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Film bulk acoustic resonators integrated on arbitrary substrates using a polymer support layer.

Chen G, Zhao X, Wang X, Jin H, Li S, Dong S, Flewitt AJ, Milne WI, Luo JK - Sci Rep (2015)

Bottom Line: Results show when the polymer thickness is greater than a critical value, d, the FBARs have similar performance to devices using alternative architectures.The polymer support makes the resonators insensitive to the underlying substrate.Yields over 95% have been achieved on roughened silicon, copper and glass.

View Article: PubMed Central - PubMed

Affiliation: Department of Information Science and Electronic Engineering, Zhejiang University and Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027, China.

ABSTRACT
The film bulk acoustic resonator (FBAR) is a widely-used MEMS device which can be used as a filter, or as a gravimetric sensor for biochemical or physical sensing. Current device architectures require the use of an acoustic mirror or a freestanding membrane and are fabricated as discrete components. A new architecture is demonstrated which permits fabrication and integration of FBARs on arbitrary substrates. Wave confinement is achieved by fabricating the resonator on a polyimide support layer. Results show when the polymer thickness is greater than a critical value, d, the FBARs have similar performance to devices using alternative architectures. For ZnO FBARs operating at 1.3-2.2 GHz, d is ~9 μm, and the devices have a Q-factor of 470, comparable to 493 for the membrane architecture devices. The polymer support makes the resonators insensitive to the underlying substrate. Yields over 95% have been achieved on roughened silicon, copper and glass.

No MeSH data available.


Related in: MedlinePlus

Comparison of the PI-FBAR and back-trench FBAR.(a) and (b) Schematics of the proposed PI-FBAR with a PI support layer and the back-trench FBAR; (c) & (d) Microscopy images of the fabricated PI-FBAR and back-trench FBAR; (e) & (f) Comparison of reflection (S11) and transmission spectra (S12) for the PI-FBAR (red lines) and trench FBAR (blue lines), showing they have similar performance with high signal amplitude and quality factor. (g) & (h) Reflection and transmission spectra of the fabricated PI-FBARs with the PI thickness as a variable. The amplitude of the resonance improves with increase in the PI thickness. (i) Comparison of the reflection spectra of the PI-FBARs obtained through FEA modeling and experimentally, showing a good agreement for the resonant frequency between them. (j) The Q-value of the resonators as a function of PI thickness. The Q-value increases initially with the increase in PI thickness, and then saturates when the PI thickness is greater than 9 μm.
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f2: Comparison of the PI-FBAR and back-trench FBAR.(a) and (b) Schematics of the proposed PI-FBAR with a PI support layer and the back-trench FBAR; (c) & (d) Microscopy images of the fabricated PI-FBAR and back-trench FBAR; (e) & (f) Comparison of reflection (S11) and transmission spectra (S12) for the PI-FBAR (red lines) and trench FBAR (blue lines), showing they have similar performance with high signal amplitude and quality factor. (g) & (h) Reflection and transmission spectra of the fabricated PI-FBARs with the PI thickness as a variable. The amplitude of the resonance improves with increase in the PI thickness. (i) Comparison of the reflection spectra of the PI-FBARs obtained through FEA modeling and experimentally, showing a good agreement for the resonant frequency between them. (j) The Q-value of the resonators as a function of PI thickness. The Q-value increases initially with the increase in PI thickness, and then saturates when the PI thickness is greater than 9 μm.

Mentions: FBARs with a PI support layer with varying thickness were fabricated to verify the model (hereafter we designate this type of device as the PI-FBAR). For comparison, back-trench etched FBARs were also fabricated at the same time with a 2 μm thickness thermal-grown SiO2 membrane. Figures 2a and 2b are 2D schematics of the PI-FBAR architecture and the back-trench FBAR on a Si substrate (3D schematics are shown in Figures S1b and S1c). All the devices have an active area of 100 × 200 μm. The substrate could be any solid material such as a copper plate, glass, metal foils or paper as shown later. A brief description of the process for the PI layer formation is as follows. A PI layer was formed on a Si substrate by spin-coating with the thickness varied from 2 to 20 μm. The PI layer was solidified by baking it at 240°C for 3 hr. The PI-FBARs were then fabricated by a three-mask process, which is the same as that used for the fabrication of the back-trench FBARs, but without the back-trench etching process stage – namely the bottom electrode formation, via formation and top electrode formation (details described in the Methods Section). Crystal structure characterization shows that the ZnO film is polycrystalline with highly-oriented columnar grains perpendicular to the substrate of (0002) crystal orientation, large grain size of 50 ~ 60 nm and small full-width at half-maximum (FWHM) of the X-ray diffraction (XRD) peak of 0.151°; this is comparable to other results obtained from ZnO thin films deposited on rigid substrates353637, demonstrating the crystalline quality of the ZnO is not compromised by being deposited on the PI layer. The details of the characterization results can be found in the SI (Figure S4).


Film bulk acoustic resonators integrated on arbitrary substrates using a polymer support layer.

Chen G, Zhao X, Wang X, Jin H, Li S, Dong S, Flewitt AJ, Milne WI, Luo JK - Sci Rep (2015)

Comparison of the PI-FBAR and back-trench FBAR.(a) and (b) Schematics of the proposed PI-FBAR with a PI support layer and the back-trench FBAR; (c) & (d) Microscopy images of the fabricated PI-FBAR and back-trench FBAR; (e) & (f) Comparison of reflection (S11) and transmission spectra (S12) for the PI-FBAR (red lines) and trench FBAR (blue lines), showing they have similar performance with high signal amplitude and quality factor. (g) & (h) Reflection and transmission spectra of the fabricated PI-FBARs with the PI thickness as a variable. The amplitude of the resonance improves with increase in the PI thickness. (i) Comparison of the reflection spectra of the PI-FBARs obtained through FEA modeling and experimentally, showing a good agreement for the resonant frequency between them. (j) The Q-value of the resonators as a function of PI thickness. The Q-value increases initially with the increase in PI thickness, and then saturates when the PI thickness is greater than 9 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4379503&req=5

f2: Comparison of the PI-FBAR and back-trench FBAR.(a) and (b) Schematics of the proposed PI-FBAR with a PI support layer and the back-trench FBAR; (c) & (d) Microscopy images of the fabricated PI-FBAR and back-trench FBAR; (e) & (f) Comparison of reflection (S11) and transmission spectra (S12) for the PI-FBAR (red lines) and trench FBAR (blue lines), showing they have similar performance with high signal amplitude and quality factor. (g) & (h) Reflection and transmission spectra of the fabricated PI-FBARs with the PI thickness as a variable. The amplitude of the resonance improves with increase in the PI thickness. (i) Comparison of the reflection spectra of the PI-FBARs obtained through FEA modeling and experimentally, showing a good agreement for the resonant frequency between them. (j) The Q-value of the resonators as a function of PI thickness. The Q-value increases initially with the increase in PI thickness, and then saturates when the PI thickness is greater than 9 μm.
Mentions: FBARs with a PI support layer with varying thickness were fabricated to verify the model (hereafter we designate this type of device as the PI-FBAR). For comparison, back-trench etched FBARs were also fabricated at the same time with a 2 μm thickness thermal-grown SiO2 membrane. Figures 2a and 2b are 2D schematics of the PI-FBAR architecture and the back-trench FBAR on a Si substrate (3D schematics are shown in Figures S1b and S1c). All the devices have an active area of 100 × 200 μm. The substrate could be any solid material such as a copper plate, glass, metal foils or paper as shown later. A brief description of the process for the PI layer formation is as follows. A PI layer was formed on a Si substrate by spin-coating with the thickness varied from 2 to 20 μm. The PI layer was solidified by baking it at 240°C for 3 hr. The PI-FBARs were then fabricated by a three-mask process, which is the same as that used for the fabrication of the back-trench FBARs, but without the back-trench etching process stage – namely the bottom electrode formation, via formation and top electrode formation (details described in the Methods Section). Crystal structure characterization shows that the ZnO film is polycrystalline with highly-oriented columnar grains perpendicular to the substrate of (0002) crystal orientation, large grain size of 50 ~ 60 nm and small full-width at half-maximum (FWHM) of the X-ray diffraction (XRD) peak of 0.151°; this is comparable to other results obtained from ZnO thin films deposited on rigid substrates353637, demonstrating the crystalline quality of the ZnO is not compromised by being deposited on the PI layer. The details of the characterization results can be found in the SI (Figure S4).

Bottom Line: Results show when the polymer thickness is greater than a critical value, d, the FBARs have similar performance to devices using alternative architectures.The polymer support makes the resonators insensitive to the underlying substrate.Yields over 95% have been achieved on roughened silicon, copper and glass.

View Article: PubMed Central - PubMed

Affiliation: Department of Information Science and Electronic Engineering, Zhejiang University and Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310027, China.

ABSTRACT
The film bulk acoustic resonator (FBAR) is a widely-used MEMS device which can be used as a filter, or as a gravimetric sensor for biochemical or physical sensing. Current device architectures require the use of an acoustic mirror or a freestanding membrane and are fabricated as discrete components. A new architecture is demonstrated which permits fabrication and integration of FBARs on arbitrary substrates. Wave confinement is achieved by fabricating the resonator on a polyimide support layer. Results show when the polymer thickness is greater than a critical value, d, the FBARs have similar performance to devices using alternative architectures. For ZnO FBARs operating at 1.3-2.2 GHz, d is ~9 μm, and the devices have a Q-factor of 470, comparable to 493 for the membrane architecture devices. The polymer support makes the resonators insensitive to the underlying substrate. Yields over 95% have been achieved on roughened silicon, copper and glass.

No MeSH data available.


Related in: MedlinePlus