WIRELESS INFORMATION NETWORK LABORATORY Device Research for the MUSE Initiative Dr. Yicheng Lu, Dr. Nuri W. Emanetoglu Ms. Jian Zhong, Ms. Ying Chen WINLAB, Electrical and Computer Engineering Dept. Rutgers University May 13, 2004 This work has been supported by the NJCST Excellence Center for Research (MUSE) grant, NJ Nanotechnology Consortium, US AFOSR, US Army CECOM, and NSF.
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WIRELESS INFORMATION NETWORK LABORATORY ......WIRELESS INFORMATION NETWORK LABORATORY Introduction: ZnO Materials • II-VI compound semiconductor: – Direct bandgap, with E g @3.32
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WIRELESS INFORMATION NETWORK LABORATORY
Device Research for the MUSE Initiative
Dr. Yicheng Lu, Dr. Nuri W. EmanetogluMs. Jian Zhong, Ms. Ying Chen
WINLAB, Electrical and Computer Engineering Dept.Rutgers University
May 13, 2004
This work has been supported by the NJCST Excellence Center for Research (MUSE) grant, NJ Nanotechnology Consortium, US AFOSR, US Army CECOM, and NSF.
Fundamental Properties of MgxZn1-xO• ZnO can be alloyed with MgO and CdO
to produce the ternary compounds MgxZn1-xO and CdxZn1-xO.
• MgxZn1-xO/ZnO heterostructures have many device applications.
• The bandgap Eg : 2.8 eV to 4.0 eV.• MgxZn1-xO can to made as a
multifunctional material:- piezoelectric.- ferroelectric ((M)xZn1-xO, with M = Li,
Mg). - diluted magnetic semiconductor.
• Physical properties can be tailored by controlling Mg composition.
∆Ec=0.9∆Eg
∆Ev=0.1∆Eg
Mg0.33Zn0.67O,Eg = 4.0eV
ZnO,Eg = 3.3eV
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Structure of ZnO films on r-sapphire
• The as-grown film on r-sapphire is dense and very smooth• The c-axis of ZnO is in the plane of the film• Interface is sharp and semi-coherent• The total misfit accommodated by strained regions
2.81 nm
ZnO
Sapphire
( )1011( )0112
(1100)
(1 1 2 0 )
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MgxZn1-xO Film Grown on r-Al2O3
Mg0.25Zn0.75O on r-Al2O3 Mg0.25Zn0.75O on r-Al2O3
� Film is smooth, dense and in epitaxial quality as shown in cross-sectional FE-SEM image.
� The film composition is determined by RBS.
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Photoresponse of ZnO• Polycrystalline ZnO as a photoconductor1,2 :
– Fast process: Solid State process, [hν → h+ + e-]– Slow process:
• Oxygen adsorption, O2(g) + e- → O2-(ad)
• Photodesorption, h+ + O2-(ad) → O2(g)
• High quality epitaxial ZnO produces large and fast photoresponse:
– Reduce grain boundaries– Reduce defects induced recombination– Reduce electron concentration by N-doping
1. Y. Takahashi, M. Kanamori, A. Kondoh, H. Minoura and Y. Ohya, Jpn. J. Appl. Phys. 33, 6611 (1994).
2. D. H. Zhang, J. Phys. D Appl. Phys. 28, 1273 (1995).
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Spectral Response and Speed of a Photoconductive UV Detector
A. Spectral ResponseCutoff Wavelength: 370nmVisible rejection ratio > two orders of
magnitude
B. Photocurrent vs. Response Time Rise Time: 1µµµµsFall Time: 1.5µµµµs
0 1 2 3 4 5
0
1
2
3
Pho
tocu
rren
t (nA
)Time (µµµµs)
Bias: 5VOptical Pulse:• <100fs• ~5.6fJ
250 300 350 400 450 500 550
1
10
100
Bias: 5VPhotoresponsivity:
~ 400A/W
Pho
tore
spon
sivi
ty (A
/W)
Wavelength (nm)
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Spectral Response and Speed of a Schottky UV Detector
A. Spectral Response Cutoff Wavelength: 370 nmVisible rejection ratio > three orders of magnitude
Phot
ocur
rent
(mA
)
Time (nSec)
TIME ( µµµµSec )PH
OT
OC
UR
RE
NT
(m
A )
Ag-ZnO-Ag Schottky Photodetector
B. Photocurrent vs. Response Time Rise Time: 12222nsFall Time: 50ns
300 320 340 360 380
10-3
10-2
10-1
100
Ag-ZnO-Ag Schottky Photodetector
RE
SP
ON
SIV
ITY
( a.
u. )
WAVELENGTH ( nm )
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MgxZn1-xO-based UV Sensor
Advantages:• Wide and direct band gap (3.3eV)• Eg tunable from 3.3 to 5.8 eV by alloying ZnO with MgO to form
MgxZn1-xO.• Large photoresponse• High photoconductivity
conductance.• Electrical field accompanying SAW interacts with carriers,
slowing acoustic wave.• Results in a phase shift/time delay across device.• Output in frequency domain. Can be read out wirelessly.
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Review of UV SAW Photodetectors• GaN UV SAW detectors:
– GaN/c-Al2O3 SAW device as photodetector, used as phase shifting element in oscillator circuit (365 nm, 60 kHz @ 221.3 MHz). D. Ciplys, R. Rimeika, M.S. Shur, S. Rumyantsev, R. Gaska, A. Sereika, J.
Yang, and M.A Khan, Appl. Phys. Lett., 80, 2020 (2002).
– GaN/c-Al2O3 device where SAW is used to transport e-h pairs generated in sensing area to MSM detector.T. Palacios, F. Calle, J. Grajal, Appl. Phys. Lett., 84, 3166 (2004).
• ZnO/LiNbO3 UV SAW detector– ZnO thin film deposited on LiNbO3 SAW device. used as
phase shifting element in oscillator circuit (365 nm, 170 kHz @ 37 MHz, 40 mW/cm2). Sharma and K. Sreenivas, Appl. Phys. Lett., 83, 3617 (2003)
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ZnO/r-Al2O3 SAW UV Detector Advantages
• The Sezawa wave mode in the ZnO/r-Al2O3 system has higher acoustic velocity and effective coupling compared to GaN/c-Al2O3 and ZnO/LiNbO3.
• This leads to larger tunability, hence higher sensitivity to UV light.
• The higher coupling also lends itself to a lower loss, more efficient zero-power remote wireless sensors.
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SAW Interaction with thin conductive film• Current induced only in thin mesa layer, which has
conductance σd
• Conductance at maximum loss: σm = vocεo(ε1+ε2)• Frequency independent.• Velocity change:
– Voltage controlled oscillators.– Adaptive and tunable filters.– Zero-power remote wireless sensors.– Fixed and tunable optical delay lines.– Tunable, multi-mode chemical/
biochemical sensors.(sensor expected to grow to ~$3-5 B in 2005, and to ~$10 B in 2010 by the most conservative estimates)
• Example: Novel MITSAW Biosensor:– Resettable and tunable, therefore increasing the sensor’s lifetime– Dual SAW modes operation (gas-phase and liquid-phase sensing);– Operating in UV and acoustic mode, increasing accuracy.– Can be integrated with Si IC: sensor-on-chip; lab-on-chip.
Gate voltageinput
REF.
2DEGmesa
SAWIDT
2DEGGround
Sensing device with chemicallyselective receptor coating
Sensoroutput
Mixer
2DEGmesa
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Other Wireless SAW Sensor Applications
• Chemical/ biochemical sensors for homeland defense, military, environmental protection
• Particle monitor• Temperature and pressure sensor• Viscosity sensor (pipelines, etc.) • Non-destructive evaluation (cracks, fissures,
etc. in pipelines, walls, etc.)
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Conclusions
1. Materials: Tailored and Multi-Functional • MOCVD growth of high quality epitaxial ZnO film on r-Al2O3 and
MgxZn1-xO film on r-Al2O3;• Achieved multifunctional ZnO and MgxZn1-xO: semiconducting,
transparent-and -conductive, piezoelectric,ferroelectric;• Material properties can be tailored by varying Mg composition in
MgxZn1-xO, as well as using multi-layer structures.
2. Sensor Devices: Tunable and Multi-Mode• ZnO/r-Al2O3 and MgxZn1-xO/r-Al2O3 SAW Devices;• ZnO- and MgxZn1-xO-based UV Sensors (photoconductive and
schottky);• Prototype zero-power, wireless UV SAW photodetector;• Prototype MITSAW device for sensing and circuit applications.
WIRELESS INFORMATION NETWORK LABORATORY Patents• “High Contrast, Ultrafast Optically Addressed Ultraviolet Light Modulator Based Upon Optical Anisotropy in ZnO Films Grown on R-plane Sapphire” (with M. Wraback, H. Shen, S. Liang* and C.R. Gorla*), US Patent No.6,366,389 (April 2, 2002)
• “Monolithically Integrated Tunable Surface Acoustic Wave Technology and Electrical Systems Provided Thereby” (with N.W. Emanetoglu), US Patent No. 6,559,736 B1 (May 6, 2003)
• “Surface Acoustic Wave Technology and Sensors Provided Thereby”, (with N.W. Emanetoglu), US Patent # 6,621,192 B2, Sept. 16, 2003.
• “Tailoring Piezoelectric Properties Using MgxZn1-xO and MgxZn1-xO/ZnO Structures”, (with N.W. Emanetoglu), US Patent # 6,716,479 , April 6, 2004.
• "Room-temperature ZnO Spintronics" (with Pan Wu) , filed in April, 2002.• “Fabrication of Ag Schottky Diodes on MgxZn1-xO”, (with H. Sheng, S. Muthukumar&, N.W. Emanetoglu, J. Zhong), filed in May, 2002
• "Biosensors Using ZnO-based Nanostrutures" (with Z.Zhang, H.Shang, N.W. Emanetoglu, M. Inouye and O. Mironitchenko), field in May, 2002
• “Selective Growth and Fabrication of ZnO Single Nanotip and Nanotip Arrays”, (with S. Muthukumar, N.W. Emanetoglu.), filed in Sept., 2002
• “Tailoring Piezoelectric Properties Using ZnO and AlxGa1-xN (0 x 1) Multilayer Structures”, (with Ying Chen and N.W. Emanetoglu), Invention Disclosure, filed June 2003.
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2003-2004 Publication List• “ZnO Nanotips Grown on Si Substrates by Metalorganic Chemical Vapor Deposition”, accepted
to appear in the Journal of Electronic Materials, 2004 (J. Zhong, S. Muthukumar, G. Saraf, H. Chen, Y. Chen, Y. Lu)
• “Li Diffusion In Epitaxial ZnO Thin Films”, accepted to appear in the JEM, 2004 (P. Wu, J. Zhong, N.W. Emanetoglu Y. Chen, S. Muthukumar, Y. Lu)
• “Wet Chemical Etching of (11-20) ZnO Films”, accepted to appear in the JEM, 2004, (J. Zhu, N.W. Emanetoglu, Y.Chen, B. V. Yakshinskiy, Y.Lu)
• “Metalorganic Chemical Vapor Deposition and Characterization of Epitaxial MgxZn1-xO (0<x<0.33) Films on r-Sapphire Substrates”, J. Crys. Growth, vol. 261,no.2-3, pp. 316-23 (S. Muthukumar, Y. Chen, J. Zhong, F. Cosandey, Y. Lu, T. Siegrist)
• “Characterization of MgxZn1-xO Bulk Acoustic Wave Devices”, IEEE Trans. Ultrasonics, Ferroelectrics, and Frequency Control, vol. 50, no. 10, pp. 1272-8, Oct. 2003 (R.H. Wittstruck, X. Tong, N. W. Emanetoglu, P. Wu, J. Zhu, Y. Lu, A. Ballato)
• “Ga-doped ZnO single-crystal nanotips grown on fused silica by metalorganic chemical vapor deposition”, Appl. Phys. Lett., vol. 83, n. 16, pp.3401-3, Oct. 2003 (J. Zhong, S. Muthukumar, Y. Chen, Y. Lu, H. M. Ng, W. Jiang, E. L. Garfunkel)
• “Surface Acoustic Waves in ZnO/AlxGa1-xN/c-Sapphire Structures”, Y. Chen, N.W. Emanetoglu, Y. Chen, G. Saraf, Y. Lu, A. Parekh, V. Merai, M. Prophristic, D. Lu, D.S. Lee, E. A. Armour, Proc. of 2003 IEEE International Ultrasonics Symposium, pp.2130-2133, 2003
• “SAW Analysis of the MgxZn1-xO/SiO2/Si System”, H. Wu, N.W. Emanetoglu, G.Saraf, J. Zhu, P. Wu, Y. Chen,Y. Lu, Proc. of 2003 IEEE International Ultrasonics Symposium, pp. 897-900,2003