Transcript ZnO-based Multifunctional and Tunable Sensors - dimacs

ZnO-based Multifunctional and
Tunable Sensors
Dr. Yicheng Lu
WINLAB
Dept. of Electrical and Computer Engineering
Rutgers University
Sept. 23 2003
The project has been supported by NSF under the grants ECS 00-88549,
CCR 013096, ECS 0224188 and by US Army CECOM, and by NJCST
Excellent Center program (MUSE).
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Introduction: ZnO Materials for Sensors
II-VI compound semiconductor:
 Direct bandgap, with Eg 3.32 eV.
 Bandgap engineering: alloy with Cd or Mg
to tailor bandgap from 2.8eV to 4.0eV.
[0 0 0 1]
Multi-functional:
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Zinc
Hexagonal wurtzite class crystal =>
piezoelectricty with large coupling
coefficient.
Large and fast photoconductivity => optical
sensing.
Al or Ga doping => transparent conductive
oxide.
Li & Mg doping => ferroelectric.
Alloyed with Mn => magnetic oxide
semiconductor.
Integrate electrical, optical and
piezoelectrical properties => MITSAW chip
for sensor technology
Oxygen
[-1 2 -1 0]
[1 1 -2 0]
[2 -1 -1 0]
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Structure of ZnO Films on r-sapphire
ZnO
(1 1 2 0 )
(1 100)
( 01 1 2 )
(10 1 1)
2.81 nm
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
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Advantages of MITSAW Biosensors
ZnO/r-Al2O3 structures: high
frequency & low loss operation;
MITSAW biosensor:
resettable and tunable, therefore
increasing the sensor’s lifetime
Dual SAW modes operation (gasphase and liquid-phase sensing);
Operating in UV and acoustic mode
(SAW and BAW), increasing the
accuracy.
It can be integrated with Si IC
through SOS technology: sensor-onchip; lab-on-chip
2DEG Sensing device with chemically
mesa
selective receptor coating
Mixer
Sensor
output
REF.
SAW
IDT
Gate voltage
input
2DEG
Ground
2DEG
mesa
MUSE biosensor chip based on
MITSAW technology.
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MgxZn1-xO-based BAW Sensor
Al top electrode
Piezoelectric ZnO
or Mg xZn 1-xO
Al bond pad
n++ ZnO bottom electrode
r-sapphire substrate
Physical structure of a MgxZn1-xO bulk
acoustic wave device
Simulated BAW frequency response
extrapolation of Mg tailoring function
Operating at high frequency.
Can be integrated with electronic circuits on silicon chip => smart sensor.
An array of micromachined thin film resonators (TFRs) will selective
coatings.
Dramatically improve sensor reliability and allow detection and
measurement of multiple chemicals simultaneously.
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Zero-Power Remote Wireless Sensors
Interrogation pulse
Antenna
Voltage input
2DEG Mesa
SAW IDT
Reflectors
RF stage
DSP unit
Control unit
(e.g. PC)
Sensor response
Interrogation unit
Substrate
Wireless SAW Sensor
Base station sends interrogation pulse.
The antenna picks the pulse; the SAW IDT launches a wave packet.
The wave packet travels across the delay path, is reflected by the
reflecting array.
The reflected wave generates a signal at the IDT.
The antenna send a response pulse.
2DEG bias determines acoustic velocity, hence response delay time.
Thus the device is a wireless read-out element for a voltage-generating
sensor, wireless tags, etc.
Application for wireless and networked sensors for homeland security.
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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
100
Transmission (%)
80
x=0
x=0.18
x=0.25
x=0.34
x=0.60
60
40
20
0
200
250
300
350
400
Wavelength (nm)
450
500
Applications:
 DNA sensors for bio defense
 Sensors for missile defense
 Flame detection
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Nanostructured Biosensors
ZnO nanotip and nanotip arrays
 Binding sites for biomolecules, such as DNA
 High device density
 Fast response
ZnO biosensors will be used to detect RNA-DNA, DNADNA, protein-protein, protein-DNA, and protein-small
molecules interactions.
Experiments have proved the ZnO nanotips greatly
enhance the immobilization of DNA
and protein molecules.
Examples:
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proteins - DNA-RNA
whole bacterial cells - tissues
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Broad Impact
Multifunctional and tunable sensors have a variety of very
important practical applications
 health care (medical and genetic diagnostics)
 environmental monitoring (control of pollution and detection of
hazardous chemicals)
 food analysis (detection of ingredients, contamination etc.)
 detection of biological warfare agents.
As an example, a world market for over trillion sensors by 2010 is
estimated, growing to ~$3-5B in 2005.
The research results strengthen nation’s technology capabilities in
the emerging area of multi-mode, multifunctional biological and
biochemical sensors
Accelerate deployment of biochemical sensor networks, secure
wireless systems for national and state-level public infrastructure
uses such as environmental monitoring, hospital management, and
homeland security.
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Achievements of ZnO Research at Rutgers
High quality MOCVD ZnO and MgxZn1-xO thin films on
R-Al2O3 and SiO2/Si.
Low loss ZnO/R-Al2O3 SAW devices.
The first high speed ZnO MSM photoconductive and
Schottky UV photodetectors.
The first optically addressed normal incidence ZnO UV
high contrast modulator.
The first ZnO Schottky devices on R-Al2O3.
Novel ZnO nanostructures.
Novel MITSAW chip technology.
5 patents awarded and 8 more pending
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