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Tuning the Resonant Frequency of Resonators

Using Molecular Surface Self-assembly Approach

Wenpeng Liu†, Jingwei Wang

†, Yifei Yu

†, Ye Chang

†, Ning Tang

†, Hemi Qu

†, Yanyan Wang

†,

Wei Pang†, Hao Zhang

†, Daihua Zhang

†, Huaping Xu

§, and Xuexin Duan*

†

† State Key Laboratory of Precision Measuring Technology & Instruments, College of

Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072,

China

§Key Lab of Organic Optoelectronics & Molecular Engineering, Department of Chemistry,

Tsinghua University, Beijing 100084, China

*E-mail: xduan@tju.edu.cn.

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Supporting movie legends

Movie S1. A home-made full-automatic dipping robot for molecular LbL self-assembly.

1. FBAR FABRICATION

Figure S1 shows the FBAR fabrication process. A swimming pool (SP) was generated on

the silicon substrate. Then, the SP was filled with silicon dioxide as sacrificial layer by CVD

and followed by chemical mechanical polish (CMP). Next, the BE (Mo) was deposited on the

surface of sacrificial layer, followed by PZ layer (AlN) deposition. The TE (Mo) and PS layer

(AlN) were deposited successively to form the FBAR structure. Then, the gold pads was

formed by physical vapor deposition (PVD) and lift-off process to realize electrical

connection. Finally, the sacrificial layer was released by hydrofluoric acid to form a cavity

under the FBAR structure. FBAR utilizes piezoelectric effect of PZ layer to convert an

electric input signal into a mechanical resonance first, and then, the mechanical resonance is

transformed into electric output signal, while only the resonant frequency signal-where the

thickness of piezoelectric layer is near the integer times of signal half-wavelength in the

piezoelectric material-could pass through this sandwich structure, and the other waveband

attenuates when propagating in the piezoelectric layer, resulting in a resonant effect.

Figure S1. FBAR fabrication process.

Due to the variations in the semiconductor fabrication processes, however, FBARs are

prone to deviate from the desired working frequency. For example, Figure S2 shows a

distribution diagram of FBAR filters’ working frequency from a 4-inch wafer level after the

whole semiconductor fabrication process. The annular distribution contributes mainly to the

un-uniform deposition of piezoelectric layer. Range more than 30 MHz decreases the calling

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quality in wireless communication field, and leads to the technique of ‘frequency tuning’. So

we demonstrate a new method to tune the resonant frequency of micro-fabricated resonators

using a molecular layer-by-layer (LbL) self-assembly approach.

Figure S2. Distribution of working frequency diagram of FBAR filters from a 4-inch

wafer level after fabrication.

2. CONTACT ANGLE MEASUREMENT

To verify the quality of silanization and the following LbL assembly on AlN film, the

water contact angles on AlN-Si substrate after each chemical treatment step were recorded.

Figure S3 showed the images in the contact angle measurement on AlN-Si substrate. The

original value was 79° as shown in Figure S3(a). After air plasma treatment for 5 min, the

water drops below 5 °(See Figure S3(b)) while the contact angle increased up to 61°(See

Figure S3(c)) after silanization. This phenomenon was in accordance with the same

silanization procedure on quartz substrate. Then PAA and PVP were deposited onto the NH2-

functionalized AlN-Si substrate. Figure S3(d) and Figure S3(e) showed the contact angle

measurement images after the first PAA and PVP bilayer assembly successively.

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Figure S3. Contact angle images in the silanization and the first bilayer assembly process on

AlN-Si substrate.

3. SPECTRA ANALYSES OF AMINO SILANIZATION ON ALN FILM

FTIR spectra was used to charaterize the amino functionalization on AlN surface. It was

obtained by Bruker Vertex 70v IR spectrometer equipped with a attenuated total reflection

(ATR) accessory. A liquid nitrogen cooled mercury-cadmium-telluride (MCT) detector was

used to record the FTIR spectra at permanent vacuum condition. With the above

characteristics, the monolayers of silanization on semicondutor substrates could be analyzed

with high sensitivity. Figure S4 showed the FTIR spectra of APTES modified AlN film on

silicon substrate. The NH2 vibration is found at 1570 cm-1, the peaks at 2860 and 2930 cm

-1

are relating to the CH2 stretch, which confirms the presence of the APTES molecules after

amino silanization.

1500 2000 2800 3000 3200

0.000

0.001

0.002

0.003

0.004

CH2 stretch

Absorbance

Wavenumber ( cm-1 )

NH2 vibration

Figure S4. FTIR spectra of NH2-modified AlN film on silicon substrate.

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Beisdes ATR-FTIR, 5(6)-Carboxytetramethylrhodamine N-succinimidyl ester (TAMRA

dye) (Sigma) was used to further prove the amino silanization on AlN film.TAMRA served as

an amine coupling reagent to form 5(6)-carboxytetramethylrhodamine derivatized compounds

with primary amine. A quatz slide with 300 nm AlN film on both sides was amino silanized

by APTES, followed by incubation at 0.1mg/ml TAMRA for 20 min. Figure S5 showed the

UV-vis spectra of the treated quartz slide. The absorption band at 554 nm was assigned to the

presence of TAMRA dye which again demonstrated the prsesnce of the NH2 group at the AlN

surface.

300 400 500 600 700

0.000

0.002

0.004

0.006

Abs

Wavelength ( nm )

Tamra

Figure S5. UV-vis spectra of NH2-modified AlN film after incubation in TAMRA solution

for 20 min. The AlN film was deposited on the surface of a quatz slide.

4. HOME-MADE FULL-AUTOMATIC DIPPING ROBOT AND SPINNING SYSTEM

In order to maintain the uniformity of the deposited polymer layers, a home-made full-

automatic dipping robot was invented for multiple polymer layers depositions (> 5 layers)

(See Figure S6(a)). Two motors were used to control the horizontal and vertical movements.

A mechanical arm holding the samples was fixed to one motor. Four beakers containing

solutions were placed around the dipping robot. Labview and an online camera were used to

remote control the PAA/PVP assembly process by computer programming and data

acquisition (DAQ) output. The dipping robot worked in a sealed environment at low

temperature to reduce the volatilization of solutions.

For spinning system, a mini spin coater was introduced to realize the spinning process.

The samples were fixed on the spin coater tightly and the solutions were pumped onto the

surface of the samples by a programming syringe pump (See Figure S6(b)).

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Figure S6. Home-made full-automatic dipping robot (a) and spinning system (b).

5. REMOVAL OF PAA/PVP FILMS FROM ALN-SI SUBSTRATE

Oxygen plasma with high power was used to remove the PAA/PVP film. Here, five

PAA/PVP bilayers were deposited onto the AlN-Si substrate through spinning method. The

concentration of solutions was 0.1mg/ml. Figure S7 showed the UV-vis reflection spectra at

each step. After the PAA/PVP deposition, the curve shifted right (from the black curve to the

red), indicating a successful assembly result. After oxygen plasma treatment for 20 min

(600W), the curve almost returned to the original (the blue curve), meaning a total remove of

the polymer films. So the resonator with polymer films could be regenerated by oxygen

plasma which was attractive from the economical point of view.

200 250 300 350 400

0

10

20

30

40

50

60

70

R ( % )

WaveLength ( nm )

Before LBL

After LBL

After Plasma

0.0

0.0

Figure S7. UV-vis reflection spectra of PAA/PVP coated substrate before and after high

power oxygen plasma treatment.