BAW Resonator Temperature Control via Heater and Sensor
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Solution Overview
Problem
Acoustic resonators in electronic devices experience frequency drift due to physical stresses, particularly differential stress caused by temperature changes and uneven expansion of materials in chip-scale packages, leading to significant frequency shifts that exceed tolerance limits in high-accuracy applications.
Innovation Solution
Incorporating a bulk acoustic wave (BAW) resonator structure with an integrated heater and heat sensor to maintain a constant temperature, reducing physical contact with the substrate and using a piezoelectric layer with doped AlN for improved heat conduction, while minimizing thermal conduction through the substrate and employing a microcap structure for hermetic sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the acoustic resonator is mounted on a PCB through chip-scale packaging, then the device can be integrated into electronic systems, but frequency drift occurs due to thermal expansion and physical stress from the PCB
Solution Approach 1:
The resonator structure is segmented into distinct functional layers (piezoelectric layer, buffer layer, substrate) that can independently manage different physical stresses and thermal expansions, reducing the transfer of mechanical stress from the PCB to the resonating element
Solution Approach 2:
A buffer layer is introduced as an intermediary between the resonator and the substrate/PCB. This buffer layer absorbs and isolates thermal expansion forces and mechanical stress, preventing them from directly affecting the resonator's frequency while still allowing electrical connectivity
2Adaptability or versatility
If the resonator operates at varying temperatures, then the device can function in different environmental conditions, but frequency drift increases due to thermal effects
Solution Approach 1:
The patent modifies the physical parameters of the resonator structure, including the piezoelectric material composition and layer thicknesses, to create a resonator whose frequency characteristics are less sensitive to temperature variations. The buffer layer's thermal expansion coefficient is specifically chosen to match or compensate for the resonator materials
Solution Approach 2:
The buffer layer is designed with specific thermal expansion properties that counteract the thermal expansion effects on the resonator. When the PCB expands or contracts with temperature changes, the buffer layer absorbs this dimensional change, preventing it from being transmitted to the resonator and causing frequency drift
3Ease of manufacture
If the resonator is in direct contact with the substrate, then manufacturing is simplified, but thermal conduction causes frequency instability
Solution Approach 1:
A buffer layer serves as a thermal and mechanical intermediary between the resonator and substrate. This layer reduces thermal conduction while maintaining structural support and electrical connectivity, preventing temperature fluctuations from directly affecting the resonator frequency
Solution Approach 2:
The buffer layer is positioned specifically at the interface between the resonator and substrate, providing localized thermal and mechanical isolation where it is most needed, while the rest of the resonator structure maintains its original design for simplicity
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 solution effectively reduces frequency drift by maintaining a stable temperature and minimizing thermal and physical interactions with the substrate, achieving frequency stability within the required tolerance limits for high-accuracy electronic applications.
Implementation Method 1
a heating coil disposed over a first side of the piezoelectric layer and substantially around a perimeter adjacent to the active area of the BAW resonator. The heating coil comprises a resistor configured to receive a heater current
Implementation Method 2
a heat sensor disposed over a second side of the piezoelectric layer and opposing the first side, the heat sensor configured to adjust the heater current in response to a temperature of the heating coil
Implementation Method 3
A piezoelectric layer is disposed over at least a portion of the first electrode, and extends over at least one of the plurality of sides having the first electrode extending thereover
Implementation Method 4
using a piezoelectric layer with doped AlN for improved heat conduction
Data Source
AI summary
A bulk acoustic wave (BAW) resonator device comprises a heating coil disposed over a first side of the piezoelectric layer and substantially around a perimeter adjacent to the active area of the acoustic resonator, the heating coil comprising a resistor configured to receive a heater current; and a heat sensor disposed over a second side of the piezoelectric layer and opposing the first side, the heat sensor configured to adjust the heater current in response to a temperature of the heating coil.