PhD Thesis Arne Lüker final version V4 - Cranfield University

Relative
diel.
diel.
constant
Constant
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications
370
360
350
340
330
320
310
-3 -2,25 -1,5 -0,75 0 0,75 1,5 2,25 3
Voltage [V]
Fig. 5.9: Permittivity and dielectric loss of PST 50/50 from –3V to +3V at 10MHz
To measure the permittivity and dielectric loss in this frequency range by using the
equipment the University of Birmingham offers, a CPW 2 , with all the involved
advantages and disadvantages (substrate losses, fringing fields etc. …), was build upon
the PST thin film. The dielectric constant and
loss were measured twice, at the end auf the
CPW and in the middle. The variance of the
dielectric constant of both measurements was
found to be negligible, whereas the extraction
of the true loss needed a more profound
mathematical treatment, Fig. 5.10. For a
detailed description of the measurement and
the physical background see Ref. 15.
The permittivity was measured between 370
and 360 with a little decrease up to 110 MHz,
this compares well with the measurement at low frequencies. The dielectric loss is with
measured 7 % approximately 5 % higher compared to the low frequency range. But the
2 CPW (Coplanar Waveguide). A short and good introduction is given at:
www.microwaves101.com/encyclopedia/coplanarwaveguide.cfm
0,5
0,45
0,4
0,35
0,3
0,25
0,2
0,15
0,1
0,05
0
diel. loss
101
Loss, end
Loss, middel
Loss, real
Fig. 5.10: Comparison of measured losses on a CPW.
4 1
tanδ real = tanδ
middel − tanδ
3 3
end