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Enabling electrically tunable radio frequency components with advanced
microfabrication and thin film techniques
ZHANG Ying-cong(张颖聪), GE Jin-qun(葛晋群), WANG Guo-an(王国安)*
Department of Electrical Engineering, University of South Carolina, Columbia, SC 29208, United States
© Central South University 2022
Abstract: Multi-function, multiband, cost-effective, miniaturized reconfigurable radio frequency (RF) components are
highly demanded in modern and future wireless communication systems. This paper discusses the needs and
implementation of multiband reconfigurable RF components with microfabrication techniques and advanced materials.
RF applications of fabrication methods such as surface and bulk micromachining techniques are reviewed, especially on
the development of RF microelectromechanical systems (MEMS) and other tunable components. Works on the
application of ferroelectric and ferromagnetic materials are investigated, which enables RF components with continuous
tunability, reduced size, and enhanced performance. Methods and strategies with nano-patterning to improve high
frequency characteristics of ferromagnetic thin film (e. g., ferromagnetic resonance frequency and losses) and their
applications on the development of fully electrically tunable RF components are fully demonstrated.
Key words: tunable RF components; bulk micromachining; surface micromachining; thin film techniques
Cite this article as: ZHANG Ying-cong, GE Jin-qun, WANG Guo-an. Enabling electrically tunable radio frequency
components with advanced microfabrication and thin film techniques [J]. Journal of Central South University, 2022, 29
(10): 3248−3260. DOI: https://doi.org/10.1007/s11771-022-5165-8.
1 Introduction
Over the decades, wireless communication
technologies have been well developed and widely
exploited in transportation systems [1], smart
agriculture [2−3], wearable devices [4 −5], military
[6] and satellite communication [7]. As shown in
Figure 1, the evolving wireless communication
technologies demand radio frequency (RF)
components with wide bandwidth, multi-bands and
multiple functionalities, frequency reconfigurability,
low cost, and miniaturization.
Many efforts have been spent in the design and
implementation of advanced RF components with
various fabrication techniques and material
technologies. Micromachining is a fabrication
technique that manufactures micro- or nano-scale
RF devices with high reliability and low cost. Based
on this, bulk micromachining and surface
micromachining have been widely utilized in
manufacturing frequency tunable RF components,
including RF MEMS switches [8 −11], RF filters
[12−14], and antennas [15 −16]. Femtosecond laser
technique is another general fabrication method in
nano/micro scale [17−19].
Multiple reconfigurable technologies are
investigated with MEMS switch structure [20] and
complementary split ring resonators (CSRRs) [21]
enabled with advanced fabrication process, which
provides digital frequency tunability. To achieve
continuous tunability, integration of material
techniques is proposed and developed [22−24] with
ferroelectric and ferromagnetic materials.
DOI: https://doi.org/10.1007/s11771-022-5165-8
J. Cent. South Univ. (2022) 29: 3248
－
3260
Foundation item:
Projects(1253929,
1910853)
supported by the National Science Foundation
Received date:
2022-05-25;
Accepted date:
2022-09-20
Corresponding author:
WANG Guo-an,
PhD,
Professer;
E-mail:
gwang@cec.sc.edu;
ORCID:
https://orcid.org/0000-0003-3142-8395
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Ferroelectric materials, such as barium strontium
titanate (BST) and lead zirconate titanate (PZT),
have high and continuously tunable permittivity
with applied electric field. Similarly, the
permeability of ferromagnetic materials, such as
cobalt and permalloy (Py), can be tuned with the
external magnetic field. By properly integrating
ferroelectric and ferromagnetic materials in the RF
components and RF substrate, good miniaturization,
enhanced performance, and fully electrically tunable
operating frequency can be achieved.
This paper introduces the state-of-the-art
multiband and multifunction reconfigurable RF
designs from the perspectives of micromachining
fabrication and material techniques. In Section 2,
micromachining fabrication techniques and their
applications are discussed. Integration and
applications of ferroelectric and ferromagnetic thin
films enabled with microfabrication techniques are
presented in Section 3. Various ferroelectric and
ferromagnetic-based RF devices with reduced size,
tunable operating frequency, and enhanced
performance are discussed.
2 RF applications with micromachining
techniques
Micromachining technique is exploited for
fabricating micro- and nano-scale RF devices to
meet the growing demand of miniaturization and
elevated level of integration. Bulk micromachining
uses the etch process to selectively remove the
substrate, forming different substrate structures,
such as cavities, channels, and trenches. It can be
categorized into dry bulk micromachining and wet
bulk micromachining depending on the enchants
utilized in the fabrication process. The “wet”
chemical etchants are more likely to etch a large
surface while the “dry” reactive ion etchants can
create a deep and vertical profile [25]. Different
from the bulk micromachining, the surface
micromachining constructs the desired structure
upon the surface of the substrate. Its main
fabrication steps include deposition, patterning, and
etching. The micromachining fabrication methods
exhibit great advantages for manufacturing RF
devices with size reduction, performance
Figure 1 Applications, requirements and implementation of modern wireless communication systems with fabrication
techniques and advanced materials
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enhancement, and process compatibility.
By applying the wet micromachining method,
a high isolation MEMS switch was developed as
shown in Figure 2 [8]. A cavity was first created by
bulk etching of substrate with potassium hydroxide
(KOH). A thin metal seed layer was then deposited
and patterned to form the bottom electrode
structure, followed with a gold electroplating
process for increased thickness. Plasma enhanced
chemical vapor deposition (PECVD) Si3N4 was
grown and patterned with reactive ion etching (RIE)
as a dielectric layer on the actuation area.
Afterward, the sacrificial layer was deposited.
Finally, the top membrane was deposited and
patterned on the sacrificial layer, and the sacrificial
layer was removed with photoresist stripper to
release the MEMS structure. With this fabrication
method, the process steps were minimized, and the
experiment results showed that this switch had a
low actuation voltage of 15 V with improved
reliability.
With the surface micromachining method, a
direct approach fabricating capacitive RF MEMS
switches with photo-definable high-k metal oxides
was developed in Ref. [26], which reduces the
process complexity without the need of expensive
and high vacuum equipment of PECVD and RIE.
As depicted in Figure 3(a), a photosensitive metal-
organic precursor was deposited via spin coating
and converted to a high-k metal oxide via direct
ultraviolet exposure. Figure 3(b) shows the SEM
photo of a fabricated bridge-type switch, which has
a reliability of over 340 million cycles. Compared to
MEMS switches with silicon nitride dielectric, this
switch exhibits a low insertion loss of 0.3 dB and
high isolation of 24 dB at 20 GHz, respectively.
With remarkably high Q, near zero power
consumption and extremely high linearity, MEMS
switches have been widely applied in designing
frequency tunable RF antenna arrays, filters, and
phase shifters, with some design applications are
shown in Figure 4. However, besides the low tuning
speed (~μs), today ’s RF MEMS devices are
predominantly based on electrostatic actuation,
which results in undesirable high contact resistance,
probability of stiction, and low power handling
capability with only digital tunable capacitance at
up and down state. To tackle these challenges, other
technologies are required to accomplish
continuously tunable RF components with fast
Figure 2 MEMS fabrication process flow with bulk micromachining techniques [8]
Figure 3 (a) Direct fabrication process of metal oxide patterns using photosensitive metal-organic compounds; (b) SEM
photo of the fabricated MEMS switch [26]
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response time (~ns), thus the integration of novel
materials and fabrication enabled techniques are
proposed and developed as discussed in Section 3.
3 Reconfigurable technologies with thin
film and techniques
Ferroelectric materials have high and
electrically tunable permittivity with an applied
electric field, while ferromagnetic materials have
high permeability, and their permeability can be
changed with an external magnetic field. By proper
design and integration of ferroelectric and
ferromagnetic materials, continuously tunable RF
devices can be achieved with improved
performance.
3.1 Ferroelectric thin film enabled RF
applications
Ferroelectric materials, such as BST and PZT,
are crystalline materials that exhibit spontaneous
electrical polarization switchable by an external
electric field, resulting in the tunable permittivity.
An RF MEMS switch [22] is first implemented with
surface micromachining method and the application
of ferroelectric materials, which provides both
digital and analog tunable capacitance. The
fabrication flow is shown in Figure 5(a). The BST
dielectric layer was deposited with a combustion
chemical vapor deposition (CCVD) technology on
the bottom metal electrode. The silicon nitride layer
was then deposited with plasma enhanced chemical
vapor deposition (PECVD) and patterned using RIE
to isolate the separate the actuation electrode from
direct contact to the top electrode. The SEM photo
of the switch is shown in Figure 5(b). In this
structure configuration, when the top electrode
touches the bottom BST layer with actuation
voltage, the dielectric constant of BST is tunable
with additional voltage bias applied between the top
electrode and the bottom electrode underneath the
BST layer, providing a possibility of making
linearly tunable MEMS capacitor. The measured
C−V characteristics in Figure 5(c) shows that the
capacitance of the switch on the down state is
continuously tunable from 130.0 to 71.2 pF by
applying biasing voltage from 1 V to 5 V. The
tuning range is 182% and the Q factor is 260.
With the integration of MEMS switches and
ferroelectric thin film (e. g., BST), a frequency and
bandwidth tunable bandpass filter was designed
[28]. In this work, BST layer was deposited with
CCVD method and patterned on sapphire substrate
with liftoff process, the filter structure and the
MEMS switches are fabricated with standard
surface micromachining techniques. The operating
frequency is tunable with voltage-controlled
capacitance from the BST-based MIM capacitors,
and the bandwidth is tuned with MEMS switch
dependent coupling coefficient. The experiment
results show that the center frequency of the filter is
tunable continuously from 30 GHz to 35 GHz with
the insertion loss of 10.0 dB to 2.7 dB by applying
voltage from 0 to 40 V. The fractional bandwidths of
9.6% and 4.8% have been achieved for wideband
and narrowband configuration.
Other ferroelectric materials such as PZT
(PbZrxTi1-xO3) thin film is also attractive for the
implementation of tunable RF components. PZT has
the ABO3 perovskite structure with Zr- and Ti-ions
occupying the center, Pb-ions in the corners and
O-ions at the face centers, which enables the PZT to
have high and tunable permittivity with the applied
external biasing electric field. Due to its
Figure 4 Examples of RF MEMS components: (a) Dual band and dual polarization antenna [27], (b) Frequency and
bandwidth tunable filter [28]; (c) Phase shifter [29]
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extraordinary ferroelectric and mechanical
properties, PZT has been applied in designing an
integrated piezoMEMS single pole double throw
(SP2T) switch and contour-mode tunable filters
[30], and PZT ferroelectric capacitor (FeCAP) based
RF resonator [31]. There are several methods to
grow PZT thin film including chemical vapor
deposition (CVD), molecular beam epitaxy (MBE),
sol-gel method, and sputtering. The sol-gel method
is the most convenient and less expensive method,
where the solution is prepared first followed by the
growth of an intermediate layer as needed. The PZT
solution is spun over the sample and rotated at a
very high speed to form a uniform layer. Two stages
of temperature treatment are required: pyrolysis and
crystallization. As shown in Figure 6, an optimized
annealing process was developed in Ref. [23] to
grow high quality PZT thin film.
In summary, ferroelectric materials provide
controllable and high capacitance density, and have
been widely implemented in reconfigurable RF
devices such as phased array antennas, oscillators,
and filters. However, it only offers high capacitance
tuning ratios. To further increase the tunability range
and impedance matching performance, inductive
Figure 5 (a) Process flow; (b) SEM photo; (c) Measured C−V characteristics of the BST enabled tunable switch [22]
Figure 6 Photos of PZT film (a) after spin coated
with sol-gel method, (b) 500 ° C, and (c) 600 ℃
crystallization; (d) Optimized crystallization temperature
profile [23]
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tunability is highly desirable besides capacitive
tunability.
3.2 Ferromagnetic thin film enabled applications
Ferromagnetic films (e. g., Py, CoNbZr) have
been explored for high-performance reconfigurable
magnetic microwave devices. Magnetic dipoles
spontaneously align in the same direction within the
individual magnetic domain of ferromagnetic
materials. When the ferromagnetic material is
exposed to a magnetic field, magnetic domains are
aligned in the same direction as the bias field and
maintain magnetic properties even in the absence of
a magnetic field, resulting in high and stable
permeability. The permeability of ferromagnetic
materials is thus tunable with an external magnetic
field, which is bulky, noisy, requires comparatively
high-power consumption for operation, and is
difficult to integrate with modern mobile
communication systems. Furthermore, the high-
frequency application of ferromagnetic materials is
often limited by the low ferromagnetic resonant
(FMR) frequency which is below 1 GHz for the
un-patterned ferromagnetic film.
Many efforts have been devoted to reducing
the magnetic loss and improving FMR frequency of
ferromagnetic film, among which patterning
magnetic thin films with high aspect ratio is one of
the most promising methods [32]. The properly
patterned ferromagnetic thin films have built-in high
shape anisotropy fields providing a self-biasing
field, thus increases FMR frequency. A FMR
frequency of above 6 GHz has been achieved with
patterning Py (Ni80Fe20) film into nanoscale stripes
with length and width of 10 µm and 150 nm
(Figure 7), respectively. To minimize the need of
bulk external magnetic bias field, DC current has
been utilized to electrically tune the permeability of
ferromagnetic thin film [23, 32]. The static magnetic
field generated by DC current tilts the
magnetization direction in the film away from its
easy axis towards the hard axis, which in turn
decreases the material’s magnetic moments:
saturation magnetization and anisotropy field. The
equivalent permeability of Py thin film is thus tuned
accordingly.
DC current tunable Py enabled slow wave
transmission line structure (SWS) was reported in
Ref. [33]. Py was deposited with DC magnetron
sputter and patterned as 10 µm×150 nm slim bars
with E-beam lithography. The photo of the SWS and
patterned Py film is shown in Figure 8(a). The
measured results showed that the Py enabled SWS
to provide the same phase shift with 42% further
size reduction when compared to regular SWS. The
inductance per unit length of the SWS is tunable
from 963 nH/m to 895 nH/m with biasing DC
current applied from 0 to 150 mA. The slow wave
structure provides a fixed 90° phase shift from
4.00 GHz to 3.81 GHz as shown in Figure 8(b).
Permalloy was also applied with other design
techniques such as electromagnetic bandgap (EBG)
Figure 7 (a) SEM photo and zoom-in view of nano-patterned Py films; (b) Tuning setup of DC current [23]
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coplanar waveguide (CPW) to develop bandpass
filter [34]. Gold CPW layer was first deposited on
the substrate with E-beam evaporation method and
patterned with the lift-off process. Subsequently,
100 nm thick Py thin film was directly deposited on
the top of the CPW signal line utilizing DC
magnetron sputter and was patterned as long bars
using lift-off method. The fabrication process is
shown in Figure 9. DC current was applied between
the input and output ports of the resonator
generating DC magnetic field; thus, the inductance
of the transmission line could be tuned, further
tuning the operation frequency of the bandpass filter.
In addition to being integrated directly in the
specific structure of individual components,
ferromagnetic thin films have also been applied in
the design of an engineered substrate [35 −37],
which has high and electrically tunable permittivity
and permeability with reduced loss to enable a more
flexible tunable technology. The engineered
substrate is implemented with patterned Py thin
films on silicon substrate. As shown in Figure 10(a),
a layer of 100 nm Py in an array of 15 μm×20 μm
patterns with 10 μm gaps among them is deposited
on a regular RF dielectric substrate. The effective
permeability of the substrate is tunable with the
static magnetic field produced from the applied DC
current through gold bias lines beneath the Py
patterns. The engineered substrate has both high
equivalent permeability and permittivity, and it can
be used to implement miniaturized antenna with
increased bandwidth and improved radiation
efficiency. The miniaturization factor of the antenna
is described as n=εrμr, where μr and εr refer to
the relative permeability and permittivity in
substrate, respectively. Furthermore, with
selectively designed relative permeability and
permittivity, the characteristic impedance of the
substrate (η=η0μr/εr, η0 refers to the characteristic
impedance in free space) becomes closer to the
Figure 8 (a) Photo and (b) electrical phase tunability of Py enabled slow wave transmission line [33]
Figure 9 Fabrication process steps of the Py enabled tunable bandpass filter [34]
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impedance of the free space η0, which allows
wideband impedance matching. Figure 10(b) shows
a miniaturized patch antenna implemented on the
engineered substrate. Permeability of the
ferromagnetic thin film patterns embedded in the
engineered substrate is tuned with the applied DC
current through the metal bias pad, and the
operating frequency of the antenna can be shifted
from 2.38 GHz to 2.43 GHz, as shown in
Figure 10(c).
Py thin film enabled engineered substrate
provides a flexible solution in designing arbitrary
frequency agile devices with the state-of-the-art
design techniques for wide and flexible tunability.
Figure 11 shows other frequency reconfigurable RF
passives on the engineered substrate, which fully
demonstrates the flexible design efficacy. Both
transmission line-based phase shifter and bandpass
filter were directly fabricated on a Rogers 4350
substrate and bonded with the engineered substrate
[35]. The center frequency of the bandpass filter is
tunable from 2.42 GHz to 2.56 GHz with the
applied DC current increased from 0 to 500 mA.
And the transmission line on the engineered
substrate provides continuous 90° phase shift from
0.95 GHz to 1.02 GHz.
Higher permeability with larger tunability
could be achieved with multiple or thicker layers of
Py thin films in the engineered substrate. A square
loop type frequency selective surface (FSS) was
developed on the engineered substrate consisting of
Roger RT/Duriod 5880 substrate embedded with 10
layers of 100 nm thick Py thin films [36]. By
increasing the DC biasing current from 0 mA to
500 mA, the substrate permeability can be tuned
from 2.398 to 2.018 with the tunability of 19%,
resulting in the working frequency shifting from
2.450 GHz to 2.672 GHz.
Ferromagnetic materials have found many
applications in designing miniaturized and tunable
RF components. The limitations of ferromagnetic
materials, such as high magnetic loss and low FMR
frequency, have been improved by selectively
patterning the ferromagnetic thin films. The
engineered substrate enabled with ferromagnetic
materials shows great flexibility and superiority in
the design of arbitrary tunable RF components. In
addition, the increased equivalent permeability of
Figure 10 (a) Photo of the engineered substrate with embedded 100 nm thick Py patterns; (b) Structure and (c) Measured
reflection losses of antenna on engineered substrate under different DC current bias [37]
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the substrate can increase the antenna bandwidth
and efficiency, which is a promising aspect that
deserves further research work, especially for the
design of ultra-wideband antennas.
3.3 Integration of ferroelectric and ferromagnetic
materials for fully electrically tunable
technology
A more flexible tuning strategy can be
achieved with the integration of ferroelectric and
ferromagnetic materials, which provides both
tunable permittivity and permeability to enable RF
components with continuous capacitive and
inductive tunability. Moreover, the characteristics
impedance of a transmission line can be defined as
Z0µL/C. By varying the inductance and the
capacitance of a transmission line base component
with the same ratio, a fixed characteristic impedance
can be realized. Therefore, the dual tunability of
permittivity and permeability not only increases the
tuning range and design flexibility, but also enables
the capability of retaining the same characteristic
impedance for improved high frequency
performance.
Py and PZT were integrated in the design of
tunable slowwave transmission line elements with
cascaded wide and narrow signal line sections in
Refs. [38−39]. As shown in Figure 12, the Py film
was deposited on the narrow sections of slowwave
line and patterned in nanometer dimensions, while
the PZT layer was patterned between wide sections
of the signal line and ground. The detailed
fabrication process is shown in Figure 12(a), and the
CPW structure was fabricated on the high resistivity
silicon with surface micromachining techniques.
First, the SiO2 layer was deposited on the silicon
with inductively coupled plasma chemical vapor
deposition (ICP-CVD) to increase the adhesion
between PZT and substrate. PZT precursor was then
prepared with the standard sol-gel method and spin-
coated on the substrate. After PZT thin film was
crystallized with the optimized temperature profile
as discussed in Section 3.1, the wet etching method
was used to pattern the PZT thin film. After
completing PZT patterning, Au film was deposited
with the E-beam evaporator and patterned with lift-
off process to form the step impedance signal line
and ground. Py thin film was then deposited on the
Figure 11 (a) Photo and (c) measured results of phase shifter; (b) Photo and (d) measured results of bandpass filter on
the engineered substrate [37]
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top of the signal line by DC magnetron sputter and
was patterned as long bars using E-beam
lithography and lift-off method. The SEM photo of
the fabricated device is shown in Figure 12(b).
When DC voltage is applied between the signal line
and the ground, static electric field is generated,
which changes the spontaneous electric polarization
in the PZT film, and consequently, its equivalent
permittivity is reduced. When 200 mA DC current is
provided between two ports of phase shifter, the
working frequency of 90° phase shift tuning range is
2% from 1.98 to 2.04 GHz. The tuning range is 5%
from 1.98 to 2.08 GHz when 8 V DC voltage is
added between the signal line and the ground. When
both 8 V DC voltage and 200 mA DC current are
applied, the working frequency of the proposed
phase shifter is tunable from 1.98 to 2.12 GHz with
a tunability of 7.1%. Compared to regular slowwave
line, the results showed that inductance and
capacitance density of Py and PZT enabled line has
increased 13.3% and 36.0%, respectively.
To further increase the tunability range,
electrically tunable phase shifter is designed with
PZT based metal-insulator-metal (MIM) capacitor
and solenoid inductor with Py core [40]. An
electrically tunable microwave solenoid inductor
was firstly fabricated with surface micromachining
technique. The bottom Au layer of solenoid winding
was deposited on high resistivity silicon with
E-beam evaporator and patterned with lift-off
process. Afterward, Py thin film was deposited on
top of the bottom solenoid Au wires utilizing DC
magnetron sputter and was patterned as long bars
using lift-off method. Then SiO2 film was deposited
with inductively coupled plasma chemical vapor
deposition and was patterned with wet etching to
form the insulator between the top and bottom layer
of solenoid winding. Then another layer of Py film
was deposited and patterned following the
deposition of the Au layer to form the top layer of
solenoid windings. The photo of the phase shifter,
MIM capacitor, and solenoid inductor are showed in
Figure 13(a). RF signal and DC current were
Figure 12 (a) Fabrication process and (b) SEM photo of
Py and PZT enabled slow wave transmission line [39]
Figure 13 (a) Photo of phase shifter with Py enabled
solenoid inductor and PZT based MIM capacitor (insert);
(b) Measured phase shift tunability [40] (DCV is the DC
voltage; DCC is the DC current)
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simultaneously provided through bias tees. The
inductance tunable range of a single solenoid
inductor was from 1.14 nH to 1.02 nH with the DC
current increasing from 0 to 150 mA. Phase shifter
was designed by connecting three solenoid
inductors and four MIM capacitors. The capacitance
of the MIM capacitors could be controlled by tuning
the permittivity of the PZT thin film with the
applied DC voltage between the ground and the
signal line. The results in Figure 13(b) show that the
phase of the phase shifter changed from 59.2° to
43.8° at 2 GHz, which represents a 26.9% of
tunability.
Performance of some ferroelectric and
ferromagnetic materials and fabrication techniques
enabled RF devices is summarized in Table 1.
4 Conclusions
In this paper, state-of-art tunable RF passives
enabled with micromachining fabrication techniques
and thin film material are reviewed. The bulk
micromachining and the surface micromachining
techniques and their applications in implementing
RF MEMS switches and reconfigurable MEMS
components are discussed. Reconfigurable RF
technologies enabled with thin film and
microfabrication techniques are studied. Deposition
process of PZT is fully optimized for the improved
properties, electrically tunability of ferromagnetic
material is fulfilled with the applied DC current,
method and strategy of nano-patterning material
with high aspect ratio to increase FMR frequency of
ferromagnetic material with reduced magnetic loss
has been investigated in this paper. The direct
applications of ferroelectric and ferromagnetic thin
films in the design of tunable RF passives with
continuous capacitive and inductive tuning
capability are investigated and fully demonstrated
the design efficacy. Finally, a fully flexible
electrically tunable technology with the integration
of ferromagnetic and ferroelectric materials for
engineered substrate and RF components is
scrutinized.
Contributors
ZHANG Ying-cong drafted the manuscript. GE
Jin-qun edited the manuscript and implemented
partial of the research work. WANG Guo-an
developed and managed the research and edited the
manuscript.
Table 1 Thin film enabled tunable RF devices
Category
Ferroelectric
material
Ferromagnetic
material
Integration of
ferroelectric and
ferromagnetic
material
Material
BST
BST
PZT
Py
Py
Py
PZT and
Py
PZT and
Py
Application
MEMS switch [22]
Filter [28]
MEMS switch [30]
Slowwave transmission line
element [33]
Filter [34]
Tunable passives on engineered
substrate [35−37]
Slowwave element with
patterned Py and PZT
edge capacitors [38−39]
Phase shifter with cascaded Py
solenoid inductors and PZT MIM
capacitors [40]
Reported performance
Insertion loss is 0.6 dB, isolation is 25 dB at 20 GHz,
continuous capacitance tunability of 182% with the
applied voltage from 1 to 5 V
Frequency tunable from 30 to 35 GHz with the applied
voltage from 0 to 40 V, insertion loss ranges from 10.0 to
2.7 dB, fractional bandwidths of tuning ratio of
2:1 (9.6% and 4.8%)
Frequency tunable from DC to 500 MHz, insertion loss is
0.4 dB and isolation is 40 dB
Size reduction of 42% with 0.3 dB extra loss at 6 GHz
Tunable inductance from 746 to 687 nH/m with DC current
from 0 to 150 mA. Frequency tunable from 4 to 4.02 GHz
Tunable frequency BPF-Balun from 2.450 to 2.672 GHz [35];
Frequency tunable FSS from 2.21 to 2.15 GHz [36];
Tunable frequency of antenna from 2.38 to 2.43 GHz [37].
2% inductive tunability, 5% capacitive tunability, and 7.1%
dual tunability [38]; Inductance tunable from 12.1 to
11.2 nH/cm, and capacitance tunable from 81.6 to 60.4 pF/m,
and phase shift of 32 °/cm at 2 GHz [39]
9.1% inductive tunability, 17.6% capacitive tunability,
26.9% dual tunability, and phase shift of 210 °/cm at 2 GHz
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Conflict of interest
ZHANG Ying-cong, GE Jin-qun, and WANG
Guo-an declare that they have no conflict of interest.
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(Edited by ZHENG Yu-tong)
利用先进微加工技术和薄膜材料实现电可调射频器件
摘要摘要：：多功能、多频段、高性价比、小型化的可重构射频器件在现代无线通信系统有着广泛应用，在
未来也有极大的需求。本文介绍了基于先进薄膜材料和微加工技术设计制备的多频段、可重构射频器
件。对表面微加工和体微加工技术等制造工艺的射频应用，特别是在射频微机电系统和电可调射频器
件中的应用着重进行了探讨。此外，本文还综述了利用铁电和铁磁薄膜材料集成设计制备的连续可
调、小型化、高性能射频器件，探讨了利用纳米图案结构工艺来增强铁磁薄膜的高频性能(例如：铁磁
共振频率和损耗)的设计方法和策略，并示范了基于此实现的全电学可调的射频器件。
关键词关键词：：可调谐射频器件；体微加工技术；表面微加工技术；薄膜材料
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