TPoS Resonator Crystal Orientation for Low TCF
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Solution Overview
Problem
Conventional quartz oscillators have large size and are not suitable for high integration with electronic circuitry, leading to high temperature coefficient of frequency (TCF) issues and increased power consumption in silicon-based resonators, which require complex compensation techniques that can reduce quality factor (Q) and increase insertion loss.
Innovation Solution
A thin-film piezoelectric-on-silicon (TPoS) resonator with a monocrystalline silicon resonator body having [100] and [110] crystallographic orientations offset relative to the nodal line, doped to a high concentration, and featuring lower and upper metal electrodes with an aluminum nitride layer, which reduces TCF and enhances Q by concentrating acoustic energy near the center, supporting both capacitive and piezoelectric transduction modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional quartz oscillators are used, then frequency stability is achieved, but device size becomes large and integration with electronic circuitry is difficult
Solution Approach 1:
The patent uses silicon as a substitute material that copies the functional properties of quartz for piezoelectric resonance, while being compatible with standard silicon fabrication processes. This allows achieving quartz-like frequency stability with the manufacturing advantages of silicon, enabling miniaturization and integration.
Solution Approach 2:
The patent replaces the mechanical cutting and mounting processes required for quartz crystals with semiconductor fabrication techniques. Silicon resonators can be fabricated using standard CMOS-compatible processes, eliminating the need for delicate mechanical assembly and enabling direct integration with electronic circuitry.
2Ease of manufacture
If silicon-based resonators are used for integration, then device size is reduced and integration is improved, but temperature coefficient of frequency increases requiring complex compensation
Solution Approach 1:
The patent modifies the crystallographic orientation parameter of the silicon resonator body, using specific orientations such as <110> or <100> that inherently provide lower temperature coefficients of frequency. This parameter change allows achieving both good integration capability and reduced TCF without requiring complex compensation circuits.
3Reliability
If temperature compensation techniques are applied to reduce TCF, then frequency stability is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent converts the naturally higher TCF of silicon into a benefit by using it to achieve a desired operating frequency point, then using the specific crystallographic orientation to minimize TCF variations around that point. This approach eliminates the need for active compensation circuits, reducing both complexity and power consumption while maintaining frequency stability.
4Reliability
If fabrication techniques are used to reduce TCF, then temperature stability is improved, but resonator quality factor decreases and insertion loss increases
Solution Approach 1:
The patent changes the crystallographic orientation parameter of the silicon resonator to orientations that naturally exhibit lower TCF and higher quality factor. By selecting specific orientations such as <110> or <100>, the resonator achieves both temperature stability and low insertion loss through its inherent material properties rather than through lossy compensation techniques.
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 TPoS resonator achieves significantly lower TCF, high Q factors, and reduced insertion loss, enabling efficient frequency stability and integration with electronic circuitry while minimizing power consumption.
Implementation Method 1
an aluminum nitride layer, which reduces TCF and enhances Q by concentrating acoustic energy near the center
Implementation Method 2
thin-film piezoelectric-on-silicon (TPoS) resonator
Implementation Method 3
supporting both capacitive and piezoelectric transduction modes
Data Source
AI summary
A TPoS resonator includes a substrate and a resonator body suspended over the substrate by at least a first pair of fixed supports (e.g., tethers) that attach to first and second ends of the resonator body. The resonator body includes monocrystalline silicon, which has a [100] crystallographic orientation that is offset by ±α degrees relative to a nodal line of the resonator body (e.g., tether-to-tether axis) when the resonator body is operating at a resonant frequency, where a is a real number in a range from about 5 to about 19 and, more preferably, in a range from about 7 to about 17. The resonator may be an extensional-mode resonator and the resonator body may be rectangular-shaped with unequal length and width dimensions.