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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.


Analysis and modeling of the FBAR with a polymer support layer architecture.(a) Schematic of the PI-FBAR architecture, (b) Comparison of acoustic impedance of various materials used in FBAR fabrication, (c) Summary of the displacements in the PE layer and Si in the PI-FBAR architecture as a function of PI layer thickness, (d) Displacements in layers of the PI-FBAR architecture with varying PI thickness, clearly showing the wave is confined and diminishes within the PI layer when its thickness is greater than 9 μm, and no acoustic energy is transmitted to the elastic Si substrate. The thicknesses of the ZnO and Si layers are 2.0 and 20 μm, respectively for the modeling. (Note Figure 1d is not based on an exact 2D figure, but rather viewed from a wide angle towards to narrow one. For clearer view, please see the 3D figures in Figure S2b in SI).
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f1: Analysis and modeling of the FBAR with a polymer support layer architecture.(a) Schematic of the PI-FBAR architecture, (b) Comparison of acoustic impedance of various materials used in FBAR fabrication, (c) Summary of the displacements in the PE layer and Si in the PI-FBAR architecture as a function of PI layer thickness, (d) Displacements in layers of the PI-FBAR architecture with varying PI thickness, clearly showing the wave is confined and diminishes within the PI layer when its thickness is greater than 9 μm, and no acoustic energy is transmitted to the elastic Si substrate. The thicknesses of the ZnO and Si layers are 2.0 and 20 μm, respectively for the modeling. (Note Figure 1d is not based on an exact 2D figure, but rather viewed from a wide angle towards to narrow one. For clearer view, please see the 3D figures in Figure S2b in SI).

Mentions: Consider an FBAR consisting of a PE layer sandwiched by two metal electrodes, sitting on a polymer support layer on a substrate as shown in Figure 1a. For simplicity, it is assumed that the bottom electrode has similar properties to those of the PE layer, and it can be considered as part of the PE layer during the analysis as shown in Figure S1a in supplementary information (SI). Under RF signal excitation, standing (plane) waves are generated between the two electrodes. The reflectance, R, and transmittance, T, of the plane waves at an interface with the support layer are given by2324where Zi = ρiVi represents the acoustic impedance, and ρi and Vi are the material density and acoustic velocity of the piezoelectric (i = 1) and support (i = 2) layers. When Z1 = Z2, R = 0 and T = 1, and there is total transmission of the waves into the bottom layer and no wave confinement within the PE layer; when Z1 ≫ Z2, R = 1 and T = 0, and there is total reflection, resulting in perfect confinement of the acoustic wave. For other cases, part of the acoustic wave is transmitted through the interface, and propagates with attenuation into the support and substrate layers. For FBARs, R = 1 would be the ideal case, and this is approached using the Bragg reflector or a membrane-over-air structure as air has zero acoustic impedance. However, equation 1 and 2 indicate that FBARs may be made on substrates with a polymer support layer which has extremely small Z2 compared with Z1. Figure 1b shows the acoustic impedance for materials normally used in fabricating FBAR devices1125262728293031, indicating various polymer materials with Z close to that of air might be used as the support layer to fabricate FBARs directly on substrates without either the removal of the back material or use of the Bragg reflector.


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)

Analysis and modeling of the FBAR with a polymer support layer architecture.(a) Schematic of the PI-FBAR architecture, (b) Comparison of acoustic impedance of various materials used in FBAR fabrication, (c) Summary of the displacements in the PE layer and Si in the PI-FBAR architecture as a function of PI layer thickness, (d) Displacements in layers of the PI-FBAR architecture with varying PI thickness, clearly showing the wave is confined and diminishes within the PI layer when its thickness is greater than 9 μm, and no acoustic energy is transmitted to the elastic Si substrate. The thicknesses of the ZnO and Si layers are 2.0 and 20 μm, respectively for the modeling. (Note Figure 1d is not based on an exact 2D figure, but rather viewed from a wide angle towards to narrow one. For clearer view, please see the 3D figures in Figure S2b in SI).
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Related In: Results  -  Collection

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Show All Figures
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f1: Analysis and modeling of the FBAR with a polymer support layer architecture.(a) Schematic of the PI-FBAR architecture, (b) Comparison of acoustic impedance of various materials used in FBAR fabrication, (c) Summary of the displacements in the PE layer and Si in the PI-FBAR architecture as a function of PI layer thickness, (d) Displacements in layers of the PI-FBAR architecture with varying PI thickness, clearly showing the wave is confined and diminishes within the PI layer when its thickness is greater than 9 μm, and no acoustic energy is transmitted to the elastic Si substrate. The thicknesses of the ZnO and Si layers are 2.0 and 20 μm, respectively for the modeling. (Note Figure 1d is not based on an exact 2D figure, but rather viewed from a wide angle towards to narrow one. For clearer view, please see the 3D figures in Figure S2b in SI).
Mentions: Consider an FBAR consisting of a PE layer sandwiched by two metal electrodes, sitting on a polymer support layer on a substrate as shown in Figure 1a. For simplicity, it is assumed that the bottom electrode has similar properties to those of the PE layer, and it can be considered as part of the PE layer during the analysis as shown in Figure S1a in supplementary information (SI). Under RF signal excitation, standing (plane) waves are generated between the two electrodes. The reflectance, R, and transmittance, T, of the plane waves at an interface with the support layer are given by2324where Zi = ρiVi represents the acoustic impedance, and ρi and Vi are the material density and acoustic velocity of the piezoelectric (i = 1) and support (i = 2) layers. When Z1 = Z2, R = 0 and T = 1, and there is total transmission of the waves into the bottom layer and no wave confinement within the PE layer; when Z1 ≫ Z2, R = 1 and T = 0, and there is total reflection, resulting in perfect confinement of the acoustic wave. For other cases, part of the acoustic wave is transmitted through the interface, and propagates with attenuation into the support and substrate layers. For FBARs, R = 1 would be the ideal case, and this is approached using the Bragg reflector or a membrane-over-air structure as air has zero acoustic impedance. However, equation 1 and 2 indicate that FBARs may be made on substrates with a polymer support layer which has extremely small Z2 compared with Z1. Figure 1b shows the acoustic impedance for materials normally used in fabricating FBAR devices1125262728293031, indicating various polymer materials with Z close to that of air might be used as the support layer to fabricate FBARs directly on substrates without either the removal of the back material or use of the Bragg reflector.

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.