Etch-A-Sketch Resonator

ETCH-A-SKETCH
RESONATOR
Renyuan Wang1, Sunil A. Bhave1 and Kushal Bhattacharjee2
1Cornell
University, 2RFMD
Reconfigurable RF Front-End
Figure from DARPA RF-FPGA BAA
Reconfigurable RF Front-End
Control Signal
…
…
Can we actually “program” the physical response of the
device itself? Instead of choosing from an array of devices
with different responses?
Electrode Shaping
Shaped electrodes to target specific mode of oscillation
Beam Resonator
Contour Mode Resonators
f0
3f0
5f0
[Elwenspoek et al, MEMS 1992]
Piezoelectric Domain Engineered Lithium Niobate for
Reconfigurable RF MEMS Resonators
What if we “shape” the resonator
material, instead of electrode?
Thorlabs PPLN
PPLN is commonly used for
optical frequency doubling.
Poling Mechanism of Lithium Niobate
E-field
• Crystal Orientation determined by the positive ion positions
relative to the oxygen ions
• The metal ions have two stable positions, a strong electric field
can “kick” them into either location
• Coercive field for white LN is ~21kV/mm, for 1um thin film, the
required voltage is 21V
• Using sharp AFM tip can even lower the required voltage
1 Micron Pitch on LN Thin-Film
AFM Tip
Note the dirt attracted by the sample.
AFM Tip Based Domain “Shaping”
Z cut LiNbO3
• Poling is well studied
• Easy to pole with commercially
available AFM systems
AFM Tip
+
G+
G+
y z x
IDT period=4.5um
AFM Tip Based Domain “Shaping”
Coupling through
d21 coefficient
+
G+
G+
Direction of
Displacement
y
z
x
G
Top view of two stripes
on the resonator
x
y
+y
G
x
Simulated Mode Shape
5um
S
G
S
G
Deformation
Device Fabrication
Gold
1um LN Device Layer
1um LN Device Layer
Si Carrier Wafer
Si Carrier Wafer
(a)
(b)
Ion Mill
Photoresist
Resonator
1um LN Device Layer
Si Carrier Wafer
Si Carrier Wafer
(c)
(d)
Poling – Released LN Thin Film
80V Poling Voltage
Width (x-direction) = 72um
y
x
In Phase
Out of Phase
20um
10um
IDT Finger
4um Domain
+GPeriod
+G
+
+G
+G
+
y
Mode Vibrate in
the y-direction
z
x
y
Mode Vibrate in
the x-direction
z
x
Poling – Released LN Thin Film
+G
+G
+G
+
y
z
Mode Vibrate in
x
the y-direction
IDT period=4.5um
+G
+
z
Mode Vibrate in y x
the x-direction Domain Period
4um
592MHz
Before
Poling
592MHz
After
Poling
681MHz
Conclusion
 We demonstrated a reconfigurable RF MEMS
resonator based on piezoelectric domain engineering
 Just like Etch-A-Sketch, we were able to “write” and
“erase” the resonator frequency post-processing
 The technology can also enable post-processing
trimming for LN thin-film devices