Preparation and characterization of ZnO microcantilever for nanoactuation
Peihong Wang
0
Hejun Du
0
Shengnan Shen
0
1
Mingsheng Zhang
1
Bo Liu
1
0
School of Mechanical and Aerospace Engineering, Nanyang Technological University
, 50 Nanyang Avenue,
Singapore
, 639798,
Republic of Singapore
1
Data Storage Institute, 5 Engineering Drive 1
,
Singapore
, 117608,
Republic of Singapore
Zinc oxide [ZnO] thin films are deposited using a radiofrequency magnetron sputtering method under room temperature. Its crystalline quality, surface morphology, and composition purity are characterized by X-ray diffraction [XRD], atomic force microscopy [AFM], field-emission scanning electron microscopy [FE-SEM], and energy-dispersive X-ray spectroscopy [EDS]. XRD pattern of the ZnO thin film shows that it has a high c-axispreferring orientation, which is confirmed by a FE-SEM cross-sectional image of the film. The EDS analysis indicates that only Zn and O elements are contained in the ZnO film. The AFM image shows that the film's surface is very smooth and dense, and the surface roughness is 5.899 nm. The microcantilever (Au/Ti/ZnO/Au/Ti/SiO2/Si) based on the ZnO thin film is fabricated by micromachining techniques. The dynamic characterizations of the cantilever using a laser Doppler vibrometer show that the amplitude of the cantilever tip is linear with the driving voltage, and the amplitude of this microcantilever's tip increased from 2.1 to 13.6 nm when the driving voltage increased from 0.05 to 0.3 Vrms. The calculated transverse piezoelectric constant d31 of the ZnO thin film is -3.27 pC/N. This d31 is high compared with other published results. This ZnO thin film will be used in smart slider in hard disk drives to do nanoactuation in the future.
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Introduction
As the recording density of hard disk drive [HDD]
further increases, the spacing between the slider and the
disk decreases quickly. A 10-Tb/in2 recording density
requires a 2 to 3 nm or even less of head-media spacing
when HDD is working [1]. In that case, contact between
slider and disk will not be avoided completely. So, it is
necessary to detect the slider-disk contact and then
adjust the spacing to decrease the damage to the
headdisk interface. Due to quick response and contact
detection ability, many piezoelectric sensors/actuators based
on bulk and thin film lead zirconate titanate [PZT] have
been proposed in order to solve the above problem
[2,3]. However, it is hard to fabricate a bulk PZT
material into a microscale dimension. Meanwhile, the
deposition of PZT thin film usually requires processing at over
600C [4], which is not compatible with fabrication of
magnetic heads in HDD technology. Compared to PZT
material, ZnO thin film also has good piezoelectric
quality, and its microfabrication does not need head process
under very high temperature [5]. So, ZnO film-based
piezoelectric sensors/actuators are being designed and
used in smart slider to detect the head-disk contact and
then adjust the flying height in our ongoing project.
There were many papers about the fabrication and
characterization of ZnO films in the past decades [6-8].
However, few reports presented the piezoelectric quality
of ZnO film quantitatively. In this paper, a ZnO thin film
for the application of nanoactuator was deposited using a
radiofrequency [RF] magnetron sputtering system under
room temperature and was characterized by X-ray
diffraction [XRD], energy-dispersive X-ray spectroscopy
[EDS], field-emission scanning electron microscopy
[FESEM], and atomic force microscopy [AFM]. Moreover, a
ZnO film-based piezoelectric microcantilever was
fabricated by micromachining techniques. The dynamic
response of the piezoelectric cantilever was measured
using a laser Doppler vibrometer [LDV]. The calculation
result showed that the transverse piezoelectric constant
d31 of the ZnO thin film is -3.27 pC/N. This d31 is high
compared with other published results. In the future, this
ZnO thin film will be used in smart slider to do
nanoactuation in HDDs.
Experimental details
ZnO thin films were deposited by RF magnetron
sputtering system using a ZnO target (99.99%) with a diameter
of 2 in. and a thickness of 3 mm. The substrate
comprised p-type silicon (100) with a SiO2 layer and a Au/Ti
seed layer. The thickness of the SiO2 layer and the Au/Ti
seed layer were 1 m and 300 nm/50 nm, respectively.
The chamber was down to 5 10-6 Torr using a
molecular pump before introducing mixed Ar and O2 gases. In
the deposition of the ZnO thin film, the RF power was 70
W, the working pressure was 0.8 Pa, the O2/(Ar + O2)
gas ratio was 0.25, and the substrate temperature was at
room temperature. The above deposition condition was
from our previous optimization result. The
corresponding deposition rate of the ZnO film was about 0.28 m/h,
and the deposition time was 4.5 h.
The ZnO piezoelectric microcantilever was fabricated
by micromachining techniques. The substrate was (100)
p-type silicon wafer on which a 1 m of silicon dioxide
[SiO2] was grown using a thermal oxidation method.
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