International Conference on Enabling Science and Nanotechnology 2012 (ESciNano 2012)
5-7 January 2012, Persada Johor International Convention Center, Johor Bahru, MALAYSIA
ESciNano 2012 – http://www.fke.utm.my/mine/escinano2012
Compatibility of Ferroelectric Films in Development of Transmission Lines for
MMIC
Rafidah Ahmad
*a
, Hanisah M. Nadzar
a
, Suhana. Sulaiman
a
, Salina Mohamad
b
, M. Rusop
b
and Z.Awang
a
a
Microwave Technology Centre,
b
Nano-ElecTronic Center (NET), Faculty of Electrical Engineering,
Universiti Teknologi MARA, Shah Alam, 40450 Selangor, Malaysia.
*imarazak97@yahoo.com
Ferroelectric materials offer promising features that are useful for microelectronic devices but they
have not been popular for microwave integrated circuits due their preparation methods which are not
compatible with integrated circuit manufacturing. In contrast, new dielectric materials are required for
microwave integrated circuits (MIC) so that their performance is improved. Improved materials are
needed to build transmission lines, which are basic building blocks in integrated circuit architecture. The
main issues facing monolithic microwave integrated circuit (MMIC) technology today are power
consumption and reliability. These are due to the high loss, poor resistivity and low permittivity dielectric
materials used currently in MMIC [1]. There is therefore an urgent need to replace existing dielectrics
with those that offer better high frequency response in terms of less loss, high resistivity and high
permittivity. The main issues facing monolithic microwave integrated circuit (MMIC) technology today
are power consumption and reliability. These are due to the high loss, poor resistivity and low
permittivity dielectric materials used currently in MMIC [1,2]. There is therefore an urgent need to
replace existing dielectrics with those that offer better high frequency response in terms of less loss, high
resistivity and high permittivity.
The purpose of this paper is to investigate the material parameters which affect transmission lines
built on ferroelectric lead zirconate titanate (PZT) and magnesium zinc oxide (MgZnO) thin films at high
frequency. The characteristics are studied by investigating the effect on the return loss of the lines by
varying the permittivity of both thin films. The width of the transmission lines were calculated based on
the 50 of characteristic impedance for each film. The length of the line was set at 100 μm and the
thickness was 0.1 μm. The PZT and MgZnO film thickness was 0.5 and 0.36 μm, and the structures were
simulated over 1 to 10 GHz. With the relative permittivity of 87 and 112 for PZT while 10.5 and 18 for
MgZnO, the return loss (RL) was computed at 10 GHz for same structures. The variations of
r
were
simulated to predict their RL. The results show that the PZT structures exhibit high reflection
performance, compared to MgZnO due to its high permittivity which led to narrow lines width. However,
these findings clearly observed the viability of using PZT and MgZnO as new dielectric materials for
microwave integrated circuits depending on their chosen application and band frequency.
Fig. 1 shows structure of PZT and MgZnO films deposited on a Si substrate which acts as a
mechanical support layer. Figs. 2 and 3 present the performance of return loss of thin film microstrip
(TFM) lines when the structure was designed on PZT films and MgZnO. The PZT and MgZnO TFM
lines were characterized for dielectric constant of 112 and 18. The significant different of simulated S
11
differ by 3 dB than measured for PZT and 2 dB for MgZnO. The advantages using ferroelectric films like
PZT because it offers huge circuit reduction due to its relative permittivity. By comparing with Si
3
Ni
4
,
PZT is capable to miniaturize the circuit size up to 15 times while MgZnO offers four times of size
reductions. Figs. 4 and 5 show the characteristic impedances, Z
o
of transmission line for PZT and MgZnO.
The high
r
values shown by PZT films in turn make 50 lines very thin for fabrication and this make the
task of reducing the mismatch difficult while MgZnO has high Z
o
consistent with conventional microstrip
structures. It is possible to hypothesize that MgZnO offer less reflections due to the fact that its lower
r
compared to PZT. Although MgZnO offers less circuit size reduction compared with PZT, both are
suitable for MIC applications. It was due to the fact that MgZnO is far more stable at lower frequency
than PZT. In conclusion, both films are suitable to be used for MMIC device development. The material
selection is very essential depending on the chosen frequency band and applications. The rf properties of
these new dielectric materials makes MgZnO may operates at L and S-band while PZT suitable at X and
Ku-band respectively.
9781457707988/12/$26.00©2012IEEE