ENEE-698E 1 st presentation by: Saeed Esmaili Sardari September 11, 2007

Piezoelectric Field Effect Transistor and Nanoforce Sensor Based on a Single ZnO Nanowire Xudong Wang, Jun Zhou, Jinhui Song, Jin Liu, Ningsheng Xu, and Zhong L. Wang School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia , and School of Physics and Engineering, State Key Lab of Optoelectronic Materials and Technologies, SunYat-Sen (Zhongshan) University, Guangzhou, , China NANO LETTERS 2006 Vol. 6, No

Presentation Outline  Introduction ZnO properties Piezoelectricity  FET NW FET  PEFET Structure Experimental results Theoretical explanations  Nanoforce sensor  Conclusions and summary

Introduction  ZnO is a II-VI compound semiconductor Wurtzite crystal structure Wurtzite  Hegzagonal closed pack ( HCP ) Direct wide band gap ~ 3.4 eV Conduction is primarily thru electrons Among the tetrahedrally bonded semiconductors; highest piezoelectric tensor [or at least comparable to GaN, AlN ]piezoelectric  The electromechanical coupling is high

FET  Applied electric filed on the channel, controls the current between source and drain  Nanowire FETs use a nanowire—a quasi 1 dimensional structure, as the channelnanowire NW might be exposed as the gate or It can be attached to a gate contact

PEFET  An FET without gate electrode  A PEFET exploits the piezoelectric property of the NW to create the current controlling field

Structure  “ZnO NWs were synthesized by the well-established technique of thermal evaporation in a tube furnace.  A single NW sample was prepared by aligning the NW on the edge of a silicon substrate using a probe station. The extended length of the NW was 100 um, while the other side of the NW was fixed onto the silicon substrate by conductive sliver paint, through which the NW was connected to the negative electrode of the power source. The silicon substrate was placed on the sample stage of an SEM with the NW pointing at the tungsten needle tip.”

Structure

Experimental Results

Theoretical Explanation The drop in current can be attributed to the following 2 reasons:  Carrier Trapping due to induced charges Due to the compression and the stretch of the ZnO NW, positively and negatively charged surfaces are produced  Channel narrowing due to depletion region expansion

Theoretical Explanation

Nanoforce Sensor

Conclusions and Summary  A new type of FETs are suggested  Semiconducting and piezoelectric properties of ZnO are key parameters of the new PE- FET  Nanoforce sensors can be fabricated using PE-FETs The major limitation is that the sensor should work in linear region of the NW It can be used for forces <17 nN  PEFET can also be used in biosensros

References  1 Nano Letters, 2005, 5,  2 Science, ,

Thanks

ZnO crystal structure  Back Back

Energy Triangle  Back Back

NW FET Picture from ref#2  Back Back

Nanowire Picture from ref#1  Back Back