FBAR Biosensor with Insulating Layer for Mass Sensitivity
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Solution Overview
Problem
Existing devices for detecting substances in fluids have limited mass sensitivity due to inadequate design and materials, which affects the accuracy and reliability of resonance frequency measurements.
Innovation Solution
A device with a piezoacoustic thin-film resonator integrated with a CMOS readout circuit, an electrical insulation layer of silicon dioxide, and aluminum electrode layers, optimized for shear thickness oscillations and high resonance frequencies (500 MHz to 10 GHz), enhancing mass sensitivity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thin-film resonator is applied directly to a silicon substrate, then structural support is provided, but acoustic coupling occurs between the substrate and resonator reducing mass sensitivity
Solution Approach 1:
An acoustic mirror consisting of multiple layers with alternating acoustic impedances is introduced between the silicon substrate and the thin-film resonator. This intermediary structure reflects acoustic waves back into the resonator, preventing energy loss into the substrate and thereby increasing mass sensitivity without compromising structural support.
2Reliability
If electrode layers are made thicker to reduce resistance noise, then electrical stability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The electrode layers are constructed as composite structures combining materials with different properties. This allows optimization of both electrical conductivity and mechanical characteristics while maintaining manageable layer thicknesses, thereby achieving electrical stability without excessive complexity in the layer structure.
3Adaptability or versatility
If the resonator is exposed to the environment for substance detection, then detection functionality is enabled, but the resonator is contaminated and mass sensitivity is reduced
Solution Approach 1:
A thin, selective protective coating is applied to the resonator surface. This film acts as a barrier against environmental contamination while allowing the resonator to maintain its mass sensitivity for detecting target substances. The coating provides environmental protection without significantly adding to the resonator's mass.
4Measurement precision
If resonance frequency is increased to 500 MHz to 10 GHz for higher mass sensitivity, then detection precision improves, but manufacturing precision requirements increase
Solution Approach 1:
The resonator design parameters including layer thicknesses, material compositions, and geometric dimensions are optimized to achieve resonance frequencies in the 500 MHz to 10 GHz range. By carefully selecting and adjusting these parameters, high mass sensitivity is achieved while keeping manufacturing precision requirements within feasible limits through systematic parameter optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves significantly higher mass sensitivity and stability, allowing for precise detection of biomolecules and gases, with reduced resistance noise and acoustic losses, and improved compatibility with CMOS circuits.
Implementation Method 1
a piezoelectric thin-film resonator with at least one piezoelectric layer... an alternating excitation field can be coupled into the piezoelectric layer by electrical control of the electrode layers
Implementation Method 2
the thin-film resonator due to an alternating excitation field coupled into the piezoelectric layer to a resonance oscillation with a resonance frequency fR
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a device for detecting at least one substance of a fluid, comprising a piezoacoustic thin film resonator having at least one piezoelectric layer, an electrode layer arranged on the piezoelectric layer, at least one further electrode layer arranged on the piezoelectric layer, and at least one adsorption surface for adsorbing the substance of the fluid, wherein the piezoelectric layer, the electrode layers, and the adsorption surface are designed and arranged on each other in such a way that by electrically activating the electrode layers, an excitation alternating field can be coupled into the piezoelectric layer, the thin film resonator can be excited to a resonance oscillation at a resonance frequency fR because of an excitation alternating field coupled into the piezoelectric layer, and the resonance frequency fR depends on an amount of the substance adsorbed on the adsorption surface. The device is characterized in that at least one electrical insulating layer for electrically insulating the electrode layer is arranged directly on a side of at least one of the electrode layers facing away from the piezoelectric layer. Particularly advantageous is the combination of an electrode layer made of aluminum and an insulating layer made of silicon dioxide. A relatively high mass sensitivity thus results. The device is used particularly as a biosensor for detecting and analyzing biomolecules.