Unlocking High-Performance Si RF Platforms with SiGe HBT and RFSOI Switch Technologies

This paper presents a comprehensive solution for the cointegration of SiGe Heterojunction Bipolar Transistors (HBTs) and Partially Depleted (PDSOI) Radio-Frequency (RF) switches using 3D sequential integration (3DSI). The proposed platform combines the best-in-class active and passive devices for high-performance RF front-end modules (FEM), which are essential for 5G and future 6G wireless systems.

Key Contributions:

1. Challenges and Motivation:

• SiGe HBTs are ideal for high-performance RF power amplifiers (PAs) due to their superior RF performance, but integrating them with CMOS-based RF switches has been challenging due to compatibility issues, especially thermal budget constraints.

• The goal of the paper is to demonstrate a monolithic RF platform that integrates SiGe HBTs, PDSOI RF switches, and passive components using 3D sequential integration without compromising on the performance of each component.

2. Thermally Stable Local Trap-Rich (LTR) Layer:

• The local trap-rich (LTR) process is essential for improving RF linearity and device performance. This process involves the implantation of trap-rich regions into high-resistivity (HR) Si substrates to form a local TR layer that enhances substrate isolation.

• Thermal stability of the local TR layer was tested with annealing at 600°C and 800°C, showing no performance degradation, making it suitable for integration into high-performance RF systems.

3. SiGe HBT Thermal Stability:

• Thermal stability of SiGe HBTs was analyzed to understand how the silicide contacts (poly-silicon) perform under various thermal budgets. Silicide agglomeration was found to be a major limiting factor, but with careful process control, a thermal budget of 550°C was found to be safe for the SiGe HBTs, ensuring their stability while integrating them with other components.

4. PDSOI RF Switch Performance at 600°C:

• The PDSOI RF switches were fabricated at 600°C using low-temperature process flows. These devices demonstrated excellent RF performance, with an RF voltage (RFVmax) of 2.7V and RON×COFF = 96 fs, which is a significant breakthrough in the field.

• Low temperature (LT) PDSOI RF switches showed comparable performance to high temperature (HT) switches in terms of insertion loss, RF power handling, and linearity. The RFVmax was very close to the HT switch, demonstrating the capability of LT RF switches for 600°C processing.

5. RF Characterization and Results:

• The insertion loss and harmonic performance of the LT PDSOI switches were evaluated, showing that they perform on par with HT devices.

• The linearity and RF power handling capabilities were measured using S-parameter and harmonic measurements, showing that the LT switches exhibit excellent linearity and high power handling similar to the HT RF switches.

6. Conclusion and Future Work:

• The paper successfully demonstrates the cointegration of SiGe HBTs and PDSOI RF switches with the 3DSI approach, overcoming the key challenges related to thermal budgets, integration of active devices, and passive components.

• This work enables the development of fully integrated RF front-end modules for next-generation wireless communication systems, with high-performance SiGe HBTs and low-temperature PDSOI switches.

• Future work includes improving RFVmax and RON×COFF performance, optimizing thermal stability, and expanding the integration to fully monolithic RF modules with advanced process flows.

Conclusion:

This work presents a high-performance, scalable solution for integrating SiGe HBTs, PDSOI RF switches, and passive components using 3D sequential integration for advanced RF applications. The approach addresses major challenges in thermal stability and device performance, paving the way for cost-effective, compact, and high-performance RF systems for 5G and 6G technologies.