SAW Resonator Stack Using Plasma-Modified Silicon to Cut RF Loss
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Solution Overview
Problem
Existing surface acoustic wave (SAW) devices using silicon substrates face high-frequency loss and deterioration of Q performance due to parasitic conducting layers, and the manufacturing processes are costly and complex.
Innovation Solution
A surface acoustic wave device is developed with a modified substrate surface layer formed on a support substrate through plasma surface treatment, which includes a low acoustic velocity layer and a piezoelectric layer, reducing the need for additional trap-rich layers and simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a silicon substrate is used as a high acoustic velocity support substrate, then the acoustic velocity is improved, but high-frequency loss increases and Q performance deteriorates due to parasitic conducting layers
Solution Approach 1:
An amorphous silicon layer is introduced as an intermediary between the silicon substrate and the piezoelectric layer. This intermediate layer acts as a mediator that suppresses carrier generation at the interface, thereby reducing high-frequency loss while maintaining the high acoustic velocity benefit of the silicon substrate.
Solution Approach 2:
The amorphous silicon layer is formed using a simple and cost-effective low-temperature plasma CVD process rather than expensive LPCVD or sputtering equipment. This disposable-like thin layer provides the necessary carrier suppression function at low manufacturing cost.
2Loss of energy
If amorphous silicon or polysilicon is laminated on the silicon substrate to suppress carriers, then high-frequency loss is reduced, but manufacturing cost increases due to expensive LPCVD, PECVD, or sputtering equipment
Solution Approach 1:
The amorphous silicon layer is formed using a simple and cost-effective low-temperature plasma CVD process rather than expensive LPCVD or sputtering equipment. This disposable-like thin layer provides the necessary carrier suppression function at low manufacturing cost.
Solution Approach 2:
The deposition temperature parameter is changed from high-temperature LPCVD to low-temperature plasma CVD. This parameter change enables the formation of amorphous silicon at lower costs using simpler equipment, while still achieving the desired carrier suppression effect.
3Reliability
If ion implantation is used to form a trap-rich layer, then carrier mobility is reduced and resistance is maintained, but productivity decreases and manufacturing cost increases due to high-cost facilities
Solution Approach 1:
The mechanical ion implantation process is replaced with a plasma-based chemical vapor deposition process. This substitution eliminates the need for high-cost ion implantation facilities and improves productivity while achieving similar or better interface resistance characteristics through amorphous silicon formation.
4Loss of energy
If a four-layer laminating structure is used to reduce high-frequency loss, then Q performance is improved, but device complexity and manufacturing process are increased
Solution Approach 1:
The functions of the substrate and the trap-rich layer are merged into a single amorphous silicon layer formed on the silicon substrate. This merging reduces the number of layers from four to three, simplifying the device structure and manufacturing process while maintaining the carrier suppression function.
Solution Approach 2:
The amorphous silicon layer serves multiple functions: it acts as both the substrate surface modification layer and the trap-rich layer that suppresses carriers. This multi-functionality eliminates the need for separate trap-rich layer deposition, reducing device complexity.
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 proposed solution reduces high-frequency loss and maintains Q performance comparable to devices with trap-rich layers, while significantly simplifying the manufacturing process and reducing costs.
Implementation Method 1
a modified substrate surface layer formed on the surface of the support substrate through plasma surface treatment
Implementation Method 2
surface acoustic wave (SAW) resonator
Implementation Method 3
a piezoelectric layer formed on the low acoustic velocity layer
Data Source
AI summary
Provided is a surface acoustic wave device and a method of manufacturing the same. The surface acoustic wave device includes: a semiconductor support substrate; a modified substrate surface layer formed on a surface of the support substrate; a low acoustic velocity layer formed on the modified substrate surface layer; a piezoelectric layer formed on the low acoustic velocity layer; and a plurality of IDT electrodes disposed on the piezoelectric layer, wherein surface roughness of one side of the modified substrate surface layer is 0.2nm or lower.