BAW Resonator Temperature Sensing and Heating for Frequency Stability
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Solution Overview
Problem
Bulk-acoustic-wave (BAW) resonators experience frequency instability due to temperature sensitivity, and integrating temperature sensors based on bipolar-junction-transistor (BJT) or N-Well architectures with micro-electromechanical system (MEMS) technology is challenging, leading to thermal gradients and fabrication complexity.
Innovation Solution
Integrate a heater and temperature sensor in the same layer level as the electrodes of the BAW device, eliminating the need for additional masks and reducing thermal gradients, while using a temperature-coefficient-of-frequency (TCF) dielectric layer to tune the TCF curve for stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors based on BJT or N-Well architectures are integrated with MEMS technology, then temperature sensing capability is achieved, but thermal gradients and fabrication complexity increase
Solution Approach 1:
The patent combines the temperature sensor and heater into the same metal layer level as the BAW device electrodes, eliminating the need for separate fabrication processes. This merging approach integrates multiple functions (temperature sensing, heating, and acoustic wave generation) into a unified structure that uses the same deposited metal layers, thereby reducing fabrication complexity while maintaining temperature measurement capability
Solution Approach 2:
The metal layers serving as electrodes for the BAW device are made multi-functional by also forming the temperature sensor and heater within the same layer structure. This universal use of metal layers allows the device to perform acoustic wave generation, temperature sensing, and thermal compensation functions simultaneously without requiring additional dedicated layers or complex multi-step fabrication processes
2Measurement precision
If temperature sensors are integrated at different layer levels, then temperature sensing is achieved, but thermal gradients increase
Solution Approach 1:
The patent positions the temperature sensor at the same metal layer level as the BAW device electrodes, creating a thermal equipotential relationship between the sensor and the acoustic wave generation region. This co-planar arrangement ensures that the temperature sensor measures the actual temperature of the device without being influenced by thermal gradients that would exist if the sensor were positioned at a different elevation, thereby achieving accurate temperature sensing while minimizing thermal gradient effects
3Measurement precision
If additional masks are used for integrating temperature sensors, then temperature sensing capability is achieved, but manufacturing complexity increases
Solution Approach 1:
The temperature sensor is merged with the electrode structure such that both are formed using the same metal deposition and patterning steps. This combining approach allows the temperature sensor to be created as an inherent part of the electrode fabrication process, eliminating the need for additional photolithography masks and reducing manufacturing complexity while maintaining the ability to sense temperature accurately
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 maintains a constant elevated temperature, reducing frequency errors and ensuring stable operation by integrating the heater and sensor in the same layer, thus stabilizing the BAW device's frequency regardless of ambient conditions.
Implementation Method 1
A BAW resonator includes a piezoelectric thin film between top and bottom electrodes, and may perform conversion between electrical energy and mechanical energy
Implementation Method 2
A resistive heating element is located in a same metal layer level as the first electrode and laterally adjacent to the first electrode
Data Source
AI summary
An acoustic-wave device includes a first electrode located over a substrate. A piezoelectric film is located over the first electrode and at least partially overlaps the first electrode. A second electrode is located over the piezoelectric film and at least partially overlaps the first electrode and the piezoelectric film. A temperature sensor is located in a same layer level as the first or second electrode. A heater may also be located in a same layer level as the first electrode. A closed-loop system may operate using the temperature sensor and the heater to maintain an operating temperature that provides highly stable operation.