Scanning Force Microscope Using Piezoelectric Excitation and Detection

Toshihiro ITOH  Takahiro OHASHI  Tadatomo SUGA  

IEICE TRANSACTIONS on Electronics   Vol.E78-C   No.2   pp.146-151
Publication Date: 1995/02/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Micromachines and Micro Electro Mechanical Systems)
SFM,  piezoelectric microcantilever,  ZnO,  piezoelectric excitation,  deflection detection,  

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This paper reports on a new dynamic scanning force microscope (SFM), in which the piezoelectric microcantilever is utilized for the lever excitation and displacement sensing. Piezoelectric cantilevers can detect their deflection without external sensing elements and be vibrated with no oscillator outside. The cantilever integrated with the deflection detector and the oscillator changes the conventional construction of a dynamic SFM and expands its range of applicability. The microcantilever used consists of a ZnO layer sandwiched with Au electrodes deposited on a thin beam of thermally grown SiO2. The length, width and thickness of the lever are 125 µm, 50 µm and 3.5 µm, respectively. We have characterized this cantilever by measuring the charge spectrum and the frequency dependence of the admittance. From the charge spectrum the mechanical quality factor measured 300 in free vibration. Typical piezoelectric constant of the ZnO film was estimated approximately as 80% of single-crystal's value. The piezoelectric cantilever can be vibrated by applying the voltage with the frequency near the resonance to the piezoelectric layer. The excited amplitude per unit voltage at the resonance frequency was calculated as about 5 µm/V. The cantilever amplitude can be detected by measuring the current between electrodes, since the admittance depends on the quality factor. We have constructed a dynamic SFM without external oscillator and detector, and successfully obtained the surface images of a sol-gel derived PZT film in the cyclic contact operation mode. The longitudinal resolution of the SFM system was 0.3 nm at a 125 Hz bandwidth.