PDF《Piezoelectric-Potential-Controlled》

Piezoelectric-Potential-Controlled Polarity-Reversible Schottky Diodes and Switches of ZnO Wires Jun Zhou,?,? Peng Fei,?,§ Yudong Gu,?,§ Wenjie Mai,? Yifan Gao,? Rusen Yang,? Gang Bao,? and Zhong Lin Wang*,? School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, Department of Biomedical Engineering, Georgia Institute of Technology and Emory UniVersity, Atlanta, Georgia 30332, and Department of AdVanced Materials and Nanotechnology, College of Engineering, Peking UniVersity,

100084 Beijing, China Received August 14,

2008 ABSTRACT Using a two-end bonded ZnO piezoelectric-?ne-wire (PFW) (nanowire, microwire) on a ?exible polymer substrate, the strain-induced change in I-V transport characteristic from symmetric to diode-type has been observed.

This phenomenon is attributed to the asymmetric change in Schottky-barrier heights at both source and drain electrodes as caused by the strain-induced piezoelectric potential-drop along the PFW, which have been quanti?ed using the thermionic emission-diffusion theory. A new piezotronic switch device with an on and off ratio of ?120 has been demonstrated. This work demonstrates a novel approach for fabricating diodes and switches that rely on a strain governed piezoelectric-semiconductor coupling process. Binary switching is the principle of many electronic devices for applications such as data storage and logic circuits. Up to now most of the nanoscale switches are operated by an electrostatic force between a suspended carbon nanotube (CNTs)/nanowire and its counter electrode to switch between on and off depending on mechanical contact.1-3 As the size of the devices reaching nanoscale, a small gap of ?10 nm is required to be maintained between the CNTs/nanowire and the electrode for electro-mechanical switching. In such a case, the van der Waals interaction between the CNT and the electrode may be strong enough to bind the two together so that the device cannot perform the off function as required. Furthermore, the random thermal vibration at the tip of CNT may also become suf?ciently large at conven- tional operating temperatures, which can strongly increase the device instability.4 As a result, the reliability, lifetime and manufacturability of these devices are challenged. The Schottky barrier diode, a metal-semiconductor (MS) rectifying junction that generally exhibits switching effect, may overcome the drawbacks. ZnO, a material that exhibits semiconductor and piezoelectric properties, is likely a candidate for fabricating diode-based switching devices. Recently, various novel devices have been fabricated using ZnO nanowires/nanobelts by utilizing its coupled piezoelec- tric and semiconducting properties (piezotronic effect), such as nanogenerators,5,6 piezoelectric ?eld effect transistors and chemical sensors,7,8 piezoelectric diodes,9 triggers,10 trans- ducer and actuator,11 and ?exible piezotronic strain sensors.12 In this letter, we report a new type ?exible piezotronic switch device that is built using a single ZnO piezoelectric ?ne wire (PFW) (nanowire, microwire). Its operation mech- anism relies on the piezoelectric potential induced asym- metric change in Schottky-barrier height (SBH) at the source and drain electrodes. The change of SBH is caused by the combined effects from strain-induced band structure change and piezoelectric potential. The device demonstrated here presents a new electromechanical switch built based on piezotronic effect.13 For this study, the device was fabricated by bonding an ultralong ZnO PFW laterally on a polystyrene (PS) substrate, which has a thickness much larger than the diameter of the PFW, as schematically shown in the upper-inset of Figure 1a. The detail device fabrication process was introduced elsewhere.12 Brie?y, single ZnO PFW (typical diameter of several micrometers and length of several hundred microme- ters to several millimeters), which was synthesized by a high temperature physical vapor deposition process,14 was placed on PS substrate (typical length of ?3 cm, width of ?5 mm * To whom correspondence should be addressed. E-mail: zlwang@ gatech.edu. ? Georgia Institute of Technology. ? Georgia Institute of Technology and Emory University. § Peking University. NANO LETTERS