BAW Resonator Electrode Structure for Energy Confinement and Low Resistance
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Solution Overview
Problem
BAW resonators using heavy metals for electrodes face high resistance and ohmic loss, especially at high frequencies, leading to deteriorated filter characteristics.
Innovation Solution
A BAW resonator design with a support base, acoustic mirror layer, intermediate layer, and electrodes structured to provide acoustic impedance variations, using materials with lower impedance for the electrodes and higher impedance for the intermediate layer to confine energy while reducing wire resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a heavy metal with high acoustic impedance (such as Mo) is used for the first electrode to confine energy within the BAW resonator, then the energy confinement effect is improved, but the wire resistance becomes high
Solution Approach 1:
The first electrode is divided into multiple layers: a lower electrode layer with high acoustic impedance (Mo, W, or Pt) for energy confinement, and an upper electrode layer with low acoustic impedance (Al or Al alloy) for low resistance. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between energy confinement and wire resistance.
Solution Approach 2:
Different regions of the first electrode are assigned different material properties: the lower layer near the acoustic mirror uses high acoustic impedance material for reflection, while the upper layer contacting the piezoelectric layer uses low resistance material for electrical conduction. This local differentiation of material quality optimizes both energy confinement and electrical performance.
2Speed
If the first electrode thickness is reduced to accommodate higher resonant frequencies, then the resonant frequency performance is improved, but ohmic loss increases resulting in deterioration of filter characteristics
Solution Approach 1:
The first electrode is segmented into two functional layers that together provide the necessary electrical performance at reduced thickness. The lower layer provides acoustic impedance matching while the upper layer provides low resistance, allowing the total electrode thickness to be optimized for high frequency operation without excessive ohmic loss.
Solution Approach 2:
The first electrode uses a composite structure combining dissimilar materials with complementary properties: high acoustic impedance materials (Mo, W, Pt) for acoustic performance and low resistance materials (Al, Al alloy) for electrical performance. This composite approach enables simultaneous optimization of frequency response and loss characteristics.
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 design effectively confines energy within the resonator, reducing wire resistance and maintaining efficient filter characteristics.
Implementation Method 1
A bulk acoustic wave (BAW) resonator includes a piezoelectric layer formed of a piezoelectric material between two electrode layers. The BAW resonator is used, for example, as an electronic part, such as a BAW filter or the like, in an electronic device utilizing an piezoelectric effect of the piezoelectric layer.
Implementation Method 2
an acoustic mirror layer including one pair of a high acoustic impedance layer and a low acoustic impedance layer, or two or more pairs of high acoustic impedance layers and low acoustic impedance layers, in which the high acoustic impedance layers and the low acoustic impedance layers are alternately stacked
Data Source
Figure 1
AI summary
A BAW resonator that exhibits an effect of confining energy within the BAW resonator, while reducing wire resistance, is provided. The BAW resonator (1) of the present invention includes a support base (10), an acoustic mirror layer (20) in which one pair of a high acoustic impedance layer (21) and a low acoustic impedance layer (22) or two or more pairs in which high acoustic impedance layers (21) and low acoustic impedance layer (22) are alternately stacked, a first electrode (40), a piezoelectric layer (50) having a wurtzite crystal structure, and a second electrode (60) stacked in this order, wherein an intermediate layer (30) formed of an insulator is provided between the acoustic mirror layer (20) and the first electrode (40), the intermediate layer (30) has an acoustic impedance that is higher than an acoustic impedance of each low acoustic impedance layer (21), and the first electrode (40) has an acoustic impedance that is lower than an acoustic impedance of each high acoustic impedance layer (21).