Piezoelectric Resonator Multi-Step Mesa Structure

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Solution Overview

Problem

In multi-step mesa-type thickness-shear-mode piezoelectric resonator elements with a small X-side ratio, the thickness-shear vibration mode couples with spurious modes like contour vibration modes, leading to increased Crystal Impedance (CI) values, which affects performance.

Innovation Solution

A piezoelectric resonator element with a multi-step mesa structure is designed, featuring a rectangular excitation portion with sides parallel to the X-axis as long sides and Z′-axis as short sides, where the side surfaces parallel to the X-axis are in one plane, and those parallel to the Z′-axis have steps, optimizing the dimensions to suppress coupling between thickness-shear and spurious modes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a resonator has a small side ratio to achieve miniaturization, then the size is reduced, but the thickness-shear mode couples with contour vibration modes leading to increased Crystal Impedance

Engineering Contradiction:

Improveresonator sizeVSAvoidCrystal Impedance

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The resonator structure is segmented into a mesa portion and a peripheral portion with different thicknesses. The peripheral portion has a smaller thickness than the mesa portion, creating a stepped configuration that traps vibration energy within the mesa region and reduces coupling with contour modes at the boundaries.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the resonator are given different local properties: the mesa portion maintains a larger thickness for effective vibration, while the peripheral portion has a reduced thickness to minimize its influence on the primary vibration mode and reduce spurious mode coupling.

Inventive Principle:

Principle #3Local quality

2Reliability

If the lateral walls of the boundary portion are configured as sloped or curved surfaces to prevent short-circuiting, then electrode short-circuiting is prevented, but the manufacturing complexity increases

Engineering Contradiction:

Improveelectrode connectionVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The boundary structure is segmented into discrete steps rather than continuous slopes or curves. This stepped configuration prevents electrode short-circuiting through clear separation while being manufacturable using standard photolithography and etching processes.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The mechanical shaping of sloped or curved lateral walls is replaced with a photolithography-based stepped structure. This substitutes complex mechanical machining with simpler planar fabrication processes, reducing manufacturing complexity while achieving the same electrical isolation function.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 decreases the CI value, enabling miniaturization while maintaining strong energy trapping and reducing coupling with spurious modes, thereby improving the resonator's performance.

Implementation Method 1

AT-cut piezoelectric resonator elements use a thickness-shear vibration mode which is ideal for obtaining excellent temperature properties as their primary vibration mode

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

JP-A-58-47316 discloses a piezoelectric resonator that vibrates in a so-called mesa-type thickness-shear vibration mode where an energy-trapping effect equivalent to a bevel or convex structure is obtained

Methodology Applied

Scientific EffectEnergy trapping effect:

Implementation Method 3

a resonator having a small side ratio is likely to be affected by a mode (contour vibration mode) associated with the contour of the resonator, and a thickness-shear mode is suppressed by being coupled to the contour vibration mode

Methodology Applied

Scientific EffectVibration mode coupling suppression:

Data Source

PatentUS9231184B2Piezoelectric resonator element and piezoelectric resonator

Publication Date: 2016.01.05 SEIKO EPSON CORP

AI summary

A piezoelectric resonator element includes a piezoelectric substrate formed of an AT-cut quartz crystal substrate in which the thickness direction thereof is a direction parallel to the Y′ axis; and excitation electrodes disposed so as to face vibrating regions on both front and rear principal surfaces of the piezoelectric substrate. The piezoelectric substrate includes a rectangular excitation portion in which sides parallel to the X axis are long sides thereof, and sides parallel to the Z′ axis are short sides thereof; and a peripheral portion having a smaller thickness than the excitation portion and formed around the excitation portion. Each of side surfaces of the excitation portion extending in a direction parallel to the X axis is present in one plane, and each of side surfaces of the excitation portion extending in a direction parallel to the Z′ axis has a step.