In this blog post we will provide an overview of how you can design piezo MEMS resonators for RF filters extremely fast and accurately using OnScale, thereby reducing cost, risk and time to market.
At OnScale we have developed a fast and efficient 3D finite element method-based software to support RF design engineers in overcoming engineering challenges. OnScale also enables RF design engineers to integrate cloud-based solvers into design workflows for embedded simulations in creating RF MEMS digital prototypes.
5G RF front end
Let’s dive into the world of RF MEMS. The rollout of 5G wireless technology is based on providing ubiquitous connectivity and increased data rate. To achieve this it requires the RF front end (RFFE) of a smartphone to handle the increased data rates and access the full bandwidth of 5G wireless systems. Typically the RFFE comprises of power amplifiers, filters, duplexes, clocks, switches and low-noise amplifiers. The analogue component, which is the oscillator, sets the frequency such that the window is open at the right position in the RF spectrum. The RF filter ensures the window has the right width to pass data at the needed bandwidth. The requirements for 5G filter applications would include complex multiplexing, increasing integration, additional filters and the capability to handle much higher frequencies.
Overall the 5G RF front end system architecture is extremely complex and requires a smaller footprint compared to the current technology, with more than a hundred RF filters required to fit into a smartphone. To meet all these requirements, modeling and simulation tools play an increasingly important role in addressing all these complexities and achieving a desired 5G filter design.
Typical workflow of RF MEMS filter design
The typical workflow for the design and development of RF MEMS filters is based on a mask layout design. RF designers typically start with a 2D mask layout, which in this case consists of SAW resonators: three series SAWs and two shunts. We must then use multiple simulation tools, which include:
• Acoustic simulation to estimate the bandwidth, impedance and the Q factor
• Thermal simulations to determine the frequency shift due to temperature change and packaging thermal stresses
• EM simulations for parasitic metal losses and power handling
• Circuit modeling to estimate the filter response, insertion loss and attenuation loss for the filter die
Given the complexity and the lack of standardization in any FEA software we must simultaneously juggle between 3D fast acoustic thermal simulations and electromagnetic simulations. It can be very difficult to go between each FEA simulation tool during this complex process.
The main design challenge is the accurate modeling and full 3D simulation of these acoustic resonators. Typical simulations of this device would require at least 15 million degrees of freedom to accurately capture the propagation of acoustic waves in an anisotropic piezoelectric material for the development of these devices. There lies the main problem in legacy FEA solvers: with these solvers it can take a few days to simulate these devices, meaning only a handful of designs can be simulated in a working week. What’s more, sometimes running a simulation can take weeks, and sometimes it’s not even possible to run a simulation.
How OnScale can help
This is where OnScale’s fast solvers and cloud computing capabilities come in. Our solvers allow RF engineers to simulate their devices in just a few minutes, which previously was not possible. OnScale also provides users with the capability to run all their simulations in parallel, which effectively means that thousands of potential designs can be evaluated in a matter of minutes or hours. This provides RF design engineers with a clear picture of the entire design space and most importantly allows quick prototyping in a few weeks.