SAW IDT Copper Stack With Intermediate Layers for Self-Heating
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Solution Overview
Problem
Surface acoustic wave (SAW) devices experience mechanical losses and self-heating issues due to copper grain growth, which affects their performance and durability.
Innovation Solution
Incorporating one or more intermediate layers between copper layers in the interdigital transducer (IDT) of SAW devices to inhibit copper grain growth, thereby reducing mechanical losses and self-heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper layers are used in the interdigital transducer (IDT) of SAW devices, then electrical conductivity is improved, but copper grain growth causes mechanical losses and self-heating
Solution Approach 1:
A titanium (Ti) intermediate layer is introduced between the copper (Cu) layers and the piezoelectric substrate. This Ti layer acts as a grain growth barrier that prevents copper grains from growing into the piezoelectric substrate, thereby reducing mechanical losses and self-heating while maintaining the electrical conductivity of the copper layers. The Ti layer serves as a mediator that blocks the harmful grain growth pathway without compromising the functional performance of the IDT.
2Ease of manufacture
If copper grain growth is allowed, then manufacturing simplicity is maintained, but mechanical losses and self-heating increase
Solution Approach 1:
The titanium intermediate layer is integrated into the existing sputtering deposition process without requiring additional complex fabrication steps. The Ti layer is deposited between copper layer deposits during the same manufacturing run, maintaining ease of manufacture while effectively blocking grain growth and reducing self-heating losses.
3Loss of energy
If intermediate layers are added to inhibit grain growth, then mechanical losses are reduced, but device complexity increases
Solution Approach 1:
The titanium intermediate layer is applied selectively only at critical interfaces where grain growth occurs (between Cu layers and at the Cu-piezoelectric substrate interface), rather than throughout the entire device structure. This localized approach reduces mechanical losses while minimizing the increase in overall device complexity.
Solution Approach 2:
The thin Ti intermediate layer (approximately 5 nm) provides effective grain growth blocking with minimal impact on device architecture. The layer's thinness ensures that it does not significantly increase device complexity while still achieving the desired reduction in mechanical losses.
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 use of intermediate layers results in smaller copper grain sizes, leading to reduced mechanical losses and self-heating, improved compression behavior, and enhanced power durability for SAW devices.
Implementation Method 1
one or more intermediate layers formed between copper (Cu) layers of the busbars and fingers of an interdigital transducer (IDT). The one or more intermediate layers may inhibit copper grain growth
Data Source
AI summary
Certain aspects of the present disclosure provide a surface acoustic wave (SAW) device with one or more intermediate layers for reduced self-heating and methods for fabricating such a SAW device. One example SAW device generally includes a piezoelectric layer and an interdigital transducer (IDT) disposed above the piezoelectric layer. The IDT generally includes a first electrode having a first busbar and a first plurality of fingers. The first electrode generally includes a first copper layer disposed above the piezoelectric layer, a first intermediate layer disposed above the first copper layer, the first intermediate layer comprising a different material than the first copper layer, and a second copper layer disposed above the first intermediate layer.