Online proceedings - EDA Publishing Association

11-13
May 2011, Aix-en-Provence, France
Design Number
Fig. 9. Design number versus applied resonant frequency
mode of the structure, modal analysis was performed. Thirty
modes were simulated for six different volume of
piezoelectric energy harvester. The mode with the highest
displacement was identified as mode of interest [3].
A range of 230 Hz to 1.5 kHz resonant frequency for five
different designs is simulated to get maximum power output
at the ambient resonant frequency. Fig. 10 shows the effect of
resonance frequency to the output power produced. The
lower the resonant frequency, the higher the output power
produced. The highest output power is 3.056 W at 232 Hz
resonant frequency. The power output produced is enough to
power the wireless condition monitoring circuits since power
plants generate ambient vibrations at low frequencies.
C. The effect of chosen piezoelectric material on output
power.
MEMS technology has introduced the concept of
many functional materials with new fabrication process
which allow a creation of miniature devices consuming less
power, reliable and integrate multiple functions. One of the
main functional materials is piezoelectric thin film.
Piezoelectric materials develop charge on the sample surfaces
when exposed to applied stresses or vibration. [6].
The choice of the piezoelectric thin films depends
on the process complexity, piezoelectric coupling coefficient
and CMOS compatibility. The most common materials used
are aluminium nitride (AlN), zinc oxide (ZnO) and lead
zicronate titanate (PZT). PZT provides highest coupling
coefficient. However, PZT thin film deposition is very
complex and hazardous due to lead contamination. AlN and
ZnO are both wurtzite structure materials with the polar
direction [6]. Low deposition temperature is kept during
sputtering process to obtain high quality of piezoelectric AlN
and ZnO films and to allow complete integration capabilities
with CMOS technology [6]. The low deposition temperature
also offers the use of standard Al for metallization layers
(electrodes). The sputter deposition techniques for both AlN
and ZnO is also well-known standard deposition and is less
complex compared to the deposition of PZT. Therefore, the
simulations are shown to discuss the effect of AlN and ZnO
piezoelectric materials only.
Fig. 10. Output power produced versus applied resonant frequency
The main material properties for the analysis are
piezoelectric strain coefficient; dielectric constant and
stiffness matrix. The material properties for ZnO and AlN
piezoelectric material are summarized in Table IV and Table
V [5] [7]. The Dielectric entries shown are relative values to
vacuum permittivity 0 = 8.85 x 10 -12 c/(vm) [5].
The aim of the simulation analysis is to compare the
output power produced at the resonance frequency for two
different piezoelectric material used: AlN and ZnO. Table
VII and Fig. 11 show that zinc oxide provides more energy
output compared to aluminium Nitride (AlN). At 242 Hz
resonant frequency, the peak power output produced for ZnO
is 3.0560 µW and 0.8000 µW for AlN for the same volume
TABLE IV
ZINC OXIDE AND ALUMINUM NITRIDE PIEZOELECTRIC PROPERTIES
Parameter ZnO AlN
Density ( kg/m 3 ) 5.8 e -13 3.2 e -15
Coupling Coefficient, k 0.33 0.24
Relative dielectric
constant,
10.9 10.5
TABLE V
ELASTIC CONSTANTS FOR ZINC OXIDE , [C ZnO] 6X6 AND ALUMINUM NITRIDE , [C AIN] 6X6
C COLUMN X ROW ZnO (N/m 2 ) AlN (N/m 2 )
C 11 2.907 x 10 5 3.450 x 10 5
C 21 1.21 x 10 5 1.250 x 10 5
C 22 2.907 x 10 5 3.450 x 10 5
C 31 1.051 x 10 5 1.200 x 10 5
C 32 1.051 x 10 5 1.200 x 10 5
C 33 2.109 x 10 5 3.950 x 10 5
C 44 4.430 x 10 4 1.100 x 10 5
C 55 4.240 x 10 4 1.180 x 10 5
C 66 4.240 x 10 4 1.180 x 10 5
TABLE VI
PIEZOELECTRIC STRAIN COUPLING MATRIX COEFFICIENT FOR ZINC OXIDE , [dZnO] 3X6
AND ALUMINUM NITRIDE , [d AIN] 3X6
Parameters ZnO (C/m 2 ) AlN (C/m 2 )
d 31 -5.430 x 10 -6 -5.800 x 10 -1
d 33 1.167 x 10 -5 1.55
d 15 1.134 x 10 -5 4.800 x 10 -1
- d 15 -1.134 x 10 -5 -4.800 x 10 -1
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