1 ZnO-based Multifunctional and Tunable Sensors Dr. Yicheng Lu WINLAB Dept. of Electrical and Computer Engineering Rutgers University Sept The project has been supported by NSF under the grants ECS , CCR , ECS and by US Army CECOM, and by NJCST Excellent Center program (MUSE).

2 Introduction: ZnO Materials for Sensors II-VI compound semiconductor: Direct bandgap, with E g  3.32 eV. Bandgap engineering: alloy with Cd or Mg to tailor bandgap from 2.8eV to 4.0eV. Multi-functional: 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

3 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

4 Advantages of MITSAW Biosensors ZnO/r-Al 2 O 3 structures: high frequency & low loss operation; 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 (SAW and BAW), increasing the accuracy. It can be integrated with Si IC through SOS technology: sensor-on- chip; lab-on-chip MUSE biosensor chip based on MITSAW technology.

5 Mg x Zn 1-x O-based BAW Sensor 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. Physical structure of a Mg x Zn 1-x O bulk acoustic wave device Simulated BAW frequency response extrapolation of Mg tailoring function

6 Zero-Power Remote Wireless Sensors 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.

7 Mg x Zn 1-x O-based UV Sensor Advantages:  Wide and direct band gap (3.3eV)  E g tunable from 3.3 to 5.8 eV by alloying ZnO with MgO to form Mg x Zn 1-x O.  Large photoresponse  High photoconductivity Applications:  DNA sensors for bio defense  Sensors for missile defense  Flame detection

8 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, DNA- DNA, 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: proteins - DNA-RNA whole bacterial cells - tissues

9 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 The research results strengthen nation’s technology capabilities in the emerging area of multi-mode, multifunctional biological and biochemical sensors homeland security 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.

10 Achievements of ZnO Research at Rutgers High quality MOCVD ZnO and Mg x Zn 1-x O thin films on R-Al 2 O 3 and SiO 2 /Si. Low loss ZnO/R-Al 2 O 3 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-Al 2 O 3. Novel ZnO nanostructures. Novel MITSAW chip technology. 5 patents awarded and 8 more pending