This paper reports the development and characterization of a novel switching device for use in microwave systems. The device utilizes a switching mechanism based on nanoionics, in which mobile ions within a solid electrolyte undergo an electrochemical process to form and remove a conductive metallic "bridge" to define the change of state. The nanoionics-based switch has demonstrated an insertion loss of approx.0.5dB, isolation of >30dB, low voltage operation (1V), low power (approx. micro-W) and low energy (approx. nJ) consumption, and excellent linearity up to 6 GHz. The switch requires fewer bias operations (due to non-volatile nature) and has a simple planar geometry allowing for novel device structures and easy integration into microwave power distribution circuits

Kozicki, Michael N.

Lee, Richard Q.

Morse, Jacki

Mueller, Carl H.

Nessel, James A.

Ren, Minghan

NASA Technical Reports Server

 A Novel Nanoionics-based Switch for Microwave Applications 
James A. Nessel1, Richard Q. Lee1, Carl H. Mueller2, Michael N. Kozicki3, Minghan Ren3, and Jacki 
Morse3 
1NASA Glenn Research Center, Cleveland, OH, 44135, USA  
2Analex Corporation, Cleveland, OH, 44135, USA 
3Arizona State University, Tempe, AZ, 85287, USA 
 
Abstract  —  This paper reports the development and 
characterization of  a novel switching device for use in 
microwave systems.  The device utilizes a switching mechanism 
based on nanoionics, in which mobile ions within a solid 
electrolyte undergo an electrochemical process to form and 
remove a conductive metallic “bridge” to define the change of 
state.  The nanoionics-based switch has demonstrated an 
insertion loss of ~0.5dB, isolation of >30dB, low voltage operation 
(1V), low power (~μW) and low energy (~nJ) consumption, and 
excellent linearity up to 6 GHz. The switch requires fewer bias 
operations (due to non-volatile nature) and has a simple planar 
geometry allowing for novel device structures and easy 
integration into microwave power distribution circuits. 
Index Terms — microwave switches, nanotechnology. 
I. INTRODUCTION 
Nanoionics is an emerging field receiving increasing 
interest in the development of novel nanotech devices [1]-[4].  
This technology concerns itself with materials and devices 
that rely on ion transport and chemical change at the 
nanoscale.  The chemical change can take the form of an 
oxidation/reduction reaction of ionic metal species within 
some base material to essentially “grow” metal on the surface 
(or within) a film at low energies.  Exploiting this effect is the 
basis for devices such as resistance-change memory cells [1]-
[2], tunable resonators [3], and microfluidic valves [4].   
In this paper, we report on the first development of a novel 
switching mechanism for microwave applications based on 
nanoionic materials. Because the nanoionics-based switch is 
electrochemical in nature, several unique advantages become 
apparent which gives this technology the potential to 
overcome some of the issues in solid state and radiofrequency 
microelectromechanical (RF MEMS)-based systems.  Firstly, 
the process is non-volatile.  No power is required to maintain 
a particular state (ON or OFF), but only to change states.  As 
a result, fewer bias operations are needed.  The process is also 
low energy, requiring on the order of nJ to operate.  Power 
consumption is thus comparable to MEMS devices.  There are 
no moving parts (as in MEMS devices), eliminating this point 
of failure and enhancing speed.  To activate a nanoionic 
device, only on the order of tenths of a volt is necessary, 
superior to solid state and MEMS-based switches.  Metal ion 
conductivity in these base films is comparable to electron 
conductivity in semiconductors, indicating the switching 
speed has the potential to be competitive with solid state 
switches.  Finally, the fabrication process of nanoionics-based 
switches is trivial in nature, requiring only as little as 5 
processing steps using common semiconductor fabrication 
tools.  Compared to solid state and MEMS devices, which 
may require several sacrificial layers and masks for 
fabrication, this should result in an unparalleled ease of 
integration and reduction in cost.   
II. NANOIONIC DEVICE PHYSICS (OVERVIEW) 
The fundamental operation of the nanoionic switch is rooted 
in the phenomenon of ion conduction in solid electrolytes.  
Synonymous with liquid electrolytes (e.g., lead-acid batteries), 
solid electrolytes consist of mobile ions which undergo 
oxidation/reduction reactions at the anode and cathode of the 
system.  The fundamental difference between solid electrolyte 
and liquid electrolyte behavior is that the mobile ions are of a 
single polarity while the opposite polarity species remain 
fixed.  The fixed ions essentially create a solid matrix in 
which mobile ions can “hop” into neighboring potential wells.  
Based on this short-range hopping mechanism for conduction, 
the ionic conductivity of solid electrolytes can locally 
approach electronic conductivity levels realizable in today’s 
semiconductors [1]. 
Many inorganic and organic materials can conduct ions to 
some extent but it is the compounds of elements in the column 
of the Periodic Table headed by oxygen, the so-called 
chalcogens, that are of most interest in the context of 
electrochemical switching devices, principally because of 
their high ion availability and mobility at normal device 
operating temperatures.  When a metal ion is introduced into 
the chalcogenide base, the ions nucleate on the chalcogen-rich 
regions within the base glass, resulting in a ternary that takes 
the form of a dispersed nanoscale metal ion-rich phase in a 
continuous glassy matrix [5].  This allows the electrolyte to 
have a relatively high resistivity (necessary for a high off 
resistance state), while containing large quantities of highly 
https://ntrs.nasa.gov/search.jsp?R=20080047667 2019-08-30T05:52:03+00:00Z
 2
mobile metal ions (see Fig. 1(a)).  In this application, a base glass of GeSe2 is utilized and saturated with Ag+ ions. 
    
 (a) (b) (c) (d) 
Fig. 1. Device operation for a coplanar series switch. (a) switch is off, (b) small bias forces electrons in cathode to reduce silver ions in 
substrate, (c) process halts when path is formed, and (d) process is reversed with application of reverse bias. 
 
 
For an ion current to flow in an electrolyte, an oxidizable 
electrode is made positive (anode) with respect to an opposing 
electrode (cathode) and sufficient bias is applied, typically on 
the order of a few tenths of a volt or more.  For Ag+-saturated 
GeSe2, silver at the anode is oxidized to form an excess of 
Ag+ ions within the chalcogenide base glass.  The applied 
field causes the ions to flow toward the cathode through the 
coordinated hopping mechanism described above.  At the 
cathode, a reduction reaction occurs with injected electrons to 
re-form silver metal, as shown in Fig. 1(b).  The number of 
atoms electrodeposited by the reduction of ions will 
correspond to the number of electrons that take part in the 
process (supplied by the external circuit).  Each metal ion 
undergoing reduction will be balanced by a metal atom 
becoming oxidized to avoid the formation of an internal 
electric field due to the build up of charge.  The process will 
continue until the programmed voltage/current limits supplied 
by the external power source is met.  If the current limit is 
made sufficiently high (~μA), a conductive silver bridge is 
formed which connects the two electrodes (Fig. 1(c)).  Once 
this conduction path is formed, no further power is required to 
maintain it. To reverse this process, the electrodeposit is made 
positive with respect to the original oxidizable electrode, 
causing the dissolution of the metal bridge (Fig. 1(d)).  During 
the dissolution of the electrodeposit, the balance is maintained 
by deposition of metal back onto the silver electrode.  Once 
the electrodeposit has been completely dissolved, the process 
self-terminates.  Note that for this process to occur, a metal 
ion-rich anode is required to induce appreciable ion current 
flow.  Further, to be reversible, the opposing electrode must 
be made electrochemically inert (not oxidizable).   
III. MICROWAVE SWITCH DESIGN AND OPERATION 
The preliminary design of a microwave series switch 
exploiting this nanoionic behavior consisted of a simple two-
electrode coplanar geometry. A representative circuit layout 
can be seen in the microphotograph of Fig. 2.  Two electrodes 
of dissimilar metals (Ag anode, Ni cathode) are Au-plated to 
1.5 μm thick onto a 500 μm thick quartz substrate (εr = 3.9).  
A gap of 10 μm separates the two electrodes.  Within this gap, 
a thin film (~100 nm) of silver-saturated GeSe2 glass is 
deposited which represents the active area of the device.  
Several iterations provided the framework for an optimal 
geometry based on the nanoionic material characteristics and 
coplanar layout.  The end result consisted of a 50-Ω 
transmission line which tapers to a higher impedance 
(narrowed width) towards the gap.  As will be discussed later, 
it is this tapering effect which helps to reduce capacitive 
coupling in the switch in the OFF state, but remains the 
primary source of loss in the ON state.  A simple photoresist 
passivation layer atop the “active” area was implemented to 
provide protection. 
To operate the device, a voltage of nominally 1V and a 
current limit of 10 mA were used.  Higher voltages induced 
faster growth rates, whereas higher current limits reduced the 
overall resistive loss of the electrochemically grown metal, 
but results in higher power requirements to operate the switch.  
The application of a positive voltage relative to the Ni (inert) 
electrode induces silver growth and enables the device to be 
turned ON.  Reversing polarity of the applied voltage removes 
the electrochemically grown silver and forces the device into 
the OFF state.  Fig. 3 is a microphotograph of the conductive 
metallic pathways that form when the device is ON.  From the 
inset of Fig. 3, an atomic force microscope image shows that 
much of the silver growth occurs on the surface of the thin 
film.  
 
 
Passivation Layer 
Au-plated 
Ag electrode 
Au-plated 
Ni electrode 
Gap in Switch 
 3
Fig. 2. Microphotograph of coplanar nanoionic switch design. 
Fig. 3. Microphotograph (larger image in figure) and associated 
Atomic Force Microscope (AFM) image (smaller inset on right) of 
nanoionics-based switch in the ON state. 
IV. MEASUREMENTS AND RESULTS 
A. Insertion Loss and Isolation 
To measure the microwave performance of the device, test 
samples were individually diced and mounted onto a brass 
mounting fixture.  The circuit was connected to an Agilent 
E8361A Vector Network Analyzer in order to measure ON 
state insertion loss and OFF state isolation.  An Agilent 
E3646A DC Power Supply was utilized to provide the 
necessary voltage/current to change the state of the device 
(nominally 1V/10mA (ON) and -1V/10mA (OFF)).  A plot of 
these results is shown in Fig. 4 for a typical nanoionic switch. 
 
Fig. 4. The insertion loss (S21) of the switch in the ON state is 
better than -0.5 dB over the 1 to 6 GHz range (commercial ISM 
Band), while the isolation in the OFF state is better than -35 dB.   
From the plot, we observe that an ON state insertion loss of 
~0.5 dB is realizable, with an OFF state isolation of better 
than 35 dB over the DC to 6 GHz band.  These measured 
results are comparable to MEMS and solid state-based RF 
switch performance in the same frequency range.  At 
frequencies much greater than this, the series switch design 
tends to perform poorly, maintaining good insertion loss 
characteristics, but reducing isolation (due to capacitive edge 
coupling at the gap).  Further, repeatability of this 
performance over several cycles also requires improvement. 
B. Linearity and Power Handling 
Power measurements were performed using an Anritsu 
ML2437A power meter and Anritsu MG3691B signal 
generator.  A switch was mounted on the same brass mounting 
fixture while various frequencies (500 MHz – 4 GHz) of 
varying power were fed into a switch.  Attenuation pads at the 
input and output to the switch were used to reduce signal 
reflection within the system.  Frequency and power range 
limits were determined by the dynamic range of the signal 
generator and available components. 
From Fig. 5, we observe that devices typically demonstrated 
linearity over the range of measured power from -20 dBm to 
+20 dBm, with device breakdown typically occurring at ~400-
500 mW.  Further, no change is evident in the power transfer 
curve at different frequencies of operation, demonstrating the 
device’s wide bandwidth operation potential. 
 
 
Fig. 5. Power transfer curve of a typical nanoionics-based switch 
over its operating range for frequencies between 500 MHz and 4 
GHz.   
 
D. Speed 
The speed of operation of the nanoionic switch is a function 
of the distance the electrodeposit has to traverse.  That is, the 
wider the gap between electrodes, the longer the response 
time of the switch.  Although the switching speed was not 
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
1 2 3 4 5 6
Frequency (GHz)
S2
1 
(d
B
)
S2
1 
(d
B
)
OFF State Isolation
ON State Insertion Loss
Typical ON/OFF Characteristics of 
Nanoionics-based Switch
S2
1 
(d
B
)
S2
1 
(d
B
)
S2
1 
(d
B
)
S2
1 
(d
B
)
Power In vs Power Out
-25
-15
-5
5
15
25
-20 -10 0 10 20 30
Power In (dBm)
Po
w
er
 O
ut
 (d
Bm
)
500MHz
1GHz
2GHz
4GHz
Power IN vs. Power OUT for a typical 
Nanoionics-based Switch
Po
w
er
 O
ut
 (d
Bm
)
NiAg
NiAg10 µm gap
conductive filaments
 4
directly measured, results inferred from [6] indicate that the 
electrodeposition rate of silver within a chalcogenide glass 
occurs at a velocity of approximately 1 nm/ns.  Therefore, for 
a 10 μm gap, a switching speed of around 10 μs is expected.  
Obviously the smaller the gap size, the faster the switch 
operation, but other considerations such as OFF state isolation 
limit the optimization of speed, at least for a coplanar-type 
structure. 
V. NOVEL MICROWAVE APPLICATIONS 
The potential for novel device structures given this type of 
switch represents an attractive area which warrants further 
development.  One such concept is that of a single-pole-N-
throw switch (SPNT).  Since the active switching element is 
comprised of simply a thin film area, the addition of extra 
electrodes (ports) in contact with the active area makes 
possible the creation of SPNT switches, as shown in the 
diagram of Fig. 6.  By merely applying the necessary voltage 
across the proper electrodes, a conductive pathway can be 
formed/dissolved amongst one of several different paths, 
limited only by available space and maximum coupling level 
requirements.  Further, the ability to deposit vias of this 
nanoionic material allows for the formation of multilayer 
control circuits.  This has the advantage of compacting circuit 
footprints and reducing overall circuit losses, while 
maintaining an unprecedented ease of integration.   
 
 
Fig 6. Drawing of a potential SP5T nanoionic switch, showing 
multiple horizontal, as well as vertical, switching paths. 
 
One such application for this switch is in low loss phased 
array technology.  For conventional discrete phase shifters 
based on a solid state or MEMS approach, approximately 2N 
switches are required for an N-bit phase shifter, with 2-3 
control lines per switch, contributing to the overall loss and 
complexity of the circuit.  Implementing the nanoionic 
topology described above, we believe that it is possible to 
develop an N-bit phase shifter with only 2 nanoionic switches 
and N+2 control lines.  In doing so, line losses (and not switch 
loss) will be the primary contributor to total phase shifter loss.  
Further, circuit complexity will be minimized. 
VI. Conclusion 
A novel microwave switch employing a nanoionics 
approach is discussed.  The development and characterization 
of a coplanar series switch design indicates that, upon further 
optimization, this type of switch has the potential to perform 
comparably with the state-of-the-art solid state and MEMS-
based microwave switches presently in development, with 
several inherent advantages, i.e., it is nonvolatile (fewer bias 
operations required), easily integrable, and makes possible the 
realization of novel device structures (e.g., multilayer circuit 
control, SPNT switches).  However, further improvement of 
device performance (repeatability, losses, frequency range) is 
still necessary to compete with solid state and RF MEMS 
technology, but highly realizable. 
ACKNOWLEDGEMENT 
The authors wish to acknowledge the NASA Glenn 
Research Center Independent Research and Development 
Fund for support of this project. 
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Nanoionic Switch


A Novel Nanoionics-Based Switch for Microwave Applications

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