Spring 2007 - February 9
Dept of Physics & Astronomy
University of Maine, Orono, Maine
Nuri W. Emanetoglu
Electrical and Computer Engineering Department, UMaine
Novel Integrated Piezoelectric and Optoelectronic sensors and Devices and their system applications
ZnO is an emerging wide bandgap semiconductor (3.32 eV at room temperature), and is also a well known piezoelectric material. The ZnO research at Rutgers has pursued both optoelectronic and piezoelectric applications, culminating in integrated acousto-opto-electronic devices. This research covers material growth, mainly with metal organic chemical vapor deposition (MOCVD), fabrication process development, device design, fabrication and testing. The ZnO/ r-plane sapphire (r-Al2O3) system, with its high effective coupling and high acoustic velocities, is attractive for surface acoustic wave (SAW) filters and resonators operating in the low GHz region. Acoustic wave property tailoring, by using the new piezoelectric ternary compound magnesium zinc oxide (MgxZn1-xO) and MgxZn1-xO/ ZnO heterostructures, has been demonstrated. Two novel devices, the monolithically integrated tunable surface acoustic wave (MITSAW) device and SAW UV photodetector, which integrate ZnO’s electrical, optical and piezoelectric properties using multilayer structures on r-plane sapphire (r-Al2O3) substrates will be presented. The interaction between the free carriers in the semiconducting layer with the electrical field accompanying the propagating SAW in the piezoelectric layer changes the SAW velocity. This perturbation of the SAW velocity results in a phase shift in the device output. In the MITSAW device, a gate bias voltage modulates the carrier concentration in the semiconducting layer, and therefore the acoustic velocity. In the SAW UV detector, the carriers are generated in the semiconducting layer by absorption of UV light. In the ZnO/r-Al2O3 system, the first higher order acoustic wave mode, the Sezawa mode, has higher acoustic velocity and larger coupling coefficient than the base Rayleigh wave mode, which results in a larger phase shift in both devices. These novel ZnO integrated SAW optoelectronic devices could be used as passive remote wireless sensors, voltage-controlled oscillators and chemical/biochemical sensors for gas-phase and liquid-phase sensing. Sensors based on ZnO thin film resonators on Si substrates, as well as LiNbO3 SAW devices utilizing ZnO nanotip arrays for DNA and protein binding enhancement were also demonstrated.
The ZnO research was supported by the NSF (ECS-0088549, CCR-0103096, ECS-0224166), and by the NJ Commission on Science and Technology Excellence Center Program.
Friday, February 9, 2007
140 Bennett Hall