LiNbO3-Glass POI wafer +SAW--Improved TCF of Low Velocity LN HAL SAW Resonators using Glass Substrate

Paper Download

Improved_TCF_of_Low_Velocity_LN_HAL_SAW_Resonators_using_Glass_Substrate.pdf

OMedaSemi can provide diverse composite X-o-X Wafer, we use surface actived bonding technology to bond diverse material . you can click this page to know our composite wafer and our surface actived bonding technology

The article *"Improved TCF of Low Velocity LN HAL SAW Resonators using Glass Substrate"* explores advancements in surface acoustic wave (SAW) resonators made from lithium niobate (LN) on a glass substrate. Here’s a summary:

### Key Points:

1. **Objective**: The study aims to improve the temperature coefficient of frequency (TCF) of Hetero Acoustic Layer (HAL) SAW resonators by replacing the quartz (Qz) substrate with a glass substrate, which has a lower coefficient of linear thermal expansion (CTE).

2. **Background**: SAW filters, commonly used in smartphones, face challenges related to their size and thermal stability. LN HAL SAW resonators offer high performance, including low phase velocity, high impedance ratio (Z-ratio), and wide bandwidth, but suffer from poor TCF due to the negative TCF of LN and Qz substrates.

3. **Method**:

   - A low-CTE glass substrate was used to replace Qz, aiming to reduce the TCF of the resonator. 

   - The device consisted of copper interdigital transducers (IDTs) on an LN thin film bonded to a glass substrate.

   - Simulations and experiments measured the performance in terms of frequency, Z-ratio, bandwidth, and TCF.

4. **Results**:

   - The LN/glass SAW resonator achieved a significant improvement in TCF, reducing it by approximately 45% compared to the LN/Qz resonator.

   - The device exhibited a phase velocity of 3,034 m/s and a Z-ratio of 70 dB, with a bandwidth of 14%.

   - However, the improvement in TCF came at the cost of a reduced Z-ratio (by 10 dB) compared to the previous LN/Qz resonator.

5. **Conclusion**:

   - Substituting Qz with a glass substrate improved the TCF but also affected the Z-ratio.

   - Further optimization, such as thinning the LN layer or using glass substrates with even lower CTE, could further enhance performance.

   - Increasing the thickness of the copper IDTs could also help reduce the phase velocity, making the resonator more efficient.

This study demonstrates the potential of using glass substrates to improve the thermal stability of LN-based SAW resonators, which could lead to more reliable and compact RF filters in mobile devices.