mV/pH which is close to the calcu-ated average sensitivity. Considering a maximum Nernst responsef 59 mV/pH at 293 K, an error of 1 K leads to 0.2 mV/pH whichesults a variation of ±0.4 mV/pH in sensor output in room temper-ture (300 ± 2 K). Therefore, temperature effect on sensor outputs within experimental error and negligible. In comparison, theuper-Nernstian sensitivity achieved in our PdO EGFET sensor isigher than the previously reported sensitivity for PdO thin film20]. Recently, super-Nernstian response was achieved throughouble gate MOSFET configuration [22,23]. The capacitive couplingetween its bottom gate and top gate can be controlled so thatny higher desired super-Nernstian sensitivity of over 59 mV/pHan be attained via a well optimized design of bottom gate and topate. This certainly does not apply to our PdO EGEFT system, as weave opted for an easier configuration. Super-Nernstian responsechieved in several reported articles, including our observationoes not violate the concept of ‘Nernst Law’ or ‘Site Binding Modelor insulator-electrolyte interface’, rather it is an exception of theNernst Law’ and ‘Site Binding Model’. The super-Nernstian coulde related to the enhanced proton-exchange process [24] due tohe increased oxidation state of PdO metal-oxide. The differencen fabrication conditions lead to different oxidation states of the

etal-oxide thin film as higher oxidation states resulted in higherensitivity [25]. Ultimately we believe that the enhanced PdO for-ation through two-step oxidation (reactive E-beam and furnace

nnealing in optimal O2 flow) could be responsible for the super-ernstian pH response in our study.

.3. Sensitivity and linearity (saturation region)

Saturation occurs when a channel has been created, allow-ng current to flow between the drain and source. With differentmounts of H+ ions accumulated on the surface in response tohe pH buffer solution, saturation sensitivity and linearity can beerived from the IDS–VDS curves in buffer solutions ranging fromH 2 to pH 12. Fig. 4(a) demonstrated the IDS–VDS characteristics ofdO sensor in pH = 2 to 12 when MOSFET was operating in the sat-ration region at VREF of 2 V. It shows that the IDS–VDS curve shiftsownward with an increase in pH values. For the saturation regionf the PdO EGFET, the IDS–VDS can be expressed as

DS = W�nCox

2L[(VREF − VT(EGFET))

2] (4)

The pH current sensitivity can be expressed as follows,√

I (y ) −√

I (y ) �√

I

H current sensitivity = DS 2 DS 1

pH(y2) − pH(y1)= DS

�pH(5)

The derived pH current sensitivity was approximately 1.08�A)1/2/pH which is also notably high, with a linearity of 99.92%

regime for different pH values from 2 to 12. (b) Linearity of the IDS of PdO EGFETsensor in saturation region.

as shown in Fig. 4(b). The result is an indication that√

IDS linearlydepends on the pH value in the saturation region.

3.4. Stability and reliability

Moreover, the stability of the device was investigated. For real-time response, we have used program in Agilent Easy Expert

Fig. 5. Real-time IDS responses of PdO sensor in a pH loop of 2 → 12 → 2 at VREF of2 V.

A. Das et al. / Sensors and Actuators B 205 (2014) 199–205 203

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ig. 6. Hysteresis characteristic of PdO sensor in a pH loop of 7 → 4 → 7 → 10 → 7ver a period of 25 min.

or 60 s in each buffer solution of different pH values (pH loop: → 12 → 2) at a VREF of 2 V and VDS = 100 mV. The cyclic step deter-ines the accuracy of the sensor within a period of 660 s. It is a

eal-time exhibition of reliability, such that the IDS decreases lin-arly as the pH value increases and vice versa. As shown in thisgure, the fabricated PdO EGFET has exhibited almost perfect sym-etric response together with low hysteresis due to the buffer

olution variations.Fig. 6 shows the hysteresis effect of the PdO sensing membrane.

ysteresis is known to be related to chemical interaction betweenons in an electrolyte and slow reacting surface-sites underneathhe membrane surface and/or the surface defects of the membrane26]. For hysteresis characteristic, we have measured a family ofD–VG curves for each pH value when PdO sensing membrane wasmmersed in alternating cycles of pH buffer solutions i.e. pH 7 → pH

→ pH 7 → pH 10 → pH 7 for 5 min in each pH buffer solution. Next,he reference bias voltage for a fixed drain current of 100 �A werextracted from each curve and plotted with different pH values.he net hysteresis was calculated as a difference between the initialeference voltage and final reference voltage at pH 7 to be 7.9 mV.n addition, drift in the reference voltage or threshold voltage ofGFET was studied for long-term reliability of electrochemical sen-ors which relates to OH− adsorption on sensing film surface atifferent buffer solutions [27]. The potential drift phenomenon isommon in ion selective pH sensors and the 3–10 mV drift is con-idered small [28]. In this work, the drift of the PdO sensor waseasured in pH 7 buffer solution for 12 h. The drift property is com-

ared by calculating the drift rate, �VREF/h. For drift characteristic,e also measured a family of ID–VG curve in pH 7 for 12 h for long-

erm drift measurement. Similarly, the reference bias voltage forxed drain current of 100 �A were extracted from each curve andlotted with time. Our PdO pH sensor drift was characterized by ini-ial drift of 7.4 mV and long-term drift rate of 2.32 mV/h as shown inig. 7. As threshold voltage shifted toward positive direction duringrift measurement, therefore it is believed that initial fast drift maye caused by OH− ion adsorption in PdO sensing surface site andemaining lower long-term drift caused by slow diffusion of OH−

n slowly reacting buried site of PdO film. When compared to ouresult, lower drift of 0.38 mV/h and 0.3 ± 0.1 mV/h were achievedn ruthenium oxide [25] and iridium oxide [29] metal-oxide pHensors. Nonetheless our PdO film has lower long-term drift rateompared to other reported result on SnO2 [30], a-WO3 [31] sensingembrane.

As the sensor suffers damage after being immersed in solution,

rom the experimental observation, we would like to mention thathe PdO sensor chip we have fabricated has shown good sensingroperties in terms of sensitivity and linearity for 6–7 complete

Fig. 7. Drift characteristic of PdO measured in pH 7 for 12 h.

cycles (pH 2 → pH 12 → pH 2) of measurements in the pH rangefrom 2 to 12. After that sensitivity and linearity properties degradewith no such visual degradation on the PdO surface.

4. Conclusions

In this study, we have reintroduced the PdO thin film based sen-sor via EGFET technique. Top-view FE-SEM image has suggesteda relatively smooth surface morphology of PdO film preparedthrough a two-step process. Material analysis with XPS confirmedthe chemical state of PdO through Pd 3d5/2 and Pd 3d3/2 doublet,Pd 3p5/2 and O 1s binding energy peak positions. The fabricatedPdO sensor seemed suitable for pH sensing, as super-Nernstian sen-sitivity of 62.87 ± 2 mV/pH, linearity of 99.97%, low hysteresis of7.9 mV and drift rate of 2.32 mV/h were achieved. The sensitivityand linearity (both in linear and saturation regime), reversibility,hysteresis effect, and drift analysis have indicated the sensor chip tobe reasonably accurate, stable and reliable in pH testing. As a result,the performance of a PdO-based sensor in EGFET configuration notonly benefits disposability in replacing damaged sensing mem-branes, but also maintaining an adequate pH-sensing standard.Thus, palladium oxide based EGFET shows great promise in bio-chemical sensing applications.

Acknowledgement

This work was financially supported by the National ScienceCouncil (NSC), Taiwan currently known as Ministry of Science andTechnology (MOST), under contract no. NSC-101-2221-E-182-047-MY2.

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iographies

Atanu Das received his B.S. and M.S. degrees in Physicsfrom Vidyasagar University, India in 1999 and 2001respectively. He received Ph.D. degree in Electronics Engi-neering from Chang Gung University, Taiwan in 2013.Currently, he is a post-doctoral researcher in CompoundSemiconductor Research Group, Department of Electronic

Engineering, Chang Gung University, Taiwan. His mainresearch interests are GaN-based material growth inMOCVD, HEMT fabrication and characterization, high k forgate oxide and memory application, and electrochemicalsensors.

ors B 205 (2014) 199–205

Danny Hsu Ko received his B.S. degree in Chemical Sci-ence from University of Auckland, New Zealand in 2012.In 2013, he joined Professor Liann-Be Chang’s researchteam in chemical sensor research. Currently, he is pur-suing his M.S. degree in Department of Optoelectronics atChang Gung University. His main research interests arenanomaterials, biosensor and optoelectronic devices.

Chia-Hsin Chen received his B.S. degree in ElectronicsEngineering from Chang Gung University, Taiwan in 2013.In 2013, he joined Professor Ray-Ming Lin’s research groupin GaN-based Device Research. Currently, he is pursuinghis M.S. degree in Department of Electronics at ChangGung University. His main research interest is fabricationof GaN-based MOS HEMT devices.

Liann-Be Chang received his B.S. degree from the Chiao-Tung University, Taiwan (1980) and the Ph.D. degreefrom the National Defense University, Taiwan (1987).Hence he was a post-doctoral fellow of the Universityof Illinois at Urbana-Champaign, U.S.A. in 1987–1988.He was a chief instrument engineer of Taiwan PowerCo., Third nuclear power plant (1982–1984). He was alsoan associate professor, full professor and chairman ofthe Electronic Engineering Department, National DefenseUniversity (1998–2004). Later, he became a Chairmanof the Electronic Engineering Department, Chang GungUniversity, 2004–2007. He is currently the vice Dean ofCollege of Engineering and Director of the Green Technol-

ogy Research Center, Chang Gung University. His multidisciplinary research interestincludes the on design and fabrication of optoelectronic and microwave devicessuch as: PD, MSM, PIN, LED, MESFET, HEMT and III–V solar cells, SPR biosensors andcompound semiconductor based EIS, EGFETs and LAPS devices.

Chao-Sung Lai received the B.S. and Ph.D. degrees fromNational Chiao Tung University, Hsinchu, Taiwan, in 1991and 1996, respectively. In 1996, he joined the NationalNano Device Laboratory, Hsinchu, Taiwan, where he hasbeen engaged in the research of SOI devices. He won theLam Award 1997. In 1997, he joined the Chang Gung Uni-versity and Tao-Yuan, Taiwan, as an assistant professor,where he has been engaged in the research of the char-acterization and reliability of deep-submicron MOSFETs,nitrided thin gate oxides, shallow trench isolation and themodeling of dielectrics’ reliability. He was the consultantof the Nan-Ya Technology Inc. for the 0.18 �m Logic-Teamsince 1997. In 2001, he visited the UC-Berkeley in the

Department of Electrical Engineering for sabbatical research under Professor ChenMing Hu in the Device Group. He was the consultant of the Nan-Ya TechnologyInc. for the Flash Memory since 2001. He is the director of Bio-Sensor Group forBio-Medical Research Center at Chang Gung University from 2007.

Fu-Chuan Chu received his B.S. degree from the Depart-ment of Electronics Engineering, Lee-Ming Institute ofTechnology, Taipei, Taiwan and M.S. degree from theDepartment of Electronics Engineering, Chung ChengInstitute of Technology, National Defense University,

received his Ph.D. degree in 2014 from Department ofElectronic Engineering, Chang Gung University, Taoyuan,Taiwan. His research interests are epitaxy and fabricationof GaN-based HEMTs structure for RF applications.

ctuat

A. Das et al. / Sensors and A

Lee Chow is a professor at the Department of Physics,University of Central Florida, Orlando. He received hisB.S. in Physics in 1972 from National Central University,Taiwan. He received Ph.D. in Physics from Clark Univer-sity, Worcester, MA, USA in 1981. In 1981–1982, he waspost-doc in Physics at the University of North Carolina,Chapel Hill, NC. He joined University of Central Florida in

1983 as an assistant professor, and was promoted to asso-ciate professor in 1988 and to professor in 1998. His areasof expertise include chemical bath deposition, nanofabri-cation of carbon nanotubes and metal oxides, diffusion insemiconductors, high TC and diamond thin films.

ors B 205 (2014) 199–205 205

Ray-Ming Lin received Ph.D. degrees in Electrical Engi-neering from National Taiwan University, Taiwan in 1997.During his Ph.D. work, he majored in the MBE growthand device application of metamorphic InGaAs/GaAs andInAlAs/GaAs buffer layers, quantum dot light emittingdiode, room temperature infrared sensor. 1997–1999 hejoined the Planning & Evaluation Division at National Sci-ence Council, Taiwan as an assistance research fellow.Since August 1999, he has been with the Department ofElectronic Engineering of the Chang Gung University atTao-Yuan, Taiwan where he is presently a full Professor.Since August 2001, Professor Lin has been the Director of

Right and Technology Transfer Center at the Chang Gung

University. His current research interests are in the areas of MOCVD technologydevelopment for the growth of nitride-based heterostructures, in situ fabrication oflow-dislocation density, high-efficiency optoelectronic and high electron mobilitytransistor (HEMT) device structures and nano-biosensors.