Tuning the Resonant Frequency of Resonators Using Molecular ...
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: [email protected].
1
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 2
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 NH2functionalized 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.
3
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. 0.004
Absorbance
0.003
0.002
CH2 stretch
0.001
NH2 vibration 0.000
1500
2000
2800
3000
3200
-1
Wavenumber ( cm ) Figure S4. FTIR spectra of NH2-modified AlN film on silicon substrate. 4
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. 0.006
Abs
0.004
Tamra
0.002
0.000
300
400
500
600
700
Wavelength ( nm ) 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 fullautomatic 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)).
5
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.
0.0
70
Before LBL After LBL After Plasma
60
R(%)
50 40 30 20 10 0 0.0
200
250 300 350 WaveLength ( nm )
400
Figure S7. UV-vis reflection spectra of PAA/PVP coated substrate before and after high power oxygen plasma treatment.
6
†
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: [email protected].
1
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 2
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 NH2functionalized 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.
3
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. 0.004
Absorbance
0.003
0.002
CH2 stretch
0.001
NH2 vibration 0.000
1500
2000
2800
3000
3200
-1
Wavenumber ( cm ) Figure S4. FTIR spectra of NH2-modified AlN film on silicon substrate. 4
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. 0.006
Abs
0.004
Tamra
0.002
0.000
300
400
500
600
700
Wavelength ( nm ) 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 fullautomatic 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)).
5
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.
0.0
70
Before LBL After LBL After Plasma
60
R(%)
50 40 30 20 10 0 0.0
200
250 300 350 WaveLength ( nm )
400
Figure S7. UV-vis reflection spectra of PAA/PVP coated substrate before and after high power oxygen plasma treatment.
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