Elastic Wave Terminal Layout for Lower Capacitance Leakage
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Solution Overview
Problem
Elastic wave devices experience degradation in characteristics due to electrostatic capacitance between the support substrate and piezoelectric film, and are prone to operation faults due to leakage currents when connected to electronic components.
Innovation Solution
The elastic wave device includes a multilayer body with a support substrate made of high acoustic-velocity material, a piezoelectric film, and insulating films to reduce electrostatic capacitance and increase electrical resistance, featuring a configuration with ground terminals directly on the support substrate and signal terminals indirectly connected via insulating films, along with under bump metal layers and bumps to minimize leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If under bump metal layers are disposed on the insulating layer to connect to external sources, then electrical connection is achieved, but electrostatic capacitance is generated between the support substrate and piezoelectric film which degrades device characteristics
Solution Approach 1:
A first insulating film is introduced as an intermediary layer between the support substrate and the piezoelectric film. This insulating film acts as a mediator that reduces the electrostatic capacitance between these two components, thereby preventing degradation of device characteristics while maintaining proper electrical connections through the under bump metal layers.
Solution Approach 2:
The invention changes the electrical parameters of the system by introducing an insulating film with specific dielectric properties. This modifies the capacitance parameter between the support substrate and piezoelectric film, reducing it to acceptable levels. The insulating film's material properties and thickness are optimized to achieve the desired capacitance reduction.
2Reliability
If under bump metal layers are directly connected to wiring on the support substrate, then electrical resistance is reduced, but leakage current flows into connected electronic components causing operation faults
Solution Approach 1:
The electrical connection path is segmented into multiple isolated sections. The first insulating film divides the connection path, creating electrically isolated zones. This segmentation prevents leakage current from propagating along the support substrate to connected electronic components, while maintaining necessary electrical connections through controlled pathways via the under bump metal layers.
Solution Approach 2:
The first insulating film serves as an intermediary barrier that controls current flow. It allows necessary signal transmission while blocking leakage current paths, thus protecting connected electronic components from operation faults caused by substrate leakage.
3Reliability
If the support substrate is charged due to pyroelectric effect, then electric charge is generated, but potential difference creates electrostatic capacitance that degrades fractional bandwidth and Q factor
Solution Approach 1:
The first insulating film acts as a protective intermediary between the piezoelectric film and support substrate. When the piezoelectric film generates electric charge through the pyroelectric effect during heating or cooling, this insulating film prevents direct charge transfer to the support substrate, thereby avoiding potential difference formation and electrostatic capacitance generation that would degrade fractional bandwidth and Q factor.
Solution Approach 2:
The introduction of the insulating film changes the electrical parameter relationships in the device. It modifies the charge distribution and potential difference characteristics, reducing the electrostatic capacitance parameter that negatively affects device performance metrics such as fractional bandwidth and Q factor.
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
This configuration effectively reduces electrostatic capacitance and minimizes the degradation of elastic wave device characteristics, while reducing the likelihood of operation faults in connected electronic components by managing electrical resistance and charge transfer.
Implementation Method 1
When mounting or using an elastic wave device, a piezoelectric film is heated or cooled. At this time, electric charge is generated by the pyroelectric effect.
Implementation Method 2
The high acoustic-velocity material is a material through which bulk waves propagate at a higher acoustic velocity than elastic waves propagating through the piezoelectric film.
Implementation Method 3
The acoustic reflection layer includes a low acoustic-impedance layer having relatively low acoustic impedance and a high acoustic-impedance layer having relatively high acoustic impedance.
Data Source
AI summary
An elastic wave device includes a multilayer body, an antenna terminal, a ground terminal, a signal terminal, an IDT electrode, and an insulating film. The multilayer body includes a support substrate and a piezoelectric film disposed on the support substrate. The antenna terminal is disposed on or above the support substrate. The ground terminal is directly disposed on the support substrate. The signal terminal is disposed above the support substrate. The IDT electrode is disposed on the piezoelectric film. The insulating film is disposed between the support substrate and the signal terminal. The multilayer body includes one of a layer made of a high acoustic-velocity material and an acoustic reflection layer.