Piezoelectric Resonator Electrode Segmentation for High Q
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Solution Overview
Problem
Conventional piezoelectric resonators face challenges in maintaining high quality factor Q due to increased motional resistance from long interconnect metal traces, which degrades stability and frequency accuracy, especially in temperature-sensitive applications like OCXOs.
Innovation Solution
The design incorporates a piezoelectric layer with inner and outer electrodes, where the inner electrode is connected to a circuit for charge collection, and the outer electrode is either floating or connected to ground, allowing for independent optimization of motional resistance and modal confinement, with gaps between electrodes less than an acoustic wavelength to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If long interconnect metal traces are used to connect the resonator to the base substrate, then the electrical connection is achieved, but the motional resistance increases and quality factor Q decreases
Solution Approach 1:
The resonator structure is segmented into distinct functional regions: an active resonating region, a heater region, a strain relief suspension region, and a via and bond pad region. This segmentation allows the resonator to be physically separated from long interconnect traces, reducing the effective electrical path length and minimizing the impact of trace resistance on the overall quality factor Q.
Solution Approach 2:
A thermal resistive region acts as an intermediary between the heater region and the via and bond pad region. This intermediary structure provides a controlled thermal path while maintaining electrical isolation, allowing the resonator to achieve both thermal management and low-resistance electrical connections without requiring long metal traces that would degrade Q.
2Reliability
If the resonator is enclosed in a sealed can with heater for temperature control, then frequency stability is improved, but device size and complexity increase
Solution Approach 1:
The resonator structure integrates multiple functions into a single compact device: the active resonating region provides frequency generation, the heater region provides temperature control, and the strain relief suspension region provides mechanical support. This multi-functionality eliminates the need for a separate sealed can structure, achieving frequency stability without increasing device complexity.
Solution Approach 2:
The heater region is nested within or adjacent to the active resonating region, allowing the temperature control function to be integrated directly into the resonator structure. This nesting approach enables the resonator to maintain frequency stability through internal temperature control without requiring an external sealed can enclosure.
3Reliability
If the outer electrode is connected to ground or left floating, then modal confinement is optimized, but electrical connection complexity increases
Solution Approach 1:
The outer electrode is designed with different electrical connection options (grounded or floating) depending on the specific application requirements. This local quality approach allows the electrode configuration to be optimized for modal confinement in each specific case without requiring a complex universal connection system. The inner electrode remains connected to the circuit for charge collection, while the outer electrode's connection status can be independently determined.
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 enhances modal confinement and frequency stability over temperature, maintaining high quality factor Q while allowing for independent adjustment of motional resistance, thus improving the performance of piezoelectric resonators in applications requiring precise frequency control.
Implementation Method 1
a piezoelectric resonator operates by resonating in response to a stimulus, which may be a physical event, such as acceleration or force or pressure, or an electrical signal
Implementation Method 2
gaps between electrodes less than an acoustic wavelength to minimize interference
Data Source
AI summary
A resonator includes a piezoelectric layer comprising a piezoelectric material, the piezoelectric layer having a first surface and a second surface; an inner electrode disposed on the first surface of the piezoelectric layer, the inner electrode connected to a circuit; and an outer electrode surrounding the inner electrode on the first surface of the piezoelectric layer, the outer electrode left floating or connected to ground. The inner electrode and the outer electrode are separated by at least one gap smaller than an acoustic wavelength. One single piece electrode or multiple piece electrodes may be disposed on the second surface of the piezoelectric layer. The outer electrodes are configured for optimal modal confinement of an acoustic resonance while the inner electrodes are configured to produce a higher motional resistance than the interconnect resistance for maintaining high Q.